fix: brace-group the filtered export dump so $BASHPID expands in the parent shell

Follow-up for salvaged PR #69380. The snippet
'export -p | grep -vE ... > $tmp.$BASHPID || true' attaches the redirect to
the grep pipeline segment, so $BASHPID expands inside grep's pipeline
subshell — a DIFFERENT pid than the parent shell that expands the follow-up
'mv $tmp' operand. The dump landed in an orphaned temp file, mv failed
silently (2>/dev/null), and the shared snapshot never updated again:
exported env / venv activation stopped persisting between commands
(tests/tools/test_local_shell_init.py TestSnapshotEndToEnd caught it).

Wrap the pipeline in a brace group and attach the redirect to the group so
the expansion happens in the current shell, matching mv's expansion. Also
rename the shell-init probe var HERMES_SESSION_ENV_PROBE ->
HERMES_STICKY_ENV_PROBE: it matched the HERMES_SESSION_ prefix the salvaged
fix now intentionally strips from snapshots, and the snippet-shape test is
updated to pin the brace-group contract.

tests/tools/test_local_shell_init.py

@@ -194,12 +194,12 @@ class TestSnapshotEndToEnd:
         env = LocalEnvironment(cwd=str(tmp_path), timeout=15)
         try:
             first = env.execute(
-                'export HERMES_SESSION_ENV_PROBE="sticky"; '
+                'export HERMES_STICKY_ENV_PROBE="sticky"; '
                 'export PATH="/tmp/hermes-session-bin:$PATH"; '
-                'echo "first=$HERMES_SESSION_ENV_PROBE"'
+                'echo "first=$HERMES_STICKY_ENV_PROBE"'
             )
             second = env.execute(
-                'echo "second=$HERMES_SESSION_ENV_PROBE"; echo "PATH=$PATH"'
+                'echo "second=$HERMES_STICKY_ENV_PROBE"; echo "PATH=$PATH"'
             )
         finally:
             env.cleanup()

tests/tools/test_snapshot_session_id_leak.py

@@ -58,7 +58,14 @@ def test_export_snippet_shape():
     assert "export -p" in snippet
     assert "grep -vE" in snippet
     assert "/tmp/snap.tmp.$BASHPID" in snippet
-    assert snippet.rstrip().endswith("|| true")
+    # The redirection must be attached to a brace group wrapping the pipeline,
+    # NOT to the grep segment: a redirect on grep expands $BASHPID inside
+    # grep's pipeline subshell (a different PID than the parent shell that
+    # expands the follow-up ``mv`` operand), silently orphaning the dump and
+    # breaking snapshot env persistence entirely.
+    assert snippet.lstrip().startswith("{ ")
+    assert "|| true; }" in snippet
+    assert snippet.rstrip().endswith("> /tmp/snap.tmp.$BASHPID")
 
 
 # ---------------------------------------------------------------------------

tools/environments/base.py

@@ -412,9 +412,20 @@ def _export_dump_excluding_session_vars(tmp_path: str) -> str:
     persist across sessions in the shared snapshot. ``grep -vE`` returns exit 1
     when it filters everything, so ``|| true`` keeps the pipeline's success
     contract intact for the callers that chain on it.
+
+    The pipeline MUST be wrapped in a brace group with the redirection applied
+    to the group, not to the last pipeline segment. *tmp_path* typically embeds
+    ``$BASHPID`` for concurrency-safe temp names; a redirection attached
+    directly to ``grep`` is expanded inside grep's own pipeline subshell, where
+    ``$BASHPID`` resolves to the grep subshell's PID — while the caller's
+    follow-up ``mv $tmp`` expands in the parent shell to a DIFFERENT PID. The
+    dump then lands in an orphaned temp file and the snapshot silently never
+    updates (all exported-env persistence breaks). The brace-group redirect is
+    expanded in the current shell, keeping both expansions consistent.
     """
     return (
-        f"export -p | grep -vE '{_SNAPSHOT_EXCLUDED_ENV_REGEX}' > {tmp_path} || true"
+        f"{{ export -p | grep -vE '{_SNAPSHOT_EXCLUDED_ENV_REGEX}' || true; }} "
+        f"> {tmp_path}"
     )
 
 
@@ -678,9 +689,14 @@ class BaseEnvironment(ABC):
         # Chain mv on the export succeeding so a failed/partial dump never
         # replaces a good snapshot; drop the temp on failure so it isn't
         # orphaned (cleaned up wholesale in LocalEnvironment.cleanup too).
+        # NOTE: the redirection must be attached to a brace group, not to the
+        # grep pipeline segment — ``_snap_tmp`` embeds ``$BASHPID``, and a
+        # redirect on grep is expanded inside grep's pipeline subshell (a
+        # different PID than the parent shell that expands the ``mv`` operand),
+        # silently orphaning the dump. See _export_dump_excluding_session_vars.
         if self._snapshot_ready:
             parts.append(
-                f"{{ export -p | grep -vE '{_SNAPSHOT_EXCLUDED_ENV_REGEX}' > {_snap_tmp} "
+                f"{{ {_export_dump_excluding_session_vars(_snap_tmp)} "
                 f"&& mv -f {_snap_tmp} {_quoted_snap}; }} "
                 f"2>/dev/null || rm -f {_snap_tmp} 2>/dev/null || true"
             )