feat: improve Lit client robustness for message handling

[doitundoit]

Summary

This PR improves the Lit client's robustness when handling agent response messages.

Changes

• History fallback: Added fallback mechanism to retrieve agent messages from history when status.message.parts is empty
• String-encoded JSON handling: Parse string-encoded JSON data parts that some agents may return
• Debug logging: Added console.debug statements for better traceability during development

Affected file:

• samples/client/lit/shell/client.ts

Verification

• TypeScript build passes (npm run build:tsc)

Related

Split from #396 as requested by reviewer to keep commit scope narrow and targeted.

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[paullewis]

Nit: might be worth adding a bit of an explanation to this but approving all the same.

[doitundoit]

Nit: might be worth adding a bit of an explanation to this but approving all the same.

Hi, thanks for the feedback! I've added concise comments explaining the rationale behind the history fallback and JSON parsing logic for better clarity.

[zeroasterisk]

Thanks for improving the Lit shell client robustness, @doitundoit! The history-based fallback for session resumption is a good idea. 🙏

The Lit shell client has been significantly updated since this PR was opened, and the A2A SDK response format has evolved as well. This PR would need a substantial rebase against the current codebase. Closing as stale — but the insight about handling empty status parts via history fallback is worth filing as a focused issue if you find it's still needed!