fix(purchases): don't leak raw persistence error into audit-gap status (refs #623)

[cristim]

Summary

Follow-up to a CodeRabbit review comment on #623 that landed right at merge time, so it couldn't be folded into that PR.

recordHistoryAuditGap (added in #623) embedded the raw SavePurchaseHistory error (histErr) verbatim into exec.Error. That field is surfaced to clients via the history status_description, so an internal storage error (e.g. SQL constraint text like monthly_cost violates not-null constraint) leaked to the UI.

Fix

• Log histErr server-side via logging.Errorf for diagnosis.
• Store only a generic, user-safe note in exec.Error ("commitment X purchased but its history record failed to save") with no raw error interpolation.
• Extend the existing audit-gap regression test (TestManager_ExecuteAndFinalize_HistorySaveFailure_StaysVisible) with NotContains assertions on the raw error text, so it fails-on-regression if the leak is reintroduced.

The #621 invariants are preserved: a history-write failure still keeps the completed purchase visible (the note is still recorded), the execution still stays completed (not failed), and dollar totals are unaffected.

Test plan

• go test ./internal/purchase/ -run TestManager_ExecuteAndFinalize_HistorySaveFailure_StaysVisible passes; the new NotContains assertions fail against the pre-fix code
• gofmt / go vet clean

Refs #623.

Summary by CodeRabbit

Release Notes

• Bug Fixes
  • Refined error messaging for purchase history failures to exclude internal technical details from user-facing notifications while preserving essential context information.

[cristim]

@coderabbitai review

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 6c6e9689-c5ea-4700-b714-a46adc3ff9ea

📥 Commits

Reviewing files that changed from the base of the PR and between 7cbcb0c and 06579b7.

📒 Files selected for processing (2)

• internal/purchase/execution.go
• internal/purchase/execution_test.go

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📝 Walkthrough

Walkthrough

Error sanitization in purchase history failure path: when SavePurchaseHistory fails, recordHistoryAuditGap now logs the raw database error server-side while updating the user-facing error message to be generic and safe, omitting persistence details.

Changes

Purchase History Audit Gap Error Sanitization

Layer / File(s)	Summary
Error message sanitization in history save failure internal/purchase/execution.go, internal/purchase/execution_test.go	recordHistoryAuditGap logs the raw persistence error via logging.Errorf and updates exec.Error with a generic "commitment purchased but its history record failed to save" message without including error details. Tests add negative assertions to verify raw database constraint text does not appear in exec.Error.

Estimated Code Review Effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

Possibly Related PRs

• LeanerCloud/CUDly#623: Earlier PR that introduced the audit-gap recordHistoryAuditGap behavior to keep completed purchases visible; this PR enhances error message handling in that same path.
• LeanerCloud/CUDly#233: Related test assertions that ensure exec.Error is sanitized when purchase execution/history persistence fails.

Suggested Labels

severity/medium, effort/s, type/bug

Poem

🐰 Errors stay safe, hidden from sight,
Raw logs on server, users sleep tight,
History stumbled? A generic note,
No constraint tales in what we quote!
Secrets are logged, but truth stays mute.

🚥 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 title accurately describes the main fix: preventing raw persistence errors from leaking into user-facing audit-gap status messages.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
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.

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• Create PR with unit tests
• Commit unit tests in branch fix/audit-gap-error-leak

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