fix(anthropic): remove mcp_ tool prefix on OAuth path that triggers overage gate

[zccyman]

Summary

Remove the mcp_ tool name prefix that was applied to all tools on the Anthropic OAuth path. This prefix triggered Anthropic's overage gate for Pro/Max subscribers, causing every tool-bearing request to fail with HTTP 400 "out of extra usage".

Fixes #28849

Problem

build_anthropic_kwargs() unconditionally prefixed every tool name with mcp_ when is_oauth=True:

# Before (removed)
if is_oauth:
    for tool in anthropic_tools:
        tool["name"] = "mcp_" + tool["name"]  # e.g. "mcp_terminal"

Anthropic treats mcp_-prefixed tools as MCP server extensions, billing them against a separate "extra usage" bucket. Pro/Max subscribers who have extra usage disabled get an immediate HTTP 400 rejection — even when 95%+ of their included quota remains unused.

Root Cause

The prefix was modeled after Claude Code CLI's behavior, but Claude Code only prefixes tools from user-installed MCP servers — not its built-in tools like Read, Write, Bash. Hermes was incorrectly prefixing all tools including built-in ones (terminal, read_file, web_search, etc.).

Fix

Removed the mcp_ prefix logic entirely (steps 3 and 4 in the OAuth block). Tool names are now passed through unchanged.

Testing

• 4 new tests in tests/agent/test_oauth_mcp_prefix_removed.py:
  • Tool names not prefixed on OAuth path
  • Tool names not prefixed on non-OAuth path
  • Tool names in message history not prefixed
  • No crash when tools=None
• 163 total tests passed (4 new + 159 existing anthropic adapter + oauth guard tests)

[teknium1]

Thanks for writing this up and adding focused tests. I don’t think this PR is salvageable as-is because the premise no longer matches the maintained contract on main.

Problems

• The linked issue #28849 has a maintainer comment saying the mcp_ prefix is required for Anthropic OAuth subscription tokens to access tools at all; removing it would block tool-bearing requests for subscription users rather than route them through included quota.
• Current main intentionally still prefixes bare OAuth tools in agent/anthropic_adapter.py:2352 through agent/anthropic_adapter.py:2360.
• Main’s regression coverage asserts that contract: tests/agent/test_anthropic_mcp_prefix_strip.py:202 expects read_file to be sent as mcp_read_file on OAuth. The related fix already landed more narrowly in eea9553a9c, skipping only already-prefixed native MCP tools to avoid mcp_mcp_....

Suggested changes

• Don’t remove the prefix wholesale. Any follow-up should preserve bare-tool prefixing and handle extra-usage-disabled OAuth users through guidance/account recovery instead.

Automated hermes-sweeper review.

[teknium1]

This assertion conflicts with the maintained OAuth contract on current main: tests/agent/test_anthropic_mcp_prefix_strip.py:202 expects bare OAuth tools to be sent with the mcp_ prefix, and #28849 was closed by a maintainer as intended behavior.

[kshitijk4poor]

Closing in favor of #47723, which addresses the same root cause — Anthropic's OAuth billing classifier rejecting single-underscore mcp_ tool names with HTTP 400 'extra usage, not plan limits'. #47723 takes the double-underscore mcp__ route (verified on a live Max subscription to bill to plan) plus a symmetric response-side round-trip, and also covers mcp_<server>_<tool> MCP-server tools. Your diagnosis of the overage-gate trigger was correct — thank you. Tracking the fix in #47723.