fix(anthropic): remove Claude Code fingerprinting from OAuth Messages API path (#16957)

* fix(anthropic): remove Claude Code fingerprinting from OAuth Messages API path

OAuth requests now identify as Hermes on the wire. Removed:

  - "You are Claude Code, Anthropic's official CLI for Claude." system
    prompt prepend
  - Hermes Agent → Claude Code / Nous Research → Anthropic
    system-prompt substitutions
  - mcp_ tool-name prefix on outgoing tool schemas + message history
  - Matching mcp_ strip on inbound tool_use blocks (strip_tool_prefix path
    removed from AnthropicTransport.normalize_response, + all 5 call
    sites in run_agent.py and auxiliary_client.py)
  - user-agent: claude-cli/<v> (external, cli) and x-app: cli headers on
    the Messages API client

Added:

  - OAuth path strips context-1m-2025-08-07 — Anthropic rejects OAuth
    requests carrying it with HTTP 400 'This authentication style is
    incompatible with the long context beta header.'

Kept (auth plumbing, not identity spoofing):

  - _is_oauth_token classifier and is_oauth flag threading
  - Bearer vs x-api-key auth routing
  - _OAUTH_ONLY_BETAS (claude-code-20250219, oauth-2025-04-20) — backend
    requires these on the OAuth-gated Messages endpoint
  - _OAUTH_CLIENT_ID (Claude Code's) — Anthropic doesn't issue OAuth
    creds to third parties; this is the only way the login flow works
  - claude-cli/<v> User-Agent on the OAuth token exchange + refresh
    endpoints at platform.claude.com/v1/oauth/token — bare requests get
    Cloudflare 1010 blocked

Verified live against api.anthropic.com with a fresh sk-ant-oat01-*
token:

  - claude-haiku-4-5 simple message: HTTP 200, 'OK' response
  - claude-haiku-4-5 tool call: HTTP 200, stop_reason=tool_use, tool
    named 'terminal' (no mcp_ prefix) round-tripped correctly
  - Outgoing wire: no user-agent, no x-app, real Hermes identity in
    system prompt, real tool name in schema

Closes/supersedes #16820 (mcp_ PascalCase normalization patch — no longer
needed since the mcp_ round-trip is gone).

* fix(anthropic): resolve_anthropic_token() reads credential pool first

Close the gap where ~/.hermes/auth.json → credential_pool.anthropic
(where hermes login + dashboard PKCE flow write OAuth tokens) was not
in resolve_anthropic_token()'s source list.

Before: users who authed via hermes login got the token written into
the pool, but legacy fallback code paths (auxiliary_client, models
catalog fetch, explicit-runtime path) that call resolve_anthropic_token()
saw None and raised 'No Anthropic credentials found' — even though the
token was sitting in auth.json.

New priority 1: pool.select() with env-sourced entries skipped. Skipping
env:* entries preserves the existing env-var priority logic further
down the chain (static env OAuth → refreshable Claude Code upgrade via
_prefer_refreshable_claude_code_token).

Surfaced while writing the hermes-agent-dev skill playbook for
'finding a live OAuth token for an E2E test'.

---------

Co-authored-by: teknium1 <teknium@users.noreply.github.com>

tests/agent/test_anthropic_adapter.py

@@ -68,6 +68,33 @@ class TestBuildAnthropicClient:
             assert "fine-grained-tool-streaming-2025-05-14" in betas
             assert "api_key" not in kwargs
 
+    def test_oauth_does_not_send_claude_code_spoof_headers(self):
+        """OAuth requests identify as Hermes — no claude-cli UA, no x-app: cli.
+
+        Anthropic's OAuth-gated Messages API accepts requests from non-Claude-Code
+        clients as long as auth is correct and the OAuth beta headers are present.
+        See commit that removed fingerprinting for the live-test write-up.
+        """
+        with patch("agent.anthropic_adapter._anthropic_sdk") as mock_sdk:
+            build_anthropic_client("sk-ant-oat01-" + "x" * 60)
+            headers = mock_sdk.Anthropic.call_args[1]["default_headers"]
+            assert "user-agent" not in {k.lower() for k in headers}
+            assert "x-app" not in {k.lower() for k in headers}
+
+    def test_oauth_strips_context_1m_beta(self):
+        """context-1m-2025-08-07 is incompatible with OAuth auth — must be stripped.
+
+        Anthropic returns HTTP 400 "This authentication style is incompatible
+        with the long context beta header." when OAuth traffic carries it.
+        """
+        with patch("agent.anthropic_adapter._anthropic_sdk") as mock_sdk:
+            build_anthropic_client("sk-ant-oat01-" + "x" * 60)
+            betas = mock_sdk.Anthropic.call_args[1]["default_headers"]["anthropic-beta"]
+            assert "context-1m-2025-08-07" not in betas
+            # But other common betas still flow through
+            assert "interleaved-thinking-2025-05-14" in betas
+            assert "oauth-2025-04-20" in betas
+
     def test_api_key_uses_api_key(self):
         with patch("agent.anthropic_adapter._anthropic_sdk") as mock_sdk:
             build_anthropic_client("sk-ant-api03-something")