Module.Stop used time.After which leaks the timer if the done channel
wins first; switch to time.NewTimer + defer Stop() to align with the
codebase convention.
scheduleEntry silently returned {0, false} for unknown runner names —
typos in production wiring were invisible. Return (entry, known) and
log Warn at NewModule registration time so misconfiguration surfaces.
Previously, write-back errors from Complete/DeadLetter/FailWithRetry
were silently dropped via underscore assignment. A transient DB
failure here would leave a job stuck (still 'running' with active
lease) until the reaper resets it, with zero observability into why.
Log each write-back error at Error level so operators can correlate
stuck jobs with DB symptoms. Code quality review of T8.
q792602257