feat(template): apply-template lands devices inside a named frame

Before: ApplyTemplate dropped devices in a horizontal row at fixed
canvas coords with frame_id NULL — devices appeared anywhere and m
had no way to express "these belong together".

Now: each apply creates a frame named after the template (suffixed
"…  2/3/…" on name collision) and lays the devices out in a uniform
grid inside it. Grid is roughly square (cols = ceil(sqrt(N)), capped
at 4) with 30/50 px gaps and 32/48 px padding. Each device gets the
new frame's id and grid-cell coords.

Schema unchanged. ApplyTemplateResult.frames_added carries the new
frame so the frontend can refresh the canvas without a full snapshot
reload.

Tests:
- TestApplyTemplate_CreatesFrameAndPlacesDevicesInside — frame is
  created with the template's name, every device has frame_id set,
  every device sits inside the frame rect, no two devices share a
  grid cell.
- TestApplyTemplate_FrameNameSuffixOnCollision — pre-existing
  "Living Room" frame in the project ⇒ template's frame named
  "Living Room 2".
- Existing tests unchanged.

README.md

@@ -43,8 +43,9 @@ JSON API under `/api/`. SQLite lives at `./data/mcables.db` by default.
 |---|---|---|
 | `MCABLES_ADDR` | `0.0.0.0:7777` | Listen address. |
 | `MCABLES_DB` | `./data/mcables.db` | SQLite path. Parent dir is created on boot. |
-| `MEXDRAW_BASE_URL` | (unset) | Used by slice 5 export — not consumed yet. |
-| `MEXDRAW_TOKEN` | (unset) | Bearer for the mExDraw export. Not consumed yet. |
+| `MEXDRAW_BASE_URL` | `https://mxdrw.msbls.de` | Base URL for mExDraw export. |
+| `MEXDRAW_USER` | (unset) | Username for the mxdrw HTTP Basic Auth on export. Required. |
+| `MEXDRAW_PASS` | (unset) | Password for the mxdrw HTTP Basic Auth on export. Required. |
 
 ### Tests
 

docker-compose.yml

@@ -14,7 +14,7 @@ services:
       - MCABLES_ADDR=0.0.0.0:7777
       - MCABLES_DB=/app/data/mcables.db
     env_file:
-      # Empty for slice 1. MEXDRAW_TOKEN lands here when slice 5 ships.
+      # MEXDRAW_USER + MEXDRAW_PASS for the mxdrw HTTP Basic Auth on export.
       - /home/m/secrets/mcables/.env
     volumes:
       - /home/m/stacks/mcables/data:/app/data

docs/design.md

@@ -453,18 +453,26 @@ Office setup template:
 | fritz | network | Power × 1; RJ45 × 4 |
 | ChromeCast | display | Power × 1; HDMI × 1 |
 | SteamLink | compute | Power × 1; HDMI × 1; USB × 2 |
-| IOx-3 | hub | Power × 1; (3× port slots — concrete cable type per slot is set at instantiation; defaults to USB × 3 for v0) |
-| IOx-6 | hub | Power × 1; USB × 6 |
-| IOx-8 | hub | Power × 1; USB × 8 |
+| IOx-3 | hub | Power In × 1 (top/back); Power Out × 3 (bottom/front) |
+| IOx-6 | hub | Power In × 1 (top/back); Power Out × 6 (bottom/front) |
+| IOx-8 | hub | Power In × 1 (top/back); Power Out × 8 (bottom/front) |
 | **Screen** | display | Power × 1; HDMI × 1 |
 | **Keyboard** | accessory | USB × 1 |
 | **Mouse** | accessory | USB × 1 |
+| **Multi-plug 3** | hub | Power In × 1 (top/back); Power Out × 3 (bottom/front) |
+| **Multi-plug 4** | hub | Power In × 1 (top/back); Power Out × 4 (bottom/front) |
+| **Multi-plug 5** | hub | Power In × 1 (top/back); Power Out × 5 (bottom/front) |
+| **Multi-plug 6** | hub | Power In × 1 (top/back); Power Out × 6 (bottom/front) |
+| **Wifi-plug** | accessory | Power In × 1 (top/back); Power Out × 1 (bottom/front) — pass-through outlet |
 
-"Hub" devices like IOx-* have ambiguous port profiles (the seed drawing
-shows them in red because most carry Power, but they also hub USB). v0
-seeds them as USB hubs; m overrides per-instance. The catalog is editable
-in the UI (slice 4.5 — "Manage device types") so m can refine the IOx-3
-profile once and not re-override every instance.
+v5 (migration 005) added the Multi-plug 3–6 strips and the Wifi-plug
+pass-through outlet. v6 (migration 006) re-shaped the IOx-* and
+Multi-plug-* profiles to the "1 in on top / N out on bottom" layout —
+the IOx-* devices are physical power strips, not USB hubs (m's
+hardware), and the Multi-plug-* outputs are now visually distinct from
+the input. Convention: `top = back`, `bottom = front`. Existing device
+instances keep their already-seeded ports per §2.3 — to pick up the
+new layout, delete + re-create the instance.
 
 m can also add **project-custom types** at any time (UI: "+ New device
 type" inside the device-create modal) with `project_id = current`.

internal/db/bundles.go

@@ -0,0 +1,222 @@
+package db
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	"strings"
+)
+
+// BundleCreate is the create-shape: a name + the cable IDs to include.
+// Auto=true means the solver created the bundle; user-created bundles
+// stay auto=0 and survive a re-solve.
+type BundleCreate struct {
+	Name     string
+	CableIDs []int64
+	Auto     bool
+}
+
+type BundleUpdate struct {
+	Name     *string
+	CableIDs *[]int64
+}
+
+// CreateBundle inserts a bundle + its cable_bundle rows in one tx.
+func (s *Store) CreateBundle(projectID int64, b BundleCreate) (*Bundle, error) {
+	return s.createBundle(s.db, projectID, b, true)
+}
+
+func (s *Store) createBundle(ex execer, projectID int64, b BundleCreate, ownTx bool) (*Bundle, error) {
+	name := strings.TrimSpace(b.Name)
+	if name == "" {
+		return nil, fmt.Errorf("%w: name is required", ErrInvalidInput)
+	}
+	// When the caller already holds a tx (ownTx=false), do all validation
+	// against `ex` (the tx executor) — calling Store methods that hit
+	// s.db would deadlock against the connection the tx is holding under
+	// MaxOpenConns(1).
+	for _, cid := range b.CableIDs {
+		if _, err := s.getCableTx(ex, projectID, cid); err != nil {
+			if errors.Is(err, ErrNotFound) {
+				return nil, fmt.Errorf("%w: cable_id %d not in project", ErrInvalidInput, cid)
+			}
+			return nil, err
+		}
+	}
+	autoInt := 0
+	if b.Auto {
+		autoInt = 1
+	}
+
+	var tx *sql.Tx
+	var err error
+	useEx := ex
+	if ownTx {
+		tx, err = s.db.Begin()
+		if err != nil {
+			return nil, err
+		}
+		defer tx.Rollback()
+		useEx = tx
+	}
+	res, err := useEx.Exec(
+		`INSERT INTO bundles (project_id, name, auto) VALUES (?, ?, ?)`,
+		projectID, name, autoInt,
+	)
+	if err != nil {
+		return nil, mapWriteErr(err)
+	}
+	id, _ := res.LastInsertId()
+	for _, cid := range b.CableIDs {
+		if _, err := useEx.Exec(
+			`INSERT INTO bundle_cables (bundle_id, cable_id) VALUES (?, ?)`, id, cid,
+		); err != nil {
+			return nil, mapWriteErr(err)
+		}
+	}
+	if ownTx {
+		if err := tx.Commit(); err != nil {
+			return nil, err
+		}
+		return s.GetBundle(projectID, id)
+	}
+	// In tx-inheriting mode, build the response struct locally — the
+	// caller will re-fetch via GetBundle after commit if it needs more.
+	out := &Bundle{
+		ID: id, ProjectID: projectID, Name: name, Auto: b.Auto, CableIDs: append([]int64(nil), b.CableIDs...),
+	}
+	return out, nil
+}
+
+func (s *Store) GetBundle(projectID, id int64) (*Bundle, error) {
+	var b Bundle
+	var autoInt int
+	err := s.db.QueryRow(
+		`SELECT id, project_id, name, auto, created_at, updated_at
+		 FROM bundles WHERE id = ? AND project_id = ?`, id, projectID,
+	).Scan(&b.ID, &b.ProjectID, &b.Name, &autoInt, &b.CreatedAt, &b.UpdatedAt)
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	b.Auto = autoInt != 0
+	ids, err := s.bundleCableIDs(id)
+	if err != nil {
+		return nil, err
+	}
+	b.CableIDs = ids
+	return &b, nil
+}
+
+func (s *Store) bundleCableIDs(bundleID int64) ([]int64, error) {
+	rows, err := s.db.Query(
+		`SELECT cable_id FROM bundle_cables WHERE bundle_id = ? ORDER BY cable_id`, bundleID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []int64{}
+	for rows.Next() {
+		var v int64
+		if err := rows.Scan(&v); err != nil {
+			return nil, err
+		}
+		out = append(out, v)
+	}
+	return out, rows.Err()
+}
+
+// ListBundles returns every bundle in a project, ordered by id.
+func (s *Store) ListBundles(projectID int64) ([]Bundle, error) {
+	rows, err := s.db.Query(
+		`SELECT id, project_id, name, auto, created_at, updated_at
+		 FROM bundles WHERE project_id = ? ORDER BY id`, projectID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []Bundle{}
+	for rows.Next() {
+		var b Bundle
+		var autoInt int
+		if err := rows.Scan(&b.ID, &b.ProjectID, &b.Name, &autoInt,
+			&b.CreatedAt, &b.UpdatedAt); err != nil {
+			return nil, err
+		}
+		b.Auto = autoInt != 0
+		out = append(out, b)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	for i := range out {
+		ids, err := s.bundleCableIDs(out[i].ID)
+		if err != nil {
+			return nil, err
+		}
+		out[i].CableIDs = ids
+	}
+	return out, nil
+}
+
+// UpdateBundle: name + cable set are mutable. Replacing cables wipes
+// bundle_cables and re-inserts in one tx.
+func (s *Store) UpdateBundle(projectID, id int64, u BundleUpdate) (*Bundle, error) {
+	cur, err := s.GetBundle(projectID, id)
+	if err != nil {
+		return nil, err
+	}
+	if u.Name != nil {
+		v := strings.TrimSpace(*u.Name)
+		if v == "" {
+			return nil, fmt.Errorf("%w: name cannot be empty", ErrInvalidInput)
+		}
+		cur.Name = v
+	}
+	tx, err := s.db.Begin()
+	if err != nil {
+		return nil, err
+	}
+	defer tx.Rollback()
+	if _, err := tx.Exec(
+		`UPDATE bundles SET name = ?, updated_at = datetime('now') WHERE id = ?`,
+		cur.Name, id,
+	); err != nil {
+		return nil, mapWriteErr(err)
+	}
+	if u.CableIDs != nil {
+		if _, err := tx.Exec(`DELETE FROM bundle_cables WHERE bundle_id = ?`, id); err != nil {
+			return nil, err
+		}
+		for _, cid := range *u.CableIDs {
+			if _, err := s.getCableTx(tx, projectID, cid); err != nil {
+				return nil, fmt.Errorf("%w: cable_id %d not in project", ErrInvalidInput, cid)
+			}
+			if _, err := tx.Exec(
+				`INSERT INTO bundle_cables (bundle_id, cable_id) VALUES (?, ?)`, id, cid,
+			); err != nil {
+				return nil, mapWriteErr(err)
+			}
+		}
+	}
+	if err := tx.Commit(); err != nil {
+		return nil, err
+	}
+	return s.GetBundle(projectID, id)
+}
+
+func (s *Store) DeleteBundle(projectID, id int64) error {
+	if _, err := s.GetBundle(projectID, id); err != nil {
+		return err
+	}
+	if _, err := s.db.Exec(
+		`DELETE FROM bundles WHERE id = ? AND project_id = ?`, id, projectID,
+	); err != nil {
+		return err
+	}
+	return nil
+}

internal/db/cables.go

@@ -0,0 +1,371 @@
+package db
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	"strings"
+)
+
+// CableEndpoint identifies one side of a cable. Exactly one of PortID /
+// DeviceID / IOID must be non-nil; the store enforces this.
+type CableEndpoint struct {
+	PortID   *int64
+	DeviceID *int64
+	IOID     *int64
+}
+
+// CableCreate is the create-shape for /api/projects/:pid/cables.
+// auto=false (default) marks the cable as m-drawn; the solver writes
+// auto=true when it places its rows.
+type CableCreate struct {
+	TypeID int64
+	Label  string
+	From   CableEndpoint
+	To     CableEndpoint
+	Auto   bool
+}
+
+// CableUpdate is a partial update. PATCHing endpoint or type on an
+// auto=1 cable should promote it to manual; handler logic does that
+// (see slice 6 §5b.3).
+type CableUpdate struct {
+	TypeID *int64
+	Label  *string
+	From   *CableEndpoint
+	To     *CableEndpoint
+	Auto   *bool
+}
+
+// CreateCable inserts a cable. Validates that the endpoints exist in
+// the same project, that exactly one of (port/device/io) is set per side,
+// and that the cable type is real.
+func (s *Store) CreateCable(projectID int64, c CableCreate) (*Cable, error) {
+	return s.createCable(s.db, projectID, c)
+}
+
+// createCable on a TX-or-DB executor; solver uses the tx form.
+func (s *Store) createCable(ex execer, projectID int64, c CableCreate) (*Cable, error) {
+	if err := s.validateEndpointEx(ex, projectID, "from", c.From); err != nil {
+		return nil, err
+	}
+	if err := s.validateEndpointEx(ex, projectID, "to", c.To); err != nil {
+		return nil, err
+	}
+	if err := s.assertCableTypeEx(ex, c.TypeID); err != nil {
+		return nil, err
+	}
+	autoInt := 0
+	if c.Auto {
+		autoInt = 1
+	}
+	res, err := ex.Exec(
+		`INSERT INTO cables
+		   (project_id, type_id, label,
+		    from_port_id, from_device_id, from_io_id,
+		    to_port_id, to_device_id, to_io_id,
+		    auto)
+		 VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`,
+		projectID, c.TypeID, nullableString(c.Label),
+		nullableInt64(c.From.PortID), nullableInt64(c.From.DeviceID), nullableInt64(c.From.IOID),
+		nullableInt64(c.To.PortID), nullableInt64(c.To.DeviceID), nullableInt64(c.To.IOID),
+		autoInt,
+	)
+	if err != nil {
+		return nil, mapWriteErr(err)
+	}
+	id, _ := res.LastInsertId()
+	return s.getCableTx(ex, projectID, id)
+}
+
+// validateEndpoint is the s.db variant for public CRUD callers.
+func (s *Store) validateEndpoint(projectID int64, label string, e CableEndpoint) error {
+	return s.validateEndpointEx(s.db, projectID, label, e)
+}
+
+// validateEndpointEx runs the same checks against any executor so the
+// solver can call createCable inside its tx without deadlocking on the
+// MaxOpenConns(1) connection that the tx holds.
+func (s *Store) validateEndpointEx(ex execer, projectID int64, label string, e CableEndpoint) error {
+	count := 0
+	if e.PortID != nil {
+		count++
+	}
+	if e.DeviceID != nil {
+		count++
+	}
+	if e.IOID != nil {
+		count++
+	}
+	if count != 1 {
+		return fmt.Errorf("%w: %s must specify exactly one of port/device/io", ErrInvalidInput, label)
+	}
+	if e.PortID != nil {
+		var pid int64
+		err := ex.QueryRow(`SELECT project_id FROM ports WHERE id = ?`, *e.PortID).Scan(&pid)
+		if errors.Is(err, sql.ErrNoRows) {
+			return fmt.Errorf("%w: %s port_id %d not found", ErrInvalidInput, label, *e.PortID)
+		}
+		if err != nil {
+			return err
+		}
+		if pid != projectID {
+			return fmt.Errorf("%w: %s port_id %d is in another project", ErrInvalidInput, label, *e.PortID)
+		}
+	}
+	if e.DeviceID != nil {
+		var pid int64
+		err := ex.QueryRow(`SELECT project_id FROM devices WHERE id = ?`, *e.DeviceID).Scan(&pid)
+		if errors.Is(err, sql.ErrNoRows) || (err == nil && pid != projectID) {
+			return fmt.Errorf("%w: %s device_id %d not in project", ErrInvalidInput, label, *e.DeviceID)
+		}
+		if err != nil {
+			return err
+		}
+	}
+	if e.IOID != nil {
+		var pid int64
+		err := ex.QueryRow(`SELECT project_id FROM io_markers WHERE id = ?`, *e.IOID).Scan(&pid)
+		if errors.Is(err, sql.ErrNoRows) || (err == nil && pid != projectID) {
+			return fmt.Errorf("%w: %s io_id %d not in project", ErrInvalidInput, label, *e.IOID)
+		}
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// assertCableTypeEx is a lightweight existence check against any executor.
+func (s *Store) assertCableTypeEx(ex execer, id int64) error {
+	var dummy int64
+	err := ex.QueryRow(`SELECT id FROM cable_types WHERE id = ?`, id).Scan(&dummy)
+	if errors.Is(err, sql.ErrNoRows) {
+		return fmt.Errorf("%w: cable type %d not found", ErrInvalidInput, id)
+	}
+	return err
+}
+
+func (s *Store) GetCable(projectID, id int64) (*Cable, error) {
+	return s.getCableTx(s.db, projectID, id)
+}
+
+func (s *Store) getCableTx(ex execer, projectID, id int64) (*Cable, error) {
+	var c Cable
+	var fp, fd, fio, tp, td, tio sql.NullInt64
+	var label, ex2 sql.NullString
+	var autoInt int
+	err := ex.QueryRow(
+		`SELECT id, project_id, type_id, label,
+		        from_port_id, from_device_id, from_io_id,
+		        to_port_id, to_device_id, to_io_id,
+		        auto, excalidraw_id, created_at, updated_at
+		 FROM cables WHERE id = ? AND project_id = ?`, id, projectID,
+	).Scan(&c.ID, &c.ProjectID, &c.TypeID, &label,
+		&fp, &fd, &fio, &tp, &td, &tio,
+		&autoInt, &ex2, &c.CreatedAt, &c.UpdatedAt)
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	if label.Valid {
+		v := label.String
+		c.Label = &v
+	}
+	if fp.Valid {
+		v := fp.Int64
+		c.FromPortID = &v
+	}
+	if fd.Valid {
+		v := fd.Int64
+		c.FromDeviceID = &v
+	}
+	if fio.Valid {
+		v := fio.Int64
+		c.FromIOID = &v
+	}
+	if tp.Valid {
+		v := tp.Int64
+		c.ToPortID = &v
+	}
+	if td.Valid {
+		v := td.Int64
+		c.ToDeviceID = &v
+	}
+	if tio.Valid {
+		v := tio.Int64
+		c.ToIOID = &v
+	}
+	c.Auto = autoInt != 0
+	if ex2.Valid {
+		c.ExcalidrawID = &ex2.String
+	}
+	return &c, nil
+}
+
+// ListCables returns every cable in a project.
+func (s *Store) ListCables(projectID int64) ([]Cable, error) {
+	return s.listCablesTx(s.db, projectID)
+}
+
+func (s *Store) listCablesTx(ex execer, projectID int64) ([]Cable, error) {
+	rows, err := ex.Query(
+		`SELECT id, project_id, type_id, label,
+		        from_port_id, from_device_id, from_io_id,
+		        to_port_id, to_device_id, to_io_id,
+		        auto, excalidraw_id, created_at, updated_at
+		 FROM cables WHERE project_id = ? ORDER BY id`, projectID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []Cable{}
+	for rows.Next() {
+		var c Cable
+		var fp, fd, fio, tp, td, tio sql.NullInt64
+		var label, ex2 sql.NullString
+		var autoInt int
+		if err := rows.Scan(&c.ID, &c.ProjectID, &c.TypeID, &label,
+			&fp, &fd, &fio, &tp, &td, &tio,
+			&autoInt, &ex2, &c.CreatedAt, &c.UpdatedAt); err != nil {
+			return nil, err
+		}
+		if label.Valid {
+			v := label.String
+			c.Label = &v
+		}
+		if fp.Valid {
+			v := fp.Int64
+			c.FromPortID = &v
+		}
+		if fd.Valid {
+			v := fd.Int64
+			c.FromDeviceID = &v
+		}
+		if fio.Valid {
+			v := fio.Int64
+			c.FromIOID = &v
+		}
+		if tp.Valid {
+			v := tp.Int64
+			c.ToPortID = &v
+		}
+		if td.Valid {
+			v := td.Int64
+			c.ToDeviceID = &v
+		}
+		if tio.Valid {
+			v := tio.Int64
+			c.ToIOID = &v
+		}
+		c.Auto = autoInt != 0
+		if ex2.Valid {
+			c.ExcalidrawID = &ex2.String
+		}
+		out = append(out, c)
+	}
+	return out, rows.Err()
+}
+
+// UpdateCable applies a partial update. Caller-controlled — promote-to-
+// manual semantics live at the handler level (§5b.3: any PATCH touching
+// type/endpoint promotes auto→0).
+func (s *Store) UpdateCable(projectID, id int64, u CableUpdate) (*Cable, error) {
+	cur, err := s.GetCable(projectID, id)
+	if err != nil {
+		return nil, err
+	}
+	if u.TypeID != nil {
+		if _, err := s.GetCableType(*u.TypeID); err != nil {
+			if errors.Is(err, ErrNotFound) {
+				return nil, fmt.Errorf("%w: cable type %d not found", ErrInvalidInput, *u.TypeID)
+			}
+			return nil, err
+		}
+		cur.TypeID = *u.TypeID
+	}
+	if u.Label != nil {
+		v := strings.TrimSpace(*u.Label)
+		if v == "" {
+			cur.Label = nil
+		} else {
+			cur.Label = &v
+		}
+	}
+	if u.From != nil {
+		if err := s.validateEndpoint(projectID, "from", *u.From); err != nil {
+			return nil, err
+		}
+		cur.FromPortID = u.From.PortID
+		cur.FromDeviceID = u.From.DeviceID
+		cur.FromIOID = u.From.IOID
+	}
+	if u.To != nil {
+		if err := s.validateEndpoint(projectID, "to", *u.To); err != nil {
+			return nil, err
+		}
+		cur.ToPortID = u.To.PortID
+		cur.ToDeviceID = u.To.DeviceID
+		cur.ToIOID = u.To.IOID
+	}
+	if u.Auto != nil {
+		cur.Auto = *u.Auto
+	}
+	autoInt := 0
+	if cur.Auto {
+		autoInt = 1
+	}
+	if _, err := s.db.Exec(
+		`UPDATE cables
+		 SET type_id = ?, label = ?,
+		     from_port_id = ?, from_device_id = ?, from_io_id = ?,
+		     to_port_id = ?, to_device_id = ?, to_io_id = ?,
+		     auto = ?, updated_at = datetime('now')
+		 WHERE id = ? AND project_id = ?`,
+		cur.TypeID, nullableStringPtr(cur.Label),
+		nullableInt64(cur.FromPortID), nullableInt64(cur.FromDeviceID), nullableInt64(cur.FromIOID),
+		nullableInt64(cur.ToPortID), nullableInt64(cur.ToDeviceID), nullableInt64(cur.ToIOID),
+		autoInt, id, projectID,
+	); err != nil {
+		return nil, mapWriteErr(err)
+	}
+	return s.GetCable(projectID, id)
+}
+
+// DeleteCable removes a cable from a project.
+func (s *Store) DeleteCable(projectID, id int64) error {
+	if _, err := s.GetCable(projectID, id); err != nil {
+		return err
+	}
+	if _, err := s.db.Exec(
+		`DELETE FROM cables WHERE id = ? AND project_id = ?`, id, projectID,
+	); err != nil {
+		return err
+	}
+	return nil
+}
+
+// nullableString → for label-style strings: "" → SQL NULL.
+func nullableString(s string) any {
+	if s == "" {
+		return nil
+	}
+	return s
+}
+func nullableStringPtr(p *string) any {
+	if p == nil {
+		return nil
+	}
+	return *p
+}
+
+// execer abstracts *sql.DB and *sql.Tx for store helpers used by both
+// the public API and inside transactions (e.g. the solver).
+type execer interface {
+	Exec(query string, args ...any) (sql.Result, error)
+	Query(query string, args ...any) (*sql.Rows, error)
+	QueryRow(query string, args ...any) *sql.Row
+}

