fix(aws/ec2): reject empty or unknown RI tenancy and scope

[cristim]

What

The EC2 RI client now rejects an empty, host or unknown tenancy and an empty or unknown scope before any AWS call. Before this change it silently picked shared (default) tenancy and Region scope.

Three call sites shared the defaults:

• buildEC2OfferingQuery: the purchase path through PurchaseCommitment, ValidateOffering and GetOfferingDetails.
• FindConvertibleOffering: the auto-exchange target lookup. The offering ID it returns gets bought by the exchange.
• ListTargetOfferings: the exchange target picker.

parseEC2Tenancy and parseEC2Scope replace canonicalizeEC2Tenancy / canonicalizeEC2Scope. They return types.Tenancy / types.Scope and still accept the legacy pre-#598 spellings (shared, region, availability-zone, any casing). ec2OfferingQuery.scope is now types.Scope.

Why

Issue #23, Bug 2. A recommendation with an empty Tenancy searched for and bought a shared-tenancy RI. If the workload runs on Dedicated Instances, that RI covers nothing. The term fallback (Bug 1) was already fixed on main.

AWS references:

• SDK DescribeReservedInstancesOfferingsInput.InstanceTenancy (ec2 v1.251.2): "The host value cannot be used with this parameter. Use the default or dedicated values only. Default: default". An omitted tenancy means shared tenancy on AWS's side too, so the client has to reject the empty value itself. host gets an error because no RI product exists for it.
• types.Scope has two values: Region and Availability Zone. The scope filter takes the same values.
• Cost Explorer EC2InstanceDetails.Tenancy ("dedicated or shared"). The parser (providers/aws/recommendations/parser_services.go resolveEC2Tenancy / resolveEC2Scope) always fills both fields, mapping a nil CE tenancy to default and a missing AZ to Region. Freshly collected recs are not affected.

Consumers checked (read-only): the platform's listTargetOfferings handler and its auto-exchange adapters pass tenancy and scope from DescribeReservedInstances, which always returns both. The MCP aws_ec2_ri tool always sets both, and providers/aws/ladder already rejects empty values. Legacy DB rows with empty details already fail on the existing empty-Platform check.

How verified

New tests in client_test.go:

• TestPurchaseCommitment_InvalidTenancyOrScope_ErrorsBeforeAPICall
• TestFindConvertibleOffering_InvalidTenancyOrScope_ErrorsBeforeAPICall
• TestListTargetOfferings_InvalidTenancyOrScope_ErrorsBeforeAPICall

Each test runs five cases: empty, host and unknown tenancy; empty and unknown scope. The mock returns a matching default-tenancy offering, so a silent default goes through to a purchase.

On origin/main with only the new call-path tests applied (all 15 subtests fail, because the purchase succeeds):

--- FAIL: TestPurchaseCommitment_InvalidTenancyOrScope_ErrorsBeforeAPICall/empty_tenancy (0.01s)
--- FAIL: TestPurchaseCommitment_InvalidTenancyOrScope_ErrorsBeforeAPICall/empty_scope (0.01s)
            	Error:      	An error is expected but got nil.
FAIL	github.com/LeanerCloud/cloud-commitments-go/providers/aws/services/ec2

With the fix: all pass. Mutation check: putting "" back into the default case of parseEC2Tenancy makes the empty_tenancy subtest of all three call-path tests fail, along with TestParseEC2Tenancy/empty_errors.

Commands (GOTOOLCHAIN=go1.26.6 GOWORK=off GOFLAGS='-p=2 -count=1' AWS_EC2_METADATA_DISABLED=true, in providers/aws): go build ./..., go vet ./..., go test ./..., go test -race ./services/ec2/, golangci-lint run ./... (no issues). No other module imports the EC2 client.

Not in this PR

• Issue ARCH-04 followup: EC2 client silent term + tenancy fallbacks not covered by PR #1207 #23 finding A07-032 (the offeringClass default in describeInputFromQuery) is still open, so this PR does not close the issue.
• The comments and error messages in providers/aws/ladder/purchase.go and pkg/common/service_details_codec.go still describe the EC2 client defaulting tenancy and scope. Both checks still work; only the wording is stale now.

Refs #23

Summary by CodeRabbit

• Bug Fixes
  • EC2 offering searches now reject empty or unsupported tenancy and scope values instead of silently defaulting them.
  • Accepted legacy spellings continue to work, including shared, lowercase tenancy values, and common regional or availability-zone terms.

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📥 Commits

Reviewing files that changed from the base of the PR and between 1f8f73f and 5032530.

📒 Files selected for processing (2)

• providers/aws/services/ec2/client.go
• providers/aws/services/ec2/client_test.go

📝 Walkthrough

Walkthrough

EC2 offering lookup paths now parse tenancy and scope into AWS enum values. They reject empty or unsupported inputs instead of applying defaults. Supported legacy spellings remain accepted.

Changes

EC2 offering validation

Layer / File(s)	Summary
Parse and validate tenancy and scope providers/aws/services/ec2/client.go, providers/aws/services/ec2/client_test.go	Parsers map supported spellings to EC2 enum values. Purchase query construction rejects invalid values. Tests cover parser results and invalid inputs across offering lookup paths.
Convertible-offering lookup providers/aws/services/ec2/client.go	FindConvertibleOffering uses parsed tenancy and scope values and returns errors for invalid inputs.
Target-offering listing providers/aws/services/ec2/client.go, providers/aws/services/ec2/client_test.go	ListTargetOfferings validates tenancy and scope before normalizing other parameters. Requests and returned offerings use the parsed values. Tests cover accepted spellings and request filters.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Merge Risk: 🔵 Low · up to 1f8f7

Empty tenancy or scope in exchange lookups is now rejected instead of silently defaulting to shared tenancy and regional scope. This is intended. Any external caller that relied on the defaults must now pass the source RI's values. The risk is low and limited to such callers.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 73.68% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 19 functions across 2 files.	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 clearly and concisely describes the main change: rejecting empty or unknown RI tenancy and scope values.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Inline comments:
Review comments at @providers/aws/services/ec2/client.go:
- Around line 782-788: Update the callers of FindConvertibleOffering and
ListTargetOfferings to pass the source RI’s tenancy and scope, ensuring omitted
values are resolved to the established default and Region values before these
lookup methods are called.

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• providers/aws/services/ec2/client.go
• providers/aws/services/ec2/client_test.go

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