refactor: Replace except Exception broad-catch blocks with specific exceptions

[YaronZaki]

Problem Statement

8 except Exception blocks across the codebase silently swallow all errors, masking bugs in API handlers (user.py:262,317), Telegram notifications (notifications.py:46), airdrop claims (claim_airdrops.py:74,110), and alert mixin (alert.py:40).

Evidence

# quantara/web_app/api/user.py:262,317
except Exception as e:  # Catches everything

# quantara/web_app/telegram/notifications.py:46
except Exception as e:  # Swallows notification failures

# quantara/web_app/tasks/claim_airdrops.py:74,110
except Exception as e:  # Swallows airdrop errors

# quantara/web_app/contract_tools/mixins/alert.py:40
except Exception as e:  # Swallows alert errors

Impact

Medium — silent failures in production. Database connection errors, validation errors, and network failures all caught identically. No differentiation between retryable errors and fatal errors. Sentry receives overly broad reports that are hard to triage.

Proposed Solution

Replace each except Exception with specific exception types: except sqlalchemy.exc.SQLAlchemyError for DB ops, except aiohttp.ClientError for network, except ValueError, TypeError for data. Add Sentry capture for truly unexpected exceptions.

Acceptance Criteria

• All 8 except Exception blocks replaced with specific exception types
• Each handler logs contextual info (wallet_id, operation, etc.)
• Truly unexpected exceptions captured and reported to Sentry
• No behavior change for expected error scenarios
• All existing tests pass

File Map

• quantara/web_app/api/user.py:262,317 — replace broad catches
• quantara/web_app/telegram/notifications.py:46 — replace broad catch
• quantara/web_app/tasks/claim_airdrops.py:74,110 — replace broad catches
• quantara/web_app/contract_tools/mixins/alert.py:40 — replace broad catch

Testing Strategy

• Unit: For each replacement, write tests raising specific exceptions and verify correct handling
• Integration: Simulate database connection failure, verify correct exception type caught

Security Considerations

Silently swallowed exceptions can mask security-relevant failures. Specific exception handling makes error behavior predictable and auditable.

Definition of Done

• Code implemented and peer-reviewed
• Tests written and passing for each replaced handler
• No new linting errors
• PR linked and merged

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Labels: refactoring
Priority: Medium
Difficulty: Intermediate
Estimated Effort: 4h

[BigElv]

Hi maintainer I would love to work on this

[samieazubike]

Hi maintainer! Kindly assign the issue to me. I can create a PR within 12hr

[grantfox-oss]

🦊 GrantFox — @BigElv has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #52)
2. Your PR will be reviewed by the Quantarq maintainers

Good luck! Track your progress on GrantFox.