Regenerate incomplete cached reconstruction depth maps #139

At PR #20 head 74f7a98, recon/recon/depth.py:187-188 trusts a cached NPZ's existence. If the model process stops while writing that NPZ, the matching capture cache key survives. A retry skips generation and fails at np.load on line 206 rather than regenerating the damaged file.

Validate cached depth archives before skipping inference, or publish them by atomic rename after writing completes. Use a truncated small NPZ fixture and a mocked model invocation to verify that the next attempt repairs the cache. This demonstrated path fails loudly rather than producing a false placement result.

Confirmed P2 follow-up under the manager's convergence rule. This worker remains a draft handoff.

Review: #20 (comment)