diff --git a/backend/apps/outputs/runtime.py b/backend/apps/outputs/runtime.py
index d34095e4..a2421c00 100644
--- a/backend/apps/outputs/runtime.py
+++ b/backend/apps/outputs/runtime.py
@@ -34,6 +34,7 @@ from backend.apps.outputs.runtime_proc import (
     RECENT_ERRORS_MAX,
     TERMINATE_GRACE_SECONDS,
     background_priority_kwargs,
+    ensure_force_port_shim,
     find_free_port,
     is_new_mode,
     is_port_free,
@@ -207,6 +208,8 @@ class AppRuntime:
             return await self.p_start_old_mode()
 
     async def p_start_new_mode(self) -> bool:
+        # Legacy workspaces (scaffolded pre-multi-instance) ignore the forced ports; self-heal their run.sh so a second instance stops colliding on the primary's ports.
+        ensure_force_port_shim(self.workspace_path)
         env_path = os.path.join(self.workspace_path, ".env")
         fp_raw = read_env_value(env_path, "FRONTEND_PORT")
         bp_raw = read_env_value(env_path, "BACKEND_PORT")
diff --git a/backend/apps/outputs/runtime_proc.py b/backend/apps/outputs/runtime_proc.py
index 2f8702d2..e5c56a48 100644
--- a/backend/apps/outputs/runtime_proc.py
+++ b/backend/apps/outputs/runtime_proc.py
@@ -210,6 +210,56 @@ def write_env_value(env_path: str, key: str, value: str) -> None:
         logger.exception("failed writing %s=%s to %s", key, value, env_path)
 
 
+def ensure_force_port_shim(workspace_path: str) -> None:
+    """Retrofit the per-instance port override into a legacy workspace's `run.sh`.
+
+    Apps scaffolded before the multi-instance patch have a run.sh that sources
+    `.env` and then pins every instance to the same FRONTEND_PORT/BACKEND_PORT,
+    so opening a SECOND instance collides on the primary's ports and its preview
+    never binds ("Starting preview" forever). This injects the exact override
+    block the current template ships (inert unless OPENSWARM_FORCE_*_PORT is set,
+    i.e. only for secondary instances), leaving the primary untouched. Idempotent;
+    mirrors Patch 1a in scripts/fetch-webapp-template.sh."""
+    run_sh = os.path.join(workspace_path, "run.sh")
+    if not os.path.isfile(run_sh):
+        return
+    try:
+        with open(run_sh, encoding="utf-8") as f:
+            lines = f.readlines()
+    except Exception:
+        return
+    if any("OPENSWARM_FORCE_FRONTEND_PORT" in ln for ln in lines):
+        return
+    block = [
+        "\n",
+        "# Per-instance port overrides: OpenSwarm passes these when the user opens a SECOND instance of the app, so it boots on fresh ports instead of colliding with the primary's .env-pinned ones.\n",
+        'if [[ -n "${OPENSWARM_FORCE_FRONTEND_PORT:-}" ]]; then\n',
+        '    export FRONTEND_PORT="$OPENSWARM_FORCE_FRONTEND_PORT"\n',
+        "fi\n",
+        'if [[ -n "${OPENSWARM_FORCE_BACKEND_PORT:-}" ]]; then\n',
+        '    export BACKEND_PORT="$OPENSWARM_FORCE_BACKEND_PORT"\n',
+        "fi\n",
+    ]
+    out: list[str] = []
+    sourced = False
+    inserted = False
+    for ln in lines:
+        out.append(ln)
+        if 'source "$ROOT_DIR/.env"' in ln:
+            sourced = True
+        elif sourced and not inserted and ln.strip() == "fi":
+            out.extend(block)
+            inserted = True
+    if not inserted:
+        logger.warning("run.sh in %s lacks a recognizable `source .env` block; secondary instances may collide on ports", workspace_path)
+        return
+    try:
+        with open(run_sh, "w", encoding="utf-8") as f:
+            f.writelines(out)
+    except Exception:
+        logger.exception("failed injecting per-instance port shim into %s", run_sh)
+
+
 def is_new_mode(workspace_path: str) -> bool:
     """A workspace is "new-mode" (webapp-template scaffold) if it has a
     `run.sh` at its root. Old-mode workspaces are flat `index.html`-only
diff --git a/frontend/src/app/pages/Dashboard/canvas/DashboardHeader.tsx b/frontend/src/app/pages/Dashboard/canvas/DashboardHeader.tsx
index 63dc9453..765889e7 100644
--- a/frontend/src/app/pages/Dashboard/canvas/DashboardHeader.tsx
+++ b/frontend/src/app/pages/Dashboard/canvas/DashboardHeader.tsx
@@ -10,7 +10,7 @@ import { useAppDispatch } from '@/shared/hooks';
 import DashboardGlyph from './DashboardGlyph';
 import ShareButton from '@/app/components/share/ShareButton';
 import type { AgentSession } from '@/shared/state/agentsSlice';
-import { saveLayout } from '@/shared/state/dashboardLayoutSlice';
+import { saveLayout, viewCardKey } from '@/shared/state/dashboardLayoutSlice';
 import type { CardPosition, ViewCardPosition, BrowserCardPosition, NotePosition, WorkflowCardPosition, WorkflowsHubPosition } from '@/shared/state/dashboardLayoutSlice';
 import type { Output } from '@/shared/state/outputsSlice';
 import type { CanvasActions } from '../hooks/interaction/useCanvasControls';
@@ -73,7 +73,8 @@ const DashboardHeader: React.FC<DashboardHeaderProps> = ({
     .map((vc) => {
       const output = outputs[vc.output_id];
       if (!output) return null;
-      return { id: vc.output_id, name: output.name, card: vc };
+      const label = (vc.instance ?? 1) > 1 ? `${output.name} #${vc.instance}` : output.name;
+      return { id: viewCardKey(vc.output_id, vc.instance), name: label, card: vc };
     })
     .filter(Boolean) as Array<{ id: string; name: string; card: ViewCardPosition }>;