feat: require environment_subdomain or an explicit use_legacy_domain opt-out

[armando-rodriguez-cko]

Summary

Makes the merchant-specific subdomain (MSSD) mandatory. Callers must now call environment_subdomain(...), or explicitly opt out with the new use_legacy_domain(), which raises a DeprecationWarning from its first release. Setting both, or neither, raises CheckoutArgumentException at build time. MSSD is no longer beta and non-MSSD usage will be deprecated, so the previous silent fallback to api.checkout.com had to go.

Changes

• checkout_sdk/checkout_sdk_builder.py — the subdomain is held as a string and the EnvironmentSubdomain is built when the configuration is assembled, so environment_subdomain() no longer has to be called after environment(); new use_legacy_domain(); new _validate_environment_settings() and _requires_environment_subdomain()
• checkout_sdk/environment_subdomain.py — create_url_with_subdomain raises on an invalid subdomain instead of returning the URL unchanged
• checkout_sdk/default_sdk.py, oauth_sdk.py, previous/previous_sdk.py — validate before building; Previous/ABC exempted; the duplicated with/without-subdomain branches in all three build() methods are gone
• tests/checkout_default_sdk_test.py — covers all four combinations plus an invalid subdomain
• tests/checkout_configuration_test.py — the parameterised bad-subdomain case now asserts the raise instead of the silent fallback
• tests/conftest.py + five other fixtures — every client the suite builds now chooses a domain, through configure_domain

Fixed along the way

environment_subdomain() used to build the URLs from whatever environment was set at call time, so calling it before environment() silently produced the wrong host.

The long import line in tests/payments/request_apm_payments_integration_test.py is wrapped only because pre-commit lints staged files, so touching that file surfaced a pre-existing line-too-long.

Verification

544 tests passing, 0 failing, 217 skipped. flake8 and pylint pre-commit hooks pass.

API Reference

• https://api-reference.checkout.com/#section/Base-URLs
• https://www.checkout.com/docs/developer-resources/api/api-endpoints

Breaking changes

Yes, two. This needs a major release, classified and versioned when the release is cut.

1. The merchant-specific subdomain is mandatory for the Default and DefaultOAuth platforms. Code that omitted it and relied on the implicit fallback to api.checkout.com / access.checkout.com now fails at client construction. Migration: set the subdomain, or use the legacy-domain opt-out as a temporary measure. The Previous (ABC) platform is unaffected.
2. An invalid subdomain now fails instead of being silently ignored. Callers passing a malformed value keep working against the shared host today; after this change they fail fast. This one is easy to miss because it is not what the ticket asked for, so it needs its own line in the release notes.

README

Updated in this PR: a "Subdomain value" section above the Default example, the subdomain added to the configuration samples, and a "Legacy domain (emergency use only)" section at the bottom.

Notes

The suite routes every client it builds through a single helper that uses the shared hosts. Applying the merchant-specific subdomain there looked better, since it is the path merchants are being moved to, but the sandbox OAuth clients are not provisioned for it: .NET CI failed 224 integration tests with invalid_client when the token request went to {subdomain}.access.sandbox.checkout.com. Binding those OAuth clients to the subdomain is a platform task and should land before merchants are told the subdomain is mandatory.

Reference implementation: checkout-sdk-net#590. Tracked as INT-1688.

No version bump here: that happens on master when the release is cut, per the release workflow.

[agent-wall-e]

🔴 Risk Classification: MAJOR

Approval route: AI Review + Human Approval Required
Rollback controls: Change-freeze window + documented rollback plan

Classification reasons

• security_sensitive_path:checkout_sdk/oauth_sdk.py
• security_sensitive_path:tests/oauth_integration_test.py

Operational gates

• ✅ jira_ticket (INT-1688)
• ✅ independent_review

Files analysed: 15

---

_{wall-e 2026.06.19-02 · policy 376219bc71e6…}

[agent-wall-e]

🔬 Debug — why this classification?

Each reason code emitted by the classifier, its source clause in the AI in SDLC Control Framework, and what it means.

