docs: augment agent platform architecture plan + task breakdown

- Augmented 2026-03-15-agent-platform-architecture.md with 6 missing
  sections: Teams Architecture, REST Route Specifications, /provider
  OAuth flow (URL+clipboard), preferences mutable migration, Test
  Strategy (per-task), and Phase Execution Order (wave plan)
- Created spin-off plan stubs: gatekeeper-service.md,
  task-queue-unification.md, chroot-sandboxing.md
- Added P8-007 through P8-019 to TASKS.md (13 new tasks)
- Created Gitea issues #160-#172, Phase 8 milestone ms-165
- Updated MISSION-MANIFEST.md (Phase 8 in-progress)
- Updated scratchpad with session 14 decisions

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/scratchpads/mvp-20260312.md

@@ -238,3 +238,31 @@ Issues closed: #52, #55, #57, #58, #120-#134
 - TUI: --agent and --project flags, agent name display in top bar, agentId in socket payload.
 - Types: agentId added to ChatMessagePayload.
 - Tests: 23/23 gateway tests pass (updated ownership test for user-scoped missions).
+
+### Session 14 — Platform Architecture Plan Augmentation + Task Breakdown
+
+| Session | Date       | Milestone | Tasks Done | Outcome                                                       |
+| ------- | ---------- | --------- | ---------- | ------------------------------------------------------------- |
+| 14      | 2026-03-15 | Phase 8   | P8-018     | Augmented plan, created 13 issues, created Phase 8 milestone. |
+
+**Decisions made:**
+
+- This plan is Phase 7 feature extension work, not Phase 8 beta scope. P8-001–P8-004 (SSO, LLM, perf, release gate) are deferred to far future.
+- `/provider` OAuth in TUI: URL-to-clipboard + Valkey poll token pattern (same as Pi agent)
+- Add `mutable` column to preferences now (P8-007 DB migration)
+- Teams architecture: `teams` + `team_members` tables, `teamId`/`ownerType` on projects. Workspace path branches on owner type: `users/<uid>/` vs `teams/<tid>/`.
+- Phase dependency chain decided: Wave 1 (DB+Types) → Wave 2 (TUI+toolhardening) → Wave 3 (gateway registry, gating) → Wave 4 (prefs+commands) → Wave 5 (reload+GC) → Wave 6 (workspaces) → Wave 7 (autocomplete) → Wave 8 (verify).
+
+**Plan augmentations added:**
+
+- Teams Architecture section (DB schema, workspace paths, RBAC)
+- REST Route Specifications table
+- `/provider` OAuth flow (URL+clipboard+polling)
+- Preferences `mutable` migration spec
+- Test Strategy (per-task test files + key test cases)
+- Phase Execution Order (dependency graph + wave plan)
+
+**Issues created:** #160–#172 (Gitea milestone ms-165)
+**P8-018 closed:** Spin-off stubs created (gatekeeper-service.md, task-queue-unification.md, chroot-sandboxing.md)
+
+**Next:** Begin execution at Wave 1 — P8-007 (DB migrations) + P8-008 (Types) in parallel.