fix(gcp): CUD recommender ID does not match any documented Google recommender

[cristim]

Reviewed commit: be11bdcb5 (origin/main), from the 2026-07-28 full-repo review.

Severity: HIGH. GCP CUD recommendations may be permanently zero, indistinguishable from "no savings available".

Where

providers/gcp/services/computeengine/client.go:255

What

The parent is built as:

projects/{p}/locations/{region}/recommenders/google.billing.CostInsight.commitmentRecommender

Google's published commitment recommenders are google.compute.commitment.UsageCommitmentRecommender (regional) and google.cloudbilling.commitment.SpendBasedCommitmentRecommender (global). This ID matches neither.

The sibling GCP clients all use plausible documented IDs (google.cloudsql.instance.PerformanceRecommender, google.storage.bucket.CostRecommender, google.memorystore.redis.PerformanceRecommender); this one has no counterpart. Every test that exercises it injects a mock (client_test.go:972 echoes the same literal), so no test would catch a wrong ID.

Failure scenario

ListRecommendations returns NOT_FOUND / INVALID_ARGUMENT for the unknown recommender. GetRecommendations propagates it (:277), collectRegion counts every region's compute call as failed, and since compute is one of four attempted services, the partial-failure path returns the other three services' results with a nil error.

GCP CUD recommendations are then permanently zero with only a WARN log, indistinguishable from "no CUD savings available".

Fix direction

Verify against the live Recommender API and switch to google.compute.commitment.UsageCommitmentRecommender. Add a startup or integration check that a known-good project returns a non-error response.

Related

Same shape as the Azure literals tracked by LeanerCloud/cloud-commitments-cli#1508 / LeanerCloud/cloud-commitments-cli#1318 and needs the same live-catalog verification. providers/gcp is not covered by CI (LeanerCloud/cloud-commitments-cli#1478).

[cristim]

Resolved by merged PR #162 (merge commit 2d2116e), retained in current main 5fb4663. This is the same invalid recommender-ID defect tracked in #134.

Independent gpt-6-astra review confirmed that the production Compute client requests the regional google.compute.commitment.UsageCommitmentRecommender documented in Google's recommender catalog. The real Recommender SDK fixture rejects any other parent, checks routing metadata and pagination tokens, and exercises successful nonempty, empty and denied responses through the public adapter. Fresh uncached race execution of TestComputeRecommendationsThroughSDK passed in 2.019s; the tested providers/gcp and pkg trees were verified identical to current main.

Verification limit: this is local real-SDK transport evidence under the user's accepted local-verification review path. No authenticated request against a live Google project was performed. General partial-service error aggregation was not changed by this fix; the invalid-ID cause reported here is removed.

The implementation, regression coverage and original review record are in #162. No duplicate implementation PR is needed.