fix(aws/ladder): scope RI utilization query to EC2+region for reshape decisions (follow-up to #1361)

[cristim]

Summary

• GetRIUtilization (providers/aws/recommendations/utilization.go) built GetReservationUtilizationInput with no Filter at all, grouping only by SUBSCRIPTION_ID. This blends utilization across every reserved-resource type in the account (RDS, ElastiCache, OpenSearch, Redshift, standard EC2 RIs) and every region into a single number.
• The ladder ConvertibleRI (buffer) layer (providers/aws/ladder/layer_states.go) reads this as "this account/region's EC2 convertible-RI utilization" and uses it to decide whether to trigger a real RI reshape/exchange (pkg/ladder/allocate.go, ActionReshape). An underutilized RI in an unrelated service or region could trigger a reshape, or a genuinely poorly-utilized convertible RI could be masked by healthy unrelated reservations blended into the same aggregate. Real-money-decision correctness bug, follow-up to feat(ladder): integrate stranded phase-2 AWS capability onto main #1361 (merged).
• Fix: add a Filter scoping SERVICE=Amazon Elastic Compute Cloud - Compute and REGION=<region> to the CE call (mirrors the existing serviceRegionFilter pattern in coverage.go). Threaded a region parameter through GetRIUtilization and its callers.
• Also intersect the (now EC2+region-scoped) response against the account's own convertible RI IDs (ListConvertibleReservedInstances) before aggregating in GetLayerStates, since a standard (non-convertible) EC2 RI in the same account/region would otherwise still pass the SERVICE+REGION filter and blend into the layer's UtilizationPct. This was a clean, contained addition since GetLayerStates already has both the RI list and the utilization slice in scope, so it's included rather than deferred as a follow-up.

Test plan

• go build ./... -- exit 0
• go vet ./... -- exit 0
• go test ./providers/aws/... ./internal/api/... ./internal/server/... -- exit 0
• go test ./... (full suite) -- exit 0
• New regression tests added: TestGetRIUtilization_ScopesToEC2AndRegion, TestGetRIUtilization_EmptyRegionOmitsRegionFilter (providers/aws/recommendations/utilization_test.go), TestGetLayerStates_RILayer_UtilizationExcludesUnrelatedReservations (providers/aws/ladder/ladder_test.go) -- all confirmed to FAIL against the pre-fix code (verified manually by reverting the fix locally) and PASS after
• golangci-lint run on touched packages -- 0 new issues introduced by this diff (pre-existing repo debt in touched files left untouched, out of scope); note the CI-pinned v2.10.1 binary could not be installed in this sandbox (external-script-execution policy), so this was verified with the locally available v2.11.4 instead
• gocyclo -over 10 on touched files -- exit 0, no output

Out of scope / documented follow-up

• The MEDIUM finding in computeEC2CoveragePct (layer_states.go) -- the one-colon pool-key heuristic also matches ElastiCache/OpenSearch/Redshift/MemoryDB pool keys, not just EC2 -- was not fixed here. No engine decision currently consumes CoveragePct (confirmed by an earlier review), so today's impact is a wrong reported metric only, not a money-affecting decision. Filing as a separate follow-up issue.

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Review details

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: edae349b-6366-4d47-ac48-341b3131fded

📥 Commits

Reviewing files that changed from the base of the PR and between 1cc33d3 and b60f2a9.

📒 Files selected for processing (11)

• internal/api/handler_ri_exchange.go
• internal/api/handler_ri_exchange_integration_test.go
• internal/api/handler_ri_exchange_test.go
• internal/server/handler_ri_exchange.go
• internal/server/ladder_write.go
• providers/aws/ladder/interfaces.go
• providers/aws/ladder/ladder_test.go
• providers/aws/ladder/layer_states.go
• providers/aws/recommendations/utilization.go
• providers/aws/recommendations/utilization_test.go
• providers/aws/service_client.go

✨ Finishing Touches

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• Create PR with unit tests
• Commit unit tests in branch fix/1361-ce-utilization-filter

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[cristim]

Filed the deferred computeEC2CoveragePct finding as a separate follow-up: #1482 (lower priority -- no engine decision currently consumes CoveragePct, so it's a wrong reported metric only, not a live money-affecting decision like the fix in this PR).

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[coderabbitai]

@cristim Thanks for tracking the deferred computeEC2CoveragePct concern in #1482. I’ll review the PR with the EC2/region utilization scoping and convertible-RI filtering changes as the focus.

---

✏️ Learnings added

Learnt from: cristim
URL: https://github.com/LeanerCloud/CUDly/pull/1479

Timestamp: 2026-07-21T19:59:45.581Z
Learning: In `providers/aws/ladder/layer_states.go`, `computeEC2CoveragePct` uses a one-colon pool-key heuristic that can also match ElastiCache, OpenSearch, Redshift, and MemoryDB pool keys. As of PR `#1479`, no ladder engine decision consumes `CoveragePct`, so this is a reporting-metric correctness issue rather than a live money-affecting decision; it is tracked separately in GitHub issue `#1482`.

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[cristim]

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