fix(opencode): a -wal left without its -shm is read, not ignored (Issue #60, Linux item 5, review)

_ro_connect read every database without both sidecars as immutable, which
skips a -wal's committed rows: a recovered DB+WAL with no -shm showed no
sessions (planner-reviewer-codex-01). That state - no writer runs without
a -shm - is now read from a private DB+WAL copy, where SQLite may rebuild
the index, loaded into memory; nothing beside the source is touched. The
query matrix gains the walonly state.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_issue60_linux_fixes.py

@@ -135,8 +135,9 @@ def _wal_writer(db: Path, ws: Path) -> sqlite3.Connection:
 @pytest.fixture
 def wal_home(tmp_path, monkeypatch):
     """(adapter, ctx, db, ws, make(state)) - make builds the database in one
-    of three states: `clean` (closed: no sidecars), `leftover` (both sidecars
+    of four states: `clean` (closed: no sidecars), `leftover` (both sidecars
     left behind by a writer that is gone, the rows only in the -wal),
+    `walonly` (the same without its -shm: the committed rows still count),
     `writer` (a live writer whose rows are only in the -wal)."""
     home, ws = tmp_path / "home", tmp_path / "ws"
     ws.mkdir()
@@ -150,11 +151,11 @@ def wal_home(tmp_path, monkeypatch):
     def make(state):
         if state == "clean":
             _wal_writer(db, ws).close()
-        elif state == "leftover":
+        elif state in ("leftover", "walonly"):
             src = tmp_path / "src" / "opencode.db"
             src.parent.mkdir()
             conn = _wal_writer(src, ws)
-            for suffix in ("", "-wal", "-shm"):
+            for suffix in ("", "-wal", "-shm")[:3 if state == "leftover" else 2]:
                 shutil.copyfile(str(src) + suffix, str(db) + suffix)
             conn.close()
         else:
@@ -170,6 +171,7 @@ def wal_home(tmp_path, monkeypatch):
 @pytest.mark.parametrize("state,listing", [
     ("clean", ["opencode.db"]),
     ("leftover", ["opencode.db", "opencode.db-shm", "opencode.db-wal"]),
+    ("walonly", ["opencode.db", "opencode.db-wal"]),
     ("writer", ["opencode.db", "opencode.db-shm", "opencode.db-wal"]),
 ])
 def test_a_query_reads_right_and_leaves_the_sidecars_alone(wal_home, state, listing, query):