Wait for tool confirmation before sending responses

[Haihan-Jiang]

Summary

• stop emitting placeholder function responses for tool calls that are waiting on HITL confirmation
• keep the adk_request_confirmation event as the pending client signal
• update functiontool, MCP toolset, parallel HITL, and A2A expectations

Fixes #876

Testing

• go test ./internal/llminternal ./tool/functiontool ./tool/mcptoolset
• go test ./agent/remoteagent/v2 ./internal/llminternal ./tool/functiontool ./tool/mcptoolset
• go test ./runner ./agent/... ./internal/llminternal ./tool/...
• git diff --check

Note: go test ./... exposed an unrelated transient ordering failure in server/adkrest/internal/services TestDebugTelemetryGetSpansBySessionID; rerunning that package-specific test passed.

[Haihan-Jiang]

This is ready for review. The flow now waits for tool confirmation before sending function responses, with parallel/HITL coverage added. The visible checks are green.

[indurireddy-TF]

Hi @Haihan-Jiang Thanks for putting this PR together to resolve the confirmation bug. Some merge conflicts have appeared on your branch. Could you please resolve them so we can proceed with the review?

[Haihan-Jiang]

Thanks for the heads up. I rebased the branch on the latest main and resolved the conflicts.

I also re-ran the affected packages locally:

• go test ./agent/remoteagent/v2 ./internal/llminternal ./tool/functiontool ./tool/mcptoolset

The updated head is feb05d9, and GitHub shows the commit signature as valid.