Fix flashcard order race condition

[tpaulshippy]

Summary

• Fixes a race condition in create_flashcard where concurrent requests could create flashcards with duplicate order values, causing a UNIQUE constraint violation
• Uses select_for_update() on the initial deck lookup to acquire a row lock before querying MAX(order), ensuring serialized access

Test Added

• Added test_flashcard_order_increments to verify flashcard ordering works correctly

Summary by CodeRabbit

• Bug Fixes
  • Improved flashcard creation reliability by enhancing database transaction handling to prevent data conflicts during concurrent operations.
• Tests
  • Added a new test to verify flashcard order increments work correctly.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: ab1c9370-e5dc-46ab-badd-611089ee9730

📥 Commits

Reviewing files that changed from the base of the PR and between a96746f and 9bbd913.

📒 Files selected for processing (1)

• back/bots/tests/test_chat.py

📝 Walkthrough

Walkthrough

The create_flashcard tool's deck retrieval is modified to apply select_for_update() when fetching an existing deck by profile and name within a transaction, ensuring pessimistic row locking. Indentation is adjusted so the locked re-fetch occurs in the correct conditional branch before subsequent operations.

Changes

Cohort / File(s)	Summary
Database Locking for Deck Retrieval back/bots/models/chat.py	Added select_for_update() to deck retrieval in create_flashcard tool to prevent concurrent access issues during transactions. Adjusted indentation of the re-fetch operation to occur in the intended conditional branch.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Poem

🐰 A lock upon the deck so fine,
No race conditions here to dine,
With atoms safe and rows held tight,
The flashcards flow both day and night! ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title 'Fix flashcard order race condition' directly and accurately describes the main change: fixing a concurrency issue in flashcard ordering by adding row locking with select_for_update().
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/flashcard-order-race-condition

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