fix(gcp/computeengine): stamp PaymentOption="monthly" to match peer GCP services (followup to #709) #718

Symptom

providers/gcp/services/computeengine/client.go:804 stamps rec.PaymentOption = "upfront" on every Compute Engine CUD recommendation it emits. Peer GCP services (cloudsql, memorystore, cloudstorage) consistently stamp "monthly". After PR #709's NormalizePaymentOption is in place, the normalizer coerces this to "monthly" with a WARN log — which means a WARN fires on every single GCP Compute Engine recommendation emitted by a healthy collector.

Root cause

GCP CUDs are billed monthly across the commitment term. There is no "upfront" billing tier in GCP. The buildCommitmentRequests function at providers/gcp/services/computeengine/client.go:350-373 confirms this — it takes only a Plan (TWELVE_MONTH / THIRTY_SIX_MONTH) and never reads PaymentOption.

The "upfront" literal at line 804 is leftover from when the codebase modelled all providers with AWS-style tokens. Other GCP services were fixed (or always correctly stamped "monthly"); this one was missed.

Fix

One-line change at providers/gcp/services/computeengine/client.go:804:

-    rec.PaymentOption = "upfront"
+    rec.PaymentOption = "monthly"

After this lands, the NormalizePaymentOption WARN log goes silent on the GCP Compute Engine path (no more all-upfront → monthly with WARN per rec), and the stamping is consistent across all GCP service emitters.

Tests

• Update any test in providers/gcp/services/computeengine/client_test.go that asserts the stamped value (change expected "upfront" to "monthly").
• Spot-check downstream consumers (internal/purchase/execution.go, internal/recommendations/*) to confirm they don't have a GCP-Compute-Engine-specific branch that depends on "upfront" — if they do, that's a separate bug surfaced by this fix.

Why this matters

• Log hygiene: WARN-per-rec on a healthy pipeline pollutes ops dashboards and trains operators to ignore the WARN level.
• Consistency: 4 GCP services should stamp the same canonical token. Drift here is technical debt.
• Forward-compat: any future GCP service added by mirroring computeengine will inherit the bug; mirroring cloudsql/memorystore/cloudstorage won't.

Related

• PR fix(config): accept provider-canonical payment options in plan validator #709 (fix(config): accept provider-canonical payment options in plan validator) — added the normalizer that masks this bug today.
• providers/gcp/services/{cloudsql,memorystore,cloudstorage}/client.go — peer services with the correct "monthly" stamp.