Reason code	Kind	Clause	Meaning
security_sensitive_path — checkout_sdk/oauth_sdk.py	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).
security_sensitive_path — tests/oauth_integration_test.py	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).

Kinds:

• classifying — this rule contributed to the chosen tier.
• informational — context only; did not by itself decide the tier.

See issue #3 for the proposal to formalise this map as Appendix A of the standards doc.

_{wall-e 2026.06.19-02 · debug}

[agent-wall-e]

🔵 Advisory review: Sound, but needs your judgement

This PR needs a human approval. The code itself reads as correct; whether it should land depends on context I don't have.

This PR enforces that Default and OAuth SDK callers must now explicitly set either environment_subdomain or use_legacy_domain at build time, removing the silent fallback to shared hosts. The implementation is technically correct and internally consistent, but the breaking-change severity and the acknowledged gap (sandbox OAuth clients not yet provisioned for MSSD, forcing every integration test fixture to opt into the deprecated path) are business/deployment decisions a human must weigh.

For you to decide

• The PR description explicitly acknowledges that sandbox OAuth clients are not provisioned for MSSD, meaning every integration test fixture must use use_legacy_domain() — this creates a situation where the 'deprecated emergency fallback' is the only working path for tests, which undermines the signal the deprecation warning is meant to send.
• The _environment_subdomain property is evaluated lazily at build time (once in oauth_sdk.py via environment_subdomain = self._environment_subdomain), so _validate_environment_settings is called and then _environment_subdomain is called a second time independently — this is correct but slightly fragile since the property constructs a new EnvironmentSubdomain object each call; no bug today, but worth noting.
• In oauth_sdk.py, _validate_environment_settings() is called before environment_subdomain is assigned to the local variable; if _subdomain is non-None and valid, EnvironmentSubdomain.__init__ will be called once during validation (via the property) and once when assigned — EnvironmentSubdomain.__init__ itself calls create_url_with_subdomain which can raise, but validation already guards this, so no double-raise risk; still, the property is called twice per build() invocation.
• The PreviousSdk._validate_environment_settings() is now called in build() with _requires_environment_subdomain() returning False, so for Previous: neither subdomain nor legacy domain is required, but if a caller sets both, the 'cannot both be set' exception still fires — this is the correct and documented behaviour, just worth a reviewer confirming it is intentional.
• The README 'Legacy domain' section says 'Exactly one of environment_subdomain(...) or use_legacy_domain() must be set' but does not caveat the Previous platform exception in that same sentence, which could mislead Previous SDK users reading that section.
• The decision of whether to ship a mandatory-MSSD breaking change before sandbox OAuth infrastructure is ready (forcing all test fixtures onto the deprecated path) is a product/platform timing call that cannot be resolved from the diff alone.

---

_{This is not an approval. wall-e cannot auto-approve this PR — it is an opinion to help whoever does. Advisory review · us.anthropic.claude-sonnet-4-6 · wall-e 2026.06.19-02}

[agent-wall-e]

🔴 Risk Classification: MAJOR

Approval route: AI Review + Human Approval Required
Rollback controls: Change-freeze window + documented rollback plan

Classification reasons

• security_sensitive_path:checkout_sdk/oauth_sdk.py
• security_sensitive_path:tests/oauth_integration_test.py

Operational gates

• ✅ jira_ticket (INT-1688)
• ✅ independent_review

Files analysed: 15

---

_{wall-e 2026.06.19-02 · policy 376219bc71e6…}

[agent-wall-e]

🔬 Debug — why this classification?

Each reason code emitted by the classifier, its source clause in the AI in SDLC Control Framework, and what it means.

Reason code	Kind	Clause	Meaning
security_sensitive_path — checkout_sdk/oauth_sdk.py	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).
security_sensitive_path — tests/oauth_integration_test.py	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).

Kinds:

• classifying — this rule contributed to the chosen tier.
• informational — context only; did not by itself decide the tier.

See issue #3 for the proposal to formalise this map as Appendix A of the standards doc.

