fix(ai): handle db failures in session history fetch (#83)

[qscetxxxl]

Description

Refactored _fetch_session_history in backend/app/ai/service.py to stop using broad exception blocks.

• Catches OperationalError to raise a 500 Internal Server Error if the PostgreSQL database is entirely unreachable.
• Catches generic SQLAlchemyError for transient query issues to log them and safely return an empty list.

Fixes #83

Summary by CodeRabbit

• Bug Fixes
  • Improved error handling for database connectivity issues, distinguishing between critical failures and transient errors to provide clearer feedback to users when the service is temporarily unavailable.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 1afa18af-9ffb-4d47-b7ae-b3fa0127bfc2

📥 Commits

Reviewing files that changed from the base of the PR and between fca82d4 and 98cb5bb.

📒 Files selected for processing (1)

• backend/app/ai/service.py

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📝 Walkthrough

Walkthrough

The PR refines error handling in the AI service's session history retrieval method. Previously, a broad exception catch masked database failures by silently returning empty history. The changes now distinguish critical database connectivity loss (OperationalError) from transient errors, raising an HTTP 500 for connectivity failures while logging and gracefully degrading for transient issues.

Changes

AI Service Database Error Handling

Layer / File(s)	Summary
Exception handling for session history fetch backend/app/ai/service.py	Imports HTTPException, status, and OperationalError, then refactors _fetch_session_history to raise HTTP 500 on critical database connectivity loss while logging and suppressing transient SQLAlchemyError cases.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Poem

🐰 A rabbit hops through database logs,
Spotting errors hiding in the fog—
Now when the connection falls away,
The service speaks up right away! 🌐

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title accurately summarizes the main change: handling database failures in session history fetch, matching the code modifications.
Linked Issues check	✅ Passed	The code changes implement all objectives from issue #83: distinguish OperationalError (500 response) from transient SQLAlchemyError (logged, empty list returned), preventing silent failures.
Out of Scope Changes check	✅ Passed	All changes in backend/app/ai/service.py are directly aligned with issue #83 requirements for refactoring database error handling; no out-of-scope modifications detected.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[rishabh0510rishabh]

hey @qscetxxxl
Thank you for your contribution!
The CI workflow is currently failing due to a linting error: there is a trailing whitespace on line 210 of backend/app/ai/service.py.
Please remove any extra spaces at the end of that line and push the update. Once fixed, the checks should pass.

Let me know if you need any assistance!