diff --git a/scripts/ci/e2e_runner_pool.py b/scripts/ci/e2e_runner_pool.py
index 9c5a19dbef69..cd3f265b60af 100644
--- a/scripts/ci/e2e_runner_pool.py
+++ b/scripts/ci/e2e_runner_pool.py
@@ -120,6 +120,7 @@
 
 import argparse
 import dataclasses
+import json
 import datetime as dt
 import os
 from collections.abc import Callable, Mapping, Sequence
@@ -240,8 +241,9 @@ def ui_owned_runner(label: str | None, *, test_filter: str | None, owned: str |
     """A UI run's pool, moved off Blacksmith onto an owned pool with machines (see the module docstring).
 
     Any other run, or an owned label, comes back unchanged, as does every
-    label when no owned pool of the lane's Xcode pin has a slot count: a
-    fleet drained by zeroing CI_OWNED_POOL_SLOTS keeps UI runs off it.
+    label when no owned pool of the lane's Xcode pin has machines in
+    `owned_slots` (the online runners when main() read them, else
+    CI_OWNED_POOL_SLOTS): a drained fleet, its runners offline, keeps UI runs off it.
     """
     if (not ui_run(test_filter) or not label or pr_runner_pool.persistent(label)
             or (owned or "").strip() != "1" or not owned_target(test_filter, owned_ui)):
@@ -496,28 +498,39 @@ def resolve(
                            owned_slots=owned_slots, pr_xcode_app=pr_xcode_app, log=log) or label
 
 
-def read_live_owned(repo: str, env: Mapping[str, str], owned: str | None,
-                    pr_xcode_app: str | None) -> tuple[dict[str, int], dict[str, int]] | None:
-    """Idle and online runners per owned label (and its root label) from the runners API, or None.
+def read_live_runners(repo: str, env: Mapping[str, str], owned: str | None,
+                      pr_xcode_app: str | None) -> list[Mapping[str, Any]] | None:
+    """The repository's runners from the runners API, or None.
 
-    Needs the org App's token (ROUTE_TOKEN) and owned pools on; any error
-    leaves the snapshot to decide.
+    Needs the org App's token (ROUTE_TOKEN), owned pools on and a pin that
+    names an owned pool; any error leaves the snapshot and CI_OWNED_POOL_SLOTS to decide.
     """
     token = (env.get("ROUTE_TOKEN") or "").strip()
-    if not token or not repo or (owned or "").strip() != "1":
-        return None
-    labels = pr_runner_pool.owned_pools(pr_xcode_app)
-    labels += tuple(pr_runner_pool.root_label(label) for label in labels)
-    if not labels:
+    if not token or not repo or (owned or "").strip() != "1" or not pr_runner_pool.owned_pools(pr_xcode_app):
         return None
     try:
-        runners = pr_runner_pool.GitHub(token, repo).runners()
+        return pr_runner_pool.GitHub(token, repo).runners()
     except Exception as error:  # noqa: BLE001 - the snapshot path still decides
         print(f"could not list runners ({error}); using the snapshot", file=sys.stderr)
         return None
+
+
+def live_owned(runners: Sequence[Mapping[str, Any]] | None,
+               pr_xcode_app: str | None) -> tuple[dict[str, int], dict[str, int]] | None:
+    """Idle and online runners per owned label (and its root label), or None without a listing."""
+    if runners is None:
+        return None
+    labels = pr_runner_pool.owned_pools(pr_xcode_app)
+    labels += tuple(pr_runner_pool.root_label(label) for label in labels)
     return pr_runner_pool.live_owned_free(runners, labels), pr_runner_pool.live_online(runners, labels)
 
 
+def read_live_owned(repo: str, env: Mapping[str, str], owned: str | None,
+                    pr_xcode_app: str | None) -> tuple[dict[str, int], dict[str, int]] | None:
+    """Idle and online runners per owned label (and its root label) from the runners API, or None."""
+    return live_owned(read_live_runners(repo, env, owned, pr_xcode_app), pr_xcode_app)
+
+
 def main(argv: Sequence[str] | None = None, env: Mapping[str, str] | None = None) -> int:
     env = os.environ if env is None else env
     parser = argparse.ArgumentParser(description=__doc__.splitlines()[0])
@@ -544,12 +557,18 @@ def main(argv: Sequence[str] | None = None, env: Mapping[str, str] | None = None
     run_id = (env.get("GITHUB_RUN_ID") or "").strip()
     now = dt.datetime.now(dt.timezone.utc)
 
