[eric] dashboards: drop orphan session cards from GET so a dead-session card stops 404ing on load

backend/apps/dashboards/dashboards.py

@@ -363,10 +363,45 @@ async def generate_name(dashboard_id: str):
     return {"name": dashboard.name, "auto_named": True}
 
 
+def _strip_orphan_session_cards(data: dict) -> None:
+    """Drop layout cards (and expanded ids) whose agent session no longer exists
+    anywhere, in memory OR on disk. The frontend mounts an AgentChat per card and
+    GETs its session; a card pointing at a vanished session (e.g. an empty
+    never-saved session) 404s on every load and flashes a dead "connect a model"
+    card before the client reconciles it away. The `gone()` test is the exact
+    condition that makes GET /sessions/{id} 404, so it removes precisely those
+    cards and nothing else. Filtering the RESPONSE (never the stored file) is
+    non-destructive: a wrong check can only hide a card for one response, not
+    delete it. Drafts have no backend session yet, so they're always kept."""
+    from backend.apps.agents.agent_manager import agent_manager
+    from backend.apps.agents.manager.session.session_store import _load_session_data
+    layout = data.get("layout")
+    if not isinstance(layout, dict):
+        return
+    cards = layout.get("cards")
+    if not isinstance(cards, dict):
+        return
+
+    def gone(sid: str) -> bool:
+        if sid.startswith("draft-") or sid in agent_manager.sessions:
+            return False
+        return _load_session_data(sid) is None
+
+    orphans = [sid for sid in cards if gone(sid)]
+    for sid in orphans:
+        cards.pop(sid, None)
+    if orphans:
+        exp = layout.get("expanded_session_ids")
+        if isinstance(exp, list):
+            layout["expanded_session_ids"] = [s for s in exp if s not in orphans]
+
+
 @dashboards.router.get("/{dashboard_id}")
 async def get_dashboard(dashboard_id: str):
     dashboard = _load(dashboard_id)
-    return dashboard.model_dump(mode="json")
+    data = dashboard.model_dump(mode="json")
+    _strip_orphan_session_cards(data)
+    return data
 
 
 @dashboards.router.put("/{dashboard_id}")

backend/tests/test_v2_invariants.py

@@ -594,6 +594,33 @@ async def test_mcp_gate_only_forwards_activated_servers():
             assert forwarded == (set(active) & set(names)), f"mismatch for active={active}"
 
 
+def test_dashboard_get_strips_only_orphan_session_cards():
+    """A layout card whose session vanished (gone from memory AND disk) makes the
+    frontend GET /sessions/{id} 404 on every load and flash a dead card. The
+    dashboard GET filters those orphan cards out of the response, but must keep
+    live (in-memory) cards, on-disk cards, and drafts. Non-destructive: only the
+    response is filtered, never the stored layout."""
+    from types import SimpleNamespace
+    from backend.apps.dashboards import dashboards as D
+    data = {"layout": {
+        "cards": {
+            "live": {"session_id": "live"},      # in memory
+            "ondisk": {"session_id": "ondisk"},  # closed but on disk
+            "draft-1": {"session_id": "draft-1"},  # unsent draft, no backend session yet
+            "ghost": {"session_id": "ghost"},    # gone from memory AND disk -> would 404
+        },
+        "expanded_session_ids": ["live", "ghost"],
+    }}
+    fake_mgr = SimpleNamespace(sessions={"live": object()})
+    on_disk = {"ondisk": {"id": "ondisk"}}
+    with patch("backend.apps.agents.agent_manager.agent_manager", fake_mgr), \
+         patch("backend.apps.agents.manager.session.session_store._load_session_data",
+               side_effect=lambda sid: on_disk.get(sid)):
+        D._strip_orphan_session_cards(data)
+    assert set(data["layout"]["cards"].keys()) == {"live", "ondisk", "draft-1"}, "only the ghost should be dropped"
+    assert data["layout"]["expanded_session_ids"] == ["live"], "ghost dropped from expanded too"
+
+
 def test_banned_models_not_offered():
     """Claude Fable (banned) and Gemini 3.1 Pro (no working lane: AG can't serve
     it, AI Studio key 429s pro-preview) were pulled from the picker. Guard so a