feat(#462): add federation capabilities verb (#674)

docs/scratchpads/FED-M3-07-capabilities.md

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+# FED-M3-07 — Capabilities Verb Scratchpad
+
+## Objective
+
+Implement `GET /api/federation/v1/capabilities` in `apps/gateway/src/federation/server/verbs/capabilities.controller.ts`.
+
+## Scope
+
+- Add read-only capabilities controller under federation server verbs.
+- Use `FederationAuthGuard` only; active grant is sufficient and no native RBAC/scope-service eval runs.
+- Response shape: `{ resources, excluded_resources, max_rows_per_query, supported_verbs }` derived from grant scope.
+- Register controller in `FederationModule`.
+- Unit-test happy path, defaults, no-context guard seam, and invalid scope handling.
+
+## Constraints / assumptions
+
+- Issue: #462.
+- Branch: `feat/federation-m3-verb-capabilities` from `origin/main` (`3eeed04e`).
+- Depends on M3-03 auth guard; guard attaches `request.federationContext.scope` after active-grant validation.
+- ASSUMPTION: `supported_verbs` is the M3 verb set from `@mosaicstack/types` (`list`, `get`, `capabilities`).
+- ASSUMPTION: `filters`/`rate_limit` are intentionally omitted for FED-M3-07 because the card’s response shape lists only the four required fields.
+- Budget: no explicit hard cap from orchestrator; working cap ~4K-8K tokens for card implementation + tests + PR cycle.
+
+## Plan
+
+1. Write controller unit tests first.
+2. Implement controller and module registration.
+3. Run scoped tests + typecheck/lint/format.
+4. Run Codex code/security review and remediate.
+5. Commit, queue guard, push, PR via wrapper.
+
+## Progress
+
+- 2026-06-24: Intake complete; fresh worktree created from origin/main.
+- 2026-06-24: Added `CapabilitiesController`, registered it in `FederationModule`, and added 5 unit tests.
+- 2026-06-24: Code/security reviews passed with no findings.
+
+## Tests run
+
+- `pnpm --filter @mosaicstack/gateway test -- capabilities.controller.spec.ts` — PASS (5 tests).
+- `pnpm --filter @mosaicstack/gateway typecheck` — PASS.
+- `pnpm --filter @mosaicstack/gateway lint` — PASS.
+- `pnpm format:check` — PASS.
+- `pnpm typecheck` — PASS (41/41 turbo tasks).
+- `pnpm lint` — PASS (23/23 turbo tasks).
+- `pnpm test` — FAIL in pre-existing/live-DB integration suite: `apps/gateway/src/__tests__/cross-user-isolation.test.ts` cleanup hit PostgreSQL connection/schema state for the `messages` table. Changed capabilities tests passed; failure is outside FED-M3-07 surface. No `fleet-personas.spec` flake encountered.
+
+## Review evidence
+
+- `~/.config/mosaic/tools/codex/codex-code-review.sh --uncommitted` — PASS/approve, no findings.
+- `~/.config/mosaic/tools/codex/codex-security-review.sh --uncommitted` — PASS, risk level none, no findings.
+
+## Risks / blockers
+
+- Full repo `pnpm test` may hit known `fleet-personas.spec` flake per orchestrator; ignore that specific flake if encountered.
+- Previous card saw local DB schema issue in `cross-user-isolation.test.ts`; scoped capabilities tests should be authoritative for this surface.
+
+## Acceptance evidence mapping
+
+| Acceptance criterion                                                       | Evidence                                                                                                                   |
+| -------------------------------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------- |
+| GET `/api/federation/v1/capabilities` exists                               | Route metadata test in `capabilities.controller.spec.ts`; scoped test PASS                                                 |
+| Uses active-grant auth guard and no RBAC eval                              | Guard metadata test confirms only `FederationAuthGuard`; controller has no service injections/RBAC calls; scoped test PASS |
+| Response enumerates resources/excluded/max rows/supported verbs from scope | Happy-path/default scope tests + response schema parse; scoped test PASS                                                   |
+| Read-only/no persistence side effects                                      | Controller only parses request `federationContext.scope` and returns a DTO; no DB/service dependency; code review PASS     |