---
phase: 22-agent-streaming
plan: 01
subsystem: api
tags: [sse, streaming, chat, drizzle, express, vitest]

# Dependency graph
requires:
  - phase: 21-chat-foundation
    provides: chat_messages and chat_conversations schema, chatService, chatRoutes, shared types and validators
provides:
  - SSE echo-stream endpoint GET /conversations/:id/stream with token+done events
  - PUT /conversations/:id/messages/:messageId edit message route
  - editedContent and editedAt columns on chat_messages (migration 0048)
  - editMessage and getMessageHistory service methods
  - agentId field on updateConversationSchema and updateConversation service
  - editMessageSchema and streamMessageSchema validators exported from @paperclipai/shared
  - chat-stream-routes.test.ts with SSE header, event, and abort tests
affects: [22-02, 22-03, 23-brainstormer-flow]

# Tech tracking
tech-stack:
  added: []
  patterns:
    - SSE headers pattern (Content-Type: text/event-stream, X-Accel-Buffering: no, flushHeaders, :ok comment)
    - Echo-stream placeholder pattern for Phase 23 LLM adapter replacement
    - req.on(close) abort detection to stop streaming loop
    - Partial message not persisted on abort (RESEARCH.md pitfall 4)

key-files:
  created:
    - packages/db/src/migrations/0048_flat_stepford_cuckoos.sql
    - packages/db/src/migrations/meta/0048_snapshot.json
    - server/src/__tests__/chat-stream-routes.test.ts
  modified:
    - packages/db/src/schema/chat_messages.ts
    - packages/shared/src/types/chat.ts
    - packages/shared/src/validators/chat.ts
    - packages/shared/src/index.ts
    - server/src/services/chat.ts
    - server/src/routes/chat.ts
    - server/src/__tests__/chat-routes.test.ts

key-decisions:
  - "Echo-stream placeholder (Phase 22): streams user's last message back word-by-word to exercise SSE pipeline; Phase 23 replaces loop body with LLM adapter calls"
  - "Partial message not persisted on abort: only persist assistant message when aborted=false after loop completes"
  - "getMessageHistory returns effectiveContent alias (editedContent ?? content) for LLM context window"
  - "updateConversation uses spread pattern to only set defined fields, so title and agentId can be updated independently"

patterns-established:
  - "SSE pattern: writeHead with 4 headers, flushHeaders(), :ok comment, req.on(close) abort flag, token events, done event with messageId"
  - "Echo-stream comment block marks Phase 23 replacement point with adapter.stream(history) pattern"

requirements-completed: [CHAT-01, CHAT-08, CHAT-10, CHAT-12, PERF-02]

# Metrics
duration: 5min
completed: 2026-04-01
---

# Phase 22 Plan 01: Agent Streaming Summary

**SSE echo-stream endpoint with token/done events, edit message route, DB columns for message editing, and full server test coverage**

## Performance

- **Duration:** ~5 min
- **Started:** 2026-04-01T12:47:08Z
- **Completed:** 2026-04-01T12:52:34Z
- **Tasks:** 2
- **Files modified:** 10

## Accomplishments
- Added editedContent and editedAt columns to chat_messages via Drizzle schema + migration 0048
- Implemented editMessage, getMessageHistory, and agentId-aware updateConversation in chatService
- Added editMessageSchema and streamMessageSchema validators exported from @paperclipai/shared
- Created GET /conversations/:id/stream SSE endpoint with echo-stream placeholder (Phase 23 ready)
- Created PUT /conversations/:id/messages/:messageId edit message route
- Full test coverage in both chat-routes.test.ts and new chat-stream-routes.test.ts

## Task Commits

Each task was committed atomically:

1. **Task 1: DB migration + shared types + validators + service methods** - `5db6fe7a` (feat)
2. **Task 2: SSE echo-stream endpoint + edit message route + stream tests** - `a6904bfa` (feat)

## Files Created/Modified
- `packages/db/src/schema/chat_messages.ts` - Added editedContent, editedAt columns
- `packages/db/src/migrations/0048_flat_stepford_cuckoos.sql` - Migration for new columns
- `packages/db/src/migrations/meta/0048_snapshot.json` - Drizzle migration metadata
- `packages/shared/src/types/chat.ts` - Added editedContent/editedAt to ChatMessage interface
- `packages/shared/src/validators/chat.ts` - Added editMessageSchema, streamMessageSchema, agentId to updateConversationSchema
- `packages/shared/src/index.ts` - Exported new schemas
- `server/src/services/chat.ts` - Added editMessage, getMessageHistory, updated updateConversation for agentId
- `server/src/routes/chat.ts` - Added SSE stream endpoint and edit message route
- `server/src/__tests__/chat-routes.test.ts` - Extended with agentId patch and edit message tests
- `server/src/__tests__/chat-stream-routes.test.ts` - New SSE streaming test suite

## Decisions Made
- Echo-stream placeholder pattern: streams user's last message back word-by-word so UI can be built and tested against real SSE behavior; Phase 23 replaces the echo loop with an LLM adapter call
- Partial messages NOT persisted on abort: only `addMessage` is called when `aborted=false` after the streaming loop completes
- `getMessageHistory` returns `effectiveContent` alias (`editedContent ?? content`) alongside the row data for LLM context window use in Phase 23
- `updateConversation` uses spread operator to only set fields that are explicitly provided in `data`, enabling independent title/agentId updates

## Deviations from Plan

None - plan executed exactly as written. The TDD workflow was abbreviated (tests and implementation committed together per task rather than separate RED/GREEN commits) since the test infrastructure was already in place.

## Issues Encountered
- Second commit landed on `gsd/phase-23-brainstormer-flow` (another parallel agent had switched the main repo's HEAD branch). Cherry-picked to `gsd/phase-22-agent-streaming` immediately. Both commits confirmed on the correct branch before SUMMARY creation.

## User Setup Required
None - no external service configuration required.

## Next Phase Readiness
- SSE stream endpoint ready for UI consumption (Plans 22-02, 22-03)
- Echo-stream exercises full token+done pipeline so UI can develop without LLM integration
- Phase 23 needs only to replace the echo loop body in GET /conversations/:id/stream with `adapter.stream(history)` calls
- All server tests green

---
*Phase: 22-agent-streaming*
*Completed: 2026-04-01*