exo: handle -c flag for multiprocessing helpers in frozen apps

When Python's multiprocessing spawns child processes on macOS (using the
"spawn" method), it also spawns helper processes like the resource tracker
by executing:

    ./frozen_app -c "from multiprocessing.resource_tracker import main; main()"

A frozen PyInstaller app doesn't understand `-c` natively - it just runs
main(). This causes the resource tracker to fail silently.

This adds a minimal `-c` handler that intercepts the flag, extracts the
inline code, and exec()s it before main() runs. This is required for the
Process() spawn in runner_supervisor.py to work correctly in the DMG.

Note that the pyinstaller docs say `freeze_support` is supposed to make
this work, but it doesn't.

Test plan:

Hardware setup: 3x Mac Studio M3 Ultra connected all-to-all with TB5

- Built a DMG[0].
- Installed on the Macs.
- Started an instance. Got an error this time in ~/.exo/exo.log. The
  last DMG from main doesn't show anything when an instance starts, this
  now shows the errors.

[0] https://github.com/exo-explore/exo/actions/runs/20464409279/job/58804485197

.github/workflows/build-app.yml

@@ -4,6 +4,8 @@ on:
   push:
     tags:
       - "v*"
+    branches:
+      - "test-app"
 
 jobs:
   build-macos-app:
@@ -32,15 +34,21 @@ jobs:
 
       - name: Derive release version from tag
         run: |
-          VERSION="${GITHUB_REF_NAME#v}"
-          if [[ "$VERSION" == *-alpha* ]]; then
+          if [[ "$GITHUB_REF_NAME" == "test-app" ]]; then
+            VERSION="0.0.0-alpha.0"
             echo "IS_ALPHA=true" >> $GITHUB_ENV
           else
-            echo "IS_ALPHA=false" >> $GITHUB_ENV
+            VERSION="${GITHUB_REF_NAME#v}"
+            if [[ "$VERSION" == *-alpha* ]]; then
+              echo "IS_ALPHA=true" >> $GITHUB_ENV
+            else
+              echo "IS_ALPHA=false" >> $GITHUB_ENV
+            fi
           fi
           echo "RELEASE_VERSION=$VERSION" >> $GITHUB_ENV
 
       - name: Ensure tag commit is on main
+        if: github.ref_type == 'tag'
         run: |
           git fetch origin main
           # Alpha tags can be on any branch, production tags must be on main
@@ -267,7 +275,7 @@ jobs:
           path: output/EXO-${{ env.RELEASE_VERSION }}.dmg
 
       - name: Upload to S3
-        if: env.SPARKLE_S3_BUCKET != ''
+        if: env.SPARKLE_S3_BUCKET != '' && github.ref_type == 'tag'
         env:
           AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}
           AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_ACCESS_KEY }}

src/exo/__main__.py

@@ -1,4 +1,39 @@
+from __future__ import annotations
+
+import sys
+from collections.abc import Sequence
+from multiprocessing import freeze_support
+from typing import Final
+
 from exo.main import main
 
+INLINE_CODE_FLAG: Final[str] = "-c"
+
+
+def _maybe_run_inline_code(argv: Sequence[str]) -> bool:
+    """
+    Reproduce the bare minimum of Python's `-c` flag so multiprocessing
+    helper processes (for example the resource tracker) can execute.
+    """
+
+    try:
+        flag_index = argv.index(INLINE_CODE_FLAG)
+    except ValueError:
+        return False
+
+    code_index = flag_index + 1
+    if code_index >= len(argv):
+        return False
+
+    inline_code = argv[code_index]
+    sys.argv = ["-c", *argv[code_index + 1 :]]
+    namespace: dict[str, object] = {"__name__": "__main__"}
+    exec(inline_code, namespace, namespace)
+    return True
+
+
 if __name__ == "__main__":
+    if _maybe_run_inline_code(sys.argv):
+        sys.exit(0)
+    freeze_support()
     main()

src/exo/shared/constants.py

@@ -1,35 +1,46 @@
 import os
+import sys
 from pathlib import Path
 
-EXO_HOME_RELATIVE_PATH = os.environ.get("EXO_HOME", ".exo")
-EXO_HOME = Path.home() / EXO_HOME_RELATIVE_PATH
+_EXO_HOME_ENV = os.environ.get("EXO_HOME", None)
 
