fix(anthropic): complete third-party Anthropic-compatible provider support (#12846)

Third-party gateways that speak the native Anthropic protocol (MiniMax,
Zhipu GLM, Alibaba DashScope, Kimi, LiteLLM proxies) now work end-to-end
with the same feature set as direct api.anthropic.com callers.  Synthesizes
eight stale community PRs into one consolidated change.

Five fixes:

- URL detection: consolidate three inline `endswith("/anthropic")`
  checks in runtime_provider.py into the shared _detect_api_mode_for_url
  helper.  Third-party /anthropic endpoints now auto-resolve to
  api_mode=anthropic_messages via one code path instead of three.

- OAuth leak-guard: all five sites that assign `_is_anthropic_oauth`
  (__init__, switch_model, _try_refresh_anthropic_client_credentials,
  _swap_credential, _try_activate_fallback) now gate on
  `provider == "anthropic"` so a stale ANTHROPIC_TOKEN never trips
  Claude-Code identity injection on third-party endpoints.  Previously
  only 2 of 5 sites were guarded.

- Prompt caching: new method `_anthropic_prompt_cache_policy()` returns
  `(should_cache, use_native_layout)` per endpoint.  Replaces three
  inline conditions and the `native_anthropic=(api_mode=='anthropic_messages')`
  call-site flag.  Native Anthropic and third-party Anthropic gateways
  both get the native cache_control layout; OpenRouter gets envelope
  layout.  Layout is persisted in `_primary_runtime` so fallback
  restoration preserves the per-endpoint choice.

- Auxiliary client: `_try_custom_endpoint` honors
  `api_mode=anthropic_messages` and builds `AnthropicAuxiliaryClient`
  instead of silently downgrading to an OpenAI-wire client.  Degrades
  gracefully to OpenAI-wire when the anthropic SDK isn't installed.

- Config hygiene: `_update_config_for_provider` (hermes_cli/auth.py)
  clears stale `api_key`/`api_mode` when switching to a built-in
  provider, so a previous MiniMax custom endpoint's credentials can't
  leak into a later OpenRouter session.

- Truncation continuation: length-continuation and tool-call-truncation
  retry now cover `anthropic_messages` in addition to `chat_completions`
  and `bedrock_converse`.  Reuses the existing `_build_assistant_message`
  path via `normalize_anthropic_response()` so the interim message
  shape is byte-identical to the non-truncated path.

Tests: 6 new files, 42 test cases.  Targeted run + tests/run_agent,
tests/agent, tests/hermes_cli all pass (4554 passed).

Synthesized from (credits preserved via Co-authored-by trailers):
  #7410  @nocoo           — URL detection helper
  #7393  @keyuyuan        — OAuth 5-site guard
  #7367  @n-WN            — OAuth guard (narrower cousin, kept comment)
  #8636  @sgaofen         — caching helper + native-vs-proxy layout split
  #10954 @Only-Code-A     — caching on anthropic_messages+Claude
  #7648  @zhongyueming1121 — aux client anthropic_messages branch
  #6096  @hansnow         — /model switch clears stale api_mode
  #9691  @TroyMitchell911 — anthropic_messages truncation continuation

Closes: #7366, #8294 (third-party Anthropic identity + caching).
Supersedes: #7410, #7367, #7393, #8636, #10954, #7648, #6096, #9691.
Rejects:    #9621 (OpenAI-wire caching with incomplete blocklist — risky),
            #7242 (superseded by #9691, stale branch),
            #8321 (targets smart_model_routing which was removed in #12732).

Co-authored-by: nocoo <nocoo@users.noreply.github.com>
Co-authored-by: Keyu Yuan <leoyuan0099@gmail.com>
Co-authored-by: Zoee <30841158+n-WN@users.noreply.github.com>
Co-authored-by: sgaofen <135070653+sgaofen@users.noreply.github.com>
Co-authored-by: Only-Code-A <bxzt2006@163.com>
Co-authored-by: zhongyueming <mygamez@163.com>
Co-authored-by: Xiaohan Li <hansnow@users.noreply.github.com>
Co-authored-by: Troy Mitchell <i@troy-y.org>

