feat(macos): replace rootless Docker spike with rootless podman

Podman avoids the CAP_SYS_ADMIN requirement that makes rootless Docker
impossible here: with no subordinate UID range configured it falls back
to a single-UID self-mapping, which an unprivileged process may write
itself, so newuidmap is never invoked. The image build therefore strips
/etc/subuid and /etc/subgid entries rather than adding them.

The agent-facing surface is unchanged — docker and docker compose talk
to podman's Docker-compatible API socket.

Two device nodes need relaxing as root inside the bottle (0666 on
/dev/fuse and /dev/net/tun); both already exist and neither needs a
capability the bottle lacks, unlike CAP_SYS_ADMIN.

Verified live on macOS 26 / Apple Container 1.0.0: service starts with
zero added capabilities, compose pulls and serves from the workspace on
a published port, and a nested container cannot reach the network
outside the egress path.

Known limitation, not yet addressed: the agent base image is Debian
bookworm, whose podman 4.3.1 swallows container exit codes through the
compat API (docker run returns 0 regardless). podman 5.4.2 on trixie
fixes it; the base bump is a separate PR. The acceptance test asserts
on an in-band marker rather than an exit code so it cannot false-pass
in the meantime.

Nested containers give no isolation from the agent itself — root inside
one is the agent user outside it. They are a build/test convenience;
the bottle remains the security boundary.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GnMp8SUGH57hZX7192Rv2F

README.md

@@ -75,6 +75,22 @@ On compatible macOS hosts, the default backend requires Apple's `container` CLI
 
 Use `BOT_BOTTLE_BACKEND=docker ./cli.py start <agent>` on hosts where neither Apple Container nor KVM is available and Docker is the desired backend.
 
+> **Experimental containers-in-bottle spike (#392):** a bottle may set
+> `docker_access: true`. On the macOS backend this starts a guest-local,
+> rootless **podman** service after the bottle is registered, exposing its
+> Docker-compatible API socket — the agent still uses `docker` and `docker
+> compose`. It does not mount Docker Desktop's socket or add outer VM
+> capabilities. Rootless Docker was tried first and does not work here at
+> all: Apple Container's capability bounding set omits `CAP_SYS_ADMIN`,
+> which the kernel requires to write a multi-range `uid_map`. See
+> [`docs/research/rootless-docker-in-apple-container-spike.md`](docs/research/rootless-docker-in-apple-container-spike.md).
+>
+> The tradeoff to understand before enabling it: podman avoids that
+> requirement by falling back to a single-UID mapping, so nested containers
+> provide **no isolation from the agent itself** — `root` inside a nested
+> container is the agent user outside it. Nested containers are a build/test
+> convenience, not a security boundary. The bottle remains the boundary.
+
 ### Firecracker on Linux
 
 On Linux, a KVM-capable host defaults to the Firecracker backend. It needs:

bot_bottle/backend/macos_container/bottle_plan.py

@@ -20,6 +20,7 @@ class MacosContainerBottlePlan(BottlePlan):
     # bottle is registered. See launch.py's stamp for why it lives here and not
     # only in the exec-time proxy env.
     identity_token: str = ""
+    docker_access: bool = False
 
     @property
     def container_name(self) -> str:

bot_bottle/backend/macos_container/launch.py

@@ -64,6 +64,7 @@ from .gateway_hosts import (
     refresh_gateway_host,
     set_gateway_host,
 )
+from . import rootless_podman
 from .bottle_plan import MacosContainerBottlePlan
 from ...orchestrator.config_store import resolve_teardown_timeout
 from .consolidated_launch import (
@@ -171,6 +172,10 @@ def launch(
         # token above, so — unlike the run-time env — the plan CAN carry it.
         plan = dataclasses.replace(plan, identity_token=ctx.identity_token)
 
+        exec_env = {
+            **_identity_proxy_env(endpoint, ctx.identity_token),
+            **rootless_podman.guest_env(plan.docker_access),
+        }
         bottle = MacosContainerBottle(
             plan.container_name,
             teardown,
@@ -184,10 +189,16 @@ def launch(
             ),
             terminal_color=plan.spec.color,
             agent_workdir=plan.workspace_plan.workdir,
-            exec_env=_identity_proxy_env(endpoint, ctx.identity_token),
+            exec_env=exec_env,
         )
         bottle.prompt_path = provision(plan, bottle)
 
+        if plan.docker_access:
+            rootless_podman.prepare_guest_devices(
+                plan.container_name, container_mod.exec_container_as_root,
+            )
+            rootless_podman.start(bottle)
+
         yield bottle
     finally:
         teardown()
@@ -199,15 +210,22 @@ def _build_images(plan: MacosContainerBottlePlan) -> MacosContainerBottlePlan:
     committed = read_committed_image(plan.slug)
     if committed and container_mod.image_exists(committed):
         info(f"using committed image {committed!r}")
-        return dataclasses.replace(
+        plan = dataclasses.replace(
             plan,
             agent_provision=dataclasses.replace(
                 plan.agent_provision, image=committed,
             ),
         )
-    container_mod.build_image(
-        plan.image, _REPO_DIR, dockerfile=plan.dockerfile_path,
-    )
+    else:
+        container_mod.build_image(
+            plan.image, _REPO_DIR, dockerfile=plan.dockerfile_path,
+        )
+    if plan.docker_access:
+        image = rootless_podman.build_image(plan.image, container_mod.build_image)
+        plan = dataclasses.replace(
+            plan,
+            agent_provision=dataclasses.replace(plan.agent_provision, image=image),
+        )
     return plan
 
 

bot_bottle/backend/macos_container/resolve_plan.py

@@ -44,4 +44,5 @@ def resolve_plan(
         egress_plan=egress_plan,
         supervise_plan=supervise_plan,
         agent_provision=agent_provision_plan,
+        docker_access=manifest.bottle.docker_access,
     )

