CableGUI/docs/design.md

# mCables — Design v4

Cable-management **framework + solver** for m's setup. Inventor shift 1
design, revised through v2 (rescope to multi-project framework), v3
(global cable_types + guardrails), and now **v4 — solver-as-core**.

Sources: the live `Cable-Management.excalidraw` on mxdrw.msbls.de (used as
the *visual-grammar reference*, not a bootstrap import target),
`mai-memory` (`mcables`, `m`), and the live mDock services for deploy
conventions (§10). v4 driven by m's product-vision clarification:

> "we provide a cable manager — I say what devices we have, the app tells
> me how to bundle cables and how the most efficient connection looks like"

mCables shifts from a manual draw-and-click editor to a **solver** that
takes a list of devices + the connections m needs and emits the cable
plan + bundle recommendations. The manual editor stays (it's the only way
to inspect + tweak the plan) but is no longer the primary surface.

> **What changed in v4** (new mental model on top of v3 mechanics)
> - **Hybrid device-type catalog** (§2.1, §3.1). A built-in `device_types`
>   table seeds common devices (NAS, PC, Mac, TV, Soundbar, Switch, fritz,
>   ChromeCast, SteamLink, IOx-3/6/8, Notebook, …) with default port
>   profiles (`device_type_ports` rows: cable_type + count + label).
>   Adding a device → pick a type → ports auto-seed. m can override per
>   instance (this PC has 3 USB, not 2). Catalog is extendable per project.
> - **`connection_requirements` table** (§2.2). m declares "NAS must
>   connect to Switch via RJ45" once. Many per device. The solver consumes
>   these.
> - **`POST /api/projects/:pid/solve` endpoint** (§3.2). Reads devices +
>   their ports + connection_requirements + frame positions, emits a diff
>   of `cables` + `bundles`. Two modes: `?preview=1` returns the diff
>   without applying; default applies.
> - **Solver objective: maximum bundling** (§5). Prefer routes that
>   consolidate cables into trunks even at higher total length. Visually
>   cleaner setups, easier mental model. v0 uses the v3 same-endpoints
>   bundle rule; path-based bundling is slice 6+.
> - **UI: device-type dropdown** on device-create, **Connection
>   Requirements** left panel, **Solve** button next to Export. Inspector
>   shows type + ports + unmet requirements (selected device) or the
>   driving requirement + bundle (selected cable).
> - **Slices reshape** (§8). Catalog seeding lands early (slice 1.5); the
>   solver MVP and connection-requirements UI move ahead of the
>   bundle-rendering polish.
>
> **What carried over from v3 (unchanged in v4)**
> - mCables is a framework: top-level `projects`, each backed by one
>   `.excalidraw` drawing. `UNIQUE(projects.name)`.
> - `cable_types` is global. Migration 001 seeds Power/USB/HDMI/DP/RJ45.
> - `devices` UNIQUE(project_id, name); `frame_id` nullable; FrameRef
>   tri-state on PATCH.
> - IO diamonds = wall-outlet terminators (type=Power by convention).
> - `projects.drawing_name` auto-defaults to `<name>.excalidraw`.
> - `DELETE /api/projects/:pid?confirm=<name>` guardrail.
> - No cable inventory metadata; visual + connectivity structure only.
> - DB at `./data/mcables.db` (gitignored). Bind `0.0.0.0:7777` LAN, no auth.
> - Deploy on mDock under `/home/m/stacks/mcables/`, raw docker-compose.
>
> **What's superseded in v4**
> - The "manual draw-a-cable port-to-port" flow from v3 §7 is *kept* as a
>   tweak path on the solver output, but is no longer the *primary* device-
>   connecting flow. The solve button is the headline action.
> - The v3 §8 slice order changes — catalog + types-driven devices + solver
>   come earlier; the manual-draw-cable slice slides later. See new §8.

---

## 0. The seed drawing — visual grammar reference

`Cable-Management.excalidraw` on mxdrw.msbls.de is **not** ingested at
runtime. It is the visual-grammar reference we lock the export onto so that
when m rebuilds LOFT and OFFICE inside mCables, the exported `.excalidraw`
looks like the seed.

Concrete numbers from the live file (180 elements):

| Kind | Count | Excalidraw shape | What it represents |
|---|---|---|---|
| Frames | 2 | `frame` (`name`) | Sub-areas inside a project (`desk`, `rack`, …) |
| Devices | 27 | `rectangle` with bound text | Hardware items |
| Ports | 74 | `ellipse` ~12×9 | Connectors on a device edge, colour = cable type |
| Cables | 31 | `arrow` | Typed connections between ports/devices/outlets |
| IO markers | 6 | `diamond` text=`IO` | **Wall outlet / power-entry terminators** (type=Power) |
| Legend | 5 | `text` | Colour key in the top-left of the frame |
| Lines | 5 | `line` | **Decorative** (separator under the legend). Ignored. |

**Legend → cable type → colour**, picked up directly from the seed:

| Type | Colour | Hex |
|---|---|---|
| Power | red | `#e03131` |
| USB | green | `#2f9e44` |
| HDMI | blue | `#1971c2` |
| DP | purple | `#9c36b5` |
| RJ45 | yellow | `#ffd500` |

Three observations about the seed's visual grammar — these constrain the
**exporter** (§4):

1. **Ports sit on a device edge as small ellipses (~12×9)**, coloured by
   cable type. They are not children of the device in the Excalidraw sense
   (no `containerId`/`boundElements` link) — purely positional. When we
   export from mCables we mimic that: port ellipse at `(device.x +
   port.x_offset, device.y + port.y_offset)`, stroke colour = type colour.
2. **Cable arrows bind to elements**. In the seed: 44 endpoints to ellipses
   (ports), 12 to whole rectangles (device-level, no specific port), 3 to
   diamonds (wall outlets). Our exporter sets `startBinding.elementId` /
   `endBinding.elementId` to whichever Excalidraw element ID we wrote for
   the port / device / IO marker.
3. **IO diamonds = wall outlets.** They are terminals: a cable goes from a
   device-port → an IO marker, meaning "this cable plugs into a wall socket
   outside the diagram". They are always type=Power in m's setup but the
   schema doesn't enforce that (a future "network jack in the wall"
   wouldn't fit, and we can lift the constraint then).

---

## 1. Frontend stack — vanilla JS + SVG

**Locked**: vanilla ES modules (TS-typed via JSDoc, no build step) + SVG
diagram surface, served from a single Go binary via `embed.FS`.

Why this fits m: matches the no-build-step preference; same single-binary
aesthetic as `m`, `mai`, `youpcms`, `mExDraw`. Type-checking is opt-in via
`make typecheck` (`tsc --noEmit`), not gating runtime. SVG is one DOM node
per port/device/cable → trivial hit-testing, CSS-driven colouring by
`data-type=hdmi`, drag via pointer events + `getScreenCTM()`.

Escape hatch only if state for half-drawn cables + multi-select gets
painful: switch to Preact-via-CDN-ESM (still no build step). Not v0.

