Implemented the next missing parity slice around session env var subprocess merging.

Wires session_env_vars.py into agent_tools._build_subprocess_env so that
variables set via the session registry now reach spawned children, matching
utils/shell/bashProvider.ts:249. Per-call extra_env still wins so explicit
tool overrides take precedence over session defaults.

PARITY_CHECKLIST.md

@@ -707,7 +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`
+- [x] Session-scoped env-var registry (`utils/sessionEnvVars.ts`) ported in `src/session_env_vars.py` and merged into spawned subprocess env via `_build_subprocess_env` (mirrors `utils/shell/bashProvider.ts`)
 - [x] Display formatters from `utils/format.ts` (`formatFileSize`, `formatSecondsShort`, `formatDuration`, `formatNumber`, `formatTokens`) ported in `src/format_utils.py`
 
 Missing major utility categories:

src/agent_tools.py

@@ -15,6 +15,7 @@ from pathlib import Path
 from typing import TYPE_CHECKING, Any, Callable, Iterator, Union
 
 from .agent_types import AgentPermissions, AgentRuntimeConfig, ToolExecutionResult
+from .session_env_vars import get_session_env_vars
 
 if TYPE_CHECKING:
     from .account_runtime import AccountRuntime
@@ -3321,6 +3322,11 @@ def _build_subprocess_env(context: ToolExecutionContext) -> dict[str, str]:
         for key, value in os.environ.items()
         if not _is_sensitive_env_var(key)
     }
+    # Mirror utils/shell/bashProvider.ts: session env vars (set via /env)
+    # apply to spawned children, layered above the parent env but below
+    # explicit per-call extras.
+    for key, value in get_session_env_vars().items():
+        env[key] = value
     env.update(context.extra_env)
     return env
 

tests/test_agent_tools_security.py

@@ -9,6 +9,7 @@ from pathlib import Path
 from src.agent_tools import (
     ToolExecutionError,
     ToolPermissionError,
+    _build_subprocess_env,
     _ensure_shell_allowed,
     _is_sensitive_env_var,
     _resolve_path,
@@ -16,6 +17,10 @@ from src.agent_tools import (
     default_tool_registry,
 )
 from src.agent_types import AgentPermissions, AgentRuntimeConfig
+from src.session_env_vars import (
+    clear_session_env_vars,
+    set_session_env_var,
+)
 
 
 def _make_context(
@@ -230,5 +235,35 @@ class TestIsSensitiveEnvVar(unittest.TestCase):
         self.assertTrue(_is_sensitive_env_var("db_password"))
 
 
+# ---------------------------------------------------------------------------
+# _build_subprocess_env – session env var merging
+# ---------------------------------------------------------------------------
+class TestBuildSubprocessEnv(unittest.TestCase):
+    def setUp(self):
+        clear_session_env_vars()
+
+    def tearDown(self):
+        clear_session_env_vars()
+
+    def test_session_env_var_appears_in_subprocess_env(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            ctx = _make_context(tmp)
+            set_session_env_var("CLAW_SESSION_FOO", "from-session")
+            env = _build_subprocess_env(ctx)
+            self.assertEqual(env["CLAW_SESSION_FOO"], "from-session")
+
+    def test_extra_env_overrides_session_env(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            config = AgentRuntimeConfig(cwd=Path(tmp))
+            ctx = build_tool_context(
+                config,
+                tool_registry=default_tool_registry(),
+                extra_env={"CLAW_OVERRIDE_ME": "from-extra"},
+            )
+            set_session_env_var("CLAW_OVERRIDE_ME", "from-session")
+            env = _build_subprocess_env(ctx)
+            self.assertEqual(env["CLAW_OVERRIDE_ME"], "from-extra")
+
+
 if __name__ == "__main__":
     unittest.main()