docs: agent platform architecture plan — augmentation + task breakdown (#173)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

docs/plans/task-queue-unification.md

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+# Task Queue Unification — @mosaic/queue as Unified Orchestration Layer
+
+> **Status:** Stub — deferred. Referenced from `2026-03-15-agent-platform-architecture.md` (Task Queue & Orchestration section).
+> Implement after Workspaces (P8-015) is complete. Requires workspace file structure to be in place.
+
+**Date:** 2026-03-15
+**Packages:** `packages/queue`, `packages/coord`, `packages/db`, `apps/gateway`
+
+---
+
+## Problem Statement
+
+Two disconnected task systems exist:
+
+1. **`@mosaic/coord`** — file-based missions (`mission.json`, `TASKS.md`), file locks, subprocess spawning. Single-machine orchestrator pattern.
+2. **PG tables** (`tasks`, `mission_tasks`, `missions`) — DB-backed CRUD, REST API, Brain repos.
+
+An agent using `coord_mission_status` gets file data. The dashboard shows DB data. They are never in sync.
+
+---
+
+## Vision
+
+`@mosaic/queue` becomes the unified task orchestration service bridging PG, workspace files, and Valkey:
+
+- DB is source of truth for structured state (status, assignees, timestamps)
+- Workspace files (`TASKS.md`, PRDs) are working copies for agent interaction
+- Valkey handles real-time assignment queues and agent claim locks
+- Flatfile fallback for no-DB single-machine deployments (preserves `@mosaic/coord` pattern)
+
+---
+
+## Scope (To Be Designed)
+
+- [ ] `@mosaic/queue` refactor — elevate from ioredis primitive to task orchestration service
+- [ ] DB ↔ file sync layer — writes to PG propagate to `TASKS.md`; file edits by agents sync back
+- [ ] Task assignment queue — Valkey-backed RPUSH/BLPOP for agent task claiming
+- [ ] Agent claim locks — `mosaic:queue:project:{id}:lock:{taskId}` with TTL
+- [ ] `@mosaic/coord` consolidation — file-based ops ported into queue service; `@mosaic/coord` becomes thin adapter or deprecated
+- [ ] Flatfile fallback — queue service writes JSON manifests when PG unavailable
+- [ ] Status pub/sub — real-time task status updates via Valkey pub/sub
+- [ ] Dependency resolution — block task assignment until dependencies are met
+- [ ] Orchestrator monitor — gateway process watches task queue, assigns next based on dependency graph
+- [ ] API surface — queue service exposes typed interface used by agents, gateway, and CLI
+
+---
+
+## Dependencies
+
+- Workspaces (P8-015) — file sync targets the workspace directory structure
+- Teams architecture (P8-007) — project ownership determines queue namespacing
+- DB schema stable — task/mission tables must not change mid-unification
+
+---
+
+## References
+
+- Original design context: `docs/plans/2026-03-15-agent-platform-architecture.md` → "Task Queue & Orchestration" section
+- Current `@mosaic/coord` implementation: `packages/coord/src/`
+- Current `@mosaic/queue` implementation: `packages/queue/src/`