fix: skip output schema validation when tool result isError

[codefromthecrypt]

Summary

When a tool returns isError: true, its structuredContent is not required to conform to the tool's outputSchema. The Inspector UI was still validating it, showing a spurious "Validation Error" that obscured the actual server-provided error message.

This is the Inspector-side counterpart to modelcontextprotocol/typescript-sdk#1428, which fixes the same validation skip in the SDK's callTool() client method.

Type of Change

• Bug fix
• Test updates

Changes Made

• client/src/components/ToolResults.tsx — added && !isError guard before calling validateToolOutput, matching the SDK behavior
• client/src/components/__tests__/ToolsTab.test.tsx — added test case confirming error results with non-conforming structuredContent do not trigger validation errors

Related Issues

Depends on modelcontextprotocol/typescript-sdk#1428 for the SDK / CLI-level fix.

Testing

• Tested in UI mode
• Tested with SSE transport
• Added/updated automated tests

Test Results and/or Instructions

1. Connect to an MCP server that has a tool with an outputSchema
2. Call the tool in a way that triggers an isError: true response with structuredContent that doesn't match the schema
3. Verify the UI shows the server's error content without a "Validation Error" banner

Checklist

• Code follows the style guidelines (ran npm run prettier-fix)
• Self-review completed

Breaking Changes

None.

Additional Context

Reproduced against IntelliJ's MCP server (get_repositories tool) which returns isError: true with structuredContent containing projects instead of the schema-required roots.

Before:

After:

[codefromthecrypt]

draft until modelcontextprotocol/typescript-sdk#1428 is released, as there are two layers of bugs in the UI.

[codefromthecrypt]

Closing this out until there is a path forward the spec allows modelcontextprotocol/modelcontextprotocol#2145