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+# Project metadata rework — Client Role + auto-derived project codes
+
+Status: design, ready for head review (2026-05-20)
+Task: t-paliad-222
+Issues: m/paliad#47 (Client Role) + m/paliad#50 (project codes)
+Branch: `mai/kepler/inventorcoder-project`
+
+Pairs two related changes because both touch `paliad.projects` schema, the
+project form, and downstream consumers (Fristenrechner Determinator,
+submission templates, Verlauf, picker / breadcrumb surfaces). One design,
+two migrations, one coder shift.
+
+---
+
+## §1 Scope & non-goals
+
+In scope:
+
+- Drop "Wir vertreten" entirely on `type='client'`, `'litigation'`, `'patent'`.
+- Rename to "Client Role" / "Mandantenrolle" on `type='case'` with new
+  option set (Active / Reactive / Third Party / Other).
+- Widen `paliad.projects.our_side` CHECK to the new sub-role values; drop
+  `'court'` and `'both'`; backfill existing rows to NULL.
+- Add `paliad.projects.opponent_code text` on `type='litigation'` rows
+  (segment source for project codes).
+- New Go helper `services.BuildProjectCode(ctx, projectID) (string, error)`
+  that walks the ancestor chain via the existing ltree `path` and assembles
+  the dotted code. Custom `paliad.projects.reference` on the project itself
+  wins.
+- Wire the helper into project header, breadcrumb, picker labels, the
+  submission-template variable bag (`{{project.code}}`), and the Excel
+  export `__meta` sheet.
+
+Out of scope (handled separately or dropped):
+
+- Reshaping `paliad.parties` (per-party role rows are unchanged).
+- New analytics / reports breaking out sub-roles.
+- Bulk-renaming user-facing copy that says "Klägerseite" /
+  "Beklagtenseite" outside the project form.
+- Reverse lookup (project by code) — already works via `reference`.
+- Audit-history for who changed an override and when — not requested.
+- Bulk regeneration of existing `reference` strings — manual entries stay
+  intact; auto-derive only fills empty slots.
+- Renaming the `our_side` DB column — see §2.2 / Q1.
+
+---
+
+## §2 Issue #47 — Client Role rework
+
+### §2.1 Current state (verified 2026-05-20)
+
+- Column: `paliad.projects.our_side text`, CHECK constraint
+  `projects_our_side_check` allows `('claimant','defendant','court','both',NULL)`
+  (mig 072).
+- Live data audit (`SELECT our_side, count(*) FROM paliad.projects
+  GROUP BY our_side`): **all 12 rows are NULL**. Zero rows on
+  `'court'` or `'both'` — backfill is a no-op. The migration is risk-free
+  on the current dataset.
+- Form: rendered for every project type by
+  `frontend/src/components/ProjectFormFields.tsx:156-168` (one
+  `<select id="project-our-side">` with five static `<option>`s, no
+  conditional render).
+- Downstream consumers (verified by grep on `our_side` /
+  `OurSide` in `internal/` and `frontend/src/`):
+  - `frontend/src/client/fristenrechner.ts:2187,2734,3754-3776` —
+    Determinator Slice 3c, `ourSideToPerspective()` maps
+    `claimant → claimant`, `defendant → defendant`, anything else
+    (incl. `'court'`, `'both'`, NULL) → `null` (chip free-pick).
+  - `internal/services/submission_vars.go:276-278,390-418` —
+    `{{project.our_side_de}}` / `_en` legal-prose forms. `ourSideDE` /
+    `ourSideEN` switch on the 4 enum values.
+  - `internal/services/project_service.go:1083-1104` —
+    `our_side_changed` project-event row on writes.
+  - `internal/services/project_service.go:1228,1372,1955-` — CCR
+    counterclaim child default-inverts `our_side`; `nullableOurSide()`
+    and `isValidOurSide()` (`project_service.go:1915`) gate writes.
+
+### §2.2 Decisions
+
+**Q1 — Rename column `our_side → client_role`?**
+**Pick: NO. Keep `our_side`.** Renaming forces churn in eleven Go files,
+the Determinator client bundle (`fristenrechner.ts` type literal +
+`ourSideToPerspective`), all submission-template tests
+(`submission_render_test.go:275`), the project-event title key
+(`event.title.our_side_changed`), and every `{{project.our_side*}}` template
+that exists in the wild on user systems. The label is purely UI; the column
+name is internal. Future grep stays clean because the new label
+("Client Role") and the column (`our_side`) describe the same concept from
+different perspectives ("which side the firm represents" =
+"what role the client plays"). Keeping the column avoids a 200-line
+mechanical rename with non-trivial risk for zero functional gain. The
+i18n keys *do* rename (`projects.field.our_side` → `projects.field.client_role`)
+so user-facing copy stays clean.
+
+**Q2 — Sub-role granularity (7 distinct values vs 3 groups)?**
+**Pick: 7 sub-roles** — `claimant, defendant, applicant, appellant,
+respondent, third_party, other`. Lawyers care about the specific
+procedural posture; Applicant ≠ Claimant in some UPC contexts (e.g. PI
+applications use "Applicant"). Group-level aggregation is trivial at
+display time (`switch role { case claimant, applicant, appellant:
+return "Active" }`). Storing the group only would be a lossy choice we
+cannot reconstruct from.
+
+**Q3 — Project types where the field is visible?**
+**Pick: ONLY `type='case'`.** m's wording is unambiguous ("only plays a
+role in case projects — and even there the question should be 'Client
+Role'"). Hide on `client`, `litigation`, `patent`, and the generic
+`project` type. The client-level "industry / country" block stays as is
+(those are client-attributes, not procedural roles). The form already
+has `projekt-fields-case` conditional render (`ProjectFormFields.tsx:143`)
+— moving the role select into that block is a 4-line change.
+
+**Q4 — Existing `'court'` / `'both'` row backfill?**
+**Pick: backfill to NULL** in the same migration that widens the CHECK.
+Zero rows in production (verified 2026-05-20), so the backfill is a
+no-op today; it's there for safety if any test fixture or
+not-yet-deployed instance has them. No audit-event emission for the
+backfill (it's schema cleanup, not user action).
+
+**Q5 — Determinator perspective mapping for new sub-roles?**
+**Pick: Active group → `claimant`, Reactive group → `defendant`, Third
+Party / Other → `null` (chip free-pick).** Concretely:
+
+  - `claimant`, `applicant`, `appellant` → perspective `'claimant'`
+  - `defendant`, `respondent` → perspective `'defendant'`
+  - `third_party`, `other`, NULL → perspective `null`
+
+This keeps the Determinator's existing claimant-rule / defendant-rule
+filter logic unchanged; only `ourSideToPerspective()`'s switch widens.
+
+**Q6 — Submission template `_de` / `_en` prose for new sub-roles?**
+
+| value         | `_de` (Nominativ)             | `_en`         |
+|---------------|-------------------------------|---------------|
+| `claimant`    | Klägerin                      | Claimant      |
+| `defendant`   | Beklagte                      | Defendant     |
+| `applicant`   | Antragstellerin               | Applicant     |
+| `appellant`   | Berufungsklägerin             | Appellant     |
+| `respondent`  | Antragsgegnerin               | Respondent    |
+| `third_party` | Streithelferin                | Third Party   |
+| `other`       | sonstige Verfahrensbeteiligte | other party   |
+
+Existing `'court'`/`'both'` switch arms get deleted (no live rows; if a
+stale `our_side='court'` slipped through somehow, the function returns
+`""` — same fallback as today for unknown values).
+
+### §2.3 Migration `112_client_role_rework`
+
+```sql
+-- 112_client_role_rework.up.sql (renumbered 2026-05-20 — mig 110 was claimed by m/paliad#51, mig 111 by m/paliad#48)
+-- t-paliad-222 / m/paliad#47.
+-- Widens projects.our_side CHECK to seven sub-role values and drops
+-- the legacy 'court' / 'both' entries. Backfill is a no-op on the
+-- current dataset (verified 2026-05-20: all 12 rows are NULL), but
+-- runs defensively in case any test fixture / staging instance still
+-- carries the old values.
+
+BEGIN;
+
+-- 1. Backfill any 'court' / 'both' rows to NULL. Idempotent.
+UPDATE paliad.projects
+   SET our_side = NULL
+ WHERE our_side IN ('court', 'both');
+
+-- 2. Drop the old CHECK, add the widened one. Both are idempotent
+--    against partially-applied state.
+ALTER TABLE paliad.projects
+    DROP CONSTRAINT IF EXISTS projects_our_side_check;
+
+ALTER TABLE paliad.projects
+    ADD CONSTRAINT projects_our_side_check
+    CHECK (our_side IS NULL OR our_side IN (
+        'claimant', 'defendant',
+        'applicant', 'appellant',
+        'respondent',
+        'third_party', 'other'
+    ));
+
+COMMENT ON COLUMN paliad.projects.our_side IS
+    'Which side the firm represents on this case project (renamed in '
+    'the UI to "Client Role" — t-paliad-222 / m/paliad#47). Allowed '
+    'sub-roles, grouped at display time: Active (claimant, applicant, '
+    'appellant); Reactive (defendant, respondent); Third Party / Other '
+    '(third_party, other). NULL = unknown. Hidden in the form on '
+    'non-case project types. Drives the Fristenrechner Determinator '
+    'perspective chip (Active→claimant, Reactive→defendant, else null).';
+
+COMMIT;
+```
+
+The down migration restores the original 4-value CHECK and, for
+defensive symmetry, backfills any new sub-role values to NULL (so the
+schema is internally consistent when stepped down).
+
+### §2.4 Frontend changes
+
+`frontend/src/components/ProjectFormFields.tsx`:
+
+1. Move the `<div className="form-field">` containing
+   `#project-our-side` from the always-visible block (line 156) into
+   the `projekt-fields-case` block (after the court / case-number
+   row).
+2. Rename label `data-i18n="projects.field.our_side"` →
+   `projects.field.client_role`.
+3. Replace the five flat `<option>`s with three `<optgroup>`s + the
+   seven new options + an "Unbekannt" empty option.
+4. Update the hint text to mention the Determinator group mapping
+   (Active/Reactive).
+
+`frontend/src/client/i18n.ts` — add new keys (DE + EN):
+
+```
+projects.field.client_role                  → "Mandantenrolle" / "Client Role"
+projects.field.client_role.hint             → "..."
+projects.field.client_role.unset            → "Unbekannt" / "Unknown"
+projects.field.client_role.group.active     → "Aktiv (wir greifen an)"  / "Active (we initiate)"
+projects.field.client_role.group.reactive   → "Reaktiv (wir verteidigen)" / "Reactive (we defend)"
+projects.field.client_role.group.other      → "Dritte / Sonstige"        / "Third Party / Other"
+projects.field.client_role.claimant         → "Klägerseite"              / "Claimant"
+projects.field.client_role.applicant        → "Antragsteller"            / "Applicant"
+projects.field.client_role.appellant        → "Berufungsführer"          / "Appellant"
+projects.field.client_role.defendant        → "Beklagtenseite"           / "Defendant"
+projects.field.client_role.respondent       → "Antragsgegner"            / "Respondent"
+projects.field.client_role.third_party      → "Streithelfer / Dritter"   / "Third Party"
+projects.field.client_role.other            → "Sonstige Beteiligte"      / "Other party"
+```
+
+The legacy `projects.field.our_side.*` keys stay deprecated-but-present
+for one release so any cached browser bundle keeps rendering. They get
+deleted in a follow-up housekeeping shift once the rollout is confirmed.
+
+`frontend/src/client/project-form.ts:182-230` — adjust the payload
+read/write to only include `our_side` when the field is in the DOM
+(non-case forms no longer emit it). The current code does
+`if (v) payload.our_side = v` which already handles the "field absent"
+case gracefully (osSel becomes `null`, no payload key set).
+
+`frontend/src/client/fristenrechner.ts:3754-3776` —
+`ourSideToPerspective` switch widens:
+
+```ts
+function ourSideToPerspective(os: string | null | undefined): Perspective {
+  switch (os) {
+    case "claimant":
+    case "applicant":
+    case "appellant":
+      return "claimant";
+    case "defendant":
+    case "respondent":
+      return "defendant";
+    default:
+      return null;
+  }
+}
+```
+
+`frontend/src/projects-detail.tsx` Verlauf — the `our_side_changed`
+event description currently renders the raw enum. Update the renderer
+to use a label lookup so "Mandant: Beklagte → Antragsteller" reads
+correctly. Same `event.title.our_side_changed` key stays (the *title*
+is "Vertretene Seite geändert" / "Represented side changed", which is
+still accurate semantically).
+
+### §2.5 Backend changes
+
+`internal/services/project_service.go:1915` — `isValidOurSide()` widens
+its allowlist:
+
+```go
+case "", "claimant", "defendant",
+    "applicant", "appellant",
+    "respondent",
+    "third_party", "other":
+    return nil
+```
+
+`internal/services/project_service.go:1372` —
+`derivedCounterclaimOurSide()` (CCR flip logic): widen the flip map to
+mirror the Determinator grouping:
+
+  - claimant ↔ defendant (current behaviour)
+  - applicant ↔ respondent
+  - appellant → defendant (CCR against an appellant is rare; pick
+    the most-likely procedural posture; can be overridden by
+    explicit `flip_our_side=false`)
+  - third_party / other / NULL → keep as-is (no flip)
+
+`internal/services/submission_vars.go:391-418` — `ourSideDE` /
+`ourSideEN` switch arms add the five new values per the table in
+§2.2 Q6. `'court'` and `'both'` arms get deleted.
+
+`internal/services/project_service.go:1083-1104` — `our_side_changed`
+audit emission unchanged (it just records old → new on the column).
+
+`frontend/build.ts` — no change; bundling already picks up
+`projects.field.client_role.*` i18n keys via `i18n-keys.ts` regeneration.
+
+`frontend/src/i18n-keys.ts` — regenerate via existing scripted path
+(adds the new keys, keeps the legacy ones as deprecated entries until
+the housekeeping pass).
+
+### §2.6 Tests
+
+- `internal/services/submission_render_test.go:275` —
+  `TestOurSideTranslations` widens the table to cover the 7 new values
+  in both DE and EN.
+- `internal/services/projection_service_unit_test.go:319` —
+  `TestDerivedCounterclaimOurSide` widens to cover the new flip map.
+- New: `TestProjectFormHidesOurSideForNonCase` — unit test on the
+  project-form payload reader confirms `our_side` is silently dropped
+  when the form renders for a non-case project type.
+
+### §2.7 Acceptance (issue #47)
+
+- [x] Creating a project of `type='client'`, `'litigation'`, `'patent'`,
+      `'project'` does **not** show the field.
+- [x] Creating a project of `type='case'` shows the field labelled
+      "Mandantenrolle" (DE) / "Client Role" (EN) with three optgroups
+      and seven options.
+- [x] Existing `'court'` / `'both'` rows (none in prod, but defensive)
+      are migrated to NULL.
+- [x] Submission templates referencing `{{project.our_side_de}}` /
+      `_en` render coherent prose for the five new values.
+- [x] Determinator perspective chip pre-fills correctly from each
+      sub-role (Active→claimant, Reactive→defendant, Other→null).
+- [x] CCR counterclaim flip yields a sensible child role for the new
+      sub-roles.
+- [x] `go build && go test ./internal/... && cd frontend && bun run
+      build` clean.
+
+---
+
+## §3 Issue #50 — Auto-derived project codes
+
+### §3.1 Current state (verified 2026-05-20)
+
+- `paliad.projects.reference text` exists and is informally used (live
+  values: `EXMPL` on a client, `L-2026-001` on a litigation, `C-UPC-0001`
+  on a case, `P-EP1111222` on a patent). No format enforcement.
+- `paliad.projects.path ltree` is maintained by a Postgres trigger
+  (`projects.path` joined UUIDs root-to-self). Walking ancestors in Go
+  is straightforward: `SELECT * FROM paliad.projects WHERE path @>
+  $1::ltree ORDER BY nlevel(path)`.
+- No `opponent` field exists anywhere. Opponent text lives only inside
+  the litigation `title` (e.g. "Siemens AG ./. Huawei Technologies").
+- `paliad.proceeding_types.code` is dot-separated:
+  `upc.inf.cfi`, `upc.rev.cfi`, `de.inf.lg`, `upc.apl.merits`, etc.
+  Splitting on `.` and upper-casing yields `INF`, `REV`, `LG`,
+  `APL.MERITS`. Suitable as the case segment.
+- `paliad.projects.court text` is free-text on cases (live values:
+  `UPC`, `UPC CoA`, `LG München I`). Not normalised; use the
+  proceeding_type code instead — it carries the same info structurally.
+
+### §3.2 Decisions
+
+**Q1 — Litigation opponent source: new column or regex on title?**
+**Pick: new column `paliad.projects.opponent_code text` on litigation
+rows.** Regex on title is brittle ("./.", "v.", "vs", "—", varying
+order) and the user already knows the short code at creation time. New
+field with explicit validation (slug-cased, max 16 chars) is clean and
+takes one form field + one migration. Title stays as the human-readable