---

## 2. SQLite schema

`./data/mcables.db` (project-local, gitignored). WAL mode, FKs on.
Driver: **`modernc.org/sqlite`** (cgo-free — clean cross-compile, simple
Dockerfile).

```sql
-- 001_init.sql
PRAGMA journal_mode = WAL;
PRAGMA foreign_keys = ON;

-- A project IS a drawing. LOFT and OFFICE are separate projects.
-- One project ↔ one .excalidraw file in mExDraw.
CREATE TABLE projects (
    id              INTEGER PRIMARY KEY,
    name            TEXT NOT NULL UNIQUE,        -- "LOFT", "OFFICE"
    drawing_name    TEXT NOT NULL,               -- mExDraw drawing name, e.g. "LOFT.excalidraw"
    description     TEXT NOT NULL DEFAULT '',
    created_at      TEXT NOT NULL DEFAULT (datetime('now')),
    updated_at      TEXT NOT NULL DEFAULT (datetime('now'))
);

-- Cable types: GLOBAL legend, one set shared across all projects.
-- Migration 001 seeds the 5 defaults (Power/USB/HDMI/DP/RJ45) once.
-- Renaming or recolouring a type from anywhere in the UI propagates to
-- every project's legend and to every cable already typed as it.
CREATE TABLE cable_types (
    id              INTEGER PRIMARY KEY,
    name            TEXT NOT NULL UNIQUE,        -- "Power", "USB", "HDMI", "DP", "RJ45"
    color           TEXT NOT NULL,               -- "#e03131"
    created_at      TEXT NOT NULL DEFAULT (datetime('now')),
    updated_at      TEXT NOT NULL DEFAULT (datetime('now'))
);

-- v4 — device-type catalog. Seeded built-in types live globally (so
-- multiple projects share the "NAS" definition without duplication).
-- Per-project custom types are also allowed (project_id non-null for those).
-- Renaming a built-in type doesn't propagate retroactively to existing
-- devices that already had their ports seeded — they own their port set
-- from the moment they were created.
CREATE TABLE device_types (
    id              INTEGER PRIMARY KEY,
    project_id      INTEGER REFERENCES projects(id) ON DELETE CASCADE,
                                                  -- NULL = built-in (shared), non-null = project-custom
    name            TEXT NOT NULL,                -- "NAS", "PC", "TV", "Switch", "IOx-8", "Custom-Foo"
    kind            TEXT NOT NULL DEFAULT 'generic',
                                                  -- coarse category for UI grouping: 'storage', 'compute',
                                                  -- 'display', 'audio', 'network', 'hub', 'accessory',
                                                  -- 'generic'
    icon            TEXT,                         -- emoji or short symbol (🖥, 📺, 🔊, 📡) — UI hint
    description     TEXT NOT NULL DEFAULT '',
    built_in        INTEGER NOT NULL DEFAULT 0,   -- 1 for migration-seeded rows, 0 for user-created
    created_at      TEXT NOT NULL DEFAULT (datetime('now')),
    updated_at      TEXT NOT NULL DEFAULT (datetime('now')),
    UNIQUE (project_id, name)                     -- two projects can both have a custom "Foo";
                                                  -- built-ins (project_id NULL) get UNIQUE on name globally
);
CREATE INDEX device_types_project_idx ON device_types(project_id);

-- v4 — port profile per device type. "NAS has 1 Power + 1 RJ45" is two
-- rows; "PC has 1 Power + 1 RJ45 + 1 HDMI + 2 USB" is four rows.
-- When a device is created with type_id=X, the seeder inserts `count`
-- rows into the `ports` table for each device_type_ports entry,
-- numbering label as "<label_prefix> N" if count > 1.
CREATE TABLE device_type_ports (
    id              INTEGER PRIMARY KEY,
    device_type_id  INTEGER NOT NULL REFERENCES device_types(id) ON DELETE CASCADE,
    cable_type_id   INTEGER NOT NULL REFERENCES cable_types(id)  ON DELETE RESTRICT,
    label_prefix    TEXT NOT NULL DEFAULT '',     -- "HDMI", "USB", "Power" — UI label root
    count           INTEGER NOT NULL DEFAULT 1 CHECK (count >= 1),
    -- Position hint: the seeder lays ports along the device edge using
    -- these biases (0..1 along the edge fraction). NULL = even spread.
    edge            TEXT NOT NULL DEFAULT 'bottom' CHECK (edge IN ('top','bottom','left','right')),
    sort_order      INTEGER NOT NULL DEFAULT 0
);
CREATE INDEX device_type_ports_type_idx ON device_type_ports(device_type_id);

-- A frame is a named container *inside* a project: 'desk', 'rack', 'media'.
CREATE TABLE frames (
    id              INTEGER PRIMARY KEY,
    project_id      INTEGER NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
    name            TEXT NOT NULL,
    x               REAL NOT NULL DEFAULT 0,
    y               REAL NOT NULL DEFAULT 0,
    width           REAL NOT NULL DEFAULT 1200,
    height          REAL NOT NULL DEFAULT 800,
    excalidraw_id   TEXT,                        -- stable across exports
    created_at      TEXT NOT NULL DEFAULT (datetime('now')),
    updated_at      TEXT NOT NULL DEFAULT (datetime('now')),
    UNIQUE (project_id, name),
    UNIQUE (project_id, excalidraw_id)
);
CREATE INDEX frames_project_idx ON frames(project_id);

-- Devices live in a frame (and transitively in a project).
-- Stored project_id is denormalised for cheap project-scoped queries; FK
-- to frame_id is the structural truth. Both are kept consistent in code.
--
-- v4 — type_id (nullable) lets a device inherit its port profile from
-- a `device_types` row. Once ports are seeded the device "owns" them;
-- changing/clearing type_id later does not retroactively re-seed (m's
-- per-instance overrides survive). Custom freeform devices (no template)
-- keep type_id NULL — that's the v3 "just a rectangle" device.
CREATE TABLE devices (
    id              INTEGER PRIMARY KEY,
    project_id      INTEGER NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
    frame_id        INTEGER REFERENCES frames(id) ON DELETE SET NULL,
    type_id         INTEGER REFERENCES device_types(id) ON DELETE SET NULL,
                                                  -- v4: nullable; SET NULL on type delete so we don't
                                                  -- cascade-delete a device the user still wants
    name            TEXT NOT NULL,
    color           TEXT NOT NULL DEFAULT '#1e1e1e',
    x               REAL NOT NULL,
    y               REAL NOT NULL,
    width           REAL NOT NULL,
    height          REAL NOT NULL,
    excalidraw_id   TEXT,
    created_at      TEXT NOT NULL DEFAULT (datetime('now')),
    updated_at      TEXT NOT NULL DEFAULT (datetime('now')),
    UNIQUE (project_id, name),                   -- no two devices in one project share a name
    UNIQUE (project_id, excalidraw_id)
);
CREATE INDEX devices_project_idx ON devices(project_id);
CREATE INDEX devices_frame_idx   ON devices(frame_id);
CREATE INDEX devices_type_idx    ON devices(type_id);

-- Ports belong to a device. x_offset/y_offset are relative to the device's
-- top-left so ports follow when the device moves. project_id denormalised.
CREATE TABLE ports (
    id              INTEGER PRIMARY KEY,
    project_id      INTEGER NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
    device_id       INTEGER NOT NULL REFERENCES devices(id) ON DELETE CASCADE,
    type_id         INTEGER NOT NULL REFERENCES cable_types(id) ON DELETE RESTRICT,
    label           TEXT,                        -- optional ("HDMI 1", "USB-C rear")
    x_offset        REAL NOT NULL,
    y_offset        REAL NOT NULL,
    excalidraw_id   TEXT,
    created_at      TEXT NOT NULL DEFAULT (datetime('now')),
    updated_at      TEXT NOT NULL DEFAULT (datetime('now')),
    UNIQUE (project_id, excalidraw_id)
);
CREATE INDEX ports_project_idx ON ports(project_id);
CREATE INDEX ports_device_idx  ON ports(device_id);
CREATE INDEX ports_type_idx    ON ports(type_id);

-- IO markers = wall outlets / power-entry terminators.
-- One end of a Power cable. They are NOT bridges and they do NOT pair.
CREATE TABLE io_markers (
    id              INTEGER PRIMARY KEY,
    project_id      INTEGER NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
    frame_id        INTEGER REFERENCES frames(id) ON DELETE SET NULL,
    label           TEXT NOT NULL DEFAULT 'IO',  -- "Wall A", "UPS rear", …
    x               REAL NOT NULL,
    y               REAL NOT NULL,
    excalidraw_id   TEXT,
    created_at      TEXT NOT NULL DEFAULT (datetime('now')),
    updated_at      TEXT NOT NULL DEFAULT (datetime('now')),
    UNIQUE (project_id, excalidraw_id)
);
CREATE INDEX io_markers_project_idx ON io_markers(project_id);
CREATE INDEX io_markers_frame_idx   ON io_markers(frame_id);

-- A cable. Each endpoint is exactly one of (port, device, io-marker).
-- All foreign-key targets must be in the same project_id as the cable —
-- enforced in code (the CHECK below only enforces the one-non-null rule).
CREATE TABLE cables (
    id              INTEGER PRIMARY KEY,
    project_id      INTEGER NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
    type_id         INTEGER NOT NULL REFERENCES cable_types(id) ON DELETE RESTRICT,
    label           TEXT,
    from_port_id    INTEGER REFERENCES ports(id)      ON DELETE SET NULL,
    from_device_id  INTEGER REFERENCES devices(id)    ON DELETE SET NULL,
    from_io_id      INTEGER REFERENCES io_markers(id) ON DELETE SET NULL,
    to_port_id      INTEGER REFERENCES ports(id)      ON DELETE SET NULL,
    to_device_id    INTEGER REFERENCES devices(id)    ON DELETE SET NULL,
    to_io_id        INTEGER REFERENCES io_markers(id) ON DELETE SET NULL,
    excalidraw_id   TEXT,
    created_at      TEXT NOT NULL DEFAULT (datetime('now')),
    updated_at      TEXT NOT NULL DEFAULT (datetime('now')),
    CHECK (
        (from_port_id IS NOT NULL) + (from_device_id IS NOT NULL) + (from_io_id IS NOT NULL) = 1
    ),
    CHECK (
        (to_port_id IS NOT NULL) + (to_device_id IS NOT NULL) + (to_io_id IS NOT NULL) = 1
    ),
    UNIQUE (project_id, excalidraw_id)
);
CREATE INDEX cables_project_idx     ON cables(project_id);
CREATE INDEX cables_from_port_idx   ON cables(from_port_id);
CREATE INDEX cables_to_port_idx     ON cables(to_port_id);
CREATE INDEX cables_from_device_idx ON cables(from_device_id);
CREATE INDEX cables_to_device_idx   ON cables(to_device_id);
CREATE INDEX cables_type_idx        ON cables(type_id);

-- Bundles: named groups of cables that physically run together, within
-- a single project (a bundle does not span LOFT ↔ OFFICE).
CREATE TABLE bundles (
    id              INTEGER PRIMARY KEY,
    project_id      INTEGER NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
    name            TEXT NOT NULL,
    auto            INTEGER NOT NULL DEFAULT 0,
    created_at      TEXT NOT NULL DEFAULT (datetime('now')),
    updated_at      TEXT NOT NULL DEFAULT (datetime('now')),
    UNIQUE (project_id, name)
);
CREATE INDEX bundles_project_idx ON bundles(project_id);

CREATE TABLE bundle_cables (
    bundle_id       INTEGER NOT NULL REFERENCES bundles(id) ON DELETE CASCADE,
    cable_id        INTEGER NOT NULL REFERENCES cables(id)  ON DELETE CASCADE,
    PRIMARY KEY (bundle_id, cable_id)
);
CREATE INDEX bundle_cables_cable_idx ON bundle_cables(cable_id);

-- v4 — connection_requirements: the input m gives the solver.
-- "NAS must connect to Switch via RJ45" is one row. Many per device.
--
-- preferred_cable_type_id is the cable type m intends — the solver
-- needs it to match port colours. NULL means "solver picks" (the solver
-- will pick the unique cable_type that is compatible with both ends'
-- available port types; if ambiguous it surfaces an error for m).
--
-- must_connect = 1 (default) means the solver MUST satisfy this; an
-- unsatisfiable must_connect surfaces as a hard error in the solve
-- result. must_connect = 0 = "nice to have, drop if you run out of
-- ports". Used for templates that over-spec.
--
-- The (from_device_id, to_device_id) pair is normalised on insert so
-- (A,B) and (B,A) are the same requirement — UNIQUE on the unordered
-- pair + cable type prevents duplicates.
CREATE TABLE connection_requirements (
    id                       INTEGER PRIMARY KEY,
    project_id               INTEGER NOT NULL REFERENCES projects(id) ON DELETE CASCADE,
    from_device_id           INTEGER NOT NULL REFERENCES devices(id) ON DELETE CASCADE,
    to_device_id             INTEGER NOT NULL REFERENCES 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)),
    notes                    TEXT NOT NULL DEFAULT '',
    -- Order-normalised pair: lo = MIN(from, to), hi = MAX(from, to). Set
    -- in code on insert; the UNIQUE then prevents (A,B,Power) AND
    -- (B,A,Power) from coexisting. Stored alongside the m-facing
    -- from/to so the UI doesn't have to denormalise.
    pair_lo                  INTEGER NOT NULL,
    pair_hi                  INTEGER NOT NULL,
    CHECK (from_device_id != to_device_id),
    UNIQUE (project_id, pair_lo, pair_hi, preferred_cable_type_id),
    created_at               TEXT NOT NULL DEFAULT (datetime('now')),
    updated_at               TEXT NOT NULL DEFAULT (datetime('now'))
);
CREATE INDEX conn_reqs_project_idx ON connection_requirements(project_id);
CREATE INDEX conn_reqs_pair_idx    ON connection_requirements(project_id, pair_lo, pair_hi);
CREATE INDEX conn_reqs_from_idx    ON connection_requirements(from_device_id);
CREATE INDEX conn_reqs_to_idx      ON connection_requirements(to_device_id);
```

