The CI runs go test with -race; the agent runner has two pump goroutines
(pumpStdout + pumpStderr) writing through the sender concurrently, and
the unprotected fakeSender slice append raced. The cancel_test had a
local 'safeSender' workaround for the same issue; promote that mutex
onto fakeSender itself so every test in the package is race-clean
without per-test variants.
- fakeSender grows mu sync.Mutex; Send takes/releases. New snapshot()
helper for tests that want a stable copy.
- cancel_test drops its local safeSender + sync import; uses fakeSender.
Verified: go test -race ./... passes across all packages.
steve
24529d8fa7