fix(xai): add custom_tool_call_input delta and done response stream events

[syjcnss]

Background

The PR #10523 missed two stream events: custom_tool_call_input.delta and custom_tool_call_input.done.

The following testcase will trigger an error:

import { xai } from '@ai-sdk/xai';
import { streamText } from 'ai';

const { fullStream, usage: usagePromise } = streamText({
  model: xai.responses('grok-4-1-fast-reasoning'),
  system: 'You are a news reporter.',
  tools: {
    x_search: xai.tools.xSearch(),
  },
  prompt: 'search for the latest news in x',
});

const sources = new Set<string>();
let lastToolName = '';

for await (const event of fullStream) {
  switch (event.type) {
    case 'tool-call':
      lastToolName = event.toolName;
      if (event.providerExecuted) {
        console.log(`[Calling ${event.toolName} on server...]`);
      }
      break;

    case 'tool-result':
      console.log(`[${lastToolName} completed]`);
      break;

    case 'text-delta':
      process.stdout.write(event.text);
      break;

    case 'source':
      if (event.sourceType === 'url') {
        sources.add(event.url);
      }
      break;
  }
}

const usage = await usagePromise;
console.log(`\nSources used: ${sources.size}`);
console.log(`Token usage: ${usage.inputTokens} input, ${usage.outputTokens} output`);

_TypeValidationError [AI_TypeValidationError]: Type validation failed: Value: {"sequence_number":3,"type":"response.custom_tool_call_input.delta","item_id":"ctc_aa40f122-e87a-c188-7593-50d15babb0a0_xs_call_31945317","output_index":0,"delta":"{\"query\":\"filter:news\",\"limit\":20,\"mode\":\"Latest\"}"}.

Summary

Fixed the error by adding the missed events.

Manual Verification

Ran the above test case again and saw it pass.

Checklist

• Tests have been added / updated (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)
• A patch changeset for relevant packages has been added (for bug fixes / features - run pnpm changeset in the project root)
• I have reviewed this pull request (self-review)

Related Issues

#10523

[syjcnss]

Closing it because #10765 does the samething.