fix: prevent _buildNativeTools crash when MCP tools are in toolImplementations

[buger]

Summary

• Fix TypeError: Cannot destructure property 'schema' of null when MCP tools are present in toolImplementations
• Add null check before destructuring _getToolSchemaAndDescription() return value
• Add 2 regression tests covering single and multiple MCP tools in toolImplementations

Closes #469

Root cause

After initializeMCP(), MCP tools get merged into this.toolImplementations. When _buildNativeTools() iterates all entries, it calls _getToolSchemaAndDescription(toolName) which returns null for MCP tool names (e.g. __tools___slack-send-dm). The destructuring const { schema, description } = null throws a TypeError before the if (schema && description) guard can execute.

Fix

// Before (crashes):
const { schema, description } = this._getToolSchemaAndDescription(toolName);

// After (safe):
const toolInfo = this._getToolSchemaAndDescription(toolName);
if (!toolInfo) continue;
const { schema, description } = toolInfo;

MCP tools are already handled separately via mcpBridge.getVercelTools() further down in the same method, so skipping them in the toolImplementations loop is correct.

Test plan

• 2 new tests in mcp-message-history.test.js reproducing the exact crash scenario
• All 106 test suites pass (2621 tests)

🤖 Generated with Claude Code

[probelabs]

PR Overview: Fix _buildNativeTools crash when MCP tools are in toolImplementations

Summary

This PR fixes a TypeError: Cannot destructure property 'schema' of null crash that occurs in _buildNativeTools() when MCP tools have been merged into toolImplementations.

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Files Changed Analysis

File	Status	Additions	Deletions
npm/src/agent/ProbeAgent.js	Modified	5	1
npm/tests/unit/mcp-message-history.test.js	Modified	53	0

Total: 58 additions, 1 deletion across 2 files.

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Architecture & Impact Assessment

What This PR Accomplishes

• Prevents a runtime crash when _buildNativeTools() iterates over toolImplementations containing MCP tools
• MCP tools (with names like __tools___slack-send-dm) are merged into toolImplementations during initializeMCP() but have no schema available via _getToolSchemaAndDescription()

Root Cause

The crash occurred because:

1. After initializeMCP(), MCP tools are merged into this.toolImplementations (line ~714)
2. _buildNativeTools() iterates ALL entries in toolImplementations (line ~1839)
3. _getToolSchemaAndDescription(toolName) returns null for MCP tool names
4. The destructuring const { schema, description } = null throws TypeError before the if (schema && description) guard can execute

Key Technical Change

// Before (crashes):
const { schema, description } = this._getToolSchemaAndDescription(toolName);

// After (safe):
const toolInfo = this._getToolSchemaAndDescription(toolName);
if (!toolInfo) continue;
const { schema, description } = toolInfo;

MCP tools are correctly handled separately via mcpBridge.getVercelTools() later in the same method, so skipping them in the toolImplementations loop is the correct behavior.

Affected System Components

flowchart TD
    A[initializeMCP] -->|merges MCP tools| B[toolImplementations]
    B -->|iterates all entries| C[_buildNativeTools]
    C -->|calls| D[_getToolSchemaAndDescription]
    D -->|returns null for MCP tools| E{null check}
    E -->|skip| F[Continue loop]
    C -->|later| G[mcpBridge.getVercelTools]
    G -->|provides| H[MCP tools in Vercel format]

Loading

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Scope Discovery & Context Expansion

Related Code Paths

• ProbeAgent.initialize() (~line 704-724): Merges MCP tools into toolImplementations
• ProbeAgent.getSystemMessage() (~line 2916-2922): Also merges MCP tools (lazy init path)
• ProbeAgent._buildNativeTools() (~line 1637-1947): The fixed method
• mcpBridge.getVercelTools(): Provides properly formatted MCP tools

Test Coverage

• 2 new regression tests in mcp-message-history.test.js:
  1. Single MCP tool in toolImplementations (reproduces exact crash scenario)
  2. Multiple MCP tools in toolImplementations
• All 106 test suites pass (2621 tests)

Potential Related Areas to Verify

• DSL runtime MCP integration (npm/src/agent/dsl/)
• createExecutePlanTool MCP handling (npm/src/tools/executePlan.js)
• MCP bridge implementations (npm/src/agent/mcp/)

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Labels

• tags.review-effort: 1 (trivial - single null check fix with clear tests)
• tags.label: bug

Metadata

• Review Effort: 1 / 5
• Primary Label: bug

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Last updated: 2026-03-03T21:29:24.669Z | Triggered by: pr_opened | Commit: 5706d02

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[probelabs]

✅ Security Check Passed

No security issues found – changes LGTM.

✅ Architecture Check Passed

No architecture issues found – changes LGTM.

✅ Security Check Passed

No security issues found – changes LGTM.

\n\n

✅ Architecture Check Passed

No architecture issues found – changes LGTM.

\n\n

✅ Performance Check Passed

No performance issues found – changes LGTM.

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Powered by Visor from Probelabs

Last updated: 2026-03-03T21:22:53.910Z | Triggered by: pr_opened | Commit: 5706d02

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