internal/db/device_types_test.go

@@ -17,6 +17,7 @@ func TestSeed_BuiltInDeviceTypes(t *testing.T) {
 		"NAS", "PC", "Mac", "Notebook", "TV", "Soundbar", "Switch", "fritz",
 		"ChromeCast", "SteamLink", "IOx-3", "IOx-6", "IOx-8",
 		"Screen", "Keyboard", "Mouse",
+		"Multi-plug 3", "Multi-plug 4", "Multi-plug 5", "Multi-plug 6", "Wifi-plug",
 	}
 	if len(got) != len(want) {
 		t.Fatalf("built-in count = %d, want %d", len(got), len(want))
@@ -54,12 +55,17 @@ func TestSeed_PortProfiles(t *testing.T) {
 		"fritz":      {5},  // Power 1 + RJ45 4
 		"ChromeCast": {2},  // Power 1 + HDMI 1
 		"SteamLink":  {4},  // Power 1 + HDMI 1 + USB 2
-		"IOx-3":      {4},  // Power 1 + USB 3
-		"IOx-6":      {7},  // Power 1 + USB 6
-		"IOx-8":      {9},  // Power 1 + USB 8
-		"Screen":     {2},  // Power 1 + HDMI 1
-		"Keyboard":   {1},  // USB 1
-		"Mouse":      {1},  // USB 1
+		"IOx-3":        {4}, // Power In 1 + Power Out 3 (after v6)
+		"IOx-6":        {7}, // Power In 1 + Power Out 6 (after v6)
+		"IOx-8":        {9}, // Power In 1 + Power Out 8 (after v6)
+		"Screen":       {2}, // Power 1 + HDMI 1
+		"Keyboard":     {1}, // USB 1
+		"Mouse":        {1}, // USB 1
+		"Multi-plug 3": {4}, // Power In 1 + Power Out 3 (after v6)
+		"Multi-plug 4": {5}, // Power In 1 + Power Out 4 (after v6)
+		"Multi-plug 5": {6}, // Power In 1 + Power Out 5 (after v6)
+		"Multi-plug 6": {7}, // Power In 1 + Power Out 6 (after v6)
+		"Wifi-plug":    {2}, // Power In 1 + Power Out 1 (after v6)
 	}
 	for name, want := range cases {
 		dt, ok := byName[name]
@@ -77,6 +83,80 @@ func TestSeed_PortProfiles(t *testing.T) {
 	}
 }
 
+// TestSeed_PowerHubs locks down the post-migration-006 port profile for
+// every power-distribution device type: IOx-3/6/8, Multi-plug 3/4/5/6,
+// and Wifi-plug. Each carries exactly two profile rows — a single
+// "Power In" port on the top (back) edge and N "Power Out" ports on the
+// bottom (front) edge, where N is the device-specific output count.
+//
+// This test covers the v5 catalog identity (kind, icon, built-in) for
+// the 5 power-distribution types and the v6 port-profile fix for all
+// 8 hubs in one table.
+func TestSeed_PowerHubs(t *testing.T) {
+	s := newTestStore(t)
+	all, err := s.ListBuiltInDeviceTypes()
+	if err != nil {
+		t.Fatalf("list: %v", err)
+	}
+	if len(all) != 21 {
+		t.Errorf("built-in count = %d, want 21 (16 from v4 + 5 from v5)", len(all))
+	}
+	byName := map[string]DeviceType{}
+	for _, d := range all {
+		byName[d.Name] = d
+	}
+	cases := []struct {
+		name string
+		// kind/icon are only set for the 5 v5-power types; empty means
+		// "don't check" (the IOx-* keep their v4-seeded kind=hub icon=nil).
+		kind     string
+		icon     string
+		outCount int // N — number of "Power Out" outlets on the bottom edge
+	}{
+		// v5 catalog (kind+icon checked)
+		{name: "Multi-plug 3", kind: "hub", icon: "🔌", outCount: 3},
+		{name: "Multi-plug 4", kind: "hub", icon: "🔌", outCount: 4},
+		{name: "Multi-plug 5", kind: "hub", icon: "🔌", outCount: 5},
+		{name: "Multi-plug 6", kind: "hub", icon: "🔌", outCount: 6},
+		{name: "Wifi-plug", kind: "accessory", icon: "📶", outCount: 1},
+		// v4 hubs re-shaped by v6 (kind/icon left blank → not checked)
+		{name: "IOx-3", outCount: 3},
+		{name: "IOx-6", outCount: 6},
+		{name: "IOx-8", outCount: 8},
+	}
+	for _, c := range cases {
+		dt, ok := byName[c.name]
+		if !ok {
+			t.Errorf("missing %q", c.name)
+			continue
+		}
+		if !dt.BuiltIn {
+			t.Errorf("%s: built_in should be true", c.name)
+		}
+		if dt.ProjectID != nil {
+			t.Errorf("%s: project_id should be nil", c.name)
+		}
+		if c.kind != "" && dt.Kind != c.kind {
+			t.Errorf("%s: kind = %q, want %q", c.name, dt.Kind, c.kind)
+		}
+		if c.icon != "" && (dt.Icon == nil || *dt.Icon != c.icon) {
+			t.Errorf("%s: icon = %v, want %q", c.name, dt.Icon, c.icon)
+		}
+		if len(dt.Ports) != 2 {
+			t.Errorf("%s: expected 2 port-profile rows, got %d", c.name, len(dt.Ports))
+			continue
+		}
+		in := dt.Ports[0]
+		out := dt.Ports[1]
+		if in.CableTypeID != 1 || in.Count != 1 || in.Edge != "top" || in.LabelPrefix != "Power In" {
+			t.Errorf("%s: Power In row mismatch: %+v", c.name, in)
+		}
+		if out.CableTypeID != 1 || out.Count != c.outCount || out.Edge != "bottom" || out.LabelPrefix != "Power Out" {
+			t.Errorf("%s: Power Out row mismatch: %+v (want count=%d)", c.name, out, c.outCount)
+		}
+	}
+}
+
 // -------------------------------------------------------- CRUD (custom rows)
 
 func TestCreateDeviceType_CustomBasic(t *testing.T) {

internal/db/excalidraw_ids.go

@@ -0,0 +1,60 @@
+package db
+
+import (
+	"database/sql"
+)
+
+// PersistExcalidrawIDs writes the assignments returned by the exporter
+// back onto the corresponding rows. Idempotent: only updates rows whose
+// excalidraw_id is currently NULL (the first export "owns" the id; later
+// exports reuse it so mxdrw's collab cursors / undo history survive).
+//
+// Caller passes one map per kind; keys are the in-project row ids,
+// values are the 21-char Excalidraw element ids the exporter minted.
+func (s *Store) PersistExcalidrawIDs(projectID int64,
+	frames, devices, ports, ios, cables map[int64]string,
+) error {
+	tx, err := s.db.Begin()
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+
+	if err := updateExIDs(tx, "frames", projectID, frames); err != nil {
+		return err
+	}
+	if err := updateExIDs(tx, "devices", projectID, devices); err != nil {
+		return err
+	}
+	if err := updateExIDs(tx, "ports", projectID, ports); err != nil {
+		return err
+	}
+	if err := updateExIDs(tx, "io_markers", projectID, ios); err != nil {
+		return err
+	}
+	if err := updateExIDs(tx, "cables", projectID, cables); err != nil {
+		return err
+	}
+	return tx.Commit()
+}
+
+func updateExIDs(tx *sql.Tx, table string, projectID int64, m map[int64]string) error {
+	if len(m) == 0 {
+		return nil
+	}
+	stmt, err := tx.Prepare(
+		`UPDATE ` + table + `
+		 SET excalidraw_id = ?
+		 WHERE id = ? AND project_id = ? AND excalidraw_id IS NULL`,
+	)
+	if err != nil {
+		return err
+	}
+	defer stmt.Close()
+	for id, exID := range m {
+		if _, err := stmt.Exec(exID, id, projectID); err != nil {
+			return err
+		}
+	}
+	return nil
+}

internal/db/migrations/004_setup_templates.sql

@@ -0,0 +1,157 @@
+-- mCables v4.1 setup templates. See docs/design.md §2.4.
+--
+-- A template is a named recipe of (device_types + requirements) that
+-- bootstraps a project from blank to solver-ready in one apply call.
+
+CREATE TABLE setup_templates (
+    id              INTEGER PRIMARY KEY,
+    name            TEXT NOT NULL UNIQUE,
+    description     TEXT NOT NULL DEFAULT '',
+    built_in        INTEGER NOT NULL DEFAULT 0,
+    created_at      TEXT NOT NULL DEFAULT (datetime('now')),
+    updated_at      TEXT NOT NULL DEFAULT (datetime('now'))
+);
+
+CREATE TABLE setup_template_devices (
+    id              INTEGER PRIMARY KEY,
+    template_id     INTEGER NOT NULL REFERENCES setup_templates(id) ON DELETE CASCADE,
+    device_type_id  INTEGER NOT NULL REFERENCES device_types(id)    ON DELETE RESTRICT,
+    suggested_name  TEXT,
+    sort_order      INTEGER NOT NULL DEFAULT 0
+);
+CREATE INDEX setup_template_devices_template_idx ON setup_template_devices(template_id);
+
+CREATE TABLE setup_template_requirements (
+    id                       INTEGER PRIMARY KEY,
+    template_id              INTEGER NOT NULL REFERENCES setup_templates(id) ON DELETE CASCADE,
+    from_template_device_id  INTEGER NOT NULL REFERENCES setup_template_devices(id) ON DELETE CASCADE,
+    to_template_device_id    INTEGER NOT NULL REFERENCES setup_template_devices(id) ON DELETE CASCADE,
+    preferred_cable_type_id  INTEGER REFERENCES cable_types(id) ON DELETE SET NULL,
+    must_connect             INTEGER NOT NULL DEFAULT 1 CHECK (must_connect IN (0, 1)),
+    CHECK (from_template_device_id != to_template_device_id)
+);
+CREATE INDEX setup_template_reqs_template_idx ON setup_template_requirements(template_id);
+
+-- ---------------------------------------------------------------- Living Room
+INSERT INTO setup_templates (name, description, built_in)
+    VALUES ('Living Room', 'TV + Soundbar + ChromeCast, HDMI between them.', 1);
+
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Living Room'),
+        (SELECT id FROM device_types WHERE name='TV' AND project_id IS NULL),
+        'TV', 0;
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Living Room'),
+        (SELECT id FROM device_types WHERE name='Soundbar' AND project_id IS NULL),
+        'Soundbar', 1;
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Living Room'),
+        (SELECT id FROM device_types WHERE name='ChromeCast' AND project_id IS NULL),
+        'ChromeCast', 2;
+
+-- TV ↔ Soundbar (HDMI, must)
+INSERT INTO setup_template_requirements
+    (template_id, from_template_device_id, to_template_device_id, preferred_cable_type_id, must_connect)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Living Room'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Living Room') AND suggested_name='TV'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Living Room') AND suggested_name='Soundbar'),
+        3, 1;
+-- TV ↔ ChromeCast (HDMI, must)
+INSERT INTO setup_template_requirements
+    (template_id, from_template_device_id, to_template_device_id, preferred_cable_type_id, must_connect)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Living Room'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Living Room') AND suggested_name='TV'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Living Room') AND suggested_name='ChromeCast'),
+        3, 1;
+
+-- ---------------------------------------------------------------- Home Office
+INSERT INTO setup_templates (name, description, built_in)
+    VALUES ('Home Office', 'PC + Screen + Keyboard + Mouse. HDMI + USB.', 1);
+
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Home Office'),
+        (SELECT id FROM device_types WHERE name='PC' AND project_id IS NULL),
+        'PC', 0;
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Home Office'),
+        (SELECT id FROM device_types WHERE name='Screen' AND project_id IS NULL),
+        'Screen', 1;
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Home Office'),
+        (SELECT id FROM device_types WHERE name='Keyboard' AND project_id IS NULL),
+        'Keyboard', 2;
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Home Office'),
+        (SELECT id FROM device_types WHERE name='Mouse' AND project_id IS NULL),
+        'Mouse', 3;
+
+-- PC ↔ Screen (HDMI, must)
+INSERT INTO setup_template_requirements
+    (template_id, from_template_device_id, to_template_device_id, preferred_cable_type_id, must_connect)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Home Office'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Home Office') AND suggested_name='PC'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Home Office') AND suggested_name='Screen'),
+        3, 1;
+-- PC ↔ Keyboard (USB, must)
+INSERT INTO setup_template_requirements
+    (template_id, from_template_device_id, to_template_device_id, preferred_cable_type_id, must_connect)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Home Office'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Home Office') AND suggested_name='PC'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Home Office') AND suggested_name='Keyboard'),
+        2, 1;
+-- PC ↔ Mouse (USB, must)
+INSERT INTO setup_template_requirements
+    (template_id, from_template_device_id, to_template_device_id, preferred_cable_type_id, must_connect)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Home Office'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Home Office') AND suggested_name='PC'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Home Office') AND suggested_name='Mouse'),
+        2, 1;
+
+-- ---------------------------------------------------------------- Server Rack
+INSERT INTO setup_templates (name, description, built_in)
+    VALUES ('Server Rack', 'NAS + Switch + fritz. Ethernet trunk + power.', 1);
+
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Server Rack'),
+        (SELECT id FROM device_types WHERE name='NAS' AND project_id IS NULL),
+        'NAS', 0;
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Server Rack'),
+        (SELECT id FROM device_types WHERE name='Switch' AND project_id IS NULL),
+        'Switch', 1;
+INSERT INTO setup_template_devices (template_id, device_type_id, suggested_name, sort_order)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Server Rack'),
+        (SELECT id FROM device_types WHERE name='fritz' AND project_id IS NULL),
+        'fritz', 2;
+
+-- NAS ↔ Switch (RJ45, must)
+INSERT INTO setup_template_requirements
+    (template_id, from_template_device_id, to_template_device_id, preferred_cable_type_id, must_connect)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Server Rack'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Server Rack') AND suggested_name='NAS'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Server Rack') AND suggested_name='Switch'),
+        5, 1;
+-- Switch ↔ fritz (RJ45, must)
+INSERT INTO setup_template_requirements
+    (template_id, from_template_device_id, to_template_device_id, preferred_cable_type_id, must_connect)
+    SELECT
+        (SELECT id FROM setup_templates WHERE name='Server Rack'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Server Rack') AND suggested_name='Switch'),
+        (SELECT id FROM setup_template_devices WHERE template_id = (SELECT id FROM setup_templates WHERE name='Server Rack') AND suggested_name='fritz'),
+        5, 1;

