Fix deadlock when bundle script hooks write large stderr output#5499
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Script hook output was read sequentially (stdout to EOF, then stderr), so a hook writing more than the OS pipe buffer (~64KiB) to stderr while stdout was still open blocked forever. Spool stderr to memory in a goroutine while streaming stdout, then log it after stdout EOF, keeping the existing output order. Co-authored-by: Isaac
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Integration test reportCommit: e4cb1f7
30 interesting tests: 15 SKIP, 8 flaky, 7 KNOWN
Top 50 slowest tests (at least 2 minutes):
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Co-authored-by: Isaac
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janniklasrose
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Jun 17, 2026
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Integration test reportCommit: 0437746
626 interesting tests: 549 MISS, 60 FAIL, 11 KNOWN, 4 PANIC, 2 SKIP
Top 50 slowest tests (at least 2 minutes):
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Why
Found during a full-repo review of the CLI. Bundle script hooks (
experimental.scripts) can deadlock a deploy forever. Hook output was read sequentially: stdout to EOF first, then stderr. A hook that writes more than the OS pipe buffer (about 64KiB) to stderr while stdout is still open blocks on the stderr write and never closes stdout, so the script and the CLI wait on each other indefinitely.Changes
Before, stderr was only read after stdout reached EOF (via
io.MultiReader); now stderr is drained concurrently, so the hook can never block on a full stderr pipe. Inbundle/scripts/scripts.go, a goroutine spools stderr to memory while stdout is streamed line by line, and the spooled stderr is logged after stdout EOF. This keeps the existing stdout-then-stderr output order (no interleaving), so observable output is unchanged for hooks that complete today. The line logging loop is extracted into alogOutputhelper and still emits a final line without a trailing newline.Test plan
TestExecuteLargeStderrOutputDoesNotDeadlockwrites well over the pipe buffer to stderr before touching stdout; verified it deadlocks against the previous implementation (killed by the test context after 60s) and passes in ~0.05s with the fixgo test -race ./bundle/scriptspasses, including the existing no-trailing-newline testacceptance/bundle/scriptspass for both engines with no output changes./task fmt-q,./task lint-q,./task checksall cleanThis pull request and its description were written by Isaac.