_{wall-e 2026.06.19-02 · debug}

[agent-wall-e]

🔴 Risk Classification: MAJOR

Approval route: AI Review + Human Approval Required
Rollback controls: Change-freeze window + documented rollback plan

Classification reasons

• security_sensitive_path:.github/workflows/build-main.yml
• security_sensitive_path:.github/workflows/build-pull-request.yml
• security_sensitive_path:.github/workflows/build-release.yml
• security_sensitive_path:checkout_sdk/oauth_sdk.py
• security_sensitive_path:tests/oauth_integration_test.py

Operational gates

• ✅ jira_ticket (INT-1688)
• ✅ independent_review

Files analysed: 18

---

_{wall-e 2026.06.19-02 · policy 376219bc71e6…}

[agent-wall-e]

🔬 Debug — why this classification?

Each reason code emitted by the classifier, its source clause in the AI in SDLC Control Framework, and what it means.

Reason code	Kind	Clause	Meaning
security_sensitive_path — .github/workflows/build-main.yml	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).
security_sensitive_path — .github/workflows/build-pull-request.yml	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).
security_sensitive_path — .github/workflows/build-release.yml	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).
security_sensitive_path — checkout_sdk/oauth_sdk.py	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).
security_sensitive_path — tests/oauth_integration_test.py	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).

Kinds:

• classifying — this rule contributed to the chosen tier.
• informational — context only; did not by itself decide the tier.

See issue #3 for the proposal to formalise this map as Appendix A of the standards doc.

_{wall-e 2026.06.19-02 · debug}

[agent-wall-e]

🔴 Risk Classification: MAJOR

Approval route: AI Review + Human Approval Required
Rollback controls: Change-freeze window + documented rollback plan

Classification reasons

• security_sensitive_path:.github/workflows/build-main.yml
• security_sensitive_path:.github/workflows/build-pull-request.yml
• security_sensitive_path:.github/workflows/build-release.yml
• security_sensitive_path:checkout_sdk/oauth_sdk.py
• security_sensitive_path:tests/oauth_integration_test.py

Operational gates

• ✅ jira_ticket (INT-1688)
• ✅ independent_review

Files analysed: 17

---

_{wall-e 2026.06.19-02 · policy 376219bc71e6…}

[agent-wall-e]

🔬 Debug — why this classification?

Each reason code emitted by the classifier, its source clause in the AI in SDLC Control Framework, and what it means.

Reason code	Kind	Clause	Meaning
security_sensitive_path — .github/workflows/build-main.yml	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).
security_sensitive_path — .github/workflows/build-pull-request.yml	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).
security_sensitive_path — .github/workflows/build-release.yml	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).
security_sensitive_path — checkout_sdk/oauth_sdk.py	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).
security_sensitive_path — tests/oauth_integration_test.py	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).

Kinds:

• classifying — this rule contributed to the chosen tier.
• informational — context only; did not by itself decide the tier.

See issue #3 for the proposal to formalise this map as Appendix A of the standards doc.

_{wall-e 2026.06.19-02 · debug}

[agent-wall-e]

🔴 Risk Classification: MAJOR

Approval route: AI Review + Human Approval Required
Rollback controls: Change-freeze window + documented rollback plan

Classification reasons

• security_sensitive_path:checkout_sdk/oauth_sdk.py
• security_sensitive_path:tests/oauth_integration_test.py

Operational gates

• ✅ jira_ticket (INT-1688)
• ✅ independent_review

Files analysed: 14

---

_{wall-e 2026.06.19-02 · policy 376219bc71e6…}

[agent-wall-e]

🔬 Debug — why this classification?

Each reason code emitted by the classifier, its source clause in the AI in SDLC Control Framework, and what it means.

Reason code	Kind	Clause	Meaning
security_sensitive_path — checkout_sdk/oauth_sdk.py	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).
security_sensitive_path — tests/oauth_integration_test.py	classifying	§2.1 M4/M5	Path matched a sensitive pattern (auth, secrets, crypto, PCI, migrations, network IaC).

Kinds:

• classifying — this rule contributed to the chosen tier.
• informational — context only; did not by itself decide the tier.

See issue #3 for the proposal to formalise this map as Appendix A of the standards doc.

_{wall-e 2026.06.19-02 · debug}

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud