SSE client disconnects and never reconnects — UI goes blank

[neocody]

Summary

CodeNomad UI goes completely blank/white intermittently. All workspace instances show "Instance Disconnected". Requires manually closing tabs or restarting the app to recover.

Environment

• CodeNomad: 0.11.5-dev-20260228-482313f6 (also reproduced on stable 0.11.4)
• OpenCode: 1.2.18
• macOS: 15.7.4 (24G517), MacBookPro18,4 ARM64

Root Cause (from debug log)

The Electron renderer's SSE connection to the CodeNomad backend drops and never auto-reconnects:

Line 16:     {"level":20,"component":"sse","clientId":1,"msg":"SSE client connected"}
Line 179747: {"level":20,"component":"sse","clientId":1,"msg":"SSE client disconnected"}

After the disconnect:

• The backend continues running normally — workspace events keep publishing, plugin pongs continue, OpenCode serve processes stay alive
• But no new SSE client connects — there is no reconnection logic
• The UI receives no more events and goes blank

Evidence

• Only 1 SSE client connected for the entire session (clientId: 1)
• After disconnect, ~18,815 more log lines of workspace events published to nobody
• Zero errors/warnings in the log (all level 20 = DEBUG) — the disconnect is silent
• No crash report generated — the backend doesn't crash, it just loses its UI listener
• Separately, an EXC_BREAKPOINT (SIGTRAP) crash was observed in the Electron renderer's V8 garbage collector (CppHeap::CollectGarbageInYoungGenerationForTesting), which may be triggering the SSE disconnect

Related Crash Report

A macOS crash report was generated for CodeNomad Helper (Renderer):

Exception: EXC_BREAKPOINT (SIGTRAP)
Termination: Trace/BPT trap: 5
Faulting thread: 0
Stack: Electron Framework → CppHeap::CollectGarbageInYoungGenerationForTesting
       → TraceTraitFromInnerAddressImpl::GetTraceDescriptor
       → v8::PropertyDescriptor::set() const
       → v8::Value::IsFunction() const

Expected Behavior

• SSE client should auto-reconnect on disconnect with exponential backoff
• UI should show a "reconnecting..." indicator instead of going blank
• If reconnection fails after retries, UI should prompt to reload rather than staying blank

Steps to Reproduce

1. Open CodeNomad with multiple workspace tabs (3-5)
2. Use normally for an extended session
3. Eventually the UI goes blank across all tabs
4. Debug log shows SSE client disconnect with no reconnection attempt

Debug Log

Available on request (512KB, 198K lines, captured with --debug flag).

[neocody]

Update: After further investigation, the root cause is on the OpenCode side, not CodeNomad.

OpenCode's serve process closes the /event SSE endpoint after ~7 seconds:

service=server method=GET path=/event request
service=server status=started method=GET path=/event request
service=server status=completed duration=7171 method=GET path=/event request  ← server closes it

There are existing OpenCode issues tracking this:

• SSE event streams leak memory on client disconnect anomalyco/opencode#15645 — SSE event streams leak memory on client disconnect
• Server becomes unresponsive after external client disconnects during SSE streaming anomalyco/opencode#15149 — Server becomes unresponsive after external client disconnects during SSE streaming
• Memory leak: serve and web commands leak child processes on exit; SSE heartbeat interval leaks on server-initiated close anomalyco/opencode#14091 — serve command SSE heartbeat interval leaks on server-initiated close

That said, CodeNomad should still implement SSE reconnection logic as a resilience measure — when the SSE stream drops (for any reason), the UI should auto-reconnect rather than going blank.

[shantur]

It seems to me OpenCode process was crashed or in a weird state.

[VooDisss]

@shantur maybe bot could evaluate if CN really needs fixing? Here is context from my agent for evaluation:

---

Complete Root Cause Analysis with Exact File Locations

The Bug: Missing onclose Handler

Exact location: packages/ui/src/lib/api-client.ts:320-323

// Current code (LINES 320-323):
source.onerror = () => {
  sseLogger.warn("EventSource error, closing stream")
  onError?.()
}
// ❌ MISSING: source.onclose handler here

Problem: When the Electron renderer crashes, the browser's EventSource fires onclose (not onerror). The reconnection callback onError is only called from onerror, so scheduleReconnect() in server-events.ts is never triggered.

---

The Exists-But-Unreachable Reconnection Logic

Exact location: packages/ui/src/lib/server-events.ts:38-47

// This logic EXISTS but is UNREACHABLE:
private scheduleReconnect() {
  if (this.source) {
    this.source.close()
    this.source = null
  }
  logSse("Events stream disconnected, scheduling reconnect", { delayMs: this.retryDelay }) // ← Never logged!
  setTimeout(() => {
    this.retryDelay = Math.min(this.retryDelay * 2, RETRY_MAX_DELAY)
    this.connect()  // ← Never called
  }, this.retryDelay)
}

Evidence from issue: The debug log shows "SSE client disconnected" on the server side but the log message at line 43 ("Events stream disconnected, scheduling reconnect") never appears — proving the callback is never invoked.

---

The Call Chain (Why It's Broken)

1. api-client.ts:31 — Creates EventSource with callback to scheduleReconnect:

   this.source = serverApi.connectEvents((event) => this.dispatch(event), () => this.scheduleReconnect())

2. api-client.ts:320-322 — Only onerror calls the callback:

   source.onerror = () => {
     sseLogger.warn("EventSource error, closing stream")
     onError?.()  // ← Only fires on error, NOT on close
   }

3. When renderer crashes → EventSource fires onclose → onError callback never called → scheduleReconnect() never called

---

Fix 1: Add onclose Handler (Minimal Fix)

File: packages/ui/src/lib/api-client.ts
Lines to modify: 320-323

// AFTER (lines 320-326):
source.onerror = () => {
  sseLogger.warn("EventSource error")
  onError?.()
}
source.onclose = () => {           // ← ADD THIS BLOCK
  sseLogger.warn("EventSource closed")
  onError?.()
}
return source

---

Fix 2: Use ReadyState Check (More Robust)

File: packages/ui/src/lib/api-client.ts
Lines to modify: 320-323

// AFTER:
source.onerror = () => {
  // EventSource fires onerror for both errors AND closed states
  // Check readyState to determine if we should reconnect
  if (source.readyState === EventSource.CLOSED) {
    sseLogger.warn("EventSource closed (not error), triggering reconnect")
    onError?.()
  } else {
    sseLogger.warn("EventSource error")
    onError?.()
  }
}
return source

---

Why This Isn't Caught By Tests

Search confirms no SSE tests exist:

No files matching **/*sse*.test.ts

---

Additional Gap: No UI Reconnection Indicator

The reconnection logic in server-events.ts only logs — there's no:

• UI notification ("Reconnecting...")
• Retry counter exposed to UI
• Max retries before giving up

The issue states expected behavior includes:

"UI should show a 'reconnecting...' indicator instead of going blank"

---

Summary Table

File	Line	Current State	Fix
packages/ui/src/lib/api-client.ts	320-323	Only onerror handler	Add onclose handler or check readyState
packages/ui/src/lib/server-events.ts	43	Log exists but never fires	Works after fix #1
No UI indicator	-	Missing	Future enhancement

[shantur]

@neocody - Is this still an issue?