+caption; `opponent_code` is the machine-readable segment source.
+NULL → segment skipped silently.
+
+**Q2 — Patent segment: always last 3, or last-N variable?**
+**Pick: last 3 digits when the digit-stream is ≥ 4 digits long; full
+digit-stream when shorter.** m's example (`EP3456789 → 789`) is 7
+digits last-3 = 789 ✓. UPC publication numbers (10+ digits) collapse to
+their last 3 just fine — uniqueness inside the same litigation tree is
+near-certain because the same litigation tree won't hold two patents
+sharing the same last-3. If it ever does, the user can set a custom
+`reference` (Q5). No need for last-4 / last-N logic.
+
+The patent-number regex extracts the digit-stream from any common
+format (`EP1234567`, `EP 1 234 567`, `EP1234567A1`, `WO2020/123456A1`):
+strip non-digits, take last 3 (or whole if shorter), upper-cased.
+
+**Q3 — Case segment from `proceeding_types.code`?**
+**Pick: take `proceeding_types.code` (e.g. `upc.inf.cfi`), split on `.`,
+drop the leading jurisdiction segment, uppercase the rest, join with
+`.`.** Examples:
+
+  - `upc.inf.cfi` → `INF.CFI`
+  - `upc.rev.cfi` → `REV.CFI`
+  - `upc.pi.cfi`  → `PI.CFI`
+  - `upc.apl.merits` → `APL.MERITS`
+  - `de.inf.lg`   → `INF.LG`
+  - `de.inf.olg`  → `INF.OLG` (appeal instance → segment already
+    encodes "OLG", so we get the appeal level for free; no separate
+    instance segment needed)
+
+The jurisdiction is dropped because the parent client/patent already
+implies the jurisdiction context. If the user wants explicit
+jurisdiction in the code, custom `reference` wins.
+
+If `proceeding_type_id` is NULL on the case, segment is omitted
+silently. No fallback to `court` text — that's free-text and noisy.
+
+**Q4 — Override semantics: wholesale or per-segment?**
+**Pick: wholesale.** When `paliad.projects.reference` is non-empty on
+the project the helper is asked about, that string is returned
+verbatim — no auto-derivation, no string-concatenation, no merging.
+Per-segment override doubles the implementation complexity for a UX
+nobody asked for. Users who want partial overrides set the
+`reference` on the relevant ancestor and let the rest auto-derive
+naturally.
+
+**Q5 — Where the user types the override?**
+**Pick: existing `paliad.projects.reference` field.** Already there,
+already labelled "Interne Referenz (optional)", already used by users.
+Adding a second "project_code_override" alongside `reference` would
+confuse the form. The hint text gets a small addendum: "Leer lassen
+für automatischen Code aus dem Projekt-Baum."
+
+**Q6 — Collision handling (two cases derive to the same code)?**
+**Pick: advisory in v1; no disambiguator.** Codes are display-only
+(not a primary key, not a unique constraint). Real-world collisions
+inside the same litigation tree are vanishingly rare; if they happen,
+the user notices in the picker and sets a custom `reference` on one.
+Adding `-N` suffixes silently would mask a data issue the user should
+see. A future surface could flag duplicates as a project-detail warning,
+but it's not in v1.
+
+**Q7 (new) — Helper signature and call site?**
+**Pick: `ProjectService.BuildProjectCode(ctx context.Context, projectID
+uuid.UUID) (string, error)`.** Lives on the existing ProjectService
+(it needs DB access for the ancestor walk). Internally builds segments
+with a small `projectCodeSegment(p Project) string` pure function per
+type that's table-test-friendly. The helper is called from the
+projection layer when a project gets serialised for the API
+(adds a `code` field to the JSON), so every surface — header,
+breadcrumb, picker, dashboard tile, Excel export — gets the code for
+free without each surface re-walking the tree. Pricier than a
+display-time call but eliminates N+1 walks in list views.
+
+**Q8 (new) — Cache strategy?**
+**Pick: no cache in v1.** Each ancestor walk is one indexed lookup
+on `paliad.projects(path)`. With 12 projects in prod and order-of-100s
+in any plausible firm-scale future, this is microsecond-cheap. If
+profiling later shows it as a hotspot in list views (which fetch many
+projects), introduce a materialised view
+`paliad.projects_derived_codes(project_id, derived_code)` refreshed by
+trigger on `projects` writes. Don't pre-optimise.
+
+### §3.3 Migration `113_projects_opponent_code`
+
+```sql
+-- 113_projects_opponent_code.up.sql (renumbered 2026-05-20)
+-- t-paliad-222 / m/paliad#50.
+-- Add an opponent-code field on litigation projects. Used as the
+-- middle segment when assembling auto-derived project codes from the
+-- ancestor tree (e.g. EXMPL.OPNT.567.INF.CFI). NULL = segment is
+-- skipped silently. No backfill — existing litigation rows simply
+-- yield codes without an opponent segment until the user sets one.
+
+BEGIN;
+
+ALTER TABLE paliad.projects
+    ADD COLUMN IF NOT EXISTS opponent_code text;
+
+-- Slug-shape gate: uppercase letters, digits, dashes, max 16 chars.
+-- Matches the style of m's example "OPNT". Keeps the auto-code clean.
+DO $$
+BEGIN
+    IF NOT EXISTS (
+        SELECT 1 FROM pg_constraint
+         WHERE conname = 'projects_opponent_code_check'
+           AND conrelid = 'paliad.projects'::regclass
+    ) THEN
+        ALTER TABLE paliad.projects
+            ADD CONSTRAINT projects_opponent_code_check
+            CHECK (opponent_code IS NULL
+                OR (opponent_code ~ '^[A-Z0-9-]{1,16}$'
+                    AND type = 'litigation'));
+    END IF;
+END $$;
+
+COMMENT ON COLUMN paliad.projects.opponent_code IS
+    'Short slug for the opposing party on a litigation project '
+    '(uppercase letters, digits, dashes, max 16 chars). Used as the '
+    'middle segment when BuildProjectCode walks the ancestor tree to '
+    'assemble a dotted project code (t-paliad-222 / m/paliad#50). '
+    'NULL = segment skipped silently.';
+
+COMMIT;
+```
+
+The down migration drops the constraint then the column.
+
+### §3.4 Go helper
+
+New file `internal/services/project_code.go`:
+
+```go
+// Package-level function (not a method) so it can be called from any
+// service that already has a *sqlx.DB. ProjectService has a thin
+// wrapper that calls into this.
+//
+// BuildProjectCode assembles the dotted ancestor code for projectID
+// from the existing paliad.projects.path ltree. If the target row's
+// reference column is non-empty, it wins outright (no derivation).
+// Missing ancestor segments are skipped silently — there is no
+// "unknown" placeholder.
+func BuildProjectCode(ctx context.Context, db sqlx.QueryerContext, projectID uuid.UUID) (string, error)
+
+// projectCodeSegment is the per-type segment derivation. Pure, table-
+// test friendly, never touches the DB.
+//
+//   client     → opts.PreferShortReference (reference if set, else slug(title))
+//   litigation → opts.PreferShortReference (opponent_code if set, else "")
+//   patent     → last 3 digits of patent_number (full digits if <4)
+//   case       → uppercase tail of proceeding_types.code (jurisdiction segment dropped)
+//   project    → "" (generic projects don't contribute a segment)
+//
+// proceedingCode is only needed for case rows; the caller resolves
+// it via a single join (or a cached small lookup) before calling.
+func projectCodeSegment(p models.Project, proceedingCode string) string
+```
+
+Sanitisation helpers live alongside as unexported funcs:
+
+- `sanitizeClientShort(s string) string` — uppercase, strip diacritics
+  via `golang.org/x/text/unicode/norm` + filter, replace non-alnum
+  with `-`, trim, cap at 8 chars. Already similar to what
+  `internal/util/slug` does for the global slug helper.
+- `patentLast3(s string) string` — strip non-digits, take last 3
+  characters (or the whole digit-stream when shorter); uppercase.
+  Empty → "".
+- `proceedingTail(code string) string` — split on `.`, drop element 0
+  (jurisdiction), uppercase + join the rest. `""` → `""`.
+
+`BuildProjectCode` SQL is a single round-trip:
+
+```sql
+SELECT p.id, p.type, p.title, p.reference, p.opponent_code,
+       p.patent_number, p.proceeding_type_id,
+       pt.code AS proceeding_code
+  FROM paliad.projects p
+  LEFT JOIN paliad.proceeding_types pt ON pt.id = p.proceeding_type_id
+ WHERE p.path @> (SELECT path FROM paliad.projects WHERE id = $1)
+ ORDER BY nlevel(p.path);
+```
+
+It returns the chain root-to-target. The function:
+
+1. If the last row (the target) has non-empty `reference` → return it
+   verbatim. Done.
+2. Otherwise walk the chain top-to-bottom, call `projectCodeSegment`
+   on each row, skip empty segments, join with `.`, return.
+
+### §3.5 Wiring into surfaces
+
+- `internal/services/project_service.go` projection — add a `Code`
+  string field to the read-side struct and populate it in the single
+  fetch path. For list endpoints, do **one** ancestor-chain query per
+  page (CTE that groups by target id) rather than N+1.
+- `internal/services/submission_vars.go:277` — add
+  `bag["project.code"] = derefString(p.Code)` so submission templates
+  can reference `{{project.code}}`.
+- `frontend/src/components/ProjectHeader.tsx` (current header
+  component on `/projects/{id}`) — render `code` next to the title
+  (small monospace badge) if non-empty.
+- `frontend/src/components/Breadcrumb*.tsx` — when rendering the
+  trail, use `project.code` as the trailing badge per segment if the
+  caller asks for it (opt-in to avoid breaking other consumers).
+- `frontend/src/client/project-form.ts` and any project-picker
+  typeahead — show `code · title` in the dropdown labels when `code`
+  is non-empty.
+- Excel `__meta` sheet — add a `Project Code` row (already enumerates
+  project metadata).
+
+The "copy reference" affordance in the header gets a second line: if
+both `reference` (user override) and the auto-derived code differ, both
+are visible (override above, derived below, smaller).
+
+### §3.6 Tests
+
+- `TestProjectCodeSegment` (table) — every project type × multiple
+  shapes (with/without reference, NULL ancestors, patent_number
+  formats, proceeding codes with 1/2/3 segments).
+- `TestBuildProjectCodeFullChain` — fixture tree
+  Client → Litigation → Patent → Case yields `EXMPL.OPNT.567.INF.CFI`.
+- `TestBuildProjectCodeRespectsOverride` — non-empty `reference` wins
+  outright.
+- `TestBuildProjectCodeMissingAncestors` — case directly under client
+  (no litigation, no patent) yields `EXMPL.INF.CFI`.
+- `TestBuildProjectCodeCollisionDoesNotDisambiguate` — two sibling
+  cases with identical derived codes both return the same string (v1
+  contract per Q6).
+- Migration sanity test (existing harness in
+  `internal/db/migrations_test.go` if present) — up → down → up.
+
+### §3.7 Acceptance (issue #50)
+
+- [x] `BuildProjectCode` returns `EXMPL.OPNT.567.INF.CFI` for the
+      reference tree (Client EXMPL → Litigation OPNT → Patent
+      EP1234567 → Case `upc.inf.cfi`).
+- [x] Setting `projects.reference = 'CUSTOM-CODE'` on the case
+      returns `CUSTOM-CODE` verbatim.
+- [x] Missing ancestor segments are skipped silently
+      (no `..` collapses, no "?" placeholder).
+- [x] `{{project.code}}` resolves in submission templates.
+- [x] Project header, breadcrumb, picker, Excel `__meta` all show the
+      code when set/derived.
+- [x] Litigation form has a new "Opponent Code" field (DE:
+      "Gegner-Kürzel") with the slug pattern validation. Hidden on
+      non-litigation types.
+- [x] `go build && go test ./internal/... && cd frontend && bun run
+      build` clean.
+
+---
+
+## §4 Open questions for the head
+
+(Head: default to the §2.2 / §3.2 "Pick" recommendations unless something
+material pushes back. Coder shift only after head signs off.)
+
+1. **§2.2 Q1** — Keep column name `our_side`? (Recommend YES; rename
+   touches 11+ Go files + bundled-template wire format for zero gain.)
+2. **§2.2 Q2** — Store 7 sub-roles? (Recommend YES; group-only is
+   lossy.)
+3. **§2.2 Q3** — Hide the field on `litigation` and `patent` too, not
+   just on `client`? (Recommend YES per m's "only on case projects".)
+4. **§2.2 Q6** — German prose forms use feminine grammatical gender
+   (Klägerin, Beklagte) per the existing translation table? Or
+   masculine / neutral? (Recommend feminine to match existing
+   `ourSideDE` — keeps consistency with already-rendered templates.)
+5. **§3.2 Q1** — Add a dedicated `opponent_code` column on
+   litigations? (Recommend YES; regex-on-title is brittle.)
+6. **§3.2 Q2** — Patent segment = last 3 digits (variable for
+   <4-digit numbers)? (Recommend YES, matches m's example.)
+7. **§3.2 Q3** — Case segment drops the jurisdiction prefix from
+   `proceeding_types.code` (so `upc.inf.cfi` → `INF.CFI`, not
+   `UPC.INF.CFI`)? (Recommend YES — jurisdiction is implied by the
+   ancestor client/patent context.)
+8. **§3.2 Q7** — `BuildProjectCode` populates a `code` field on every
+   projected Project JSON (not lazy per-render)? (Recommend YES;
+   simpler consumers, one DB round-trip per list page.)
+9. **§3.2 Q8** — No cache / materialised view in v1? (Recommend YES;
+   profile later if list views get slow.)
+
+---
+
+## §5 Implementation order (coder phase)
+
+1. **Mig 112** (client role widen + backfill) → mig 113 (opponent_code).
+   *Renumbered twice on 2026-05-20 — mig 110 claimed by m/paliad#51 project_type_other; mig 111 claimed by m/paliad#48 project_admin_and_select; boltzmann's gap-tolerant runner hard-fails on collisions so this is a strict rebump.*
+   Run `ls internal/db/migrations/ | tail` first to verify slot
+   availability (boltzmann's gap-tolerant runner means 110 is fine
+   even if 109 was the last applied).
+2. **Backend** — `isValidOurSide`, `ourSideDE/EN`,
+   `derivedCounterclaimOurSide`, new `project_code.go` package
+   + ProjectService wiring + projection `Code` field.
+3. **Frontend** — `ProjectFormFields.tsx` (conditional render + new
+   options + opponent_code field on litigation block), `i18n.ts` keys,
+   `fristenrechner.ts` `ourSideToPerspective` widen, header /
+   breadcrumb / picker code-badge wiring.
+4. **Tests** — pinning tests above; `go test ./internal/...` clean.
+5. **Build verification** — `go build && cd frontend && bun run build`
+   clean.
+6. **Commit per slice** — three commits (migration + backend, frontend,
+   tests) keep review tractable.
+
+---
+
+## §6 Risks & rollback
+
+- **Submission templates in the wild.** Users may have downloaded /
+  customised submission templates that still reference
+  `{{project.our_side_de}}` for `our_side='court'` or `'both'`. After
+  this change those values are unreachable, so the template arm
+  returns `""`. Already the fallback behaviour for unknown values;
+  no breakage, just an empty render. Mention in release notes.
+- **Browser cache.** Users with a stale bundle still see the old
+  "Wir vertreten" form for one cache-bust cycle. The legacy i18n keys
+  stay until housekeeping (§2.4), so labels still resolve.
+- **Migration down path.** Stepping down from 110 restores the old
+  4-value CHECK; new sub-role rows would violate it. The down
+  migration backfills new sub-roles → NULL to stay consistent.
+- **Per-tree opponent_code uniqueness.** Two litigations under the
+  same client with the same `opponent_code` would derive identical
+  case codes. Per Q6 we accept this; users see it in the picker and
+  customise `reference` if it bothers them.
+- **No new env vars, no Dokploy compose change** — both changes are
+  pure code + schema; deploy is the existing main-push → webhook →
+  Dokploy auto-redeploy path.
diff --git a/frontend/src/client/fristenrechner.ts b/frontend/src/client/fristenrechner.ts
index 58908b9..9e13f53 100644
--- a/frontend/src/client/fristenrechner.ts
+++ b/frontend/src/client/fristenrechner.ts
@@ -187,12 +187,21 @@ interface ProjectOption {
   // (Slice 3b) can scope the cascade by the project's jurisdiction
   // without an extra fetch.
   proceeding_type_id?: number | null;
-  // our_side carries which side the firm represents on this project
-  // (t-paliad-164). When a user selects an Akte, the perspective chip
-  // pre-locks to this value; a small hint above the strip flags the
+  // our_side carries which side the firm represents on this case
+  // project (Client Role; t-paliad-164, widened in t-paliad-222).
+  // When a user selects an Akte, the perspective chip pre-locks via
+  // ourSideToPerspective(); a small hint above the strip flags the
   // pre-selection and the user can still click another chip to
   // override. NULL/undefined leaves the chip unset (free-pick).
-  our_side?: "claimant" | "defendant" | "court" | "both" | null;
+  our_side?:
+    | "claimant"
+    | "defendant"
+    | "applicant"
+    | "appellant"
+    | "respondent"
+    | "third_party"
+    | "other"
+    | null;
 }
 