bot_bottle/backend/macos_container/rootless-podman-init.sh

@@ -0,0 +1,89 @@
+#!/bin/sh
+set -eu
+
+uid="$(id -u)"
+if [ "$uid" -eq 0 ]; then
+    echo "refusing to run rootless podman as root" >&2
+    exit 1
+fi
+
+for command in podman docker fuse-overlayfs slirp4netns; do
+    command -v "$command" >/dev/null 2>&1 || {
+        echo "missing rootless podman prerequisite: $command" >&2
+        exit 1
+    }
+done
+
+# The inverse of the rootless-Docker check, and the whole point of the podman
+# variant: a subordinate range would push podman onto newuidmap, which cannot
+# write a multi-range uid_map without CAP_SYS_ADMIN in this guest.  An empty
+# range keeps it on the single-UID self-mapping an unprivileged process may
+# write itself.
+if grep -q "^$(id -un):" /etc/subuid 2>/dev/null; then
+    echo "unexpected subordinate UID range for $(id -un): podman would" >&2
+    echo "require CAP_SYS_ADMIN via newuidmap in this guest" >&2
+    exit 1
+fi
+
+for device in /dev/fuse /dev/net/tun; do
+    [ -r "$device" ] && [ -w "$device" ] || {
+        echo "device $device is not readable/writable by $(id -un)" >&2
+        exit 1
+    }
+done
+
+export XDG_RUNTIME_DIR="${XDG_RUNTIME_DIR:-/tmp/bot-bottle-podman-run}"
+config="$HOME/.config/containers"
+mkdir -p "$XDG_RUNTIME_DIR" "$config"
+chmod 700 "$XDG_RUNTIME_DIR"
+
+# ignore_chown_errors is required, not incidental: with a single-UID mapping
+# there is no second UID for image layers to be chowned to, so layers that
+# record other owners would otherwise fail to extract.
+cat > "$config/storage.conf" <<'CONF'
+[storage]
+driver="overlay"
+[storage.options.overlay]
+mount_program="/usr/bin/fuse-overlayfs"
+ignore_chown_errors="true"
+CONF
+
+# No cgroup delegation reaches this guest, so asking podman to manage cgroups
+# fails; events_logger=file avoids the journald socket that is equally absent.
+cat > "$config/containers.conf" <<'CONF'
+[containers]
+cgroups="disabled"
+[engine]
+cgroup_manager="cgroupfs"
+events_logger="file"
+CONF
+
+# Registry pulls egress through the bottle's proxy like everything else. The
+# token-bearing proxy URL is already in the agent's environment; persisting it
+# inside this disposable VM does not broaden its authority.
+python3 - <<'PY'
+import json
+import os
+from pathlib import Path
+
+proxy = os.environ.get("HTTPS_PROXY") or os.environ.get("https_proxy", "")
+no_proxy = os.environ.get("NO_PROXY") or os.environ.get("no_proxy", "")
+config = {"proxies": {"default": {
+    "httpProxy": proxy,
+    "httpsProxy": proxy,
+    "noProxy": no_proxy,
+}}}
+path = Path.home() / ".docker" / "config.json"
+path.parent.mkdir(parents=True, exist_ok=True)
+path.write_text(json.dumps(config), encoding="utf-8")
+path.chmod(0o600)
+PY
+
+if docker info >/dev/null 2>&1; then
+    exit 0
+fi
+
+log=/tmp/bot-bottle-rootless-podman.log
+nohup podman system service --time=0 \
+    "unix://$XDG_RUNTIME_DIR/podman.sock" \
+    >"$log" 2>&1 </dev/null &

bot_bottle/backend/macos_container/rootless_podman.py

@@ -0,0 +1,132 @@
+"""Experimental rootless podman bootstrap for Apple-container bottles.
+
+The service and every nested container remain inside the existing per-bottle
+VM.  This module refuses to compensate for missing prerequisites with outer
+capabilities, a privileged container, or a host Docker socket.
+
+Podman is used rather than rootless Docker for one specific reason: Apple
+Container's capability bounding set omits `CAP_SYS_ADMIN`, which the kernel
+requires to write a multi-range `uid_map` via `newuidmap`.  Rootless Docker
+has no path that avoids that write.  Podman does — with no subordinate UID
+range configured it falls back to a single-UID self-mapping, which an
+unprivileged process may write itself.  See
+`docs/research/rootless-docker-in-apple-container-spike.md`.
+
+That fallback is why `build_image` *removes* the agent user's `/etc/subuid`
+and `/etc/subgid` entries instead of adding them: their presence is precisely
+what would send podman down the `newuidmap` path that cannot work here.
+
+The agent still talks to `docker` and `docker compose`; those speak to
+podman's Docker-compatible API socket, so nothing in the agent's habits
+changes.
+"""
+
+from __future__ import annotations
+
+import shlex
+import shutil
+import tempfile
+import time
+from pathlib import Path
+from typing import Callable
+
+from ...log import die, info
+
+_INIT = "/usr/local/libexec/bot-bottle/rootless-podman-init"
+_RUNTIME_DIR = "/tmp/bot-bottle-podman-run"
+_SOCKET = f"{_RUNTIME_DIR}/podman.sock"
+_LOG = "/tmp/bot-bottle-rootless-podman.log"
+READY_RETRIES = 30
+
+# Apple Container creates both device nodes 0600 root:root, so the agent user
+# cannot open them: /dev/fuse blocks the fuse-overlayfs storage driver and
+# /dev/net/tun blocks slirp4netns, which rootless podman uses for the default
+# bridge network that stock compose files expect.  Relaxing the modes needs no
+# capability the bottle does not already hold — unlike CAP_SYS_ADMIN, which is
+# what killed the rootless-Docker approach.
+_GUEST_DEVICES = ("/dev/fuse", "/dev/net/tun")
+
+
+def build_image(
+    base_image: str,
+    build: Callable[..., None],
+) -> str:
+    """Layer spike-only tooling on an already-built provider image."""
+    image = f"{base_image}-rootless-podman"
+    init_script = Path(__file__).with_name("rootless-podman-init.sh")
+    with tempfile.TemporaryDirectory(prefix="bot-bottle-rootless-podman.") as tmp:
+        context = Path(tmp)
+        shutil.copy2(init_script, context / "rootless-podman-init.sh")
+        (context / "Dockerfile").write_text(
+            "FROM docker:28-cli AS docker_cli\n"
+            f"FROM {base_image}\n"
+            "USER root\n"
+            "COPY --from=docker_cli /usr/local/bin/docker /usr/local/bin/docker\n"
+            "COPY --from=docker_cli /usr/local/libexec/docker/cli-plugins/"
+            "docker-compose /usr/local/libexec/docker/cli-plugins/docker-compose\n"
+            "RUN apt-get update \\\n"
+            " && apt-get install -y --no-install-recommends podman "
+            "fuse-overlayfs slirp4netns uidmap \\\n"
+            " && rm -rf /var/lib/apt/lists/* \\\n"
+            # Deliberate: an empty subordinate range keeps podman on the
+            # single-UID mapping that needs no CAP_SYS_ADMIN.  Adding ranges
+            # here would reintroduce the newuidmap failure this spike exists
+            # to route around.
+            " && sed -i '/^node:/d' /etc/subuid /etc/subgid\n"
+            "COPY rootless-podman-init.sh "
+            "/usr/local/libexec/bot-bottle/rootless-podman-init\n"
+            "RUN chmod 0755 /usr/local/libexec/bot-bottle/rootless-podman-init\n"
+            "USER node\n",
+            encoding="utf-8",
+        )
+        build(image, str(context), dockerfile=str(context / "Dockerfile"))
+    return image
+
+
+def guest_env(enabled: bool) -> dict[str, str]:
+    """Environment consumed by the Docker CLI inside an enabled bottle."""
+    if not enabled:
+        return {}
+    return {
+        "DOCKER_HOST": f"unix://{_SOCKET}",
+        "XDG_RUNTIME_DIR": _RUNTIME_DIR,
+    }
+
+
+def prepare_guest_devices(container_name: str, exec_as_root: Callable[..., None]) -> None:
+    """Make /dev/fuse and /dev/net/tun openable by the agent user.
+
+    Runs as root inside the bottle because the agent must not be able to
+    re-mode device nodes itself.  No outer capability is involved.
+    """
+    exec_as_root(
+        container_name,
+        ["sh", "-c", f"chmod 0666 {' '.join(_GUEST_DEVICES)}"],
+    )
+
+
+def start(bottle: object) -> None:
+    """Start and verify the unprivileged service through the bottle exec API."""
+    info("starting experimental rootless podman service")
+    result = bottle.exec(shlex.quote(_INIT))  # type: ignore[attr-defined]
+    if result.returncode != 0:
+        detail = (result.stderr or result.stdout or "").strip()
+        die(f"rootless podman bootstrap failed: {detail or '<no output>'}")
+
+    for _ in range(READY_RETRIES):
+        result = bottle.exec("docker info >/dev/null 2>&1")  # type: ignore[attr-defined]
+        if result.returncode == 0:
+            info("rootless podman service is ready")
+            return
+        time.sleep(0.2)
+
+    logs = bottle.exec(  # type: ignore[attr-defined]
+        f"tail -n 80 {_LOG} 2>/dev/null || true"
+    )
+    die(
+        "rootless podman did not become ready without additional outer "
+        f"privileges:\n{(logs.stdout or logs.stderr or '<no log>').strip()}"
+    )
+
+
+__all__ = ["build_image", "guest_env", "prepare_guest_devices", "start"]