### 2.1 Migration sequence

- **001_init.sql** (v3) — projects, frames, devices (no type_id), ports,
  cable_types (5 seeded), io_markers, cables, bundles, bundle_cables.
- **002_device_catalog.sql** (v4 NEW) — `device_types` +
  `device_type_ports`. Seeds the built-in catalog (§2.2). Adds
  `devices.type_id` (`ALTER TABLE devices ADD COLUMN type_id INTEGER
  REFERENCES device_types(id) ON DELETE SET NULL`) and the matching
  index.
- **003_connection_requirements.sql** (v4 NEW) — `connection_requirements`.

Slice 1 already shipped 001. Slices 1.5 (catalog) and 1.6 (requirements)
land 002 and 003.

### 2.2 Built-in catalog seed (002 INSERTs)

The 11 built-in types m's setup uses today, with their default port
profiles. Stored as `(project_id NULL, built_in 1)`:

| `device_types.name` | `kind` | Default ports (cable_type × count) |
|---|---|---|
| NAS | storage | Power × 1; RJ45 × 1 |
| PC | compute | Power × 1; RJ45 × 1; HDMI × 1; USB × 2 |
| Mac | compute | Power × 1; HDMI × 1; USB × 2 |
| Notebook | compute | Power × 1; USB × 2 |
| TV | display | Power × 1; HDMI × 2 |
| Soundbar | audio | Power × 1; HDMI × 1 |
| Switch | network | Power × 1; RJ45 × 5 |
| 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 |

"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.

m can also add **project-custom types** at any time (UI: "+ New device
type" inside the device-create modal) with `project_id = current`.