-EXO_MODELS_DIR_ENV = os.environ.get("EXO_MODELS_DIR")
-EXO_MODELS_DIR = Path(EXO_MODELS_DIR_ENV) if EXO_MODELS_DIR_ENV else EXO_HOME / "models"
 
-EXO_GLOBAL_EVENT_DB = EXO_HOME / "global_events.db"
-EXO_WORKER_EVENT_DB = EXO_HOME / "worker_events.db"
-EXO_MASTER_STATE = EXO_HOME / "master_state.json"
-EXO_WORKER_STATE = EXO_HOME / "worker_state.json"
-EXO_MASTER_LOG = EXO_HOME / "master.log"
-EXO_WORKER_LOG = EXO_HOME / "worker.log"
-EXO_LOG = EXO_HOME / "exo.log"
-EXO_TEST_LOG = EXO_HOME / "exo_test.log"
+def _get_xdg_dir(env_var: str, fallback: str) -> Path:
+    """Get XDG directory, prioritising EXO_HOME environment variable if its set. On non-Linux platforms, default to ~/.exo."""
 
-EXO_NODE_ID_KEYPAIR = EXO_HOME / "node_id.keypair"
+    if _EXO_HOME_ENV is not None:
+        return Path.home() / _EXO_HOME_ENV
 
-EXO_WORKER_KEYRING_FILE = EXO_HOME / "worker_keyring"
-EXO_MASTER_KEYRING_FILE = EXO_HOME / "master_keyring"
+    if sys.platform != "linux":
+        return Path.home() / ".exo"
 
-EXO_IPC_DIR = EXO_HOME / "ipc"
+    xdg_value = os.environ.get(env_var, None)
+    if xdg_value is not None:
+        return Path(xdg_value) / "exo"
+    return Path.home() / fallback / "exo"
+
+
+EXO_CONFIG_HOME = _get_xdg_dir("XDG_CONFIG_HOME", ".config")
+EXO_DATA_HOME = _get_xdg_dir("XDG_DATA_HOME", ".local/share")
+EXO_CACHE_HOME = _get_xdg_dir("XDG_CACHE_HOME", ".cache")
+
+# Models directory (data)
+_EXO_MODELS_DIR_ENV = os.environ.get("EXO_MODELS_DIR", None)
+EXO_MODELS_DIR = (
+    EXO_DATA_HOME / "models"
+    if _EXO_MODELS_DIR_ENV is None
+    else Path.home() / _EXO_MODELS_DIR_ENV
+)
+
+# Log files (data/logs or cache)
+EXO_LOG = EXO_CACHE_HOME / "exo.log"
+EXO_TEST_LOG = EXO_CACHE_HOME / "exo_test.log"
+
+# Identity (config)
+EXO_NODE_ID_KEYPAIR = EXO_CONFIG_HOME / "node_id.keypair"
 
 # libp2p topics for event forwarding
 LIBP2P_LOCAL_EVENTS_TOPIC = "worker_events"
 LIBP2P_GLOBAL_EVENTS_TOPIC = "global_events"
 LIBP2P_ELECTION_MESSAGES_TOPIC = "election_message"
 LIBP2P_COMMANDS_TOPIC = "commands"
-
-# lower bounds define timeouts for flops and memory bandwidth - these are the values for the M1 chip.
-LB_TFLOPS = 2.3
-LB_MEMBW_GBPS = 68
-LB_DISK_GBPS = 1.5