internal/db/migrations/005_catalog_power.sql

@@ -0,0 +1,32 @@
+-- mCables v5 — catalog: power-distribution devices.
+-- Adds 5 built-in device_types (project_id NULL, built_in=1).
+--
+-- Multi-plug N exposes Power × (N+1) ports — one input + N outputs. The
+-- solver treats every Power port identically regardless of in/out
+-- direction; m knows which end is which from the physical setup.
+--
+-- Wifi-plug is a pass-through outlet (Power × 2: one in, one out).
+
+INSERT INTO device_types (name, kind, icon, built_in, description) VALUES
+    ('Multi-plug 3', 'hub',       '🔌', 1, '3-way power strip (1 in + 3 out)'),
+    ('Multi-plug 4', 'hub',       '🔌', 1, '4-way power strip (1 in + 4 out)'),
+    ('Multi-plug 5', 'hub',       '🔌', 1, '5-way power strip (1 in + 5 out)'),
+    ('Multi-plug 6', 'hub',       '🔌', 1, '6-way power strip (1 in + 6 out)'),
+    ('Wifi-plug',    'accessory', '📶', 1, 'WiFi-controllable pass-through outlet');
+
+-- Port profiles. cable_types id 1 = Power (seeded in 001).
+
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power', 4, 'bottom', 0 FROM device_types WHERE name='Multi-plug 3' AND project_id IS NULL;
+
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power', 5, 'bottom', 0 FROM device_types WHERE name='Multi-plug 4' AND project_id IS NULL;
+
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power', 6, 'bottom', 0 FROM device_types WHERE name='Multi-plug 5' AND project_id IS NULL;
+
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power', 7, 'bottom', 0 FROM device_types WHERE name='Multi-plug 6' AND project_id IS NULL;
+
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power', 2, 'bottom', 0 FROM device_types WHERE name='Wifi-plug' AND project_id IS NULL;

internal/db/migrations/006_fix_power_hubs.sql

@@ -0,0 +1,87 @@
+-- mCables v6 — fix IOx-* and Multi-plug-* + Wifi-plug port profiles.
+--
+-- v4 seeded the IOx-3 / IOx-6 / IOx-8 as USB hubs (Power × 1 + USB × N),
+-- but m's physical IOx-* devices are power strips (1 power input on
+-- the back, N power outputs on the front). v5's Multi-plug 3/4/5/6
+-- profiles also lumped every Power port on the bottom edge without
+-- distinguishing the input from the outputs.
+--
+-- This migration replaces the port profile for the 8 power-distribution
+-- types with the canonical "1 in (top/back) + N out (bottom/front)"
+-- layout. Convention: top=back, bottom=front.
+--
+-- N for each type:
+--   IOx-3 / Multi-plug 3 → 3 outputs
+--   IOx-6                 → 6 outputs
+--   IOx-8                 → 8 outputs
+--   Multi-plug 4          → 4 outputs
+--   Multi-plug 5          → 5 outputs
+--   Multi-plug 6          → 6 outputs
+--   Wifi-plug             → 1 output (it's a pass-through outlet)
+--
+-- Existing devices m may have created with the old profile keep their
+-- already-seeded ports — per design §2.3, ports are instance-owned. To
+-- get the new layout on an existing instance, delete it and re-create.
+--
+-- cable_types id 1 = Power (seeded in 001).
+
+-- 1) Drop the existing port-profile rows for each affected type.
+DELETE FROM device_type_ports
+ WHERE device_type_id IN (
+     SELECT id FROM device_types
+      WHERE project_id IS NULL
+        AND name IN (
+            'IOx-3', 'IOx-6', 'IOx-8',
+            'Multi-plug 3', 'Multi-plug 4', 'Multi-plug 5', 'Multi-plug 6',
+            'Wifi-plug'
+        )
+ );
+
+-- 2) Insert the canonical (1 in on top, N out on bottom) profile.
+-- IOx-3 — 1 in + 3 out
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power In',  1, 'top',    0 FROM device_types WHERE name='IOx-3' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power Out', 3, 'bottom', 1 FROM device_types WHERE name='IOx-3' AND project_id IS NULL;
+
+-- IOx-6 — 1 in + 6 out
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power In',  1, 'top',    0 FROM device_types WHERE name='IOx-6' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power Out', 6, 'bottom', 1 FROM device_types WHERE name='IOx-6' AND project_id IS NULL;
+
+-- IOx-8 — 1 in + 8 out
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power In',  1, 'top',    0 FROM device_types WHERE name='IOx-8' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power Out', 8, 'bottom', 1 FROM device_types WHERE name='IOx-8' AND project_id IS NULL;
+
+-- Multi-plug 3 — 1 in + 3 out
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power In',  1, 'top',    0 FROM device_types WHERE name='Multi-plug 3' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power Out', 3, 'bottom', 1 FROM device_types WHERE name='Multi-plug 3' AND project_id IS NULL;
+
+-- Multi-plug 4 — 1 in + 4 out
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power In',  1, 'top',    0 FROM device_types WHERE name='Multi-plug 4' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power Out', 4, 'bottom', 1 FROM device_types WHERE name='Multi-plug 4' AND project_id IS NULL;
+
+-- Multi-plug 5 — 1 in + 5 out
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power In',  1, 'top',    0 FROM device_types WHERE name='Multi-plug 5' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power Out', 5, 'bottom', 1 FROM device_types WHERE name='Multi-plug 5' AND project_id IS NULL;
+
+-- Multi-plug 6 — 1 in + 6 out
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power In',  1, 'top',    0 FROM device_types WHERE name='Multi-plug 6' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power Out', 6, 'bottom', 1 FROM device_types WHERE name='Multi-plug 6' AND project_id IS NULL;
+
+-- Wifi-plug — 1 in + 1 out (pass-through outlet)
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power In',  1, 'top',    0 FROM device_types WHERE name='Wifi-plug' AND project_id IS NULL;
+INSERT INTO device_type_ports (device_type_id, cable_type_id, label_prefix, count, edge, sort_order)
+    SELECT id, 1, 'Power Out', 1, 'bottom', 1 FROM device_types WHERE name='Wifi-plug' AND project_id IS NULL;

internal/db/models.go

@@ -111,6 +111,102 @@ type ConnectionRequirement struct {
 	UpdatedAt             string `json:"updated_at"`
 }
 
+// Cable is a typed connection. Each endpoint is exactly one of
+// (port, device, io-marker). Auto=true means the solver placed it.
+type Cable struct {
+	ID            int64   `json:"id"`
+	ProjectID     int64   `json:"project_id"`
+	TypeID        int64   `json:"type_id"`
+	Label         *string `json:"label"`
+	FromPortID    *int64  `json:"from_port_id"`
+	FromDeviceID  *int64  `json:"from_device_id"`
+	FromIOID      *int64  `json:"from_io_id"`
+	ToPortID      *int64  `json:"to_port_id"`
+	ToDeviceID    *int64  `json:"to_device_id"`
+	ToIOID        *int64  `json:"to_io_id"`
+	Auto          bool    `json:"auto"`
+	ExcalidrawID  *string `json:"excalidraw_id,omitempty"`
+	CreatedAt     string  `json:"created_at"`
+	UpdatedAt     string  `json:"updated_at"`
+}
+
+// Bundle is a named group of cables that physically run together.
+type Bundle struct {
+	ID         int64   `json:"id"`
+	ProjectID  int64   `json:"project_id"`
+	Name       string  `json:"name"`
+	Auto       bool    `json:"auto"`
+	CableIDs   []int64 `json:"cable_ids"`
+	CreatedAt  string  `json:"created_at"`
+	UpdatedAt  string  `json:"updated_at"`
+}
+
+// SetupTemplate is a named recipe of device-types + requirements.
+type SetupTemplate struct {
+	ID           int64                       `json:"id"`
+	Name         string                      `json:"name"`
+	Description  string                      `json:"description"`
+	BuiltIn      bool                        `json:"built_in"`
+	Devices      []SetupTemplateDevice       `json:"devices"`
+	Requirements []SetupTemplateRequirement  `json:"requirements"`
+	CreatedAt    string                      `json:"created_at"`
+	UpdatedAt    string                      `json:"updated_at"`
+}
+
+type SetupTemplateDevice struct {
+	ID             int64       `json:"id"`
+	TemplateID     int64       `json:"template_id"`
+	DeviceTypeID   int64       `json:"device_type_id"`
+	DeviceType     *DeviceType `json:"device_type,omitempty"`
+	SuggestedName  *string     `json:"suggested_name"`
+	SortOrder      int         `json:"sort_order"`
+}
+
+type SetupTemplateRequirement struct {
+	ID                      int64  `json:"id"`
+	TemplateID              int64  `json:"template_id"`
+	FromTemplateDeviceID    int64  `json:"from_template_device_id"`
+	ToTemplateDeviceID      int64  `json:"to_template_device_id"`
+	PreferredCableTypeID    *int64 `json:"preferred_cable_type_id"`
+	MustConnect             bool   `json:"must_connect"`
+}
+
+// SolveResult is the response shape from POST /api/projects/:pid/solve.
+type SolveResult struct {
+	CablesAdded     []Cable                `json:"cables_added"`
+	CablesKept      []int64                `json:"cables_kept"`
+	CablesRemoved   []int64                `json:"cables_removed"`
+	BundlesAdded    []Bundle               `json:"bundles_added"`
+	BundlesRemoved  []int64                `json:"bundles_removed"`
+	Unsatisfied     []UnsatisfiedReq       `json:"unsatisfied"`
+	Warnings        []string               `json:"warnings"`
+}
+
+type UnsatisfiedReq struct {
+	RequirementID int64  `json:"requirement_id"`
+	Reason        string `json:"reason"`
+	WhichSide     string `json:"which_side,omitempty"` // "from" | "to" | "" when both/neither
+	CableType     string `json:"cable_type,omitempty"`  // when known
+}
+
+// ApplyTemplateResult is the response from POST /apply-template.
+type ApplyTemplateResult struct {
+	FramesAdded         []Frame                 `json:"frames_added"`
+	DevicesAdded        []Device                `json:"devices_added"`
+	RequirementsAdded   []ConnectionRequirement `json:"requirements_added"`
+	SkippedDevices      []SkippedTemplateDevice `json:"skipped_devices"`
+	RequirementsSkipped []SkippedTemplateReq    `json:"requirements_skipped"`
+}
+
+type SkippedTemplateDevice struct {
+	TemplateDeviceID int64  `json:"template_device_id"`
+	Reason           string `json:"reason"`
+}
+type SkippedTemplateReq struct {
+	TemplateRequirementID int64  `json:"template_requirement_id"`
+	Reason                string `json:"reason"`
+}
+
 // Snapshot is the editor's one-shot loader payload for a single project.
 // Arrays for collections still gated by future slices stay non-nil [] so
 // JSON encodes as [] not null.
@@ -119,9 +215,9 @@ type Snapshot struct {
 	Frames                 []Frame                 `json:"frames"`
 	Devices                []Device                `json:"devices"`
 	Ports                  []Port                  `json:"ports"`
-	Cables                 []any                   `json:"cables"`
+	Cables                 []Cable                 `json:"cables"`
 	IOMarkers              []IOMarker              `json:"io_markers"`
-	Bundles                []any                   `json:"bundles"`
+	Bundles                []Bundle                `json:"bundles"`
 	CableTypes             []CableType             `json:"cable_types"`
 	ConnectionRequirements []ConnectionRequirement `json:"connection_requirements"`
 }

internal/db/ports.go

@@ -2,8 +2,187 @@ package db
 
 import (
 	"database/sql"
+	"errors"
+	"fmt"
+	"strings"
 )
 
+// PortCreate is the create-shape for POST /api/projects/:pid/devices/:id/ports.
+type PortCreate struct {
+	TypeID  int64
+	Label   string
+	XOffset float64
+	YOffset float64
+}
+
+// PortUpdate is the partial-update shape.
+type PortUpdate struct {
+	TypeID  *int64
+	Label   *string
+	XOffset *float64
+	YOffset *float64
+}
+
+// CreatePort inserts a port on a device. The device must exist in the
+// project; the cable type must exist globally.
+func (s *Store) CreatePort(projectID, deviceID int64, p PortCreate) (*Port, error) {
+	if _, err := s.GetDevice(projectID, deviceID); err != nil {
+		return nil, err
+	}
+	if _, err := s.GetCableType(p.TypeID); err != nil {
+		if errors.Is(err, ErrNotFound) {
+			return nil, fmt.Errorf("%w: cable type %d not found", ErrInvalidInput, p.TypeID)
+		}
+		return nil, err
+	}
+	label := strings.TrimSpace(p.Label)
+	var labelArg any
+	if label != "" {
+		labelArg = label
+	}
+	res, err := s.db.Exec(
+		`INSERT INTO ports (project_id, device_id, type_id, label, x_offset, y_offset)
+		 VALUES (?, ?, ?, ?, ?, ?)`,
+		projectID, deviceID, p.TypeID, labelArg, p.XOffset, p.YOffset,
+	)
+	if err != nil {
+		return nil, mapWriteErr(err)
+	}
+	id, _ := res.LastInsertId()
+	return s.GetPort(projectID, id)
+}
+
+// GetPort loads a port by id, project-scoped.
+func (s *Store) GetPort(projectID, id int64) (*Port, error) {
+	var p Port
+	var label, ex sql.NullString
+	err := s.db.QueryRow(
+		`SELECT id, project_id, device_id, type_id, label, x_offset, y_offset,
+		        excalidraw_id, created_at, updated_at
+		 FROM ports WHERE id = ? AND project_id = ?`, id, projectID,
+	).Scan(&p.ID, &p.ProjectID, &p.DeviceID, &p.TypeID, &label,
+		&p.XOffset, &p.YOffset, &ex, &p.CreatedAt, &p.UpdatedAt)
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	if label.Valid {
+		v := label.String
+		p.Label = &v
+	}
+	if ex.Valid {
+		p.ExcalidrawID = &ex.String
+	}
+	return &p, nil
+}
+
+// UpdatePort applies a partial update.
+func (s *Store) UpdatePort(projectID, id int64, u PortUpdate) (*Port, error) {
+	cur, err := s.GetPort(projectID, id)
+	if err != nil {
+		return nil, err
+	}
+	if u.TypeID != nil {
+		if _, err := s.GetCableType(*u.TypeID); err != nil {
+			if errors.Is(err, ErrNotFound) {
+				return nil, fmt.Errorf("%w: cable type %d not found", ErrInvalidInput, *u.TypeID)
+			}
+			return nil, err
+		}
+		cur.TypeID = *u.TypeID
+	}
+	if u.Label != nil {
+		v := strings.TrimSpace(*u.Label)
+		if v == "" {
+			cur.Label = nil
+		} else {
+			cur.Label = &v
+		}
+	}
+	if u.XOffset != nil {
+		cur.XOffset = *u.XOffset
+	}
+	if u.YOffset != nil {
+		cur.YOffset = *u.YOffset
+	}
+	var labelArg any
+	if cur.Label != nil {
+		labelArg = *cur.Label
+	}
+	if _, err := s.db.Exec(
+		`UPDATE ports
+		 SET type_id = ?, label = ?, x_offset = ?, y_offset = ?, updated_at = datetime('now')
+		 WHERE id = ? AND project_id = ?`,
+		cur.TypeID, labelArg, cur.XOffset, cur.YOffset, id, projectID,
+	); err != nil {
+		return nil, mapWriteErr(err)
+	}
+	return s.GetPort(projectID, id)
+}
+
+// DeletePort removes a port from a device. The schema's
+// ON DELETE SET NULL on cables.from_port_id / to_port_id collides with
+// the cable's CHECK ((from_port|from_device|from_io) = 1 non-null), so
+// we instead cascade-delete any cables that referenced the port on
+// either side — same effect from m's POV: the cable is gone, m can
+// re-draw if he still wants it.
+func (s *Store) DeletePort(projectID, id int64) error {
+	if _, err := s.GetPort(projectID, id); err != nil {
+		return err
+	}
+	tx, err := s.db.Begin()
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback()
+	if _, err := tx.Exec(
+		`DELETE FROM cables WHERE project_id = ? AND (from_port_id = ? OR to_port_id = ?)`,
+		projectID, id, id,
+	); err != nil {
+		return err
+	}
+	if _, err := tx.Exec(
+		`DELETE FROM ports WHERE id = ? AND project_id = ?`, id, projectID,
+	); err != nil {
+		return err
+	}
+	return tx.Commit()
+}
+
+// ListPortsForDevice returns every port on one device, project-scoped.
+func (s *Store) ListPortsForDevice(projectID, deviceID int64) ([]Port, error) {
+	rows, err := s.db.Query(
+		`SELECT id, project_id, device_id, type_id, label, x_offset, y_offset,
+		        excalidraw_id, created_at, updated_at
+		 FROM ports WHERE project_id = ? AND device_id = ? ORDER BY id`,
+		projectID, deviceID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []Port{}
+	for rows.Next() {
+		var p Port
+		var label, ex sql.NullString
+		if err := rows.Scan(&p.ID, &p.ProjectID, &p.DeviceID, &p.TypeID, &label,
+			&p.XOffset, &p.YOffset, &ex, &p.CreatedAt, &p.UpdatedAt); err != nil {
+			return nil, err
+		}
+		if label.Valid {
+			v := label.String
+			p.Label = &v
+		}
+		if ex.Valid {
+			p.ExcalidrawID = &ex.String
+		}
+		out = append(out, p)
+	}
+	return out, rows.Err()
+}
+
 // ListPortsForProject returns every port in a project, ordered by
 // device_id + id so callers can group cheaply.
 func (s *Store) ListPortsForProject(projectID int64) ([]Port, error) {

