fix(smolmachines): docker push fails on Docker Desktop — daemon-side route differs from host loopback

`./cli.py start <agent>` under CLAUDE_BOTTLE_BACKEND=smolmachines
died at `docker push localhost:<port>/claude-bottle:<id>` with
`Get "http://localhost:<port>/v2/": context deadline exceeded`.

Cause: chunk 4c bound the ephemeral registry to `127.0.0.1::5000`
and used `localhost:<port>` as the only image-ref hostname. On
Docker Desktop the daemon runs inside its own Linux VM — its
`localhost` is the VM's loopback, not the host's, so the daemon
cannot reach a registry bound to the host's 127.0.0.1.

Fix: bind the registry to all interfaces (`-p :5000`) so it's
reachable from both sides, and yield two endpoints:

  - `daemon_endpoint` — `host.docker.internal:<port>` on Docker
    Desktop (daemon-side hostname for the host VM gateway),
    `localhost:<port>` on a native Linux daemon that shares the
    host's network namespace. Used for `docker tag` + `docker
    push`.
  - `host_endpoint` — always `localhost:<port>`. Used for
    `smolvm pack create`, which runs as a host process.

The registry stores images by repo+tag, so a push to
`host.docker.internal:<port>/cb:<id>` and a pull from
`localhost:<port>/cb:<id>` resolve to the same blob — the
hostname in a ref is just routing.

Detection uses `docker info --format '{{.OperatingSystem}}'`,
which returns "Docker Desktop" on macOS/Windows Desktop and the
host's OS name on native daemons.

Trade-off: all-interface binding briefly publishes the registry
on every interface (~5-10s during prepare). The pushed image is
built from the public repo Dockerfile (no secrets), the port is
random, and the window is short — acceptable for v1 of a
personal dev tool.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

claude_bottle/backend/smolmachines/local_registry.py

@@ -5,13 +5,36 @@ conversion path (PRD 0023 chunk 4c).
 can't read the local docker daemon's image cache, an OCI layout
 directory, or a `docker save` tarball. To convert the agent's
 Dockerfile-built image into a `.smolmachine` artifact we run a
-short-lived `registry:2.8.3` container on `127.0.0.1:<random>`,
-push the locally-tagged image into it, and let smolvm pull from
-there. The registry container is torn down as soon as the pack
-completes.
+short-lived `registry:2.8.3` container, push the locally-tagged
+image into it, and let smolvm pull from there. The registry
+container is torn down as soon as the pack completes.
 
-Loopback-only bind + the host's docker layer cache mean the round
-trip is fast (~5s) and there's no exposed surface on the LAN."""
+Two routing hostnames, one registry container. On Docker Desktop
+(macOS/Windows) the docker daemon runs inside its own Linux VM,
+so its `localhost` is *not* the host's loopback — a registry
+bound to `127.0.0.1::<port>` on the host is unreachable from the
+daemon side, and `docker push` fails with `context deadline
+exceeded`. The fix: bind to all interfaces so both routes work,
+and yield two refs:
+
+  - `daemon_endpoint`: how the docker CLI/daemon dials the
+    registry (`host.docker.internal:<port>` on Docker Desktop,
+    `localhost:<port>` on a native Linux daemon that shares the
+    host's network namespace).
+  - `host_endpoint`: how `smolvm pack create` (a host process)
+    dials the registry. Always `localhost:<port>` — the port
+    binding includes loopback either way.
+
+The registry stores images by repo+tag; the hostname in the ref
+is just routing, so a push to `host.docker.internal:<port>/cb:abc`
+and a pull of `localhost:<port>/cb:abc` hit the same stored
+blob.
+
+Trade-off: binding to all interfaces puts the registry on every
+network interface briefly (~5-10s during prepare). The agent
+image we push is built from the repo's public Dockerfile — no
+secrets in it — and the user is on their own machine; the LAN
+exposure window is short and the contents non-sensitive."""
 
 from __future__ import annotations
 
@@ -21,6 +44,7 @@ import subprocess
 import time
 import uuid
 from contextlib import contextmanager
+from dataclasses import dataclass
 from typing import Iterator
 
 from ...log import die
@@ -40,10 +64,21 @@ REGISTRY_IMAGE = os.environ.get(
 _READY_TIMEOUT_S = 10.0
 
 
+@dataclass(frozen=True)
+class RegistryEndpoints:
+    """The two `<host>:<port>` strings to embed in image refs. They
+    point at the same registry container; only the routing
+    hostname differs."""
+
+    daemon_endpoint: str
+    host_endpoint: str
+
+
 @contextmanager
-def ephemeral_registry() -> Iterator[int]:
-    """Bring up a `registry:2.8.3` container on a random loopback
-    port, yield the port, force-remove the container on exit.
+def ephemeral_registry() -> Iterator[RegistryEndpoints]:
+    """Bring up a `registry:2.8.3` container on a random host port,
+    yield the daemon-side + host-side endpoints, force-remove the
+    container on exit.
 
