fix(ai-chat): avoid stale MCP tool calls pinning isStreaming

[cjol]

This PR fixes #1614, where useAgentChat().isStreaming could remain true after aborting while a server-side MCP tool call was in flight.

Investigation summary:

• Reproduced the issue interactively using the examples/ai-chat app connected to an MCP server with a delayed tool.
• Confirmed that aborting returned the AI SDK chat status to ready, but the UI still derived isStreaming: true from a persisted input-available tool part.
• Added temporary diagnostics and found that the app defines onToolCall for browser/client tools, while the delayed MCP tool is server-owned.
• Discovered the old derivation treated any latest-assistant input-available tool part as pending client work whenever onToolCall existed, even when that tool was an MCP/server-side tool the client did not handle.
• Binary-searched several candidate fixes interactively and narrowed the necessary change to tracking the lifetime of actual onToolCall callbacks rather than using the presence of onToolCall as a proxy.

Problem:

• Server-side MCP tools can leave a tool part in input-available if the user aborts before the tool output arrives.
• Apps may still define onToolCall for unrelated browser tools.
• The previous hook logic combined those facts and kept isStreaming true indefinitely, including after reconnect/hydration.

Solution:

• Track tool call IDs only while an onToolCall callback is actually in flight.
• Derive pending client-tool streaming state from those in-flight callback IDs instead of from !!onToolCall.
• Preserve the existing behavior where asynchronous client-side tool callbacks keep isStreaming true while they are actively running.
• Add a regression test for a stale server-side/MCP-style tool part that onToolCall does not handle.
• Add a patch changeset for @cloudflare/ai-chat.

[changeset-bot]

🦋 Changeset detected

Latest commit: d85f5dc

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@cloudflare/ai-chat	Patch

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[devin-ai-integration]

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agents

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@cloudflare/ai-chat

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hono-agents

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@cloudflare/shell

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@cloudflare/think

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@cloudflare/voice

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@cloudflare/worker-bundler

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commit: d85f5dc

[threepointone]

clean, lgtm, thanks! will land after CI passes (I rebased)