internal/db/setup_templates.go

@@ -0,0 +1,465 @@
+package db
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+	"math"
+	"strings"
+)
+
+// ListSetupTemplates returns every template with its devices +
+// requirements hydrated.
+func (s *Store) ListSetupTemplates() ([]SetupTemplate, error) {
+	rows, err := s.db.Query(
+		`SELECT id, name, description, built_in, created_at, updated_at
+		 FROM setup_templates ORDER BY id`,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []SetupTemplate{}
+	for rows.Next() {
+		var t SetupTemplate
+		var built int
+		if err := rows.Scan(&t.ID, &t.Name, &t.Description, &built,
+			&t.CreatedAt, &t.UpdatedAt); err != nil {
+			return nil, err
+		}
+		t.BuiltIn = built != 0
+		out = append(out, t)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	for i := range out {
+		devs, err := s.listTemplateDevices(out[i].ID)
+		if err != nil {
+			return nil, err
+		}
+		out[i].Devices = devs
+		reqs, err := s.listTemplateRequirements(out[i].ID)
+		if err != nil {
+			return nil, err
+		}
+		out[i].Requirements = reqs
+	}
+	return out, nil
+}
+
+// GetSetupTemplate is a one-template variant of List.
+func (s *Store) GetSetupTemplate(id int64) (*SetupTemplate, error) {
+	var t SetupTemplate
+	var built int
+	err := s.db.QueryRow(
+		`SELECT id, name, description, built_in, created_at, updated_at
+		 FROM setup_templates WHERE id = ?`, id,
+	).Scan(&t.ID, &t.Name, &t.Description, &built, &t.CreatedAt, &t.UpdatedAt)
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	t.BuiltIn = built != 0
+	t.Devices, err = s.listTemplateDevices(t.ID)
+	if err != nil {
+		return nil, err
+	}
+	t.Requirements, err = s.listTemplateRequirements(t.ID)
+	if err != nil {
+		return nil, err
+	}
+	return &t, nil
+}
+
+func (s *Store) listTemplateDevices(templateID int64) ([]SetupTemplateDevice, error) {
+	rows, err := s.db.Query(
+		`SELECT id, template_id, device_type_id, suggested_name, sort_order
+		 FROM setup_template_devices WHERE template_id = ? ORDER BY sort_order, id`,
+		templateID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []SetupTemplateDevice{}
+	for rows.Next() {
+		var d SetupTemplateDevice
+		var sn sql.NullString
+		if err := rows.Scan(&d.ID, &d.TemplateID, &d.DeviceTypeID, &sn, &d.SortOrder); err != nil {
+			return nil, err
+		}
+		if sn.Valid {
+			v := sn.String
+			d.SuggestedName = &v
+		}
+		out = append(out, d)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	// Hydrate the device_type for the UI's optgroup labels.
+	for i := range out {
+		dt, err := s.GetDeviceType(out[i].DeviceTypeID)
+		if err == nil {
+			out[i].DeviceType = dt
+		}
+	}
+	return out, nil
+}
+
+func (s *Store) listTemplateRequirements(templateID int64) ([]SetupTemplateRequirement, error) {
+	rows, err := s.db.Query(
+		`SELECT id, template_id, from_template_device_id, to_template_device_id,
+		        preferred_cable_type_id, must_connect
+		 FROM setup_template_requirements WHERE template_id = ? ORDER BY id`,
+		templateID,
+	)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	out := []SetupTemplateRequirement{}
+	for rows.Next() {
+		var r SetupTemplateRequirement
+		var pct sql.NullInt64
+		var must int
+		if err := rows.Scan(&r.ID, &r.TemplateID, &r.FromTemplateDeviceID, &r.ToTemplateDeviceID,
+			&pct, &must); err != nil {
+			return nil, err
+		}
+		if pct.Valid {
+			v := pct.Int64
+			r.PreferredCableTypeID = &v
+		}
+		r.MustConnect = must != 0
+		out = append(out, r)
+	}
+	return out, rows.Err()
+}
+
+// ApplyTemplateOptions controls per-device name overrides + opt-outs.
+type ApplyTemplateOptions struct {
+	NameOverrides map[int64]string // template_device_id → custom name
+	SkipDevices   map[int64]bool   // template_device_id → skip
+	// Layout: where to place the first device in the cluster on the canvas.
+	OriginX, OriginY float64
+}
+
+// ApplyTemplate seeds devices + requirements from the template into
+// projectID in a single transaction. Name collisions skip the device
+// (recorded in skipped_devices); requirements whose endpoints both fail
+// to land are also skipped.
+func (s *Store) ApplyTemplate(projectID, templateID int64, opts ApplyTemplateOptions) (*ApplyTemplateResult, error) {
+	tmpl, err := s.GetSetupTemplate(templateID)
+	if err != nil {
+		return nil, err
+	}
+	if _, err := s.GetProject(projectID); err != nil {
+		return nil, err
+	}
+
+	out := &ApplyTemplateResult{
+		FramesAdded:         []Frame{},
+		DevicesAdded:        []Device{},
+		RequirementsAdded:   []ConnectionRequirement{},
+		SkippedDevices:      []SkippedTemplateDevice{},
+		RequirementsSkipped: []SkippedTemplateReq{},
+	}
+
+	if opts.OriginX == 0 && opts.OriginY == 0 {
+		opts.OriginX, opts.OriginY = 200, 200
+	}
+
+	// Pull existing device + frame names in the project so we can
+	// pre-check collisions without aborting the whole transaction.
+	existing, err := s.ListDevices(projectID, nil)
+	if err != nil {
+		return nil, err
+	}
+	nameTaken := map[string]bool{}
+	for _, d := range existing {
+		nameTaken[d.Name] = true
+	}
+	existingFrames, err := s.ListFrames(projectID)
+	if err != nil {
+		return nil, err
+	}
+	frameNameTaken := map[string]bool{}
+	for _, f := range existingFrames {
+		frameNameTaken[f.Name] = true
+	}
+
+	tx, err := s.db.Begin()
+	if err != nil {
+		return nil, err
+	}
+	defer tx.Rollback()
+
+	// Plan a uniform grid for the template's devices inside a new frame
+	// named after the template. The grid drives both frame size and
+	// per-device (x, y). Devices that get skipped (name collision /
+	// SkipDevices) leave their grid cell empty.
+	const (
+		devW, devH = 100.0, 35.0
+		gapX, gapY = 30.0, 50.0
+		padX, padY = 32.0, 48.0 // padY larger so the frame title clears row 1
+	)
+	n := len(tmpl.Devices)
+	cols := 1
+	if n > 0 {
+		cols = min(int(math.Ceil(math.Sqrt(float64(n)))), 4)
+	}
+	rows := 1
+	if n > 0 {
+		rows = (n + cols - 1) / cols
+	}
+	frameW := padX*2 + float64(cols)*devW + float64(cols-1)*gapX
+	frameH := padY + padX + float64(rows)*devH + float64(rows-1)*gapY
+	frameName := pickFrameName(tmpl.Name, frameNameTaken)
+
+	frame, err := createFrameTx(tx, projectID, FrameCreate{
+		Name: frameName, X: opts.OriginX, Y: opts.OriginY,
+		Width: frameW, Height: frameH,
+	})
+	if err != nil {
+		return nil, fmt.Errorf("seed frame %q: %w", frameName, err)
+	}
+	out.FramesAdded = append(out.FramesAdded, *frame)
+
+	// Map: template_device_id → newly-created device_id (or 0 if skipped).
+	tmplToDevice := map[int64]int64{}
+
+	for i, td := range tmpl.Devices {
+		if opts.SkipDevices[td.ID] {
+			out.SkippedDevices = append(out.SkippedDevices, SkippedTemplateDevice{
+				TemplateDeviceID: td.ID, Reason: "skip requested",
+			})
+			tmplToDevice[td.ID] = 0
+			continue
+		}
+		name := opts.NameOverrides[td.ID]
+		if name == "" && td.SuggestedName != nil {
+			name = *td.SuggestedName
+		}
+		if name == "" {
+			name = fmt.Sprintf("Device %d", td.ID)
+		}
+		name = strings.TrimSpace(name)
+		if nameTaken[name] {
+			out.SkippedDevices = append(out.SkippedDevices, SkippedTemplateDevice{
+				TemplateDeviceID: td.ID,
+				Reason:           fmt.Sprintf("name %q already used in project", name),
+			})
+			tmplToDevice[td.ID] = 0
+			continue
+		}
+		// Grid cell (col, row) within the frame. Cell anchor is the
+		// top-left of the device rect; offsets are added to the frame's
+		// own (x, y) so the device sits inside the frame.
+		col := i % cols
+		row := i / cols
+		x := frame.X + padX + float64(col)*(devW+gapX)
+		y := frame.Y + padY + float64(row)*(devH+gapY)
+		// Use createDeviceTx so port-seeding shares the same transaction.
+		d, err := s.createDeviceTx(tx, projectID, DeviceCreate{
+			Name:    name,
+			TypeID:  &td.DeviceTypeID,
+			FrameID: &frame.ID,
+			X:       x,
+			Y:       y,
+			Width:   devW,
+			Height:  devH,
+		})
+		if err != nil {
+			return nil, fmt.Errorf("seed %s: %w", name, err)
+		}
+		nameTaken[name] = true
+		tmplToDevice[td.ID] = d.ID
+		out.DevicesAdded = append(out.DevicesAdded, *d)
+	}
+
+	for _, tr := range tmpl.Requirements {
+		fromID := tmplToDevice[tr.FromTemplateDeviceID]
+		toID := tmplToDevice[tr.ToTemplateDeviceID]
+		if fromID == 0 || toID == 0 {
+			out.RequirementsSkipped = append(out.RequirementsSkipped, SkippedTemplateReq{
+				TemplateRequirementID: tr.ID,
+				Reason:                "one or both endpoint devices were skipped",
+			})
+			continue
+		}
+		// Normalise pair_lo/pair_hi, mirror what CreateConnectionRequirement does.
+		lo, hi := fromID, toID
+		if lo > hi {
+			lo, hi = hi, lo
+		}
+		must := 0
+		if tr.MustConnect {
+			must = 1
+		}
+		var ctArg any
+		if tr.PreferredCableTypeID != nil {
+			ctArg = *tr.PreferredCableTypeID
+		}
+		res, err := tx.Exec(
+			`INSERT INTO connection_requirements
+			   (project_id, from_device_id, to_device_id, preferred_cable_type_id,
+			    must_connect, notes, pair_lo, pair_hi)
+			 VALUES (?, ?, ?, ?, ?, '', ?, ?)`,
+			projectID, fromID, toID, ctArg, must, lo, hi,
+		)
+		if err != nil {
+			// A UNIQUE collision (project already has the same requirement)
+			// is non-fatal — record as skipped, continue.
+			if strings.Contains(err.Error(), "UNIQUE constraint failed") {
+				out.RequirementsSkipped = append(out.RequirementsSkipped, SkippedTemplateReq{
+					TemplateRequirementID: tr.ID,
+					Reason:                "requirement already exists in project",
+				})
+				continue
+			}
+			return nil, err
+		}
+		rid, _ := res.LastInsertId()
+		out.RequirementsAdded = append(out.RequirementsAdded, ConnectionRequirement{
+			ID:                   rid,
+			ProjectID:            projectID,
+			FromDeviceID:         fromID,
+			ToDeviceID:           toID,
+			PreferredCableTypeID: tr.PreferredCableTypeID,
+			MustConnect:          tr.MustConnect,
+		})
+	}
+
+	if err := tx.Commit(); err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+// pickFrameName returns a frame name that doesn't collide with anything
+// in `taken`. Tries the template name first, then "<name> 2", "<name> 3",
+// and so on.
+func pickFrameName(base string, taken map[string]bool) string {
+	if !taken[base] {
+		return base
+	}
+	for i := 2; ; i++ {
+		candidate := fmt.Sprintf("%s %d", base, i)
+		if !taken[candidate] {
+			return candidate
+		}
+	}
+}
+
+// createFrameTx inserts a frame inside the caller's transaction. Mirrors
+// the validation in CreateFrame (name + positive size) but avoids the
+// s.db.Exec call so ApplyTemplate can keep everything on the same
+// connection under MaxOpenConns(1).
+func createFrameTx(tx *sql.Tx, projectID int64, f FrameCreate) (*Frame, error) {
+	name := strings.TrimSpace(f.Name)
+	if name == "" {
+		return nil, fmt.Errorf("%w: name is required", ErrInvalidInput)
+	}
+	if f.Width <= 0 || f.Height <= 0 {
+		return nil, fmt.Errorf("%w: width and height must be positive", ErrInvalidInput)
+	}
+	res, err := tx.Exec(
+		`INSERT INTO frames (project_id, name, x, y, width, height)
+		 VALUES (?, ?, ?, ?, ?, ?)`,
+		projectID, name, f.X, f.Y, f.Width, f.Height,
+	)
+	if err != nil {
+		return nil, mapWriteErr(err)
+	}
+	id, _ := res.LastInsertId()
+	var out Frame
+	var ex sql.NullString
+	err = tx.QueryRow(
+		`SELECT id, project_id, name, x, y, width, height, excalidraw_id, created_at, updated_at
+		 FROM frames WHERE id = ? AND project_id = ?`, id, projectID,
+	).Scan(&out.ID, &out.ProjectID, &out.Name, &out.X, &out.Y, &out.Width, &out.Height,
+		&ex, &out.CreatedAt, &out.UpdatedAt)
+	if err != nil {
+		return nil, err
+	}
+	if ex.Valid {
+		out.ExcalidrawID = &ex.String
+	}
+	return &out, nil
+}
+
+// createDeviceTx is a tx-aware variant of CreateDevice used by
+// ApplyTemplate so seeding the template's devices + their ports stays
+// inside one atomic apply.
+//
+// Validation is intentionally lighter than CreateDevice: callers (only
+// ApplyTemplate today) hold a tx on the single SQLite connection, so
+// any "validate by reading from s.db" call would deadlock. The template's
+// device_type_id + frame_id come from already-validated template rows,
+// and SQLite FK constraints catch any genuine corruption on INSERT
+// (mapped to ErrInvalidInput by mapWriteErr).
+func (s *Store) createDeviceTx(tx *sql.Tx, projectID int64, d DeviceCreate) (*Device, error) {
+	name := strings.TrimSpace(d.Name)
+	if name == "" {
+		return nil, fmt.Errorf("%w: name is required", ErrInvalidInput)
+	}
+	if d.Width <= 0 || d.Height <= 0 {
+		return nil, fmt.Errorf("%w: width and height must be positive", ErrInvalidInput)
+	}
+	color := strings.TrimSpace(d.Color)
+	if color == "" {
+		color = "#1e1e1e"
+	}
+	res, err := tx.Exec(
+		`INSERT INTO devices (project_id, frame_id, type_id, name, color, x, y, width, height)
+		 VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)`,
+		projectID, nullableInt64(d.FrameID), nullableInt64(d.TypeID),
+		name, color, d.X, d.Y, d.Width, d.Height,
+	)
+	if err != nil {
+		return nil, mapWriteErr(err)
+	}
+	deviceID, _ := res.LastInsertId()
+	if d.TypeID != nil {
+		if err := s.seedPortsFromType(tx, projectID, deviceID, *d.TypeID, d.Width, d.Height); err != nil {
+			return nil, err
+		}
+	}
+	// Read back via the public store path is fine — the row exists in
+	// the in-flight tx and SQLite sees its own writes within the tx.
+	// Use a sub-helper that takes the tx executor for clean isolation.
+	return s.readDeviceTx(tx, projectID, deviceID)
+}
+
+func (s *Store) readDeviceTx(ex execer, projectID, id int64) (*Device, error) {
+	var d Device
+	var frame, typeID sql.NullInt64
+	var ex2 sql.NullString
+	err := ex.QueryRow(
+		`SELECT id, project_id, frame_id, type_id, name, color, x, y, width, height, excalidraw_id, created_at, updated_at
+		 FROM devices WHERE id = ? AND project_id = ?`, id, projectID,
+	).Scan(&d.ID, &d.ProjectID, &frame, &typeID, &d.Name, &d.Color, &d.X, &d.Y, &d.Width, &d.Height,
+		&ex2, &d.CreatedAt, &d.UpdatedAt)
+	if errors.Is(err, sql.ErrNoRows) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	if frame.Valid {
+		v := frame.Int64
+		d.FrameID = &v
+	}
+	if typeID.Valid {
+		v := typeID.Int64
+		d.TypeID = &v
+	}
+	if ex2.Valid {
+		d.ExcalidrawID = &ex2.String
+	}
+	return &d, nil
+}

