Implemented the next missing parity slice around session-scoped environment variables.

PARITY_CHECKLIST.md

@@ -707,6 +707,7 @@ Done:
 - [x] Basic git status snapshot
 - [x] Basic shell/subprocess handling
 - [x] Bundled small portable utilities — `utils/array.ts`, `utils/set.ts`, `utils/objectGroupBy.ts`, `utils/xml.ts`, `utils/uuid.ts` ported in `src/small_utils.py`
+- [x] Session-scoped env-var registry (`utils/sessionEnvVars.ts`) ported in `src/session_env_vars.py`
 
 Missing major utility categories:
 

src/session_env_vars.py

@@ -0,0 +1,46 @@
+"""Session-scoped environment variables — Python port of
+``utils/sessionEnvVars.ts``.
+
+These are env vars set during a session (via the upstream ``/env`` slash
+command in npm) and applied only to spawned child processes — not to the
+host Python REPL/agent process itself. Bash and similar tool providers
+read this map to merge into ``subprocess`` environments.
+
+Mirrors the upstream module-level singleton: callers import the helpers
+directly rather than passing a registry around.
+"""
+
+from __future__ import annotations
+
+from collections.abc import Mapping
+from types import MappingProxyType
+
+_session_env_vars: dict[str, str] = {}
+
+
+def get_session_env_vars() -> Mapping[str, str]:
+    """Return a read-only view of the current session env vars."""
+    return MappingProxyType(_session_env_vars)
+
+
+def set_session_env_var(name: str, value: str) -> None:
+    """Set ``name=value`` for the rest of this session's child processes."""
+    _session_env_vars[name] = value
+
+
+def delete_session_env_var(name: str) -> None:
+    """Remove ``name`` from the session env (no-op if absent)."""
+    _session_env_vars.pop(name, None)
+
+
+def clear_session_env_vars() -> None:
+    """Drop every session-scoped env var."""
+    _session_env_vars.clear()
+
+
+__all__ = [
+    'get_session_env_vars',
+    'set_session_env_var',
+    'delete_session_env_var',
+    'clear_session_env_vars',
+]

tests/test_session_env_vars.py

@@ -0,0 +1,63 @@
+"""Tests for ``src/session_env_vars.py``."""
+
+from __future__ import annotations
+
+import unittest
+
+from src.session_env_vars import (
+    clear_session_env_vars,
+    delete_session_env_var,
+    get_session_env_vars,
+    set_session_env_var,
+)
+
+
+class SessionEnvVarsTest(unittest.TestCase):
+    def setUp(self) -> None:
+        clear_session_env_vars()
+
+    def tearDown(self) -> None:
+        clear_session_env_vars()
+
+    def test_starts_empty(self) -> None:
+        self.assertEqual(dict(get_session_env_vars()), {})
+
+    def test_set_and_get(self) -> None:
+        set_session_env_var('FOO', 'bar')
+        self.assertEqual(get_session_env_vars()['FOO'], 'bar')
+
+    def test_set_overwrites_existing(self) -> None:
+        set_session_env_var('FOO', 'one')
+        set_session_env_var('FOO', 'two')
+        self.assertEqual(get_session_env_vars()['FOO'], 'two')
+
+    def test_delete_removes(self) -> None:
+        set_session_env_var('FOO', 'bar')
+        delete_session_env_var('FOO')
+        self.assertNotIn('FOO', get_session_env_vars())
+
+    def test_delete_missing_is_noop(self) -> None:
+        delete_session_env_var('NEVER_SET')
+        self.assertEqual(dict(get_session_env_vars()), {})
+
+    def test_clear_drops_everything(self) -> None:
+        set_session_env_var('A', '1')
+        set_session_env_var('B', '2')
+        clear_session_env_vars()
+        self.assertEqual(dict(get_session_env_vars()), {})
+
+    def test_returned_mapping_is_read_only(self) -> None:
+        set_session_env_var('FOO', 'bar')
+        view = get_session_env_vars()
+        with self.assertRaises(TypeError):
+            view['FOO'] = 'mutated'  # type: ignore[index]
+
+    def test_view_reflects_subsequent_mutations(self) -> None:
+        view = get_session_env_vars()
+        self.assertNotIn('FOO', view)
+        set_session_env_var('FOO', 'bar')
+        self.assertEqual(view['FOO'], 'bar')
+
+
+if __name__ == '__main__':
+    unittest.main()