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>

tests/test_issue60_linux_fixes.py

@@ -9,6 +9,8 @@
    (binary, HOME, XDG_DATA_HOME) in a process.
 2. A graceful stop whose `/exit` worked says so: the agent exits instead of
    turning `working`, so the delivery is unconfirmed, and no kill step ran.
+3. opencode's auth check is the binary alone (2.x needs no login), and create
+   takes the adapter's verdict instead of running `opencode --version`.
 """
 
 from __future__ import annotations
@@ -279,3 +281,75 @@ def test_the_graceful_stop_reports_what_happened(mam_sandbox, mock_herdr, mock_a
     else:
         # The kill step runs, so it is named.
         assert "still alive → kill-session" in out, out
+
+
+# ---------------------------------------------------------------------------
+# 3. opencode's auth check is the binary
+# ---------------------------------------------------------------------------
+def _executable(path: Path) -> Path:
+    path.parent.mkdir(parents=True, exist_ok=True)
+    path.write_text("#!/bin/sh\n")
+    path.chmod(0o755)
+    return path
+
+
+@pytest.fixture
+def bare_home(tmp_path, monkeypatch):
+    """An empty HOME_DIR and a PATH with no opencode."""
+    monkeypatch.setenv("HOME_DIR", str(tmp_path / "home"))
+    monkeypatch.setenv("PATH", str(tmp_path / "empty-bin"))
+    for var in ("ANTHROPIC_API_KEY", "OPENAI_API_KEY", "GEMINI_API_KEY", "GROQ_API_KEY"):
+        monkeypatch.delenv(var, raising=False)
+    return tmp_path
+
+
+def test_keys_and_auth_json_without_the_binary_are_not_enough(bare_home, monkeypatch):
+    opencode = get_adapter("opencode")
+    assert opencode.auth_ok() is False
+    monkeypatch.setenv("ANTHROPIC_API_KEY", "test-key")
+    assert opencode.auth_ok() is False
+    auth = bare_home / "home" / ".local" / "share" / "opencode" / "auth.json"
+    auth.parent.mkdir(parents=True)
+    auth.write_text("{}")
+    assert opencode.auth_ok() is False
+
+
+@pytest.mark.parametrize("where", ["path", "home"])
+def test_the_binary_alone_is_enough(bare_home, monkeypatch, where):
+    if where == "path":
+        _executable(bare_home / "bin" / "opencode")
+        monkeypatch.setenv("PATH", str(bare_home / "bin"))
+    else:
+        _executable(bare_home / "home" / ".opencode" / "bin" / "opencode")
+    assert get_adapter("opencode").auth_ok() is True
+
+
+def test_the_auth_ok_command_exits_with_the_verdict(bare_home):
+    def rc(*args):
+        env = dict(os.environ, PYTHONPATH=str(SKILLS))
+        return subprocess.run([sys.executable, "-m", "lib_py.agents", "auth-ok", *args],
+                              capture_output=True, text=True, env=env).returncode
+
+    assert rc("opencode") == 1
+    _executable(bare_home / "home" / ".opencode" / "bin" / "opencode")
+    assert rc("opencode") == 0
+    assert rc("no-such-agent") == 1
+
+
+def test_create_decides_opencode_auth_without_running_it(mam_sandbox, mock_herdr, mock_agents, monkeypatch):
+    # Every opencode call create makes is logged; --version was the old check.
+    log = mam_sandbox / "opencode-calls.log"
+    wrap = mam_sandbox / "logbin" / "opencode"
+    wrap.parent.mkdir()
+    wrap.write_text(f'#!/bin/sh\necho "$*" >> "{log}"\nexec "{shutil.which("opencode")}" "$@"\n')
+    wrap.chmod(0o755)
+    monkeypatch.setenv("PATH", f"{wrap.parent}:{os.environ['PATH']}")
+    for var in ("ANTHROPIC_API_KEY", "OPENAI_API_KEY", "GEMINI_API_KEY", "GROQ_API_KEY"):
+        monkeypatch.delenv(var, raising=False)
+    create = mam_sandbox / ".agents" / "skills" / "multi-agent-mux-create" / "scripts" / "create_session.sh"
+    res = subprocess.run(["bash", str(create), "--workspace", str(mam_sandbox), "--agent", "opencode",
+                          "--role", "creator", "--no-onboard"],
+                         capture_output=True, text=True, cwd=str(mam_sandbox), timeout=300)
+    assert res.returncode == 0, res.stdout + res.stderr
+    calls = log.read_text().splitlines() if log.exists() else []
+    assert "--version" not in calls, calls