docs(nested-containers): record what live verification established

Documents the proxy-layer precedence that took four attempts to get
right, the blob-CDN routes every registry needs alongside its own, the
podman 5 networking packages and how each one fails when absent, and
the BusyBox wget caveat. Closes the DNS open question: public
resolution inside a nested container fails by design; reaching the
proxy was the real problem.

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

docs/prds/prd-new-nested-containers.md

@@ -78,8 +78,15 @@ describe the one thing the design refuses to do.
   prerequisite it needs (podman, the storage/network helpers, writable device
   nodes, an *empty* subordinate range) rather than degrading.
 - The derived image `…-nested-containers` layers the Docker CLI, the compose
-  plugin, `fuse-overlayfs`, `slirp4netns`, and `uidmap` onto the agent image.
-  Podman itself already ships in every built-in image (#451).
+  plugin, and podman 5's networking stack — `passt` (pasta), `netavark`,
+  `nftables`, `aardvark-dns` — plus `fuse-overlayfs`, `slirp4netns`, and
+  `uidmap` onto the agent image. Podman itself already ships in every built-in
+  image (#451), but with `--no-install-recommends`, so none of the networking
+  pieces arrive with it. Each absence fails at a different and misleading
+  layer: no pasta and nothing starts; no `nft` and containers are created but
+  never start; no aardvark-dns and DNS inside a container fails while
+  everything else looks healthy. Image pulls keep working throughout, which is
+  what makes these read as compat-API bugs.
 - `BottleBackend.supports_nested_containers` — false by default, so a backend
   that cannot honor the flag fails in the shared `prepare` template.
 
@@ -91,16 +98,56 @@ reaches the guest), `events_logger="file"` (no journald socket).
 ### Registry reach
 
 Image pulls egress through the bottle's proxy like everything else, so each
-registry needs a route. Docker Hub and GHCR need `preserve_auth: true` — their
+registry needs a route — **and so does the CDN it redirects blobs to**, which
+is a separate host: `production.cloudfront.docker.com` for Docker Hub,
+`pkg-containers.githubusercontent.com` for GHCR, `cdn0*.quay.io` for quay.
+Without those the pull authenticates, fetches the manifest, and then 403s
+partway through. Docker Hub and GHCR need `preserve_auth: true` — their
 token dance uses a client-fetched per-scope bearer token that the proxy would
 otherwise strip. Layer pulls should also set `dlp.outbound_detectors: false`
 and `dlp.inbound_detectors: false`: body scanning on a multi-hundred-MB layer
 is what triggers #455, and a registry route's scanned bodies are compressed
 layer blobs rather than anything a detector can read.
 
+### Reaching the network from a nested container
+
+Public DNS inside a nested container fails by design: everything egresses
+through the proxy. What was actually broken was reaching the proxy at all, and
+it took four attempts to fix because podman applies proxy settings at several
+layers and the last writer wins:
+
+| Layer | Applies to |
+|---|---|
+| `~/.docker/config.json` proxies block | **every container the Docker CLI starts** — client-side, beats everything below |
+| service environment | podman's own pulls, non-CLI API clients |
+| `containers.conf` `env` | native `podman run` |
+| `containers.conf` `hosts_file`, `http_proxy` | native `podman run` only — the compat API ignores both |
+
+The gateway is named `bot-bottle-gateway`, which resolves only through the
+bottle's `/etc/hosts`; a nested container gets its own. Since no config key
+reaches the compat path, the name is resolved in the bottle and the *address*
+is substituted into the proxy URL at each layer above. `NO_PROXY` keeps the
+name, which is matched against what a client asks for.
+
+The gateway TLS-intercepts, so the CA bundle is mounted read-only and
+`SSL_CERT_FILE`, `CURL_CA_BUNDLE`, `REQUESTS_CA_BUNDLE`, and
+`NODE_EXTRA_CA_CERTS` point at it — no distro-specific trust commands.
+
+## Verified on macOS 26 / Apple Container 1.0.0 / podman 5.4.2
+
+With plain `docker`, no extra flags: image pulls from Docker Hub, GHCR, and
+quay; `docker run` with correct exit-code propagation; `docker compose` up,
+logs, down, and a published port curl'd from the bottle; `curl https://quay.io`
+and `https://pypi.org/simple/` returning 200 from inside a nested container;
+and `https://example.com` returning **403** — the egress allowlist applies to
+nested containers, not just the bottle.
+
+Alpine's BusyBox `wget` drops the connection after TLS interception and
+reports "error getting response". The proxy logs the decrypted request, and
+`curl` on the same host succeeds, so this is a BusyBox client limitation
+rather than anything in the egress path.
+
 ## Open questions
 
 - Whether the `docker` and `firecracker` backends want an equivalent, or
   whether guest-local containers stay macOS-only.
-- Outbound networking *from* a nested container (DNS, proxy env, CA) beyond
-  what the compat socket gives the bottle itself.