feat: add POST /pulls/{owner}/{repo}/{index}/assignees route

Register the PR assignees route pointing to the existing AssignIssue
handler, which works for both issues and PRs via the Gitea API.
Add integration tests covering valid, HTMX, and missing assignee cases.

Closes leeworks-agents/gitea-mobile#228

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/gitea/client.go

@@ -972,6 +972,40 @@ func (c *Client) SetIssueState(ctx context.Context, token, owner, repo string, i
 	return nil
 }
 
+// MergePull merges a pull request using the specified merge style.
+// Valid styles: "merge", "rebase", "rebase-merge", "squash".
+// If style is empty, defaults to "merge".
+func (c *Client) MergePull(ctx context.Context, token, owner, repo string, index int64, style, title, message string) error {
+	if style == "" {
+		style = "merge"
+	}
+
+	payload := map[string]string{
+		"Do": style,
+	}
+	if title != "" {
+		payload["merge_message_field"] = title
+	}
+	if message != "" {
+		payload["merge_message_field"] = message
+	}
+
+	jsonData, err := json.Marshal(payload)
+	if err != nil {
+		return fmt.Errorf("marshaling merge request: %w", err)
+	}
+
+	path := fmt.Sprintf("/repos/%s/%s/pulls/%d/merge", owner, repo, index)
+	resp, err := c.doRequest(ctx, token, http.MethodPost, path, strings.NewReader(string(jsonData)))
+	if err != nil {
+		return fmt.Errorf("merging pull request: %w", err)
+	}
+	resp.Body.Close()
+
+	c.InvalidateAll()
+	return nil
+}
+
 // AddComment creates a comment on an issue and returns the created Comment.
 func (c *Client) AddComment(ctx context.Context, token, owner, repo string, index int64, body string) (*Comment, error) {
 	return c.PostComment(ctx, token, owner, repo, index, body)

internal/gitea/client_test.go

@@ -1516,3 +1516,81 @@ func TestGetChangedFiles_Error(t *testing.T) {
 		t.Errorf("error should contain status code 404, got: %v", err)
 	}
 }
+
+func TestMergePull(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodPost {
+			t.Errorf("expected POST, got %s", r.Method)
+		}
+		if r.URL.Path != "/api/v1/repos/owner1/repo1/pulls/5/merge" {
+			t.Errorf("unexpected path: %s", r.URL.Path)
+		}
+		if r.Header.Get("Authorization") != "token test-token" {
+			t.Error("missing or wrong Authorization header")
+		}
+
+		var body map[string]string
+		if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+			t.Fatalf("failed to decode body: %v", err)
+		}
+		if body["Do"] != "squash" {
+			t.Errorf("expected Do=squash, got %q", body["Do"])
+		}
+
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer server.Close()
+
+	c := NewClient(server.URL)
+	c.setCache("pulls-org1", "should-be-invalidated")
+
+	err := c.MergePull(context.Background(), "test-token", "owner1", "repo1", 5, "squash", "", "")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	// Verify cache was invalidated.
+	_, ok := c.getFromCache("pulls-org1")
+	if ok {
+		t.Error("expected cache to be invalidated after MergePull")
+	}
+}
+
+func TestMergePull_DefaultStyle(t *testing.T) {
+	var receivedStyle string
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var body map[string]string
+		if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+			t.Fatalf("failed to decode body: %v", err)
+		}
+		receivedStyle = body["Do"]
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer server.Close()
+
+	c := NewClient(server.URL)
+	err := c.MergePull(context.Background(), "test-token", "owner1", "repo1", 5, "", "", "")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if receivedStyle != "merge" {
+		t.Errorf("expected default style 'merge', got %q", receivedStyle)
+	}
+}
+
+func TestMergePull_Error(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusMethodNotAllowed)
+		fmt.Fprintln(w, `{"message":"not mergeable"}`)
+	}))
+	defer server.Close()
+
+	c := NewClient(server.URL)
+	err := c.MergePull(context.Background(), "test-token", "owner1", "repo1", 5, "merge", "", "")
+	if err == nil {
+		t.Fatal("expected error for 405 response, got nil")
+	}
+	if !strings.Contains(err.Error(), "405") {
+		t.Errorf("error should contain status code 405, got: %v", err)
+	}
+}

internal/handlers/handlers.go

@@ -56,6 +56,7 @@ func (h *Handler) RegisterRoutes(mux *http.ServeMux) {
 	mux.HandleFunc("GET /pulls/{owner}/{repo}/{index}", h.PullDetail)
 	mux.HandleFunc("POST /pulls/{owner}/{repo}/{index}/review", h.SubmitReview)
 	mux.HandleFunc("POST /pulls/{owner}/{repo}/{index}/state", h.SetPullState)
+	mux.HandleFunc("POST /pulls/{owner}/{repo}/{index}/assignees", h.AssignIssue)
 
 	// Settings (handled separately for auth bypass).
 	settingsHandler := &SettingsHandler{

internal/handlers/integration_test.go

@@ -726,6 +726,66 @@ func TestIntegration_AssignIssue_MissingAssignee(t *testing.T) {
 	}
 }
 
+// --- Issue #228: Integration tests for POST /pulls/{owner}/{repo}/{index}/assignees ---
+
+func TestIntegration_AssignPull_Valid(t *testing.T) {
+	h, srv := newTestHandlerWithMock(t)
+	defer srv.Close()
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("POST /pulls/{owner}/{repo}/{index}/assignees", h.AssignIssue)
+
+	form := url.Values{"assignee": {"user1"}}
+	req := reqWithToken(http.MethodPost, "/pulls/test-org/repo1/1/assignees", form.Encode())
+	w := httptest.NewRecorder()
+
+	mux.ServeHTTP(w, req)
+
+	if w.Code != http.StatusSeeOther {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusSeeOther)
+	}
+}
+
+func TestIntegration_AssignPull_HTMX(t *testing.T) {
+	h, srv := newTestHandlerWithMock(t)
+	defer srv.Close()
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("POST /pulls/{owner}/{repo}/{index}/assignees", h.AssignIssue)
+
+	form := url.Values{"assignee": {"user1"}}
+	req := reqWithToken(http.MethodPost, "/pulls/test-org/repo1/1/assignees", form.Encode())
+	req.Header.Set("HX-Request", "true")
+	w := httptest.NewRecorder()
+
+	mux.ServeHTTP(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusOK)
+	}
+	body := w.Body.String()
+	if !contains(body, "Assigned to user1") {
+		t.Errorf("expected 'Assigned to user1' in HTMX response, got: %s", body)
+	}
+}
+
+func TestIntegration_AssignPull_MissingAssignee(t *testing.T) {
+	h, srv := newTestHandlerWithMock(t)
+	defer srv.Close()
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("POST /pulls/{owner}/{repo}/{index}/assignees", h.AssignIssue)
+
+	req := reqWithToken(http.MethodPost, "/pulls/test-org/repo1/1/assignees", "")
+	w := httptest.NewRecorder()
+
+	mux.ServeHTTP(w, req)
+
+	if w.Code != http.StatusBadRequest {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusBadRequest)
+	}
+}
+
 // --- Issue #118: Integration tests for CloseIssue and AddComment ---
 
 func TestIntegration_CloseIssue(t *testing.T) {