readAndConsumeHandoffResult was over the code-health CC target (21 > 20).
Extract its phases into module-private helpers in handoff-result.ts:
consumeHandoffResultFile (read, parse, rename-to-.corrupt, unlink),
handoffRunMismatch (run_id validity, run_id / started_at correlation; returns
the exact log line it used to emit) and toHandoffResult (field coercion).
Check order, log lines, and the JSON-`null` body path (still logs "no
finished_at") are unchanged. Behaviour unchanged.
3c6a7dfe41