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fix(anthropic): skip mcp_ prefix on outgoing tool schemas when already prefixed
Companion to the GH-25255 incoming-strip fix from @hayka-pacha. Without this, build_anthropic_kwargs unconditionally added 'mcp_' to every tool name in step 3, so a native MCP server tool registered as 'mcp_composio_X' was sent as 'mcp_mcp_composio_X' on the wire. The incoming strip only removes ONE prefix, which still worked on first call, but on subsequent calls the model pattern-matched the single-prefixed form from message history and produced names that stripped to 'composio_X' — registry miss, dispatch fail. The history-rewrite block (#4) already has this guard. Apply the same guard to the schema-rewrite block (#3) so round-trip is symmetric. Added 4 outgoing-side tests. Existing 7 incoming-side tests still pass. Author map: hayka-pacha added for PR #25270 salvage attribution. Refs GH-25255.
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Lines changed: 71 additions & 1 deletion

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‎agent/anthropic_adapter.py‎

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@@ -2122,9 +2122,13 @@ def build_anthropic_kwargs(
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block["text"] = text
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# 3. Prefix tool names with mcp_ (Claude Code convention)
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# Skip names that already begin with the marker — native MCP server
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# tools (from mcp_servers: in config.yaml) are registered under their
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# full mcp_<server>_<tool> name and would double-prefix otherwise,
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# breaking round-trip registry lookup in normalize_response. GH-25255.
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if anthropic_tools:
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for tool in anthropic_tools:
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if "name" in tool:
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if "name" in tool and not tool["name"].startswith(_MCP_TOOL_PREFIX):
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tool["name"] = _MCP_TOOL_PREFIX + tool["name"]
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# 4. Prefix tool names in message history (tool_use and tool_result blocks)

‎scripts/release.py‎

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@@ -196,6 +196,7 @@
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"[email protected]": "aqilaziz", # PR #26406 salvage (preserve native audio outside Telegram)
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"[email protected]": "karthikeyann", # PR #26609 salvage (DM-topic routing pin)
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"[email protected]": "kunci115", # PR #27098 salvage (thread-not-found retry)
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"[email protected]": "hayka-pacha", # PR #25270 salvage (registry-aware mcp_ prefix strip)
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"[email protected]": "chromalinx", # PR #27014 salvage (commands for groups+DM)
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"[email protected]": "booker1207", # PR #25132 salvage (gate profile bots by allowed topics)
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"[email protected]": "kiranvk-2011", # PR #24815 salvage (image documents → vision)

‎tests/agent/test_anthropic_mcp_prefix_strip.py‎

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@@ -183,3 +183,68 @@ def test_both_stripped_and_full_registered_prefers_full(self):
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# Both exist — the condition `get_entry(stripped) and not get_entry(name)`
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# is False because get_entry(name) IS truthy, so we keep the full name.
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assert result.tool_calls[0].name == "mcp_foo"
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class TestAnthropicOAuthOutgoingPrefix:
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"""Verify the outgoing-side companion fix: build_anthropic_kwargs must not
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double-prefix tool names that already start with ``mcp_`` (native MCP server
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tools registered as ``mcp_<server>_<tool>``). GH-25255."""
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def _build(self, tools, is_oauth=True):
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from agent.anthropic_adapter import build_anthropic_kwargs
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return build_anthropic_kwargs(
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model="claude-sonnet-4-6",
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messages=[{"role": "user", "content": "Hi"}],
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tools=tools,
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max_tokens=4096,
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reasoning_config=None,
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is_oauth=is_oauth,
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)
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def test_oauth_adds_prefix_to_bare_tool_name(self):
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"""OAuth + bare name → prefix added (existing Claude Code convention)."""
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kwargs = self._build([{
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"type": "function",
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"function": {"name": "read_file", "description": "x", "parameters": {}},
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}])
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names = [t["name"] for t in kwargs["tools"]]
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assert names == ["mcp_read_file"]
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def test_oauth_does_not_double_prefix_native_mcp_tool(self):
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"""OAuth + already-prefixed native MCP name → left alone."""
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kwargs = self._build([{
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"type": "function",
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"function": {
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"name": "mcp_composio_COMPOSIO_SEARCH_TOOLS",
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"description": "x",
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"parameters": {},
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},
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}])
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names = [t["name"] for t in kwargs["tools"]]
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# Must NOT become "mcp_mcp_composio_..." — that breaks the round-trip
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# because normalize_response only strips ONE mcp_ prefix.
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assert names == ["mcp_composio_COMPOSIO_SEARCH_TOOLS"]
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def test_oauth_mixed_native_and_bare_tools(self):
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"""Mixed: native MCP preserved, bare names prefixed."""
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kwargs = self._build([
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{"type": "function", "function": {"name": "read_file",
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"description": "x", "parameters": {}}},
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{"type": "function", "function": {"name": "mcp_composio_SEARCH",
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"description": "y", "parameters": {}}},
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{"type": "function", "function": {"name": "terminal",
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"description": "z", "parameters": {}}},
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])
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names = sorted(t["name"] for t in kwargs["tools"])
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assert names == ["mcp_composio_SEARCH", "mcp_read_file", "mcp_terminal"]
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def test_non_oauth_path_untouched(self):
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"""Non-OAuth requests never get the prefix — schemas pass through as-is."""
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kwargs = self._build([
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{"type": "function", "function": {"name": "read_file",
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"description": "x", "parameters": {}}},
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{"type": "function", "function": {"name": "mcp_composio_SEARCH",
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"description": "y", "parameters": {}}},
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], is_oauth=False)
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names = sorted(t["name"] for t in kwargs["tools"])
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assert names == ["mcp_composio_SEARCH", "read_file"]

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