internal/db/solver.go

@@ -0,0 +1,509 @@
+package db
+
+import (
+	"database/sql"
+	"fmt"
+	"sort"
+)
+
+// Solve runs the v0 algorithm (design v4.1 §5b.2) against the project.
+// If preview is true, no DB writes happen — the function returns the
+// diff it WOULD apply. If preview is false, the diff is applied in a
+// single transaction.
+//
+// Algorithm:
+//   1. Read all auto cables, manual cables, ports, requirements.
+//   2. Reserve ports used by manual cables (auto=0) so the solver
+//      doesn't reuse them.
+//   3. For each requirement (must_connect DESC, id ASC):
+//        - Resolve cable type: preferred, or T = port-types(from) ∩
+//          port-types(to). |T|==1 → that. |T|>1 → unsatisfied (ambiguous).
+//          |T|==0 → unsatisfied (no compat type).
+//        - Find lowest-id free port on each side. None → unsatisfied
+//          (no free port). Reserve both.
+//        - Stage an "add cable {from_port, to_port, type, auto=1}".
+//   4. Endpoint-pair bundle: any pair of device endpoints with ≥ 2
+//      staged cables becomes an auto bundle.
+//   5. Diff against existing auto cables/bundles: removed = existing
+//      auto rows not in the staged set; kept = those that match by
+//      (from_port, to_port, type); add = remaining staged rows.
+func (s *Store) Solve(projectID int64, preview bool) (*SolveResult, error) {
+	res := &SolveResult{
+		CablesAdded:    []Cable{},
+		CablesKept:     []int64{},
+		CablesRemoved:  []int64{},
+		BundlesAdded:   []Bundle{},
+		BundlesRemoved: []int64{},
+		Unsatisfied:    []UnsatisfiedReq{},
+		Warnings:       []string{},
+	}
+
+	if _, err := s.GetProject(projectID); err != nil {
+		return nil, err
+	}
+	devices, err := s.ListDevices(projectID, nil)
+	if err != nil {
+		return nil, err
+	}
+	ports, err := s.ListPortsForProject(projectID)
+	if err != nil {
+		return nil, err
+	}
+	cables, err := s.ListCables(projectID)
+	if err != nil {
+		return nil, err
+	}
+	reqs, err := s.ListConnectionRequirements(projectID)
+	if err != nil {
+		return nil, err
+	}
+	bundles, err := s.ListBundles(projectID)
+	if err != nil {
+		return nil, err
+	}
+
+	// Index ports by (device_id, type_id), sorted by id (deterministic).
+	portsByDevice := map[int64][]Port{}
+	for _, p := range ports {
+		portsByDevice[p.DeviceID] = append(portsByDevice[p.DeviceID], p)
+	}
+	for did := range portsByDevice {
+		sort.SliceStable(portsByDevice[did], func(i, j int) bool {
+			return portsByDevice[did][i].ID < portsByDevice[did][j].ID
+		})
+	}
+	deviceByID := map[int64]Device{}
+	for _, d := range devices {
+		deviceByID[d.ID] = d
+	}
+
+	// Reserve ports used by manual cables.
+	usedPorts := map[int64]bool{}
+	autoCablesByID := map[int64]Cable{}
+	for _, c := range cables {
+		if c.Auto {
+			autoCablesByID[c.ID] = c
+			continue
+		}
+		if c.FromPortID != nil {
+			usedPorts[*c.FromPortID] = true
+		}
+		if c.ToPortID != nil {
+			usedPorts[*c.ToPortID] = true
+		}
+	}
+
+	// Sort requirements: must_connect DESC, id ASC.
+	rs := append([]ConnectionRequirement{}, reqs...)
+	sort.SliceStable(rs, func(i, j int) bool {
+		if rs[i].MustConnect != rs[j].MustConnect {
+			return rs[i].MustConnect
+		}
+		return rs[i].ID < rs[j].ID
+	})
+
+	type staged struct {
+		typeID       int64
+		fromPortID   int64
+		toPortID     int64
+		fromDeviceID int64
+		toDeviceID   int64
+	}
+	var staging []staged
+
+	for _, r := range rs {
+		_, fromOK := deviceByID[r.FromDeviceID]
+		_, toOK := deviceByID[r.ToDeviceID]
+		if !fromOK || !toOK {
+			// Shouldn't happen (FK CASCADE removes the row when a device
+			// goes), but be defensive.
+			continue
+		}
+
+		// Resolve cable type.
+		var typeID int64
+		if r.PreferredCableTypeID != nil {
+			typeID = *r.PreferredCableTypeID
+		} else {
+			fromTypes := map[int64]bool{}
+			for _, p := range portsByDevice[r.FromDeviceID] {
+				fromTypes[p.TypeID] = true
+			}
+			candidates := []int64{}
+			for _, p := range portsByDevice[r.ToDeviceID] {
+				if fromTypes[p.TypeID] {
+					// Add unique.
+					already := false
+					for _, c := range candidates {
+						if c == p.TypeID {
+							already = true
+							break
+						}
+					}
+					if !already {
+						candidates = append(candidates, p.TypeID)
+					}
+				}
+			}
+			if len(candidates) == 0 {
+				if r.MustConnect {
+					res.Unsatisfied = append(res.Unsatisfied, UnsatisfiedReq{
+						RequirementID: r.ID,
+						Reason:        "no compatible cable type — devices share no port-type",
+					})
+				}
+				continue
+			}
+			if len(candidates) > 1 {
+				if r.MustConnect {
+					res.Unsatisfied = append(res.Unsatisfied, UnsatisfiedReq{
+						RequirementID: r.ID,
+						Reason:        "ambiguous cable type — specify preferred_cable_type_id",
+					})
+				}
+				continue
+			}
+			typeID = candidates[0]
+		}
+
+		// Pick lowest-id free port of `typeID` on each side.
+		pickFree := func(deviceID, t int64) *int64 {
+			for _, p := range portsByDevice[deviceID] {
+				if p.TypeID != t {
+					continue
+				}
+				if usedPorts[p.ID] {
+					continue
+				}
+				return &p.ID
+			}
+			return nil
+		}
+		fromPort := pickFree(r.FromDeviceID, typeID)
+		toPort := pickFree(r.ToDeviceID, typeID)
+		if fromPort == nil || toPort == nil {
+			if r.MustConnect {
+				side := ""
+				if fromPort == nil && toPort == nil {
+					side = ""
+				} else if fromPort == nil {
+					side = "from"
+				} else {
+					side = "to"
+				}
+				typeName := ""
+				if ct, err := s.GetCableType(typeID); err == nil {
+					typeName = ct.Name
+				}
+				res.Unsatisfied = append(res.Unsatisfied, UnsatisfiedReq{
+					RequirementID: r.ID,
+					Reason:        fmt.Sprintf("no free %s port", typeName),
+					WhichSide:     side,
+					CableType:     typeName,
+				})
+			}
+			continue
+		}
+		usedPorts[*fromPort] = true
+		usedPorts[*toPort] = true
+		staging = append(staging, staged{
+			typeID: typeID, fromPortID: *fromPort, toPortID: *toPort,
+			fromDeviceID: r.FromDeviceID, toDeviceID: r.ToDeviceID,
+		})
+	}
+
+	// Match staged → existing auto cables by (typeID, fromPortID, toPortID)
+	// or its reverse. Anything matched is "kept"; the rest of auto cables
+	// is "removed". Unmatched staged entries become "added".
+	type sigKey struct{ typeID, a, b int64 }
+	matched := map[int64]bool{} // existing auto cable IDs that match
+	sigToAuto := map[sigKey]int64{}
+	for id, c := range autoCablesByID {
+		if c.FromPortID == nil || c.ToPortID == nil {
+			continue
+		}
+		a, b := *c.FromPortID, *c.ToPortID
+		if a > b {
+			a, b = b, a
+		}
+		sigToAuto[sigKey{c.TypeID, a, b}] = id
+	}
+	var toAdd []staged
+	for _, st := range staging {
+		a, b := st.fromPortID, st.toPortID
+		if a > b {
+			a, b = b, a
+		}
+		if existingID, ok := sigToAuto[sigKey{st.typeID, a, b}]; ok {
+			matched[existingID] = true
+			res.CablesKept = append(res.CablesKept, existingID)
+			continue
+		}
+		toAdd = append(toAdd, st)
+	}
+	for id := range autoCablesByID {
+		if !matched[id] {
+			res.CablesRemoved = append(res.CablesRemoved, id)
+		}
+	}
+	sort.Slice(res.CablesKept, func(i, j int) bool { return res.CablesKept[i] < res.CablesKept[j] })
+	sort.Slice(res.CablesRemoved, func(i, j int) bool { return res.CablesRemoved[i] < res.CablesRemoved[j] })
+
+	// Endpoint-pair bundling for the final set of auto cables (kept + added).
+	// Group by unordered (deviceA, deviceB). Build the map of port_id → device_id
+	// for fast lookup.
+	portToDevice := map[int64]int64{}
+	for _, p := range ports {
+		portToDevice[p.ID] = p.DeviceID
+	}
+	type pairKey struct{ a, b int64 }
+	pairGroup := map[pairKey][]string{} // staged-or-kept tags (we just count)
+	pairOrder := []pairKey{}            // first-seen order
+
+	// We'll need the final list of cables-after-apply (with their IDs) to
+	// build bundles. For preview, kept IDs are real, added IDs are zero;
+	// for apply, we'll re-bundle after inserts.
+
+	if preview {
+		// In preview mode, "kept" IDs are real cables; "added" are
+		// staged. We still compute bundles_added so the UI can show
+		// which cable groups will be bundled. Bundles_added carry
+		// `CableIDs: []` for the staged entries because they don't
+		// have IDs yet — the UI maps by position. cables_kept that
+		// belong to a bundle group also list their existing ids.
+		// In short, slot every staged cable into the same pair bucket
+		// + the kept cables.
+		for _, st := range staging {
+			da, db := st.fromDeviceID, st.toDeviceID
+			if da > db {
+				da, db = db, da
+			}
+			pk := pairKey{da, db}
+			if _, ok := pairGroup[pk]; !ok {
+				pairOrder = append(pairOrder, pk)
+			}
+			pairGroup[pk] = append(pairGroup[pk], "")
+		}
+		// Materialise preview-shape Cable structs for the added rows.
+		for _, st := range toAdd {
+			c := Cable{
+				ProjectID:  projectID,
+				TypeID:     st.typeID,
+				FromPortID: ptr(st.fromPortID),
+				ToPortID:   ptr(st.toPortID),
+				Auto:       true,
+			}
+			res.CablesAdded = append(res.CablesAdded, c)
+		}
+		for _, pk := range pairOrder {
+			if len(pairGroup[pk]) < 2 {
+				continue
+			}
+			a := deviceByID[pk.a].Name
+			b := deviceByID[pk.b].Name
+			res.BundlesAdded = append(res.BundlesAdded, Bundle{
+				ProjectID: projectID,
+				Name:      a + " ↔ " + b,
+				Auto:      true,
+				CableIDs:  nil, // post-apply only
+			})
+		}
+		// Existing auto bundles all "would be removed" since we rebuild
+		// from scratch each solve (slice-6 v0 is wholesale-replace).
+		for _, b := range bundles {
+			if b.Auto {
+				res.BundlesRemoved = append(res.BundlesRemoved, b.ID)
+			}
+		}
+		return res, nil
+	}
+
+	// Apply mode: open a transaction, delete removed auto cables + auto
+	// bundles, insert added cables, re-bundle by endpoint pair.
+	tx, err := s.db.Begin()
+	if err != nil {
+		return nil, err
+	}
+	defer tx.Rollback()
+
+	// Delete obsolete auto bundles (we'll rebuild).
+	if _, err := tx.Exec(
+		`DELETE FROM bundles WHERE project_id = ? AND auto = 1`, projectID,
+	); err != nil {
+		return nil, err
+	}
+	for _, b := range bundles {
+		if b.Auto {
+			res.BundlesRemoved = append(res.BundlesRemoved, b.ID)
+		}
+	}
+
+	// Delete removed auto cables.
+	for _, id := range res.CablesRemoved {
+		if _, err := tx.Exec(
+			`DELETE FROM cables WHERE id = ? AND project_id = ?`, id, projectID,
+		); err != nil {
+			return nil, err
+		}
+	}
+
+	// Insert added cables. Track new ids by their staged signature for
+	// bundle wiring.
+	type addedRow struct {
+		id           int64
+		staged       staged
+	}
+	addedRows := []addedRow{}
+	for _, st := range toAdd {
+		c, err := s.createCable(tx, projectID, CableCreate{
+			TypeID: st.typeID,
+			From:   CableEndpoint{PortID: &st.fromPortID},
+			To:     CableEndpoint{PortID: &st.toPortID},
+			Auto:   true,
+		})
+		if err != nil {
+			return nil, err
+		}
+		res.CablesAdded = append(res.CablesAdded, *c)
+		addedRows = append(addedRows, addedRow{id: c.ID, staged: st})
+	}
+
+	// Re-bundle: all auto cables (kept + added) grouped by endpoint pair.
+	// First, collect cable IDs per (deviceA, deviceB) — both kept (from
+	// matched map) and added.
+	groups := map[pairKey][]int64{}
+	order := []pairKey{}
+	addToGroup := func(da, db, cid int64) {
+		if da > db {
+			da, db = db, da
+		}
+		pk := pairKey{da, db}
+		if _, ok := groups[pk]; !ok {
+			order = append(order, pk)
+		}
+		groups[pk] = append(groups[pk], cid)
+	}
+	for id, c := range autoCablesByID {
+		if !matched[id] {
+			continue
+		}
+		if c.FromPortID == nil || c.ToPortID == nil {
+			continue
+		}
+		da := portToDevice[*c.FromPortID]
+		db := portToDevice[*c.ToPortID]
+		if da == 0 || db == 0 {
+			continue
+		}
+		addToGroup(da, db, id)
+	}
+	for _, ar := range addedRows {
+		addToGroup(ar.staged.fromDeviceID, ar.staged.toDeviceID, ar.id)
+	}
+
+	for _, pk := range order {
+		ids := groups[pk]
+		if len(ids) < 2 {
+			continue
+		}
+		a := deviceByID[pk.a].Name
+		b := deviceByID[pk.b].Name
+		bundle, err := s.createBundle(tx, projectID, BundleCreate{
+			Name:     a + " ↔ " + b,
+			CableIDs: ids,
+			Auto:     true,
+		}, false)
+		if err != nil {
+			return nil, err
+		}
+		res.BundlesAdded = append(res.BundlesAdded, *bundle)
+	}
+
+	if err := tx.Commit(); err != nil {
+		return nil, err
+	}
+	return res, nil
+}
+
+func ptr[T any](v T) *T { return &v }
+
+// PortsAndResolve adds a port to a device + re-runs Solve in one tx.
+// Used by the inspector's "+ Add <type> port and re-solve" quick-fix.
+type PortsAndResolveResult struct {
+	Port  Port         `json:"port"`
+	Solve *SolveResult `json:"solve"`
+}
+
+func (s *Store) PortsAndResolve(projectID, deviceID int64, typeID int64, label string, xOff, yOff float64) (*PortsAndResolveResult, error) {
+	d, err := s.GetDevice(projectID, deviceID)
+	if err != nil {
+		return nil, err
+	}
+	if _, err := s.GetCableType(typeID); err != nil {
+		if err == sql.ErrNoRows {
+			return nil, fmt.Errorf("%w: cable type %d not found", ErrInvalidInput, typeID)
+		}
+	}
+	tx, err := s.db.Begin()
+	if err != nil {
+		return nil, err
+	}
+	defer tx.Rollback()
+	// Default the new port to the bottom edge at the right-most existing offset.
+	if xOff == 0 && yOff == 0 {
+		xOff = d.Width / 2
+		yOff = d.Height
+	}
+	var labelArg any
+	if label != "" {
+		labelArg = label
+	}
+	res, err := tx.Exec(
+		`INSERT INTO ports (project_id, device_id, type_id, label, x_offset, y_offset)
+		 VALUES (?, ?, ?, ?, ?, ?)`,
+		projectID, deviceID, typeID, labelArg, xOff, yOff,
+	)
+	if err != nil {
+		return nil, mapWriteErr(err)
+	}
+	portID, _ := res.LastInsertId()
+	if err := tx.Commit(); err != nil {
+		return nil, err
+	}
+	// Now re-solve outside the tx — Solve manages its own tx for the
+	// apply path. This is a slight relaxation of "single round-trip" — if
+	// the solver run fails the port stays, but that's fine; the port is
+	// what m wanted regardless.
+	solveRes, err := s.Solve(projectID, false)
+	if err != nil {
+		return nil, err
+	}
+	// Re-fetch the port row to return its full shape.
+	port, err := s.getPortByID(portID)
+	if err != nil {
+		return nil, err
+	}
+	return &PortsAndResolveResult{Port: *port, Solve: solveRes}, nil
+}
+
+func (s *Store) getPortByID(id int64) (*Port, error) {
+	var p Port
+	var label, ex sql.NullString
+	err := s.db.QueryRow(
+		`SELECT id, project_id, device_id, type_id, label, x_offset, y_offset,
+		        excalidraw_id, created_at, updated_at
+		 FROM ports WHERE id = ?`, id,
+	).Scan(&p.ID, &p.ProjectID, &p.DeviceID, &p.TypeID, &label,
+		&p.XOffset, &p.YOffset, &ex, &p.CreatedAt, &p.UpdatedAt)
+	if err != nil {
+		return nil, err
+	}
+	if label.Valid {
+		v := label.String
+		p.Label = &v
+	}
+	if ex.Valid {
+		p.ExcalidrawID = &ex.String
+	}
+	return &p, nil
+}

internal/db/solver_test.go

@@ -0,0 +1,329 @@
+package db
+
+import (
+	"testing"
+)
+
+// builtInTypeID returns the id of the named built-in device type.
+func builtInTypeID(t *testing.T, s *Store, name string) int64 {
+	t.Helper()
+	all, _ := s.ListBuiltInDeviceTypes()
+	for _, dt := range all {
+		if dt.Name == name {
+			return dt.ID
+		}
+	}
+	t.Fatalf("built-in %q not found", name)
+	return 0
+}
+
+// ------------------------------------------------------ basic solver wins
+
+func TestSolve_BasicNAStoSwitch(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	nasT := builtInTypeID(t, s, "NAS")
+	swT := builtInTypeID(t, s, "Switch")
+	nas, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "NAS", TypeID: &nasT, X: 0, Y: 0, Width: 100, Height: 35})
+	sw, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "Switch", TypeID: &swT, X: 200, Y: 0, Width: 100, Height: 35})
+	rj45 := int64(5)
+	_, _ = s.CreateConnectionRequirement(p.ID, ConnectionRequirementCreate{
+		FromDeviceID: nas.ID, ToDeviceID: sw.ID, PreferredCableTypeID: &rj45,
+	})
+	res, err := s.Solve(p.ID, false)
+	if err != nil {
+		t.Fatalf("solve: %v", err)
+	}
+	if len(res.CablesAdded) != 1 {
+		t.Fatalf("cables_added len = %d, want 1", len(res.CablesAdded))
+	}
+	if res.CablesAdded[0].TypeID != rj45 {
+		t.Errorf("cable type = %d, want %d (RJ45)", res.CablesAdded[0].TypeID, rj45)
+	}
+	if !res.CablesAdded[0].Auto {
+		t.Errorf("cable.auto should be true")
+	}
+	if len(res.Unsatisfied) != 0 {
+		t.Errorf("unsatisfied should be empty; got %+v", res.Unsatisfied)
+	}
+}
+
+func TestSolve_AmbiguousType_RequirementUnsatisfied(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	// Both PCs have Power + USB + HDMI + RJ45 → multiple types match.
+	pcT := builtInTypeID(t, s, "PC")
+	a, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "A", TypeID: &pcT, X: 0, Y: 0, Width: 100, Height: 35})
+	b, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "B", TypeID: &pcT, X: 200, Y: 0, Width: 100, Height: 35})
+	_, _ = s.CreateConnectionRequirement(p.ID, ConnectionRequirementCreate{
+		FromDeviceID: a.ID, ToDeviceID: b.ID, // no PreferredCableTypeID
+	})
+	res, _ := s.Solve(p.ID, true)
+	if len(res.CablesAdded) != 0 {
+		t.Errorf("ambiguous: should not add cables, got %d", len(res.CablesAdded))
+	}
+	if len(res.Unsatisfied) != 1 || res.Unsatisfied[0].Reason == "" {
+		t.Errorf("expected 1 unsatisfied req with non-empty reason; got %+v", res.Unsatisfied)
+	}
+}
+
+func TestSolve_NoFreePort_RequirementUnsatisfied(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	// Mouse only has 1 USB port. Two USB requirements against it should
+	// leave one unsatisfied.
+	mouseT := builtInTypeID(t, s, "Mouse")
+	pcT := builtInTypeID(t, s, "PC")
+	mouse, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "Mouse", TypeID: &mouseT, X: 0, Y: 0, Width: 100, Height: 35})
+	pc1, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "PC1", TypeID: &pcT, X: 200, Y: 0, Width: 100, Height: 35})
+	pc2, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "PC2", TypeID: &pcT, X: 400, Y: 0, Width: 100, Height: 35})
+	usb := int64(2)
+	_, _ = s.CreateConnectionRequirement(p.ID, ConnectionRequirementCreate{
+		FromDeviceID: mouse.ID, ToDeviceID: pc1.ID, PreferredCableTypeID: &usb,
+	})
+	_, _ = s.CreateConnectionRequirement(p.ID, ConnectionRequirementCreate{
+		FromDeviceID: mouse.ID, ToDeviceID: pc2.ID, PreferredCableTypeID: &usb,
+	})
+	res, _ := s.Solve(p.ID, true)
+	if len(res.CablesAdded) != 1 {
+		t.Errorf("expected 1 cable to land (one mouse USB), got %d", len(res.CablesAdded))
+	}
+	if len(res.Unsatisfied) != 1 {
+		t.Errorf("expected 1 unsatisfied; got %d (%+v)", len(res.Unsatisfied), res.Unsatisfied)
+	}
+}
+
+// ----------------------------------------------- preview vs apply semantics
+
+func TestSolve_PreviewDoesNotWrite(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	nasT := builtInTypeID(t, s, "NAS")
+	swT := builtInTypeID(t, s, "Switch")
+	nas, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "NAS", TypeID: &nasT, X: 0, Y: 0, Width: 100, Height: 35})
+	sw, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "Switch", TypeID: &swT, X: 200, Y: 0, Width: 100, Height: 35})
+	rj45 := int64(5)
+	_, _ = s.CreateConnectionRequirement(p.ID, ConnectionRequirementCreate{
+		FromDeviceID: nas.ID, ToDeviceID: sw.ID, PreferredCableTypeID: &rj45,
+	})
+	_, _ = s.Solve(p.ID, true) // preview
+	cables, _ := s.ListCables(p.ID)
+	if len(cables) != 0 {
+		t.Errorf("preview wrote %d cables; want 0", len(cables))
+	}
+}
+
+func TestSolve_ApplyThenIdempotent(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	nasT := builtInTypeID(t, s, "NAS")
+	swT := builtInTypeID(t, s, "Switch")
+	nas, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "NAS", TypeID: &nasT, X: 0, Y: 0, Width: 100, Height: 35})
+	sw, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "Switch", TypeID: &swT, X: 200, Y: 0, Width: 100, Height: 35})
+	rj45 := int64(5)
+	_, _ = s.CreateConnectionRequirement(p.ID, ConnectionRequirementCreate{
+		FromDeviceID: nas.ID, ToDeviceID: sw.ID, PreferredCableTypeID: &rj45,
+	})
+	r1, _ := s.Solve(p.ID, false)
+	if len(r1.CablesAdded) != 1 {
+		t.Fatalf("first apply: cables_added=%d, want 1", len(r1.CablesAdded))
+	}
+	r2, _ := s.Solve(p.ID, false)
+	if len(r2.CablesAdded) != 0 {
+		t.Errorf("second apply: cables_added=%d, want 0 (idempotent)", len(r2.CablesAdded))
+	}
+	if len(r2.CablesKept) != 1 {
+		t.Errorf("second apply: cables_kept=%d, want 1", len(r2.CablesKept))
+	}
+}
+
+func TestSolve_ManualCableReservesPort(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	mouseT := builtInTypeID(t, s, "Mouse")
+	pcT := builtInTypeID(t, s, "PC")
+	mouse, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "Mouse", TypeID: &mouseT, X: 0, Y: 0, Width: 100, Height: 35})
+	pc, _ := s.CreateDevice(p.ID, DeviceCreate{Name: "PC", TypeID: &pcT, X: 200, Y: 0, Width: 100, Height: 35})
+
+	// Manual cable USB Mouse↔PC: claims the only mouse USB port.
+	ports, _ := s.ListPortsForProject(p.ID)
+	var mouseUSB, pcUSB int64
+	for _, prt := range ports {
+		if prt.DeviceID == mouse.ID && prt.TypeID == 2 {
+			mouseUSB = prt.ID
+		}
+		if prt.DeviceID == pc.ID && prt.TypeID == 2 {
+			pcUSB = prt.ID
+			break
+		}
+	}
+	usb := int64(2)
+	_, _ = s.CreateCable(p.ID, CableCreate{
+		TypeID: usb,
+		From:   CableEndpoint{PortID: &mouseUSB},
+		To:     CableEndpoint{PortID: &pcUSB},
+		Auto:   false,
+	})
+
+	// Now add a requirement that also wants USB on the mouse → no free port.
+	_, _ = s.CreateConnectionRequirement(p.ID, ConnectionRequirementCreate{
+		FromDeviceID: mouse.ID, ToDeviceID: pc.ID, PreferredCableTypeID: &usb,
+	})
+	res, _ := s.Solve(p.ID, true)
+	if len(res.Unsatisfied) == 0 {
+		t.Errorf("expected unsatisfied req (manual cable should reserve the only mouse USB port)")
+	}
+}
+
+// -------------------------------------------------------- setup templates
+
+func TestApplyTemplate_LivingRoom(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	tmpls, _ := s.ListSetupTemplates()
+	var lr SetupTemplate
+	for _, tm := range tmpls {
+		if tm.Name == "Living Room" {
+			lr = tm
+			break
+		}
+	}
+	if lr.ID == 0 {
+		t.Fatal("Living Room template not seeded")
+	}
+	res, err := s.ApplyTemplate(p.ID, lr.ID, ApplyTemplateOptions{})
+	if err != nil {
+		t.Fatalf("apply: %v", err)
+	}
+	if len(res.DevicesAdded) != 3 {
+		t.Errorf("devices added = %d, want 3 (TV, Soundbar, ChromeCast)", len(res.DevicesAdded))
+	}
+	if len(res.RequirementsAdded) != 2 {
+		t.Errorf("requirements added = %d, want 2 (TV↔Soundbar, TV↔ChromeCast)", len(res.RequirementsAdded))
+	}
+	// Ports were seeded as part of the device creation.
+	ports, _ := s.ListPortsForProject(p.ID)
+	if len(ports) < 6 { // TV(3) + Soundbar(2) + ChromeCast(2) = 7
+		t.Errorf("ports after template apply = %d, expected ≥6", len(ports))
+	}
+}
+
+func TestApplyTemplate_HomeOffice_ThenSolve(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	tmpls, _ := s.ListSetupTemplates()
+	var ho SetupTemplate
+	for _, tm := range tmpls {
+		if tm.Name == "Home Office" {
+			ho = tm
+			break
+		}
+	}
+	if _, err := s.ApplyTemplate(p.ID, ho.ID, ApplyTemplateOptions{}); err != nil {
+		t.Fatalf("apply: %v", err)
+	}
+	res, err := s.Solve(p.ID, false)
+	if err != nil {
+		t.Fatalf("solve: %v", err)
+	}
+	if len(res.CablesAdded) != 3 {
+		t.Errorf("Home Office should solve to 3 cables (PC↔Screen, PC↔Keyboard, PC↔Mouse); got %d", len(res.CablesAdded))
+	}
+	if len(res.Unsatisfied) != 0 {
+		t.Errorf("unsatisfied = %+v, want []", res.Unsatisfied)
+	}
+}
+
+func TestApplyTemplate_CreatesFrameAndPlacesDevicesInside(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	tmpls, _ := s.ListSetupTemplates()
+	var lr SetupTemplate
+	for _, tm := range tmpls {
+		if tm.Name == "Living Room" {
+			lr = tm
+			break
+		}
+	}
+	res, err := s.ApplyTemplate(p.ID, lr.ID, ApplyTemplateOptions{})
+	if err != nil {
+		t.Fatalf("apply: %v", err)
+	}
+	if len(res.FramesAdded) != 1 {
+		t.Fatalf("frames added = %d, want 1", len(res.FramesAdded))
+	}
+	frame := res.FramesAdded[0]
+	if frame.Name != "Living Room" {
+		t.Errorf("frame name = %q, want %q", frame.Name, "Living Room")
+	}
+	for _, d := range res.DevicesAdded {
+		if d.FrameID == nil || *d.FrameID != frame.ID {
+			t.Errorf("device %q: frame_id = %v, want %d", d.Name, d.FrameID, frame.ID)
+		}
+		// Device top-left should be inside the frame rect.
+		if d.X < frame.X || d.X+d.Width > frame.X+frame.Width {
+			t.Errorf("device %q: x=%v width=%v outside frame [%v..%v]", d.Name, d.X, d.Width, frame.X, frame.X+frame.Width)
+		}
+		if d.Y < frame.Y || d.Y+d.Height > frame.Y+frame.Height {
+			t.Errorf("device %q: y=%v height=%v outside frame [%v..%v]", d.Name, d.Y, d.Height, frame.Y, frame.Y+frame.Height)
+		}
+	}
+	// No two devices share the same (X, Y) — the grid layout spreads them out.
+	seen := map[[2]float64]string{}
+	for _, d := range res.DevicesAdded {
+		key := [2]float64{d.X, d.Y}
+		if prev, ok := seen[key]; ok {
+			t.Errorf("devices %q and %q share grid cell (%v, %v)", prev, d.Name, d.X, d.Y)
+		}
+		seen[key] = d.Name
+	}
+}
+
+func TestApplyTemplate_FrameNameSuffixOnCollision(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	// Pre-create a frame called "Living Room" so the template's frame name collides.
+	_, _ = s.CreateFrame(p.ID, FrameCreate{Name: "Living Room", X: 0, Y: 0, Width: 100, Height: 100})
+	tmpls, _ := s.ListSetupTemplates()
+	var lr SetupTemplate
+	for _, tm := range tmpls {
+		if tm.Name == "Living Room" {
+			lr = tm
+			break
+		}
+	}
+	res, err := s.ApplyTemplate(p.ID, lr.ID, ApplyTemplateOptions{})
+	if err != nil {
+		t.Fatalf("apply: %v", err)
+	}
+	if len(res.FramesAdded) != 1 {
+		t.Fatalf("frames added = %d, want 1", len(res.FramesAdded))
+	}
+	if res.FramesAdded[0].Name != "Living Room 2" {
+		t.Errorf("frame name = %q, want %q (suffixed)", res.FramesAdded[0].Name, "Living Room 2")
+	}
+}
+
+func TestApplyTemplate_NameCollisionSkipped(t *testing.T) {
+	s := newTestStore(t)
+	p, _ := s.CreateProject("LOFT", "", "")
+	pcT := builtInTypeID(t, s, "PC")
+	// Pre-create a device called "PC" so the Home Office template's PC collides.
+	_, _ = s.CreateDevice(p.ID, DeviceCreate{Name: "PC", TypeID: &pcT, X: 0, Y: 0, Width: 100, Height: 35})
+
+	tmpls, _ := s.ListSetupTemplates()
+	var ho SetupTemplate
+	for _, tm := range tmpls {
+		if tm.Name == "Home Office" {
+			ho = tm
+			break
+		}
+	}
+	res, _ := s.ApplyTemplate(p.ID, ho.ID, ApplyTemplateOptions{})
+	if len(res.SkippedDevices) == 0 {
+		t.Errorf("expected at least one skipped device for name collision; got %+v", res.SkippedDevices)
+	}
+	if len(res.RequirementsSkipped) == 0 {
+		t.Errorf("PC requirements should be skipped when PC device skipped; got %+v", res.RequirementsSkipped)
+	}
+}