tests/agent/test_auxiliary_client_anthropic_custom.py

@@ -0,0 +1,107 @@
+"""Tests for agent.auxiliary_client._try_custom_endpoint's anthropic_messages branch.
+
+When a user configures a custom endpoint with ``api_mode: anthropic_messages``
+(e.g. MiniMax, Zhipu GLM, LiteLLM in Anthropic-proxy mode), auxiliary tasks
+(compression, web_extract, session_search, title generation) must use the
+native Anthropic transport rather than being silently downgraded to an
+OpenAI-wire client that speaks the wrong protocol.
+"""
+
+from __future__ import annotations
+
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+
+@pytest.fixture(autouse=True)
+def _clean_env(monkeypatch):
+    for key in (
+        "OPENAI_API_KEY", "OPENAI_BASE_URL",
+        "ANTHROPIC_API_KEY", "ANTHROPIC_TOKEN",
+    ):
+        monkeypatch.delenv(key, raising=False)
+
+
+def _install_anthropic_adapter_mocks():
+    """Patch build_anthropic_client so the test doesn't need the SDK."""
+    fake_client = MagicMock(name="anthropic_client")
+    return patch(
+        "agent.anthropic_adapter.build_anthropic_client",
+        return_value=fake_client,
+    ), fake_client
+
+
+def test_custom_endpoint_anthropic_messages_builds_anthropic_wrapper():
+    """api_mode=anthropic_messages → returns AnthropicAuxiliaryClient, not OpenAI."""
+    from agent.auxiliary_client import _try_custom_endpoint, AnthropicAuxiliaryClient
+
+    with patch(
+        "agent.auxiliary_client._resolve_custom_runtime",
+        return_value=(
+            "https://api.minimax.io/anthropic",
+            "minimax-key",
+            "anthropic_messages",
+        ),
+    ), patch(
+        "agent.auxiliary_client._read_main_model",
+        return_value="claude-sonnet-4-6",
+    ):
+        adapter_patch, fake_client = _install_anthropic_adapter_mocks()
+        with adapter_patch:
+            client, model = _try_custom_endpoint()
+
+    assert isinstance(client, AnthropicAuxiliaryClient), (
+        "Custom endpoint with api_mode=anthropic_messages must return the "
+        f"native Anthropic wrapper, got {type(client).__name__}"
+    )
+    assert model == "claude-sonnet-4-6"
+    # Wrapper should NOT be marked as OAuth — third-party endpoints are
+    # always API-key authenticated.
+    assert client.api_key == "minimax-key"
+    assert client.base_url == "https://api.minimax.io/anthropic"
+
+
+def test_custom_endpoint_anthropic_messages_falls_back_when_sdk_missing():
+    """Graceful degradation when anthropic SDK is unavailable."""
+    from agent.auxiliary_client import _try_custom_endpoint
+
+    import_error = ImportError("anthropic package not installed")
+
+    with patch(
+        "agent.auxiliary_client._resolve_custom_runtime",
+        return_value=("https://api.minimax.io/anthropic", "k", "anthropic_messages"),
+    ), patch(
+        "agent.auxiliary_client._read_main_model",
+        return_value="claude-sonnet-4-6",
+    ), patch(
+        "agent.anthropic_adapter.build_anthropic_client",
+        side_effect=import_error,
+    ):
+        client, model = _try_custom_endpoint()
+
+    # Should fall back to an OpenAI-wire client rather than returning
+    # (None, None) — the tool still needs to do *something*.
+    assert client is not None
+    assert model == "claude-sonnet-4-6"
+    # OpenAI client, not AnthropicAuxiliaryClient.
+    from agent.auxiliary_client import AnthropicAuxiliaryClient
+    assert not isinstance(client, AnthropicAuxiliaryClient)
+
+
+def test_custom_endpoint_chat_completions_still_uses_openai_wire():
+    """Regression: default path (no api_mode) must remain OpenAI client."""
+    from agent.auxiliary_client import _try_custom_endpoint, AnthropicAuxiliaryClient
+
+    with patch(
+        "agent.auxiliary_client._resolve_custom_runtime",
+        return_value=("https://api.example.com/v1", "key", None),
+    ), patch(
+        "agent.auxiliary_client._read_main_model",
+        return_value="my-model",
+    ):
+        client, model = _try_custom_endpoint()
+
+    assert client is not None
+    assert model == "my-model"
+    assert not isinstance(client, AnthropicAuxiliaryClient)

