diff --git a/backend/apps/agents/browser/browser_agent.py b/backend/apps/agents/browser/browser_agent.py
index bbed1706..021ac694 100644
--- a/backend/apps/agents/browser/browser_agent.py
+++ b/backend/apps/agents/browser/browser_agent.py
@@ -3261,6 +3261,60 @@ async def evict_dead_card(dashboard_id: str | None, browser_id: str) -> None:
     await asyncio.sleep(P_EVICT_SETTLE_S)
 
 
+# The user can still scroll back through the last few results; everything older is a site-isolated renderer process held for nobody. Small on purpose.
+P_KEEP_IDLE_AGENT_CARDS = 3
+
+
+async def reap_idle_agent_cards(dashboard_id: str | None, keep: int = P_KEEP_IDLE_AGENT_CARDS) -> int:
+    """Drop all but the newest `keep` finished agent-spawned cards; returns how many went.
+
+    The frontend does fade a spawned card away when its parent finishes, but that removal is owned
+    by the card's OWN component: switch dashboards, quit, or unmount it inside the 3s timer and the
+    card survives, persisted, forever (measured: 8 stranded cards on one dashboard, 6 of them with
+    the keep-open flag clear, so every one was supposed to be gone). Each survivor remounts a live
+    webview on the next launch, and they accumulate for as long as the user keeps using the agent.
+    So the bound lives here, at the point of allocation, where no unmounted component can skip it.
+    Never touches a user's own card, and never one an agent is driving right now."""
+    if not dashboard_id:
+        return 0
+    try:
+        from backend.apps.agents.agent_manager import agent_manager
+        from backend.apps.dashboards.dashboards import load, save
+
+        dash = load(dashboard_id)
+        idle: list[tuple] = []
+        for bid, card in dash.layout.browser_cards.items():
+            spawned = getattr(card, "spawned_by", None)
+            if not spawned or bid in ACTIVE_AGENT_CARDS:
+                continue
+            parent = agent_manager.get_session(spawned)
+            if parent is not None and getattr(parent, "status", "") == "running":
+                continue
+            born = getattr(card, "created_at", None)
+            # A float key never raises the way comparing a naive datetime to an aware one would; cards from before the field existed sort to 0 and reap first, which is correct, they are the oldest thing here.
+            idle.append((born.timestamp() if born else 0.0, bid))
+        if len(idle) <= keep:
+            return 0
+        idle.sort()
+        doomed = [bid for _, bid in idle[:len(idle) - keep]]
+        for bid in doomed:
+            del dash.layout.browser_cards[bid]
+            DEAD_CARDS.discard(bid)
+        dash.updated_at = datetime.now()
+        save(dash)
+        for bid in doomed:
+            try:
+                await ws_manager.broadcast_global("dashboard:browser_card_evict", {
+                    "dashboard_id": dashboard_id, "browser_id": bid})
+            except Exception:
+                pass
+        logger.info(f"[browser-agent] reaped {len(doomed)} idle agent cards, kept newest {keep}: {doomed}")
+        return len(doomed)
+    except Exception as e:
+        logger.info(f"[browser-agent] idle-card reap skipped ({e})")
+        return 0
+
+
 async def p_create_browser_card(dashboard_id: str, url: str, parent_session_id: str | None = None) -> str:
     """Create a new browser card on the dashboard and return its browser_id."""
     from backend.apps.dashboards.dashboards import load, save
@@ -3281,6 +3335,7 @@ async def p_create_browser_card(dashboard_id: str, url: str, parent_session_id:
         height=800,
         spawned_by=parent_session_id,
         dashboard_id=dashboard_id,
+        created_at=datetime.now(),
     )
     dashboard.layout.browser_cards[browser_id] = card
     dashboard.updated_at = datetime.now()
@@ -3366,6 +3421,8 @@ async def run_browser_agents(
             # the keychain, and holding a lock across that would serialize every card creation.
             await borrow_signin_before_nav(host_src, "")
             async with p_card_pick_lock:
+                # Before allocating, collect what earlier runs left behind, else a session's cards only ever grow.
+                await reap_idle_agent_cards(dashboard_id)
                 browser_id = find_reusable_card(dashboard_id, host_src, parent_session_id)
                 if browser_id:
                     reused = True
diff --git a/backend/apps/dashboards/models.py b/backend/apps/dashboards/models.py
index ea766691..9245fdbe 100644
--- a/backend/apps/dashboards/models.py
+++ b/backend/apps/dashboards/models.py
@@ -48,6 +48,8 @@ class BrowserCardPosition(BaseModel):
     dashboard_id: Optional[str] = None
     # Chat session this browser lives inside (renders over the chat's dock slot); None = free card.
     docked_to: Optional[str] = None
+    # When this card was spawned, so the idle-agent-card reaper can keep the newest and drop the rest. Cards saved before this field existed read as None and reap first, which is right: they are the oldest thing on the canvas.
+    created_at: Optional[datetime] = None
 
