feat: add title parameter to merge_pull_request tool (#134)

## Summary
- Add missing `title` parameter to `merge_pull_request` tool for custom merge commit titles
- Use `params.GetIndex()` for consistent index parameter handling (supports both string and number inputs)
- Add test for `MergePullRequestFn`

Closes #120

## Test plan
- [x] `go test ./operation/pull/ -run TestMergePullRequestFn` passes
- [x] All existing tests pass (`go test ./...`)
- [x] Build succeeds (`make build`)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/134
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: silverwind <silverwind@noreply.gitea.com>
Co-committed-by: silverwind <silverwind@noreply.gitea.com>

operation/pull/pull.go

@@ -182,7 +182,8 @@ var (
 		mcp.WithString("repo", mcp.Required(), mcp.Description("repository name")),
 		mcp.WithNumber("index", mcp.Required(), mcp.Description("pull request index")),
 		mcp.WithString("merge_style", mcp.Description("merge style: merge, rebase, rebase-merge, squash, fast-forward-only"), mcp.Enum("merge", "rebase", "rebase-merge", "squash", "fast-forward-only"), mcp.DefaultString("merge")),
-		mcp.WithString("message", mcp.Description("custom merge commit message (optional)")),
+		mcp.WithString("title", mcp.Description("custom merge commit title")),
+		mcp.WithString("message", mcp.Description("custom merge commit message")),
 		mcp.WithBoolean("delete_branch", mcp.Description("delete the branch after merge"), mcp.DefaultBool(false)),
 	)
 
@@ -845,9 +846,9 @@ func MergePullRequestFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.Call
 	if !ok {
 		return to.ErrorResult(errors.New("repo is required"))
 	}
-	index, ok := req.GetArguments()["index"].(float64)
+	index, err := params.GetIndex(req.GetArguments(), "index")
-	if !ok {
+	if err != nil {
-		return to.ErrorResult(errors.New("index is required"))
+		return to.ErrorResult(err)
 	}
 
 	mergeStyle := "merge"
@@ -855,6 +856,11 @@ func MergePullRequestFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.Call
 		mergeStyle = style
 	}
 
+	title := ""
+	if t, exists := req.GetArguments()["title"].(string); exists {
+		title = t
+	}
+
 	message := ""
 	if msg, exists := req.GetArguments()["message"].(string); exists {
 		message = msg
@@ -872,26 +878,27 @@ func MergePullRequestFn(ctx context.Context, req mcp.CallToolRequest) (*mcp.Call
 
 	opt := gitea_sdk.MergePullRequestOption{
 		Style:                  gitea_sdk.MergeStyle(mergeStyle),
+		Title:                  title,
 		Message:                message,
 		DeleteBranchAfterMerge: deleteBranch,
 	}
 
-	merged, resp, err := client.MergePullRequest(owner, repo, int64(index), opt)
+	merged, resp, err := client.MergePullRequest(owner, repo, index, opt)
 	if err != nil {
-		return to.ErrorResult(fmt.Errorf("merge %v/%v/pr/%v err: %v", owner, repo, int64(index), err))
+		return to.ErrorResult(fmt.Errorf("merge %v/%v/pr/%v err: %v", owner, repo, index, err))
 	}
 
 	if !merged && resp != nil && resp.StatusCode >= 400 {
-		return to.ErrorResult(fmt.Errorf("merge %v/%v/pr/%v failed: HTTP %d %s", owner, repo, int64(index), resp.StatusCode, resp.Status))
+		return to.ErrorResult(fmt.Errorf("merge %v/%v/pr/%v failed: HTTP %d %s", owner, repo, index, resp.StatusCode, resp.Status))
 	}
 
 	if !merged {
-		return to.ErrorResult(fmt.Errorf("merge %v/%v/pr/%v returned merged=false", owner, repo, int64(index)))
+		return to.ErrorResult(fmt.Errorf("merge %v/%v/pr/%v returned merged=false", owner, repo, index))
 	}
 
 	successMsg := map[string]any{
 		"merged":         merged,
-		"pr_index":       int64(index),
+		"pr_index":       index,
 		"repository":     fmt.Sprintf("%s/%s", owner, repo),
 		"merge_style":    mergeStyle,
 		"branch_deleted": deleteBranch,