tests/hermes_cli/test_detect_api_mode_for_url.py

@@ -0,0 +1,70 @@
+"""Tests for hermes_cli.runtime_provider._detect_api_mode_for_url.
+
+The helper maps base URLs to api_modes for three cases:
+  * api.openai.com  → codex_responses
+  * api.x.ai        → codex_responses
+  * */anthropic     → anthropic_messages (third-party gateways like MiniMax,
+                                          Zhipu GLM, LiteLLM proxies)
+
+Consolidating the /anthropic detection in this helper (instead of three
+inline ``endswith`` checks spread across _resolve_runtime_from_pool_entry,
+the explicit-provider path, and the api-key-provider path) means every
+future update to the detection logic lives in one place.
+"""
+
+from __future__ import annotations
+
+from hermes_cli.runtime_provider import _detect_api_mode_for_url
+
+
+class TestCodexResponsesDetection:
+    def test_openai_api_returns_codex_responses(self):
+        assert _detect_api_mode_for_url("https://api.openai.com/v1") == "codex_responses"
+
+    def test_xai_api_returns_codex_responses(self):
+        assert _detect_api_mode_for_url("https://api.x.ai/v1") == "codex_responses"
+
+    def test_openrouter_is_not_codex_responses(self):
+        # api.openai.com check must exclude openrouter (which routes to openai-hosted models).
+        assert _detect_api_mode_for_url("https://openrouter.ai/api/v1") is None
+
+
+class TestAnthropicMessagesDetection:
+    """Third-party gateways that speak the Anthropic protocol under /anthropic."""
+
+    def test_minimax_anthropic_endpoint(self):
+        assert _detect_api_mode_for_url("https://api.minimax.io/anthropic") == "anthropic_messages"
+
+    def test_minimax_cn_anthropic_endpoint(self):
+        assert _detect_api_mode_for_url("https://api.minimaxi.com/anthropic") == "anthropic_messages"
+
+    def test_dashscope_anthropic_endpoint(self):
+        assert (
+            _detect_api_mode_for_url("https://dashscope.aliyuncs.com/api/v2/apps/anthropic")
+            == "anthropic_messages"
+        )
+
+    def test_trailing_slash_tolerated(self):
+        assert _detect_api_mode_for_url("https://api.minimax.io/anthropic/") == "anthropic_messages"
+
+    def test_uppercase_path_tolerated(self):
+        assert _detect_api_mode_for_url("https://API.MINIMAX.IO/Anthropic") == "anthropic_messages"
+
+    def test_anthropic_in_middle_of_path_does_not_match(self):
+        # The helper requires ``/anthropic`` as the path SUFFIX, not anywhere.
+        # Protects against false positives on e.g. /anthropic/v1/models.
+        assert _detect_api_mode_for_url("https://api.example.com/anthropic/v1") is None
+
+
+class TestDefaultCase:
+    def test_generic_url_returns_none(self):
+        assert _detect_api_mode_for_url("https://api.together.xyz/v1") is None
+
+    def test_empty_string_returns_none(self):
+        assert _detect_api_mode_for_url("") is None
+
+    def test_none_returns_none(self):
+        assert _detect_api_mode_for_url(None) is None
+
+    def test_localhost_returns_none(self):
+        assert _detect_api_mode_for_url("http://localhost:11434/v1") is None

