AppendLogStore crashes session with 'storage.disk_full' ENOSPC when wire.jsonl append fails

Summary

AppendLogStore propagates a raw ENOSPC from FileStorageService.append straight up to the user as an unhandled StorageError, killing the session mid-tool-call instead of degrading gracefully.

Repro environment

• Kimi Code CLI (no auth / sign-in flow active)
• Local disk full (verified via df -h / → 100% use, 0 available on /dev/nvme0n1p4)
• Long-running session with multiple parallel subagents and many worktrees
• Triggered by the agent's tool subprocess writing to /home/wolf/.kimi-code/sessions/<session_id>/agents/main/wire.jsonl

Stack trace (verbatim)

[unexpected] StorageError: storage append failed: no space left on device
  at toStorageIoError (/home/runner/work/kimi-code/kimi-code/apps/kimi-code/dist-native/intermediates/main.cjs:229849:9)
  at FileStorageService.append (/home/runner/work/kimi-code/kimi-code/apps/kimi-code/dist-native/intermediates/main.cjs:234166:11)
  at async AppendLogStore.drain (/home/runner/work/kimi-code/kimi-code/apps/kimi-code/dist-native/intermediates/main.cjs:281837:6)
  at async AppendLogStore.finishOwnedFlush (/home/runner/work/kimi-code/kimi-code/apps/kimi-code/dist-native/intermediates/main.cjs:281818:5) {
  code: 'storage.disk_full',
  details: {
    path: '/home/wolf/.kimi-code/sessions/wd_moagan_5e37ed5db49d/session_2cd2367c-6894-4116-afb2-4714469526d1/agents/main/wire.jsonl',
    op: 'append',
    errno: 'ENOSPC'
  },
[cause]: Error: ENOSPC: no space left on device, write
  at async write (node:internal/fs/promises:745:8)
  at async writeFileHandle (node:internal/fs/promises:502:7)
  at async fsCall (node:internal/fs/promises:467:12)
  at async FileStorageService.append (/home/runner/work/kimi-code/kimi-code/apps/kimi-code/dist-native/intermediates/main.cjs:234159:31)
  at async AppendLogStore.drain (/home/runner/work/kimi-code/kimi-code/apps/kimi-code/dist-native/intermediates/main.cjs:281837:6)
  at async AppendLogStore.finishOwnedFlush (/home/runner/work/kimi-code/kimi-code/apps/kimi-code/dist-native/intermediates/main.cjs:281818:5) {
  errno: -28,
  code: 'ENOSPC',
  syscall: 'write'
  }
}

Expected behaviour

A disk-full error on the session wire log should be degraded, not fatal:

1. The agent should receive a structured error like StorageError with code: 'storage.disk_full' that surfaces the disk-full state to the user (clearly + actionable), but
2. The session runtime should:
   • Stop trying to append to wire.jsonl (don't retry indefinitely)
   • Switch the log store to a read-only or buffer-flushed mode
   • Allow the user to clean up disk and resume
   • NOT kill the subprocess that's mid-tool-call

Actual behaviour

The StorageError propagates up unhandled from AppendLogStore.drain → finishOwnedFlush and surfaces as an [unexpected] log line. The terminal UI then drops the user back to the auth gate ("You're not signed in. Sign up or leave feedback on GitHub") which is unrelated to the actual error — looks like a UX fallback when the session crashes.

Suggested fix

// AppendLogStore.finishOwnedFlush (apps/kimi-code/dist-native/intermediates/main.cjs:281818)
async finishOwnedFlush() {
  try {
    await this.fileStorage.append(/* ... */);
  } catch (err) {
    if (isDiskFullError(err)) {
      // Switch to read-only mode; flush buffer to a recovery file or drop
      this.transitionToReadOnly(err);
      this.emit('storage.degraded', { reason: 'disk_full', path: this.path });
      return; // do not rethrow
    }
    throw err;
  }
}

And separately: the error-surfacing UX should never redirect to the auth gate on a non-auth error. The "You're not signed in" message is a separate bug that masks the real StorageError from the user.

Related

• The session was actively in the middle of a 13-hour cleanup task when this fired, so losing the wire.jsonl means losing the audit trail of the cleanup work.
• Recovery: the user can rm -rf old worktree target/ dirs (~12 GB each) and restart; session resumes from prior compaction boundary, but the trailing tool calls are lost.

Suggested severity

P1 / high — kills in-progress work without recovery, surfaces an unrelated auth UI on the crash.

Start with AppendLogStore.drain and finishOwnedFlush in apps/kimi-code/dist-native/intermediates/main.cjs, then trace FileStorageService.append and the StorageError handling. Done means disk-full append failures stop retries, preserve the session process, and surface an actionable storage error instead of the auth gate; the separate auth fallback should not mask non-auth failures.