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/adapters/opencode.py

@@ -39,13 +39,6 @@ def _ro_connect(db: str):
 # (binary, HOME, XDG_DATA_HOME) -> the db `debug paths` printed for them.
 _DB_PATHS = {}
 
-_PROVIDER_ENV_VARS = (
-    'ANTHROPIC_API_KEY',
-    'OPENAI_API_KEY',
-    'GEMINI_API_KEY',
-    'GROQ_API_KEY'
-)
-
 class OpenCodeAgentAdapter(BaseAgentAdapter):
     @property
     def name(self) -> str:
@@ -322,11 +315,10 @@ class OpenCodeAgentAdapter(BaseAgentAdapter):
         return f"{binary} --auto --standalone"
 
     def auth_ok(self, run_cmd: Optional[Any] = None) -> bool:
-        if any(os.environ.get(v) for v in _PROVIDER_ENV_VARS):
-            return True
+        # opencode 2.x needs no login: a fresh HOME runs a free default model
+        # and local providers have no key, so the binary is the whole check.
         home = os.environ.get("HOME_DIR") or os.environ.get("HOME") or os.path.expanduser("~")
-        auth_file = f"{home}/.local/share/opencode/auth.json"
-        return os.path.exists(auth_file)
+        return bool(shutil.which("opencode")) or os.path.exists(f"{home}/.opencode/bin/opencode")
 
     def discover(self, ctx: DiscoveryContext) -> list:
         db = self._resolve_db(ctx)