feat(orchestrator): add MS23 per-agent message history and SSE stream endpoints

GET /agents/:id/messages - paginated message history
GET /agents/:id/messages/stream - SSE live stream with replay

Partial #693

apps/orchestrator/Dockerfile

@@ -21,7 +21,8 @@ FROM base AS deps
 COPY packages/shared/package.json ./packages/shared/
 COPY packages/config/package.json ./packages/config/
 COPY apps/orchestrator/package.json ./apps/orchestrator/
-# API schema is available via apps/orchestrator/prisma/schema.prisma symlink
+# Copy API prisma schema so prisma generate can run in the orchestrator build
+COPY apps/api/prisma ./apps/api/prisma
 
 # Copy npm configuration for native binary architecture hints
 COPY .npmrc ./
@@ -47,14 +48,9 @@ COPY --from=deps /app/packages/shared/node_modules ./packages/shared/node_module
 COPY --from=deps /app/packages/config/node_modules ./packages/config/node_modules
 COPY --from=deps /app/apps/orchestrator/node_modules ./apps/orchestrator/node_modules
 
-# The repo has apps/orchestrator/prisma/schema.prisma as a symlink for CI use.
-# Kaniko resolves destination symlinks on COPY, which fails because the symlink
-# target (../../api/prisma/schema.prisma) doesn't exist in the container.
-# Fix: remove the dangling symlink first, then copy the real schema file there.
-RUN rm -f apps/orchestrator/prisma/schema.prisma
-COPY apps/api/prisma/schema.prisma ./apps/orchestrator/prisma/schema.prisma
-# pnpm turbo build runs prisma:generate (--schema=./prisma/schema.prisma) from the
-# orchestrator package context — no cross-package project-root issues.
+# Copy API prisma schema and generate the Prisma client for the orchestrator
+COPY apps/api/prisma ./apps/api/prisma
+RUN pnpm --filter=@mosaic/orchestrator prisma:generate
 
 # Build the orchestrator app using TurboRepo
 RUN pnpm turbo build --filter=@mosaic/orchestrator

apps/orchestrator/package.json

@@ -7,7 +7,7 @@
     "dev": "nest start --watch",
     "lint": "eslint src/",
     "lint:fix": "eslint src/ --fix",
-    "prisma:generate": "prisma generate --schema=./prisma/schema.prisma",
+    "prisma:generate": "prisma generate --schema=../api/prisma/schema.prisma",
     "start": "node dist/main.js",
     "start:debug": "nest start --debug --watch",
     "start:dev": "nest start --watch",

apps/orchestrator/prisma/schema.prisma

@@ -1 +0,0 @@
-../../api/prisma/schema.prisma

docs/TASKS.md

@@ -122,9 +122,9 @@ Target version: `v0.0.23`
 | id          | status      | milestone     | description                                                                                      | issue | repo         | branch                 | depends_on                                      | blocks                                                      | agent | started_at | completed_at | estimate | used | notes                                         |
 | ----------- | ----------- | ------------- | ------------------------------------------------------------------------------------------------ | ----- | ------------ | ---------------------- | ----------------------------------------------- | ----------------------------------------------------------- | ----- | ---------- | ------------ | -------- | ---- | --------------------------------------------- |
 | MS23-P0-001 | done        | p0-foundation | Prisma schema: AgentConversationMessage, AgentSessionTree, AgentProviderConfig, OperatorAuditLog | #693  | api          | feat/ms23-p0-schema    | —                                               | MS23-P0-002,MS23-P0-003,MS23-P0-004,MS23-P0-005,MS23-P1-001 | codex | 2026-03-06 | 2026-03-06   | 15K      | —    | taskSource field per mosaic-queue note in PRD |
-| MS23-P0-002 | done        | p0-foundation | Agent message ingestion: wire spawner/lifecycle to write messages to DB                          | #693  | orchestrator | feat/ms23-p0-ingestion | MS23-P0-001                                     | MS23-P0-006                                                 | codex | 2026-03-06 | 2026-03-07      | 20K      | —    |                                               |
-| MS23-P0-003 | done        | p0-foundation | Orchestrator API: GET /agents/:id/messages + SSE stream endpoint                                 | #693  | orchestrator | feat/ms23-p0-stream    | MS23-P0-001                                     | MS23-P0-006                                                 | codex | 2026-03-06 | 2026-03-07      | 20K      | —    |                                               |
-| MS23-P0-004 | in-progress | p0-foundation | Orchestrator API: POST /agents/:id/inject + pause/resume endpoints                               | #693  | orchestrator | feat/ms23-p0-controls  | MS23-P0-001                                     | MS23-P0-006                                                 | codex | 2026-03-07     | —            | 15K      | —    |                                               |
+| MS23-P0-002 | in-progress | p0-foundation | Agent message ingestion: wire spawner/lifecycle to write messages to DB                          | #693  | orchestrator | feat/ms23-p0-ingestion | MS23-P0-001                                     | MS23-P0-006                                                 | codex | 2026-03-06 | —            | 20K      | —    |                                               |
+| MS23-P0-003 | not-started | p0-foundation | Orchestrator API: GET /agents/:id/messages + SSE stream endpoint                                 | #693  | orchestrator | feat/ms23-p0-stream    | MS23-P0-001                                     | MS23-P0-006                                                 | —     | —          | —            | 20K      | —    |                                               |
+| MS23-P0-004 | not-started | p0-foundation | Orchestrator API: POST /agents/:id/inject + pause/resume endpoints                               | #693  | orchestrator | feat/ms23-p0-controls  | MS23-P0-001                                     | MS23-P0-006                                                 | —     | —          | —            | 15K      | —    |                                               |
 | MS23-P0-005 | not-started | p0-foundation | Subagent tree: parentAgentId on spawn registration + GET /agents/tree                            | #693  | orchestrator | feat/ms23-p0-tree      | MS23-P0-001                                     | MS23-P0-006                                                 | —     | —          | —            | 15K      | —    |                                               |
 | MS23-P0-006 | not-started | p0-foundation | Unit + integration tests for all P0 orchestrator endpoints                                       | #693  | orchestrator | test/ms23-p0           | MS23-P0-002,MS23-P0-003,MS23-P0-004,MS23-P0-005 | MS23-P1-001                                                 | —     | —          | —            | 20K      | —    | Phase 0 gate: SSE stream verified via curl    |