bot_bottle/manifest_bottle.py

@@ -44,6 +44,9 @@ class ManifestBottle:
     # daemon that exposes egress MCP tools to the agent. Set
     # `supervise: false` to skip the gateway.
     supervise: bool = True
+    # Experimental guest-local container engine (issue #392). Backends must
+    # implement this without granting access to a host/shared daemon.
+    docker_access: bool = False
 
     @classmethod
     def from_dict(cls, name: str, raw: object) -> "ManifestBottle":
@@ -123,7 +126,15 @@ class ManifestBottle:
                 f"(was {type(supervise_raw).__name__})"
             )
 
+        docker_access_raw = d.get("docker_access", False)
+        if not isinstance(docker_access_raw, bool):
+            raise ManifestError(
+                f"bottle '{name}' docker_access must be a boolean "
+                f"(was {type(docker_access_raw).__name__})"
+            )
+
         return cls(
             env=env, agent_provider=agent_provider, git=git,
             git_user=git_user, egress=egress, supervise=supervise_raw,
+            docker_access=docker_access_raw,
         )

bot_bottle/manifest_extends.py

@@ -54,6 +54,7 @@ def _merge_two_bottles_runtime(base: "ManifestBottle", override: "ManifestBottle
         git_user=merged_git_user,
         egress=merged_egress,
         supervise=override.supervise,
+        docker_access=override.docker_access,
     )
 
 
@@ -206,6 +207,7 @@ def _fold_two_bottles(
         git_user=merged_git_user,
         egress=merged_egress,
         supervise=later.supervise,
+        docker_access=later.docker_access,
     ), merged_repos_raw
 
 
@@ -266,6 +268,11 @@ def _merge_bottles(
     merged_supervise = (
         child.supervise if "supervise" in child_raw else parent.supervise
     )
+    merged_docker_access = (
+        child.docker_access
+        if "docker_access" in child_raw
+        else parent.docker_access
+    )
     validate_egress_routes(name, merged_egress.routes)
 
     return ManifestBottle(
@@ -275,6 +282,7 @@ def _merge_bottles(
         git_user=merged_git_user,
         egress=merged_egress,
         supervise=merged_supervise,
+        docker_access=merged_docker_access,
     )
 
 

bot_bottle/manifest_schema.py

@@ -16,7 +16,10 @@ _FILENAME_RX = re.compile(r"^[a-z][a-z0-9-]*$")
 # sets dies with a "did you mean" pointer: typos should not silently
 # ghost into an empty config.
 BOTTLE_KEYS = frozenset(
-    {"env", "extends", "agent_provider", "git-gate", "egress", "supervise"}
+    {
+        "env", "extends", "agent_provider", "git-gate", "egress", "supervise",
+        "docker_access",
+    }
 )
 AGENT_KEYS_REQUIRED: frozenset[str] = frozenset()
 AGENT_KEYS_OPTIONAL = frozenset({"bottle", "skills", "git-gate"})