### 2.3 Why ports are still instance-owned

When m picks a type to create a device, the seeder calls `count` × INSERT
into `ports`. From that moment on, ports are instance-level rows owned by
that device. Deleting a port from this PC doesn't touch other PCs;
changing a type's port profile (in slice 4.5) doesn't retroactively
re-seed already-created devices — it only affects subsequent device
creations.

Trade-off acknowledged: m may want a "re-seed from type" action later
(slice 5+) to wipe + reset a device's ports. Out of v0 scope; not
blocked by the schema.

**FK shape — why `project_id` on every project-scoped row, not just transitively:**

The structural truth is `cable → port → device → frame → project`. But
project-scoped queries ("give me all cables in OFFICE") would otherwise need
three joins. Denormalising `project_id` onto every project-scoped row is a
small, load-bearing pragma: `cables WHERE project_id=?` is a one-column
index hit. The cost: code must keep `project_id` consistent with `frame_id`
/ `device_id` on insert+update. That's enforced at the Go layer
(`internal/db/store.go` setter functions), not by SQL — `CHECK` constraints
in SQLite can't reference another table.

`cable_types` is the **one global table** — it has no `project_id`.
Cables reference it cross-project. Renaming or recolouring a type updates
the legend everywhere immediately and re-renders every cable of that type
on the next paint.

`ON DELETE CASCADE` from `projects` cleanly wipes a project's whole subgraph
in one statement, which is what we want when m says "delete OFFICE". The
cascade does **not** touch `cable_types` (no FK to projects).

---

## 3. Go HTTP API

Single binary `cmd/mcables`, `net/http`, no router framework. Listens on
`0.0.0.0:7777` by default (overridable via `MCABLES_ADDR`). Static frontend
from `embed.FS` at `/`, JSON API under `/api/`.

```
GET    /                                            → index.html (embedded)
GET    /assets/*                                    → JS/CSS/SVG (embedded)
GET    /api/healthz                                 → 200 ok

# Projects — top-level
GET    /api/projects                                → [Project, …]
POST   /api/projects                                ← {name, drawing_name?, description?}
                                                     If drawing_name is omitted, server defaults to
                                                     "<name>.excalidraw". No cable-type seeding —
                                                     cable_types is global (see /api/cable-types).
GET    /api/projects/:pid                           → full snapshot
                                                      {project, frames, devices, ports, cables,
                                                       io_markers, bundles}
                                                      Plus the global cable_types (clients can also
                                                      fetch them via /api/cable-types). Editor's
                                                      one-shot loader.
PATCH  /api/projects/:pid                           ← partial {name, drawing_name, description}
DELETE /api/projects/:pid?confirm=<name>            Confirmation guardrail — the query param must
                                                     equal the project's current name. 400 if missing
                                                     or mismatched. Cascades through all child rows
                                                     (frames, devices, ports, cables, io_markers,
                                                     bundles, bundle_cables). Does NOT touch
                                                     cable_types.

# Cable types — GLOBAL, NOT under a project
GET    /api/cable-types                             → [CableType, …]
POST   /api/cable-types                             ← {name, color}            # name must be unique globally
PATCH  /api/cable-types/:id                         ← {name?, color?}          # affects every project's legend + every cable using this type
DELETE /api/cable-types/:id                                                    # blocked if any cable still references it (ON DELETE RESTRICT)

# Inside a project — everything below scoped under :pid
GET    /api/projects/:pid/frames
POST   /api/projects/:pid/frames                    ← {name, x, y, width, height}
PATCH  /api/projects/:pid/frames/:id
DELETE /api/projects/:pid/frames/:id

GET    /api/projects/:pid/devices
POST   /api/projects/:pid/devices                   ← {name, type_id?, frame_id?, x, y, width, height, color?}
                                                     v4: type_id (optional) seeds ports from the catalog;
                                                     without it, a freeform device (no ports) is created.
PATCH  /api/projects/:pid/devices/:id               (e.g. {x, y} on drag). type_id can be set or cleared;
                                                     clearing does NOT delete existing ports (instance-owned).
DELETE /api/projects/:pid/devices/:id

GET    /api/projects/:pid/devices/:id/ports
POST   /api/projects/:pid/devices/:id/ports         ← {type_id, x_offset, y_offset, label?}
PATCH  /api/projects/:pid/ports/:id
DELETE /api/projects/:pid/ports/:id

GET    /api/projects/:pid/cables
POST   /api/projects/:pid/cables                    ← {type_id, from_{port|device|io}_id,
                                                      to_{port|device|io}_id, label?}
PATCH  /api/projects/:pid/cables/:id
DELETE /api/projects/:pid/cables/:id

GET    /api/projects/:pid/io-markers
POST   /api/projects/:pid/io-markers                ← {frame_id?, label, x, y}
PATCH  /api/projects/:pid/io-markers/:id
DELETE /api/projects/:pid/io-markers/:id

GET    /api/projects/:pid/bundles                   → [{Bundle, cable_ids: [int]}, …]
POST   /api/projects/:pid/bundles                   ← {name, cable_ids: [int]}
GET    /api/projects/:pid/bundles/suggestions       → [{name, cable_ids}, …]    (see §5)
PATCH  /api/projects/:pid/bundles/:id
DELETE /api/projects/:pid/bundles/:id

# v4 — Device-type catalog (mostly global, project-scoped writes for custom rows)
GET    /api/device-types                            → built-in catalog (project_id NULL) — read-only listing
GET    /api/projects/:pid/device-types              → built-ins + this project's custom types, merged
POST   /api/projects/:pid/device-types              ← {name, kind?, icon?, description?, ports: [{cable_type_id, count, label_prefix?, edge?}]}
                                                     Creates a project-custom row (built_in=0); inserts
                                                     device_type_ports rows in the same transaction.
PATCH  /api/projects/:pid/device-types/:id          ← partial. Only project-custom types are PATCHable;
                                                     mutating a built-in row → 403 (UI hides edit affordance).
                                                     Editing ports replaces the device_type_ports rows;
                                                     existing devices' ports are NOT retroactively reseeded.
DELETE /api/projects/:pid/device-types/:id          Only project-custom; built-ins → 403.
                                                     ON DELETE SET NULL on devices.type_id so devices
                                                     keep their already-seeded ports.

# v4 — Connection requirements (the solver's input)
GET    /api/projects/:pid/connection-requirements   → [ConnectionRequirement, …]
POST   /api/projects/:pid/connection-requirements   ← {from_device_id, to_device_id,
                                                       preferred_cable_type_id?, must_connect?, notes?}
                                                     Server normalises (from, to) into (pair_lo, pair_hi)
                                                     before insert; duplicate (project, pair_lo, pair_hi,
                                                     preferred_cable_type_id) → 409 conflict.
PATCH  /api/projects/:pid/connection-requirements/:id
DELETE /api/projects/:pid/connection-requirements/:id

# v4 — Solver
POST   /api/projects/:pid/solve                     ← {} (or {?preview=1} to compute without applying)
                                                     → {
                                                       cables_added:    [Cable, …],
                                                       cables_kept:     [int, …],   # ids preserved by the diff
                                                       cables_removed:  [int, …],   # ids deleted (auto cables only)
                                                       bundles_added:   [{Bundle, cable_ids: [int]}, …],
                                                       bundles_removed: [int, …],
                                                       unsatisfied:     [{requirement_id, reason}, …],
                                                       warnings:        [string, …],
                                                     }
                                                     Default applies in a single transaction. ?preview=1
                                                     returns the same shape without writing. User-created
                                                     cables (auto=0 in the cables table; see §5.1) are
                                                     never touched — the solver only adds/removes its own.

# Sync — export only in MVP
POST   /api/projects/:pid/sync/export               → writes the project's drawing to mExDraw
                                                     (overwrites previous version; mExDraw keeps
                                                     git-version-history sidecar)
```

### 3.1 v4 wire-shape additions

- `ConnectionRequirement` (response):
  `{id, project_id, from_device_id, to_device_id, preferred_cable_type_id|null, must_connect: bool, notes, created_at, updated_at}`.
- `DeviceType` (response):
  `{id, project_id|null, name, kind, icon|null, description, built_in: bool, ports: [{cable_type_id, count, label_prefix, edge, sort_order}]}`.
- `cables` gets an `auto: bool` field on the row (slice 5.5 migration adds
  the column with default 0; the solver sets 1 on its own creations). The
  v3 cable rows m hand-drew keep `auto=0`. `POST /api/.../cables`
  continues to default `auto=0`; only the solver writes `auto=1`.

