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KRATOS
2a8802e39c
* fix: cap unbounded exec_command output buffer to prevent OOM kill
execOutputBuffer.data accumulated every byte a backgrounded exec_command
session wrote, with no size cap, unlike buffer.recent which is correctly
bounded to recentExecOutputBytes for the /ps preview. drainString() only
clears data when the agent actually polls that session again — so a
long-lived background session nobody polls (e.g. a dev server left running
after the run that started it was cancelled) grows this buffer forever as
long as the process keeps writing, with no ceiling.
Traced this directly to a real crash: a session that had been running for
~5.5 hours (an earlier turn invoking swarm agents got cancelled mid-flight,
per that session's own event log) accumulated to ~42.7GB of compressed
memory, at which point macOS's memorystatus killed the process outright
("killing zero due to low-swap").
Fixed by capping data at maxExecOutputBufferBytes (2MiB), trimming from the
front like recent already does, and surfacing a one-time truncation notice
on the next drain so data loss is visible rather than silent.
* fix: pre-push review findings on the exec_command buffer-cap fix
Ran an adversarial review before opening the PR. It found the truncation
notice added alongside the buffer cap didn't actually work: prefixing
execOutputTruncatedMessage into drainString()'s text meant the notice
always sat ~2MiB before the end of the combined output, but the tool's
own downstream truncateExecOutput() keeps at most a 400KB tail (even at
the maximum allowed max_output_tokens) — so the notice was reliably
swallowed, or chopped into an unreadable fragment at smaller budgets.
Verified with direct reproductions against the real functions.
Fixed by moving the signal out of the text stream entirely:
- execOutputBuffer gains consumeTruncated() (read+reset, called once per
collect()) and peekTruncated() (read-only, for status views) instead of
injecting a marker into the drained bytes.
- collect() now returns (string, bool); both call sites thread the bool
through to execToolResult, which sets meta["output_buffer_truncated"]
and appends the notice to the response body *after* truncateExecOutput
runs, so it can never be re-truncated or land in a discarded region.
- Also flagged: a session torn down without ever being polled again after
truncation loses the signal entirely, since nothing drains/logs it on
teardown. Full audit-trail logging felt like overkill for a soft
transparency signal on top of a hard memory-safety fix, but exposed
peekTruncated() on ExecSessionSnapshot and surfaced it in the /ps row
(background_terminals.go) so it's visible any time a still-running
session is checked — covers the common case (the review's own scenario:
a long-lived dev server nobody's polling but that's still alive) even
though a session reaped before ever being looked at is still a gap.
New tests: reworked TestExecOutputBufferCapsUndrainedData for the
consume/peek API, and TestExecToolResultSurfacesBufferTruncationOutsideByteBudget
reproducing the review's exact failure case (max_output_tokens=1) and
proving the notice now survives it.