Codewalkers/.planning/phases/20-real-time-subscriptions/20-01-SUMMARY.md

phase, plan, subsystem, tags, requires, provides, affects, tech-stack, key-files, key-decisions, patterns-established, duration, completed

phase	plan	subsystem	tags	requires	provides	affects	tech-stack	key-files	key-decisions	patterns-established	duration	completed
20-real-time-subscriptions	01	api	trpc sse subscriptions async-generators streaming event-bus	phase provides 01.1-hexagonal-events EventBus port interface and EventEmitterBus adapter phase provides 16-frontend-scaffold tRPC HTTP adapter and Vite proxy configuration	SSE streaming support in tRPC HTTP adapter Three subscription procedures (onEvent, onAgentUpdate, onTaskUpdate) EventBus-to-async-generator bridge (eventBusIterable helper) SubscriptionEvent type in shared package for frontend consumption	20-02-frontend-subscriptions 21-frontend-polish	added patterns queue-based async generator for event bridge tracked SSE for reconnection	created modified src/trpc/subscriptions.ts src/server/trpc-adapter.ts src/trpc/router.ts packages/shared/src/types.ts packages/shared/src/index.ts	Queue + deferred promise pattern for bridging push (EventBus) to pull (async generator) tracked() wrapper on each event for client-side reconnection via lastEventId Fallback AbortSignal when opts.signal is undefined (AbortController().signal) Vite proxy works for SSE without changes (http-proxy streams by default)	eventBusIterable: Reusable async generator factory for any subset of EventBus events Subscription procedure pattern: input with optional lastEventId, yield* from eventBusIterable	4min	2026-02-04

Plan 20-01: SSE Streaming & Subscription Procedures Summary

tRPC SSE streaming via async generators bridging EventBus domain events to three subscription endpoints

Performance

• Duration: 4 min
• Started: 2026-02-04
• Completed: 2026-02-04
• Tasks: 2
• Files modified: 5

Accomplishments

• Fixed tRPC HTTP adapter to stream ReadableStream responses instead of buffering (required for SSE)
• Created subscriptions module with queue-based async generator bridging EventBus to tRPC subscriptions
• Added onEvent, onAgentUpdate, and onTaskUpdate subscription procedures to the router
• Exported SubscriptionEvent type from shared package for frontend consumption

Task Commits

Each task was committed atomically:

1. Task 1: Fix HTTP adapter for SSE streaming and add subscription procedures - e5d8dbb (feat)
2. Task 2: Update shared types and verify SSE integration - 42154d6 (feat)

Files Created/Modified

• src/trpc/subscriptions.ts - EventBus-to-async-generator bridge with tracked SSE events
• src/server/trpc-adapter.ts - Stream ReadableStream responses instead of buffering
• src/trpc/router.ts - Three subscription procedures (onEvent, onAgentUpdate, onTaskUpdate)
• packages/shared/src/types.ts - SubscriptionEvent interface for frontend
• packages/shared/src/index.ts - Re-export SubscriptionEvent

Decisions Made

• 20-01: Queue + deferred promise pattern for bridging push (EventBus) to pull (async generator)
• 20-01: tracked() wrapper on each event for client-side reconnection via lastEventId
• 20-01: Fallback AbortSignal (new AbortController().signal) when opts.signal is undefined
• 20-01: Vite proxy works for SSE without changes (http-proxy streams chunked responses by default)

Deviations from Plan

Auto-fixed Issues

1. [Rule 3 - Blocking] TrackedEnvelope type annotation

• Found during: Task 1 (subscriptions module)
• Issue: ReturnType<typeof tracked<string, SubscriptionEventData>> is invalid TS — generic type inference on typeof of a generic function doesn't work
• Fix: Import TrackedEnvelope type directly from @trpc/server and use TrackedEnvelope<SubscriptionEventData> as return type
• Files modified: src/trpc/subscriptions.ts
• Verification: npm run build succeeds
• Committed in: e5d8dbb (Task 1 commit)

2. [Rule 3 - Blocking] opts.signal potentially undefined

• Found during: Task 1 (subscription procedures)
• Issue: opts.signal has type AbortSignal | undefined in tRPC subscription context, but eventBusIterable requires AbortSignal
• Fix: Fallback to new AbortController().signal when opts.signal is undefined
• Files modified: src/trpc/router.ts
• Verification: npm run build succeeds
• Committed in: e5d8dbb (Task 1 commit)

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Total deviations: 2 auto-fixed (2 blocking) Impact on plan: Both auto-fixes necessary for type safety. No scope creep.

Issues Encountered

None

User Setup Required

None - no external service configuration required.

Next Phase Readiness

• Backend SSE streaming ready for frontend consumption
• Plan 20-02 can add httpSubscriptionLink to the tRPC client and wire subscription hooks
• All existing queries/mutations verified working (452 tests pass)

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Phase: 20-real-time-subscriptions Completed: 2026-02-04