🦌 Fix missing tool_result when MCP/server tool execution throws

[masudahiroto]

Summary

When an MCP or server-side tool throws during execution, the AI SDK emits a tool-error chunk instead of tool-result. The agent was silently ignoring these chunks, so no TOOL_CALL_RESULT event was sent to the client. This left conversation history without a tool_result for the failed tool_use, causing the Anthropic API to reject subsequent requests with: "tool_use ids were found without tool_result blocks immediately after".

This fix handles tool-error chunks by emitting a TOOL_CALL_RESULT event containing the error message, ensuring conversation history remains complete and the session can continue after a tool failure.

Changes

• packages/server/src/agents/AISDKAgent.ts: Handle tool-error stream chunk by emitting TOOL_CALL_RESULT with error content instead of ignoring it
• packages/server/src/agents/AISDKAgent.test.ts: Add unit tests verifying TOOL_CALL_RESULT is emitted on MCP tool error and server tool error
• apps/example-nest-mcp-server/src/tools.service.ts: Add always_fail tool for testing error handling scenarios
• apps/example/src/pages/RemoteMcpToolsPage.tsx: Document the new mcp_always_fail tool in the page description
• apps/example/test/mcp-tool-error-recovery.e2e.test.ts: Add E2E test verifying conversation continues normally after a tool error
• bun.lock: Bump package versions to 1.9.3

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Created by deer — review carefully.

[mm-zacharydavison]

Is there AG-UI TOOL_CALL_ERROR event we should use instead?

[masudahiroto]

AG-UI doesn't define TOOL_CALL_ERROR event.
https://docs.ag-ui.com/concepts/events#tool-call-events

Client-side tool also treated error message same as normal tool call.

use-ai/packages/client/src/hooks/useToolSystem.ts

Lines 353 to 357 in 6405dbc

	} catch (err) {
	console.error('Tool execution error:', err);
	client.sendToolResponse(toolCallId, {
	error: err instanceof Error ? err.message : 'Unknown error',
	});

So, I think we should use TOOL_CALL_RESULT here.