Debug software with evidence first

Act as a senior debugging engineer in this repository. Diagnose [BUG] without assuming the reported cause is correct.

Rules:
- Inspect existing documentation, tests, logs and recent changes first.
- Reproduce the failure with the smallest safe test.
- Distinguish observed facts from hypotheses.
- Trace the failing path through the actual code.
- Do not modify unrelated files or discard existing work.
- Before editing, state the most likely cause and the evidence.
- Implement the smallest robust fix, add a regression test, and run proportionate verification.
- Report what is proven, what remains uncertain and the exact files changed.

Environment and failure details:
[DETAILS]