🪲 BUG-#36: Fix race condition in SQLite save()

[FernandoCelmer]

Summary

• Add UniqueConstraint("uid", "mailbox") to RawModel for explicit upsert support
• Replace check-then-insert pattern in StorageSQLite.save() with SQLite's INSERT OR REPLACE via sqlalchemy.dialects.sqlite.insert and on_conflict_do_update
• Eliminates race condition where concurrent syncs could duplicate records

Closes #36

[FernandoCelmer]

🔍 Code Review

Code issues found: 1

See inline comment below.

[FernandoCelmer]

[Suggestion]

Problem — With SQLite's INSERT ... ON CONFLICT DO UPDATE, result.rowcount returns 1 for both inserts and updates (any affected row = 1). This means save() now always returns True, never False for updates.

The docstring still says "Returns True if inserted, False if updated", which is now incorrect.

Failure scenario —

storage = StorageSQLite()
storage.save(raw)          # -> True (inserted) OK
storage.save(raw)          # -> True (updated, but claims inserted) WRONG

This directly affects sync.py:_save_one() which uses the return value to count result.inserted vs result.updated. After this PR, result.updated will always be 0.

Fix — Either update the docstring and _save_one() to not rely on the distinction, or check existence before the upsert:

existing = session.query(RawModel.uid).filter(
    RawModel.uid == raw.uid, RawModel.mailbox == raw.mailbox
).first()
session.execute(stmt)
session.commit()
return existing is None  # True if new, False if updated