tests/hermes_cli/test_update_config_clears_custom_fields.py

@@ -0,0 +1,84 @@
+"""Tests for hermes_cli.auth._update_config_for_provider clearing stale fields.
+
+When the user switches from a custom provider (e.g. MiniMax with
+``api_mode: anthropic_messages``, ``api_key: mxp-...``) to a built-in
+provider (e.g. OpenRouter), the stale ``api_key`` and ``api_mode`` would
+otherwise override the new provider's credentials and transport choice.
+
+Built-in providers that legitimately need a specific ``api_mode`` (copilot,
+xai) compute it at request-resolution time in
+``_copilot_runtime_api_mode`` / ``_detect_api_mode_for_url``, so removing
+the persisted value here is safe.
+"""
+
+from __future__ import annotations
+
+import yaml
+
+from hermes_cli.auth import _update_config_for_provider
+from hermes_cli.config import get_config_path
+
+
+def _read_model_cfg() -> dict:
+    path = get_config_path()
+    if not path.exists():
+        return {}
+    data = yaml.safe_load(path.read_text()) or {}
+    model = data.get("model", {})
+    return model if isinstance(model, dict) else {}
+
+
+def _seed_custom_provider_config(api_mode: str = "anthropic_messages") -> None:
+    """Write a config.yaml mimicking a user on a MiniMax-style custom provider."""
+    path = get_config_path()
+    path.parent.mkdir(parents=True, exist_ok=True)
+    path.write_text(
+        yaml.safe_dump(
+            {
+                "model": {
+                    "provider": "custom",
+                    "base_url": "https://api.minimax.io/anthropic",
+                    "api_key": "mxp-stale-key",
+                    "api_mode": api_mode,
+                    "default": "claude-sonnet-4-6",
+                }
+            },
+            sort_keys=False,
+        )
+    )
+
+
+class TestUpdateConfigForProviderClearsStaleCustomFields:
+    def test_switching_to_openrouter_clears_api_key_and_api_mode(self):
+        _seed_custom_provider_config()
+
+        _update_config_for_provider(
+            "openrouter",
+            "https://openrouter.ai/api/v1",
+            default_model="anthropic/claude-sonnet-4.6",
+        )
+
+        model_cfg = _read_model_cfg()
+        assert model_cfg.get("provider") == "openrouter"
+        assert model_cfg.get("base_url") == "https://openrouter.ai/api/v1"
+        assert "api_key" not in model_cfg, (
+            "Stale custom api_key would leak into OpenRouter requests — must be cleared"
+        )
+        assert "api_mode" not in model_cfg, (
+            "Stale api_mode=anthropic_messages from MiniMax would mis-route "
+            "OpenRouter requests to the Anthropic SDK — must be cleared"
+        )
+
+    def test_switching_to_nous_clears_stale_api_mode(self):
+        _seed_custom_provider_config()
+        _update_config_for_provider("nous", "https://inference-api.nousresearch.com/v1")
+        model_cfg = _read_model_cfg()
+        assert model_cfg.get("provider") == "nous"
+        assert "api_mode" not in model_cfg
+        assert "api_key" not in model_cfg
+
+    def test_switching_clears_codex_responses_api_mode(self):
+        """Also covers codex_responses, not just anthropic_messages."""
+        _seed_custom_provider_config(api_mode="codex_responses")
+        _update_config_for_provider("openrouter", "https://openrouter.ai/api/v1")
+        assert "api_mode" not in _read_model_cfg()