 
 class DashboardLayout(BaseModel):
diff --git a/backend/tests/test_deadcard_evict.py b/backend/tests/test_deadcard_evict.py
index 898d11e7..c6aa6c58 100644
--- a/backend/tests/test_deadcard_evict.py
+++ b/backend/tests/test_deadcard_evict.py
@@ -2,6 +2,7 @@
 torn down (renderer unmount + layout removal) BEFORE recovery spawns a fresh card,
 so two heavy pages never co-exist and starve the renderer. Pins evict_dead_card."""
 import asyncio
+from datetime import datetime, timedelta
 
 import backend.apps.agents.browser.browser_agent as ba
 
@@ -55,8 +56,9 @@ def test_evict_without_a_dashboard_deletes_nothing(monkeypatch):
 
 
 class FakeCard:
-    def __init__(self, spawned_by=None):
+    def __init__(self, spawned_by=None, created_at=None):
         self.spawned_by = spawned_by
+        self.created_at = created_at
 
 
 def test_user_card_is_never_evicted(monkeypatch):
@@ -66,3 +68,75 @@ def test_user_card_is_never_evicted(monkeypatch):
     asyncio.run(ba.evict_dead_card("dash-1", "browser-user"))
     assert not broadcasts and not saved
     assert "browser-user" in dash.layout.browser_cards
+
+
+# --- the idle-card reaper: cards a FINISHED run left behind ------------------------------------
+# The frontend's fade-and-remove is owned by the card's own component, so a dashboard switch or a
+# quit strands it. These pin the backend bound that holds no matter what the UI did.
+
+def p_born(n):
+    return datetime(2026, 1, 1) + timedelta(minutes=n)
+
+
+def p_reap_patch(monkeypatch, cards, running=()):
+    broadcasts, saved, dash = p_patch(monkeypatch, cards)
+
+    class FakeSession:
+        def __init__(self, status):
+            self.status = status
+
+    class FakeManager:
+        def get_session(self, sid):
+            return FakeSession("running") if sid in running else FakeSession("completed")
+
+    import backend.apps.agents.agent_manager as am
+    monkeypatch.setattr(am, "agent_manager", FakeManager(), raising=True)
+    return broadcasts, saved, dash
+
+
+def test_idle_agent_cards_are_reaped_down_to_the_newest_few(monkeypatch):
+    cards = {f"browser-{i}": FakeCard("sess-old", p_born(i)) for i in range(8)}
+    broadcasts, saved, dash = p_reap_patch(monkeypatch, cards)
+    assert asyncio.run(ba.reap_idle_agent_cards("dash-1", keep=3)) == 5
+    # the newest three survive, the five older ones are gone and the renderer was told about each
+    assert sorted(dash.layout.browser_cards) == ["browser-5", "browser-6", "browser-7"]
+    assert len([b for b in broadcasts if b[0] == "dashboard:browser_card_evict"]) == 5
+    assert saved
+
+
+def test_reaper_never_touches_user_cards_or_live_runs(monkeypatch):
+    cards = {
+        "browser-user": FakeCard(None, p_born(0)),           # the user's own, oldest of all
+        "browser-live": FakeCard("sess-live", p_born(1)),    # its agent is still running
+        "browser-driving": FakeCard("sess-old", p_born(2)),  # being driven RIGHT NOW
+        "browser-idle-a": FakeCard("sess-old", p_born(3)),
+        "browser-idle-b": FakeCard("sess-old", p_born(4)),
+    }
+    _, _, dash = p_reap_patch(monkeypatch, cards, running=("sess-live",))
+    ba.ACTIVE_AGENT_CARDS.add("browser-driving")
+    try:
+        # keep=0 is the harshest possible sweep: anything that survives is protected by rule, not luck
+        assert asyncio.run(ba.reap_idle_agent_cards("dash-1", keep=0)) == 2
+    finally:
+        ba.ACTIVE_AGENT_CARDS.discard("browser-driving")
+    assert sorted(dash.layout.browser_cards) == ["browser-driving", "browser-live", "browser-user"]
+
+
+def test_cards_from_before_created_at_existed_reap_first(monkeypatch):
+    # An older build's cards have no timestamp. They are the oldest thing on the canvas, so they
+    # must go before anything stamped, never outlive it on a technicality.
+    cards = {
+        "browser-legacy": FakeCard("sess-old", None),
+        "browser-new": FakeCard("sess-old", p_born(1)),
+    }
+    _, _, dash = p_reap_patch(monkeypatch, cards)
+    assert asyncio.run(ba.reap_idle_agent_cards("dash-1", keep=1)) == 1
+    assert list(dash.layout.browser_cards) == ["browser-new"]
+
+
+def test_reaper_is_quiet_when_there_is_nothing_to_collect(monkeypatch):
+    cards = {"browser-a": FakeCard("sess-old", p_born(1))}
+    broadcasts, saved, dash = p_reap_patch(monkeypatch, cards)
+    assert asyncio.run(ba.reap_idle_agent_cards("dash-1", keep=3)) == 0
+    assert not broadcasts and not saved
+    assert "browser-a" in dash.layout.browser_cards