fix: skip reserved ADK framework names in MCP toolsets

[NewPeople-star]

Link to Issue or Description of Change

Closes #1513.

MCP tools named set_model_response or transfer_to_agent can collide with ADK's framework tools and abort request construction with Duplicate tool name.

Following the requested scope, both McpToolset and McpAsyncToolset now skip these five framework-reserved names with a warning, matching ADK Python:

• set_model_response
• transfer_to_agent
• adk_request_confirmation
• adk_request_credential
• adk_request_input

The exclusion applies before user-defined filters, even when a filter explicitly selects a reserved name. Other server tool names, including google_search, retain their existing behavior. The async toolset keeps its internal cache intact so the session can still be closed when every server tool is filtered out.

Testing Plan

Unit Tests:

• Added regression tests for both MCP toolsets.
• All 96 selected related tests pass locally, including 12 new regression cases.

The new tests cover reserved names, normal tool ordering, empty results, name and predicate filters, context forwarding, session cleanup, and construction of a request containing ADK's SetModelResponseTool.

Against the original production code, the new suite produced 8 assertion failures and 2 Duplicate tool name errors. With the fix, all 12 pass. Google Java formatting and git diff --check also pass. The full core test suite was not run.

Manual End-to-End (E2E) Tests:

Not run against external MCP or LLM services; the regression tests use mocked MCP clients.

To verify manually, connect either toolset to an MCP server exposing an ordinary tool and the five reserved names. Confirm that only the ordinary tool is returned and warnings identify the skipped names. Use the toolset with an agent that adds set_model_response or transfer_to_agent and confirm request construction succeeds.

Checklist

• I have read the contribution guide.
• My pull request contains a single commit.
• I have performed a self-review of the code.
• I have commented the async cache-preservation behavior.
• I have added regression tests demonstrating the fix.
• New and relevant existing unit tests pass locally.
• I have manually tested my changes end-to-end.

No dependent changes are required.

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[gemini-code-assist]

Code Review

This pull request introduces a mechanism to filter out MCP server tools that collide with reserved ADK framework tool names by introducing McpToolNameFilter and applying it to both McpAsyncToolset and McpToolset. A new test suite is also added to verify this behavior. The feedback suggests adding a null check for toolName in McpToolNameFilter to prevent potential NullPointerExceptions and deduplicating the warning logs to avoid flooding.

[gemini-code-assist]

To prevent log flooding when getTools() is called repeatedly, we should ensure that the warning for a skipped reserved tool name is logged only once. Additionally, we should add a null check for toolName to prevent potential NullPointerException when calling RESERVED_NAMES.contains(toolName) (since ImmutableSet does not permit null elements).

package com.google.adk.tools.mcp;

import com.google.common.collect.ImmutableSet;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import org.jspecify.annotations.Nullable;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/** Excludes MCP server tools that collide with ADK framework tools. */
final class McpToolNameFilter {
  private static final Logger logger = LoggerFactory.getLogger(McpToolNameFilter.class);
  private static final Set<String> warnedTools = ConcurrentHashMap.newKeySet();

  // Keep these framework-reserved names aligned with ADK Python's MCP toolset.
  private static final ImmutableSet<String> RESERVED_NAMES =
      ImmutableSet.of(
          "set_model_response",
          "transfer_to_agent",
          "adk_request_confirmation",
          "adk_request_credential",
          "adk_request_input");

  private McpToolNameFilter() {}

  static boolean isAllowed(@Nullable String toolName) {
    if (toolName == null) {
      return false;
    }
    if (RESERVED_NAMES.contains(toolName)) {
      if (warnedTools.add(toolName)) {
        logger.warn(
            "Skipping MCP tool '{}' because it collides with a reserved ADK framework tool name.",
            toolName);
      }
      return false;
    }
    return true;
  }
}