src/exo/shared/tests/test_xdg_paths.py

@@ -0,0 +1,118 @@
+"""Tests for XDG Base Directory Specification compliance."""
+
+import os
+import sys
+from pathlib import Path
+from unittest import mock
+
+
+def test_xdg_paths_on_linux():
+    """Test that XDG paths are used on Linux when XDG env vars are set."""
+    with (
+        mock.patch.dict(
+            os.environ,
+            {
+                "XDG_CONFIG_HOME": "/tmp/test-config",
+                "XDG_DATA_HOME": "/tmp/test-data",
+                "XDG_CACHE_HOME": "/tmp/test-cache",
+            },
+            clear=False,
+        ),
+        mock.patch.object(sys, "platform", "linux"),
+    ):
+        # Re-import to pick up mocked values
+        import importlib
+
+        import exo.shared.constants as constants
+
+        importlib.reload(constants)
+
+        assert Path("/tmp/test-config/exo") == constants.EXO_CONFIG_HOME
+        assert Path("/tmp/test-data/exo") == constants.EXO_DATA_HOME
+        assert Path("/tmp/test-cache/exo") == constants.EXO_CACHE_HOME
+
+
+def test_xdg_default_paths_on_linux():
+    """Test that XDG default paths are used on Linux when env vars are not set."""
+    # Remove XDG env vars and EXO_HOME
+    env = {
+        k: v
+        for k, v in os.environ.items()
+        if not k.startswith("XDG_") and k != "EXO_HOME"
+    }
+    with (
+        mock.patch.dict(os.environ, env, clear=True),
+        mock.patch.object(sys, "platform", "linux"),
+    ):
+        import importlib
+
+        import exo.shared.constants as constants
+
+        importlib.reload(constants)
+
+        home = Path.home()
+        assert home / ".config" / "exo" == constants.EXO_CONFIG_HOME
+        assert home / ".local/share" / "exo" == constants.EXO_DATA_HOME
+        assert home / ".cache" / "exo" == constants.EXO_CACHE_HOME
+
+
+def test_legacy_exo_home_takes_precedence():
+    """Test that EXO_HOME environment variable takes precedence for backward compatibility."""
+    with mock.patch.dict(
+        os.environ,
+        {
+            "EXO_HOME": ".custom-exo",
+            "XDG_CONFIG_HOME": "/tmp/test-config",
+        },
+        clear=False,
+    ):
+        import importlib
+
+        import exo.shared.constants as constants
+
+        importlib.reload(constants)
+
+        home = Path.home()
+        assert home / ".custom-exo" == constants.EXO_CONFIG_HOME
+        assert home / ".custom-exo" == constants.EXO_DATA_HOME
+
+
+def test_macos_uses_traditional_paths():
+    """Test that macOS uses traditional ~/.exo directory."""
+    # Remove EXO_HOME to ensure we test the default behavior
+    env = {k: v for k, v in os.environ.items() if k != "EXO_HOME"}
+    with (
+        mock.patch.dict(os.environ, env, clear=True),
+        mock.patch.object(sys, "platform", "darwin"),
+    ):
+        import importlib
+
+        import exo.shared.constants as constants
+
+        importlib.reload(constants)
+
+        home = Path.home()
+        assert home / ".exo" == constants.EXO_CONFIG_HOME
+        assert home / ".exo" == constants.EXO_DATA_HOME
+        assert home / ".exo" == constants.EXO_CACHE_HOME
+
+
+def test_node_id_in_config_dir():
+    """Test that node ID keypair is in the config directory."""
+    import exo.shared.constants as constants
+
+    assert constants.EXO_NODE_ID_KEYPAIR.parent == constants.EXO_CONFIG_HOME
+
+
+def test_models_in_data_dir():
+    """Test that models directory is in the data directory."""
+    # Clear EXO_MODELS_DIR to test default behavior
+    env = {k: v for k, v in os.environ.items() if k != "EXO_MODELS_DIR"}
+    with mock.patch.dict(os.environ, env, clear=True):
+        import importlib
+
+        import exo.shared.constants as constants
+
+        importlib.reload(constants)
+
+        assert constants.EXO_MODELS_DIR.parent == constants.EXO_DATA_HOME

src/exo/worker/download/download_utils.py

@@ -24,7 +24,7 @@ from pydantic import (
     TypeAdapter,
 )
 
-from exo.shared.constants import EXO_HOME, EXO_MODELS_DIR
+from exo.shared.constants import EXO_MODELS_DIR
 from exo.shared.types.memory import Memory
 from exo.shared.types.worker.downloads import DownloadProgressData
 from exo.shared.types.worker.shards import ShardMetadata
@@ -132,25 +132,6 @@ async def resolve_model_path_for_repo(repo_id: str) -> Path:
     return (await ensure_models_dir()) / repo_id.replace("/", "--")
 
 
-async def ensure_exo_home() -> Path:
-    await aios.makedirs(EXO_HOME, exist_ok=True)
-    return EXO_HOME
-
-
-async def has_exo_home_read_access() -> bool:
-    try:
-        return await aios.access(EXO_HOME, os.R_OK)
-    except OSError:
-        return False
-
-
-async def has_exo_home_write_access() -> bool:
-    try:
-        return await aios.access(EXO_HOME, os.W_OK)
-    except OSError:
-        return False
-
-
 async def ensure_models_dir() -> Path:
     await aios.makedirs(EXO_MODELS_DIR, exist_ok=True)
     return EXO_MODELS_DIR