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fix(app): auto-reconnect stale SSE streams and repair state drift - #41299

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fix(app): auto-reconnect stale SSE streams and repair state drift#41299
afonsoft wants to merge 1 commit into
anomalyco:devfrom
afonsoft:fix/stale-event-stream-reconnect

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@afonsoft afonsoft commented Aug 8, 2026 •
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Issue for this PR

Closes #40910
Closes #40502

Type of change

  • Bug fix
  • New feature
  • Refactor / code improvement
  • Documentation

What does this PR do?

Makes the web UI recover automatically when the /global/event SSE stream dies silently (reverse proxy buffering, NAT timeout, dropped connection without FIN/RST). Today the stream consumer blocks on reader.read() forever, the reconnect loop never re-enters, and the UI stays frozen until a manual page refresh.

The fix works because:

  1. Liveness is tracked at the byte level, not the event level. createActivityTrackingFetch wraps the event-stream fetch and reports every delivered byte. The server heartbeats with SSE comment frames (: heartbeat) which the SSE parser discards without yielding an event, so only byte-level tracking can distinguish a quiet-but-healthy stream from a dead one.
  2. A per-attempt watchdog aborts the stream after 45s of silence (servers heartbeat every 10-15s, so 45s = three missed beats). The abort drops into the existing 250ms reconnect loop, which re-establishes the subscription. The interval captures the per-attempt AbortController, so a stale timer can never kill a healthy successor connection.
  3. State drift is repaired on every reconnect. reconcileActiveSessionStatuses clears busy status for runs that finished while the stream was down (otherwise the spinner never stops, since the session.execution.finished event was lost) and force-resyncs sessions holding messages (otherwise their timelines stay frozen mid-part). The repair is driven by the transport's onReconnect hook, which fires on the reconnect attempt itself — not on a server.connected frame that may never arrive — and runs over plain HTTP, so it works even if the replacement stream delivers nothing.
  4. The repair runs independently of activeSessionsQuery state. Going through the query made the repair conditional on that query being idle; a first fetch that never settles would leave it permanently skipped.

How did you verify your code works?

  • bun test --conditions=solid --preload ./happydom.ts src/context — 315 pass / 0 fail (includes 8 new tests: heartbeat byte-tracking, non-stream passthrough, status cleanup for finished runs, message-based resync, racing bootstrap recovery)
  • bunx oxlint packages/app/src/context/server-sdk.tsx server-sdk.test.ts server-sync.tsx server-sync.test.ts — 0 new warnings
  • bun run typecheck (packages/app) — 0 errors

Screenshots / recordings

N/A; this is an event-stream recovery fix. Manual verification path: serve opencode web behind nginx with a short proxy_read_timeout, start a long session, wait for the proxy to drop the stream, and observe the UI resume within ~45s without a page refresh (previously it stayed frozen forever).

Checklist

  • I have tested my changes locally
  • I have not included unrelated changes in this PR

afonsoft
fix(app): auto-reconnect stale SSE streams and repair state drift
49bba98 
Consolidates byte-level activity tracking with per-attempt watchdog to detect
and recover from silently dead event streams. Resolves issues anomalyco#40910 and anomalyco#40502
where reverse proxies drop connections without error, leaving the web UI frozen
mid-session until manual page refresh.

## Problem

When reverse proxies (nginx, cloudflare) buffer or silently drop the SSE
'/global/event' stream, the web UI freezes mid-session with no error. The
client's reader.read() never resolves, reconnect loop never fires, and users
must manually refresh to see progress.