+    # A run no owned pool may take (a UI filter without owned_ui) reads no runners.
+    runners = read_live_runners(repo, env, args.owned if owned_target(args.test_filter, args.owned_ui) else "",
+                                args.pr_xcode_app)
+    # Which owned labels route (a pool, its root label): the online runners when they were read,
+    # CI_OWNED_POOL_SLOTS only when they could not be (pr_runner_pool.routing_slots()).
+    owned_slots = (args.owned_slots if runners is None else
+                   json.dumps(pr_runner_pool.routing_slots(args.owned_slots, args.pr_xcode_app, runners)))
+
     def measure() -> PoolLoad | None:
         if not token or not repo:
             raise RuntimeError("GH_TOKEN and GH_REPO are required")
-        # A run no owned pool may take (a UI filter without owned_ui) reads no runners.
-        owned = args.owned if owned_target(args.test_filter, args.owned_ui) else ""
-        idle, online = read_live_owned(repo, env, owned, args.pr_xcode_app) or (None, None)
+        idle, online = live_owned(runners, args.pr_xcode_app) or (None, None)
         return measure_load(pr_runner_pool.GitHub(token, repo), now=now,
                             exclude_run_id=int(run_id) if run_id.isdigit() else None,
                             live_owned=idle, live_online=online)
@@ -557,7 +576,7 @@ def measure() -> PoolLoad | None:
     print(resolve(
         args.requested, args.variable,
         overflow=args.overflow, order=args.order, max_queued=args.max_queued,
-        owned=args.owned, owned_slots=args.owned_slots, pr_xcode_app=args.pr_xcode_app,
+        owned=args.owned, owned_slots=owned_slots, pr_xcode_app=args.pr_xcode_app,
         test_filter=args.test_filter, owned_ui=args.owned_ui, queue_rounds=args.queue_rounds,
         measure=measure, now=now,
         log=lambda message: print(message, file=sys.stderr),
diff --git a/tests/test_run_e2e.py b/tests/test_run_e2e.py
index 6197aec45887..d0f38aa1c388 100644
--- a/tests/test_run_e2e.py
+++ b/tests/test_run_e2e.py
@@ -1,6 +1,7 @@
 #!/usr/bin/env python3
 """Exercise the focused-run launcher against a fake GitHub CLI."""
 import importlib.util
+import io
 import json
 import re
 import os
@@ -1714,6 +1715,23 @@ def test_live_owned_needs_the_token_and_owned_pools(self):
                 mock.patch("sys.stderr"):
             self.assertIsNone(read("manaflow-ai/cmux", {"ROUTE_TOKEN": "t"}, "1", "/Applications/Xcode_26.6.app"))
 
+    def test_main_routes_by_the_online_runners_not_the_slot_variable(self):
+        root = self.pool.pr_runner_pool.root_label(MINI)
+        runners = [{"status": "online", "busy": False, "labels": [{"name": MINI}, {"name": root}]}]
+        argv = ["--requested", MINI, "--owned", "1", "--owned-slots", '{"std": 40}',
+                "--pr-xcode-app", "/Applications/Xcode_26.6.app"]
+        env = {"ROUTE_TOKEN": "t", "GITHUB_REPOSITORY": "manaflow-ai/cmux"}
+
+        def run(listing):
+            with mock.patch.object(self.pool.pr_runner_pool.GitHub, "runners", **listing), \
+                    mock.patch("sys.stderr"), mock.patch("sys.stdout", new_callable=io.StringIO) as out:
+                self.assertEqual(self.pool.main(argv, env), 0)
+            return out.getvalue().strip()
+        # An online root runner turns root routing on without a root count in CI_OWNED_POOL_SLOTS.
+        self.assertEqual(run({"return_value": runners}), root)
+        # No listing: the variable decides, and it has no root count.
+        self.assertEqual(run({"side_effect": RuntimeError("403")}), MINI)
+
     def test_the_workflow_mints_the_routing_token_for_auto_only(self):
         steps = self.jobs[next(name for name, job in self.jobs.items()
                                if any(step.get("id") == "pool" for step in job.get("steps", [])))]["steps"]