fix(backend): skip gateway reconcile when no running bottles (0081)

reconcile_running_bottles() gathered the gateway attach-resources (a read of
the per-host singleton gateway's CA) *before* enumerating running bottles. On
a cold-boot bring-up of a NON-default gateway instance with no host bottles —
e.g. an isolated integration test's `-itest-` gateway — that read targeted the
default `bot-bottle-orch-gateway`, which doesn't exist for that instance, so
setUpClass died with "No such container: bot-bottle-orch-gateway" (seen on the
0081 PR's integration-docker job).

Enumerate running bottles first and return early when there are none: the
reconcile is a no-op with nothing to reattach, so the CA read is both wasted
and wrong for a non-default instance. Production (default names, real bottles)
is unchanged. Adds unit coverage for the three reconcile paths.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

bot_bottle/backend/gateway_attach.py

@@ -37,9 +37,18 @@ def reconcile_running_bottles(backend: "BottleBackend[Any, Any, Any]") -> None:
     so any attach failure aborts bring-up. Every bottle is attempted first and
     the failures are raised together, so one bring-up surfaces the full blast
     radius rather than one bottle at a time."""
+    # Enumerate the host's running bottles BEFORE gathering resources: with none
+    # to reattach, the reconcile is a no-op, and gathering resources first would
+    # read the current gateway's CA for nothing. That read targets the per-host
+    # singleton gateway, so a bring-up of a *non-default* instance with no host
+    # bottles (an isolated integration test's `-itest-` gateway) would otherwise
+    # fail looking for the default `bot-bottle-orch-gateway` (#519 review).
+    bottles = backend._running_bottles()
+    if not bottles:
+        return
     resources = backend._gateway_attach_resources()
     failures: list[str] = []
-    for bottle in backend._running_bottles():
+    for bottle in bottles:
         try:
             backend._attach_bottle_to_gateway(bottle, resources)
         except InfraLaunchError as exc: