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)