No `POST /api/sync/import` in MVP. Import is post-MVP and only ever serves
a one-shot migration use case (e.g. seeding LOFT from the legacy
Cable-Management drawing if m later changes his mind).

All write endpoints return the updated row. Errors are
`{error: "string", details?: any}`. No auth.

mExDraw HTTP credentials live in `MEXDRAW_BASE_URL` (e.g.
`https://mxdrw.msbls.de`) + `MEXDRAW_TOKEN` (bearer). The exporter calls
`PUT $MEXDRAW_BASE_URL/api/drawings/<drawing_name>.excalidraw` with the
generated scene JSON.

---

## 4. Export — DB → Excalidraw (visual-grammar conformance)

mCables generates a `.excalidraw` scene from a project's rows. The seed
drawing's grammar is the contract.

### 4.1 Element mapping

| DB row | Excalidraw element | Notes |
|---|---|---|
| `projects.drawing_name` | drawing filename in mExDraw | one drawing per project |
| `frames` | `type=frame`, `name=frames.name` | x/y/width/height straight across |
| `devices` | `type=rectangle` + bound `text` with `name` | `strokeColor=color`, `frameId=frames.excalidraw_id` |
| `ports` | `type=ellipse`, ~12×9 | `strokeColor=type.color`, absolute pos = `(device.x + port.x_offset, device.y + port.y_offset)`, no containerId binding (matches seed) |
| `io_markers` | `type=diamond` with bound `text=label` | small (~30×30), `strokeColor` = the Power cable type's colour |
| `cables` | `type=arrow` | `strokeColor=type.color`, `startBinding.elementId` = port/device/io excalidraw_id, same for end |
| `cable_types` legend (global) | one `type=text` row per `cable_types` row, top-left of the project's first frame | `strokeColor=color`, `text=name`. Pulled from the global table, regenerated each export. |
| `bundles` | (rendering open question — see §5) | post-MVP: render as a thick path; v0: ignored on export |

### 4.2 Element IDs are stable across exports

Every mCables row carries `excalidraw_id` (TEXT, generated on first export
via `crypto/rand` → 21-char Excalidraw-style ID). On re-export the same row
reuses the same ID. This means:

- m's `.excalidraw` collaborator-cursors, element-comments, and undo
  history survive a re-export.
- If m manually edits a port colour in Excalidraw (someday, once import
  exists), we can match it back to the right DB row by ID.

### 4.3 What is *not* in the export

- The legend's decorative separator lines (the 5 `type=line` elements in
  the seed) — purely visual, m said they're not load-bearing.
- Big "enclosure" rectangles like the seed's `tAs8zMDI` desk-surface. In
  v0 those are imported as plain devices when m draws them, and exported
  as plain rectangles too. No zone/enclosure concept in the schema.

### 4.4 Wall-outlet IO markers

A cable with `to_io_id != NULL` exports to an arrow whose `endBinding`
points to the IO diamond's element ID. The diamond is rendered with a small
`IO` text label (or `m.label` if customised). No pair link.

---

## 5. Bundle detection — project-scoped

A *bundle* is a set of cables that physically run together. Bundles never
cross projects (a LOFT bundle and an OFFICE bundle are separate).

MVP detection rule, on `GET /api/projects/:pid/bundles/suggestions`:

```
Within project :pid, group cables by (from_endpoint, to_endpoint):
    from_endpoint = (kind, id) where kind ∈ {port, device, io} and id = whichever *_id is set
    to_endpoint   = same shape
Treat the endpoint pair as unordered: {A, B} == {B, A}
A candidate suggestion = any group with ≥ 2 cables.
```

i.e. "two or more cables run between the same two endpoints" → almost
certainly a bundle. Types in the group can be mixed (Power + USB + HDMI
from desk → wall).

Suggestions are reviewed in the UI; clicking *Accept* creates a real
`bundles` row (`auto=0`). m can also create bundles manually by
shift-clicking cables.

Rendering bundles in the SVG view is a slice 6+ concern; in the export
they're ignored in v0 (open question §9).

---

## 5b. v4 — Solver

The solver is the headline addition in v4. m's product-vision sentence
maps onto it directly:

> "I say what devices we have, the app tells me how to bundle cables and
> how the most efficient connection looks like"

The solver reads a project's `devices` (with their `ports`) and
`connection_requirements`, and writes a set of solver-owned `cables`
(rows with `auto=1`) + `bundles`. m's hand-drawn cables (`auto=0`) are
left strictly alone — the solver only adds and removes its own.

### 5b.1 Objective: maximum bundling

Locked in by m. Prefer routes that consolidate cables into shared trunks
even at higher total length. Visually cleaner setups; easier to manage
physically (one cable bundle along the floor, not five strands).

Concretely: when assigning a cable to a path, the solver minimises the
**count of distinct trunks**, breaking ties by total length. v0
approximates a "trunk" with the pair of device endpoints (the v3 rule);
slice 6+ adds path-based trunks via frame-edge corridors.

### 5b.2 Algorithm (v0)

Pure function. No graph search; no LP. Single pass with greedy port
allocation.

```
solve(project) ⇒ {add, remove, bundles, unsatisfied}:
  let auto_cables_before = SELECT * FROM cables WHERE project=p AND auto=1
  let port_free := {port_id -> bool}  initialised TRUE for every port
                  minus ports already used by manual cables (auto=0)

  for each requirement r in order(must_connect DESC, id ASC):
    let ct = r.preferred_cable_type_id
          ?? auto_pick_cable_type(r.from_device, r.to_device)
          ?? fail("ambiguous")
    let pa = first_free_port(r.from_device, ct, port_free)
    let pb = first_free_port(r.to_device,   ct, port_free)
    if !pa or !pb:
      if r.must_connect: unsatisfied.push({r.id, reason})
      else:              skip
      continue
    port_free[pa] = port_free[pb] = false
    add.push(cable{type=ct, from_port=pa, to_port=pb, auto=1})

  // Bundle by endpoint-pair (v3 rule, applied only to auto cables).
  for each (device_a, device_b) pair with ≥ 2 add-cables:
    bundles_add.push({auto=1, cables: those add-cables})

  // Diff against auto_cables_before to compute remove[] (any prior auto
  // cable whose (from, to, type) doesn't appear in add[]).
  remove = auto_cables_before - add
  return {add, remove, bundles_add, unsatisfied}
```

`first_free_port(device, cable_type, free_map)` picks the lowest-id port
on the device whose `type_id` matches and that is still free, returning
NULL if none. The `lowest-id` tiebreak is deterministic so repeated
solves produce the same plan.

`auto_pick_cable_type(from, to)` (used when `preferred_cable_type_id` is
NULL): find the set of cable types `T = ports(from).types ∩
ports(to).types`. If `|T| == 1`, return it. If `|T| > 1`, fail
("ambiguous; specify preferred_cable_type_id"). The UI surfaces this
as a "specify type" inline edit on the requirement.

