feat: entry-level Podman support — find_docker() + rootless entrypoint

.env.example

@@ -145,6 +145,10 @@
 # Only override here if you need to force a backend without touching config.yaml:
 # TERMINAL_ENV=local
 
+# Override the container runtime binary (e.g. to use Podman instead of Docker).
+# Useful on systems where Docker's storage driver is broken or unavailable.
+# HERMES_DOCKER_BINARY=/usr/local/bin/podman
+
 # Container images (for singularity/docker/modal backends)
 # TERMINAL_DOCKER_IMAGE=nikolaik/python-nodejs:python3.11-nodejs20
 # TERMINAL_SINGULARITY_IMAGE=docker://nikolaik/python-nodejs:python3.11-nodejs20

docker/entrypoint.sh

@@ -1,13 +1,14 @@
 #!/bin/bash
-# Docker entrypoint: bootstrap config files into the mounted volume, then run hermes.
+# Docker/Podman entrypoint: bootstrap config files into the mounted volume, then run hermes.
 set -e
 
-HERMES_HOME="/opt/data"
+HERMES_HOME="${HERMES_HOME:-/opt/data}"
 INSTALL_DIR="/opt/hermes"
 
 # --- Privilege dropping via gosu ---
-# When started as root (the default), optionally remap the hermes user/group
-# to match host-side ownership, fix volume permissions, then re-exec as hermes.
+# When started as root (the default for Docker, or fakeroot in rootless Podman),
+# optionally remap the hermes user/group to match host-side ownership, fix volume
+# permissions, then re-exec as hermes.
 if [ "$(id -u)" = "0" ]; then
     if [ -n "$HERMES_UID" ] && [ "$HERMES_UID" != "$(id -u hermes)" ]; then
         echo "Changing hermes UID to $HERMES_UID"
@@ -16,13 +17,19 @@ if [ "$(id -u)" = "0" ]; then
 
     if [ -n "$HERMES_GID" ] && [ "$HERMES_GID" != "$(id -g hermes)" ]; then
         echo "Changing hermes GID to $HERMES_GID"
-        groupmod -g "$HERMES_GID" hermes
+        # -o allows non-unique GID (e.g. macOS GID 20 "staff" may already exist
+        # as "dialout" in the Debian-based container image)
+        groupmod -o -g "$HERMES_GID" hermes 2>/dev/null || true
     fi
 
     actual_hermes_uid=$(id -u hermes)
     if [ "$(stat -c %u "$HERMES_HOME" 2>/dev/null)" != "$actual_hermes_uid" ]; then
         echo "$HERMES_HOME is not owned by $actual_hermes_uid, fixing"
-        chown -R hermes:hermes "$HERMES_HOME"
+        # In rootless Podman the container's "root" is mapped to an unprivileged
+        # host UID — chown will fail.  That's fine: the volume is already owned
+        # by the mapped user on the host side.
+        chown -R hermes:hermes "$HERMES_HOME" 2>/dev/null || \
+            echo "Warning: chown failed (rootless container?) — continuing anyway"
     fi
 
     echo "Dropping root privileges"

