feat(purchases): make GCP Compute commitment creation idempotent

[cristim]

Closes #654. Refs #641 (final executor slice, after AWS #652 and Azure #653).

GCP Compute CUD creation previously named commitments cud- and ignored opts.IdempotencyToken, so a re-drive could create a second committed-use discount (financial double-purchase). Now both GCP idempotency levers are derived deterministically from the token:

• RequestId on RegionCommitments.Insert (GCP native server-side dedupe) via common.IdempotencyGUID, the same canonical-UUID derivation Azure feat(purchases): make Azure reservation purchases idempotent (refs #641) #653 uses for reservationOrderID. Same token -> same RequestId -> second Insert is a server-side no-op.
• Deterministic RFC1035-valid Name (cud-) as defense-in-depth: a re-drive that reaches Insert collides on the name and GCP returns ALREADY_EXISTS.

Empty token preserves the prior timestamp-based behaviour (CLI path). Token masked in logs via common.MaskToken (matching #652). Scope: computeengine only; CloudSQL/Storage/Memorystore stay advisory-only per #649.

Regression tests: same token on a 2nd call yields identical RequestId + name (no double-buy); empty-token CLI path stays non-idempotent. Full computeengine suite green (39 tests). A small adjacent refactor extracted buildInsertRequest to keep PurchaseCommitment under the gocyclo-10 pre-commit limit.

Once merged, #641 closes and #639 (idempotent auto-re-drive) unblocks.

Summary by CodeRabbit

Release Notes

• Bug Fixes

  • Improved idempotent request handling for commitment purchases to ensure duplicate requests with the same idempotency token are properly deduplicated and do not result in duplicate commitments.

• Tests

  • Added regression test to verify correct idempotent behavior for commitment purchase operations.

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📥 Commits

Reviewing files that changed from the base of the PR and between 12aba9d and 039ae96.

📒 Files selected for processing (2)

• providers/gcp/services/computeengine/client.go
• providers/gcp/services/computeengine/client_test.go

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📝 Walkthrough

Walkthrough

GCP Compute commitment creation is refactored to use the provided IdempotencyToken to derive a deterministic commitment name and set the GCP Insert RequestId, enabling idempotent re-drive behavior. Helper functions generate RFC1035-valid names from token digests with timestamp fallback. Tests verify that repeated calls with identical tokens produce matching request IDs and commitment IDs.

Changes

Idempotent GCP Compute Commitment Creation

Layer / File(s)	Summary
Deterministic Name and RequestId Generation providers/gcp/services/computeengine/client.go	Adds log import and introduces idempotentNameTokenLen and idempotentCommitmentName helpers to derive deterministic RFC1035-valid commitment names from IdempotencyToken (with timestamp fallback). New buildInsertRequest helper constructs the Insert request, derives the commitment name, conditionally sets GCP's RequestId idempotency key when token yields a non-empty GUID, and logs the masked token and commitment name.
PurchaseCommitment Integration providers/gcp/services/computeengine/client.go	PurchaseCommitment refactored to delegate Insert request construction to buildInsertRequest, obtaining both the request and deterministic commitment name. Commitment ID is now read from the returned name instead of the commitment payload.
Test Infrastructure and Idempotent Re-Drive Test providers/gcp/services/computeengine/client_test.go	MockCommitmentsService enhanced with insertReqs slice to record all Insert requests, enabling multi-call assertions. New TestComputeEngineClient_PurchaseCommitment_IdempotentReDrive regression test verifies two calls with the same IdempotencyToken produce identical RequestId and commitment name (non-zero UUID) and matching commitment IDs.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related issues

• LeanerCloud/CUDly#641: This PR completes the GCP Compute slice of issue #641 by implementing idempotent commitment creation via deterministic name derivation and RequestId setting from IdempotencyToken, directly unblocking auto-re-drive.

Possibly related PRs

• LeanerCloud/CUDly#638: Both PRs implement idempotent commitment creation by using PurchaseOptions.IdempotencyToken to ensure repeated PurchaseCommitment calls deduplicate consistently, addressing the same root issue across different provider implementations.

Suggested labels

enhancement, priority/p2, severity/medium, urgency/this-quarter, impact/all-users, type/feat

Poem

🐰 A token transforms to a name,
Deterministic, RFC-tame,
GCP's RequestId now stable and sound,
Re-drives duplicate-free, no second found!
The commitment persists, idempotent and true,
One purchase, one promise—our rabbit breaks through! 🎉

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 71.43% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: implementing idempotent GCP Compute commitment creation, which is the primary objective of the PR.
Linked Issues check	✅ Passed	The PR fully implements all coding requirements from #654: idempotent commitment naming via IdempotencyToken, RequestId setting via common.IdempotencyGUID, regression test for re-drive behavior, and scoping to computeengine only.
Out of Scope Changes check	✅ Passed	All changes are within scope: computeengine client refactoring and tests, with no modifications to CloudSQL/Storage/Memorystore as required.

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✨ Finishing Touches

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• Create stacked PR
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🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/654-gcp-compute-idempotency

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[cristim]

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