10: Build-Along - Invoice Intake Validation + Approval Routing

Goal: automate AP intake routing with clear, auditable decision criteria.

You will implement one practical workflow:

1. query invoice intake rows,
2. apply routing rules (auto_approve, finance_review, needs_po),
3. send an approval-routing digest email.

Why This Matters

Accounts-payable intake is repetitive and error-prone when routed manually.

This workflow makes the policy explicit and reviewable.

Final Workflow File

• examples/realworld/invoice-intake-approval-digest.gr

Business Rules

Current example rules:

• amount_usd > 5000 -> finance_review
• missing PO number -> needs_po
• otherwise -> auto_approve

Digest includes:

• per-invoice line with route decision
• summary counts per route class

Run It

CLI path:

GRAPHEME_ALLOWED_SQL_CONNECTIONS=sqlite::memory: \
GRAPHEME_ALLOWED_SMTP_DOMAINS=example.com \
  grapheme run examples/realworld/invoice-intake-approval-digest.gr --json

Workspace path:

GRAPHEME_ALLOWED_SQL_CONNECTIONS=sqlite::memory: \
GRAPHEME_ALLOWED_SMTP_DOMAINS=example.com \
  cargo run -- run examples/realworld/invoice-intake-approval-digest.gr --json

Expected Output Signals

Look for:

• "outcome": "succeeded"
• SMTP accepted state
• digest body with SUMMARY | total=... line

Required Failure Drills

1. Remove SQL allow-list env var.

• Observe policy/connectivity failure behavior.

2. Remove SMTP allow-list env var.

• Observe mail send failure behavior.

3. Raise or lower finance threshold in SQL.

• Confirm finance_review count changes in summary.

4. Populate missing PO value for one invoice.

• Confirm needs_po count drops.

Production Adaptation

1. Replace inline CTE with real AP intake table/view.
2. Externalize thresholds and routing policy.
3. Add approver metadata in output lines.
4. Add branch for paging finance-oncall when review queue spikes.

This pattern turns finance routing policy into executable, testable workflow logic.