test(opencode): the 2.x schema and CLI, a fake opencode, and an opt-in real-binary contract (Issue #60)

tests/_fake_opencode.py implements the two commands MAM calls (debug paths,
session delete) as measured on 2.0.32; unit tests never run a real opencode
(it would migrate the test database). test_real_opencode_2x_contract runs a
real 2.x opencode, when installed, in a home and tmp dir of its own with
--standalone.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VCgu9Fa9iT7TbJUSzdq4Ff

tests/_fake_opencode.py

@@ -0,0 +1,64 @@
+"""A fake opencode 2.x CLI for tests (Issue #60): only what MAM calls.
+
+- `debug paths` prints the `data` and `db` lines of the real command (the db
+  follows XDG_DATA_HOME, else HOME/.local/share; the database is not created);
+- `session delete [--standalone] [--] <id>` deletes the session and its child
+  sessions from the 2.x tables (session_v2, session_message, session_inbox,
+  session_pending, event, event_sequence) and leaves the tables a 1.x
+  migration keeps (session, message, part, todo, session_share), as the real
+  2.0.32 command was measured to do; prints `Session <id> deleted`, or
+  `Session not found: <id>` with exit 1.
+
+Tests never run a real opencode: a real one would migrate the test's
+database. The contract against a real binary is checked by the opt-in test in
+tests/test_issue60_opencode_v2.py.
+"""
+import os
+import stat
+
+SCRIPT = r'''#!/usr/bin/env python3
+import os, sqlite3, sys
+args = sys.argv[1:]
+data = os.environ.get("XDG_DATA_HOME") or os.path.join(os.environ.get("HOME", ""), ".local", "share")
+db = os.path.join(data, "opencode", "opencode.db")
+if args == ["debug", "paths"]:
+    print("data       " + os.path.dirname(db))
+    print("db         " + db)
+    sys.exit(0)
+if args[:2] == ["session", "delete"]:
+    sid = args[-1]
+    conn = sqlite3.connect(db)
+    try:
+        if not conn.execute("SELECT 1 FROM session_v2 WHERE id=?", (sid,)).fetchone():
+            print("Session not found: " + sid, file=sys.stderr)
+            sys.exit(1)
+        ids, todo = [], [sid]
+        while todo:
+            cur = todo.pop()
+            ids.append(cur)
+            todo += [r[0] for r in conn.execute("SELECT id FROM session_v2 WHERE parent_id=?", (cur,))]
+        tables = {r[0] for r in conn.execute("SELECT name FROM sqlite_master WHERE type='table'")}
+        v2 = (("session_message", "session_id"), ("session_inbox", "session_id"),
+              ("session_pending", "session_id"), ("event", "aggregate_id"),
+              ("event_sequence", "aggregate_id"), ("session_v2", "id"))
+        for t, col in v2:
+            if t in tables:
+                for i in ids:
+                    conn.execute('DELETE FROM "%s" WHERE "%s"=?' % (t, col), (i,))
+        conn.commit()
+    finally:
+        conn.close()
+    print("Session " + sid + " deleted")
+    sys.exit(0)
+sys.exit(0)
+'''
+
+
+def write(path) -> str:
+    """Write the fake as an executable `path` and return it as a str."""
+    path = str(path)
+    os.makedirs(os.path.dirname(path), exist_ok=True)
+    with open(path, "w") as f:
+        f.write(SCRIPT)
+    os.chmod(path, os.stat(path).st_mode | stat.S_IEXEC)
+    return path