fix(computer-use): add set_value to ComputerUseBackend ABC and _NoopBackend stub

tests/tools/test_computer_use.py

@@ -155,6 +155,21 @@ def test_right_click_sets_button(self, noop_backend):
         click_kw = next(c[1] for c in noop_backend.calls if c[0] == "click")
         assert click_kw["button"] == "right"
 
+    def test_set_value_routes_to_backend(self, noop_backend):
+        """set_value must reach the backend — regression for missing _NoopBackend stub."""
+        from tools.computer_use.tool import handle_computer_use
+        out = handle_computer_use({"action": "set_value", "value": "Option A", "element": 5})
+        parsed = json.loads(out)
+        assert parsed.get("ok") is True
+        assert parsed.get("action") == "set_value"
+        assert any(c[0] == "set_value" for c in noop_backend.calls)
+
+    def test_set_value_missing_value_returns_error(self, noop_backend):
+        from tools.computer_use.tool import handle_computer_use
+        out = handle_computer_use({"action": "set_value"})
+        parsed = json.loads(out)
+        assert "error" in parsed
+
 
 # ---------------------------------------------------------------------------
 # Safety guards (type / key block lists)

tools/computer_use/backend.py

@@ -142,6 +142,14 @@ def list_apps(self) -> List[Dict[str, Any]]:
     def focus_app(self, app: str, raise_window: bool = False) -> ActionResult:
         """Route input to `app` (by name or bundle ID). Default: focus without raise."""
 
+    # ── Native-value mutation ────────────────────────────────────────
+    @abstractmethod
+    def set_value(self, value: str, element: Optional[int] = None) -> ActionResult:
+        """Set a native value on an element (e.g. AXPopUpButton selection).
+
+        `element` is the 1-based SOM index returned by a prior capture call.
+        """
+
     # ── Timing ──────────────────────────────────────────────────────
     def wait(self, seconds: float) -> ActionResult:
         """Default implementation: time.sleep."""

tools/computer_use/tool.py

@@ -200,6 +200,10 @@ def focus_app(self, app: str, raise_window: bool = False) -> ActionResult:
         self.calls.append(("focus_app", {"app": app, "raise": raise_window}))
         return ActionResult(ok=True, action="focus_app")
 
+    def set_value(self, value: str, element: Optional[int] = None) -> ActionResult:
+        self.calls.append(("set_value", {"value": value, "element": element}))
+        return ActionResult(ok=True, action="set_value")
+
 
 # ---------------------------------------------------------------------------
 # Dispatch