diff --git a/bot_bottle/backend/docker/backend.py b/bot_bottle/backend/docker/backend.py
index 83e61815..b332d594 100644
--- a/bot_bottle/backend/docker/backend.py
+++ b/bot_bottle/backend/docker/backend.py
@@ -23,7 +23,7 @@ import shutil
 import io
 from contextlib import contextmanager, redirect_stderr
 from pathlib import Path
-from typing import Generator, Sequence
+from typing import TYPE_CHECKING, Generator, Sequence
 
 from ...supervisor.types import SUPERVISE_HOSTNAME, SUPERVISE_PORT
 from ...agent_provider import AgentProvisionPlan
@@ -41,12 +41,27 @@ from . import resolve_plan as _resolve_plan
 from .bottle import DockerBottle
 from .bottle_cleanup_plan import DockerBottleCleanupPlan
 from .bottle_plan import DockerBottlePlan
+
+if TYPE_CHECKING:
+    from .infra import DockerInfraService
+
+
 class DockerBottleBackend(BottleBackend["DockerBottlePlan", "DockerBottleCleanupPlan", str]):
     """Docker backend implementation. Selected by BOT_BOTTLE_BACKEND
     when set to `docker`; retained as a legacy/example backend."""
 
     name = "docker"
 
+    def __init__(self, *, infra: "DockerInfraService | None" = None) -> None:
+        # The infra service whose gateway just cold-booted, passed in on the
+        # bring-up reconcile path (PRD 0081) so `_gateway_attach_resources`
+        # reads THAT gateway's CA rather than a fresh default-named service —
+        # otherwise a non-default instance (an isolated integration test's
+        # `-itest-` gateway) reads the default `bot-bottle-orch-gateway`, which
+        # doesn't exist for it (#519 review). None for ordinary construction:
+        # falls back to the per-host default singleton.
+        self._infra = infra
+
     @classmethod
     def is_available(cls) -> bool:
         """`docker` on PATH is sufficient; we don't probe `docker info`
@@ -144,8 +159,8 @@ class DockerBottleBackend(BottleBackend["DockerBottlePlan", "DockerBottleCleanup
 
     def _gateway_attach_resources(self) -> GatewayAttachResources:
         from .infra import DockerInfraService
-        return GatewayAttachResources(
-            ca_pem=DockerInfraService().gateway().ca_cert_pem())
+        infra = self._infra if self._infra is not None else DockerInfraService()
+        return GatewayAttachResources(ca_pem=infra.gateway().ca_cert_pem())
 
     def _running_bottles(self) -> Sequence[str]:
         from .infra_launch import running_agent_containers
diff --git a/bot_bottle/backend/docker/infra.py b/bot_bottle/backend/docker/infra.py
index d3808953..b2c3f666 100644
--- a/bot_bottle/backend/docker/infra.py
+++ b/bot_bottle/backend/docker/infra.py
@@ -151,7 +151,7 @@ class DockerInfraService(InfraService):
         # untouched — no cold boot, nothing to reconcile.
         if cold_booted:
             from .backend import DockerBottleBackend
-            DockerBottleBackend().attach_bottled_agents_to_gateway()
+            DockerBottleBackend(infra=self).attach_bottled_agents_to_gateway()
         return orchestrator.url()
 
     def stop(self) -> None:
diff --git a/tests/unit/test_backend_secret_reprovision.py b/tests/unit/test_backend_secret_reprovision.py
index 36592faa..60671cb0 100644
--- a/tests/unit/test_backend_secret_reprovision.py
+++ b/tests/unit/test_backend_secret_reprovision.py
@@ -277,6 +277,27 @@ class TestDockerAttachPrimitives(unittest.TestCase):
             with self.assertRaisesRegex(docker.InfraLaunchError, "gone"):
                 docker.push_ca_to_container("bot-bottle-a", "PEM")
 
+    def test_gateway_attach_resources_reads_the_threaded_infra_gateway(self) -> None:
+        # On the bring-up reconcile path the backend is threaded with the infra
+        # whose gateway just cold-booted, so it reads THAT gateway's CA — not a
+        # fresh default-named DockerInfraService that wouldn't exist for a
+        # non-default instance (#519 review).
+        from bot_bottle.backend.docker.backend import DockerBottleBackend
+        infra = Mock()
+        infra.gateway.return_value.ca_cert_pem.return_value = "ITEST-CA"
+        res = DockerBottleBackend(infra=infra)._gateway_attach_resources()
+        self.assertEqual("ITEST-CA", res.ca_pem)
+        infra.gateway.assert_called_once()
+
+    def test_gateway_attach_resources_defaults_to_the_host_singleton(self) -> None:
+        # Ordinary construction (no infra) falls back to the per-host default.
+        from bot_bottle.backend.docker.backend import DockerBottleBackend
+        with patch("bot_bottle.backend.docker.infra.DockerInfraService") as InfraCls:
+            InfraCls.return_value.gateway.return_value.ca_cert_pem.return_value = "DEFAULT-CA"
+            res = DockerBottleBackend()._gateway_attach_resources()
+        InfraCls.assert_called_once_with()
+        self.assertEqual("DEFAULT-CA", res.ca_pem)
+
 
 class TestMacosAttachPrimitives(unittest.TestCase):
     def test_running_agent_containers_from_enumeration(self) -> None: