fix(opencode): the auth check is the binary, and create takes the adapter's verdict (Issue #60, Linux item 3)

opencode 2.x needs no login: a fresh HOME runs a free default model and a
local provider has no key, while 2.x keeps no auth.json. auth_ok is now
"opencode on PATH or under <HOME>/.opencode/bin". `python -m lib_py.agents
auth-ok <agent>` exits with an adapter's verdict, and create's opencode
branch uses it (same 7 lines) instead of its own auth.json/key test and
`opencode --version`, which wrote a line to the real opencode log.
test_a4's opencode block now pins the binary rule (decision D1, required
by the brief's item 3 and by both reviewers). Other agents are unchanged.

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

.agents/skills/lib_py/agents/__main__.py

@@ -117,6 +117,15 @@ def main():
         print(adapter.resume_spec(binary, uuid, materialized=mat))
         sys.exit(0)
 
+    elif cmd == 'auth-ok':
+        # auth-ok <agent>: exit 0 when the adapter's auth_ok() holds, else 1.
+        agent_name = sys.argv[2] if len(sys.argv) > 2 else ''
+        adapter = get_adapter(agent_name)
+        if not adapter:
+            print(f"ERROR: unknown agent {agent_name!r}", file=sys.stderr)
+            sys.exit(1)
+        sys.exit(0 if adapter.auth_ok() else 1)
+
     elif cmd == 'exit-key':
         agent_name = sys.argv[2] if len(sys.argv) > 2 else ''
         adapter = get_adapter(agent_name)