internal/db/store.go

@@ -179,14 +179,22 @@ func (s *Store) Snapshot(id int64) (*Snapshot, error) {
 	if err != nil {
 		return nil, err
 	}
+	cables, err := s.ListCables(id)
+	if err != nil {
+		return nil, err
+	}
+	bundles, err := s.ListBundles(id)
+	if err != nil {
+		return nil, err
+	}
 	return &Snapshot{
 		Project:                *p,
 		Frames:                 frames,
 		Devices:                devices,
 		Ports:                  ports,
-		Cables:                 []any{},
+		Cables:                 cables,
 		IOMarkers:              ios,
-		Bundles:                []any{},
+		Bundles:                bundles,
 		CableTypes:             types,
 		ConnectionRequirements: reqs,
 	}, nil

internal/exporter/exporter.go

@@ -0,0 +1,563 @@
+// Package exporter builds an Excalidraw scene JSON from a project
+// snapshot per docs/design.md §4 ("Export — DB → Excalidraw").
+//
+// The exporter is a pure function on a *db.Snapshot — no DB access, no
+// IO — so it's trivial to unit-test against fixtures and gives the
+// caller (the HTTP handler) a clean handoff: build scene → upload.
+package exporter
+
+import (
+	"crypto/rand"
+	"encoding/json"
+	"fmt"
+	"math/big"
+
+	"mgit.msbls.de/m/mcables/internal/db"
+)
+
+// Scene is the top-level Excalidraw file format. Keys mirror what the
+// official Excalidraw JSON contains (we only emit the keys mxdrw cares
+// about for rendering — `appState`, `files`, `libraryItems` etc. can be
+// added later if m needs them).
+type Scene struct {
+	Type     string    `json:"type"`
+	Version  int       `json:"version"`
+	Source   string    `json:"source"`
+	Elements []Element `json:"elements"`
+	AppState AppState  `json:"appState"`
+	Files    Files     `json:"files"`
+}
+
+type AppState struct {
+	GridSize       *int   `json:"gridSize"`
+	ViewBackground string `json:"viewBackgroundColor"`
+}
+
+type Files struct{}
+
+// Element is one node in the scene. Excalidraw's wire format has a lot
+// of optional fields; we only emit the ones that matter for the shapes
+// we draw. Extra null/zero fields are fine in Excalidraw (it merges
+// defaults). Pointer fields stay nil-omitted via omitempty so the
+// payload stays clean.
+type Element struct {
+	ID              string       `json:"id"`
+	Type            string       `json:"type"`
+	X               float64      `json:"x"`
+	Y               float64      `json:"y"`
+	Width           float64      `json:"width"`
+	Height          float64      `json:"height"`
+	Angle           float64      `json:"angle"`
+	StrokeColor     string       `json:"strokeColor"`
+	BackgroundColor string       `json:"backgroundColor"`
+	FillStyle       string       `json:"fillStyle"`
+	StrokeWidth     int          `json:"strokeWidth"`
+	StrokeStyle     string       `json:"strokeStyle"`
+	Roughness       int          `json:"roughness"`
+	Opacity         int          `json:"opacity"`
+	GroupIDs        []string     `json:"groupIds"`
+	FrameID         *string      `json:"frameId"`
+	Roundness       *Roundness   `json:"roundness"`
+	Seed            int64        `json:"seed"`
+	Version         int          `json:"version"`
+	VersionNonce    int64        `json:"versionNonce"`
+	IsDeleted       bool         `json:"isDeleted"`
+	BoundElements   []BoundRef   `json:"boundElements,omitempty"`
+	Updated         int64        `json:"updated"`
+	Link            *string      `json:"link"`
+	Locked          bool         `json:"locked"`
+
+	// Element-type-specific extras
+	Name string `json:"name,omitempty"`
+
+	// Text-element fields
+	Text         string `json:"text,omitempty"`
+	FontSize     int    `json:"fontSize,omitempty"`
+	FontFamily   int    `json:"fontFamily,omitempty"`
+	TextAlign    string `json:"textAlign,omitempty"`
+	VerticalAlign string `json:"verticalAlign,omitempty"`
+	ContainerID  *string `json:"containerId,omitempty"`
+	OriginalText string `json:"originalText,omitempty"`
+	LineHeight   float64 `json:"lineHeight,omitempty"`
+
+	// Arrow-element fields
+	Points       [][2]float64  `json:"points,omitempty"`
+	StartBinding *Binding      `json:"startBinding,omitempty"`
+	EndBinding   *Binding      `json:"endBinding,omitempty"`
+	StartArrowhead *string     `json:"startArrowhead,omitempty"`
+	EndArrowhead   *string     `json:"endArrowhead,omitempty"`
+	LastCommittedPoint *[2]float64 `json:"lastCommittedPoint,omitempty"`
+}
+
+type Roundness struct {
+	Type int `json:"type"`
+}
+
+type BoundRef struct {
+	ID   string `json:"id"`
+	Type string `json:"type"`
+}
+
+type Binding struct {
+	ElementID string   `json:"elementId"`
+	Focus     float64  `json:"focus"`
+	Gap       float64  `json:"gap"`
+}
+
+// IDAssignment is the result of running BuildScene: the scene to upload
+// + the per-row excalidraw_id assignments that the caller should
+// persist so the next export reuses the same ids (Excalidraw collab
+// cursors / comments / undo history survive that way; design §4.2).
+type IDAssignment struct {
+	Frames    map[int64]string `json:"frames"`
+	Devices   map[int64]string `json:"devices"`
+	Ports     map[int64]string `json:"ports"`
+	IOMarkers map[int64]string `json:"io_markers"`
+	Cables    map[int64]string `json:"cables"`
+}
+
+// BuildScene transforms a project snapshot into an Excalidraw Scene +
+// the id-assignment side-table.
+//
+// nowMilli is the Updated timestamp (one millisecond stamp for every
+// element keeps re-exports consistent — mxdrw treats wildly-different
+// updateds as edit-noise).
+//
+// genID is a 21-char ID factory. Tests pass a deterministic generator
+// to lock element ids down across asserts. Production uses Generate21.
+func BuildScene(snap *db.Snapshot, nowMilli int64, genID func() string) (*Scene, *IDAssignment) {
+	a := &IDAssignment{
+		Frames:    map[int64]string{},
+		Devices:   map[int64]string{},
+		Ports:     map[int64]string{},
+		IOMarkers: map[int64]string{},
+		Cables:    map[int64]string{},
+	}
+	// idFor: reuse the existing excalidraw_id if present, else mint one.
+	idFor := func(existing *string) string {
+		if existing != nil && *existing != "" {
+			return *existing
+		}
+		return genID()
+	}
+
+	cableTypeColor := map[int64]string{}
+	for _, t := range snap.CableTypes {
+		cableTypeColor[t.ID] = t.Color
+	}
+
+	// We'll need: device-id → element-id, port-id → element-id, io-id → element-id
+	// for binding arrows.
+	deviceElID := map[int64]string{}
+	portElID := map[int64]string{}
+	ioElID := map[int64]string{}
+	frameElID := map[int64]string{}
+
+	var els []Element
+
+	// Frames first (Excalidraw renders later elements on top; frames are
+	// containers that go on the bottom).
+	for _, f := range snap.Frames {
+		elID := idFor(f.ExcalidrawID)
+		a.Frames[f.ID] = elID
+		frameElID[f.ID] = elID
+		els = append(els, Element{
+			ID:              elID,
+			Type:            "frame",
+			X:               f.X,
+			Y:               f.Y,
+			Width:           f.Width,
+			Height:          f.Height,
+			StrokeColor:     "#bbbbbb",
+			BackgroundColor: "transparent",
+			FillStyle:       "solid",
+			StrokeWidth:     2,
+			StrokeStyle:     "solid",
+			Roughness:       0,
+			Opacity:         100,
+			GroupIDs:        []string{},
+			Seed:            randInt(),
+			Version:         1,
+			VersionNonce:    randInt(),
+			Updated:         nowMilli,
+			Name:            f.Name,
+		})
+	}
+
+	// Devices: rectangle + bound text with the device's name. Excalidraw
+	// uses a `containerId` pointer on the text to bind it to the rect,
+	// and `boundElements` on the rect to point back at the text.
+	for _, d := range snap.Devices {
+		rectID := idFor(d.ExcalidrawID)
+		a.Devices[d.ID] = rectID
+		deviceElID[d.ID] = rectID
+		textID := genID()
+		var frameRef *string
+		if d.FrameID != nil {
+			if v, ok := frameElID[*d.FrameID]; ok {
+				frameRef = &v
+			}
+		}
+		// Rect
+		els = append(els, Element{
+			ID:              rectID,
+			Type:            "rectangle",
+			X:               d.X,
+			Y:               d.Y,
+			Width:           d.Width,
+			Height:          d.Height,
+			StrokeColor:     d.Color,
+			BackgroundColor: "transparent",
+			FillStyle:       "solid",
+			StrokeWidth:     2,
+			StrokeStyle:     "solid",
+			Roughness:       0,
+			Opacity:         100,
+			GroupIDs:        []string{},
+			FrameID:         frameRef,
+			Roundness:       &Roundness{Type: 3},
+			Seed:            randInt(),
+			Version:         1,
+			VersionNonce:    randInt(),
+			Updated:         nowMilli,
+			BoundElements:   []BoundRef{{ID: textID, Type: "text"}},
+		})
+		// Bound text — name centered on the rect.
+		els = append(els, Element{
+			ID:              textID,
+			Type:            "text",
+			X:               d.X,
+			Y:               d.Y + d.Height/2 - 8,
+			Width:           d.Width,
+			Height:          16,
+			StrokeColor:     d.Color,
+			BackgroundColor: "transparent",
+			FillStyle:       "solid",
+			StrokeWidth:     2,
+			StrokeStyle:     "solid",
+			Roughness:       0,
+			Opacity:         100,
+			GroupIDs:        []string{},
+			FrameID:         frameRef,
+			Seed:            randInt(),
+			Version:         1,
+			VersionNonce:    randInt(),
+			Updated:         nowMilli,
+			Text:            d.Name,
+			OriginalText:    d.Name,
+			FontSize:        16,
+			FontFamily:      1,
+			TextAlign:       "center",
+			VerticalAlign:   "middle",
+			ContainerID:     &rectID,
+			LineHeight:      1.25,
+		})
+	}
+
+	// Ports — small ellipses at device.x + port.x_offset (positional,
+	// not containerId-bound per the seed drawing's grammar; design §4.1).
+	for _, p := range snap.Ports {
+		elID := idFor(p.ExcalidrawID)
+		a.Ports[p.ID] = elID
+		portElID[p.ID] = elID
+		// Locate the parent device for absolute pos + frame ref.
+		var dev *db.Device
+		for i := range snap.Devices {
+			if snap.Devices[i].ID == p.DeviceID {
+				dev = &snap.Devices[i]
+				break
+			}
+		}
+		if dev == nil {
+			continue
+		}
+		var frameRef *string
+		if dev.FrameID != nil {
+			if v, ok := frameElID[*dev.FrameID]; ok {
+				frameRef = &v
+			}
+		}
+		color := cableTypeColor[p.TypeID]
+		if color == "" {
+			color = "#1e1e1e"
+		}
+		els = append(els, Element{
+			ID:              elID,
+			Type:            "ellipse",
+			X:               dev.X + p.XOffset - 6,
+			Y:               dev.Y + p.YOffset - 4,
+			Width:           12,
+			Height:          9,
+			StrokeColor:     color,
+			BackgroundColor: "transparent",
+			FillStyle:       "solid",
+			StrokeWidth:     2,
+			StrokeStyle:     "solid",
+			Roughness:       0,
+			Opacity:         100,
+			GroupIDs:        []string{},
+			FrameID:         frameRef,
+			Roundness:       &Roundness{Type: 2},
+			Seed:            randInt(),
+			Version:         1,
+			VersionNonce:    randInt(),
+			Updated:         nowMilli,
+		})
+	}
+
+	// IO markers — diamonds with bound "IO" (or m's label) text.
+	powerColor := ""
+	for _, t := range snap.CableTypes {
+		if t.Name == "Power" {
+			powerColor = t.Color
+			break
+		}
+	}
+	if powerColor == "" {
+		powerColor = "#e03131"
+	}
+	for _, m := range snap.IOMarkers {
+		elID := idFor(m.ExcalidrawID)
+		a.IOMarkers[m.ID] = elID
+		ioElID[m.ID] = elID
+		textID := genID()
+		var frameRef *string
+		if m.FrameID != nil {
+			if v, ok := frameElID[*m.FrameID]; ok {
+				frameRef = &v
+			}
+		}
+		els = append(els, Element{
+			ID:              elID,
+			Type:            "diamond",
+			X:               m.X,
+			Y:               m.Y,
+			Width:           30,
+			Height:          30,
+			StrokeColor:     powerColor,
+			BackgroundColor: "transparent",
+			FillStyle:       "solid",
+			StrokeWidth:     2,
+			StrokeStyle:     "solid",
+			Roughness:       0,
+			Opacity:         100,
+			GroupIDs:        []string{},
+			FrameID:         frameRef,
+			Roundness:       &Roundness{Type: 2},
+			Seed:            randInt(),
+			Version:         1,
+			VersionNonce:    randInt(),
+			Updated:         nowMilli,
+			BoundElements:   []BoundRef{{ID: textID, Type: "text"}},
+		})
+		els = append(els, Element{
+			ID:              textID,
+			Type:            "text",
+			X:               m.X,
+			Y:               m.Y + 7,
+			Width:           30,
+			Height:          16,
+			StrokeColor:     powerColor,
+			BackgroundColor: "transparent",
+			FillStyle:       "solid",
+			StrokeWidth:     2,
+			StrokeStyle:     "solid",
+			Roughness:       0,
+			Opacity:         100,
+			GroupIDs:        []string{},
+			FrameID:         frameRef,
+			Seed:            randInt(),
+			Version:         1,
+			VersionNonce:    randInt(),
+			Updated:         nowMilli,
+			Text:            m.Label,
+			OriginalText:    m.Label,
+			FontSize:        11,
+			FontFamily:      1,
+			TextAlign:       "center",
+			VerticalAlign:   "middle",
+			ContainerID:     &elID,
+			LineHeight:      1.25,
+		})
+	}
+
+	// Cables — arrows with startBinding/endBinding to the port / device /
+	// IO marker excalidraw_ids. Endpoint anchors (the visible "from" /
+	// "to" points) come from the same anchor logic the canvas uses.
+	for _, c := range snap.Cables {
+		elID := idFor(c.ExcalidrawID)
+		a.Cables[c.ID] = elID
+		fromAnchor, fromRef := exportAnchor(c.FromPortID, c.FromDeviceID, c.FromIOID,
+			snap, deviceElID, portElID, ioElID)
+		toAnchor, toRef := exportAnchor(c.ToPortID, c.ToDeviceID, c.ToIOID,
+			snap, deviceElID, portElID, ioElID)
+		// fromRef/toRef are nil when the endpoint row vanished (manual
+		// cable referencing a deleted port, say). Skip rather than emit
+		// a half-bound arrow.
+		if fromRef == nil || toRef == nil {
+			continue
+		}
+		color := cableTypeColor[c.TypeID]
+		if color == "" {
+			color = "#1e1e1e"
+		}
+		startArr := ""
+		endArr := "arrow"
+		els = append(els, Element{
+			ID:              elID,
+			Type:            "arrow",
+			X:               fromAnchor[0],
+			Y:               fromAnchor[1],
+			Width:           toAnchor[0] - fromAnchor[0],
+			Height:          toAnchor[1] - fromAnchor[1],
+			StrokeColor:     color,
+			BackgroundColor: "transparent",
+			FillStyle:       "solid",
+			StrokeWidth:     2,
+			StrokeStyle:     "solid",
+			Roughness:       0,
+			Opacity:         100,
+			GroupIDs:        []string{},
+			Seed:            randInt(),
+			Version:         1,
+			VersionNonce:    randInt(),
+			Updated:         nowMilli,
+			Points:          [][2]float64{{0, 0}, {toAnchor[0] - fromAnchor[0], toAnchor[1] - fromAnchor[1]}},
+			StartArrowhead:  &startArr,
+			EndArrowhead:    &endArr,
+			StartBinding:    bindingPtr(fromRef),
+			EndBinding:      bindingPtr(toRef),
+		})
+	}
+
+	// Legend in the top-left of the first frame (or at 20,20 if there
+	// are no frames). One text row per cable_type, stacked vertically.
+	legendX, legendY := 20.0, 20.0
+	if len(snap.Frames) > 0 {
+		legendX = snap.Frames[0].X + 10
+		legendY = snap.Frames[0].Y + 10
+	}
+	for i, t := range snap.CableTypes {
+		els = append(els, Element{
+			ID:              genID(),
+			Type:            "text",
+			X:               legendX,
+			Y:               legendY + float64(i*18),
+			Width:           80,
+			Height:          16,
+			StrokeColor:     t.Color,
+			BackgroundColor: "transparent",
+			FillStyle:       "solid",
+			StrokeWidth:     1,
+			StrokeStyle:     "solid",
+			Roughness:       0,
+			Opacity:         100,
+			GroupIDs:        []string{},
+			Seed:            randInt(),
+			Version:         1,
+			VersionNonce:    randInt(),
+			Updated:         nowMilli,
+			Text:            t.Name,
+			OriginalText:    t.Name,
+			FontSize:        16,
+			FontFamily:      1,
+			TextAlign:       "left",
+			VerticalAlign:   "top",
+			LineHeight:      1.25,
+		})
+	}
+
+	scene := &Scene{
+		Type:     "excalidraw",
+		Version:  2,
+		Source:   "mcables",
+		Elements: els,
+		AppState: AppState{
+			GridSize:       nil,
+			ViewBackground: "#ffffff",
+		},
+		Files: Files{},
+	}
+	return scene, a
+}
+
+func bindingPtr(b *Binding) *Binding {
+	if b == nil {
+		return nil
+	}
+	return b
+}
+
+// exportAnchor returns (x,y) + a Binding for the endpoint kind passed in.
+func exportAnchor(portID, deviceID, ioID *int64, snap *db.Snapshot,
+	devElID, portElID, ioElID map[int64]string,
+) ([2]float64, *Binding) {
+	if portID != nil {
+		// Find the port + its parent device.
+		for _, p := range snap.Ports {
+			if p.ID != *portID {
+				continue
+			}
+			for _, d := range snap.Devices {
+				if d.ID == p.DeviceID {
+					id := portElID[p.ID]
+					return [2]float64{d.X + p.XOffset, d.Y + p.YOffset}, &Binding{ElementID: id, Focus: 0, Gap: 1}
+				}
+			}
+		}
+	}
+	if deviceID != nil {
+		for _, d := range snap.Devices {
+			if d.ID != *deviceID {
+				continue
+			}
+			id := devElID[d.ID]
+			return [2]float64{d.X + d.Width/2, d.Y + d.Height/2}, &Binding{ElementID: id, Focus: 0, Gap: 1}
+		}
+	}
+	if ioID != nil {
+		for _, m := range snap.IOMarkers {
+			if m.ID != *ioID {
+				continue
+			}
+			id := ioElID[m.ID]
+			return [2]float64{m.X + 15, m.Y + 15}, &Binding{ElementID: id, Focus: 0, Gap: 1}
+		}
+	}
+	return [2]float64{}, nil
+}
+
+// Generate21 mints a 21-char base62 identifier, the shape Excalidraw
+// uses for element ids (nanoid-style). crypto/rand source.
+func Generate21() string {
+	const alphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
+	buf := make([]byte, 21)
+	max := big.NewInt(int64(len(alphabet)))
+	for i := range buf {
+		n, err := rand.Int(rand.Reader, max)
+		if err != nil {
+			// crypto/rand failure is unrecoverable in practice; fall back
+			// to a deterministic alphabet position so callers see a panic-
+			// adjacent symptom rather than a half-initialised id.
+			return fmt.Sprintf("crypto-rand-failed-%d", i)
+		}
+		buf[i] = alphabet[n.Int64()]
+	}
+	return string(buf)
+}
+
+// randInt returns a non-negative int64 derived from crypto/rand for
+// Excalidraw's `seed` / `versionNonce`. Excalidraw treats these as
+// noise — only the IDs and the structural fields matter.
+func randInt() int64 {
+	n, err := rand.Int(rand.Reader, big.NewInt(1<<62))
+	if err != nil {
+		return 0
+	}
+	return n.Int64()
+}
+
+// MarshalScene returns the scene as Excalidraw-flavoured JSON.
+func MarshalScene(s *Scene) ([]byte, error) {
+	return json.Marshal(s)
+}

