diff --git a/strix/runtime/session_manager.py b/strix/runtime/session_manager.py
index a8447ebb..5bdfa3f4 100644
--- a/strix/runtime/session_manager.py
+++ b/strix/runtime/session_manager.py
@@ -49,6 +49,27 @@ _EXTRA_FILE_EXTRACT_TIMEOUT_S = 120
 _EXTRA_FILE_MODE = 0o644
 
 
+def _is_regular_login_user(uid: int) -> bool:
+    """Whether ``uid`` refers to an interactive login user whose home directory
+    can take part in the sandbox uid-remapping flow.
+
+    System/service accounts (uid below the login range, or without a usable
+    home directory) must not opt in: the sandbox image's entrypoint demotes
+    itself to ``STRIX_HOST_UID``, and a demoted system uid ends up with an
+    unwritable HOME, which panics the in-container Caido sidecar
+    ("Unable to create data directory") and silently degrades every scan.
+    """
+    import pwd
+
+    if uid < 1000:
+        return False
+    try:
+        pw_dir = pwd.getpwuid(uid).pw_dir
+    except KeyError:
+        return False
+    return bool(pw_dir) and pw_dir not in ("/", "/nonexistent")
+
+
 def _host_identity_env() -> dict[str, str]:
     # Read the platform through a local so it is not narrowed to whichever OS is
     # type-checking: comparing sys.platform directly makes one of these branches
@@ -58,7 +79,15 @@ def _host_identity_env() -> dict[str, str]:
         return {}
     # Bind-mount ownership only needs mapping on Linux, where the container uid
     # must match the host's.
-    return {"STRIX_HOST_UID": str(os.getuid()), "STRIX_HOST_GID": str(os.getgid())}
+    uid, gid = os.getuid(), os.getgid()
+    if not _is_regular_login_user(uid):
+        logger.warning(
+            "Skipping sandbox uid mapping for uid %s (system/service account): "
+            "bind-mounted workspace files will keep the container user's ownership",
+            uid,
+        )
+        return {}
+    return {"STRIX_HOST_UID": str(uid), "STRIX_HOST_GID": str(gid)}
 
 
 def build_bind_mounts(local_sources: list[dict[str, Any]]) -> list[dict[str, Any]]:
diff --git a/tests/test_host_identity_env.py b/tests/test_host_identity_env.py
new file mode 100644
index 00000000..542d4df7
--- /dev/null
+++ b/tests/test_host_identity_env.py
@@ -0,0 +1,38 @@
+import os
+from types import SimpleNamespace
+
+from strix.runtime import session_manager
+
+
+def _as(monkeypatch, uid: int, gid: int) -> None:
+    monkeypatch.setattr(os, "getuid", lambda: uid)
+    monkeypatch.setattr(os, "getgid", lambda: gid)
+
+
+def test_system_account_uid_skips_mapping(monkeypatch):
+    _as(monkeypatch, 997, 980)
+    assert session_manager._host_identity_env() == {}
+
+
+def test_uid_below_login_range_skips_mapping(monkeypatch):
+    _as(monkeypatch, 999, 999)
+    assert session_manager._host_identity_env() == {}
+
+
+def test_homeless_uid_skips_mapping(monkeypatch):
+    _as(monkeypatch, 1500, 1500)
+    monkeypatch.setattr(
+        "pwd.getpwuid", lambda uid: SimpleNamespace(pw_dir="/nonexistent")
+    )
+    assert session_manager._host_identity_env() == {}
+
+
+def test_regular_user_is_mapped(monkeypatch):
+    _as(monkeypatch, 1500, 1500)
+    monkeypatch.setattr(
+        "pwd.getpwuid", lambda uid: SimpleNamespace(pw_dir="/home/dev")
+    )
+    assert session_manager._host_identity_env() == {
+        "STRIX_HOST_UID": "1500",
+        "STRIX_HOST_GID": "1500",
+    }