docs/research/egress-proxy-oom-on-large-downloads.md

@@ -0,0 +1,86 @@
+# Egress proxy OOMs on large downloads
+
+Found on 2026-07-21 while running the rootless-podman spike
+(`docs/research/rootless-docker-in-apple-container-spike.md`). Recorded
+rather than fixed — the fix is a security-relevant decision, not a
+mechanical patch.
+
+## Summary
+
+A single large HTTPS download through the gateway kills the egress
+proxy. `mitmdump` buffers whole response bodies so the DLP detectors can
+scan them, grows past the gateway container's memory limit, and is
+OOM-killed by the cgroup. Nothing restarts it.
+
+Two properties make this worse than a failed download:
+
+- **The gateway is a per-host singleton.** Every bottle shares it, so
+  one bottle's download takes egress away from all of them.
+- **There is no restart on death.** The gateway supervisor is
+  `while : ; do wait ; done`; a killed daemon stays dead until the infra
+  container is recreated.
+
+So ordinary agent activity — pulling a container image, downloading a
+model or dataset, fetching a large tarball — is a denial of service
+against every other bottle on the host. No malice required, though it is
+trivially reachable on purpose.
+
+## Evidence
+
+Triggered by `docker compose up` pulling `quay.io/fedora/python-312`
+(two layers, ~82MB and ~83MB) inside a bottle. The pull itself
+succeeded; the *next* request failed:
+
+```
+initializing source docker://quay.io/fedora/python-312:latest:
+  pinging container registry quay.io: Get "https://quay.io/v2/":
+  proxyconnect tcp: dial tcp 192.168.128.39:9099: connect: connection refused
+```
+
+From the gateway's `dmesg`:
+
+```
+python3 invoked oom-killer: gfp_mask=0x100cca(GFP_HIGHUSER_MOVABLE), order=0
+oom-kill:constraint=CONSTRAINT_MEMCG,
+  oom_memcg=/container/bot-bottle-mac-infra,
+  task_memcg=/container/bot-bottle-mac-infra,task=mitmdump,pid=118
+Memory cgroup out of memory: Killed process 118 (mitmdump)
+  total-vm:1391936kB, anon-rss:997768kB
+```
+
+~1GB RSS against a 1024MB container. Note the amplification: ~165MB of
+layers produced ~1GB of resident memory, so the buffering is several
+copies deep (encoded body, decoded body, and the text conversion the
+regex detectors scan).
+
+Afterwards the gateway container was still running and healthy-looking —
+orchestrator, supervise, and git-http all alive — with no `mitmdump`
+process at all, and it stayed that way until the container was
+recreated. A liveness check on the container would not have caught this.
+
+## Reproduction
+
+1. Launch any bottle with an egress route to a host serving a large file.
+2. Download >~150MB over HTTPS through the proxy.
+3. `dmesg | grep -i oom` inside `bot-bottle-mac-infra`, and note that no
+   `mitmdump` process remains.
+
+Beware a false negative when checking: truncating the process listing
+(`cut -c1-45`) cuts before the binary name, because `mitmdump` runs as
+`/usr/local/bin/python3.12 /usr/local/bin/mitmdump …`.
+
+## Fix options, not yet chosen
+
+1. **Restart dead daemons.** Smallest change and strictly an
+   improvement: an OOM then degrades one download instead of removing
+   egress for every bottle. Does not stop the OOM.
+2. **Cap the scanned body size.** Above a threshold, stop buffering —
+   either skip the scan or stream it. This is the root-cause fix and a
+   security decision: a size threshold is exactly the hole an exfiltrator
+   would aim for, so "skip above N" trades a DoS for a covert channel.
+   Streaming with a bounded window keeps coverage, at more complexity.
+3. **Raise the gateway's memory limit.** Moves the threshold; does not
+   remove it.
+
+Worth noting that (1) and (2) are complementary — the restart gap is
+worth closing regardless of how the memory behaviour is resolved.

docs/research/rootless-docker-in-apple-container-spike.md

@@ -0,0 +1,353 @@
+# Rootless Docker inside Apple Container bottles
+
+Spike branch: `spike/rootless-docker-macos` (`a4d8461`)
+
+## Summary
+
+**Negative result.** Rootless Docker cannot run inside an Apple
+Container bottle without granting the bottle `CAP_SYS_ADMIN`. This is a
+kernel constraint on writing multi-range `uid_map`, not a packaging gap
+we can close with a better init script, a different base image, or more
+careful `/etc/subuid` handling.
+
+The spike was built on the premise — stated in
+`bot_bottle/backend/macos_container/rootless_docker.py` — that it would
+*"deliberately refuse to compensate for missing prerequisites with outer
+capabilities, a privileged container, or a host Docker socket."* That
+premise is exactly what the experiment falsified. The two ways forward
+are to abandon the premise (add `CAP_SYS_ADMIN` to the bottle, and with
+it most of the isolation the bottle exists to provide) or to abandon
+rootless Docker.
+
+Recommendation: abandon rootless Docker. Podman does not have this
+problem — see [Podman is not blocked by
+this](#podman-is-not-blocked-by-this) below.
+
+## Local environment
+
+Tested on 2026-07-21:
+
+```console
+$ sw_vers
+ProductName:		macOS
+ProductVersion:		26.5.1
+BuildVersion:		25F80
+
+$ container --version
+container CLI version 1.0.0 (build: release, commit: ee848e3)
+
+$ uname -a   # inside the bottle
+Linux ... 6.18.15 #1 SMP Tue Mar 17 01:36:53 UTC 2026 aarch64 GNU/Linux
+```
+
+## The failure
+
+`tests/integration/test_macos_rootless_docker_spike.py` builds the
+image, launches the bottle, and dies in `rootless_docker.start`:
+
+```
++ exec rootlesskit --net=slirp4netns --mtu=65520 ... dockerd-rootless.sh
+[rootlesskit:parent] error: failed to setup UID/GID map:
+  newuidmap 1100 [0 1000 1 1 100000 65536] failed:
+  newuidmap: write to uid_map failed: Operation not permitted
+```
+
+## Why it fails
+
+Every prerequisite you would normally suspect is present and correct in
+the guest:
+
+| Check | Result |
+| --- | --- |
+| `/usr/bin/newuidmap` | `-rwsr-xr-x root root` — setuid bit intact, survived the OCI export |
+| `/` mount options | `rw,relatime` — **not** `nosuid` |
+| `NoNewPrivs` | `0` |
+| `Seccomp` | `0`, no filters |
+| `/etc/subuid`, `/etc/subgid` | `node:100000:65536` in both |
+| user namespace | `user:[4026531837]`, identical to pid 1 — the *initial* userns |
+| `unshare -U -r true` | succeeds |
+| `/proc/sys/user/max_user_namespaces` | `4505` |
+
+The one thing that is missing is in the capability bounding set that
+Apple Container gives the container:
+
+```
+CapBnd: 00000000a80425fb
+= chown, dac_override, fowner, fsetid, kill, setgid, setuid, setpcap,
+  net_bind_service, net_raw, sys_chroot, mknod, audit_write, setfcap
+```
+
+No `CAP_SYS_ADMIN`. That is the whole story, and the chain is:
+
+1. The kernel's `map_write()` gates writing a `uid_map` on
+   `file_ns_capable(file, ns, CAP_SYS_ADMIN)` — capability over the
+   **new** user namespace, evaluated against the credentials that opened
+   `/proc/<pid>/uid_map`.
+2. `newuidmap` is setuid-root, so it runs with euid 0 — but its
+   capability sets are clamped by the bounding set, which has no
+   `CAP_SYS_ADMIN`.
+3. `cap_capable()` has a shortcut that grants *all* capabilities when
+   the caller's userns is the new namespace's parent **and**
+   `ns->owner == cred->euid`. It does not apply: the namespace was
+   created by `node` (uid 1000) while `newuidmap` runs as euid 0.
+4. So the check falls through to the effective-set test in the initial
+   userns, which fails. `EPERM`.
+
+Note that the single-line unprivileged path (`unshare -U -r`) works
+precisely because it does not go through `newuidmap` and does not need
+`CAP_SYS_ADMIN`. Only the multi-range subuid mapping that rootless
+Docker requires does.
+
+This is the same constraint that makes upstream's `dind-rootless` image
+require `--privileged`. It is not specific to Apple Container, except
+that Apple Container gives us no bounding set that includes
+`CAP_SYS_ADMIN` by default.
+
+## It does work with the capability — which is the point
+
+Adding the capability clears the failure immediately, and exposes one
+further, much smaller blocker: `/dev/net/tun` exists (the kernel has
+tun; `/proc/misc` lists `200 tun`) but Apple Container creates it
+`crw------- root root`, so uid 1000 cannot open it and `slirp4netns`
+fails with `open: Permission denied`. A `chmod 0666 /dev/net/tun` as
+root inside the bottle fixes that, and needs no capability beyond what
+the bottle already has.
+
+With both applied by hand, the daemon comes up completely:
+
+```console
+$ container run --rm -u root --cap-add CAP_SYS_ADMIN \
+    bot-bottle-claude:latest-rootless-docker sh -c '...'
+Server Version: 20.10.24+dfsg1
+Storage Driver: fuse-overlayfs
+Cgroup Driver: none
+Cgroup Version: 2
+API listen on /tmp/rt/docker.sock
+```
+
+So `rootless-docker-init.sh` and `rootless_docker.py` are *correct*.
+The spike did not fail on a bug. It failed on its own premise.
+
+Two secondary findings from that run, relevant if anyone revisits this:
+
+- Debian's `docker.io` package pins Docker **20.10** (EOL), not the 28.x
+  implied by the `docker:28-cli` compose plugin the image copies in.
+- `Cgroup Driver: none` — no resource limits on nested containers.
+
+## Why we should not just add the capability
+
+`CAP_SYS_ADMIN` is close to a superset of "root" in practical terms —
+mount, `pivot_root`, namespace manipulation, and a long tail of
+subsystem-specific powers. Granting it to the agent bottle would
+undercut the containment argument the rest of the backend is built
+around, including the deliberately narrow choices immediately adjacent
+to it in `launch.py` (`--cap-drop CAP_NET_RAW`, no `NET_ADMIN`, a
+host-only agent network). Trading all of that for nested `docker
+compose` is a bad exchange.
+
+## Podman is not blocked by this
+
+Sanity-checked on the same host, same kernel, same runtime, so the
+comparison is apples to apples:
+
+| Scenario | Result |
+| --- | --- |
+| Podman rootless, `/etc/subuid` populated | **Fails identically** — `newuidmap: write to uid_map failed: Operation not permitted` |
+| Podman rootless, no subuid ranges, `--network=host` | **Works**, no added capabilities |
+| Podman rootless, no subuid ranges, default netns, `/dev/net/tun` at `0600` | Fails — `slirp4netns: open("/dev/net/tun"): Permission denied` |
+| Podman rootless, no subuid ranges, default netns, `/dev/net/tun` at `0666` | **Works**, no added capabilities |
+
+The difference is that podman degrades gracefully when no subuid range
+is available: it falls back to a single-UID self-mapping, which an
+unprivileged process may write itself, so `newuidmap` is never invoked
+and `CAP_SYS_ADMIN` is never needed. Docker's rootless mode has no
+equivalent fallback.
+
+The cost of that fallback is real and should be weighed before building
+on it: with a single-UID mapping, every UID inside a nested container
+collapses onto the bottle's own uid 1000. There is no UID separation
+between the agent and anything it runs — `root` in a nested container is
+the agent user outside it. It also requires `ignore_chown_errors` on the
+storage driver. Whether that is acceptable depends on whether the bottle
+boundary (which is unchanged) or the nested-container boundary (which is
+effectively nil) is the one we are relying on.
+
+## What the podman spike then needed
+
+The podman implementation that replaced the Docker one on this branch
+turned up two more device-node blockers of the same shape as
+`/dev/net/tun` — Apple Container creates the node, but 0600 root:root:
+
+- **`/dev/fuse`** — blocks the `fuse-overlayfs` storage driver
+  (`fuse: failed to open /dev/fuse: Permission denied`). Without it the
