diff --git a/hermes_state.py b/hermes_state.py
index aba3b92992476..948f30e35e2f7 100644
--- a/hermes_state.py
+++ b/hermes_state.py
@@ -189,7 +189,16 @@ def _escape_like(text: str) -> str:
 
 def _cwd_prefix_clause(cwd_prefix: str) -> Tuple[str, List[str]]:
     prefix = cwd_prefix.rstrip("/\\") or cwd_prefix
-    return "(s.cwd = ? OR s.cwd LIKE ? OR s.cwd LIKE ?)", [prefix, f"{prefix}/%", f"{prefix}\\%"]
+    # ``_`` and ``%`` are LIKE wildcards but ordinary characters in a path
+    # (``my_project``), so an unescaped prefix also matches sibling directories.
+    # Escape the needle and pair it with ESCAPE; the literal separator
+    # backslash in the Windows pattern needs escaping for the same reason. The
+    # ``=`` arm is an exact compare and keeps the raw prefix.
+    esc = prefix.replace("\\", "\\\\").replace("%", "\\%").replace("_", "\\_")
+    return (
+        "(s.cwd = ? OR s.cwd LIKE ? ESCAPE '\\' OR s.cwd LIKE ? ESCAPE '\\')",
+        [prefix, f"{esc}/%", f"{esc}\\\\%"],
+    )
 
 
 def _workspace_key_clause(key: str) -> Tuple[str, List[str]]:
diff --git a/tests/test_hermes_state.py b/tests/test_hermes_state.py
index 02d4c874c9d6d..6434522ba446c 100644
--- a/tests/test_hermes_state.py
+++ b/tests/test_hermes_state.py
@@ -1121,6 +1121,35 @@ class TestPruneSessionFilters:
         assert {r["id"] for r in db.list_prune_candidates(title_like="smoke")} == {"smoke"}
         assert {r["id"] for r in db.list_prune_candidates(title_like=r"c:\tmp")} == {"winpath"}
 
+    def test_cwd_prefix_underscore_is_literal_not_a_wildcard(self, db):
+        """``_`` is a LIKE wildcard but an ordinary character in a path, so an
+        unescaped prefix also matched a same-length sibling directory — and
+        prune_sessions deletes what it matches."""
+        self._mk(db, "target", cwd="/home/me/my_project/src")
+        self._mk(db, "sibling", cwd="/home/me/myXproject/src")
+
+        rows = db.list_prune_candidates(cwd_prefix="/home/me/my_project")
+        assert {r["id"] for r in rows} == {"target"}
+
+        pruned = db.prune_sessions(older_than_days=None, cwd_prefix="/home/me/my_project")
+        assert pruned == 1
+        assert db.get_session("sibling") is not None
+
+    def test_cwd_prefix_percent_does_not_select_everything(self, db):
+        self._mk(db, "a", cwd="/home/me/one")
+        self._mk(db, "b", cwd="/home/me/two")
+
+        assert db.list_prune_candidates(cwd_prefix="/home/me/%") == []
+
+    def test_cwd_prefix_still_matches_the_directory_and_its_children(self, db):
+        """Control: the prefix must keep matching itself and anything under it."""
+        self._mk(db, "root", cwd="/home/me/proj")
+        self._mk(db, "child", cwd="/home/me/proj/src")
+        self._mk(db, "outside", cwd="/home/me/other")
+
+        rows = db.list_prune_candidates(cwd_prefix="/home/me/proj")
+        assert {r["id"] for r in rows} == {"root", "child"}
+
     def test_unknown_filter_rejected(self, db):
         import pytest as _pytest
         with _pytest.raises(TypeError):