 async function fetchProjects(): Promise<ProjectOption[]> {
@@ -3801,14 +3810,30 @@ function applyPerspective(p: Perspective) {
   triggerCascadeRefresh();
 }
 
-// ourSideToPerspective maps the project-level "Wir vertreten" enum
-// onto the chip-strip Perspective. 'court' / 'both' map to null
-// (chip cleared) — court actions are neutral to the user's side and
-// "both" is explicit no-filter intent.
+// ourSideToPerspective maps the project-level "Client Role" enum
+// (DB column: our_side) onto the chip-strip Perspective.
+//
+// Per t-paliad-222 (m/paliad#47) the field carries one of seven
+// sub-role values grouped at display time:
+//   Active   (we initiate) : claimant, applicant, appellant   → "claimant"
+//   Reactive (we defend)   : defendant, respondent            → "defendant"
+//   Other                  : third_party, other, NULL         → null
+//
+// Legacy 'court' / 'both' values no longer exist in the column
+// (mig 110 backfilled them to NULL); both fall through to the null
+// default arm if a stale value sneaks in.
 function ourSideToPerspective(os: string | null | undefined): Perspective {
-  if (os === "claimant") return "claimant";
-  if (os === "defendant") return "defendant";
-  return null;
+  switch (os) {
+    case "claimant":
+    case "applicant":
+    case "appellant":
+      return "claimant";
+    case "defendant":
+    case "respondent":
+      return "defendant";
+    default:
+      return null;
+  }
 }
 
 // applyOurSidePredefine locks the perspective from project.our_side
diff --git a/frontend/src/client/i18n.ts b/frontend/src/client/i18n.ts
index dddeb8e..32f570c 100644
--- a/frontend/src/client/i18n.ts
+++ b/frontend/src/client/i18n.ts
@@ -1210,9 +1210,30 @@ const translations: Record<Lang, Record<string, string>> = {
     "projects.field.our_side.unset": "Unbekannt / nicht gesetzt",
     "projects.field.our_side.claimant": "Klägerseite",
     "projects.field.our_side.defendant": "Beklagtenseite",
+    "projects.field.our_side.applicant": "Antragsteller",
+    "projects.field.our_side.appellant": "Berufungsführer",
+    "projects.field.our_side.respondent": "Antragsgegner",
+    "projects.field.our_side.third_party": "Streithelfer / Dritter",
+    "projects.field.our_side.other": "Sonstige Beteiligte",
     "projects.field.our_side.court": "Gericht / Tribunal",
     "projects.field.our_side.both": "Beide Seiten",
     "projects.field.our_side.none": "—",
+    "projects.field.client_role": "Mandantenrolle",
+    "projects.field.client_role.hint": "Bestimmt die Voreinstellung der Perspektive im Fristenrechner-Determinator: Aktiv → Klägerseite, Reaktiv → Beklagtenseite. Lässt sich dort jederzeit überschreiben.",
+    "projects.field.client_role.unset": "Unbekannt",
+    "projects.field.client_role.group.active": "Aktiv (wir greifen an)",
+    "projects.field.client_role.group.reactive": "Reaktiv (wir verteidigen)",
+    "projects.field.client_role.group.other": "Dritte / Sonstige",
+    "projects.field.client_role.claimant": "Klägerseite",
+    "projects.field.client_role.applicant": "Antragsteller",
+    "projects.field.client_role.appellant": "Berufungsführer",
+    "projects.field.client_role.defendant": "Beklagtenseite",
+    "projects.field.client_role.respondent": "Antragsgegner",
+    "projects.field.client_role.third_party": "Streithelfer / Dritter",
+    "projects.field.client_role.other": "Sonstige Beteiligte",
+    "projects.field.opponent_code": "Gegner-Kürzel",
+    "projects.field.opponent_code.placeholder": "z.B. OPNT",
+    "projects.field.opponent_code.hint": "Kurzes Kürzel der Gegenseite (Großbuchstaben, Ziffern, Bindestriche, max. 16 Zeichen). Wird als mittleres Segment in automatisch abgeleiteten Projekt-Codes verwendet (z.B. EXMPL.OPNT.567.INF.CFI).",
     "projects.field.status": "Status",
     "projects.error.title_required": "Titel erforderlich",
     "projects.detail.edit.type_change_warning.title": "Diese Felder werden geleert:",
@@ -3903,9 +3924,30 @@ const translations: Record<Lang, Record<string, string>> = {
     "projects.field.our_side.unset": "Unknown / not set",
     "projects.field.our_side.claimant": "Claimant side",
     "projects.field.our_side.defendant": "Defendant side",
+    "projects.field.our_side.applicant": "Applicant",
+    "projects.field.our_side.appellant": "Appellant",
+    "projects.field.our_side.respondent": "Respondent",
+    "projects.field.our_side.third_party": "Third Party",
+    "projects.field.our_side.other": "Other party",
     "projects.field.our_side.court": "Court / tribunal",
     "projects.field.our_side.both": "Both sides",
     "projects.field.our_side.none": "—",
+    "projects.field.client_role": "Client Role",
+    "projects.field.client_role.hint": "Pre-selects the perspective chip in the Fristenrechner Determinator: Active → claimant side, Reactive → defendant side. Always overridable from there.",
+    "projects.field.client_role.unset": "Unknown",
+    "projects.field.client_role.group.active": "Active (we initiate)",
+    "projects.field.client_role.group.reactive": "Reactive (we defend)",
+    "projects.field.client_role.group.other": "Third Party / Other",
+    "projects.field.client_role.claimant": "Claimant side",
+    "projects.field.client_role.applicant": "Applicant",
+    "projects.field.client_role.appellant": "Appellant",
+    "projects.field.client_role.defendant": "Defendant side",
+    "projects.field.client_role.respondent": "Respondent",
+    "projects.field.client_role.third_party": "Third Party",
+    "projects.field.client_role.other": "Other party",
+    "projects.field.opponent_code": "Opponent code",
+    "projects.field.opponent_code.placeholder": "e.g. OPNT",
+    "projects.field.opponent_code.hint": "Short slug for the opposing party (uppercase letters, digits, dashes, max 16 chars). Used as the middle segment in auto-derived project codes (e.g. EXMPL.OPNT.567.INF.CFI).",
     "projects.field.status": "Status",
     "projects.error.title_required": "Title required",
     "projects.detail.edit.type_change_warning.title": "These fields will be cleared:",
diff --git a/frontend/src/client/project-form.ts b/frontend/src/client/project-form.ts
index 17ef97a..7ea4351 100644
--- a/frontend/src/client/project-form.ts
+++ b/frontend/src/client/project-form.ts
@@ -8,6 +8,11 @@ export interface ProjectMini {
   title: string;
   type: string;
   reference?: string | null;
+  // t-paliad-222 / m/paliad#50: auto-derived dotted project code from
+  // the ancestor tree. Populated by the service projection on every
+  // /api/projects response, so the picker can show the code without an
+  // extra fetch.
+  code?: string;
 }
 
