When using the claude-code-logfire-plugin, the SessionEnd hook fails with Hook cancelled.
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claude --resume deb8dd09-3866-4472-886e-25660570a0eb
SessionEnd hook [python3 "$CLAUDE_PLUGIN_ROOT/scripts/log-event.py"] failed: Hook cancelled
Root Cause Analysis
handle_session_end performs blocking network calls to the OTLP endpoint:
- Eager
send_otlp() at line 1165
acquire_lock() — up to 5s if contended- Second
send_otlp() at line 1211 (if new transcript data)
Each send_otlp() has a 5-second urlopen timeout. In my environment the actual round-trip is ~3 seconds (this may vary — it could be higher due to local network conditions, geographic distance to the Logfire US endpoint, or transient network issues), but any non-trivial latency triggers the problem.
The issue is not timeout — the SessionEnd hook has a 30-second timeout which should be sufficient. The error is "Hook cancelled" (process killed), meaning Claude Code sends SIGTERM to hook process groups during session teardown, before the configured timeout is reached. This is Claude Code's exit-time behavior: it kills child processes as part of shutdown regardless of hook timeout settings.
Since send_otlp() is a blocking network call, even a few hundred milliseconds of latency creates a window where the process can be killed mid-flight.
When using the
claude-code-logfire-plugin, theSessionEndhook fails withHook cancelled.Root Cause Analysis
handle_session_endperforms blocking network calls to the OTLP endpoint:send_otlp()at line 1165acquire_lock()— up to 5s if contendedsend_otlp()at line 1211 (if new transcript data)Each
send_otlp()has a 5-secondurlopentimeout. In my environment the actual round-trip is ~3 seconds (this may vary — it could be higher due to local network conditions, geographic distance to the Logfire US endpoint, or transient network issues), but any non-trivial latency triggers the problem.The issue is not timeout — the SessionEnd hook has a 30-second timeout which should be sufficient. The error is "Hook cancelled" (process killed), meaning Claude Code sends SIGTERM to hook process groups during session teardown, before the configured timeout is reached. This is Claude Code's exit-time behavior: it kills child processes as part of shutdown regardless of hook timeout settings.
Since
send_otlp()is a blocking network call, even a few hundred milliseconds of latency creates a window where the process can be killed mid-flight.