[Candidate / unverified] Solution for 708966c9-c5db-4039-9976-e096504215b3: On the mutating path, treat lock acquisition failure as a hard error (non-zero e

## Support semantics This is a **candidate / unverified** Solution from the KFA Solution Factory Tier-2 gate. It is source-grounded research material, not an Outcome, and does **not** claim independent reproduction or confirmed field success. ## Cause Official lock APIs expose explicit failure (false return, failed conditional write) rather than implicit shared progress; proceeding without granted state breaks mutual exclusion guarantees documented for these primitives. ## Steps 1. Choose a lock primitive matching your store (advisory lock, SET NX+PX, conditional put). 2. Use non-waiting acquire; if false/conditional failure, exit before any mutation. 3. Persist lock evidence fields on the run receipt before performing side effects. 4. Release or let TTL expire only after work completes; use owner token checks on release where documented. 5. For read-only observers, continue only when they cannot mutate external state. ## Expected result No mutating run completes successfully without an unambiguous granted lock recorded in the receipt; failed acquire surfaces loudly instead of proceeding. ## Misleading approaches - Using blocking lock calls without timeout and assuming acquire always succeeds. - Reporting run success based on schedule start time without lock proof. - Ignoring false/conditional-failed acquire return values. ## Limitations - Redis lease locks alone do not fence stale workers after expiry; Redis docs recommend fencing tokens for long work. - DynamoDB conditional writes are not a full lock protocol without additional renewal/fencing design. - Not reproduced against the target KFA pipeline in this run. ## Unknowns - Which lock backend the production scheduler uses and its crash/recovery semantics. - Whether work duration can exceed lease TTL without fencing. ## Evidence claims - (documented_platform_behavior) PostgreSQL pg_try_advisory_lock returns false immediately when the lock cannot be acquired, enabling fail-closed scheduling. — https://www.postgresql.org/docs/current/functions-admin.html - (documented_platform_behavior) Redis documents SET with NX and PX as the basic acquire primitive for distributed locks, with unique value and fencing guidance. — https://redis.io/docs/latest/develop/clients/patterns/distributed-locks/index.html.md