 export interface ProjectFormState {
@@ -48,9 +53,11 @@ function tryGet(id: string): HTMLElement | null {
 export function showFieldsForType(typeSel: string) {
   const parentWrap = tryGet("projekt-parent-wrap") as HTMLDivElement | null;
   const clientFields = tryGet("fields-client") as HTMLDivElement | null;
+  const litigationFields = tryGet("fields-litigation") as HTMLDivElement | null;
   const patentFields = tryGet("fields-patent") as HTMLDivElement | null;
   const caseFields = tryGet("fields-case") as HTMLDivElement | null;
   if (clientFields) clientFields.style.display = typeSel === "client" ? "block" : "none";
+  if (litigationFields) litigationFields.style.display = typeSel === "litigation" ? "block" : "none";
   if (patentFields) patentFields.style.display = typeSel === "patent" ? "block" : "none";
   if (caseFields) caseFields.style.display = typeSel === "case" ? "block" : "none";
   if (parentWrap) parentWrap.style.display = typeSel === "client" ? "none" : "block";
@@ -88,18 +95,28 @@ export function initParentPicker() {
     }
     const matches = parentCandidates
       .filter((p) => {
-        const hay = (p.title + " " + (p.reference || "")).toLowerCase();
+        // Search across title + manual reference + auto-derived code
+        // so the user can type "EXMPL" or "INF.CFI" and find the row.
+        const hay = (p.title + " " + (p.reference || "") + " " + (p.code || "")).toLowerCase();
         return hay.includes(q);
       })
       .slice(0, 8);
     sugs.innerHTML = matches
-      .map(
-        (p) =>
-          `<div class="collab-suggestion" data-id="${esc(p.id)}" data-title="${esc(p.title)}">
+      .map((p) => {
+        // Render the auto-derived code (if any, and distinct from
+        // reference) as a small mono badge on the right so the user
+        // can disambiguate two same-titled projects by their tree
+        // position. Single template literal kept readable inline.
+        const code = p.code && p.code !== (p.reference || "") ? p.code : "";
+        const codeBadge = code
+          ? `<span class="entity-ref entity-ref-code">${esc(code)}</span>`
+          : "";
+        return `<div class="collab-suggestion" data-id="${esc(p.id)}" data-title="${esc(p.title)}">
             <strong>${esc(p.title)}</strong>
             <span class="entity-type-chip entity-type-${esc(p.type)}">${esc(tDyn("projects.type." + p.type) || p.type)}</span>
-          </div>`,
-      )
+            ${codeBadge}
+          </div>`;
+      })
       .join("");
     sugs.querySelectorAll<HTMLDivElement>(".collab-suggestion").forEach((el) => {
       el.addEventListener("click", () => {
@@ -174,20 +191,32 @@ export function readPayload(
     const gd = ($("project-grant-date") as HTMLInputElement).value;
     if (gd) payload.grant_date = gd + "T00:00:00Z";
   }
+  if (type === "litigation") {
+    // opponent_code is the litigation-only short slug used as the
+    // middle segment when BuildProjectCode auto-derives a project
+    // code from the ancestor tree (t-paliad-222 / m/paliad#50).
+    // Uppercased on submit so the user can type lowercase comfortably
+    // — the DB CHECK enforces the [A-Z0-9-]{1,16} pattern.
+    const ocEl = tryGet("project-opponent-code") as HTMLInputElement | null;
+    if (ocEl) {
+      const v = ocEl.value.trim().toUpperCase();
+      if (v) payload.opponent_code = v;
+      else if (!opts.omitEmpty) payload.opponent_code = "";
+    }
+  }
   if (type === "case") {
     stringField("project-court", "court");
     stringField("project-case-number", "case_number");
-  }
 
-  // our_side is type-agnostic — every project type can carry "Wir
-  // vertreten" because the Determinator picks it up regardless of
-  // type. The select uses "" for the unset option; the service maps
-  // empty string to NULL via nullableOurSide.
-  const osSel = tryGet("project-our-side") as HTMLSelectElement | null;
-  if (osSel) {
-    const v = osSel.value.trim();
-    if (v) payload.our_side = v;
-    else if (!opts.omitEmpty) payload.our_side = "";
+    // Client Role (DB column: our_side) — case-only after t-paliad-222.
+    // The select uses "" for the unset option; the service maps empty
+    // string to NULL via nullableOurSide.
+    const osSel = tryGet("project-our-side") as HTMLSelectElement | null;
+    if (osSel) {
+      const v = osSel.value.trim();
+      if (v) payload.our_side = v;
+      else if (!opts.omitEmpty) payload.our_side = "";
+    }
   }
 
   const desc = ($("project-description") as HTMLTextAreaElement).value.trim();
@@ -228,6 +257,8 @@ export function prefillForm(p: Record<string, unknown>) {
   get("project-case-number").value = String(p.case_number ?? "");
   const osSel = tryGet("project-our-side") as HTMLSelectElement | null;
   if (osSel) osSel.value = String(p.our_side ?? "");
+  const ocEl = tryGet("project-opponent-code") as HTMLInputElement | null;
+  if (ocEl) ocEl.value = String(p.opponent_code ?? "");
   getTA("project-description").value = String(p.description ?? "");
   getSel("project-status").value = String(p.status ?? "active");
 }
diff --git a/frontend/src/client/projects-detail.ts b/frontend/src/client/projects-detail.ts
index 8f63df3..1acb8b0 100644
--- a/frontend/src/client/projects-detail.ts
+++ b/frontend/src/client/projects-detail.ts
@@ -21,6 +21,12 @@ interface Project {
   path: string;
   title: string;
   reference?: string | null;
+  // t-paliad-222 / m/paliad#50: auto-derived dotted project code from
+  // the ancestor tree (e.g. EXMPL.OPNT.789.INF.CFI). Populated by the
+  // service layer on every projection; equal to `reference` when the
+  // user typed an override.
+  code?: string;
+  opponent_code?: string | null;
   description?: string | null;
   status: string;
   client_number?: string | null;
@@ -1095,6 +1101,24 @@ function renderHeader() {
   (document.getElementById("project-title-display") as HTMLElement).textContent = project.title;
   (document.getElementById("project-ref-display") as HTMLElement).textContent = project.reference || "";
 
+  // t-paliad-222 / m/paliad#50 — show the auto-derived project code
+  // as a second badge whenever it's non-empty AND distinct from the
+  // manual reference. Hides when the derived value equals reference
+  // (avoids visual duplication when the user typed the same string)
+  // or when no derivation produced a value.
+  const codeEl = document.getElementById("project-code-display") as HTMLElement | null;
+  if (codeEl) {
+    const code = project.code ?? "";
+    const ref = project.reference ?? "";
+    if (code && code !== ref) {
+      codeEl.textContent = code;
+      codeEl.style.display = "";
+    } else {
+      codeEl.textContent = "";
+      codeEl.style.display = "none";
+    }
+  }
+
   // t-paliad-177 — link from Verlauf header to standalone chart page.
   // Wired here (not in the TSX shell) because we need the resolved
   // project id, which only exists after the detail fetch settles.
diff --git a/frontend/src/components/ProjectFormFields.tsx b/frontend/src/components/ProjectFormFields.tsx
index fee40a0..398f41b 100644
--- a/frontend/src/components/ProjectFormFields.tsx
+++ b/frontend/src/components/ProjectFormFields.tsx
@@ -140,6 +140,24 @@ export function ProjectFormFields(): string {
         </div>
       </div>
 
+      {/* Litigation-specific */}
+      <div className="projekt-fields projekt-fields-litigation" id="fields-litigation" style="display:none">
+        <div className="form-field">
+          <label htmlFor="project-opponent-code" data-i18n="projects.field.opponent_code">Gegner-K&uuml;rzel</label>
+          <input
+            type="text"
+            id="project-opponent-code"
+            maxLength={16}
+            pattern="[A-Z0-9-]{1,16}"
+            placeholder="OPNT"
+            data-i18n-placeholder="projects.field.opponent_code.placeholder"
+          />
+          <p className="form-hint" data-i18n="projects.field.opponent_code.hint">
+            Kurzes K&uuml;rzel der Gegenseite (Grossbuchstaben, Ziffern, Bindestriche, max. 16 Zeichen). Wird als mittleres Segment in automatisch abgeleiteten Projekt-Codes verwendet (z.B. EXMPL.OPNT.567.INF.CFI).
+          </p>
+        </div>
+      </div>
+
       {/* Case-specific */}
       <div className="projekt-fields projekt-fields-case" id="fields-case" style="display:none">
         <div className="form-field-row">
@@ -152,20 +170,29 @@ export function ProjectFormFields(): string {
             <input type="text" id="project-case-number" placeholder="UPC_CFI_123/2026" />
           </div>
         </div>
-      </div>
 
-      <div className="form-field">
-        <label htmlFor="project-our-side" data-i18n="projects.field.our_side">Wir vertreten</label>
-        <select id="project-our-side">
-          <option value="" data-i18n="projects.field.our_side.unset">Unbekannt / nicht gesetzt</option>
-          <option value="claimant" data-i18n="projects.field.our_side.claimant">Kl&auml;gerseite</option>
-          <option value="defendant" data-i18n="projects.field.our_side.defendant">Beklagtenseite</option>
-          <option value="court" data-i18n="projects.field.our_side.court">Gericht / Tribunal</option>
-          <option value="both" data-i18n="projects.field.our_side.both">Beide Seiten</option>
-        </select>
-        <p className="form-hint" data-i18n="projects.field.our_side.hint">
-          Bestimmt die Voreinstellung der Perspektive im Fristenrechner-Determinator. L&auml;sst sich dort jederzeit &uuml;berschreiben.
-        </p>
+        <div className="form-field">
+          <label htmlFor="project-our-side" data-i18n="projects.field.client_role">Mandantenrolle</label>
+          <select id="project-our-side">
+            <option value="" data-i18n="projects.field.client_role.unset">Unbekannt</option>
+            <optgroup data-i18n-label="projects.field.client_role.group.active" label="Aktiv (wir greifen an)">
+              <option value="claimant" data-i18n="projects.field.client_role.claimant">Kl&auml;gerseite</option>
+              <option value="applicant" data-i18n="projects.field.client_role.applicant">Antragsteller</option>
+              <option value="appellant" data-i18n="projects.field.client_role.appellant">Berufungsf&uuml;hrer</option>
+            </optgroup>
+            <optgroup data-i18n-label="projects.field.client_role.group.reactive" label="Reaktiv (wir verteidigen)">
+              <option value="defendant" data-i18n="projects.field.client_role.defendant">Beklagtenseite</option>
+              <option value="respondent" data-i18n="projects.field.client_role.respondent">Antragsgegner</option>
+            </optgroup>
+            <optgroup data-i18n-label="projects.field.client_role.group.other" label="Dritte / Sonstige">
+              <option value="third_party" data-i18n="projects.field.client_role.third_party">Streithelfer / Dritter</option>
+              <option value="other" data-i18n="projects.field.client_role.other">Sonstige Beteiligte</option>
+            </optgroup>
+          </select>
+          <p className="form-hint" data-i18n="projects.field.client_role.hint">
+            Bestimmt die Voreinstellung der Perspektive im Fristenrechner-Determinator: Aktiv &rarr; Kl&auml;gerseite, Reaktiv &rarr; Beklagtenseite. L&auml;sst sich dort jederzeit &uuml;berschreiben.
+          </p>
+        </div>
       </div>
 
       <div className="form-field">
diff --git a/frontend/src/i18n-keys.ts b/frontend/src/i18n-keys.ts
index e6c73e2..ecdf235 100644
--- a/frontend/src/i18n-keys.ts
+++ b/frontend/src/i18n-keys.ts
@@ -2163,6 +2163,19 @@ export type I18nKey =
   | "projects.field.billing_reference"
   | "projects.field.case_number"
   | "projects.field.client_number"
+  | "projects.field.client_role"
+  | "projects.field.client_role.appellant"
+  | "projects.field.client_role.applicant"
+  | "projects.field.client_role.claimant"
+  | "projects.field.client_role.defendant"
+  | "projects.field.client_role.group.active"
+  | "projects.field.client_role.group.other"
+  | "projects.field.client_role.group.reactive"
+  | "projects.field.client_role.hint"
+  | "projects.field.client_role.other"
+  | "projects.field.client_role.respondent"
+  | "projects.field.client_role.third_party"
+  | "projects.field.client_role.unset"
   | "projects.field.clientmatter.hint"
   | "projects.field.collaborators"
   | "projects.field.collaborators.hint"
@@ -2180,13 +2193,21 @@ export type I18nKey =
   | "projects.field.matter_number"
   | "projects.field.netdocuments_url"
   | "projects.field.office"
+  | "projects.field.opponent_code"
+  | "projects.field.opponent_code.hint"
+  | "projects.field.opponent_code.placeholder"
   | "projects.field.our_side"
+  | "projects.field.our_side.appellant"
+  | "projects.field.our_side.applicant"
   | "projects.field.our_side.both"
   | "projects.field.our_side.claimant"
   | "projects.field.our_side.court"
   | "projects.field.our_side.defendant"
   | "projects.field.our_side.hint"
   | "projects.field.our_side.none"
+  | "projects.field.our_side.other"
+  | "projects.field.our_side.respondent"
+  | "projects.field.our_side.third_party"
   | "projects.field.our_side.unset"
   | "projects.field.parent"
   | "projects.field.parent.hint"
diff --git a/frontend/src/projects-detail.tsx b/frontend/src/projects-detail.tsx
index 2282da6..867ae7c 100644
--- a/frontend/src/projects-detail.tsx
+++ b/frontend/src/projects-detail.tsx
@@ -50,6 +50,14 @@ export function renderProjectsDetail(): string {
                       <div className="entity-detail-meta">
                         <span id="project-type-chip" className="entity-type-chip" />
                         <span className="entity-ref" id="project-ref-display" />
+                        {/* Auto-derived project code (t-paliad-222 / m/paliad#50).
+                            Rendered as a separate badge so the user can still
+                            distinguish a custom reference (left badge) from a
+                            tree-derived code (right badge); when reference is
+                            blank, the derived code IS reference and only this
+                            badge shows. Hidden via inline style until the
+                            client populates it. */}
+                        <span className="entity-ref entity-ref-code" id="project-code-display" style="display:none" title="Auto-derived project code" />
                         <span id="project-clientmatter" className="entity-ref" />
                         <span id="project-status-chip" className="entity-status-chip" />
                         <a id="project-netdocs" className="netdocs-link" target="_blank" rel="noopener" style="display:none">netDocuments &nearr;</a>
diff --git a/frontend/src/styles/global.css b/frontend/src/styles/global.css
index 699c95f..f0c5c9d 100644
--- a/frontend/src/styles/global.css
+++ b/frontend/src/styles/global.css
@@ -6793,6 +6793,17 @@ dialog.modal::backdrop {
     max-width: 100%;
 }
 
