docs(prd): resolve gate-DNS open question on 0007

Spike: container on a `--internal` user-defined network resolves
another container's name via the embedded resolver at 127.0.0.11
and reaches it over TCP, while egress to the public internet
remains blocked. The PRD's design assumption holds — no design
change needed.

docs/prds/0007-ssh-egress-gate.md

@@ -170,10 +170,14 @@ dataclass (`SSHGatePlan`) under `claude_bottle/ssh_gate.py`.
 - Connection-level audit log: socat's `-v` mode logs every
   connect/close. Worth piping into the bottle's stderr stream, or
   is that noise? Default off, reconsider if debugging gets hard.
-- Docker DNS for the `<gate-container>` hostname inside the
+- ~~Docker DNS for the `<gate-container>` hostname inside the
   agent: works via Docker's embedded resolver on user-defined
   networks. Verify on the `--internal` network specifically before
-  implementation.
+  implementation.~~ **Resolved.** Spike confirmed: a container on
+  a `--internal` user-defined network resolves another
+  container's name via the embedded resolver at 127.0.0.11 and
+  reaches it over TCP, while egress to the public internet
+  remains blocked. The PRD's design assumption holds.
 
 ## References