fix(pm-agent): the agent is IN the cluster — one git host, the cluster-local service name

An in-cluster consumer reaches a service by its *.svc.cluster.local name, which is by
design a different path from how a client outside the cluster reaches the same service.
pm-worker's host allowlist accepted TWO values: the cluster-local name and the external
hostname gitea.home.keithjackson.dev. The second is removed.

It was never needed — nothing sets it — it would route in-cluster traffic out through the
Gateway and back for no reason, and as an ACCEPTED value it widened the allowlist to a
host reachable over the namespace's world:443 egress rule, which is precisely the
injection shape the allowlist exists to refuse.

probe-validation.sh now pins that: 20 refusals, including the external hostname, the
cluster-local name over https, and the cluster-local name on the wrong port.

Also corrects a remark in the handoff entry: I cited cluster-vars' GATEWAY_VIP
(192.168.1.53) as suspicious next to the nodes' 192.168.2.x. That was noise — those base
cluster-vars values are dev-era leftovers for a decommissioned cluster and say nothing
about prod. None of the measured facts depended on it.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

infra/agent/probe-validation.sh

@@ -86,12 +86,22 @@ refuses "branch equal to the base branch"       "must not be the base branch" \
 # --- where code comes FROM and goes TO -------------------------------------
 # The namespace's egress policy permits tcp/443 to the world (the model needs it), so an
 # injected host would be REACHABLE. These are the cases that matter most.
-refuses "a redirected git host"                 "is not an allowed git host" \
+refuses "a redirected git host"                 "is not the allowed in-cluster git host" \
         PM_GITEA_URL=https://evil.invalid
-refuses "a real, reachable, WRONG git host"     "is not an allowed git host" \
+refuses "a real, reachable, WRONG git host"     "is not the allowed in-cluster git host" \
         PM_GITEA_URL=https://github.com
-refuses "the right host on a smuggled path"     "is not an allowed git host" \
+refuses "the right host on a smuggled path"     "is not the allowed in-cluster git host" \
         PM_GITEA_URL=http://gitea.gitea.svc.cluster.local:3000/../..
+# This agent is IN the cluster, so it reaches Gitea by its cluster-local service name. The
+# EXTERNAL hostname is refused too — it used to be a second accepted value, and as an
+# accepted value it widened this allowlist to a host reachable over the `world:443` egress
+# rule, which is the injection shape the allowlist exists to refuse.
+refuses "this Gitea's EXTERNAL hostname"        "is not the allowed in-cluster git host" \
+        PM_GITEA_URL=https://gitea.home.keithjackson.dev
+refuses "the cluster-local name over https"     "is not the allowed in-cluster git host" \
+        PM_GITEA_URL=https://gitea.gitea.svc.cluster.local:3000
+refuses "the cluster-local name, wrong port"    "is not the allowed in-cluster git host" \
+        PM_GITEA_URL=http://gitea.gitea.svc.cluster.local:8080
 refuses "a malformed owner"                     "PM_GITEA_OWNER is malformed" \
         'PM_GITEA_OWNER=../other-org'
 refuses "a malformed repository"                "PM_GITEA_REPO is malformed" \