diff --git a/agent/anthropic_adapter.py b/agent/anthropic_adapter.py
index 3aee7dc500f..8c06f3d517b 100644
--- a/agent/anthropic_adapter.py
+++ b/agent/anthropic_adapter.py
@@ -2122,9 +2122,13 @@ def build_anthropic_kwargs(
                 block["text"] = text
 
         # 3. Prefix tool names with mcp_ (Claude Code convention)
+        #    Skip names that already begin with the marker — native MCP server
+        #    tools (from mcp_servers: in config.yaml) are registered under their
+        #    full mcp_<server>_<tool> name and would double-prefix otherwise,
+        #    breaking round-trip registry lookup in normalize_response. GH-25255.
         if anthropic_tools:
             for tool in anthropic_tools:
-                if "name" in tool:
+                if "name" in tool and not tool["name"].startswith(_MCP_TOOL_PREFIX):
                     tool["name"] = _MCP_TOOL_PREFIX + tool["name"]
 
         # 4. Prefix tool names in message history (tool_use and tool_result blocks)
diff --git a/scripts/release.py b/scripts/release.py
index 9336e80dd2f..7debc3075da 100755
--- a/scripts/release.py
+++ b/scripts/release.py
@@ -196,6 +196,7 @@ AUTHOR_MAP = {
     "gonzes7@gmail.com": "aqilaziz",  # PR #26406 salvage (preserve native audio outside Telegram)
     "karthikeyann@users.noreply.github.com": "karthikeyann",  # PR #26609 salvage (DM-topic routing pin)
     "rino.alpin@gmail.com": "kunci115",  # PR #27098 salvage (thread-not-found retry)
+    "hayka-pacha@users.noreply.github.com": "hayka-pacha",  # PR #25270 salvage (registry-aware mcp_ prefix strip)
     "237601532+chromalinx@users.noreply.github.com": "chromalinx",  # PR #27014 salvage (commands for groups+DM)
     "booker1207@gmail.com": "booker1207",  # PR #25132 salvage (gate profile bots by allowed topics)
     "kiranvk2011@gmail.com": "kiranvk-2011",  # PR #24815 salvage (image documents → vision)
diff --git a/tests/agent/test_anthropic_mcp_prefix_strip.py b/tests/agent/test_anthropic_mcp_prefix_strip.py
index 52e55561418..102cbadca51 100644
--- a/tests/agent/test_anthropic_mcp_prefix_strip.py
+++ b/tests/agent/test_anthropic_mcp_prefix_strip.py
@@ -183,3 +183,68 @@ class TestAnthropicMcpPrefixStrip:
         # Both exist — the condition `get_entry(stripped) and not get_entry(name)`
         # is False because get_entry(name) IS truthy, so we keep the full name.
         assert result.tool_calls[0].name == "mcp_foo"
+
+
+class TestAnthropicOAuthOutgoingPrefix:
+    """Verify the outgoing-side companion fix: build_anthropic_kwargs must not
+    double-prefix tool names that already start with ``mcp_`` (native MCP server
+    tools registered as ``mcp_<server>_<tool>``). GH-25255."""
+
+    def _build(self, tools, is_oauth=True):
+        from agent.anthropic_adapter import build_anthropic_kwargs
+        return build_anthropic_kwargs(
+            model="claude-sonnet-4-6",
+            messages=[{"role": "user", "content": "Hi"}],
+            tools=tools,
+            max_tokens=4096,
+            reasoning_config=None,
+            is_oauth=is_oauth,
+        )
+
+    def test_oauth_adds_prefix_to_bare_tool_name(self):
+        """OAuth + bare name → prefix added (existing Claude Code convention)."""
+        kwargs = self._build([{
+            "type": "function",
+            "function": {"name": "read_file", "description": "x", "parameters": {}},
+        }])
+        names = [t["name"] for t in kwargs["tools"]]
+        assert names == ["mcp_read_file"]
+
+    def test_oauth_does_not_double_prefix_native_mcp_tool(self):
+        """OAuth + already-prefixed native MCP name → left alone."""
+        kwargs = self._build([{
+            "type": "function",
+            "function": {
+                "name": "mcp_composio_COMPOSIO_SEARCH_TOOLS",
+                "description": "x",
+                "parameters": {},
+            },
+        }])
+        names = [t["name"] for t in kwargs["tools"]]
+        # Must NOT become "mcp_mcp_composio_..." — that breaks the round-trip
+        # because normalize_response only strips ONE mcp_ prefix.
+        assert names == ["mcp_composio_COMPOSIO_SEARCH_TOOLS"]
+
+    def test_oauth_mixed_native_and_bare_tools(self):
+        """Mixed: native MCP preserved, bare names prefixed."""
+        kwargs = self._build([
+            {"type": "function", "function": {"name": "read_file",
+                                               "description": "x", "parameters": {}}},
+            {"type": "function", "function": {"name": "mcp_composio_SEARCH",
+                                               "description": "y", "parameters": {}}},
+            {"type": "function", "function": {"name": "terminal",
+                                               "description": "z", "parameters": {}}},
+        ])
+        names = sorted(t["name"] for t in kwargs["tools"])
+        assert names == ["mcp_composio_SEARCH", "mcp_read_file", "mcp_terminal"]
+
+    def test_non_oauth_path_untouched(self):
+        """Non-OAuth requests never get the prefix — schemas pass through as-is."""
+        kwargs = self._build([
+            {"type": "function", "function": {"name": "read_file",
+                                               "description": "x", "parameters": {}}},
+            {"type": "function", "function": {"name": "mcp_composio_SEARCH",
+                                               "description": "y", "parameters": {}}},
+        ], is_oauth=False)
+        names = sorted(t["name"] for t in kwargs["tools"])
+        assert names == ["mcp_composio_SEARCH", "read_file"]