     The container is started with `--rm` so a clean exit cleans up
     on its own; the `finally` block force-removes on abnormal exit
@@ -53,10 +88,14 @@ def ephemeral_registry() -> Iterator[int]:
         [
             "docker", "run", "-d", "--rm",
             "--name", name,
-            # `127.0.0.1::5000` = bind to loopback, pick a random host
-            # port. No LAN exposure; the container hangs around just
-            # long enough for one push + one pack-create.
-            "-p", "127.0.0.1::5000",
+            # `-p :5000` (no IP prefix) binds the container's port
+            # 5000 on a random host port across all interfaces. The
+            # registry container itself listens on 0.0.0.0:5000
+            # internally; binding to all interfaces is necessary for
+            # Docker Desktop's daemon to reach it via
+            # host.docker.internal — a 127.0.0.1-only host binding
+            # is invisible to a daemon running in its own VM.
+            "-p", "5000",
             REGISTRY_IMAGE,
         ],
         check=True,
@@ -65,7 +104,11 @@ def ephemeral_registry() -> Iterator[int]:
     try:
         port = _host_port(name)
         _wait_ready(port)
-        yield port
+        daemon_host = _daemon_side_hostname()
+        yield RegistryEndpoints(
+            daemon_endpoint=f"{daemon_host}:{port}",
+            host_endpoint=f"localhost:{port}",
+        )
     finally:
         subprocess.run(
             ["docker", "rm", "-f", name],
@@ -74,11 +117,34 @@ def ephemeral_registry() -> Iterator[int]:
         )
 
 
+def _daemon_side_hostname() -> str:
+    """Pick the hostname the docker daemon should use to dial the
+    registry. On Docker Desktop the daemon runs in its own Linux
+    VM and only sees the host via `host.docker.internal`; on
+    native Linux the daemon shares the host's network namespace
+    and `localhost` works.
+
+    `docker info --format '{{.OperatingSystem}}'` returns
+    `"Docker Desktop"` on macOS / Windows Desktop installs (and on
+    Linux Desktop, which also uses a VM). Anything else (e.g.
+    `"Debian GNU/Linux 12 (bookworm)"`) is a native daemon."""
+    r = subprocess.run(
+        ["docker", "info", "--format", "{{.OperatingSystem}}"],
+        capture_output=True,
+        text=True,
+        check=False,
+    )
+    operating_system = (r.stdout or "").strip()
+    if operating_system == "Docker Desktop":
+        return "host.docker.internal"
+    return "localhost"
+
+
 def _host_port(name: str) -> int:
     """Resolve the host-side port docker mapped to the registry's
-    container port 5000. `docker port <name> 5000/tcp` returns one or
-    more `host:port` lines; the loopback-only -p binding ensures we
-    get exactly `127.0.0.1:<port>`."""
+    container port 5000. `docker port <name> 5000/tcp` returns one
+    or more `host:port` lines (one per address family) — we take
+    the first IPv4 line."""
     r = subprocess.run(
         ["docker", "port", name, "5000/tcp"],
         capture_output=True,
@@ -90,8 +156,8 @@ def _host_port(name: str) -> int:
             f"docker port {name} 5000/tcp failed: "
             f"{(r.stderr or '').strip() or '<no stderr>'}"
         )
-    # `127.0.0.1:54321\n` — split on the last colon to handle the
-    # `host:port` shape without parsing IP literals.
+    # `0.0.0.0:54321\n[::]:54321\n` — take the first line, split
+    # on the last colon to handle either IPv4 or IPv6 host syntax.
     line = (r.stdout or "").splitlines()[0].strip()
     _, _, port_str = line.rpartition(":")
     try:
@@ -107,7 +173,10 @@ def _wait_ready(port: int) -> None:
 
     A successful TCP connect is sufficient — registry:2.8.3 binds
     after it's ready to serve `/v2/` requests, so the push that
-    follows will land on a working server."""
+    follows will land on a working server. We probe loopback
+    specifically (not host.docker.internal) because this helper
+    runs on the host, and 0.0.0.0-bound ports are reachable via
+    127.0.0.1 too."""
     deadline = time.monotonic() + _READY_TIMEOUT_S
     last_err: Exception | None = None
     while time.monotonic() < deadline: