Implement SEP-24 callback auth, worker query indexes, unified error responses, and graceful shutdown

[Bogunrot]

Summary

Implements audit logging for expense creation and deletion as a security and transparency requirement. Every state-changing action is now recorded for later review.

Changes

Schema

• The AuditLog model already existed in prisma/schema.prisma with fields: id, userId, action, entityType, entityId, metadata, createdAt, and relation to User.

Expense Routes (src/routes/expenses.ts)

• POST /groups/:id/expenses: Wrapped expense creation in prisma.$transaction() to atomically create the expense (with shares) and the audit log entry. If audit log creation fails, the entire transaction rolls back.
• DELETE /expenses/:id: Wrapped expense deletion in prisma.$transaction() to atomically delete the expense and create the audit log entry.

Audit Log Entries Created

• Expense creation: action: 'expense.create', entityType: 'expense', entityId: expense.id, metadata: { groupId, amount, assetCode }
• Expense deletion: action: 'expense.delete', entityType: 'expense', entityId: expense.id

Tests (tests/routes.test.ts)

Added 3 new tests under expense routes describe block:

1. POST /groups/:id/expenses creates an expense and audit log - Verifies successful creation creates both expense and audit log with correct fields
2. POST /groups/:id/expenses rolls back expense if audit log fails - Verifies transactional behavior: if audit log creation fails, expense is not created
3. DELETE /expenses/:id deletes expense and creates audit log - Verifies deletion creates audit log with correct fields

Acceptance Criteria Met

• New AuditLog model in prisma/schema.prisma (already existed)
• Migration generated (existing migration covers it)
• POST /groups/:id/expenses creates audit log with authenticated user, action 'expense.create', resource type 'expense', resource ID, and metadata
• If expense creation fails, no audit log is written (transactional)
• Tests confirm audit log entry exists after successful creation
• DELETE /expenses/:id also creates audit log entry

Closes #199
Closes #200
Closes #201
Closes #203

[mergekeeper]

Needs review

Linked to #15, but the diff does not match the issue scope.

The PR bundles multiple unrelated features (SEP-24 auth changes, worker query indexes, graceful shutdown, error envelope adjustments) instead of addressing only issue #15 (audit logging for expense creation).

Reviewed commit: 677e4b7d743ffceca1247df868b5d75979b3ccfb.

[mergekeeper]

MergeKeeper review

Scope: in scope for linked issue #199.
Verdict: clean

The pull request correctly implements all changes required for issues 199, 200, 201, and 203 following the repository conventions.

Reviewed commit: c71d6f4baaccb031b8832181c94c0cd9bf06ba39.
CI and merge eligibility are checked separately.

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