fix(pr_merge): send Gitea's merge_title_field; merge_message_title was silently ignored (gitea-mcp#77)

Gitea 1.27's MergePullRequestOption has merge_title_field, not merge_message_title; an unknown field is
dropped without an error, so a custom merge title never took effect. The tool's argument keeps its name.
The new test checks the field name on the wire (the existing fake never did).

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SZkhi49hfeSqBp5aZJNXsM

internal/gitea/pulls.go

@@ -107,7 +107,7 @@ func (c *Client) GetPullRequestDiff(ctx context.Context, owner, repo string, ind
 
 type MergePRArgs struct {
 	Do    string `json:"Do"`
-	Title string `json:"merge_message_title,omitempty"`
+	Title string `json:"merge_title_field,omitempty"`
 	Body  string `json:"merge_message_field,omitempty"`
 	// HeadCommitID binds the merge to the commit whose CI was checked: if the PR branch moved, Gitea refuses.
 	HeadCommitID string `json:"head_commit_id,omitempty"`

internal/tools/pr_merge_test.go

@@ -166,6 +166,22 @@ func TestPRMergeDefaultsToMergeStyleAndPassesStyleThrough(t *testing.T) {
 	assert.Equal(t, "squash", payload["Do"])
 }
 
+// Gitea 1.27's MergePullRequestOption has merge_title_field and merge_message_field. A field it does not know is
+// ignored without an error, so a custom merge title silently did nothing while this tool sent merge_message_title
+// (gitea-mcp#77). The tool's own argument keeps its name; the wire field must be Gitea's.
+func TestPRMerge_ACustomMergeTitleTravelsAsGiteasMergeTitleField(t *testing.T) {
+	f := newPRMergeFake(t, prMergeFakeOpts{})
+
+	_, err := callMerge(t, f, `{"owner":"owner","repo":"repo","number":7,"issue":42,"merge_message_title":"feat: one line","merge_message_field":"body text"}`)
+
+	require.NoError(t, err)
+	var payload map[string]any
+	require.NoError(t, json.Unmarshal(f.mergeBody, &payload))
+	assert.Equal(t, "feat: one line", payload["merge_title_field"])
+	assert.Equal(t, "body text", payload["merge_message_field"])
+	assert.NotContains(t, payload, "merge_message_title", "not a Gitea field: it is ignored without an error")
+}
+
 // TOCTOU: the gate read CI for ONE head commit. The merge must be bound to that commit, so a push to the PR branch
 // after the check makes Gitea refuse the merge instead of merging code nobody checked.
 func TestPRMerge_TheMergeIsBoundToTheCommitTheGateChecked(t *testing.T) {