tests/tools/test_docker_find.py

@@ -46,3 +46,59 @@ def test_caches_result(self):
         with patch("tools.environments.docker.shutil.which", return_value=None):
             second = docker_mod.find_docker()
         assert first == second == "/usr/local/bin/docker"
+
+    def test_env_var_override_takes_precedence(self, tmp_path):
+        """HERMES_DOCKER_BINARY overrides PATH and known-location discovery."""
+        fake_binary = tmp_path / "podman"
+        fake_binary.write_text("#!/bin/sh\n")
+        fake_binary.chmod(0o755)
+
+        with patch.dict(os.environ, {"HERMES_DOCKER_BINARY": str(fake_binary)}), \
+             patch("tools.environments.docker.shutil.which", return_value="/usr/bin/docker"):
+            result = docker_mod.find_docker()
+        assert result == str(fake_binary)
+
+    def test_env_var_override_ignored_if_not_executable(self, tmp_path):
+        """Non-executable HERMES_DOCKER_BINARY falls through to normal discovery."""
+        fake_binary = tmp_path / "podman"
+        fake_binary.write_text("#!/bin/sh\n")
+        fake_binary.chmod(0o644)  # not executable
+
+        with patch.dict(os.environ, {"HERMES_DOCKER_BINARY": str(fake_binary)}), \
+             patch("tools.environments.docker.shutil.which", return_value="/usr/bin/docker"):
+            result = docker_mod.find_docker()
+        assert result == "/usr/bin/docker"
+
+    def test_env_var_override_ignored_if_nonexistent(self):
+        """Non-existent HERMES_DOCKER_BINARY path falls through."""
+        with patch.dict(os.environ, {"HERMES_DOCKER_BINARY": "/nonexistent/podman"}), \
+             patch("tools.environments.docker.shutil.which", return_value="/usr/bin/docker"):
+            result = docker_mod.find_docker()
+        assert result == "/usr/bin/docker"
+
+    def test_podman_on_path_used_when_docker_missing(self):
+        """When docker is not on PATH, podman is tried next."""
+        def which_side_effect(name):
+            if name == "docker":
+                return None
+            if name == "podman":
+                return "/usr/bin/podman"
+            return None
+
+        with patch("tools.environments.docker.shutil.which", side_effect=which_side_effect), \
+             patch("tools.environments.docker._DOCKER_SEARCH_PATHS", []):
+            result = docker_mod.find_docker()
+        assert result == "/usr/bin/podman"
+
+    def test_docker_preferred_over_podman(self):
+        """When both docker and podman are on PATH, docker wins."""
+        def which_side_effect(name):
+            if name == "docker":
+                return "/usr/bin/docker"
+            if name == "podman":
+                return "/usr/bin/podman"
+            return None
+
+        with patch("tools.environments.docker.shutil.which", side_effect=which_side_effect):
+            result = docker_mod.find_docker()
+        assert result == "/usr/bin/docker"

tools/environments/docker.py

@@ -99,23 +99,41 @@ def _load_hermes_env_vars() -> dict[str, str]:
 
 
 def find_docker() -> Optional[str]:
-    """Locate the docker CLI binary.
+    """Locate the docker (or podman) CLI binary.
 
-    Checks ``shutil.which`` first (respects PATH), then probes well-known
-    install locations on macOS where Docker Desktop may not be in PATH
-    (e.g. when running as a gateway service via launchd).
+    Resolution order:
+    1. ``HERMES_DOCKER_BINARY`` env var — explicit override (e.g. ``/usr/bin/podman``)
+    2. ``docker`` on PATH via ``shutil.which``
+    3. ``podman`` on PATH via ``shutil.which``
+    4. Well-known macOS Docker Desktop install locations
 
-    Returns the absolute path, or ``None`` if docker cannot be found.
+    Returns the absolute path, or ``None`` if neither runtime can be found.
     """
     global _docker_executable
     if _docker_executable is not None:
         return _docker_executable
 
+    # 1. Explicit override via env var (e.g. for Podman on immutable distros)
+    override = os.getenv("HERMES_DOCKER_BINARY")
+    if override and os.path.isfile(override) and os.access(override, os.X_OK):
+        _docker_executable = override
+        logger.info("Using HERMES_DOCKER_BINARY override: %s", override)
+        return override
+
+    # 2. docker on PATH
     found = shutil.which("docker")
     if found:
         _docker_executable = found
         return found
 
+    # 3. podman on PATH (drop-in compatible for our use case)
+    found = shutil.which("podman")
+    if found:
+        _docker_executable = found
+        logger.info("Using podman as container runtime: %s", found)
+        return found
+
+    # 4. Well-known macOS Docker Desktop locations
     for path in _DOCKER_SEARCH_PATHS:
         if os.path.isfile(path) and os.access(path, os.X_OK):
             _docker_executable = path