feat(taxcode): seed default Stripe tax codes at server startup

[borbelyr-kong]

Summary by CodeRabbit

• New Features
  • Default tax codes are now automatically provisioned during server startup, making a curated set of Stripe tax codes immediately available for use in your system.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 6c2ffab7-a5d7-41b3-b615-82d1fffe54a8

📥 Commits

Reviewing files that changed from the base of the PR and between e1aef59 and 8382186.

📒 Files selected for processing (5)

• cmd/server/main.go
• openmeter/server/server_test.go
• openmeter/taxcode/defaults.go
• openmeter/taxcode/service.go
• openmeter/taxcode/service/taxcode.go

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📝 Walkthrough

Walkthrough

This PR adds default tax code provisioning to the server startup sequence. It introduces a new interface method to the TaxCodeService for seeding predefined Stripe tax codes, implements the method with idempotent conflict handling, defines the default tax code seeds, and wires the provisioning call into server initialization before meter setup.

Changes

Cohort / File(s)	Summary
Server startup integration cmd/server/main.go	Wires ProvisionDefaultTaxCodes into server startup after namespace and sandbox initialization but before meter setup; logs and exits on failure.
Service interface & implementation openmeter/taxcode/service.go, openmeter/taxcode/service/taxcode.go	Adds ProvisionDefaultTaxCodes method to the Service interface and implements it with transactional seeding of default Stripe tax codes, skipping conflicts by treating existing keys as non-fatal.
Default tax code seeds openmeter/taxcode/defaults.go	New file defining DefaultTaxCodeSeed struct and DefaultStripeTaxCodes slice containing curated Stripe tax code entries with keys, names, optional descriptions, and Stripe identifiers.
Test utilities openmeter/server/server_test.go	Adds no-op ProvisionDefaultTaxCodes method to NoopTaxCodeService for test support.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• feat(backend): add tax code service #3892: Foundational work adding the taxcode service that this PR extends with the new provisioning interface method and implementation.
• feat(subscription): dual read/write taxcode on subscription items #4011: Related through shared reliance on the taxcode.Service API surface.

Suggested reviewers

• tothandras
• turip
• GAlexIHU
• hekike

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 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 change: adding default Stripe tax code provisioning at server startup, which is reflected across multiple files in the changeset.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ 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/tax-code-seeds

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[tothandras]

I'd choose a key that's specific to our platform. When we support other providers, the same tax code will map between providers.

Suggested change

	Key: "stripe_txcd_00000000",
	Key: "non_taxable",

or we can define a format for OM

Suggested change

	Key: "stripe_txcd_00000000",
	Key: "om_......",

[tothandras]

Can't we reuse the CreateTaxCodeInput type?

[tothandras]

These should come from config.