diff --git a/roboco/runtime/transcript_retention.py b/roboco/runtime/transcript_retention.py
index 90a0ba2e..979ceaf7 100644
--- a/roboco/runtime/transcript_retention.py
+++ b/roboco/runtime/transcript_retention.py
@@ -34,7 +34,13 @@ def is_agent_owned_dir(dir_name: str, workspaces_root: str) -> bool:
     if dir_name == "-app":
         return True
     encoded_root = workspaces_root.rstrip("/").replace("/", "-")
-    return bool(encoded_root) and dir_name.startswith(encoded_root)
+    if not encoded_root:
+        return False
+    # Match the encoded root exactly or at a path boundary (next component
+    # separated by "-"), so a sibling root like "-data-workspaces2" is NOT
+    # mistaken for a descendant of "-data-workspaces" and its operator-owned
+    # transcripts pruned.
+    return dir_name == encoded_root or dir_name.startswith(encoded_root + "-")
 
 
 def _is_old_transcript(path: Path, cutoff_epoch: float) -> bool:
diff --git a/tests/unit/runtime/test_transcript_retention.py b/tests/unit/runtime/test_transcript_retention.py
index 6e728ac6..186e5dee 100644
--- a/tests/unit/runtime/test_transcript_retention.py
+++ b/tests/unit/runtime/test_transcript_retention.py
@@ -38,6 +38,16 @@ def test_is_agent_owned_dir_matches_app_and_workspaces() -> None:
     assert is_agent_owned_dir("-home-renzof-code", WORKSPACES) is False
 
 
+def test_is_agent_owned_dir_rejects_sibling_root_prefixes() -> None:
+    # A sibling workspace root that merely shares the encoded prefix without a
+    # "-" boundary must NOT be treated as agent-owned, else operator transcripts
+    # under it get pruned. Encoded root here is "-data-workspaces".
+    assert is_agent_owned_dir("-data-workspaces", WORKSPACES) is True  # exact
+    assert is_agent_owned_dir("-data-workspaces2", WORKSPACES) is False
+    assert is_agent_owned_dir("-data-workspaces2-project", WORKSPACES) is False
+    assert is_agent_owned_dir("-data-workspacesBackup-x", WORKSPACES) is False
+
+
 def test_is_agent_owned_dir_handles_root_slash_safely() -> None:
     # A pathological "/" workspaces root must not make every dir agent-owned.
     assert is_agent_owned_dir("-Users-renzof-secret", "/") is False