refactor(handlers): introduce repository layer for external-id-audit-handler (#1237 pattern)

[susumutomita]

Summary

Move every direct @aws-sdk/* import out of external-id-audit-handler/index.ts into a dedicated repository module. The handler now consumes plain JS objects from a single typed boundary; the repository owns AWS SDK Command construction + DynamoDB marshalling.

This PR demonstrates the migration pattern Issue #1237 calls for, using one representative handler as the proof-of-concept. Follow-up PRs continue the same extraction for the remaining baselined handlers (describe-stack-handler, generic-scoring-handler, portal-handler, etc).

Changes

• new infrastructure/lib/problem-deploy/handlers/external-id-audit-handler/repository.ts (165 lines) — owns CloudWatch + DynamoDB + lib-dynamodb client construction, Command shapes, and item marshalling
• index.ts shrinks from 167 → 118 lines and contains zero SDK imports
• new infrastructure/test/.../external-id-audit-handler-repository.test.ts (116 lines) — 8 unit cases asserting PutItemCommand / GetItemCommand / QueryCommand / PutMetricDataCommand are built with the expected shape (PK / SK / TTL / metric dimensions)
• existing handler test (external-id-audit-handler.test.ts) updated to mock the repository (not the SDK directly) — coverage preserved, mock boundary clearer
• .claude/harness/baselines/handler-no-direct-sdk-import.json — 6 baselined SDK-import violations removed (external-id-audit-handler is now clean per the rule introduced in feat(#986): SOLID 強制を harness に実装 (file-too-large / handler-no-direct-sdk-import + biome complexity) #1004)

Closes #1237

Regression analysis

• Behavior-preserving: same DDB items, same DDB schema, same TTL, same CloudWatch metric dimensions, same retry behavior, same StatusCodes.
• Existing 8 handler tests pass against the new repository indirection.
• New 8 repository tests assert the SDK Command shapes that the handler used to construct inline — guards against drift.
• Risk: low — narrow scope, one handler, behavior pinned by two test suites (route + command shape).

Physical impact

• NO-OP for CloudFormation / IAM / Lambda runtime — the Lambda still calls the same AWS APIs with the same parameters.
• UPDATE: external-id-audit-handler Lambda bundle (separation of concerns; no runtime behavior change; minified bytes nearly identical).
• NEW FILES: repository.ts (impl) + *-repository.test.ts (test).
• DELETE: 6 entries removed from .claude/harness/baselines/handler-no-direct-sdk-import.json.

Migration roadmap (for follow-up PRs)

Remaining baselined handlers (each ~1 PR worth):

• describe-stack-handler
• generic-scoring-handler
• portal-handler
• competitor-accounts-handler
• participant-handler (largest; recently zod-validated in PR feat(participant-handler): zod-validate every route boundary #1274 — defer)
• deploy-handler

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 5b67ec24-ee76-4a61-abec-0d8a0c7a1e6b

📥 Commits

Reviewing files that changed from the base of the PR and between eaa6cd1 and 253b29c.

📒 Files selected for processing (5)

• .claude/harness/baselines/handler-no-direct-sdk-import.json
• infrastructure/lib/problem-deploy/handlers/external-id-audit-handler/index.ts
• infrastructure/lib/problem-deploy/handlers/external-id-audit-handler/repository.ts
• infrastructure/test/problem-deploy/external-id-audit-handler-repository.test.ts
• infrastructure/test/problem-deploy/external-id-audit-handler.test.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch refactor/handlers-via-repository-1237

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[codecov]

Codecov Report

❌ Patch coverage is 73.91304% with 6 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@eaa6cd1). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
...y/handlers/external-id-audit-handler/repository.ts	66.66%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1287   +/-   ##
=======================================
  Coverage        ?   64.28%           
=======================================
  Files           ?      253           
  Lines           ?     8476           
  Branches        ?     2673           
=======================================
  Hits            ?     5449           
  Misses          ?     2199           
  Partials        ?      828           

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