fix(issue_label): schema wrongly required labels, blocking label_ids-only callers (#52 review finding)

Independent adversarial review of #52 (v0.8.0) caught a schema/implementation
mismatch: the advertised InputSchema marked "labels" as required, but Call
already treated labels/label_ids as either-or. An MCP client that validates
arguments against the advertised schema before dispatch would reject a
label_ids-only call as invalid even though the code was written to serve it —
and that path had zero test coverage either way.

Dropped "labels" from the required array (owner/repo/number remain required);
runtime validation already correctly requires at least one of labels/label_ids.
Added TestIssueLabelAppliesByIDOnly (asserts ListLabels is never called when
IDs are already known) and a schema-lock test for the fixed contract.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/tools/issue_label.go

@@ -29,10 +29,10 @@ func (t *IssueLabel) Descriptor() registry.ToolDescriptor {
 				"owner":{"type":"string"},
 				"repo":{"type":"string"},
 				"number":{"type":"integer","minimum":1},
-				"labels":{"type":"array","items":{"type":"string"}},
-				"label_ids":{"type":"array","items":{"type":"integer"}}
+				"labels":{"type":"array","items":{"type":"string"},"description":"Label names to resolve and apply. Either labels or label_ids is required."},
+				"label_ids":{"type":"array","items":{"type":"integer"},"description":"Label IDs to apply directly, skipping name resolution. Either labels or label_ids is required."}
 			},
-			"required":["owner","repo","number","labels"]
+			"required":["owner","repo","number"]
 		}`),
 	}
 }

internal/tools/issue_label_test.go

@@ -53,6 +53,52 @@ func TestIssueLabelAppliesByName(t *testing.T) {
 	assert.Contains(t, string(out), `"name":"enhancement"`)
 }
 
+// label_ids alone (no labels) must work end-to-end without hitting ListLabels
+// at all — this is the schema-level "either labels or label_ids" contract, and
+// it must never require a GET to the label list when the caller already has IDs.
+func TestIssueLabelAppliesByIDOnly(t *testing.T) {
+	var captured []byte
+	var listCalled bool
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		switch {
+		case r.Method == http.MethodGet && r.URL.Path == "/api/v1/repos/o/r/labels":
+			listCalled = true
+			w.Header().Set("Content-Type", "application/json")
+			_, _ = w.Write([]byte(labelListFixture))
+		case r.Method == http.MethodPost && r.URL.Path == "/api/v1/repos/o/r/issues/42/labels":
+			var err error
+			captured, err = io.ReadAll(r.Body)
+			require.NoError(t, err)
+			w.Header().Set("Content-Type", "application/json")
+			_, _ = w.Write([]byte(labelListFixture))
+		default:
+			t.Fatalf("unexpected request: %s %s", r.Method, r.URL.Path)
+		}
+	}))
+	defer srv.Close()
+
+	tool := tools.NewIssueLabel(gitea.NewClient(srv.URL, "tok"), allowlist.New([]string{"o"}))
+	out, err := tool.Call(context.Background(), json.RawMessage(`{"owner":"o","repo":"r","number":42,"label_ids":[1,2]}`))
+	require.NoError(t, err)
+
+	assert.False(t, listCalled, "label_ids-only must not call ListLabels")
+	var payload map[string]any
+	require.NoError(t, json.Unmarshal(captured, &payload))
+	ids, ok := payload["labels"].([]any)
+	require.True(t, ok)
+	assert.ElementsMatch(t, []any{float64(1), float64(2)}, ids)
+	assert.Contains(t, string(out), `"name":"bug"`)
+}
+
+// #52 review finding: the advertised schema wrongly required "labels", making
+// label_ids-only calls fail JSON-Schema validation before reaching Call at all.
+// Lock the fixed contract: neither is individually required.
+func TestIssueLabelSchema_NeitherLabelsNorLabelIDsRequired(t *testing.T) {
+	sch := string(tools.NewIssueLabel(gitea.NewClient("http://unused", ""), allowlist.New([]string{"o"})).Descriptor().InputSchema)
+	assert.NotContains(t, sch, `"required":["owner","repo","number","labels"]`)
+	assert.Contains(t, sch, `"required":["owner","repo","number"]`)
+}
+
 func TestIssueLabelUnknownNameNamesTheMissingLabel(t *testing.T) {
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/json")