feat(charges): add backend customer charge deletion

[turip]

Summary

• add the backend customer charge deletion facade
• require the facade-owned payment adjustment selection
• map none to ignoring both credit and invoice refunds
• support flat-fee and usage-based charges; reject credit purchases

Stack

• base: refactor(charges): make state machine invoice effects explicit #4886

Verification

• focused existing charge and server suites pass
• no new behavioral test cases are included in this split

Summary by CodeRabbit

New Features

• Added support for deleting customer charges.
• Added a “no payment adjustment” option for charge deletion.
• Charge deletion preserves immutable invoice and payment history while removing eligible invoice lines.
• Unsupported discrepancies are recorded as invoice validation issues.

Bug Fixes

• Added validation for required deletion details and payment adjustment values.
• Prevented deletion of charges belonging to another customer or credit purchases.

Greptile Summary

The PR adds a backend customer-scoped facade for deleting flat-fee and usage-based charges while rejecting credit purchases and preserving immutable billing history.

• Requires callers to explicitly select a payment adjustment policy.
• Maps none to ignoring credit and invoice refunds while retaining normal invoice lifecycle reconciliation.
• Adds service-level coverage for ownership checks, supported charge types, credit realizations, mutable invoice-line cleanup, and paid invoice preservation.

Confidence Score: 5/5

The PR appears safe to merge because no blocking failure remains.

No blocking failure remains.

Important Files Changed

Filename	Overview
openmeter/billing/charges/api.go	Adds the customer charge deletion contract, validated input, and explicit payment-adjustment enum.
openmeter/billing/charges/service/api.go	Implements customer-scoped deletion by mapping the facade policy into an internal delete patch and applying it through the existing charge workflow.
openmeter/billing/charges/service/api_test.go	Exercises supported charge types, ownership enforcement, credit-purchase rejection, realization preservation, and mutable versus immutable invoice behavior.
openmeter/billing/charges/README.md	Documents the semantics of deleting charges without compensating prior credit or payment effects.
openmeter/server/server_test.go	Updates the test no-op charge service to satisfy the expanded facade interface.

Sequence Diagram

sequenceDiagram
  participant Caller
  participant Facade as CustomerChargeAPIService
  participant Patches as ApplyPatches
  participant Charge as Charge state machine
  participant Invoice as Invoice updater
  Caller->>Facade: DeleteCustomerCharge(customer, charge, none)
  Facade->>Facade: Validate input and namespace
  Facade->>Patches: "PatchDelete(refunds = ignore)"
  Patches->>Charge: Validate ownership and apply deletion
  Charge->>Invoice: Reconcile associated invoice lines
  Invoice-->>Charge: Delete mutable lines or record immutable drift
  Charge-->>Caller: Deletion result

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_{Reviews (5): Last reviewed commit: "test(charges): remove redundant suite ho..." | Re-trigger Greptile}

Context used:

• Knowledge Base — Billing: Invoices, Charges, Tax, and Currency

[coderabbitai]

📝 Walkthrough

Walkthrough

Adds customer charge deletion with validated payment-adjustment handling. The service applies delete patches, preserves immutable payment and invoice history, removes mutable gathering lines, and records invoice validation issues for unsupported discrepancies.

Changes

Customer charge deletion

Layer / File(s)	Summary
Deletion contract and validation openmeter/billing/charges/api.go, openmeter/billing/charges/api_test.go	Adds DeleteCustomerCharge, DeleteCustomerChargeInput, and PaymentAdjustmentNone. Validation checks required identifiers and rejects unsupported payment adjustments.
Deletion service flow openmeter/billing/charges/service/api.go, openmeter/billing/charges/service/api_test.go, openmeter/server/server_test.go	Validates namespace lockdown, resolves the deletion policy, applies delete patches, enforces ownership, rejects credit-purchase deletion, and updates the no-op service implementation.
Allocation and invoice effects openmeter/billing/charges/service/api_test.go, openmeter/billing/charges/README.md	Tests preservation of credit allocations and paid invoice history, removal of gathering lines, and immutable-invoice validation issues. Documents payment-adjustment behavior.

Estimated code review effort: 4 (Complex) | ~45 minutes

Sequence Diagram(s)

sequenceDiagram
  participant Caller
  participant CustomerChargeAPIService
  participant service
  participant CustomerChargePatch
  Caller->>CustomerChargeAPIService: DeleteCustomerCharge(input)
  CustomerChargeAPIService->>service: Validate input and namespace lockdown
  service->>service: resolveDeletePolicy(paymentAdjustment)
  service->>CustomerChargePatch: Create and apply delete patch
  CustomerChargePatch-->>Caller: Return deletion result

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Possibly related PRs

• openmeterio/openmeter#4586: Both changes cover customer charge deletion, deletion state handling, and invoice-line overrides.

Suggested reviewers: chrisgacsal

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
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.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: adding backend customer charge deletion.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/charges-delete-backend-api

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[coderabbitai]

🧹 Nitpick comments (1)

openmeter/billing/charges/service/api_test.go (1)

53-59: 📐 Maintainability & Code Quality | 🔵 Trivial | 💤 Low value

Optional: drop the pass-through suite hooks.

SetupSuite and TearDownTest only call the embedded BaseSuite methods. Go promotes those methods automatically, so the overrides add no behavior. Removing them keeps the suite lean, and you can add them back when the suite needs extra setup.

♻️ Proposed cleanup

-func (s *CustomerChargeAPIDeleteTestSuite) SetupSuite() {
-	s.BaseSuite.SetupSuite()
-}
-
-func (s *CustomerChargeAPIDeleteTestSuite) TearDownTest() {
-	s.BaseSuite.TearDownTest()
-}
-

As per coding guidelines: "Do not extract trivial or single-use helpers unless the name captures non-obvious domain intent; inline pass-through wrappers."

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@openmeter/billing/charges/service/api_test.go` around lines 53 - 59, Remove
the pass-through SetupSuite and TearDownTest overrides from
CustomerChargeAPIDeleteTestSuite; rely on the embedded BaseSuite methods
promoted by Go, preserving the existing suite lifecycle behavior.

Source: Coding guidelines

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@openmeter/billing/charges/service/api_test.go`:
- Around line 53-59: Remove the pass-through SetupSuite and TearDownTest
overrides from CustomerChargeAPIDeleteTestSuite; rely on the embedded BaseSuite
methods promoted by Go, preserving the existing suite lifecycle behavior.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro Plus

Run ID: 542853e1-ed3a-4d62-88b6-167f556118b4

📥 Commits

Reviewing files that changed from the base of the PR and between 170e66c and 80a7fef.

📒 Files selected for processing (6)

• openmeter/billing/charges/README.md
• openmeter/billing/charges/api.go
• openmeter/billing/charges/api_test.go
• openmeter/billing/charges/service/api.go
• openmeter/billing/charges/service/api_test.go
• openmeter/server/server_test.go