+  only working driver is `vfs`, which copies whole layers per container.
+- **`/dev/net/tun`** — blocks `slirp4netns`, which rootless podman uses
+  for the default bridge network.
+
+Both are fixed by `chmod 0666` as root inside the bottle, which needs no
+capability the bottle does not already hold. This is categorically
+different from the `CAP_SYS_ADMIN` requirement: it is a permission on a
+node that already exists, not an outer privilege grant.
+
+One design note worth recording: the agent-facing surface stays `docker`
+and `docker compose`, pointed at podman's Docker-compatible API socket
+via `DOCKER_HOST`. Setting `netns="host"` in `containers.conf` does *not*
+propagate through that compat API — stock `docker run` and compose files
+request bridge networking explicitly — so slirp4netns (and therefore the
+`/dev/net/tun` chmod) is required for ordinary compose files to work at
+all. Host networking remains available per-workload via
+`--network=host`.
+
+Verified working in a bottle with zero added capabilities: fuse-overlayfs
+storage, the compat API socket, `docker run` on both bridge and host
+networking, and published ports.
+
+### Nested pulls collide with our own egress DLP
+
+The first live run got podman up and `docker compose` running, then
+failed on the image pull:
+
+```
+web Pulling
+initializing source docker://python:3.12-alpine: reading manifest ...
+StatusCode: 403, egress DLP: Generic Bearer JWT found in body
+```
+
+This is bot-bottle's own egress scanner, not a podman problem. The
+Docker registry auth flow carries a bearer JWT *by protocol*, and the
+`token_patterns` detector's `Generic Bearer JWT` rule
+(`Bearer\s+[A-Za-z0-9._\-]{50,}`) matches it on every pull. Any bottle
+that pulls images will hit this.
+
+The fix is per-route detector scoping, which the egress config already
+supports — drop `token_patterns` on the registry hosts and keep
+`known_secrets`:
+
+```json
+{"host": "registry-1.docker.io",
+ "dlp": {"outbound_detectors": ["known_secrets"]}}
+```
+
+That is the right trade rather than a grudging one: `known_secrets`
+matches the bottle's *actual* credential values, so real exfil through a
+registry host is still caught. `token_patterns` on a registry route only
+ever produces protocol noise.
+
+Worth generalising later: any manifest enabling `docker_access` needs
+this on its registry routes, so it probably belongs in a shared
+registry-route snippet rather than being copy-pasted per bottle.
+
+### And then registry auth collides with the Authorization strip
+
+With DLP scoped, the pull failed differently: `unauthorized:
+authentication required`. This one is architectural.
+
+`egress_addon.py` strips agent-set `Authorization` unconditionally
+before forwarding — deliberately, so an agent cannot smuggle a
+credential out in a header the DLP detectors don't recognise. A route
+may carry gateway-injected auth instead, but only from a *static* token
+in an env var (`auth_scheme` + `token_env`).
+
+Docker registry auth doesn't fit that shape. The client fetches a
+short-lived, per-repository-scope bearer token from `auth.docker.io` and
+presents it to `registry-1.docker.io`. There is no static token to
+inject, and the token the client legitimately obtained is stripped.
+
+Measured inside a bottle, by hand:
+
+| Step | Result |
+| --- | --- |
+| Fetch token from `auth.docker.io` | 200, 5409-byte token body |
+| Manifest request **with** that valid token | 401 |
+| Manifest request with **no** Authorization | 401 — identical |
+
+A valid token behaves exactly like sending none, which is direct
+evidence the header never arrives. Any nested-container workflow that
+pulls from a registry is blocked on this, so it is not a detail that can
+be deferred: pulling base images is most of what nested containers are
+for.
+
+### Registries that skip the token dance work today
+
+Not every registry needs the stripped header. Measured directly:
+
+| Registry | Manifest request with no `Authorization` |
+| --- | --- |
+| `quay.io` | 200 |
+| `mcr.microsoft.com` | 200 |
+| `registry.k8s.io` | 307 (redirect, no auth) |
+| `ghcr.io` | 401 |
+| `registry-1.docker.io` | 401 |
+
+So "just add the registry to the bottle config" genuinely works — for
+quay, MCR, registry.k8s.io, or any unauthenticated internal registry.
+Docker Hub and GHCR are the ones that need the strip resolved. The
+acceptance test uses quay for exactly this reason.
+
+Resolving it for Docker Hub means picking one of:
+
+1. **Per-route opt-in to preserve client Authorization.** Smallest
+   change. Note the compounding effect on exactly these routes: the DLP
+   scoping above already removed `token_patterns` there, so a
+   preserved-auth registry route is one where the agent may send bearer
+   tokens that neither the strip nor the pattern detector inspects.
+   `known_secrets` still applies, so the bottle's real credentials are
+   still caught.
+2. **A registry-aware gateway** that performs the token dance itself and
+   injects the result. Preserves the invariant fully; materially more
+   work, and it makes the gateway speak a specific registry protocol.
+3. **Pre-seed images at provision time** (host-side `container image
+   save` into podman storage), so bottles never pull at runtime.
+   Preserves the invariant, and limits nested containers to
+   pre-approved images — which fits the custody positioning, at the cost
+   of no ad-hoc `docker pull`.
+4. **Stop.** Nested containers are not supported on this backend.
+
+### Podman 4.3.1 silently swallows container exit codes
+
+Debian bookworm — which the current agent base image is built on —
+ships podman 4.3.1. Through its Docker-compatible API, `docker run`
+returns 0 no matter what the container did:
+
+| Command | podman 4.3.1 | podman 5.4.2 |
+| --- | --- | --- |
+| `docker run … sh -c 'exit 7'` (compat API) | **0** | 7 |
+| `docker run … sh -c 'exit 0'` (compat API) | 0 | 0 |
+| `podman run … sh -c 'exit 7'` (native) | 7 | 7 |
+
+This is worse than a broken feature: every failing command an agent runs
+via `docker run` reports success. A test suite, a build step, or a CI
+script inside a bottle would pass while failing. It also silently
+defeated the acceptance test's egress-containment assertion, which is
+why that assertion now checks an in-band marker rather than an exit
+code.
+
+Podman 5.4.2 (Debian trixie) fixes it, but needs two packages that
+bookworm's podman does not: `passt` (podman 5's default network tool)
+and `nftables` (netavark shells out to `nft`; without it every run fails
+with `unable to upgrade to tcp, received 500`). With both installed,
+exit codes propagate correctly and the compat API behaves.
+
+The open question this leaves is where podman 5 comes from, since the
+agent base is bookworm-based:
+
+1. **Move the agent images to Debian trixie.** Trixie is current stable.
+   Correct, and the blast radius is every bottle, not just this feature.
+2. **Drop the compat socket and use podman natively** (`podman-docker`
+   provides a `docker` shim; compose comes from `podman-compose`).
+   Native podman propagates exit codes correctly even on 4.3.1. Contained
+   to this feature, at the cost of `docker compose` becoming
+   `docker-compose`/`podman-compose`.
+3. **Ship bookworm's podman 4.3.1 with the compat socket** — not viable.
+   Silent false success is a correctness bug agents cannot see.
+
+## Recommendation
+
+1. Do not revive rootless Docker on this backend. This document is the
+   record of why.
+2. Nested containers, if wanted, come from podman under the
+   single-mapping constraint — with the explicit understanding that the
+   nested-container boundary carries no security weight. `root` in a
+   nested container is the agent user outside it.
+3. Nested containers are therefore a build/test convenience. The bottle
+   remains the security boundary, exactly as it was.

