[eric] router: adopt a healthy 9Router instead of evicting the one other backends are using

backend/apps/nine_router/process.py

@@ -497,7 +497,19 @@ async def p_ensure_running_impl():
     p_is_packaged = os.environ.get("OPENSWARM_PACKAGED") == "1"
 
     if is_running():
-        # In dev mode, kill stale standalone servers (from previous builds) so we can start `next dev` which always uses latest source code
+        # ADOPT a healthy router instead of evicting it. is_running() has just confirmed HTTP 200 on
+        # /v1/models, so whatever is on the port is serving; the only thing killing it establishes is
+        # who owns the process. That eviction is a thrash engine on a shared machine: every dev
+        # backend that boots kills the router the others are using, their watchdogs revive it, and
+        # the next boot kills it again. Measured with 8 backends on one box: a coverage sweep scored
+        # 1/9 with zero code change, wall times went 30s -> 202s, and one run logged 0 kills of its
+        # own against 4 revives. The original reason to kill ("stale build") does not apply to a
+        # component we pin by npm version rather than build from source. OPENSWARM_ROUTER_TAKEOVER=1
+        # restores the old behaviour for the rare case someone must force a fresh spawn.
+        if not p_is_packaged and os.environ.get("OPENSWARM_ROUTER_TAKEOVER") != "1":
+            logger.info("9Router already healthy on port %d; adopting it (set "
+                        "OPENSWARM_ROUTER_TAKEOVER=1 to force a fresh spawn)", NINE_ROUTER_PORT)
+            return
         if not p_is_packaged:
             # But never kill the instance WE already started: a second ensure call (another sub-app's lifespan races settings') would pkill our fresh next-server, leaving a dead window the boot key-sync fails into, so the cp-openai node never registers and gpt-5.* own-key dies.
             if p_process is not None and p_process.poll() is None:

backend/tests/test_router_watchdog.py

@@ -204,3 +204,34 @@ def test_detection_revival_gated_on_evidence():
                 assert ensures, "sub-only users must get a revival attempt"
 
     asyncio.run(run())
+
+
+def test_a_healthy_router_is_adopted_not_evicted():
+    """The dev-machine thrash engine, removed.
+
+    Every dev backend used to kill any 9Router it had not personally spawned, on a "stale build"
+    rationale that does not apply to a component we pin by npm version instead of building from
+    source. On a shared box that is a loop: each boot evicts the router the others are using, their
+    watchdogs revive it, the next boot evicts it again. Measured with 8 backends on one machine, a
+    coverage sweep scored 1/9 with zero code change, wall times went 30s -> 202s, and one backend
+    logged 0 kills of its own against 4 revives.
+
+    is_running() has already confirmed HTTP 200 on /v1/models before this point, so the router is
+    serving by definition; killing it settles ownership and nothing else.
+    """
+    killed = []
+    with patch.object(proc, "is_running", return_value=True), \
+         patch.object(proc, "p_process", None), \
+         patch("subprocess.run", side_effect=lambda *a, **k: killed.append(a)), \
+         patch.dict("os.environ", {"OPENSWARM_PACKAGED": "0"}, clear=False):
+        asyncio.run(proc.p_ensure_running_impl())
+    assert killed == [], "a healthy router another process owns must be adopted, never pkill'd"
+
+
+def test_takeover_escape_hatch_still_exists():
+    """Adoption must not become a trap: someone genuinely needing a fresh spawn keeps a way to get
+    one, and it is explicit rather than the silent default."""
+    import inspect
+    src = inspect.getsource(proc.p_ensure_running_impl)
+    assert "OPENSWARM_ROUTER_TAKEOVER" in src
+    assert 'os.environ.get("OPENSWARM_ROUTER_TAKEOVER") != "1"' in src