operation/pull/pull_test.go

@@ -117,6 +117,123 @@ func TestEditPullRequestFn(t *testing.T) {
 	}
 }
 
+func TestMergePullRequestFn(t *testing.T) {
+	const (
+		owner = "octo"
+		repo  = "demo"
+		index = 5
+	)
+
+	var (
+		mu        sync.Mutex
+		gotMethod string
+		gotPath   string
+		gotBody   map[string]any
+	)
+
+	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch r.URL.Path {
+		case "/api/v1/version":
+			w.Header().Set("Content-Type", "application/json")
+			_, _ = w.Write([]byte(`{"version":"1.12.0"}`))
+		case fmt.Sprintf("/api/v1/repos/%s/%s", owner, repo):
+			w.Header().Set("Content-Type", "application/json")
+			_, _ = w.Write([]byte(`{"private":false}`))
+		case fmt.Sprintf("/api/v1/repos/%s/%s/pulls/%d/merge", owner, repo, index):
+			mu.Lock()
+			gotMethod = r.Method
+			gotPath = r.URL.Path
+			var body map[string]any
+			_ = json.NewDecoder(r.Body).Decode(&body)
+			gotBody = body
+			mu.Unlock()
+			w.WriteHeader(http.StatusOK)
+		default:
+			http.NotFound(w, r)
+		}
+	})
+
+	server := httptest.NewServer(handler)
+	defer server.Close()
+
+	origHost := flag.Host
+	origToken := flag.Token
+	origVersion := flag.Version
+	flag.Host = server.URL
+	flag.Token = ""
+	flag.Version = "test"
+	defer func() {
+		flag.Host = origHost
+		flag.Token = origToken
+		flag.Version = origVersion
+	}()
+
+	req := mcp.CallToolRequest{
+		Params: mcp.CallToolParams{
+			Arguments: map[string]any{
+				"owner":         owner,
+				"repo":          repo,
+				"index":         float64(index),
+				"merge_style":   "squash",
+				"title":         "feat: my squashed commit",
+				"message":       "Squash merge of PR #5",
+				"delete_branch": true,
+			},
+		},
+	}
+
+	result, err := MergePullRequestFn(context.Background(), req)
+	if err != nil {
+		t.Fatalf("MergePullRequestFn() error = %v", err)
+	}
+
+	mu.Lock()
+	defer mu.Unlock()
+
+	if gotMethod != http.MethodPost {
+		t.Fatalf("expected POST request, got %s", gotMethod)
+	}
+	if gotPath != fmt.Sprintf("/api/v1/repos/%s/%s/pulls/%d/merge", owner, repo, index) {
+		t.Fatalf("unexpected path: %s", gotPath)
+	}
+	if gotBody["Do"] != "squash" {
+		t.Fatalf("expected Do 'squash', got %v", gotBody["Do"])
+	}
+	if gotBody["MergeTitleField"] != "feat: my squashed commit" {
+		t.Fatalf("expected MergeTitleField 'feat: my squashed commit', got %v", gotBody["MergeTitleField"])
+	}
+	if gotBody["MergeMessageField"] != "Squash merge of PR #5" {
+		t.Fatalf("expected MergeMessageField 'Squash merge of PR #5', got %v", gotBody["MergeMessageField"])
+	}
+	if gotBody["delete_branch_after_merge"] != true {
+		t.Fatalf("expected delete_branch_after_merge true, got %v", gotBody["delete_branch_after_merge"])
+	}
+
+	if len(result.Content) == 0 {
+		t.Fatalf("expected content in result")
+	}
+	textContent, ok := mcp.AsTextContent(result.Content[0])
+	if !ok {
+		t.Fatalf("expected text content, got %T", result.Content[0])
+	}
+
+	var parsed struct {
+		Result map[string]any `json:"Result"`
+	}
+	if err := json.Unmarshal([]byte(textContent.Text), &parsed); err != nil {
+		t.Fatalf("unmarshal result text: %v", err)
+	}
+	if parsed.Result["merged"] != true {
+		t.Fatalf("expected merged=true, got %v", parsed.Result["merged"])
+	}
+	if parsed.Result["merge_style"] != "squash" {
+		t.Fatalf("expected merge_style 'squash', got %v", parsed.Result["merge_style"])
+	}
+	if parsed.Result["branch_deleted"] != true {
+		t.Fatalf("expected branch_deleted=true, got %v", parsed.Result["branch_deleted"])
+	}
+}
+
 func TestGetPullRequestDiffFn(t *testing.T) {
 	const (
 		owner   = "octo"