tests/integration/test_macos_rootless_podman_spike.py

@@ -0,0 +1,154 @@
+"""Live-Mac acceptance spike for guest-local rootless podman (issue #392).
+
+Run explicitly on an Apple Silicon/macOS 26 host:
+
+    BOT_BOTTLE_ROOTLESS_PODMAN_SPIKE=1 \
+      python3 -m unittest tests.integration.test_macos_rootless_podman_spike -v
+
+The opt-in is deliberate: ordinary Linux CI cannot execute Apple Container.
+
+Podman rather than Docker because Apple Container's capability bounding set
+omits CAP_SYS_ADMIN; see
+docs/research/rootless-docker-in-apple-container-spike.md.  The agent-facing
+surface is still `docker` and `docker compose`, which talk to podman's
+Docker-compatible API socket.
+"""
+
+from __future__ import annotations
+
+import os
+import platform
+import shutil
+import tempfile
+import unittest
+from pathlib import Path
+
+from bot_bottle.backend import BottleSpec, get_bottle_backend
+from bot_bottle.manifest import ManifestIndex
+
+
+@unittest.skipUnless(
+    platform.system() == "Darwin"
+    and os.environ.get("BOT_BOTTLE_ROOTLESS_PODMAN_SPIKE") == "1",
+    "requires an explicit live-Mac rootless-podman spike run",
+)
+class TestMacosRootlessPodmanSpike(unittest.TestCase):
+    def test_compose_stays_inside_registered_bottle(self) -> None:
+        workspace = Path(tempfile.mkdtemp(prefix="rootless-podman-spike."))
+        stage = Path(tempfile.mkdtemp(prefix="rootless-podman-stage."))
+        try:
+            (workspace / "index.html").write_text("bottle-compose-ok\n")
+            (workspace / "compose.yaml").write_text(
+                "services:\n"
+                "  web:\n"
+                "    image: quay.io/prometheus/busybox\n"
+                "    working_dir: /workspace\n"
+                "    command: httpd -f -p 8000 -h /workspace\n"
+                "    volumes: ['.:/workspace']\n"
+                "    ports: ['18080:8000']\n",
+                encoding="utf-8",
+            )
+            manifest = ManifestIndex.from_json_obj({
+                "bottles": {"dev": {
+                    "docker_access": True,
+                    # A deliberately tiny image. Pulling a ~165MB one
+                    # OOM-kills the shared egress proxy, which buffers whole
+                    # response bodies to scan them — a real defect, but a
+                    # separate one from what this test covers. See the
+                    # research note.
+                    #
+                    # quay.io deliberately, not Docker Hub: the egress proxy
+                    # strips agent-set Authorization (so an agent cannot
+                    # smuggle a credential out in a header), and Docker Hub
+                    # requires a client-fetched, per-scope bearer token that
+                    # the strip therefore removes. quay serves manifests with
+                    # no Authorization at all, so a plain route is enough.
+                    #
+                    # token_patterns is still scoped off: registry traffic
+                    # carries bearer JWTs by protocol and trips the generic
+                    # rule. known_secrets stays on — it matches the bottle's
+                    # own credentials, which is the detector that catches
+                    # real exfil.
+                    "egress": {"routes": [
+                        {"host": "quay.io", "dlp": {
+                            "outbound_detectors": ["known_secrets"],
+                        }},
+                        {"host": "cdn01.quay.io", "dlp": {
+                            "outbound_detectors": ["known_secrets"],
+                        }},
+                    ]},
+                }},
+                "agents": {"spike": {
+                    "bottle": "dev", "skills": [], "prompt": "",
+                }},
+            })
+            spec = BottleSpec(
+                manifest=manifest,
+                agent_name="spike",
+                copy_cwd=True,
+                user_cwd=str(workspace),
+            )
+            backend = get_bottle_backend("macos-container")
+            plan = backend.prepare(spec, stage_dir=stage)
+            with backend.launch(plan) as bottle:
+                workdir = plan.workspace_plan.workdir
+                checks = (
+                    "docker info >/dev/null && docker compose version && "
+                    f"cd {workdir} && docker compose up -d --wait && "
+                    "curl --fail --silent http://127.0.0.1:18080/ | "
+                    "grep -q bottle-compose-ok"
+                )
+                result = bottle.exec(checks)
+                self.assertEqual(
+                    0, result.returncode,
+                    f"stdout={result.stdout!r}\nstderr={result.stderr!r}",
+                )
+                # podman's compat API reports rootlessness through its own
+                # native endpoint; the Docker-shaped SecurityOptions field does
+                # not carry it.
+                inspect = bottle.exec(
+                    "podman info --format '{{.Host.Security.Rootless}}'"
+                )
+                self.assertIn("true", inspect.stdout.lower())
+                self.assertEqual(
+                    0,
+                    bottle.exec(
+                        "test \"$(id -u)\" -ne 0"
+                    ).returncode,
+                    "the podman service must not be running as bottle root",
+                )
+                self.assertNotEqual(
+                    0,
+                    bottle.exec("test -S /var/run/docker.sock").returncode,
+                    "spike must never expose a host/rootful Docker socket",
+                )
+                # Asserted on an in-band marker, not on `docker run`'s exit
+                # code: podman 4.3.1's Docker-compat API swallows the
+                # container's status and returns 0 for everything, so an
+                # exit-code assertion here passes whether egress was blocked
+                # or wide open. That silent false pass is worse than no check
+                # at all, and it is exactly this check — the one proving a
+                # nested container cannot escape the egress path.
+                #
+                # busybox ships wget, so a failure here means egress was
+                # refused rather than the binary being absent.
+                direct = bottle.exec(
+                    "docker run --rm --env HTTP_PROXY= --env HTTPS_PROXY= "
+                    "--env http_proxy= --env https_proxy= "
+                    "quay.io/prometheus/busybox sh -c "
+                    "'wget -T 4 -qO- https://evil.example.com/ "
+                    "&& echo ESCAPED || echo CONTAINED'"
+                )
+                self.assertIn(
+                    "CONTAINED", direct.stdout,
+                    "an inner container obtained direct, unproxied egress: "
+                    f"stdout={direct.stdout!r} stderr={direct.stderr!r}",
+                )
+                self.assertNotIn("ESCAPED", direct.stdout)
+        finally:
+            shutil.rmtree(workspace, ignore_errors=True)
+            shutil.rmtree(stage, ignore_errors=True)
+
+
+if __name__ == "__main__":
+    unittest.main()

tests/unit/test_macos_container_launch_wiring.py

@@ -22,6 +22,7 @@ from bot_bottle.backend.macos_container.launch import (
     _agent_run_argv,
     _identity_proxy_env,
 )
+from bot_bottle.backend.macos_container.rootless_podman import guest_env
 from bot_bottle.manifest import ManifestIndex
 
 _BOTTLE = "bot_bottle.backend.macos_container.bottle"
@@ -76,6 +77,7 @@ def _plan(
         ),
         agent_git_gate_url=agent_git_gate_url,
         agent_supervise_url=agent_supervise_url,
+        docker_access=False,
     ))
 
 
@@ -178,6 +180,18 @@ class TestIdentityTokenDelivery(unittest.TestCase):
         self.assertNotIn("--env", argv)
 
 
+class TestRootlessPodmanEnvironment(unittest.TestCase):
+    def test_disabled_bottle_gets_no_docker_environment(self) -> None:
+        self.assertEqual({}, guest_env(False))
+
+    def test_enabled_bottle_uses_only_guest_local_socket(self) -> None:
+        env = guest_env(True)
+        self.assertEqual(
+            "unix:///tmp/bot-bottle-podman-run/podman.sock", env["DOCKER_HOST"],
+        )
+        self.assertNotIn("/var/run/docker.sock", " ".join(env.values()))
+
+
 class TestPlanIdentityToken(unittest.TestCase):
     """git-gate's gitconfig extraHeader and the supervise MCP --header read
     `getattr(plan, "identity_token", "")` at provision time and both bypass the

