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>

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

@@ -1,4 +1,4 @@
-import os, sys, sqlite3, shutil, subprocess
+import os, sys, sqlite3, shutil, subprocess, tempfile
 from urllib.parse import quote
 from typing import Optional, Any, List
 from lib_py.agents.base import BaseAgentAdapter, DiscoveryContext, scan_names, db_rows_naming, conversation_in_use
@@ -11,12 +11,29 @@ _LEGACY_TABLES = (("message", "session_id"), ("messages", "session_id"), ("part"
                   ("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."""
+    """A read that neither creates nor removes anything beside db (Issue #60).
+    Both WAL sidecars (a live writer keeps them): read through them. No -wal:
+    nothing to apply, so the file is read as immutable. A -wal without its
+    -shm (left behind - no writer runs without one) still holds committed
+    rows: they are read from a private copy, where SQLite may rebuild the
+    index, loaded into memory."""
     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)
+    wal, shm = os.path.exists(path + "-wal"), os.path.exists(path + "-shm")
+    if wal and shm:
+        return sqlite3.connect(f"file:{quote(path)}?mode=ro", uri=True)
+    if not wal:
+        return sqlite3.connect(f"file:{quote(path)}?mode=ro&immutable=1", uri=True)
+    mem = sqlite3.connect(":memory:")
+    with tempfile.TemporaryDirectory(prefix="mam-opencode-") as tmp:
+        copy = os.path.join(tmp, "opencode.db")
+        shutil.copyfile(path, copy)
+        shutil.copyfile(path + "-wal", copy + "-wal")
+        src = sqlite3.connect(copy)
+        try:
+            src.backup(mem)
+        finally:
+            src.close()
+    return mem
 
 
 # (binary, HOME, XDG_DATA_HOME) -> the db `debug paths` printed for them.