### 5b.3 Solver-owned vs. user-owned cables

`cables.auto` distinguishes them.

| Operation | Effect on `auto=0` cables | Effect on `auto=1` cables |
|---|---|---|
| POST /api/.../cables (m draws by hand) | inserts auto=0 | n/a |
| PATCH cables (m moves endpoint, relabels) | applies | applies (and the cable is "promoted" to auto=0 — m owns it now) |
| DELETE cables | applies | applies |
| POST /api/.../solve | left alone (their used ports are reserved before the solver runs) | replaced wholesale (remove[] + add[] in one tx) |

This way a manual cable m doesn't want the solver to second-guess
survives every solve. If m wants the solver to take it over, he deletes
his hand-drawn cable and re-solves; the solver re-creates an equivalent
auto cable.

### 5b.4 When solver fails

Three classes of failure surface in the response's `unsatisfied[]`:

1. **No compatible cable type** — `T = ports(from).types ∩
   ports(to).types` is empty (e.g. a Power-only device to an HDMI-only
   device). UX: edit the requirement to specify, or add a port on one of
   the devices.
2. **Ambiguous cable type** — `|T| > 1`, no preferred set. UX: pick a
   type on the requirement.
3. **No free port** — the cable type matches but every port on one side
   is already used. UX: drop a must_connect=0 requirement, or add ports.

The solver does **not** auto-add ports to a device. Reason: m said
"override per instance"; auto-adding crosses that line. The UI surfaces
the unmet requirement with a "+ Add port" affordance on the device
inspector instead.

### 5b.5 Preview vs. apply

`?preview=1` returns the same shape without writing. The UI shows a diff
modal with `add[]`, `remove[]`, `unsatisfied[]`; m clicks Apply to fire
the same endpoint without `preview=1`. Default (no flag) applies
immediately — useful for live-solve mode (open question §9).

---

## 6. Sync — export-only for v0

```
                ┌─────────────────────┐
                │ mCables DB (truth)  │
                └──────────┬──────────┘
                           │
              export       ▼
              (push)   ┌────────────────────────┐
                       │ <project>.excalidraw   │
                       │   on mxdrw.msbls.de    │
                       └────────────────────────┘
```

- mCables UI → DB: synchronous (every drag/add/remove persists immediately).
- DB → Excalidraw: **manual** button "Export to Excalidraw" in the header,
  per project. Calls `POST /api/projects/:pid/sync/export`.
- Excalidraw → DB: **not implemented** in v0. Anything m draws in
  Excalidraw stays in Excalidraw until he redraws it in mCables.

This keeps the v0 scope tight: no conflict resolution, no element-diff
import, no auto-debounce. mExDraw keeps its own version history (git
sidecar in the mdraw deploy) so a bad export is recoverable from there.

When mxdrw is unreachable: the export button shows a tooltip and disables;
the editor keeps working against the local DB.

Post-MVP, import returns as a one-shot migration tool (separate
`mcables-migrate` CLI tool, not part of the running server) for seeding
new projects from existing `.excalidraw` files.

---

## 7. UI flows

The editor lives at `/`. Layout:

```
┌────────────────────────────────────────────────────────────────────┐
│ mCables   [LOFT ▾ projects-picker]            [Export] [+ Project] │  ← header
├────────┬───────────────────────────────────────────────────────────┤
│        │                                                           │
│ Legend │                                                           │
│        │                                                           │
│ Power  │              Diagram surface (SVG)                        │
│ USB    │                                                           │
│ HDMI   │       ┌─desk─────────────┐  ┌─rack──────────┐             │
│ DP     │       │ [Mac] [Screen] … │  │ [NAS] [fritz] │             │
│ RJ45   │       └──────────────────┘  └───────────────┘             │
│ + Type │                                                           │
│        │                                                           │
│ Tools  │                                                           │
│  + Dev │                                                           │
│  + Frm │                                                           │
│  + IO  │                                                           │
│  draw  │                                                           │
│        │                                                           │
├────────┴───────────────────────────────────────────────────────────┤
│ Inspector (selection-dependent: project / frame / device / port /  │
│            cable / bundle details and actions)                     │
└────────────────────────────────────────────────────────────────────┘
```

### Flow: pick a project

Header has a dropdown "LOFT ▾". Clicking it lists all projects from
`GET /api/projects`; clicking one swaps the diagram (`GET /api/projects/:pid`
loads the full snapshot in one round-trip). The picker also shows a
`+ New Project` action → modal with `name`, `drawing_name` (defaults to
`<name>.excalidraw`), `description` → `POST /api/projects` → switches to
the new project (which has 5 seeded cable types and no frames yet).

The currently active project's id is kept in URL state
(`/?project=LOFT`) so reload returns to the same project.

### Flow: add a frame

1. `+ Frm` in the left toolbar (or `F`).
2. Click + drag on the canvas → rubber-band rectangle becomes a frame.
3. Name prompt centered in the frame; Enter → `POST .../frames`.

### Flow: add a device (v4 — type-aware)

1. `+ Dev` (or `D`) → click on canvas → device placeholder appears.
2. **First field in the inline namer: type dropdown** (replaces the
   v1 plain-name input). Options pulled from
   `GET /api/projects/:pid/device-types` — built-ins listed first
   grouped by `kind`, then project-custom rows, then `Custom (no type)`.
   Typing in the dropdown filters by `name` (m types "n" → NAS jumps
   to top). Below the dropdown: a name input pre-filled with the type
   name + a digit if a same-named device already exists ("PC", "PC-2").
3. Hit Enter → `POST .../devices` with `type_id` + name. The server
   seeds the ports from `device_type_ports` in the same transaction
   and returns the device with its `ports`.
4. Picking `Custom (no type)` keeps the v3 behaviour: rectangle, no
   ports, m adds ports manually via the inspector.
5. The device renders with its ports already visible along the
   configured edge.

### Flow: add a port

Select a device → inspector shows `+ Port` button. Click → cursor becomes
a "ghost port" of the active cable type (legend selection). Snap to device
edge → click commits → `POST .../devices/:id/ports`.

### Flow: draw a cable

Click a port → port highlights. Hover any other endpoint (port / device /
IO marker) → preview cable drawn in the source's type colour. Click commits
→ `POST .../cables`. `Shift`-click to bind to a whole device. Click an IO
diamond to terminate at a wall outlet.

### Flow: add an IO marker (wall outlet)

`+ IO` (or `I`) → click on canvas → small diamond placed → optional label
text edit → `POST .../io-markers`. By design, the only cables that
terminate at an IO marker are Power cables, but the schema doesn't enforce
that — the UI shows a soft warning if m draws a non-Power cable to an IO.

### Flow: pick / edit a cable type

Legend on the left is interactive and **global** (the same legend shows up
in every project). Click a row → that type becomes the active "drawing
type" for the current project's session. Drag the swatch → colour picker →
updates `cable_types.color` via `PATCH /api/cable-types/:id`. `+ Type` at
the bottom → "new cable type" modal — `POST /api/cable-types`. Names are
globally unique.

The modal for editing / adding shows a banner:
*"Cable types are shared across all projects. Renaming or recolouring
affects every project that uses this type."* Deleting a type that's still
in use by any cable returns a 400 with the offending cable count — the
client surfaces it as an inline error in the modal.

### Flow: drag a device

Pointer-drag → live `transform` on the SVG; on `pointerup`,
`PATCH .../devices/:id` persists `x, y`. Ports follow because their
offsets are relative.

