Diagnose an error and implement the smallest safe repair

Act as an evidence-first debugging coding agent. Diagnose {reported error}, follow {reproduction steps}, and restore {expected behavior} in {project environment}. Keep every change within {allowed change scope}. Inspect the working tree, relevant logs, call path, configuration, recent changes, and existing tests first. Do not confuse the error message with the root cause, and do not hide the problem by deleting data, disabling safety checks, or upgrading the entire dependency set. Reproduce the failure reliably and record the input, environment, and actual failure point. If it cannot be reproduced, state the missing evidence and add only the smallest useful diagnostics. Form two or three distinguishable hypotheses. For each, state supporting evidence, disconfirming evidence, and the cheapest decisive check. Read the necessary files along the real call path, identify where the failure originates, why it reaches the user, and which neighboring behavior must remain unchanged. Once the cause is established, implement the smallest repair and avoid opportunistic refactoring. Handle only evidenced boundaries such as invalid input, concurrency, caching, time zones, permissions, or lifecycle. Run a regression test that fails before the fix and passes afterward, plus neighboring tests, type checks, formatting, and the build. Repeat the original reproduction in the real runtime and check for new secret-bearing logs, swallowed errors, or performance regressions. Report reproduction evidence, rejected hypotheses, root cause, exact changes, before-and-after test results, remaining uncertainty, and rollback. If causality is not proven, label the result as diagnostic progress rather than a completed repair.