hermes: preserve legacy provider session directories

services/hermes/scripts/execution_pool_worker.py

@@ -93,6 +93,27 @@ def _state_path(assignment: dict[str, Any]) -> Path:
     return path
 
 
+def _preserve_runtime_directory(runtime: Path) -> None:
+    """Move one legacy provider directory aside before installing our symlink."""
+    parent = runtime.parent
+    if parent.is_symlink() or not parent.is_dir() or runtime.is_symlink() or not runtime.is_dir():
+        raise ProtocolError(f"provider session path is not a safe directory: {runtime.name}")
+    preserved = parent / f".hermes-legacy-{runtime.name}"
+    if preserved.exists() or preserved.is_symlink():
+        raise ProtocolError(f"provider session migration conflicts: {runtime.name}")
+    try:
+        os.rename(runtime, preserved)
+        descriptor = os.open(parent, os.O_RDONLY | getattr(os, "O_DIRECTORY", 0))
+        try:
+            os.fsync(descriptor)
+        finally:
+            os.close(descriptor)
+    except OSError as error:
+        raise ProtocolError(f"provider session migration failed: {runtime.name}") from error
+    if preserved.is_symlink() or not preserved.is_dir():
+        raise ProtocolError(f"provider session migration is unsafe: {runtime.name}")
+
+
 def _bind_provider_sessions(assignment: dict[str, Any]) -> None:
     """Attach provider session directories to this exact durable task/run."""
     parts = tuple(str(assignment[name]) for name in ("board", "task_id", "run_id"))
@@ -143,6 +164,8 @@ def _bind_provider_sessions(assignment: dict[str, Any]) -> None:
             current.resolve().relative_to(provider_root)
         if runtime.is_symlink():
             runtime.unlink()
+        elif runtime.is_dir():
+            _preserve_runtime_directory(runtime)
         elif runtime.exists():
             raise ProtocolError(f"provider session path is not a symlink: {runtime.name}")
         runtime.symlink_to(durable)

testing/tests/test_hermes_execution_pool_worker_v2.py

@@ -143,6 +143,25 @@ def test_provider_session_binding_replaces_only_owned_symlinks(tmp_path, monkeyp
         worker._bind_provider_sessions(assignment())
 
 
+def test_provider_session_binding_preserves_legacy_runtime_directories(tmp_path, monkeypatch):
+    _worker_root, _data_root, _codex, claude = prepare_provider_roots(tmp_path, monkeypatch)
+    legacy = claude / "projects"
+    (legacy / "prior-session").mkdir(parents=True)
+    (legacy / "prior-session" / "record").write_text("preserved")
+
+    worker._bind_provider_sessions(assignment())
+
+    assert legacy.is_symlink()
+    preserved = claude / ".hermes-legacy-projects/prior-session/record"
+    assert preserved.read_text() == "preserved"
+    worker._bind_provider_sessions(assignment())
+    legacy.unlink()
+    legacy.mkdir()
+    with pytest.raises(protocol.ProtocolError, match="migration conflicts"):
+        worker._bind_provider_sessions(assignment())
+    assert preserved.read_text() == "preserved"
+
+
 def test_provider_session_binding_rejects_durable_and_runtime_tampering(
     tmp_path, monkeypatch
 ):