+/* Auto-derived project code badge (t-paliad-222 / m/paliad#50).
+   Distinct from the user's manual reference badge — same mono shape,
+   subtly bracketed so the reader knows it's a derived/computed value
+   rather than something typed by hand. Renders only when distinct
+   from the manual reference (see renderHeader in projects-detail.ts). */
+.entity-ref-code {
+    opacity: 0.75;
+}
+.entity-ref-code::before { content: "[ "; }
+.entity-ref-code::after { content: " ]"; }
+
 .entity-detail-actions {
     display: flex;
     gap: 0.5rem;
diff --git a/go.mod b/go.mod
index dbb1c9e..9d043d6 100644
--- a/go.mod
+++ b/go.mod
@@ -8,6 +8,7 @@ require (
 	github.com/jmoiron/sqlx v1.4.0
 	github.com/lib/pq v1.12.3
 	github.com/xuri/excelize/v2 v2.10.1
+	golang.org/x/text v0.34.0
 )
 
 require (
@@ -20,5 +21,4 @@ require (
 	github.com/xuri/nfp v0.0.2-0.20250530014748-2ddeb826f9a9 // indirect
 	golang.org/x/crypto v0.48.0 // indirect
 	golang.org/x/net v0.50.0 // indirect
-	golang.org/x/text v0.34.0 // indirect
 )
diff --git a/internal/db/migrations/112_client_role_rework.down.sql b/internal/db/migrations/112_client_role_rework.down.sql
new file mode 100644
index 0000000..3f3dfd2
--- /dev/null
+++ b/internal/db/migrations/112_client_role_rework.down.sql
@@ -0,0 +1,30 @@
+-- Down migration for 112_client_role_rework.
+--
+-- Restores the original 4-value CHECK ('claimant','defendant',
+-- 'court','both', NULL) and backfills any rows that landed on a new
+-- sub-role value (applicant / appellant / respondent / third_party /
+-- other) to NULL so the schema is internally consistent after the
+-- step-down.
+
+BEGIN;
+
+-- Backfill new sub-role values to NULL so the old CHECK doesn't reject.
+UPDATE paliad.projects
+   SET our_side = NULL
+ WHERE our_side IN ('applicant', 'appellant', 'respondent', 'third_party', 'other');
+
+ALTER TABLE paliad.projects
+    DROP CONSTRAINT IF EXISTS projects_our_side_check;
+
+ALTER TABLE paliad.projects
+    ADD CONSTRAINT projects_our_side_check
+    CHECK (our_side IS NULL
+        OR our_side IN ('claimant', 'defendant', 'court', 'both'));
+
+COMMENT ON COLUMN paliad.projects.our_side IS
+    'Which side the firm represents on this project. Used by the '
+    'Fristenrechner Determinator (Slice 3c) to predefine the '
+    'perspective chip from the project context. Allowed: claimant, '
+    'defendant, court, both.';
+
+COMMIT;
diff --git a/internal/db/migrations/112_client_role_rework.up.sql b/internal/db/migrations/112_client_role_rework.up.sql
new file mode 100644
index 0000000..080deac
--- /dev/null
+++ b/internal/db/migrations/112_client_role_rework.up.sql
@@ -0,0 +1,51 @@
+-- mig 112 — t-paliad-222 / m/paliad#47 — Client Role rework.
+--
+-- Widens paliad.projects.our_side CHECK to seven sub-role values and
+-- drops the legacy 'court' / 'both' entries. The DB column name stays
+-- as 'our_side' (UI label changes only — see design doc §2.2 Q1).
+--
+-- New allowed sub-roles, grouped at display time:
+--   Active (we initiate)  : claimant, applicant, appellant
+--   Reactive (we defend)  : defendant, respondent
+--   Third Party / Other   : third_party, other
+--   NULL                  : unknown / not set
+--
+-- Backfill: any rows still on 'court' / 'both' fall back to NULL.
+-- Verified 2026-05-20: all 12 production rows are NULL, so this is
+-- a no-op on prod; the UPDATE runs defensively for staging / test
+-- fixtures that may carry the legacy values.
+--
+-- Idempotent so re-runs against a partially-applied state stay safe.
+
+BEGIN;
+
+-- 1. Backfill any 'court' / 'both' rows to NULL.
+UPDATE paliad.projects
+   SET our_side = NULL
+ WHERE our_side IN ('court', 'both');
+
+-- 2. Swap the CHECK constraint for the widened sub-role set.
+ALTER TABLE paliad.projects
+    DROP CONSTRAINT IF EXISTS projects_our_side_check;
+
+ALTER TABLE paliad.projects
+    ADD CONSTRAINT projects_our_side_check
+    CHECK (our_side IS NULL OR our_side IN (
+        'claimant', 'defendant',
+        'applicant', 'appellant',
+        'respondent',
+        'third_party', 'other'
+    ));
+
+COMMENT ON COLUMN paliad.projects.our_side IS
+    'Which side the firm represents on this case project (renamed in '
+    'the UI to "Client Role" / "Mandantenrolle" — t-paliad-222 / '
+    'm/paliad#47). Allowed sub-roles, grouped at display time: Active '
+    '(claimant, applicant, appellant); Reactive (defendant, '
+    'respondent); Third Party / Other (third_party, other). NULL = '
+    'unknown. The form hides the field on non-case project types. '
+    'Drives the Fristenrechner Determinator perspective chip — Active '
+    'group → claimant-perspective, Reactive → defendant-perspective, '
+    'Third Party / Other → null (chip free-pick).';
+
+COMMIT;
diff --git a/internal/db/migrations/113_projects_opponent_code.down.sql b/internal/db/migrations/113_projects_opponent_code.down.sql
new file mode 100644
index 0000000..16fc578
--- /dev/null
+++ b/internal/db/migrations/113_projects_opponent_code.down.sql
@@ -0,0 +1,11 @@
+-- Down migration for 113_projects_opponent_code.
+
+BEGIN;
+
+ALTER TABLE paliad.projects
+    DROP CONSTRAINT IF EXISTS projects_opponent_code_check;
+
+ALTER TABLE paliad.projects
+    DROP COLUMN IF EXISTS opponent_code;
+
+COMMIT;
diff --git a/internal/db/migrations/113_projects_opponent_code.up.sql b/internal/db/migrations/113_projects_opponent_code.up.sql
new file mode 100644
index 0000000..c59513d
--- /dev/null
+++ b/internal/db/migrations/113_projects_opponent_code.up.sql
@@ -0,0 +1,50 @@
+-- mig 113 — t-paliad-222 / m/paliad#50 — auto-derived project codes.
+--
+-- Adds an opponent-code slug field on litigation projects. Used as
+-- the middle segment when BuildProjectCode assembles an auto-derived
+-- project code from the ancestor tree (e.g. EXMPL.OPNT.567.INF.CFI).
+--
+-- NULL = segment skipped silently. Existing litigation rows yield
+-- codes without an opponent segment until the user fills the field.
+-- No backfill from `title` — the litigation title is free-text
+-- ("Siemens AG ./. Huawei", "Mandant vs Gegner") and any regex would
+-- be brittle; the user enters the slug once at project creation /
+-- next edit.
+--
+-- Slug shape: uppercase letters / digits / dashes, max 16 chars.
+-- Constraint also gates on type='litigation' so a stray value on a
+-- non-litigation row is rejected at the DB level (defence in depth;
+-- the form already hides the field on other types).
+--
+-- Idempotent.
+
+BEGIN;
+
+ALTER TABLE paliad.projects
+    ADD COLUMN IF NOT EXISTS opponent_code text;
+
+DO $$
+BEGIN
+    IF NOT EXISTS (
+        SELECT 1 FROM pg_constraint
+         WHERE conname  = 'projects_opponent_code_check'
+           AND conrelid = 'paliad.projects'::regclass
+    ) THEN
+        ALTER TABLE paliad.projects
+            ADD CONSTRAINT projects_opponent_code_check
+            CHECK (opponent_code IS NULL
+                OR (opponent_code ~ '^[A-Z0-9-]{1,16}$'
+                    AND type = 'litigation'));
+    END IF;
+END $$;
+
+COMMENT ON COLUMN paliad.projects.opponent_code IS
+    'Short slug for the opposing party on a litigation project '
+    '(uppercase letters, digits, dashes, max 16 chars). Used as the '
+    'middle segment when BuildProjectCode walks the ancestor tree to '
+    'assemble a dotted project code — e.g. EXMPL.OPNT.567.INF.CFI '
+    '(t-paliad-222 / m/paliad#50). NULL = segment skipped silently. '
+    'Only meaningful on type=''litigation'' rows; the CHECK enforces '
+    'that pairing.';
+
+COMMIT;
diff --git a/internal/models/models.go b/internal/models/models.go
index 22d105a..a433eb6 100644
--- a/internal/models/models.go
+++ b/internal/models/models.go
@@ -159,10 +159,35 @@ type Project struct {
 	// OurSide is which side the firm represents on this project. Used
 	// by the Fristenrechner Determinator to predefine the perspective
 	// chip from the project context (t-paliad-164). NULL = unknown /
-	// not set; Determinator falls back to free-pick. Allowed values:
-	// claimant, defendant, court, both.
+	// not set; Determinator falls back to free-pick.
+	//
+	// Allowed sub-roles (mig 112, t-paliad-222):
+	//   Active   : claimant, applicant, appellant
+	//   Reactive : defendant, respondent
+	//   Other    : third_party, other
+	//
+	// The DB column name stays as `our_side`; the UI label has moved
+	// to "Client Role" / "Mandantenrolle" on case projects and is
+	// hidden on every other project type.
 	OurSide *string `db:"our_side" json:"our_side,omitempty"`
 
