feat: align browser callback runtime and export flows

Consolidate the browser task runtime around the callback path, add safer artifact opening for Zhihu exports, and cover the new service/browser flows with focused tests and supporting docs.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/browser_bridge_contract_test.rs

@@ -0,0 +1,80 @@
+use serde_json::{json, Value};
+use sgclaw::browser::bridge_contract::{BridgeBrowserActionRequest, BridgeLifecycleCall};
+
+#[test]
+fn bridge_contract_names_match_documented_bridge_surface() {
+    let lifecycle_names = [
+        BridgeLifecycleCall::Connect.bridge_name(),
+        BridgeLifecycleCall::Start.bridge_name(),
+        BridgeLifecycleCall::Stop.bridge_name(),
+        BridgeLifecycleCall::SubmitTask.bridge_name(),
+    ];
+
+    assert_eq!(
+        lifecycle_names,
+        [
+            "sgclawConnect",
+            "sgclawStart",
+            "sgclawStop",
+            "sgclawSubmitTask",
+        ]
+    );
+}
+
+#[test]
+fn bridge_contract_represents_browser_action_requests_without_ws_business_frames() {
+    let requests = vec![
+        BridgeBrowserActionRequest::new(
+            "navigate",
+            json!({ "url": "https://www.baidu.com" }),
+            "www.baidu.com",
+        ),
+        BridgeBrowserActionRequest::new(
+            "click",
+            json!({ "selector": "#submit" }),
+            "www.zhihu.com",
+        ),
+        BridgeBrowserActionRequest::new(
+            "getText",
+            json!({ "selector": "#content" }),
+            "www.zhihu.com",
+        ),
+    ];
+
+    let serialized = serde_json::to_value(&requests).unwrap();
+    let entries = serialized.as_array().unwrap();
+    let actions = entries
+        .iter()
+        .map(|entry| entry["action"].as_str().unwrap())
+        .collect::<Vec<_>>();
+
+    assert_eq!(
+        serialized,
+        json!([
+            {
+                "action": "navigate",
+                "params": { "url": "https://www.baidu.com" },
+                "expected_domain": "www.baidu.com"
+            },
+            {
+                "action": "click",
+                "params": { "selector": "#submit" },
+                "expected_domain": "www.zhihu.com"
+            },
+            {
+                "action": "getText",
+                "params": { "selector": "#content" },
+                "expected_domain": "www.zhihu.com"
+            }
+        ])
+    );
+    assert_eq!(actions, vec!["navigate", "click", "getText"]);
+
+    let first = entries.first().unwrap();
+    let object = first.as_object().unwrap();
+    assert_eq!(object.len(), 3);
+    assert!(object.contains_key("action"));
+    assert!(object.contains_key("params"));
+    assert!(object.contains_key("expected_domain"));
+    assert_eq!(first["expected_domain"], Value::String("www.baidu.com".to_string()));
+}