ARCH-10: monthlyCostFromConvertibleRI money formula duplicated verbatim, with bare 730/8760 despite named constants [go part] #109

Split from LeanerCloud/cloud-commitments-cli#1199 (cross-component issue, monorepo split)

Severity: P3. Confidence: high. Informational.

Affected files:

• providers/aws/recommendations/parser_sp.go:241-242 (defines const hoursPerMonth = 730.0, the canonical constant)

Recommendation:
Move the shared money-display formula next to ec2svc.ConvertibleRI or into a shared exchange package with a shared HoursPerMonth constant, so callers in other repos (e.g. cloud-commitments-platform's internal/api/handler_ri_exchange.go and internal/server/handler_ri_exchange.go, which currently hardcode a bare 730) can reuse it instead of re-deriving it.

Findings from the 2026-09-02 codebase audit (A08b-044)

The same bare-constant problem has a wider footprint than the monthlyCostFromConvertibleRI duplication. 8760.0 appears as an inline literal on money paths in twelve provider files:

• Azure: providers/azure/services/cache/client.go:548, cosmosdb/client.go:548, database/client.go:567, search/client.go:463, managedredis/client.go:492, synapse/client.go:439, compute/client.go:709, savingsplans/client.go:411
• GCP: providers/gcp/services/cloudsql/client.go:363, cloudstorage/client.go:356, memorystore/client.go:350, computeengine/client.go:822

As with 730, a named constant is the fix, in the shared pricing helper both providers already import.

A second, adjacent hygiene item in the same files: the GCP billing service IDs are opaque and uncommented, e.g. services/9662-B51E-5089 at providers/gcp/services/cloudsql/client.go:350 plus the equivalents at cloudstorage/client.go:343 (services/95FF-2EF5-5EA1), memorystore/client.go:337 (services/D559-82DA-3A56) and computeengine/client.go:809 (services/6F81-5844-456A). A transposed digit there yields an empty SKU catalog that surfaces as "no pricing found" rather than an error, so naming each as a documented package constant is worth doing in the same pass.

Re-verified live on 2026-09-27: hoursPerMonth still at parser_sp.go:241-242; all twelve 8760.0 sites and all four GCP ListSKUs("services/...") literals confirmed present at the line numbers above (drifted slightly from the original audit's numbers due to unrelated commits, but all still exist as bare literals).

Acceptance criteria

• hoursPerMonth/HoursPerMonth (or equivalent) is exported from a location importable by both AWS, Azure and GCP provider packages (and, ideally, by cloud-commitments-platform's exchange handlers, which currently duplicate the formula with a bare 730).
• All twelve 8760.0 literals in the Azure and GCP client files listed above are replaced with the shared constant (or a locally-named hoursPerYear/equivalent that documents its relationship to hoursPerMonth).
• The four opaque GCP billing service IDs (9662-B51E-5089, 95FF-2EF5-5EA1, D559-82DA-3A56, 6F81-5844-456A) become named, documented package constants instead of inline string literals.
• No behavior change; this is a magic-value/duplication cleanup only.