+	// OpponentCode is the short slug for the opposing party on a
+	// litigation project (uppercase letters / digits / dashes, max 16
+	// chars). Used as the middle segment when services.BuildProjectCode
+	// assembles an auto-derived project code from the ancestor tree —
+	// e.g. EXMPL.OPNT.567.INF.CFI (t-paliad-222 / m/paliad#50). NULL
+	// → segment skipped silently. Only meaningful on type='litigation'
+	// rows; CHECK constraint (mig 113) enforces the pairing.
+	OpponentCode *string `db:"opponent_code" json:"opponent_code,omitempty"`
+
+	// Code is the auto-derived (or override) project code, computed at
+	// projection time by services.BuildProjectCode. Not a DB column —
+	// no `db:` tag — populated by service-layer projection helpers
+	// after the row is loaded. Empty on rows for which the helper has
+	// not run (e.g. raw fixtures in tests, internal projection paths
+	// that don't call the helper).
+	Code string `db:"-" json:"code,omitempty"`
+
 	// CounterclaimOf is the parent project this row is a counterclaim
 	// (CCR) against (t-paliad-174 SmartTimeline Slice 3). NULL on
 	// regular projects; non-NULL rows are CCR sub-projects rendered as
diff --git a/internal/services/project_code.go b/internal/services/project_code.go
new file mode 100644
index 0000000..f83d0c2
--- /dev/null
+++ b/internal/services/project_code.go
@@ -0,0 +1,312 @@
+package services
+
+import (
+	"context"
+	"fmt"
+	"regexp"
+	"strings"
+	"unicode"
+
+	"github.com/google/uuid"
+	"github.com/jmoiron/sqlx"
+	"github.com/lib/pq"
+	"golang.org/x/text/runes"
+	"golang.org/x/text/transform"
+	"golang.org/x/text/unicode/norm"
+
+	"mgit.msbls.de/m/paliad/internal/models"
+)
+
+// Project codes — t-paliad-222 / m/paliad#50.
+//
+// BuildProjectCode assembles a dotted code from the ancestor chain of
+// a project. Each ancestor contributes one segment derived from its
+// type-specific metadata. Missing segments (NULL ancestor field,
+// unfilled opponent_code, etc.) are skipped silently — there is no
+// placeholder.
+//
+//   client     → reference if set, else slug(title), capped at 8 chars
+//   litigation → opponent_code (the slug the user typed at litigation
+//                creation), empty → skipped
+//   patent     → last 3 digits of patent_number (full digit-stream when
+//                shorter), empty → skipped
+//   case       → uppercase tail of proceeding_types.code (jurisdiction
+//                segment dropped), empty → skipped
+//   project    → "" (generic projects don't contribute a segment)
+//
+// Custom override: if the target row's `reference` column is non-empty,
+// it wins outright — the helper returns the literal `reference` string
+// without walking the ancestor chain.
+//
+// Example: Client EXMPL → Litigation OPNT → Patent EP3456789 → Case
+// `upc.inf.cfi` → "EXMPL.OPNT.789.INF.CFI".
+//
+// Collision handling: codes are display-only (no uniqueness
+// constraint). Two cases that derive to the same code both return the
+// same string. v1 contract — users disambiguate via `reference` when it
+// matters.
+
+// projectChainRow is one row of the ancestor walk. Includes only the
+// columns BuildProjectCode needs; trimmed for cheap projection.
+type projectChainRow struct {
+	ID               uuid.UUID `db:"id"`
+	Type             string    `db:"type"`
+	Title            string    `db:"title"`
+	Reference        *string   `db:"reference"`
+	OpponentCode     *string   `db:"opponent_code"`
+	PatentNumber     *string   `db:"patent_number"`
+	ProceedingTypeID *int      `db:"proceeding_type_id"`
+	ProceedingCode   *string   `db:"proceeding_code"`
+}
+
+// BuildProjectCode walks the ancestor chain via the existing
+// paliad.projects.path ltree and returns the assembled code. One DB
+// round-trip per call; suitable for per-row use in single-project
+// projection paths.
+//
+// For list endpoints with many rows, the call still scales fine for
+// firm-scale datasets (order-of-100s); if profiling later flags it as
+// a hotspot, introduce a materialised view per the design doc §3.2 Q8.
+func BuildProjectCode(ctx context.Context, db sqlx.QueryerContext, projectID uuid.UUID) (string, error) {
+	const query = `
+		SELECT p.id, p.type, p.title, p.reference, p.opponent_code,
+		       p.patent_number, p.proceeding_type_id,
+		       pt.code AS proceeding_code
+		  FROM paliad.projects p
+		  LEFT JOIN paliad.proceeding_types pt ON pt.id = p.proceeding_type_id
+		 WHERE p.path @> (SELECT path FROM paliad.projects WHERE id = $1)
+		 ORDER BY nlevel(p.path)
+	`
+	rows := []projectChainRow{}
+	if err := sqlx.SelectContext(ctx, db, &rows, query, projectID); err != nil {
+		return "", fmt.Errorf("build project code: load chain: %w", err)
+	}
+	if len(rows) == 0 {
+		return "", nil
+	}
+	return assembleProjectCode(rows), nil
+}
+
+// PopulateProjectCodes assigns .Code on every project in `targets` via
+// a single bulk round-trip. Used by List / ListChildren / ListAncestors
+// projection paths to avoid N+1 BuildProjectCode calls.
+//
+// Empty slice → no-op. Rows that can't be matched (orphaned) get an
+// empty code rather than an error.
+func PopulateProjectCodes(ctx context.Context, db sqlx.QueryerContext, targets []models.Project) error {
+	if len(targets) == 0 {
+		return nil
+	}
+	ids := make([]string, len(targets))
+	for i, t := range targets {
+		ids[i] = t.ID.String()
+	}
+
+	// One CTE-based query: for each target id, fetch the full ancestor
+	// chain joined to proceeding_types, ordered so we can group in Go.
+	const query = `
+		WITH targets AS (
+		    SELECT id, path
+		      FROM paliad.projects
+		     WHERE id = ANY($1::uuid[])
+		)
+		SELECT t.id AS target_id,
+		       p.id, p.type, p.title, p.reference, p.opponent_code,
+		       p.patent_number, p.proceeding_type_id,
+		       pt.code AS proceeding_code,
+		       nlevel(p.path) AS chain_level
+		  FROM targets t
+		  JOIN paliad.projects p ON p.path @> t.path
+		  LEFT JOIN paliad.proceeding_types pt ON pt.id = p.proceeding_type_id
+		 ORDER BY t.id, chain_level
+	`
+	type bulkRow struct {
+		TargetID uuid.UUID `db:"target_id"`
+		projectChainRow
+		ChainLevel int `db:"chain_level"`
+	}
+
+	rows := []bulkRow{}
+	if err := sqlx.SelectContext(ctx, db, &rows, query, pq.StringArray(ids)); err != nil {
+		return fmt.Errorf("populate project codes: bulk fetch: %w", err)
+	}
+
+	chains := make(map[uuid.UUID][]projectChainRow, len(targets))
+	for _, r := range rows {
+		chains[r.TargetID] = append(chains[r.TargetID], r.projectChainRow)
+	}
+	for i := range targets {
+		targets[i].Code = assembleProjectCode(chains[targets[i].ID])
+	}
+	return nil
+}
+
+// assembleProjectCode is the pure code-assembly step, split out from
+// the DB hop so it can be table-tested without fixtures.
+//
+// Custom override: non-empty `reference` on the target row (last in
+// chain) wins; the function returns it verbatim without computing the
+// other segments.
+func assembleProjectCode(chain []projectChainRow) string {
+	if len(chain) == 0 {
+		return ""
+	}
+	target := chain[len(chain)-1]
+	if target.Reference != nil {
+		if v := strings.TrimSpace(*target.Reference); v != "" {
+			return v
+		}
+	}
+	segments := make([]string, 0, len(chain))
+	for _, p := range chain {
+		seg := projectCodeSegment(p)
+		if seg == "" {
+			continue
+		}
+		segments = append(segments, seg)
+	}
+	return strings.Join(segments, ".")
+}
+
+// projectCodeSegment returns the per-row segment string for the dotted
+// project code. Empty string → row contributes no segment (skipped by
+// the assembler). Pure; never touches the DB. Table-tested.
+func projectCodeSegment(p projectChainRow) string {
+	switch p.Type {
+	case "client":
+		if p.Reference != nil {
+			if v := sanitizeClientShort(*p.Reference); v != "" {
+				return v
+			}
+		}
+		return sanitizeClientShort(p.Title)
+	case "litigation":
+		if p.OpponentCode != nil {
+			return strings.TrimSpace(*p.OpponentCode)
+		}
+		return ""
+	case "patent":
+		if p.PatentNumber != nil {
+			return patentLast3(*p.PatentNumber)
+		}
+		return ""
+	case "case":
+		if p.ProceedingCode != nil {
+			return proceedingTail(*p.ProceedingCode)
+		}
+		return ""
+	default:
+		// 'project' (generic) and any future types contribute nothing.
+		return ""
+	}
+}
+
+// sanitizeClientShort produces an 8-char uppercase slug from a client
+// reference / title. Strips diacritics, replaces non-alphanumerics
+// with nothing, trims, caps at 8 chars. Empty input → "".
+//
+// Examples (verified by table test):
+//   "EXMPL"        → "EXMPL"
+//   "Example Co."  → "EXAMPLEC"
+//   "Müller GmbH"  → "MULLERGM"
+//   "  "           → ""
+func sanitizeClientShort(s string) string {
+	s = strings.TrimSpace(s)
+	if s == "" {
+		return ""
+	}
+	// Strip diacritics: NFD-decompose, drop combining marks, NFC-recompose.
+	t := transform.Chain(norm.NFD, runes.Remove(runes.In(unicode.Mn)), norm.NFC)
+	stripped, _, err := transform.String(t, s)
+	if err != nil {
+		stripped = s
+	}
+	var b strings.Builder
+	b.Grow(len(stripped))
+	for _, r := range stripped {
+		if unicode.IsLetter(r) || unicode.IsDigit(r) {
+			b.WriteRune(unicode.ToUpper(r))
+		}
+	}
+	out := b.String()
+	if len(out) > 8 {
+		out = out[:8]
+	}
+	return out
+}
+
+// patentDigitsPattern matches a run of digits inside a patent number.
+// Pre-compiled once to avoid per-call regex compilation cost.
+var patentDigitsPattern = regexp.MustCompile(`\d+`)
+
+// patentKindCodeSuffix matches the trailing kind code on a patent
+// publication number (A1, A2, B1, B2, C, T3, etc.). Stripped before
+// digit extraction so the kind-code's optional digit doesn't sneak
+// into the patent number proper.
+//
+// EP / WO conventions allow A, B, C, T, U as the letter; the digit is
+// optional. The regex anchors at end-of-string and tolerates trailing
+// whitespace.
+var patentKindCodeSuffix = regexp.MustCompile(`[A-Z][0-9]?\s*$`)
+
+// patentLast3 extracts the last 3 digits of a patent number, returning
+// the full digit-stream if the patent has fewer than 3 digits total.
+//
+// Strips a trailing kind-code suffix (A1, B2, C, T3 …) first so its
+// optional digit doesn't pollute the result, then collapses all digit
+// runs in the remainder to handle spaced / slashed formats. Examples:
+//
+//   "EP1234567"        → "567"
+//   "EP 1 234 567"     → "567"
+//   "EP3456789A1"      → "789"
+//   "EP1234567 B1"     → "567"
+//   "WO2020/123456A1"  → "456"
+//   "DE12"             → "12"
+//   "EP"               → ""
+//   ""                 → ""
+func patentLast3(s string) string {
+	s = strings.ToUpper(strings.TrimSpace(s))
+	if s == "" {
+		return ""
+	}
+	// Strip the trailing kind code (one or two chars at end).
+	s = patentKindCodeSuffix.ReplaceAllString(s, "")
+	matches := patentDigitsPattern.FindAllString(s, -1)
+	if len(matches) == 0 {
+		return ""
+	}
+	digits := strings.Join(matches, "")
+	if len(digits) >= 3 {
+		return digits[len(digits)-3:]
+	}
+	return digits
+}
+
+// proceedingTail takes a proceeding_types.code (e.g. "upc.inf.cfi") and
+// returns the uppercase tail with the leading jurisdiction segment
+// dropped. The jurisdiction is implied by the ancestor client / patent
+// context, so it's redundant in the code.
+//
+//   "upc.inf.cfi"     → "INF.CFI"
+//   "upc.rev.cfi"     → "REV.CFI"
+//   "upc.apl.merits"  → "APL.MERITS"
+//   "de.inf.lg"       → "INF.LG"
+//   "de.inf.olg"      → "INF.OLG"
+//   "single"          → ""        (no tail after dropping the only segment)
+//   ""                → ""
+func proceedingTail(code string) string {
+	code = strings.TrimSpace(code)
+	if code == "" {
+		return ""
+	}
+	parts := strings.Split(code, ".")
+	if len(parts) < 2 {
+		return ""
+	}
+	tail := parts[1:]
+	out := make([]string, len(tail))
+	for i, p := range tail {
+		out[i] = strings.ToUpper(p)
+	}
+	return strings.Join(out, ".")
+}
diff --git a/internal/services/project_code_test.go b/internal/services/project_code_test.go
new file mode 100644
index 0000000..0c6cdb8
--- /dev/null
+++ b/internal/services/project_code_test.go
@@ -0,0 +1,376 @@
+package services
+
+import (
+	"testing"
+
+	"github.com/google/uuid"
+)
+
+// TestProjectCodeSegment pins the per-type segment derivation rules
+// from t-paliad-222 design §3.2:
+//
+//   client     → reference if set, else sanitized title (cap 8 chars)
+//   litigation → opponent_code verbatim (empty → skipped)
+//   patent     → last 3 digits of patent_number
+//   case       → uppercase tail of proceeding_types.code
+//   project    → ""
+func TestProjectCodeSegment(t *testing.T) {
+	str := func(s string) *string { return &s }
+	intp := func(i int) *int { return &i }
+
+	cases := []struct {
+		name string
+		row  projectChainRow
+		want string
+	}{
+		// Client rows.
+		{
+			"client with reference",
+			projectChainRow{Type: "client", Title: "Example Co.", Reference: str("EXMPL")},
+			"EXMPL",
+		},
+		{
+			"client without reference falls back to slug(title)",
+			projectChainRow{Type: "client", Title: "Example Co.", Reference: nil},
+			"EXAMPLEC",
+		},
+		{
+			"client without reference, diacritics stripped",
+			projectChainRow{Type: "client", Title: "Müller GmbH"},
+			"MULLERGM",
+		},
+		{
+			"client with empty reference falls back to title",
+			projectChainRow{Type: "client", Title: "ACME", Reference: str("  ")},
+			"ACME",
+		},
+		{
+			"client with empty title and no reference → empty",
+			projectChainRow{Type: "client", Title: ""},
+			"",
+		},
+
+		// Litigation rows.
+		{
+			"litigation with opponent_code",
+			projectChainRow{Type: "litigation", Title: "X v Y", OpponentCode: str("OPNT")},
+			"OPNT",
+		},
+		{
+			"litigation without opponent_code → empty",
+			projectChainRow{Type: "litigation", Title: "X v Y", OpponentCode: nil},
+			"",
+		},
+
+		// Patent rows.
+		{
+			"patent EP1234567 → 567",
+			projectChainRow{Type: "patent", PatentNumber: str("EP1234567")},
+			"567",
+		},
+		{
+			"patent with spaces EP 3 456 789 → 789",
+			projectChainRow{Type: "patent", PatentNumber: str("EP 3 456 789")},
+			"789",
+		},
+		{
+			"patent with kind code EP3456789A1 → 789",
+			projectChainRow{Type: "patent", PatentNumber: str("EP3456789A1")},
+			"789",
+		},
+		{
+			"patent WO2020/123456 → 456",
+			projectChainRow{Type: "patent", PatentNumber: str("WO2020/123456")},
+			"456",
+		},
+		{
+			"patent shorter than 3 digits → full",
+			projectChainRow{Type: "patent", PatentNumber: str("DE12")},
+			"12",
+		},
+		{
+			"patent nil → empty",
+			projectChainRow{Type: "patent", PatentNumber: nil},
+			"",
+		},
+		{
+			"patent empty digit-stream → empty",
+			projectChainRow{Type: "patent", PatentNumber: str("EP")},
+			"",
+		},
+
+		// Case rows.
+		{
+			"case upc.inf.cfi → INF.CFI",
+			projectChainRow{Type: "case", ProceedingTypeID: intp(8), ProceedingCode: str("upc.inf.cfi")},
+			"INF.CFI",
+		},
+		{
+			"case upc.apl.merits → APL.MERITS",
+			projectChainRow{Type: "case", ProceedingTypeID: intp(11), ProceedingCode: str("upc.apl.merits")},
+			"APL.MERITS",
+		},
+		{
+			"case de.inf.lg → INF.LG",
+			projectChainRow{Type: "case", ProceedingTypeID: intp(12), ProceedingCode: str("de.inf.lg")},
+			"INF.LG",
+		},
+		{
+			"case without proceeding_code → empty",
+			projectChainRow{Type: "case", ProceedingTypeID: nil, ProceedingCode: nil},
+			"",
+		},
+		{
+			"case with single-segment code → empty (no tail)",
+			projectChainRow{Type: "case", ProceedingCode: str("single")},
+			"",
+		},
+
+		// Generic project rows contribute nothing.
+		{
+			"generic project → empty",
+			projectChainRow{Type: "project", Title: "Whatever"},
+			"",
+		},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			got := projectCodeSegment(c.row)
+			if got != c.want {
+				t.Errorf("projectCodeSegment() = %q, want %q", got, c.want)
+			}
+		})
+	}
+}
+
+// TestAssembleProjectCode covers the chain assembler, including the
+// custom-override fast-path on the target row's `reference`.
+func TestAssembleProjectCode(t *testing.T) {
+	str := func(s string) *string { return &s }
+	intp := func(i int) *int { return &i }
+
+	// The reference tree from the issue body: EXMPL → OPNT → EP3456789 → upc.inf.cfi.
+	fullChain := []projectChainRow{
+		{ID: uuid.New(), Type: "client", Title: "Example Co.", Reference: str("EXMPL")},
+		{ID: uuid.New(), Type: "litigation", Title: "Ex v Op", OpponentCode: str("OPNT")},
+		{ID: uuid.New(), Type: "patent", PatentNumber: str("EP3456789")},
+		{ID: uuid.New(), Type: "case", ProceedingTypeID: intp(8), ProceedingCode: str("upc.inf.cfi")},
+	}
+
+	cases := []struct {
+		name  string
+		chain []projectChainRow
+		want  string
+	}{
+		{
+			"reference tree → EXMPL.OPNT.789.INF.CFI",
+			fullChain,
+			"EXMPL.OPNT.789.INF.CFI",
+		},
+		{
+			"empty chain → empty",
+			nil,
+			"",
+		},
+		{
+			"override on target wins outright",
+			append(append([]projectChainRow{}, fullChain[:3]...), projectChainRow{
+				ID: uuid.New(), Type: "case", Reference: str("CUSTOM-CODE"),
+				ProceedingTypeID: intp(8), ProceedingCode: str("upc.inf.cfi"),
+			}),
+			"CUSTOM-CODE",
+		},
+		{
+			"override with surrounding whitespace is trimmed",
+			append(append([]projectChainRow{}, fullChain[:3]...), projectChainRow{
+				ID: uuid.New(), Type: "case", Reference: str("  TRIMMED  "),
+			}),
+			"TRIMMED",
+		},
+		{
+			"override empty string falls through to derivation",
+			append(append([]projectChainRow{}, fullChain[:3]...), projectChainRow{
+				ID: uuid.New(), Type: "case", Reference: str(""),
+				ProceedingTypeID: intp(8), ProceedingCode: str("upc.inf.cfi"),
+			}),
+			"EXMPL.OPNT.789.INF.CFI",
+		},
+		{
+			"missing ancestors are skipped silently — case directly under client",
+			[]projectChainRow{
+				{Type: "client", Reference: str("EXMPL")},
+				{Type: "case", ProceedingCode: str("upc.inf.cfi")},
+			},
+			"EXMPL.INF.CFI",
+		},
+		{
+			"missing patent contributes nothing; client+litigation+case",
+			[]projectChainRow{
+				{Type: "client", Reference: str("EXMPL")},
+				{Type: "litigation", OpponentCode: str("OPNT")},
+				{Type: "case", ProceedingCode: str("upc.inf.cfi")},
+			},
+			"EXMPL.OPNT.INF.CFI",
+		},
+		{
+			"target itself is a litigation row (no case below) → up to opponent code",
+			[]projectChainRow{
+				{Type: "client", Reference: str("EXMPL")},
+				{Type: "litigation", OpponentCode: str("OPNT")},
+			},
+			"EXMPL.OPNT",
+		},
+		{
+			"litigation without opponent_code is skipped silently",
+			[]projectChainRow{
+				{Type: "client", Reference: str("EXMPL")},
+				{Type: "litigation", OpponentCode: nil},
+				{Type: "patent", PatentNumber: str("EP3456789")},
+				{Type: "case", ProceedingCode: str("upc.inf.cfi")},
+			},
+			"EXMPL.789.INF.CFI",
+		},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			got := assembleProjectCode(c.chain)
+			if got != c.want {
+				t.Errorf("assembleProjectCode() = %q, want %q", got, c.want)
+			}
+		})
+	}
+}
+
+// TestPatentLast3 pins the digit-extraction rule across the common
+// patent-number formats users type.
+func TestPatentLast3(t *testing.T) {
+	cases := []struct {
+		in, want string
+	}{
+		{"EP1234567", "567"},
+		{"EP 1 234 567", "567"},
+		{"EP3456789A1", "789"},
+		{"WO2020/123456A1", "456"},
+		{"DE12", "12"},
+		{"EP", ""},
+		{"", ""},
+		{"NoDigitsAtAll", ""},
+		{"1", "1"},
+		{"12", "12"},
+		{"123", "123"},
+		{"1234", "234"},
+	}
+	for _, c := range cases {
+		t.Run(c.in, func(t *testing.T) {
+			if got := patentLast3(c.in); got != c.want {
+				t.Errorf("patentLast3(%q) = %q, want %q", c.in, got, c.want)
+			}
+		})
+	}
+}
+
+// TestSanitizeClientShort pins the client-short slug rule (uppercase,
+// strip diacritics, drop non-alnum, cap 8).
+func TestSanitizeClientShort(t *testing.T) {
+	cases := []struct {
+		in, want string
+	}{
+		{"EXMPL", "EXMPL"},
+		{"Example Co.", "EXAMPLEC"},
+		{"Müller GmbH", "MULLERGM"},
+		{"  ACME  ", "ACME"},
+		{"", ""},
+		{"   ", ""},
+		{"Hogan Lovells International LLP", "HOGANLOV"},
+		{"A&B (Patents) Ltd.", "ABPATENT"},
+		{"Société Générale", "SOCIETEG"},
+	}
+	for _, c := range cases {
+		t.Run(c.in, func(t *testing.T) {
+			if got := sanitizeClientShort(c.in); got != c.want {
+				t.Errorf("sanitizeClientShort(%q) = %q, want %q", c.in, got, c.want)
+			}
+		})
+	}
+}
+
+// TestProceedingTail pins the jurisdiction-strip rule.
+func TestProceedingTail(t *testing.T) {
+	cases := []struct {
+		in, want string
+	}{
+		{"upc.inf.cfi", "INF.CFI"},
+		{"upc.rev.cfi", "REV.CFI"},
+		{"upc.pi.cfi", "PI.CFI"},
+		{"upc.apl.merits", "APL.MERITS"},
+		{"de.inf.lg", "INF.LG"},
+		{"de.inf.olg", "INF.OLG"},
+		{"single", ""},
+		{"", ""},
+		{"a.b", "B"},
+		{"  upc.inf.cfi  ", "INF.CFI"},
+	}
+	for _, c := range cases {
+		t.Run(c.in, func(t *testing.T) {
+			if got := proceedingTail(c.in); got != c.want {
+				t.Errorf("proceedingTail(%q) = %q, want %q", c.in, got, c.want)
+			}
+		})
+	}
+}
+
+// TestValidateOpponentCode pins the slug-validation rule + the
+// type='litigation' pairing. Empty string is the explicit clear
+// sentinel and always passes.
+func TestValidateOpponentCode(t *testing.T) {
+	cases := []struct {
+		name  string
+		code  string
+		ptype string
+		wantE bool
+	}{
+		{"empty clears, any type", "", "case", false},
+		{"empty clears, litigation", "", "litigation", false},
+		{"valid slug on litigation", "OPNT", "litigation", false},
+		{"valid slug with digits on litigation", "OPNT-2026", "litigation", false},
+		{"valid slug projectType empty (Update path)", "OPNT", "", false},
+		{"lowercase rejected", "opnt", "litigation", true},
+		{"underscore rejected", "OPNT_1", "litigation", true},
+		{"too long rejected", "OPNT-AND-A-VERY-LONG-NAME", "litigation", true},
+		{"non-litigation type rejected", "OPNT", "case", true},
+		{"non-litigation type rejected (patent)", "OPNT", "patent", true},
+	}
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			err := validateOpponentCode(c.code, c.ptype)
+			if (err != nil) != c.wantE {
+				t.Errorf("validateOpponentCode(%q, %q) error = %v, wantErr=%v",
+					c.code, c.ptype, err, c.wantE)
+			}
+		})
+	}
+}
+
+// TestValidateOurSideSubRoles pins the widened allowlist (mig 112).
+func TestValidateOurSideSubRoles(t *testing.T) {
+	valid := []string{
+		"", "claimant", "defendant", "applicant", "appellant",
+		"respondent", "third_party", "other",
+	}
+	invalid := []string{"court", "both", "unknown", "CLAIMANT", "Defendant"}
+
+	for _, v := range valid {
+		t.Run("valid_"+v, func(t *testing.T) {
+			if err := validateOurSide(v); err != nil {
+				t.Errorf("validateOurSide(%q) unexpected error: %v", v, err)
+			}
+		})
+	}
+	for _, v := range invalid {
+		t.Run("invalid_"+v, func(t *testing.T) {
+			if err := validateOurSide(v); err == nil {
+				t.Errorf("validateOurSide(%q) expected error, got nil", v)
+			}
+		})
+	}
+}
diff --git a/internal/services/project_service.go b/internal/services/project_service.go
index 6041093..e9cac54 100644
--- a/internal/services/project_service.go
+++ b/internal/services/project_service.go
@@ -23,6 +23,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"regexp"
 	"slices"
 	"strings"
 	"time"
@@ -114,7 +115,7 @@ func (s *ProjectService) DB() *sqlx.DB { return s.db }
 const projectColumns = `id, type, parent_id, path, title, reference, description, status,
 	created_by, industry, country, billing_reference, client_number, matter_number,
 	netdocuments_url, patent_number, filing_date, grant_date, court, case_number,
-	proceeding_type_id, our_side, counterclaim_of, instance_level, metadata, ai_summary,
+	proceeding_type_id, our_side, opponent_code, counterclaim_of, instance_level, metadata, ai_summary,
 	created_at, updated_at`
 
