[richiemcilroy]

When the recorder dies while the experimental out-of-process muxer is recording, cap-muxer is supposed to see EOF on stdin and finish the fragment it has open. It panics instead, because the recorder's end of its stderr pipe is gone, and the open fragment is left as a 0-byte .tmp.

sequenceDiagram
    participant R as Recorder
    participant M as cap-muxer
    R--xR: SIGKILL (stdin and stderr pipe readers close)
    M->>M: stdin EOF: "stdin closed without Finish"
    M->>M: tracing writes the line to stderr: EPIPE
    M->>M: tracing-subscriber reports the write error with eprintln!: panic (exit 101)
    Note over M: write_trailer never runs: segment_NNN.m4s.tmp stays 0 bytes

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• tracing_subscriber::fmt() reports a failed write with eprintln!, which panics on a closed stderr; the error paths in main used eprintln! too (crates/cap-muxer/src/main.rs:22).
• The subscriber now runs with log_internal_errors(false), and the exit messages go through writeln!(io::stderr(), ..) with the error ignored, so a lost stderr never stops the muxer from finishing.

Effect

crates/cap-muxer/tests/orphaned.rs feeds 75 libx264 frames (keyframe every 30) to the real binary, closes its stderr reader, then stdin:

	exit code	fragments on disk
before	101 (panic)	2 finished, open one lost
after	0	3 finished

Engine-verify crash suite, Blacksmith macOS, recorder killed mid-fragment with the out-of-process muxer (on top of the per-packet flush, #2643):

kill point	before	after
frame 175	open fragment left as a 0-byte .tmp: frames 120-175 lost	finished by the orphaned muxer: complete on disk up to frame 175, 0 lost
frame 120 (rollover)	0-byte .tmp: frames 60-120 lost	complete up to frame 120, 0 lost
frame 125, 11 s into a static screen	0-byte .tmp	complete up to the last handed frame, 0 lost

Recovery keeps the finished fragment only with the pending-fragment recovery fix (#2640): the recorder's manifest still lists it as pending.

Confidence Score: 5/5

The PR appears safe to merge; both previous concerns are addressed.

Summary

Makes stderr writes non-panicking so cap-muxer can finish its open fragment after the recorder dies.

• The muxer finishes its open fragment when the recorder exits.

_{Reviews (2) · Last reviewed commit: "test(cap-muxer): always log the EOF warn..." · Reviewed by Greptile}

[capy-ai]

Capy found no issues.

View 2 other findings in Capy.

[richiemcilroy]

hey @greptileai, please re-review the PR

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Project	Deployment	Actions	Updated
cap-status	Ready	Preview	Oct 18, 2026 3:00pm UTC

[capy-ai]

Capy found no issues.

[capy-ai]

Capy found no issues.