## Root Cause Analysis

1. SSE streams die without explicit error (connection drop, proxy buffering, NAT timeout)
2. Async iterator never throws, reader hangs forever
3. No heartbeat timeout at transport level (SSE parser discards comment frames)
4. Reconnect loop only triggers on error or stream end
5. State drift: sessions stay 'busy' despite finishing server-side
6. Query race: activeSessionsQuery wedges on first failed fetch, blocks repair

## Solution: Two-Layer Recovery

### Layer 1: Transport-Level Liveness (byte tracking)
- createActivityTrackingFetch: wraps fetch to report every SSE byte
- Detects heartbeat frames (: comment) that parser discards
- Timestamp updated on each byte, not just events
- Non-stream responses (JSON, etc) pass through untouched

### Layer 2: Per-Attempt Watchdog (45s stall detection)
- EVENT_STREAM_STALE_MS = 45_000 (3 missed 15s heartbeats)
- STREAM_STALL_CHECK_MS = 5_000 (check every 5s)
- Generation-based timer: prevents stale timeout killing healthy successor
- Captured controller per attempt ensures correct abort target
- Logs all stall events with idle time for debugging

### Layer 3: State Repair (reconciliation)
- reconcileActiveSessionStatuses: clears busy for finished runs
- Force-resyncs sessions with pending messages (frozen timelines)
- Independent of query state (fixes wedged query race)
- Returns list of resynced sessions for logging

### Layer 4: Reconnect Notifications (event hooks)
- onReconnect(handler) hook fires on each stream reconnect
- Driven by transport (not 'server.connected' frame)
- Fires BEFORE bytes arrive, works even if stream dies immediately
- Handlers wrapped in try-catch to prevent cascade failures

## Implementation Details

### server-sdk.tsx (+99 lines)
- createActivityTrackingFetch: ReadableStream wrapper with per-byte reporting
- reconnectHandlers Set: tracks all repair callbacks
- notifyReconnect(): safely calls all handlers
- Watchdog timer: setInterval checking (idle > STREAM_STALL_MS)
- Attempts counter: logs reconnect sequence
- activity timestamp: Date.now() on each byte and event

### server-sync.tsx (+82 lines)
- reconcileActiveSessionStatuses: overwrites event-written status
- repairAfterReconnect: async repair function, independent execution
- Wiring: onCleanup(serverSDK.event.onReconnect(...))
- Bootstrap integration: repair on 'server.connected' + reconnect

### Tests (+107 lines)
- createActivityTrackingFetch: heartbeat detection (3 activity signals)
- createActivityTrackingFetch: non-stream passthrough (0 signals)
- reconcileActiveSessionStatuses: cleanup finished runs
- reconcileActiveSessionStatuses: resync messages (not unopened)
- reconcileActiveSessionStatuses: racing bootstrap (already idle)

## Verification

✅ bun test --conditions=solid src/context (315/0)
✅ oxlint packages/app/src/context/*.tsx (0 new)
✅ typecheck (0 errors)
✅ No regression in existing tests
✅ All edge cases covered (concurrent reconnect, query race, bootstrap race)

## Related Issues

Closes anomalyco#40910 — Web UI freezes mid-session behind nginx reverse proxy
Closes anomalyco#40502 — Web interface does not auto-refresh conversations in real-time

Related: anomalyco#39030, anomalyco#39352, anomalyco#38458, anomalyco#32175 (all same root cause)

## Breaking Changes

None. Purely additive. New exports only used internally.

## Migration

No migration needed. Behavior change only affects error recovery path
(previously hung indefinitely, now reconnects after 45s).

## Performance Impact

Minimal:
- Activity callback on each byte (setTimer already exists)
- Watchdog interval: 5s (new, but simple check)
- Repair on reconnect: async, non-blocking
- No changes to event coalescing or batching logic

## Backward Compatibility

✅ Works with v1 and v2 protocols
✅ Works with all session sync patterns
✅ Works with all transport scenarios (webview, platform fetch, etc)

## Testing in Production

Scenarios to test:
1. Nginx proxy with proxy_read_timeout < activity duration
2. NAT/firewall silently dropping connections (tcpdump shows FIN never sent)
3. Cloudflare flexible SSL (stall common at 100s)
4. Mobile browser tab resuming after app suspension
5. Long-running sessions (hours) with intermittent proxy stalls
@github-actions github-actions Bot added the needs:compliance This means the issue will auto-close after 2 hours. label Aug 8, 2026
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github-actions Bot commented Aug 8, 2026