 // CreateProjectInput is the payload for Create.
@@ -140,6 +141,12 @@ type CreateProjectInput struct {
 	CaseNumber       *string    `json:"case_number,omitempty"`
 	ProceedingTypeID *int       `json:"proceeding_type_id,omitempty"`
 	OurSide          *string    `json:"our_side,omitempty"`
+	// OpponentCode is the litigation-only short slug used as the middle
+	// segment when BuildProjectCode assembles a project code from the
+	// ancestor tree (t-paliad-222 / m/paliad#50). Empty / nil → segment
+	// skipped. Only meaningful on type='litigation' rows; the form
+	// hides the field elsewhere and the DB CHECK rejects it.
+	OpponentCode *string `json:"opponent_code,omitempty"`
 	// InstanceLevel is the procedural instance the project sits at:
 	// 'first' (default once the picker UI lands) | 'appeal' | 'cassation'.
 	// NULL = unset. Phase 3 Slice 8 (t-paliad-189, design §7) — the
@@ -179,6 +186,10 @@ type UpdateProjectInput struct {
 	CaseNumber       *string    `json:"case_number,omitempty"`
 	ProceedingTypeID *int       `json:"proceeding_type_id,omitempty"`
 	OurSide          *string    `json:"our_side,omitempty"`
+	// OpponentCode — see CreateProjectInput.OpponentCode. UPDATE path:
+	// pointer to "" clears the column (NULL); pointer to a non-empty
+	// slug sets it.
+	OpponentCode *string `json:"opponent_code,omitempty"`
 	// InstanceLevel — see CreateProjectInput.InstanceLevel. UPDATE
 	// path: caller passes a pointer to the new value to swap; pass
 	// a pointer to "" to clear (NULL the column).
@@ -249,6 +260,9 @@ func (s *ProjectService) List(ctx context.Context, userID uuid.UUID, f ProjectFi
 	if err := stmt.SelectContext(ctx, &rows, args); err != nil {
 		return nil, fmt.Errorf("list projects: %w", err)
 	}
+	if err := PopulateProjectCodes(ctx, s.db, rows); err != nil {
+		return nil, err
+	}
 	return rows, nil
 }
 
@@ -287,6 +301,11 @@ func (s *ProjectService) GetByID(ctx context.Context, userID, id uuid.UUID) (*mo
 	if err != nil {
 		return nil, fmt.Errorf("get project: %w", err)
 	}
+	code, err := BuildProjectCode(ctx, s.db, p.ID)
+	if err != nil {
+		return nil, err
+	}
+	p.Code = code
 	return &p, nil
 }
 
@@ -347,6 +366,9 @@ func (s *ProjectService) ListAncestors(ctx context.Context, userID, id uuid.UUID
 		order[id] = i
 	}
 	sortByOrder(rows, order)
+	if err := PopulateProjectCodes(ctx, s.db, rows); err != nil {
+		return nil, err
+	}
 	return rows, nil
 }
 
@@ -468,6 +490,9 @@ func (s *ProjectService) BuildTreeWithOptions(ctx context.Context, userID uuid.U
 	if err := s.db.SelectContext(ctx, &rows, query, userID); err != nil {
 		return nil, fmt.Errorf("build tree list: %w", err)
 	}
+	if err := PopulateProjectCodes(ctx, s.db, rows); err != nil {
+		return nil, err
+	}
 
 	// Step 2 — per-node deadline counts (always; cheap one-shot query).
 	type deadlineCount struct {
@@ -814,6 +839,9 @@ func (s *ProjectService) GetTree(ctx context.Context, userID, id uuid.UUID) ([]m
 	if err := s.db.SelectContext(ctx, &rows, query, root.Path, prefix, userID); err != nil {
 		return nil, fmt.Errorf("get tree: %w", err)
 	}
+	if err := PopulateProjectCodes(ctx, s.db, rows); err != nil {
+		return nil, err
+	}
 	return rows, nil
 }
 
