fix(opencode): queries open the database read-only without touching its sidecars (Issue #60, Linux item 5)

A read-write open checkpointed the WAL and deleted -wal/-shm on close; a
plain mode=ro open created missing ones and left them. _ro_connect uses the
sidecars only when both exist (a live writer keeps them) and reads the file
as immutable otherwise. verify_artifact, _has_session, discover,
_descendants and residual_artifacts (db_rows_naming takes a connect) use it;
the purge's own writes are unchanged.

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

.agents/skills/lib_py/agents/adapters/opencode.py

@@ -10,6 +10,15 @@ _LEGACY_TABLES = (("message", "session_id"), ("messages", "session_id"), ("part"
                   ("parts", "session_id"), ("todo", "session_id"), ("session_share", "session_id"),
                   ("session", "id"), ("sessions", "id"))
 
+def _ro_connect(db: str):
+    """A read that neither creates nor removes anything beside db (Issue #60):
+    the WAL sidecars are used only when both already exist (a live writer
+    keeps them); otherwise the file is read as immutable."""
+    path = os.path.abspath(db)
+    both = os.path.exists(path + "-wal") and os.path.exists(path + "-shm")
+    return sqlite3.connect(f"file:{quote(path)}?mode=ro" + ("" if both else "&immutable=1"), uri=True)
+
+
 _PROVIDER_ENV_VARS = (
     'ANTHROPIC_API_KEY',
     'OPENAI_API_KEY',
@@ -139,7 +148,7 @@ class OpenCodeAgentAdapter(BaseAgentAdapter):
         try:
             # opencode 2.x keeps sessions in session_v2 (a 1.x `session` table
             # survives a migration but is no longer written).
-            conn = sqlite3.connect(db)
+            conn = _ro_connect(db)
             r = conn.execute("SELECT directory, time_created FROM session_v2 WHERE id=?", (uuid,)).fetchone()
             conn.close()
             if not r:
@@ -202,7 +211,7 @@ class OpenCodeAgentAdapter(BaseAgentAdapter):
         """Child sessions (any depth) of uuid in session_v2 and a 1.x session table."""
         found, todo = [], [uuid]
         try:
-            conn = sqlite3.connect(f"file:{quote(os.path.abspath(db))}?mode=ro", uri=True)
+            conn = _ro_connect(db)
         except Exception:
             return found
         try:
@@ -224,7 +233,7 @@ class OpenCodeAgentAdapter(BaseAgentAdapter):
 
     def _has_session(self, db: str, uuid: str) -> bool:
         try:
-            conn = sqlite3.connect(db)
+            conn = _ro_connect(db)
             try:
                 return conn.execute("SELECT 1 FROM session_v2 WHERE id=?", (uuid,)).fetchone() is not None
             finally:
@@ -239,7 +248,7 @@ class OpenCodeAgentAdapter(BaseAgentAdapter):
         found = scan_names(os.path.join(self._data_home(ctx), "opencode"), uuid)
         for i in [uuid] + (self._descendants(db, uuid) if db and os.path.isfile(db) else []):
             rows = db_rows_naming(db, i, ("session_id", "aggregate_id"),
-                                  id_tables=(("session", "id"), ("session_v2", "id")))
+                                  id_tables=(("session", "id"), ("session_v2", "id")), connect=_ro_connect)
             found += rows if i == uuid else [f"{r} [child session {i}]" for r in rows]
         return found
 
@@ -306,7 +315,7 @@ class OpenCodeAgentAdapter(BaseAgentAdapter):
                 params.append(int(float(ctx.epoch) * 1000))
             query += " ORDER BY time_created DESC LIMIT 20"
 
-            conn = sqlite3.connect(db)
+            conn = _ro_connect(db)
             rows = conn.execute(query, params).fetchall()
             conn.close()
             candidates = []