fix(code-intelligence): a failed embedding cache write no longer discards the embedding (#13437)

[mrveiss]

Closes #13437

Thinking Path

_generate_embedding wrapped generation and the cache write in one try/except Exception:

embedding = await generate_embedding_with_fallback(...)
if embedding:
    await self._embedding_cache.put(...)   # same try
    return embedding

A failing EmbeddingCache.put therefore discarded a perfectly good vector and fell through to the SHA-256 pseudo-embedding. What makes it costly is that it fails invisibly — a well-shaped 768-dimension vector still comes back, so nothing errors. Every pattern written while the cache misbehaved was indexed under a vector encoding nothing about the code, quietly degrading code_patterns similarity search.

The cache is an optimisation. Its failure must never change the value returned.

This is the third defect of this shape in this one function. #12374 and #12407 were both a broad except swallowing something and silently substituting the pseudo-embedding. The existing test file was written for #12407 — it covers generation thoroughly and the write not at all, which is exactly the gap this fell through.

What Changed

File	Change
pattern_analysis/analyzer.py	Generation and cache write guarded separately; _hash_pseudo_embedding extracted
pattern_analysis/embedding_test.py	Three tests: cache-write failure, generation failure, generation returning nothing

A cache-write failure now logs and returns the real embedding. The hash fallback is reached only when generation itself fails or yields nothing — two of the new tests pin that, because this narrows the except, it does not remove it.

Function length. The change pushed _generate_embedding to 43 code lines against the repo's 30-line rule (it was 31 before). Extracting _hash_pseudo_embedding brings it to 34, with a 5-line helper — and lets the fallback's docstring say plainly that it encodes nothing semantic, which is the property that makes silently returning it harmful.

Verification

code_intelligence/pattern_analysis/embedding_test.py    10 passed  (was 7)
isort · black · flake8 (0)                              clean

Mutation-checked. Restoring the combined try fails the new test:

FAILED ...::TestCacheWriteFailureDoesNotDiscardTheEmbedding::test_returns_the_real_embedding_when_the_cache_write_fails

The two fallback tests pass under that mutation as well as after the fix, which is correct — they guard a path the change deliberately preserves.

Model Used

Claude Opus 5 (1M context)

[github-actions]

✅ SSOT Configuration Compliance: Passing

🎉 No hardcoded values detected that have SSOT config equivalents!