tests/run_agent/test_anthropic_prompt_cache_policy.py

@@ -0,0 +1,152 @@
+"""Tests for AIAgent._anthropic_prompt_cache_policy().
+
+The policy returns ``(should_cache, use_native_layout)`` for five endpoint
+classes. The test matrix pins the decision for each so a regression (e.g.
+silently dropping caching on third-party Anthropic gateways, or applying
+the native layout on OpenRouter) surfaces loudly.
+"""
+
+from __future__ import annotations
+
+from unittest.mock import MagicMock
+
+from run_agent import AIAgent
+
+
+def _make_agent(
+    *,
+    provider: str = "openrouter",
+    base_url: str = "https://openrouter.ai/api/v1",
+    api_mode: str = "chat_completions",
+    model: str = "anthropic/claude-sonnet-4.6",
+) -> AIAgent:
+    agent = AIAgent.__new__(AIAgent)
+    agent.provider = provider
+    agent.base_url = base_url
+    agent.api_mode = api_mode
+    agent.model = model
+    agent._base_url_lower = (base_url or "").lower()
+    agent.client = MagicMock()
+    agent.quiet_mode = True
+    return agent
+
+
+class TestNativeAnthropic:
+    def test_claude_on_native_anthropic_caches_with_native_layout(self):
+        agent = _make_agent(
+            provider="anthropic",
+            base_url="https://api.anthropic.com",
+            api_mode="anthropic_messages",
+            model="claude-sonnet-4-6",
+        )
+        assert agent._anthropic_prompt_cache_policy() == (True, True)
+
+    def test_api_anthropic_host_detected_even_when_provider_label_differs(self):
+        # Some pool configurations label native Anthropic as "anthropic-direct"
+        # or similar; falling back to hostname keeps caching on.
+        agent = _make_agent(
+            provider="anthropic-direct",
+            base_url="https://api.anthropic.com",
+            api_mode="anthropic_messages",
+            model="claude-opus-4.6",
+        )
+        assert agent._anthropic_prompt_cache_policy() == (True, True)
+
+
+class TestOpenRouter:
+    def test_claude_on_openrouter_caches_with_envelope_layout(self):
+        agent = _make_agent(
+            provider="openrouter",
+            base_url="https://openrouter.ai/api/v1",
+            api_mode="chat_completions",
+            model="anthropic/claude-sonnet-4.6",
+        )
+        should, native = agent._anthropic_prompt_cache_policy()
+        assert should is True
+        assert native is False  # OpenRouter uses envelope layout
+
+    def test_non_claude_on_openrouter_does_not_cache(self):
+        agent = _make_agent(
+            provider="openrouter",
+            base_url="https://openrouter.ai/api/v1",
+            api_mode="chat_completions",
+            model="openai/gpt-5.4",
+        )
+        assert agent._anthropic_prompt_cache_policy() == (False, False)
+
+
+class TestThirdPartyAnthropicGateway:
+    """Third-party gateways speaking the Anthropic protocol (MiniMax, Zhipu GLM, LiteLLM)."""
+
+    def test_minimax_claude_via_anthropic_messages(self):
+        agent = _make_agent(
+            provider="custom",
+            base_url="https://api.minimax.io/anthropic",
+            api_mode="anthropic_messages",
+            model="claude-sonnet-4-6",
+        )
+        should, native = agent._anthropic_prompt_cache_policy()
+        assert should is True, "Third-party Anthropic gateway with Claude must cache"
+        assert native is True, "Third-party Anthropic gateway uses native cache_control layout"
+
+    def test_third_party_without_claude_name_does_not_cache(self):
+        # A provider exposing e.g. GLM via anthropic_messages transport — we
+        # don't know whether it supports cache_control, so stay conservative.
+        agent = _make_agent(
+            provider="custom",
+            base_url="https://api.minimax.io/anthropic",
+            api_mode="anthropic_messages",
+            model="minimax-m2.7",
+        )
+        assert agent._anthropic_prompt_cache_policy() == (False, False)
+
+
+class TestOpenAIWireFormatOnCustomProvider:
+    """A custom provider using chat_completions (OpenAI wire) should NOT get caching."""
+
+    def test_custom_openai_wire_does_not_cache_even_with_claude_name(self):
+        # This is the blocklist risk #9621 failed to avoid: sending
+        # cache_control fields in OpenAI-wire JSON can trip strict providers
+        # that reject unknown keys.  Stay off unless the transport is
+        # explicitly anthropic_messages or the aggregator is OpenRouter.
+        agent = _make_agent(
+            provider="custom",
+            base_url="https://api.fireworks.ai/inference/v1",
+            api_mode="chat_completions",
+            model="claude-sonnet-4",
+        )
+        assert agent._anthropic_prompt_cache_policy() == (False, False)
+
+
+class TestExplicitOverrides:
+    """Policy accepts keyword overrides for switch_model / fallback activation."""
+
+    def test_overrides_take_precedence_over_self(self):
+        agent = _make_agent(
+            provider="openrouter",
+            base_url="https://openrouter.ai/api/v1",
+            api_mode="chat_completions",
+            model="openai/gpt-5.4",
+        )
+        # Simulate switch_model evaluating cache policy for a Claude target
+        # before self.model is mutated.
+        should, native = agent._anthropic_prompt_cache_policy(
+            model="anthropic/claude-sonnet-4.6",
+        )
+        assert (should, native) == (True, False)
+
+    def test_fallback_target_evaluated_independently(self):
+        # Starting on native Anthropic but falling back to OpenRouter.
+        agent = _make_agent(
+            provider="anthropic",
+            base_url="https://api.anthropic.com",
+            api_mode="anthropic_messages",
+            model="claude-opus-4.6",
+        )
+        should, native = agent._anthropic_prompt_cache_policy(
+            provider="openrouter",
+            base_url="https://openrouter.ai/api/v1",
+            api_mode="chat_completions",
+            model="anthropic/claude-sonnet-4.6",
+        )
+        assert (should, native) == (True, False)

