Fix memory_zone cleanup on exception

[kvr06-ai]

Summary

When an exception propagates out of nlp.memory_zone(), the cleanup code in StringStore.memory_zone() and Vocab.memory_zone() never runs. This leaves the vocab in a broken state (transient strings/lexemes not cleared, self.mem still pointing to a temporary pool), causing an AssertionError in Vocab.get() on the next call to nlp().

Fixes #13924

Root cause

Both StringStore.memory_zone() and Vocab.memory_zone() use @contextmanager with cleanup code placed after yield but without a try/finally wrapper. In a @contextmanager, code after yield only runs on normal exit. If an exception is thrown at the yield point, it propagates without executing the cleanup.

Changes

• spacy/strings.pyx: Wrap yield and cleanup (clearing transient keys, restoring self.mem) in try/finally
• spacy/vocab.pyx: Same pattern for _clear_transient_orths() and self.mem restore
• spacy/tests/vocab_vectors/test_memory_zone.py: Add regression test that raises inside a memory zone and verifies the vocab is usable afterward

Testing

• All existing test_memory_zone tests pass (no change to happy-path behavior)
• New test_memory_zone_exception_cleanup verifies:
  • vocab.in_memory_zone is False after exception
  • Pre-existing words still accessible
  • Transient words from the failed zone are cleaned up
  • Vocab accepts new words without errors

[kvr06-ai]

Hi @honnibal — this is a small fix for the memory_zone context managers in StringStore and Vocab. The cleanup code after yield doesn't run when an exception propagates through a @contextmanager (needs try/finally). The result is a corrupted vocab state that triggers an AssertionError in Vocab.get() on subsequent calls.

The fix wraps the existing cleanup in try/finally in both files. Happy-path behavior is unchanged. Would appreciate your review when you get a chance.

[honnibal]

Thanks!