Handle recoverable tool argument errors in graceful exit resume

[yuzhichang]

Summary

• return tool argument/schema errors as recoverable tool results during analyst tool execution
• keep non-argument tool errors fatal instead of masking them as retryable
• track run completion/cancel/failure explicitly so resume no longer prints success after a failed run

Testing

• go build ./adk/cancel/graceful-exit

[CLAassistant]

All committers have signed the CLA.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Updates the graceful-exit demo to provide clearer event output and more robust handling of cancellations and tool-argument errors during agent runs.

Changes:

• Added a tool middleware to convert tool argument unmarshalling/type errors into tool results (instead of failing the run).
• Improved event stream printing with numbered headers, mode/agent/role labels, and tool-call visibility for streamed and non-streamed messages.
• Refactored run termination handling to return explicit run statuses (completed/canceled/failed) for both initial run and resume.

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