@@ -873,6 +901,11 @@ func (s *ProjectService) Create(ctx context.Context, userID uuid.UUID, input Cre
 			return nil, err
 		}
 	}
+	if input.OpponentCode != nil {
+		if err := validateOpponentCode(*input.OpponentCode, input.Type); err != nil {
+			return nil, err
+		}
+	}
 	if input.InstanceLevel != nil {
 		if err := validateInstanceLevel(*input.InstanceLevel); err != nil {
 			return nil, err
@@ -883,10 +916,10 @@ func (s *ProjectService) Create(ctx context.Context, userID uuid.UUID, input Cre
 		    (id, type, parent_id, path, title, reference, description, status,
 		     created_by, industry, country, billing_reference, client_number,
 		     matter_number, netdocuments_url, patent_number, filing_date, grant_date,
-		     court, case_number, proceeding_type_id, our_side, counterclaim_of,
-		     instance_level, metadata, created_at, updated_at)
+		     court, case_number, proceeding_type_id, our_side, opponent_code,
+		     counterclaim_of, instance_level, metadata, created_at, updated_at)
 		 VALUES ($1, $2, $3, '', $4, $5, $6, $7, $8, $9, $10, $11, $12, $13,
-		         $14, $15, $16, $17, $18, $19, $20, $21, $22, $23, '{}'::jsonb, $24, $24)`,
+		         $14, $15, $16, $17, $18, $19, $20, $21, $22, $23, $24, '{}'::jsonb, $25, $25)`,
 		id, input.Type, input.ParentID,
 		input.Title, input.Reference, input.Description, status,
 		userID,
@@ -895,6 +928,7 @@ func (s *ProjectService) Create(ctx context.Context, userID uuid.UUID, input Cre
 		input.PatentNumber, input.FilingDate, input.GrantDate,
 		input.Court, input.CaseNumber, input.ProceedingTypeID,
 		nullableOurSide(input.OurSide),
+		nullableOpponentCode(input.OpponentCode),
 		input.CounterclaimOf,
 		nullableInstanceLevel(input.InstanceLevel),
 		now,
@@ -1039,6 +1073,12 @@ func (s *ProjectService) Update(ctx context.Context, userID, id uuid.UUID, input
 		}
 		appendSet("our_side", nullableOurSide(input.OurSide))
 	}
+	if input.OpponentCode != nil {
+		if err := validateOpponentCode(*input.OpponentCode, current.Type); err != nil {
+			return nil, err
+		}
+		appendSet("opponent_code", nullableOpponentCode(input.OpponentCode))
+	}
 	if input.InstanceLevel != nil {
 		if err := validateInstanceLevel(*input.InstanceLevel); err != nil {
 			return nil, err
@@ -1223,6 +1263,9 @@ func (s *ProjectService) LoadCounterclaimChildrenVisible(ctx context.Context, us
 	if err := s.db.SelectContext(ctx, &rows, query, parentID, userID); err != nil {
 		return nil, fmt.Errorf("load counterclaim children: %w", err)
 	}
+	if err := PopulateProjectCodes(ctx, s.db, rows); err != nil {
+		return nil, err
+	}
 	return rows, nil
 }
 
@@ -1382,9 +1425,21 @@ func insertCounterclaimEvent(ctx context.Context, tx *sqlx.Tx, projectID, userID
 // derivedCounterclaimOurSide computes the child's our_side from the
 // parent's our_side and the opts.FlipOurSide override.
 //
-// Default (override nil OR override=true):  claimant ↔ defendant, court
-// and both pass through unchanged. NULL parent yields NULL child — the
-// flip is meaningless without a known starting side.
+// Default (override nil OR override=true): flip across the active /
+// reactive axis using the t-paliad-222 sub-role table —
+//
+//   claimant   ↔ defendant
+//   applicant  ↔ respondent
+//   appellant  → respondent   (the CCR-against-appellant is the
+//                              defending position; appellant has no
+//                              symmetric counter-role in the new set)
+//
+// Third Party / Other (third_party, other) and NULL pass through
+// unchanged — the flip is meaningless without a clear active / reactive
+// posture. Legacy 'court' / 'both' no longer exist in the column
+// (mig 112) so they have no case arm; if a stale value sneaks in via a
+// pre-migration in-memory row it falls through to the default branch
+// and passes through unchanged, preserving previous behaviour.
 //
 // Override=false: keep parent's side as-is. R.49.2.b CCI is the named
 // edge case where the CCR sub-project shares the parent's perspective.
@@ -1405,6 +1460,12 @@ func derivedCounterclaimOurSide(parentSide *string, override *bool) string {
 		return "defendant"
 	case "defendant":
 		return "claimant"
+	case "applicant":
+		return "respondent"
+	case "respondent":
+		return "applicant"
+	case "appellant":
+		return "respondent"
 	default:
 		return side
 	}
@@ -1914,15 +1975,29 @@ func validateProjectStatus(s string) error {
 	return fmt.Errorf("%w: invalid status %q", ErrInvalidInput, s)
 }
 
-// validateOurSide checks the project-level "represented side" enum
-// (t-paliad-164). Empty string is the explicit "clear" sentinel —
-// callers pass the value as-is from the form payload, and the helper
-// accepts it so an Update can null the column. The DB-level CHECK
-// constraint enforces the same set; this validation gives a clearer
-// error than relying on the constraint to fire.
+// validateOurSide checks the project-level "Client Role" enum
+// (t-paliad-164, widened in t-paliad-222 / m/paliad#47). Empty string
+// is the explicit "clear" sentinel — callers pass the value as-is
+// from the form payload, and the helper accepts it so an Update can
+// null the column. The DB-level CHECK constraint (mig 112) enforces
+// the same set; this validation gives a clearer error than relying
+// on the constraint to fire.
+//
+// Allowed sub-roles, grouped at display time:
+//   Active (we initiate)  : claimant, applicant, appellant
+//   Reactive (we defend)  : defendant, respondent
+//   Third Party / Other   : third_party, other
+//
+// Legacy 'court' / 'both' are no longer accepted (mig 112 backfills
+// existing rows to NULL); callers that still send them get a clear
+// validation error rather than a constraint violation.
 func validateOurSide(s string) error {
 	switch strings.TrimSpace(s) {
-	case "", "claimant", "defendant", "court", "both":
+	case "",
+		"claimant", "defendant",
+		"applicant", "appellant",
+		"respondent",
+		"third_party", "other":
 		return nil
 	}
 	return fmt.Errorf("%w: invalid our_side %q", ErrInvalidInput, s)
@@ -1973,6 +2048,49 @@ func nullableOurSide(p *string) any {
 	return v
 }
 
+// opponentCodePattern matches the slug shape enforced by the
+// projects_opponent_code_check constraint (mig 113): uppercase letters,
+// digits, dashes, 1-16 chars. The DB CHECK is the source of truth; this
+// helper surfaces a friendlier ErrInvalidInput error before the write.
+var opponentCodePattern = regexp.MustCompile(`^[A-Z0-9-]{1,16}$`)
+
+// validateOpponentCode checks the litigation-only opponent_code slug
+// (t-paliad-222 / m/paliad#50). Empty string clears the column; a
+// non-empty value must match opponentCodePattern AND the row must be
+// type='litigation' (the DB CHECK enforces this pairing).
+//
+// projectType may be empty when the caller is doing a partial Update
+// against the current row's type — in that case we skip the type gate
+// (the Update layer passes current.Type instead, which always has it).
+func validateOpponentCode(s, projectType string) error {
+	v := strings.TrimSpace(s)
+	if v == "" {
+		return nil
+	}
+	if projectType != "" && projectType != "litigation" {
+		return fmt.Errorf("%w: opponent_code only valid on type=litigation (got %q)",
+			ErrInvalidInput, projectType)
+	}
+	if !opponentCodePattern.MatchString(v) {
+		return fmt.Errorf("%w: invalid opponent_code %q (allowed: %s)",
+			ErrInvalidInput, s, "[A-Z0-9-]{1,16}")
+	}
+	return nil
+}
+
+// nullableOpponentCode mirrors nullableOurSide for opponent_code: nil
+// or empty/whitespace → SQL NULL; otherwise the trimmed slug.
+func nullableOpponentCode(p *string) any {
+	if p == nil {
+		return nil
+	}
+	v := strings.TrimSpace(*p)
+	if v == "" {
+		return nil
+	}
+	return v
+}
+
 func sortByOrder(xs []models.Project, order map[uuid.UUID]int) {
 	// Insertion sort — ancestor lists are short (<20).
 	for i := 1; i < len(xs); i++ {
diff --git a/internal/services/projection_service_unit_test.go b/internal/services/projection_service_unit_test.go
index ca0dc4b..43a1c9d 100644
--- a/internal/services/projection_service_unit_test.go
+++ b/internal/services/projection_service_unit_test.go
@@ -317,8 +317,10 @@ func TestChildTypeForAxis(t *testing.T) {
 }
 
 // TestDerivedCounterclaimOurSide pins the our_side flip semantics
-// (t-paliad-174 §11 Q2):
-//   - Default (override nil): claimant ↔ defendant; court / both pass through.
+// (t-paliad-174 §11 Q2, widened in t-paliad-222 / m/paliad#47):
+//   - Default (override nil): flip across the active / reactive axis —
+//     claimant ↔ defendant, applicant ↔ respondent, appellant →
+//     respondent. third_party / other / NULL pass through.
 //   - Override true: same default-flip semantics.
 //   - Override false (R.49.2.b CCI edge case): keep parent's side.
 //   - NULL parent_side yields empty string (no flip without a starting side).
@@ -337,11 +339,15 @@ func TestDerivedCounterclaimOurSide(t *testing.T) {
 		{"nil parent + override → empty", nil, &tru, ""},
 		{"claimant → defendant (default)", str("claimant"), nil, "defendant"},
 		{"defendant → claimant (default)", str("defendant"), nil, "claimant"},
-		{"court passes through", str("court"), nil, "court"},
-		{"both passes through", str("both"), nil, "both"},
+		{"applicant → respondent (default)", str("applicant"), nil, "respondent"},
+		{"respondent → applicant (default)", str("respondent"), nil, "applicant"},
+		{"appellant → respondent (default)", str("appellant"), nil, "respondent"},
+		{"third_party passes through", str("third_party"), nil, "third_party"},
+		{"other passes through", str("other"), nil, "other"},
 		{"explicit flip=true", str("claimant"), &tru, "defendant"},
 		{"explicit flip=false keeps parent's side", str("claimant"), &fal, "claimant"},
 		{"flip=false on defendant keeps defendant", str("defendant"), &fal, "defendant"},
+		{"flip=false on applicant keeps applicant", str("applicant"), &fal, "applicant"},
 	}
 	for _, c := range cases {
 		t.Run(c.name, func(t *testing.T) {
diff --git a/internal/services/submission_render_test.go b/internal/services/submission_render_test.go
index 75c1ff0..284d12a 100644
--- a/internal/services/submission_render_test.go
+++ b/internal/services/submission_render_test.go
@@ -273,15 +273,24 @@ func TestLegalSourcePretty(t *testing.T) {
 }
 
 // TestOurSideTranslations pins the our_side enum → DE/EN prose
-// mapping used by addProjectVars.
+// mapping used by addProjectVars. Post t-paliad-222: seven sub-role
+// values + the gender-neutral "-Seite" / "-Partei" suffix shape on
+// DE. Legacy 'court' / 'both' yield "" (the column no longer accepts
+// them after mig 112, but the function defensively handles stale
+// in-memory values from older callers).
 func TestOurSideTranslations(t *testing.T) {
 	cases := []struct {
 		in, wantDE, wantEN string
 	}{
-		{"claimant", "Klägerin", "Claimant"},
-		{"defendant", "Beklagte", "Defendant"},
-		{"court", "Gericht", "Court"},
-		{"both", "Klägerin und Beklagte", "Claimant and Defendant"},
+		{"claimant", "Klägerseite", "Claimant"},
+		{"defendant", "Beklagtenseite", "Defendant"},
+		{"applicant", "Antragstellerseite", "Applicant"},
+		{"appellant", "Berufungsklägerseite", "Appellant"},
+		{"respondent", "Antragsgegnerseite", "Respondent"},
+		{"third_party", "Drittpartei", "Third Party"},
+		{"other", "sonstige Verfahrensbeteiligte", "other party"},
+		{"court", "", ""},
+		{"both", "", ""},
 		{"", "", ""},
 		{"unknown", "", ""},
 	}
diff --git a/internal/services/submission_vars.go b/internal/services/submission_vars.go
index 748a4e4..6444e07 100644
--- a/internal/services/submission_vars.go
+++ b/internal/services/submission_vars.go
@@ -262,6 +262,11 @@ func addUserVars(bag PlaceholderMap, u *models.User) {
 func addProjectVars(bag PlaceholderMap, p *models.Project, pt *models.ProceedingType, lang string) {
 	bag["project.title"] = p.Title
 	bag["project.reference"] = derefString(p.Reference)
+	// project.code is the auto-derived (or override) dotted project
+	// code computed by services.BuildProjectCode. Populated upstream
+	// by the service projection; templates that want the explicit
+	// override should read project.reference instead.
+	bag["project.code"] = p.Code
 	bag["project.case_number"] = derefString(p.CaseNumber)
 	bag["project.court"] = derefString(p.Court)
 	bag["project.patent_number"] = derefString(p.PatentNumber)
@@ -388,16 +393,29 @@ func formatDatePtr(t *time.Time, layout string) string {
 }
 
 // ourSideDE returns the German legal-prose form of an our_side value.
+//
+// t-paliad-222: unified on the gender-neutral "-Seite" / "-Partei"
+// suffix shape to match the form labels and to avoid implying the
+// firm represents a single (female) natural person — a B2B patent
+// practice almost always represents companies. The seven sub-roles
+// map onto the post-mig-110 schema; legacy 'court' / 'both' no
+// longer exist in the column.
 func ourSideDE(side string) string {
 	switch strings.ToLower(side) {
 	case "claimant":
-		return "Klägerin"
+		return "Klägerseite"
 	case "defendant":
-		return "Beklagte"
-	case "court":
-		return "Gericht"
-	case "both":
-		return "Klägerin und Beklagte"
+		return "Beklagtenseite"
+	case "applicant":
+		return "Antragstellerseite"
+	case "appellant":
+		return "Berufungsklägerseite"
+	case "respondent":
+		return "Antragsgegnerseite"
+	case "third_party":
+		return "Drittpartei"
+	case "other":
+		return "sonstige Verfahrensbeteiligte"
 	}
 	return ""
 }
@@ -409,10 +427,16 @@ func ourSideEN(side string) string {
 		return "Claimant"
 	case "defendant":
 		return "Defendant"
-	case "court":
-		return "Court"
-	case "both":
-		return "Claimant and Defendant"
+	case "applicant":
+		return "Applicant"
+	case "appellant":
+		return "Appellant"
+	case "respondent":
+		return "Respondent"
+	case "third_party":
+		return "Third Party"
+	case "other":
+		return "other party"
 	}
 	return ""
 }