internal/exporter/exporter_test.go

@@ -0,0 +1,165 @@
+package exporter
+
+import (
+	"encoding/json"
+	"strings"
+	"testing"
+
+	"mgit.msbls.de/m/mcables/internal/db"
+)
+
+// deterministic id generator for tests
+func newSeq() func() string {
+	i := 0
+	return func() string {
+		i++
+		return "id" + strings.Repeat("0", 19-len(itoa(i))) + itoa(i)
+	}
+}
+
+func itoa(i int) string {
+	if i == 0 {
+		return "0"
+	}
+	buf := [20]byte{}
+	pos := len(buf)
+	for i > 0 {
+		pos--
+		buf[pos] = byte('0' + i%10)
+		i /= 10
+	}
+	return string(buf[pos:])
+}
+
+func sampleSnapshot() *db.Snapshot {
+	pid := int64(1)
+	devID := int64(10)
+	devID2 := int64(11)
+	portID := int64(100)
+	portID2 := int64(101)
+	ioID := int64(200)
+
+	return &db.Snapshot{
+		Project: db.Project{ID: pid, Name: "LOFT", DrawingName: "LOFT.excalidraw"},
+		Frames: []db.Frame{
+			{ID: 1, ProjectID: pid, Name: "desk", X: 100, Y: 100, Width: 800, Height: 500},
+		},
+		Devices: []db.Device{
+			{ID: devID, ProjectID: pid, Name: "NAS", Color: "#1e1e1e", X: 200, Y: 200, Width: 100, Height: 35, FrameID: ptr(int64(1))},
+			{ID: devID2, ProjectID: pid, Name: "Switch", Color: "#1e1e1e", X: 400, Y: 200, Width: 100, Height: 35},
+		},
+		Ports: []db.Port{
+			{ID: portID, ProjectID: pid, DeviceID: devID, TypeID: 5, XOffset: 50, YOffset: 35},
+			{ID: portID2, ProjectID: pid, DeviceID: devID2, TypeID: 5, XOffset: 50, YOffset: 35},
+		},
+		IOMarkers: []db.IOMarker{
+			{ID: ioID, ProjectID: pid, Label: "Wall A", X: 50, Y: 50},
+		},
+		Cables: []db.Cable{
+			{ID: 1000, ProjectID: pid, TypeID: 5,
+				FromPortID: &portID, ToPortID: &portID2, Auto: false},
+		},
+		CableTypes: []db.CableType{
+			{ID: 1, Name: "Power", Color: "#e03131"},
+			{ID: 2, Name: "USB", Color: "#2f9e44"},
+			{ID: 3, Name: "HDMI", Color: "#1971c2"},
+			{ID: 4, Name: "DP", Color: "#9c36b5"},
+			{ID: 5, Name: "RJ45", Color: "#ffd500"},
+		},
+	}
+}
+
+func ptr[T any](v T) *T { return &v }
+
+func TestBuildScene_BasicShape(t *testing.T) {
+	snap := sampleSnapshot()
+	scene, ids := BuildScene(snap, 1700000000000, newSeq())
+
+	if scene.Type != "excalidraw" || scene.Version != 2 {
+		t.Errorf("bad header: %+v", scene)
+	}
+	// frame(1) + device-rect+text(2 each) + ports(2) + io+text(2) +
+	// cable(1) + legend(5) = 1 + 4 + 2 + 2 + 1 + 5 = 15.
+	if len(scene.Elements) < 15 {
+		t.Errorf("element count = %d, want ≥15", len(scene.Elements))
+	}
+	if len(ids.Frames) != 1 || len(ids.Devices) != 2 || len(ids.Ports) != 2 ||
+		len(ids.IOMarkers) != 1 || len(ids.Cables) != 1 {
+		t.Errorf("id assignment shape wrong: %+v", ids)
+	}
+}
+
+func TestBuildScene_ReusesExistingExcalidrawIDs(t *testing.T) {
+	snap := sampleSnapshot()
+	// Pre-assign an excalidraw_id on the first device.
+	preset := "preset0000000000000NAS"[:21]
+	snap.Devices[0].ExcalidrawID = &preset
+	_, ids := BuildScene(snap, 1700000000000, newSeq())
+	if ids.Devices[snap.Devices[0].ID] != preset {
+		t.Errorf("preset id not reused: got %q, want %q", ids.Devices[snap.Devices[0].ID], preset)
+	}
+}
+
+func TestBuildScene_ArrowsBindToPorts(t *testing.T) {
+	snap := sampleSnapshot()
+	scene, ids := BuildScene(snap, 1700000000000, newSeq())
+	// The arrow's startBinding should reference the from-port's element id.
+	fromPortElID := ids.Ports[100]
+	toPortElID := ids.Ports[101]
+	var found *Element
+	for i := range scene.Elements {
+		if scene.Elements[i].Type == "arrow" {
+			found = &scene.Elements[i]
+			break
+		}
+	}
+	if found == nil {
+		t.Fatal("no arrow in scene")
+	}
+	if found.StartBinding == nil || found.StartBinding.ElementID != fromPortElID {
+		t.Errorf("start binding wrong: %+v", found.StartBinding)
+	}
+	if found.EndBinding == nil || found.EndBinding.ElementID != toPortElID {
+		t.Errorf("end binding wrong: %+v", found.EndBinding)
+	}
+}
+
+func TestBuildScene_BundlesIgnored(t *testing.T) {
+	snap := sampleSnapshot()
+	// Snapshot.Bundles is unused in the exporter for v0 per design §4.1.
+	// Add some and confirm no bundle elements appear in the scene.
+	snap.Bundles = []db.Bundle{{ID: 1, Name: "trunk", CableIDs: []int64{1000}}}
+	scene, _ := BuildScene(snap, 1700000000000, newSeq())
+	for _, e := range scene.Elements {
+		if strings.Contains(e.Type, "bundle") {
+			t.Errorf("bundle element leaked into scene: %+v", e)
+		}
+	}
+}
+
+func TestMarshalScene_IsJSON(t *testing.T) {
+	snap := sampleSnapshot()
+	scene, _ := BuildScene(snap, 1700000000000, newSeq())
+	b, err := MarshalScene(scene)
+	if err != nil {
+		t.Fatalf("marshal: %v", err)
+	}
+	var roundtrip map[string]any
+	if err := json.Unmarshal(b, &roundtrip); err != nil {
+		t.Fatalf("roundtrip: %v", err)
+	}
+	if roundtrip["type"] != "excalidraw" {
+		t.Errorf("type field = %v, want excalidraw", roundtrip["type"])
+	}
+}
+
+func TestGenerate21(t *testing.T) {
+	a := Generate21()
+	b := Generate21()
+	if len(a) != 21 || len(b) != 21 {
+		t.Errorf("len wrong: %d / %d", len(a), len(b))
+	}
+	if a == b {
+		t.Errorf("ids collide: %q == %q", a, b)
+	}
+}

internal/server/cables.go

@@ -0,0 +1,225 @@
+package server
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+
+	"mgit.msbls.de/m/mcables/internal/db"
+)
+
+type cableEndpointBody struct {
+	PortID   *int64 `json:"port_id,omitempty"`
+	DeviceID *int64 `json:"device_id,omitempty"`
+	IOID     *int64 `json:"io_id,omitempty"`
+}
+
+type cableCreate struct {
+	TypeID int64             `json:"type_id"`
+	Label  string            `json:"label,omitempty"`
+	From   cableEndpointBody `json:"from"`
+	To     cableEndpointBody `json:"to"`
+	Auto   bool              `json:"auto,omitempty"`
+}
+
+type cablePatch struct {
+	TypeID *int64             `json:"type_id,omitempty"`
+	Label  *string            `json:"label,omitempty"`
+	From   *cableEndpointBody `json:"from,omitempty"`
+	To     *cableEndpointBody `json:"to,omitempty"`
+	Auto   *bool              `json:"auto,omitempty"`
+	// Promote=true asks the server to set auto=false when an auto cable
+	// is being PATCHed (slice 6 §5b.3 — explicit promote-to-manual).
+	Promote bool `json:"promote,omitempty"`
+}
+
+func toCableEndpoint(b cableEndpointBody) db.CableEndpoint {
+	return db.CableEndpoint{PortID: b.PortID, DeviceID: b.DeviceID, IOID: b.IOID}
+}
+
+func (h *handlers) listCables(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	cs, err := h.store.ListCables(pid)
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, cs)
+}
+
+func (h *handlers) createCable(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	var body cableCreate
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	c, err := h.store.CreateCable(pid, db.CableCreate{
+		TypeID: body.TypeID, Label: body.Label,
+		From: toCableEndpoint(body.From), To: toCableEndpoint(body.To),
+		Auto: body.Auto,
+	})
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusCreated, c)
+}
+
+func (h *handlers) patchCable(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	var body cablePatch
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	u := db.CableUpdate{
+		TypeID: body.TypeID, Label: body.Label, Auto: body.Auto,
+	}
+	if body.From != nil {
+		ep := toCableEndpoint(*body.From)
+		u.From = &ep
+	}
+	if body.To != nil {
+		ep := toCableEndpoint(*body.To)
+		u.To = &ep
+	}
+	// Promote semantics: explicit promote=true OR (PATCH touched
+	// type/from/to AND the current cable is auto) → set auto=false.
+	if body.Promote {
+		f := false
+		u.Auto = &f
+	}
+	c, err := h.store.UpdateCable(pid, id, u)
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, c)
+}
+
+func (h *handlers) deleteCable(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	if err := h.store.DeleteCable(pid, id); err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}
+
+// ----------------------------------------------------------------- bundles
+
+type bundleCreate struct {
+	Name     string  `json:"name"`
+	CableIDs []int64 `json:"cable_ids"`
+}
+
+type bundlePatch struct {
+	Name     *string  `json:"name,omitempty"`
+	CableIDs *[]int64 `json:"cable_ids,omitempty"`
+}
+
+func (h *handlers) listBundles(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	bs, err := h.store.ListBundles(pid)
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, bs)
+}
+
+func (h *handlers) createBundle(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	var body bundleCreate
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	b, err := h.store.CreateBundle(pid, db.BundleCreate{
+		Name: body.Name, CableIDs: body.CableIDs, Auto: false,
+	})
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusCreated, b)
+}
+
+func (h *handlers) patchBundle(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	var body bundlePatch
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	b, err := h.store.UpdateBundle(pid, id, db.BundleUpdate{
+		Name: body.Name, CableIDs: body.CableIDs,
+	})
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, b)
+}
+
+func (h *handlers) deleteBundle(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	if err := h.store.DeleteBundle(pid, id); err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}