tests/unit/test_macos_rootless_podman.py

@@ -0,0 +1,147 @@
+"""Unit coverage for the fail-closed macOS rootless-podman spike."""
+
+from __future__ import annotations
+
+import unittest
+from dataclasses import dataclass
+from pathlib import Path
+from types import SimpleNamespace
+from typing import cast
+from unittest.mock import patch
+
+from bot_bottle.backend.macos_container import rootless_podman
+from bot_bottle.backend.macos_container import launch as launch_mod
+from bot_bottle.backend.macos_container.bottle_plan import MacosContainerBottlePlan
+
+
+class _Bottle:
+    def __init__(self, results: list[SimpleNamespace]) -> None:
+        self.results = results
+        self.commands: list[str] = []
+
+    def exec(self, command: str) -> SimpleNamespace:
+        self.commands.append(command)
+        return self.results.pop(0)
+
+
+def _result(returncode: int, *, stdout: str = "", stderr: str = "") -> SimpleNamespace:
+    return SimpleNamespace(returncode=returncode, stdout=stdout, stderr=stderr)
+
+
+@dataclass(frozen=True)
+class _AgentProvision:
+    image: str
+
+
+@dataclass(frozen=True)
+class _Plan:
+    slug: str
+    image: str
+    dockerfile_path: str
+    docker_access: bool
+    agent_provision: _AgentProvision
+
+
+class TestRootlessPodmanStart(unittest.TestCase):
+    def test_bootstraps_then_waits_for_guest_local_service(self) -> None:
+        bottle = _Bottle([_result(0), _result(1), _result(0)])
+        with patch.object(rootless_podman.time, "sleep"):
+            rootless_podman.start(bottle)
+        self.assertIn("rootless-podman-init", bottle.commands[0])
+        self.assertEqual(2, bottle.commands.count("docker info >/dev/null 2>&1"))
+
+    def test_bootstrap_failure_is_fatal_without_privilege_fallback(self) -> None:
+        bottle = _Bottle([_result(1, stderr="slirp4netns missing")])
+        with patch.object(rootless_podman, "die", side_effect=RuntimeError) as die:
+            with self.assertRaises(RuntimeError):
+                rootless_podman.start(bottle)
+        self.assertIn("slirp4netns missing", die.call_args.args[0])
+        self.assertEqual(1, len(bottle.commands))
+
+    def test_timeout_reports_guest_log(self) -> None:
+        bottle = _Bottle(
+            [_result(0)]
+            + [_result(1) for _ in range(rootless_podman.READY_RETRIES)]
+            + [_result(0, stdout="operation not permitted")]
+        )
+        with patch.object(rootless_podman.time, "sleep"), \
+             patch.object(rootless_podman, "die", side_effect=RuntimeError) as die:
+            with self.assertRaises(RuntimeError):
+                rootless_podman.start(bottle)
+        self.assertIn("operation not permitted", die.call_args.args[0])
+
+
+class TestRootlessPodmanDevices(unittest.TestCase):
+    def test_relaxes_only_the_two_blocked_device_nodes_as_root(self) -> None:
+        calls: list[tuple[str, list[str]]] = []
+        rootless_podman.prepare_guest_devices(
+            "bottle-1", lambda name, argv: calls.append((name, argv)),
+        )
+        self.assertEqual(1, len(calls))
+        name, argv = calls[0]
+        self.assertEqual("bottle-1", name)
+        self.assertIn("chmod 0666 /dev/fuse /dev/net/tun", argv[-1])
+
+
+class TestRootlessPodmanImage(unittest.TestCase):
+    def test_layers_tooling_without_changing_base_image(self) -> None:
+        calls: list[tuple[str, str, str]] = []
+
+        def build(image: str, context: str, *, dockerfile: str) -> None:
+            calls.append((image, context, dockerfile))
+            text = Path(dockerfile).read_text(encoding="utf-8")
+            self.assertIn("FROM agent:base", text)
+            self.assertIn("podman fuse-overlayfs slirp4netns uidmap", text)
+            self.assertIn("USER node", text)
+            self.assertTrue((Path(context) / "rootless-podman-init.sh").is_file())
+
+        image = rootless_podman.build_image("agent:base", build)
+        self.assertEqual("agent:base-rootless-podman", image)
+        self.assertEqual("agent:base-rootless-podman", calls[0][0])
+
+    def test_strips_subordinate_ranges_so_podman_avoids_newuidmap(self) -> None:
+        """The single-UID fallback is the entire reason podman works here.
+
+        A subordinate range would send podman down the newuidmap path, which
+        cannot write a multi-range uid_map without CAP_SYS_ADMIN in an Apple
+        Container guest — the failure that killed the rootless-Docker spike.
+        """
+        seen: list[str] = []
+
+        def build(image: str, context: str, *, dockerfile: str) -> None:
+            seen.append(Path(dockerfile).read_text(encoding="utf-8"))
+
+        rootless_podman.build_image("agent:base", build)
+        text = seen[0]
+        self.assertIn("sed -i '/^node:/d' /etc/subuid /etc/subgid", text)
+        self.assertNotIn("subuid", text.replace(
+            "sed -i '/^node:/d' /etc/subuid /etc/subgid", "",
+        ))
+
+    def test_launch_builds_base_then_rootless_variant(self) -> None:
+        plan = cast(MacosContainerBottlePlan, cast(object, _Plan(
+            slug="dev-abc",
+            image="agent:base",
+            dockerfile_path="/repo/Dockerfile",
+            docker_access=True,
+            agent_provision=_AgentProvision(image="agent:base"),
+        )))
+        with patch.object(launch_mod, "read_committed_image", return_value=None), \
+             patch.object(launch_mod.container_mod, "build_image") as build, \
+             patch.object(
+                 launch_mod.rootless_podman,
+                 "build_image",
+                 return_value="agent:base-rootless-podman",
+             ) as build_rootless:
+            result = launch_mod._build_images(plan)  # pylint: disable=protected-access
+
+        build.assert_called_once_with(
+            "agent:base", launch_mod._REPO_DIR,  # pylint: disable=protected-access
+            dockerfile="/repo/Dockerfile",
+        )
+        build_rootless.assert_called_once_with("agent:base", build)
+        self.assertEqual("agent:base-rootless-podman", result.agent_provision.image)
+
+
+if __name__ == "__main__":
+    unittest.main()

tests/unit/test_manifest_bottle_merge.py

@@ -56,6 +56,12 @@ class TestMergeBottlesRuntime(unittest.TestCase):
         result = merge_bottles_runtime([base, override])
         self.assertFalse(result.supervise)
 
+    def test_docker_access_later_wins(self):
+        result = merge_bottles_runtime([
+            _bottle(docker_access=False), _bottle(docker_access=True),
+        ])
+        self.assertTrue(result.docker_access)
+
     def test_three_bottles_merged_left_to_right(self):
         b1 = _bottle(env={"A": "1", "B": "1", "C": "1"})
         b2 = _bottle(env={"B": "2", "C": "2"})

tests/unit/test_manifest_validation.py

@@ -44,13 +44,20 @@ class TestBottleValidation(unittest.TestCase):
         with self.assertRaises(ManifestError):
             ManifestBottle.from_dict("b", {"supervise": "yes"})
 
+    def test_docker_access_not_bool(self) -> None:
+        with self.assertRaises(ManifestError):
+            ManifestBottle.from_dict("b", {"docker_access": "yes"})
+
     def test_removed_runtime_field(self) -> None:
         with self.assertRaises(ManifestError):
             ManifestBottle.from_dict("b", {"runtime": "runsc"})
 
     def test_valid_minimal(self) -> None:
-        b = ManifestBottle.from_dict("b", {"supervise": False, "env": {"X": "1"}})
+        b = ManifestBottle.from_dict(
+            "b", {"supervise": False, "docker_access": True, "env": {"X": "1"}},
+        )
         self.assertFalse(b.supervise)
+        self.assertTrue(b.docker_access)
         self.assertEqual({"X": "1"}, dict(b.env))