### Flow: bundles

In the inspector with nothing else selected, "Bundle suggestions" pulls
`.../bundles/suggestions`. Each suggestion shows the cables highlighted
on the diagram + an Accept button. Manual: shift-click multiple cables →
"Group as bundle" → name it → save.

### v4 — Flow: declare connection requirements

The left sidebar gains a **Requirements** section under the legend:

```
Cable types
  Power, USB, HDMI, DP, RJ45, + Type

Requirements                       ← new in v4
  NAS ↔ Switch       RJ45    must
  PC  ↔ TV           HDMI    must
  Mac ↔ Soundbar     HDMI    nice
  + Requirement
```

Click `+ Requirement` → modal with two device pickers (autocomplete from
the project's current devices), a cable-type picker (defaults to
auto-resolve if the device pair has only one matching type), and a
must/nice toggle. `POST .../connection-requirements`.

Alternative gesture (no tool armed, no selection): **drag from device A
to device B** to seed a requirement modal with the pair pre-filled. The
solver-edge preview drags out from the source device's edge in a thin
dashed line until release.

m can also right-click a requirement row → edit / delete.

### v4 — Flow: run the solver

Header gains a **Solve** button next to **Export**.

1. Click Solve (or `S`) → `POST /api/projects/:pid/solve?preview=1`.
2. A diff modal opens listing `add[]`, `remove[]`, `unsatisfied[]` — the
   canvas behind it dims and previews the new cables in a translucent
   stroke + the to-be-removed cables in a strikethrough red.
3. Buttons:
   - **Apply** → fires `POST .../solve` (no `preview`), applies in one
     transaction, closes the modal, re-renders canvas with the real
     cables in place.
   - **Cancel** → leaves everything as it was.
4. Unsatisfied requirements get their own list at the bottom of the
   modal, each with a quick-action button: "Specify type", "+ Add port
   to device X", or "Drop requirement (set must=0)".

If `unsatisfied[]` is non-empty, the Solve button stays in a
soft-error state (yellow) until either every requirement is satisfiable
or m explicitly accepts the partial plan.

### v4 — Inspector states

| Selection | Inspector shows |
|---|---|
| nothing | empty, with "Bundle suggestions" + "Project requirements" headlines |
| project header | name, drawing_name, description (editable), device count, requirement count, Solve / Export buttons |
| frame | name (editable), x/y/w/h, contained-device count, delete |
| **device** | name + type + icon, ports grid (type / label / connected? / +Port), **unmet requirements list** (red badges with quick-fix), delete |
| **port** | type, label, parent device, current cable (if any), delete |
| **cable (auto=1)** | source/target, type, driving requirement (clickable → opens requirement edit), parent bundle (if any), label, "Promote to manual" (sets auto=0) |
| cable (auto=0) | as v3 — type, source/target, label, delete |
| bundle | name, member cables (clickable to focus), trunk segment description, auto-detected flag |

### Keyboard

`P` switch project, `F` add frame, `D` add device, `I` add IO marker,
`T` start cable from selected port, `R` add requirement,
**`S` solve project (v4)**, `E` export, `Esc` cancel, `Backspace` delete
selection, `?` show shortcuts.

---

## 8. First slices — v4 reshape

Slices 1 + 2 have shipped (see git history). v4 inserts new slices ahead
of the original 3-5 because the solver depends on the catalog + the
requirements model, not on manual cable drawing. The old "manual port +
cable draw" slice is still in scope as a tweak path on the solver
output, but it follows the solver instead of leading.

| # | Slice | Status | What's shipped |
|---|---|---|---|
| 1 | **Bootstrap + project CRUD + global cable_types** | ✅ shipped | See git: branch `mai/picasso/slice-1-bootstrap`. |
| 2 | **Frames + devices + drag** | ✅ shipped | See git: branch `mai/picasso/slice-2-frames-devices`. |
| **3 (was 4)** | **IO markers + cable-type editing** | pending | Unchanged scope. `+ IO` places a wall-outlet diamond. Legend swatch is a colour picker; renaming a type updates the legend on the fly. `+ Type` adds new global types. |
| **4 (NEW)** | **Device-type catalog + type-aware device create** | pending | Migration 002: `device_types` + `device_type_ports`, seeded with the 11 built-ins (§2.2). Migration adds `devices.type_id`. API: `GET /api/device-types`, `GET /api/projects/:pid/device-types`. Frontend: the +Dev inline namer becomes a type dropdown + name input; choosing a built-in type seeds the device's ports on the backend. Picking `Custom (no type)` falls back to v3 freeform. m can create a typed NAS + see its Power + RJ45 ports appear on the canvas. |
| **4.5 (NEW)** | **Manage device-type catalog (per project)** | pending | Modal: `POST/PATCH/DELETE /api/projects/:pid/device-types` for project-custom rows. Edit affordance hidden for built-ins. Lets m add an exotic device type without contributing to the built-in catalog. Validation: a custom type can't share a name with a built-in (already enforced by `UNIQUE(project_id, name)` + a separate code-level check against built-ins). |
| **5 (NEW)** | **Connection requirements UI + CRUD** | pending | Migration 003: `connection_requirements`. API: full CRUD under `/api/projects/:pid/connection-requirements`. Frontend: left-sidebar "Requirements" section, `+ Requirement` modal (autocomplete from project's current devices, cable-type picker, must/nice toggle). Drag from device A to device B gestures the same modal pre-filled. Inspector for a selected device lists its requirements. |
| **6 (NEW)** | **Solver MVP + Solve button** | pending | `POST /api/projects/:pid/solve` with `?preview=1` support. v0 algorithm (§5b.2): pure-function, greedy port allocation, endpoint-pair bundling (slice 6.5 is path-based bundling). Migration adds `cables.auto`. Header gains a Solve button that opens the preview-diff modal. m clicks Solve → sees the cable plan → applies. |
| **7 (was 3, slimmed)** | **Manual port + manual cable draw** | pending | The v3 flow as a tweak path on solver output. `+ Port` on an instance-owned device; click-port → click-port creates a hand-drawn cable (`auto=0`). Used to override the solver's choices or to extend its plan. |
| **8 (was 5)** | **Export to mxdrw.msbls.de** | pending | `POST .../sync/export` writes a `.excalidraw` scene per the visual grammar (§4). Bundles ignored on export in v0. |

Slices 9+ (not promised for the first coder shift):
- Path-based bundling: instead of endpoint-pair bundling, group cables that share a frame-edge corridor or a wall-axis (§5b.1 "trunk segment" definition).
- Live-solve mode: re-run solver on every device/requirement edit with a debounce + previewed-but-not-applied diff in a toast.
- Setup templates (Living Room, Home Office, Server Rack): a `setup_templates` table + `POST .../apply-template` that pre-populates `connection_requirements` from an archetype.
- Bundle rendering in the SVG (thick path with mixed-colour fan-out) and in the export.
- "Re-seed from type" action on a device.
- Cable inventory metadata (length/SKU) if m later wants it.
- Dark mode.

---

## 9. Open questions for m — v4

v3 closed all its v2 questions. v4 raises six new ones, all about the
solver semantics and UX. Worth resolving before slice 4 starts so the
coder shift doesn't backtrack:

1. **Where do paths come from?** v0 draws straight lines port-to-port +
   bundles by endpoint-pair. Three candidates for slice 6.5/9:
   (a) auto-route through frame edges (cables exit a device toward the
   nearest frame edge, traverse along edges, enter the target frame);
   (b) m draws **cable-tray polylines** on the canvas and cables snap to
   them; (c) Steiner-tree-ish path optimisation per trunk. I lean (b) +
   (a) as fallback — m gets the manual override when his layout is
   non-obvious, otherwise the system routes for him. Confirm direction.

2. **Live solve or button-only?** Two modes available:
   - **Button-only** (locked default) — m hits Solve, sees the diff,
     applies. Simple; no surprises.
   - **Live** — solver re-runs on every device/requirement edit with a
     debounce, results land in a toast "12 cables, 3 bundles, 1 unmet
     — review?". More responsive, costs ~10ms of compute per edit.
   I'd ship button-only first (slice 6); add live as an opt-in toggle
   (slice 9+). Confirm or escalate to "live always".

3. **No-compatible-port-pair UX when solving.** Three options:
   (a) Surface as "unsatisfiable" and let m manually add a port via the
   device inspector (current §5b.4 stance).
   (b) Auto-add the missing port to the device on the m's confirmation
   (single-button "Add HDMI to PC and re-solve").
   (c) Auto-add silently — bad UX, surprise mutations.
   I lean (a) with a one-click quick-fix that does (b). Confirm.

4. **Setup templates — v4 or post-MVP?** "Living Room" / "Home Office" /
   "Server Rack" archetypes that pre-populate `connection_requirements`.
   I left this out of the v4 slice list (designed in §8 "slices 9+") to
   keep v4 tight. m can build the same effect by adding requirements
   manually first time. Confirm: post-MVP OK, or do you want me to fold
   it into slice 5/6?

5. **Catalog distribution: code seed vs. JSON file.** Two paths:
   (a) seed in migration 002 via SQL INSERTs (today's design — locked-in,
   schema versioned, no user override of built-ins).
   (b) seed from a curated JSON file at `internal/db/catalog/builtin.json`
   that the migration reads. m or contributors can extend the file by
   PR; rebuild image; new built-ins appear.
   I lean (a) for v0 (simpler, doesn't need a file-loader). Open
   question: do you anticipate growing the built-in list often? If yes,
   (b) starts paying off after the second addition.

6. **Promoting a solver cable to manual.** §5b.3 says PATCHing an
   `auto=1` cable flips it to `auto=0` so the next solve doesn't replace
   it. Two surface variants:
   (a) Implicit: any PATCH that touches type/from/to on an auto cable
   promotes it. m never sees the flag.
   (b) Explicit: a "Promote to manual" button on the cable inspector
   (current §7 stance). PATCHes that only update labels stay auto.
   I leaned (b) for clarity ("the solver might overwrite this — promote
   to protect"). Confirm or override.

---

## 10. Deployment on mDock (raw docker)

Inspected mDock's live services on 2026-05-15 to lock the conventions
before writing this:

- All m-built services on mDock live under `/home/m/stacks/<project>/`
  with a single `docker-compose.yml`. Older services in `/home/m/<project>/`
  use the same pattern; the canonical-new path is `stacks/`.
- Compose v2 (`docker compose`), images built from Gitea container registry
  (`mgit.msbls.de/m/<project>:latest`), `restart: unless-stopped` on every
  service, `container_name: <project>` explicit.
- Host port mappings: deliberately collision-free across the host. Existing
  high ports in use include 3300 (mgreen), 3077 (paperless-ai), 7878
  (radarr), 8082 (mgeo-tileserver), 8989 (sonarr), 9696 (prowlarr).
  **Port 7777 is free** — taking it for mCables.
- Bind-mount volumes: `/home/m/<project>-data:/app/data` is the canonical
  pattern (mgreen). For project-local data we put `data/` *next to* the
  compose file so a `git pull && docker compose up -d` is the whole deploy:
  `/home/m/stacks/mcables/data:/app/data`.
- Secrets via `env_file: /home/m/secrets/<project>/.env` (msports-garmin
  pattern). mCables only needs `MEXDRAW_TOKEN` for export.
- No reverse proxy on mDock. Services expose ports directly on the LAN
  (mDock = `192.168.178.131` / Tailscale `mdock`). Public exposure goes via
  mlake/Dokploy + Caddy when needed — out of scope for mCables (LAN-only).
- Auto-deploy via the Gitea Actions self-hosted runner already installed
  on mDock (`/home/m/act-runner/`, label `self-hosted:host`). Push to
  `main` → workflow on mDock → `docker compose up --build -d`.

### Repo layout for mCables

```
mCables/
├── cmd/mcables/main.go        # Go binary
├── internal/
│   ├── db/                    # migrations + store
│   ├── importer/              # post-MVP only (not in MVP)
│   ├── exporter/              # DB → .excalidraw
│   └── server/                # net/http handlers
├── web/                       # embedded static frontend
│   ├── index.html
│   ├── main.js                # ES module entry
│   ├── style.css
│   └── lib/...                # SVG helpers, store, components
├── data/                      # mCables runtime DB lives here (gitignored)
│   └── .gitkeep
├── docs/design.md             # this file
├── Dockerfile
├── docker-compose.yml
├── .gitea/workflows/deploy.yml
├── .gitignore                 # data/, *.db, *.db-wal, *.db-shm
├── Makefile                   # build, typecheck, test, run
├── go.mod / go.sum
└── README.md
```

### Dockerfile sketch

Multi-stage; the final image is `scratch` because `modernc.org/sqlite` is
pure Go.

```dockerfile
# syntax=docker/dockerfile:1.7
FROM golang:1.23-alpine AS build
WORKDIR /src
COPY go.mod go.sum ./
RUN go mod download
COPY . .
RUN CGO_ENABLED=0 GOOS=linux go build -trimpath -ldflags="-s -w" \
        -o /out/mcables ./cmd/mcables

FROM gcr.io/distroless/static-debian12:nonroot
WORKDIR /app
COPY --from=build /out/mcables /app/mcables
ENV MCABLES_ADDR=0.0.0.0:7777
ENV MCABLES_DB=/app/data/mcables.db
USER nonroot:nonroot
EXPOSE 7777
ENTRYPOINT ["/app/mcables"]
```

### docker-compose.yml (on mDock at `/home/m/stacks/mcables/`)

```yaml
services:
  mcables:
    image: mgit.msbls.de/m/mcables:latest
    container_name: mcables
    restart: unless-stopped
    ports:
      - "7777:7777"
    environment:
      - TZ=Europe/Berlin
      - MCABLES_ADDR=0.0.0.0:7777
      - MCABLES_DB=/app/data/mcables.db
      - MEXDRAW_BASE_URL=https://mxdrw.msbls.de
    env_file:
      - /home/m/secrets/mcables/.env       # contains MEXDRAW_TOKEN
    volumes:
      - /home/m/stacks/mcables/data:/app/data
```

LAN URL: `http://mdock:7777` (or `http://192.168.178.131:7777`).

### Gitea Actions deploy workflow

`.gitea/workflows/deploy.yml`:

```yaml
name: deploy
on:
  push:
    branches: [main]

jobs:
  deploy:
    runs-on: self-hosted
    steps:
      - uses: actions/checkout@v4
      - name: Build image
        run: docker build -t mgit.msbls.de/m/mcables:latest .
      - name: Push image
        run: |
          echo "${{ secrets.GITEA_TOKEN }}" | \
            docker login mgit.msbls.de -u mAi --password-stdin
          docker push mgit.msbls.de/m/mcables:latest
      - name: Up
        run: |
          cd /home/m/stacks/mcables
          docker compose pull
          docker compose up -d
```

### Local-development run (no Docker)

```
make run          # go run ./cmd/mcables → :7777 against ./data/mcables.db
make typecheck    # tsc --noEmit on web/
make test         # go test ./...
```

The repo has `data/` checked-in-empty (with `.gitkeep`); `data/*.db*` is
gitignored.

---

DESIGN v4 READY FOR REVIEW