feat(agent): add screen blackout feature

- Physical displays blanked via overlay
- Remote video and input keep working
- Exclude overlay from screen capture
- Add blackout API and UI toggle
- Wire flag through capture protocol

lib/openapi/spec.go

@@ -168,10 +168,11 @@ func Spec() map[string]any {
 						"200": map[string]any{
 							"description": "Screenshot image",
 							"headers": map[string]any{
-								"X-Monitor-Left":   map[string]any{"schema": map[string]string{"type": "integer"}},
-								"X-Monitor-Top":    map[string]any{"schema": map[string]string{"type": "integer"}},
-								"X-Monitor-Width":  map[string]any{"schema": map[string]string{"type": "integer"}},
-								"X-Monitor-Height": map[string]any{"schema": map[string]string{"type": "integer"}},
+								"X-Monitor-Left":    map[string]any{"schema": map[string]string{"type": "integer"}},
+								"X-Monitor-Top":     map[string]any{"schema": map[string]string{"type": "integer"}},
+								"X-Monitor-Width":   map[string]any{"schema": map[string]string{"type": "integer"}},
+								"X-Monitor-Height":  map[string]any{"schema": map[string]string{"type": "integer"}},
+								"X-Screen-Blackout": map[string]any{"schema": map[string]string{"type": "string"}, "description": "1 when physical monitors are blacked out"},
 							},
 							"content": map[string]any{
 								"image/png":  map[string]any{"schema": map[string]string{"type": "string", "format": "binary"}},
@@ -183,6 +184,26 @@ func Spec() map[string]any {
 					}),
 				},
 			},
+			"/api/v1/blackout": map[string]any{
+				"get": map[string]any{
+					"summary":     "Read physical monitor blackout",
+					"operationId": "getBlackout",
+					"responses": auth(map[string]any{
+						"200": okJSON("Blackout state", ref("BlackoutState")),
+					}),
+				},
+				"put": map[string]any{
+					"summary":     "Black out physical monitors",
+					"operationId": "setBlackout",
+					"description": "Covers physical displays with a click-through overlay excluded from capture. Remote video and input keep working.",
+					"requestBody": jsonBody(ref("BlackoutUpdate")),
+					"responses": auth(map[string]any{
+						"200": okJSON("Blackout state", ref("BlackoutState")),
+						"400": errResp("Invalid body"),
+						"503": errResp("Blackout failed"),
+					}),
+				},
+			},
 			"/api/v1/webcam": map[string]any{
 				"get": map[string]any{
 					"summary":     "List webcams",
@@ -563,6 +584,19 @@ func Spec() map[string]any {
 						"klogging": map[string]any{"type": "boolean"},
 					},
 				},
+				"BlackoutState": map[string]any{
+					"type": "object",
+					"properties": map[string]any{
+						"enabled": map[string]any{"type": "boolean"},
+					},
+				},
+				"BlackoutUpdate": map[string]any{
+					"type":     "object",
+					"required": []string{"enabled"},
+					"properties": map[string]any{
+						"enabled": map[string]any{"type": "boolean"},
+					},
+				},
 				"ClickRequest": map[string]any{
 					"type": "object", "required": []string{"x", "y", "button"},
 					"properties": map[string]any{