feat(api): PR action routes — merge + resolve-comments

[neversettle17-101]

Summary

• Implements POST /api/v1/prs/{id}/merge and POST /api/v1/prs/{id}/resolve-comments
• Service logic lives in internal/service/pr/ as ActionManager interface + ActionService struct — following the projects controller pattern (import service package directly, no ports indirection)
• Drops internal/ports/scm.go and internal/scm/ intermediary package from earlier iterations
• Fixes P1 bug: resolveComments was guarding JSON decode with r.ContentLength > 0, which silently dropped bodies sent with chunked transfer encoding — replaced with unconditional decode + io.EOF check
• *github.Provider satisfies PRProvider via duck typing; no extra adapter layer

Test plan

• go test ./... passes (all packages green, drift guard passes)
• POST /api/v1/prs/1/merge → 501 when service is nil
• POST /api/v1/prs/1/resolve-comments → 501 when service is nil
• Unit tests in service/pr/action_service_test.go cover happy paths and all error mappings
• Unit tests in controllers/prs_test.go cover 200/404/409/422/501 for both routes

Closes #21.

🤖 Generated with Claude Code

[greptile-apps]

Greptile Summary

Adds POST /api/v1/prs/{id}/merge and POST /api/v1/prs/{id}/resolve-comments action routes, wiring a new ActionManager interface and stub ActionService in internal/service/pr/. The PR addresses several issues from prior iterations — sentinel errors now live in service/pr, the nil-service guard correctly returns 501, and the body-decode guard correctly excludes io.ErrUnexpectedEOF.

• controllers/prs.go + service/pr/errors.go: new controller with nil-guard 501s, error sentinel package corrected from controllers to service/pr, and isEmptyBody narrowed to io.EOF only.
• service/pr/action_service.go: stub ActionService with TODO placeholders for both operations; correctly parses prID via strconv.Atoi for the merge response.
• specgen/build.go + openapi.yaml: OpenAPI spec extended with both operations, schema components, and a prs tag.

Confidence Score: 5/5

Safe to merge; the core routing, error mapping, nil-service guard, and body-decode logic are all correct.

The major issues from prior review rounds have all been addressed: sentinel errors now live in service/pr (no circular-import risk), the nil-service guard correctly returns 501 via apispec.NotImplemented, and isEmptyBody is correctly narrowed to io.EOF only. The remaining findings are documentation or dead-code nits that do not affect runtime behavior. The stub nature of ActionService is clearly called out with TODOs and poses no runtime hazard since real callers must supply a non-nil ActionManager.

No files require special attention; specgen/build.go has a dead schemaNames entry and a missing 400 response unit for resolveComments, but neither affects the running server.

Important Files Changed

Filename	Overview
backend/internal/httpd/controllers/prs.go	New controller for PR action routes; nil-service guard correctly emits 501, error mapping reads from service/pr sentinels, and isEmptyBody is correctly narrowed to io.EOF only.
backend/internal/service/pr/action_service.go	Stub ActionService with TODO placeholders; Merge correctly parses prID with strconv.Atoi (parse error silently ignored, returning PRNumber 0 for non-numeric input), ResolveComments always returns Resolved: 0.
backend/internal/service/pr/errors.go	Sentinel errors correctly placed in service/pr package, eliminating the circular-import risk from the prior iteration.
backend/internal/httpd/api.go	PRsController wired with deps.PRs directly (nil when SCM not configured); no stub injection, so the nil guard in the controller fires correctly.
backend/internal/httpd/apispec/specgen/build.go	prOperations() added with correct reqBody: nil for resolveComments; ControllersResolveCommentsRequest entry in schemaNames is dead code and 400 response is undocumented.
backend/internal/httpd/controllers/prs_test.go	Good coverage of 200/404/409/422/501 for both routes; section comment at line 39 is stale (says 503 SCM_NOT_CONFIGURED but tests correctly assert 501 NOT_IMPLEMENTED).
backend/internal/httpd/controllers/dto.go	Four new DTO types added; json tags are consistent with the OpenAPI spec.
backend/internal/httpd/apispec/openapi.yaml	Both PR routes added with correct path params, response schemas, and status codes; no 400 response documented for resolveComments despite the handler returning 400 on invalid JSON.

Sequence Diagram

sequenceDiagram
    participant Client
    participant PRsController
    participant ActionManager
    participant SCMProvider

    Client->>PRsController: "POST /api/v1/prs/{id}/merge"
    alt "Svc == nil"
        PRsController-->>Client: 501 NOT_IMPLEMENTED
    else
        PRsController->>ActionManager: Merge(ctx, prID)
        ActionManager->>SCMProvider: squash-merge (TODO)
        SCMProvider-->>ActionManager: MergeResult / error
        alt success
            ActionManager-->>PRsController: "MergeResult{PRNumber, Method}"
            PRsController-->>Client: 200 MergePRResponse
        else ErrPRNotFound
            PRsController-->>Client: 404 PR_NOT_FOUND
        else ErrPRNotMergeable
            PRsController-->>Client: 409 PR_NOT_MERGEABLE
        else ErrPRPreconditions
            PRsController-->>Client: 422 PR_PRECONDITIONS_UNMET
        end
    end

    Client->>PRsController: "POST /api/v1/prs/{id}/resolve-comments"
    alt "Svc == nil"
        PRsController-->>Client: 501 NOT_IMPLEMENTED
    else
        PRsController->>PRsController: decode optional JSON body
        alt malformed JSON
            PRsController-->>Client: 400 INVALID_JSON
        else
            PRsController->>ActionManager: ResolveComments(ctx, prID, commentIDs)
            ActionManager->>SCMProvider: resolve threads (TODO)
            SCMProvider-->>ActionManager: ResolveResult / error
            alt success
                ActionManager-->>PRsController: "ResolveResult{Resolved}"
                PRsController-->>Client: 200 ResolveCommentsResponse
            else ErrNothingToResolve
                PRsController-->>Client: 422 NOTHING_TO_RESOLVE
            end
        end
    end

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_{Reviews (9): Last reviewed commit: "fix(prs): align nil-service guard with s..." | Re-trigger Greptile}

[neversettle17-101]

Removed all three dead path-param entries (ControllersProjectIDParam, ControllersSessionIDParam, ControllersPRIDParam) from schemaNames — they were never matched by the interceptor since swaggest reflects path-param structs inline rather than as $ref component schemas.