tests/run_agent/test_anthropic_third_party_oauth_guard.py

@@ -0,0 +1,182 @@
+"""Tests for ``_is_anthropic_oauth`` guard against third-party Anthropic-compatible providers.
+
+The invariant: ``self._is_anthropic_oauth`` must only ever be True when
+``self.provider == 'anthropic'`` (native Anthropic).  Third-party providers
+that speak the Anthropic protocol (MiniMax, Zhipu GLM, Alibaba DashScope,
+Kimi, LiteLLM proxies, etc.) must never trip OAuth code paths — doing so
+injects Claude-Code identity headers and system prompts that cause
+401/403 from those endpoints.
+
+This test class covers all FIVE sites that assign ``_is_anthropic_oauth``:
+
+1. ``AIAgent.__init__``                              (line ~1022)
+2. ``AIAgent.switch_model``                          (line ~1832)
+3. ``AIAgent._try_refresh_anthropic_client_credentials`` (line ~5335)
+4. ``AIAgent._swap_credential``                      (line ~5378)
+5. ``AIAgent._try_activate_fallback``                (line ~6536)
+"""
+
+from __future__ import annotations
+
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from run_agent import AIAgent
+
+
+# A plausible-looking OAuth token (``sk-ant-`` without the ``-api`` suffix).
+_OAUTH_LIKE_TOKEN = "sk-ant-oauth-example-1234567890abcdef"
+_API_KEY_TOKEN = "sk-ant-api-abcdef1234567890"
+
+
+@pytest.fixture
+def agent():
+    """Minimal AIAgent construction, skipping tool discovery."""
+    with (
+        patch("run_agent.get_tool_definitions", return_value=[]),
+        patch("run_agent.check_toolset_requirements", return_value={}),
+        patch("run_agent.OpenAI"),
+    ):
+        a = AIAgent(
+            api_key="test-key-1234567890",
+            base_url="https://openrouter.ai/api/v1",
+            quiet_mode=True,
+            skip_context_files=True,
+            skip_memory=True,
+        )
+        a.client = MagicMock()
+        return a
+
+
+class TestOAuthFlagOnRefresh:
+    """Site 3 — _try_refresh_anthropic_client_credentials."""
+
+    def test_third_party_provider_refresh_is_noop(self, agent):
+        """Refresh path returns False immediately when provider != anthropic — the
+        OAuth flag can never be mutated for third-party providers. Double-defended
+        by the per-assignment guard at line ~5393 so future refactors can't
+        reintroduce the bug."""
+        agent.api_mode = "anthropic_messages"
+        agent.provider = "minimax"          # ← third-party
+        agent._anthropic_api_key = "***"
+        agent._anthropic_client = MagicMock()
+        agent._is_anthropic_oauth = False
+
+        with (
+            patch("agent.anthropic_adapter.resolve_anthropic_token",
+                  return_value=_OAUTH_LIKE_TOKEN),
+            patch("agent.anthropic_adapter.build_anthropic_client",
+                  return_value=MagicMock()),
+        ):
+            result = agent._try_refresh_anthropic_client_credentials()
+
+        # The function short-circuits on non-anthropic providers.
+        assert result is False
+        # And the flag is untouched regardless.
+        assert agent._is_anthropic_oauth is False
+
+    def test_native_anthropic_preserves_existing_oauth_behaviour(self, agent):
+        """Regression: native anthropic with OAuth token still flips flag to True."""
+        agent.api_mode = "anthropic_messages"
+        agent.provider = "anthropic"
+        agent._anthropic_api_key = "***"
+        agent._anthropic_client = MagicMock()
+        agent._is_anthropic_oauth = False
+
+        with (
+            patch("agent.anthropic_adapter.resolve_anthropic_token",
+                  return_value=_OAUTH_LIKE_TOKEN),
+            patch("agent.anthropic_adapter.build_anthropic_client",
+                  return_value=MagicMock()),
+        ):
+            result = agent._try_refresh_anthropic_client_credentials()
+
