# Task 3 report — reconnect SSE on same-session Resume

## Status

Complete. A successful Resume of the currently active session now replaces its existing
`EventSource` connection. Resuming a different session continues to reconnect through the
session ID change only, without a generation-driven second connection.

## Implementation

- `useSessionStream` accepts an optional `generation` argument (default `0`) and includes it
  in the stream effect dependencies. A generation change therefore runs the existing cleanup,
  closes the old source, and opens the same URL again.
- `AppShell` captures whether the requested Resume ID is already active before its existing
  optimistic state updates. It increments the stream generation only after `resumeSession(id)`
  succeeds and only for that same-ID case.
- The existing optimistic session switch, phase refresh, and failed-Resume rollback remain
  unchanged. A failed POST cannot increment the generation.

## TDD evidence

- RED command:
  `cd frontend && npx vitest run src/stream/useSessionStream.test.tsx src/shell/AppShell.session-mgmt.test.tsx`
- RED result: 2 expected failures and 15 passes. The hook test observed
  `first.closed === false`; the AppShell test observed one `FakeEventSource` instead of two
  after the second same-ID Resume.
- GREEN focused result: the same command passed 2/2 files and 17/17 tests after the minimal
  production wiring.

## Full verification

- Baseline before edits: `cd frontend && npx vitest run` — 42/42 files and 251/251 tests passed.
- Focused tests: 2/2 files and 17/17 tests passed.
- Full frontend suite: `cd frontend && npx vitest run` — 42/42 files and 253/253 tests passed.
- Typecheck: `cd frontend && npx tsc -b` — exit 0.
- Production build: `cd frontend && npm run build` — exit 0; Vite transformed 4,835 modules
  and completed the production bundle.
- `git diff --check` — passed.

The suite and build retained the pre-existing MSW unhandled-request, React ref/`act`, Node type
stripping, and Vite chunk-size warnings. This task introduced no new warning category.

## Files

- `frontend/src/stream/useSessionStream.ts`
- `frontend/src/stream/useSessionStream.test.tsx`
- `frontend/src/shell/AppShell.tsx`
- `frontend/src/shell/AppShell.session-mgmt.test.tsx`
- `.superpowers/sdd/task-3-report.md`

## Self-review

- Confirmed the old EventSource is closed before the replacement is retained by React's effect
  lifecycle, and the replacement uses the identical session URL.
- Confirmed same-ID detection happens before the optimistic `setActiveSessionId(id)` call.
- Confirmed the generation increments only after a successful Resume POST; the catch/rollback
  branch is unchanged.
- Confirmed a different ID leaves the generation unchanged, so the existing session-ID effect
  change creates exactly one replacement connection.
- Confirmed the diff is frontend-only apart from this report and contains no backend, Docker,
  configuration, or session changes.

## Concerns

None.