fix(browser): address Copilot round-3 on /browser connect

* Gate `browser.progress` emit on truthy `session_id`. The TUI
  prints `messages` from the response when there's no session, so
  emitting events too would double-render. Now: with a session →
  events stream live; without one → bundled messages only.
* Resolve `system = platform.system()` once in `_browser_connect`
  and thread it through `try_launch_chrome_debug` and
  `_failure_messages` → `manual_chrome_debug_command`, so the
  generated hint is consistent (and tests are deterministic) on
  any host.
* Add `test_browser_manage_connect_no_session_skips_progress_events`
  to lock in the gating behavior.

tests/test_tui_gateway_server.py

@@ -2930,7 +2930,11 @@ def test_browser_manage_connect_default_local_reports_launch_hint(monkeypatch):
                 {
                     "id": "1",
                     "method": "browser.manage",
-                    "params": {"action": "connect", "url": "http://localhost:9222"},
+                    "params": {
+                        "action": "connect",
+                        "session_id": "sess-1",
+                        "url": "http://localhost:9222",
+                    },
                 }
             )
 
@@ -2952,6 +2956,45 @@ def test_browser_manage_connect_default_local_reports_launch_hint(monkeypatch):
     assert progress == resp["result"]["messages"]
 
 
+def test_browser_manage_connect_no_session_skips_progress_events(monkeypatch):
+    """Without a session_id the TUI prints messages from the response;
+    emitting ``browser.progress`` events would double-render. Gate the
+    emit so callers without a session see the bundled list only."""
+    monkeypatch.delenv("BROWSER_CDP_URL", raising=False)
+    emitted: list[tuple[str, dict]] = []
+    monkeypatch.setattr(
+        server,
+        "_emit",
+        lambda evt, sid, payload=None: emitted.append((evt, payload or {})),
+    )
+    fake = types.SimpleNamespace(
+        cleanup_all_browsers=lambda: None,
+        _get_cdp_override=lambda: os.environ.get("BROWSER_CDP_URL", ""),
+    )
+    with patch.dict(sys.modules, {"tools.browser_tool": fake}):
+        _stub_urlopen(monkeypatch, ok=False)
+        with (
+            patch(
+                "hermes_cli.browser_connect.try_launch_chrome_debug", return_value=False
+            ),
+            patch(
+                "hermes_cli.browser_connect.get_chrome_debug_candidates",
+                return_value=[],
+            ),
+        ):
+            resp = server.handle_request(
+                {
+                    "id": "1",
+                    "method": "browser.manage",
+                    "params": {"action": "connect", "url": "http://localhost:9222"},
+                }
+            )
+
+    assert resp["result"]["connected"] is False
+    assert resp["result"]["messages"]  # bundled list still populated
+    assert [evt for evt, _ in emitted if evt == "browser.progress"] == []
+
+
 def test_browser_manage_connect_default_local_retries_after_launch(monkeypatch):
     monkeypatch.delenv("BROWSER_CDP_URL", raising=False)
     monkeypatch.setattr(server.time, "sleep", lambda _seconds: None)