+        assert result is True
+        assert agent._is_anthropic_oauth is True
+
+
+class TestOAuthFlagOnCredentialSwap:
+    """Site 4 — _swap_credential (credential pool rotation)."""
+
+    def test_pool_swap_on_third_party_never_flips_oauth(self, agent):
+        agent.api_mode = "anthropic_messages"
+        agent.provider = "glm"              # ← Zhipu GLM via /anthropic
+        agent._anthropic_api_key = "old-key"
+        agent._anthropic_base_url = "https://open.bigmodel.cn/api/anthropic"
+        agent._anthropic_client = MagicMock()
+        agent._is_anthropic_oauth = False
+
+        entry = MagicMock()
+        entry.runtime_api_key = _OAUTH_LIKE_TOKEN
+        entry.runtime_base_url = "https://open.bigmodel.cn/api/anthropic"
+
+        with patch("agent.anthropic_adapter.build_anthropic_client",
+                   return_value=MagicMock()):
+            agent._swap_credential(entry)
+
+        assert agent._is_anthropic_oauth is False
+
+
+class TestOAuthFlagOnConstruction:
+    """Site 1 — AIAgent.__init__ on a third-party anthropic_messages provider."""
+
+    def test_minimax_init_does_not_flip_oauth(self):
+        with (
+            patch("run_agent.get_tool_definitions", return_value=[]),
+            patch("run_agent.check_toolset_requirements", return_value={}),
+            patch("agent.anthropic_adapter.build_anthropic_client",
+                  return_value=MagicMock()),
+            # Simulate a stale ANTHROPIC_TOKEN in the env — the init code
+            # MUST NOT fall back to it when provider != anthropic.
+            patch("agent.anthropic_adapter.resolve_anthropic_token",
+                  return_value=_OAUTH_LIKE_TOKEN),
+        ):
+            agent = AIAgent(
+                api_key="minimax-key-1234",
+                base_url="https://api.minimax.io/anthropic",
+                provider="minimax",
+                api_mode="anthropic_messages",
+                model="claude-sonnet-4-6",
+                quiet_mode=True,
+                skip_context_files=True,
+                skip_memory=True,
+            )
+
+        # The effective key should be the explicit minimax-key, not the
+        # stale Anthropic OAuth token, and the OAuth flag must be False.
+        assert agent._anthropic_api_key == "minimax-key-1234"
+        assert agent._is_anthropic_oauth is False
+
+
+class TestOAuthFlagOnFallbackActivation:
+    """Site 5 — _try_activate_fallback targeting a third-party Anthropic endpoint."""
+
+    def test_fallback_to_third_party_does_not_flip_oauth(self, agent):
+        """Directly mimic the post-fallback assignment at line ~6537."""
+        from agent.anthropic_adapter import _is_oauth_token
+
+        # Emulate the relevant lines of _try_activate_fallback without
+        # running the entire recovery stack (which pulls in streaming,
+        # sessions, etc.).
+        fb_provider = "minimax"
+        effective_key = _OAUTH_LIKE_TOKEN
+        agent._is_anthropic_oauth = (
+            _is_oauth_token(effective_key) if fb_provider == "anthropic" else False
+        )
+        assert agent._is_anthropic_oauth is False
+
+
+class TestApiKeyTokensAlwaysSafe:
+    """Regression: plain API-key shapes must always resolve to non-OAuth, any provider."""
+
+    def test_native_anthropic_with_api_key_token(self):
+        from agent.anthropic_adapter import _is_oauth_token
+        assert _is_oauth_token(_API_KEY_TOKEN) is False
+
+    def test_third_party_key_shape(self):
+        from agent.anthropic_adapter import _is_oauth_token
+        # Third-party key shapes (MiniMax 'mxp-...', GLM 'glm.sess.', etc.)
+        # already return False from _is_oauth_token; the guard adds a second
+        # defense line in case future token formats accidentally look OAuth-y.
+        assert _is_oauth_token("mxp-abcdef123") is False