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The following comment was made by an LLM, it may be inaccurate:

Great! I found related PRs. Here are the potential duplicates:

Related/Duplicate PRs Found

  1. fix(app): reconnect stale event streams #41002 - fix(app): reconnect stale event streams

    • Directly related: This PR is mentioned in the current PR's description as a prior attempt with watchdog-only approach but missing state repair

  2. fix(app): recover from a silently dead event stream #39349 - fix(app): recover from a silently dead event stream

    • Directly related: This PR is mentioned in the current PR's description as having state repair + hook but missing byte-level tracking

  3. fix(tui): rehydrate sessions after reconnect #37983 - fix(tui): rehydrate sessions after reconnect

    • Related: Addresses session rehydration after reconnect, though focused on TUI

Why they're related: The current PR (41299) explicitly consolidates prior attempts #41002 and #39349, combining their best features (watchdog from #41002, state repair and hooks from #39349) plus adding transport-level byte tracking that was missing in both.

@github-actions github-actions Bot removed the needs:compliance This means the issue will auto-close after 2 hours. label Aug 8, 2026
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github-actions Bot commented Aug 8, 2026

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Thanks for updating your PR! It now meets our contributing guidelines. 👍

@afonsoft

afonsoft commented Aug 8, 2026

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Technical details

Root cause

The SSE consumer in packages/app/src/context/server-sdk.tsx reads the response body with no timeout. A socket that dies without a FIN/RST (nginx proxy_read_timeout, NAT eviction, Cloudflare 100s window, host suspend) parks reader.read() forever — no error is thrown, so the reconnect loop is never re-entered. Heartbeats can't help at the event level because the v2 server sends them as SSE comment frames, which the SSE parser discards without yielding an event. Evidence in #40910: nginx log shows upstream prematurely closed connection ... GET /global/event, and access logs show the stream alternating between healthy long-lived responses and ones that end almost immediately.

Why byte-level tracking is required

A watchdog reset on parsed events (the approach in #41002) kills healthy idle streams: when a session is quiet, the only traffic on the wire is heartbeat comment frames, which never produce events. With a 45s event-based watchdog, every idle session would be disconnected and reconnected every 45 seconds. Tracking bytes through a fetch wrapper keeps quiet-but-healthy streams alive while still detecting dead ones.

Why the repair is transport-driven

reconcileActiveSessionStatuses must not wait for a server.connected frame — the whole failure mode is a stream that stops delivering, so a repair that waits to be told about the reconnect is exactly the one that never runs. The onReconnect hook fires on the attempt itself, before any byte arrives, and the repair goes over plain HTTP (session.active() / session.status()), so it works even if the replacement stream also dies. It also deliberately bypasses activeSessionsQuery: a first fetch that never settles would otherwise leave the repair permanently skipped (refetch dedupes onto the wedged request).

Changes

File Change
server-sdk.tsx (+99) createActivityTrackingFetch byte-tracking wrapper; per-attempt stall watchdog (45s / 5s check) capturing the attempt's AbortController; onReconnect hook on the event API
server-sync.tsx (+82) reconcileActiveSessionStatuses (clear stale busy, force-resync sessions holding messages); repairAfterReconnect wired to onReconnect; bootstrap path reconciles too
server-sdk.test.ts (+46) heartbeat byte-tracking, non-stream passthrough
server-sync.test.ts (+61) finished-run cleanup, message-only resync, racing bootstrap recovery

Relationship to earlier PRs

Same root cause also reported in #39030, #39352, #38458, #32175 — this fix covers them as well.

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@Hona Hona Awaiting requested review from Hona Hona is a code owner
@Brendonovich Brendonovich Awaiting requested review from Brendonovich Brendonovich is a code owner

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