Concurrent queue update loss
Scope and affected architecture
Applies when several workers mutate a queue or registry stored as one file, then merge snapshots through a version-control system or shared filesystem.
Symptom and observable signature
One worker closes an item while another appends a new item. Both operations report success, the file remains syntactically valid, and the appended item is missing after the snapshots are reconciled.
- successful operations overlap in time;
- the missing stable ID appears in a producer receipt but not final state;
- conflict resolution selected an entire file from one side;
- repository history is clean, so ordinary conflict checks do not warn.
Root mechanism
The system merges snapshots instead of logical operations. Choosing the remover's complete file silently discards the producer's append.
Minimal safe fixture
The fixture creates two in-memory snapshots from the same two-item queue. One removes job-a; the other adds job-c. A whole-snapshot merge reproduces the loss without processes, locks, disk writes, or nondeterministic timing.
python3 atlas.py run FFA-003 --mode reproduceDeterministic detector
Compare acknowledged stable-key operations with the merged state. Any accepted append absent from the result becomes accepted_operation_missing:<id>.
python3 atlas.py run FFA-003 --mode detectRepair invariant
Persist stable-key operations, apply them to the latest state, and publish with compare-and-swap semantics. On rejection, reload and replay the same idempotent operation; never force-push a stale snapshot.
Regression check
The regression mode replays remove and append against current state. It proves the final IDs are exactly job-b and job-c.
python3 atlas.py run FFA-003 --mode regressFalse positives and non-applicable cases
A whole-file merge can be correct when there is a single writer or when the file is derived from an authoritative operation log. A missing ID is also legitimate when a later acknowledged removal targets that same ID.
Provenance
Hypothetical. This is a synthetic lost-update fixture. It does not disclose or attribute a real queue, repository, organization, or incident.