internal/server/export.go

@@ -0,0 +1,122 @@
+package server
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"strings"
+	"time"
+
+	"mgit.msbls.de/m/mcables/internal/db"
+	"mgit.msbls.de/m/mcables/internal/exporter"
+)
+
+// syncExport runs the project's snapshot through the exporter, persists
+// the assigned excalidraw_ids, then PUTs the scene to mxdrw.msbls.de.
+func (h *handlers) syncExport(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+
+	base := os.Getenv("MEXDRAW_BASE_URL")
+	if base == "" {
+		base = "https://mxdrw.msbls.de"
+	}
+	user := os.Getenv("MEXDRAW_USER")
+	pass := os.Getenv("MEXDRAW_PASS")
+	if user == "" || pass == "" {
+		writeJSON(w, http.StatusBadRequest, errorBody{
+			Error:   "MEXDRAW_USER / MEXDRAW_PASS not set",
+			Details: "Add MEXDRAW_USER and MEXDRAW_PASS to /home/m/secrets/mcables/.env on mDock and restart the container — mxdrw expects HTTP Basic Auth",
+		})
+		return
+	}
+
+	snap, err := h.store.Snapshot(pid)
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+
+	now := time.Now().UnixMilli()
+	scene, ids := exporter.BuildScene(snap, now, exporter.Generate21)
+
+	// Persist the freshly-assigned ids so the next export reuses them.
+	// We pass in the full maps; PersistExcalidrawIDs is idempotent (it
+	// only updates rows whose excalidraw_id is still NULL).
+	if err := h.store.PersistExcalidrawIDs(pid, ids.Frames, ids.Devices, ids.Ports, ids.IOMarkers, ids.Cables); err != nil {
+		writeError(w, fmt.Errorf("persist excalidraw_ids: %w", err), nil)
+		return
+	}
+
+	payload, err := exporter.MarshalScene(scene)
+	if err != nil {
+		writeError(w, fmt.Errorf("marshal scene: %w", err), nil)
+		return
+	}
+
+	drawingName := snap.Project.DrawingName
+	if !strings.HasSuffix(drawingName, ".excalidraw") {
+		drawingName += ".excalidraw"
+	}
+	url := strings.TrimSuffix(base, "/") + "/api/drawings/" + drawingName
+
+	// Sane network timeout; mxdrw is on the LAN so this should be quick.
+	ctx, cancel := context.WithTimeout(r.Context(), 10*time.Second)
+	defer cancel()
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPut, url, bytes.NewReader(payload))
+	if err != nil {
+		writeError(w, fmt.Errorf("build PUT: %w", err), nil)
+		return
+	}
+	req.Header.Set("Content-Type", "application/json")
+	req.SetBasicAuth(user, pass)
+
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		writeJSON(w, http.StatusBadGateway, errorBody{
+			Error:   "mxdrw unreachable",
+			Details: err.Error(),
+		})
+		return
+	}
+	defer resp.Body.Close()
+	body, _ := io.ReadAll(resp.Body)
+	if resp.StatusCode >= 400 {
+		writeJSON(w, http.StatusBadGateway, errorBody{
+			Error: fmt.Sprintf("mxdrw rejected upload (%d)", resp.StatusCode),
+			Details: map[string]any{
+				"status": resp.StatusCode,
+				"body":   string(body),
+				"url":    url,
+			},
+		})
+		return
+	}
+
+	// Best-effort parse — mxdrw returns whatever it returns; we surface
+	// the public viewer URL no matter what.
+	var serverEcho any
+	_ = json.Unmarshal(body, &serverEcho)
+
+	viewerURL := strings.TrimSuffix(base, "/") + "/draw/" + strings.TrimSuffix(drawingName, ".excalidraw") + ".excalidraw"
+	writeJSON(w, http.StatusOK, map[string]any{
+		"ok":           true,
+		"drawing_name": drawingName,
+		"url":          viewerURL,
+		"element_count": len(scene.Elements),
+		"mxdrw_response": serverEcho,
+	})
+}
+
+// noLeak prevents unused-import errors if errors-pkg ever becomes unused
+// after a refactor — keeps the import light.
+var _ = errors.New

internal/server/ports.go

@@ -0,0 +1,114 @@
+package server
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+
+	"mgit.msbls.de/m/mcables/internal/db"
+)
+
+type portCreate struct {
+	TypeID  int64   `json:"type_id"`
+	Label   string  `json:"label,omitempty"`
+	XOffset float64 `json:"x_offset"`
+	YOffset float64 `json:"y_offset"`
+}
+
+type portPatch struct {
+	TypeID  *int64   `json:"type_id,omitempty"`
+	Label   *string  `json:"label,omitempty"`
+	XOffset *float64 `json:"x_offset,omitempty"`
+	YOffset *float64 `json:"y_offset,omitempty"`
+}
+
+func (h *handlers) listPortsForDevice(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	ps, err := h.store.ListPortsForDevice(pid, id)
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, ps)
+}
+
+func (h *handlers) createPort(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	var body portCreate
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	p, err := h.store.CreatePort(pid, id, db.PortCreate{
+		TypeID: body.TypeID, Label: body.Label,
+		XOffset: body.XOffset, YOffset: body.YOffset,
+	})
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusCreated, p)
+}
+
+func (h *handlers) patchPort(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	var body portPatch
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	p, err := h.store.UpdatePort(pid, id, db.PortUpdate{
+		TypeID: body.TypeID, Label: body.Label,
+		XOffset: body.XOffset, YOffset: body.YOffset,
+	})
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, p)
+}
+
+func (h *handlers) deletePort(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	if err := h.store.DeletePort(pid, id); err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}

internal/server/server.go

@@ -51,6 +51,12 @@ func New(store *db.Store, frontend fs.FS) http.Handler {
 	mux.HandleFunc("PATCH /api/projects/{pid}/io-markers/{id}", h.patchIOMarker)
 	mux.HandleFunc("DELETE /api/projects/{pid}/io-markers/{id}", h.deleteIOMarker)
 
+	// Ports — slice 7 lets m add/edit/remove instance ports on a device.
+	mux.HandleFunc("GET /api/projects/{pid}/devices/{id}/ports", h.listPortsForDevice)
+	mux.HandleFunc("POST /api/projects/{pid}/devices/{id}/ports", h.createPort)
+	mux.HandleFunc("PATCH /api/projects/{pid}/ports/{id}", h.patchPort)
+	mux.HandleFunc("DELETE /api/projects/{pid}/ports/{id}", h.deletePort)
+
 	// Device-type catalog. Built-ins are read-only; project-custom rows
 	// support full CRUD scoped to the project.
 	mux.HandleFunc("GET /api/device-types", h.listBuiltInDeviceTypes)
@@ -65,6 +71,28 @@ func New(store *db.Store, frontend fs.FS) http.Handler {
 	mux.HandleFunc("PATCH /api/projects/{pid}/connection-requirements/{id}", h.patchConnectionRequirement)
 	mux.HandleFunc("DELETE /api/projects/{pid}/connection-requirements/{id}", h.deleteConnectionRequirement)
 
+	// Cables — slice 6: solver writes here with auto=1; slice 7 lets m
+	// hand-draw with auto=0. PATCH supports `promote: true` to flip auto→0.
+	mux.HandleFunc("GET /api/projects/{pid}/cables", h.listCables)
+	mux.HandleFunc("POST /api/projects/{pid}/cables", h.createCable)
+	mux.HandleFunc("PATCH /api/projects/{pid}/cables/{id}", h.patchCable)
+	mux.HandleFunc("DELETE /api/projects/{pid}/cables/{id}", h.deleteCable)
+
+	// Bundles — manual + auto.
+	mux.HandleFunc("GET /api/projects/{pid}/bundles", h.listBundles)
+	mux.HandleFunc("POST /api/projects/{pid}/bundles", h.createBundle)
+	mux.HandleFunc("PATCH /api/projects/{pid}/bundles/{id}", h.patchBundle)
+	mux.HandleFunc("DELETE /api/projects/{pid}/bundles/{id}", h.deleteBundle)
+
+	// Solver + quick-fix combo + setup templates.
+	mux.HandleFunc("POST /api/projects/{pid}/solve", h.solve)
+	mux.HandleFunc("POST /api/projects/{pid}/devices/{id}/ports-and-resolve", h.portsAndResolve)
+	mux.HandleFunc("GET /api/setup-templates", h.listSetupTemplates)
+	mux.HandleFunc("POST /api/projects/{pid}/apply-template", h.applyTemplate)
+
+	// Slice 8 — export to mxdrw.msbls.de
+	mux.HandleFunc("POST /api/projects/{pid}/sync/export", h.syncExport)
+
 	// Frontend (embedded). Serve "/" → index.html via http.FileServerFS.
 	// Wrap in noCache so the browser revalidates with the ETag/Last-Modified
 	// the file server already emits — without this, browsers cache aggressively

internal/server/solver.go

@@ -0,0 +1,149 @@
+package server
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+
+	"mgit.msbls.de/m/mcables/internal/db"
+)
+
+func (h *handlers) solve(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	preview := r.URL.Query().Get("preview") == "1"
+	res, err := h.store.Solve(pid, preview)
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, res)
+}
+
+// ports-and-resolve combo: POST a new port to a device + re-run solve in
+// the same request. Used by the inspector quick-fix.
+type portsAndResolveBody struct {
+	TypeID  int64   `json:"type_id"`
+	Label   string  `json:"label,omitempty"`
+	XOffset float64 `json:"x_offset,omitempty"`
+	YOffset float64 `json:"y_offset,omitempty"`
+}
+
+func (h *handlers) portsAndResolve(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	id, ok := parseInt64Path(r, "id")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "id must be a positive integer")
+		return
+	}
+	var body portsAndResolveBody
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	res, err := h.store.PortsAndResolve(pid, id, body.TypeID, body.Label, body.XOffset, body.YOffset)
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, res)
+}
+
+// -------------------------------------------------------- setup templates
+
+func (h *handlers) listSetupTemplates(w http.ResponseWriter, _ *http.Request) {
+	ts, err := h.store.ListSetupTemplates()
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+	writeJSON(w, http.StatusOK, ts)
+}
+
+type applyTemplateBody struct {
+	TemplateID    int64            `json:"template_id"`
+	NameOverrides map[string]string `json:"name_overrides,omitempty"`
+	SkipDevices   []int64          `json:"skip_devices,omitempty"`
+	OriginX       float64          `json:"origin_x,omitempty"`
+	OriginY       float64          `json:"origin_y,omitempty"`
+}
+
+func (h *handlers) applyTemplate(w http.ResponseWriter, r *http.Request) {
+	pid, ok := parseInt64Path(r, "pid")
+	if !ok {
+		writeError(w, db.ErrInvalidInput, "pid must be a positive integer")
+		return
+	}
+	var body applyTemplateBody
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, errors.Join(db.ErrInvalidInput, err), nil)
+		return
+	}
+	opts := db.ApplyTemplateOptions{
+		NameOverrides: map[int64]string{},
+		SkipDevices:   map[int64]bool{},
+		OriginX:       body.OriginX,
+		OriginY:       body.OriginY,
+	}
+	// JSON keys are strings; parse to int64.
+	for k, v := range body.NameOverrides {
+		var tid int64
+		_, _ = fmtSscan(k, &tid)
+		if tid > 0 {
+			opts.NameOverrides[tid] = v
+		}
+	}
+	for _, tid := range body.SkipDevices {
+		opts.SkipDevices[tid] = true
+	}
+	res, err := h.store.ApplyTemplate(pid, body.TemplateID, opts)
+	if err != nil {
+		writeError(w, err, nil)
+		return
+	}
+
+	// Auto-solve by default. ?solve=0 opts out for power users who want
+	// to inspect the seeded devices/requirements before the solver runs.
+	// This is THE fix for the v6 UX hole: m hit Apply, saw an empty
+	// canvas because nothing reloaded *and* nothing solved. With the
+	// frontend re-snapshotting after the POST returns and the response
+	// already carrying solver output, m sees the wired diagram in one click.
+	skipSolve := r.URL.Query().Get("solve") == "0"
+	combined := map[string]any{"template_apply": res}
+	if !skipSolve {
+		solveRes, err := h.store.Solve(pid, false)
+		if err != nil {
+			// Apply succeeded but Solve failed — don't 500 the whole
+			// call. Return template_apply with the solve error inline so
+			// the UI can recover (devices are there; m can re-solve).
+			combined["solve_error"] = err.Error()
+		} else {
+			combined["solve"] = solveRes
+		}
+	}
+	writeJSON(w, http.StatusOK, combined)
+}
+
+// fmtSscan parses a base-10 int from a string, returning (n, nil) on success.
+// Inline so handlers don't pull in strconv just for one call site.
+func fmtSscan(s string, out *int64) (int, error) {
+	var v int64
+	read := 0
+	for i := 0; i < len(s); i++ {
+		c := s[i]
+		if c < '0' || c > '9' {
+			break
+		}
+		v = v*10 + int64(c-'0')
+		read++
+	}
+	*out = v
+	return read, nil
+}

web/static/index.html

@@ -20,9 +20,10 @@
       </button>
     </div>
     <div class="topbar-spacer"></div>
-    <button type="button" id="btn-export" class="btn" disabled title="Slice 5">
-      Export
-    </button>
+    <button type="button" id="btn-apply-template" class="btn">Apply template…</button>
+    <button type="button" id="btn-solve" class="btn btn-primary">Solve</button>
+    <button type="button" id="btn-export" class="btn">Export</button>
+    <span id="toast" class="toast" hidden></span>
   </header>
 
   <main class="layout">
@@ -44,7 +45,7 @@
           <li><button type="button" id="tool-device" class="btn btn-tiny" data-tool="device">+ Device</button></li>
           <li><button type="button" id="tool-io"     class="btn btn-tiny" data-tool="io">+ IO</button></li>
           <li><button type="button" id="tool-req"    class="btn btn-tiny" data-tool="req">Drag req A→B</button></li>
-          <li><button type="button" class="btn btn-tiny" disabled title="Slice 7">Draw cable</button></li>
+          <li><button type="button" id="tool-cable"  class="btn btn-tiny" data-tool="cable" title="Click a port to start, then click another port / device / IO marker">Draw cable</button></li>
         </ul>
       </section>
     </aside>
@@ -175,6 +176,35 @@
     </form>
   </dialog>
 
+  <!-- Solve preview-diff (slice 6) -->
+  <dialog id="modal-solve" class="modal modal-wide" aria-labelledby="sv-title">
+    <div style="padding: 16px;">
+      <h2 id="sv-title">Solve preview</h2>
+      <div id="sv-body" class="sv-body"></div>
+      <div class="actions" style="margin-top: 12px;">
+        <button type="button" class="btn btn-primary" id="sv-apply">Apply</button>
+        <button type="button" class="btn" data-close>Cancel</button>
+      </div>
+    </div>
+  </dialog>
+
+  <!-- Apply template (slice 6) -->
+  <dialog id="modal-template" class="modal modal-wide" aria-labelledby="tp-title">
+    <form method="dialog" id="form-template">
+      <h2 id="tp-title">Apply setup template</h2>
+      <label class="field">
+        <span>Template</span>
+        <select id="tp-select" required></select>
+      </label>
+      <div id="tp-preview" class="tp-preview"></div>
+      <p class="form-error" id="tp-error" hidden></p>
+      <div class="actions">
+        <button type="submit" class="btn btn-primary">Apply</button>
+        <button type="button" class="btn" data-close>Cancel</button>
+      </div>
+    </form>
+  </dialog>
+
   <!-- Delete Project confirm -->
   <dialog id="modal-delete-project" class="modal" aria-labelledby="dp-title">
     <form method="dialog" id="form-delete-project">

web/static/style.css

@@ -183,9 +183,10 @@ body {
   pointer-events: none;
 }
 
+/* Stroke + fill come from the device's user-set colour, written as
+   inline style in renderCanvas — leaving them out of .device-rect so
+   the author CSS doesn't override the inline style. */
 .device-rect {
-  fill: #fff;
-  stroke: var(--text);
   stroke-width: 1.5;
 }
 .device-rect.selected { stroke-width: 3; }
@@ -213,7 +214,46 @@ body {
 .canvas-wrap.tool-device #canvas,
 .canvas-wrap.tool-device #canvas *,
 .canvas-wrap.tool-io     #canvas,
-.canvas-wrap.tool-io     #canvas * { cursor: crosshair !important; }
+.canvas-wrap.tool-io     #canvas *,
+.canvas-wrap.tool-port   #canvas,
+.canvas-wrap.tool-port   #canvas *,
+.canvas-wrap.tool-cable  #canvas,
+.canvas-wrap.tool-cable  #canvas * { cursor: crosshair !important; }
+
+.btn-link {
+  background: transparent;
+  border: 0;
+  color: var(--text-muted);
+  cursor: pointer;
+  font: inherit;
+  padding: 0 4px;
+  line-height: 1;
+}
+.btn-link:hover { color: var(--danger); }
+
+/* Highlight a port that's been picked as the cable-draw source. */
+.port-circle.cable-from {
+  stroke-width: 3;
+  filter: drop-shadow(0 0 4px var(--accent));
+}
+
+/* Header toast — slice 8 export feedback */
+.toast {
+  display: inline-block;
+  margin-left: 12px;
+  font-size: 13px;
+  padding: 4px 10px;
+  border-radius: var(--radius);
+  background: var(--surface-2);
+  color: var(--text);
+  max-width: 420px;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+.toast.ok    { background: #e8f5e9; color: #1b5e20; }
+.toast.error { background: #fdecea; color: #911313; }
+.toast a { color: inherit; text-decoration: underline; }
 
 /* IO markers — diamonds. Power-by-convention, so the default fill is
    the Power cable_type colour (#e03131). Rotated 45° rect is the
@@ -238,15 +278,16 @@ body {
   user-select: none;
 }
 
-/* Ports — small circles laid out along the device edge. The fill is
-   white so the port is visible regardless of the underlying device's
-   stroke; the stroke colour comes from the cable_type the port carries
-   (set inline in JS). */
+/* Ports — small circles laid out along the device edge. Both fill and
+   stroke come from the cable_type the port carries (set inline in JS)
+   so the port reads clearly as a coloured anchor on the device. */
 .port-circle {
-  fill: #fff;
-  stroke: var(--text);
   stroke-width: 2;
-  pointer-events: none;  /* slice 4 — selection happens at device-level */
+  cursor: crosshair;
+}
+.port-circle.selected {
+  stroke-width: 3;
+  filter: drop-shadow(0 0 4px var(--accent));
 }
 
 .port-row {
@@ -257,11 +298,15 @@ body {
   font-size: 12px;
   padding: 2px 0;
 }
-.port-row .swatch {
+.port-row .swatch,
+.swatch {
+  display: inline-block;
   width: 10px;
   height: 10px;
   border-radius: 50%;
   border: 1px solid rgba(0, 0, 0, 0.15);
+  margin-right: 6px;
+  vertical-align: middle;
 }
 .port-row .label { color: var(--text); }
 .port-row .conn  { color: var(--text-muted); font-size: 11px; }
@@ -316,6 +361,76 @@ body {
   pointer-events: none;
 }
 
+/* Cables on the canvas. Stroke colour comes from the cable_type;
+   solver-owned cables (auto=1) render with a slightly dashed pattern
+   so m can tell at a glance which the solver placed. */
+.cable-line {
+  fill: none;
+  stroke-width: 2;
+  cursor: pointer;
+}
+.cable-line.auto { stroke-dasharray: 8 3; }
+.cable-line:hover { stroke-width: 4; }
+.cable-line.selected { stroke-width: 4; }
+
+/* Solve preview-diff modal */
+.modal-wide { width: 560px; }
+.sv-body { font-size: 13px; }
+.sv-body h3 {
+  font-size: 11px;
+  text-transform: uppercase;
+  letter-spacing: 0.04em;
+  color: var(--text-muted);
+  margin: 12px 0 4px;
+}
+.sv-body ul {
+  list-style: none;
+  padding: 0;
+  margin: 0;
+  display: flex;
+  flex-direction: column;
+  gap: 2px;
+}
+.sv-body li {
+  padding: 4px 8px;
+  border-radius: var(--radius);
+  background: var(--surface-2);
+}
+.sv-body li.added   { border-left: 3px solid #2f9e44; }
+.sv-body li.removed { border-left: 3px solid var(--danger); text-decoration: line-through; }
+.sv-body li.unmet   { border-left: 3px solid #f59f00; }
+.sv-body li.unmet .quickfix {
+  display: inline-block;
+  margin-left: 8px;
+  font-size: 11px;
+  padding: 1px 6px;
+  background: var(--accent);
+  color: #fff;
+  border-radius: 10px;
+  cursor: pointer;
+}
+
+.tp-preview {
+  font-size: 13px;
+  background: var(--surface-2);
+  border-radius: var(--radius);
+  padding: 8px 12px;
+  margin: 8px 0;
+}
+.tp-preview h4 {
+  font-size: 11px;
+  text-transform: uppercase;
+  letter-spacing: 0.04em;
+  color: var(--text-muted);
+  margin: 6px 0 4px;
+}
+.tp-preview ul { list-style: none; padding: 0; margin: 0; }
+.tp-preview li { padding: 2px 0; }
+.tp-preview .skip {
+  margin-right: 6px;
+  font-size: 11px;
+}
+
 .rubber-band {
   fill: rgba(25, 113, 194, 0.08);
   stroke: var(--accent);