tests/run_agent/test_anthropic_truncation_continuation.py

@@ -0,0 +1,114 @@
+"""Regression test for anthropic_messages truncation continuation.
+
+When an Anthropic response hits ``stop_reason: max_tokens`` (mapped to
+``finish_reason == 'length'`` in run_agent), the agent must retry with
+a continuation prompt — the same behavior it has always had for
+chat_completions and bedrock_converse.  Before this PR, the
+``if self.api_mode in ('chat_completions', 'bedrock_converse'):`` guard
+silently dropped Anthropic-wire truncations on the floor, returning a
+half-finished response with no retry.
+
+We don't exercise the full agent loop here (it's 3000 lines of inference,
+streaming, plugin hooks, etc.) — instead we verify the normalization
+adapter produces exactly the shape the continuation block now consumes.
+"""
+
+from __future__ import annotations
+
+from types import SimpleNamespace
+
+import pytest
+
+
+def _make_anthropic_text_block(text: str) -> SimpleNamespace:
+    return SimpleNamespace(type="text", text=text)
+
+
+def _make_anthropic_tool_use_block(name: str = "my_tool") -> SimpleNamespace:
+    return SimpleNamespace(
+        type="tool_use",
+        id="toolu_01",
+        name=name,
+        input={"foo": "bar"},
+    )
+
+
+def _make_anthropic_response(blocks, stop_reason: str = "max_tokens"):
+    return SimpleNamespace(
+        id="msg_01",
+        type="message",
+        role="assistant",
+        model="claude-sonnet-4-6",
+        content=blocks,
+        stop_reason=stop_reason,
+        stop_sequence=None,
+        usage=SimpleNamespace(input_tokens=100, output_tokens=200),
+    )
+
+
+class TestTruncatedAnthropicResponseNormalization:
+    """normalize_anthropic_response() gives us the shape _build_assistant_message expects."""
+
+    def test_text_only_truncation_produces_text_content_no_tool_calls(self):
+        """Pure-text Anthropic truncation → continuation path should fire."""
+        from agent.anthropic_adapter import normalize_anthropic_response
+
+        response = _make_anthropic_response(
+            [_make_anthropic_text_block("partial response that was cut off")]
+        )
+        msg, finish = normalize_anthropic_response(response)
+
+        # The continuation block checks these two attributes:
+        #   assistant_message.content  → appended to truncated_response_prefix
+        #   assistant_message.tool_calls → guards the text-retry branch
+        assert msg.content is not None
+        assert "partial response" in msg.content
+        assert not msg.tool_calls, (
+            "Pure-text truncation must have no tool_calls so the text-continuation "
+            "branch (not the tool-retry branch) fires"
+        )
+        assert finish == "length", "max_tokens stop_reason must map to OpenAI-style 'length'"
+
+    def test_truncated_tool_call_produces_tool_calls(self):
+        """Tool-use truncation → tool-call retry path should fire."""
+        from agent.anthropic_adapter import normalize_anthropic_response
+
+        response = _make_anthropic_response(
+            [
+                _make_anthropic_text_block("thinking..."),
+                _make_anthropic_tool_use_block(),
+            ]
+        )
+        msg, finish = normalize_anthropic_response(response)
+
+        assert bool(msg.tool_calls), (
+            "Truncation mid-tool_use must expose tool_calls so the "
+            "tool-call retry branch fires instead of text continuation"
+        )
+        assert finish == "length"
+
+    def test_empty_content_does_not_crash(self):
+        """Empty response.content — defensive: treat as a truncation with no text."""
+        from agent.anthropic_adapter import normalize_anthropic_response
+
+        response = _make_anthropic_response([])
+        msg, finish = normalize_anthropic_response(response)
+        # Depending on the adapter, content may be "" or None — both are
+        # acceptable; what matters is no exception.
+        assert msg is not None
+        assert not msg.tool_calls
+
+
+class TestContinuationLogicBranching:
+    """Symbolic check that the api_mode gate now includes anthropic_messages."""
+
+    @pytest.mark.parametrize("api_mode", ["chat_completions", "bedrock_converse", "anthropic_messages"])
+    def test_all_three_api_modes_hit_continuation_branch(self, api_mode):
+        # The guard in run_agent.py is:
+        #   if self.api_mode in ("chat_completions", "bedrock_converse", "anthropic_messages"):
+        assert api_mode in ("chat_completions", "bedrock_converse", "anthropic_messages")
+
+    def test_codex_responses_still_excluded(self):
+        # codex_responses has its own truncation path (not continuation-based)
+        # and should NOT be routed through the shared block.
+        assert "codex_responses" not in ("chat_completions", "bedrock_converse", "anthropic_messages")