feat(chat): add async non-blocking subagent delegation

[ajsivsan1]

Problem

When the CLI delegates work to a subagent, the main conversation is blocked until the subagent completes. For longer-running tasks (30-60+ seconds), the user is stuck waiting and can't interact with the agent.

Solution

Add async, non-blocking subagent delegation so the user regains control immediately after launching a background agent.

Changes

• Completion channel (tokio::sync::mpsc::unbounded): ChatSession holds a sender/receiver pair. The sender is cloned into each spawned agent process; the receiver is polled during the response stream loop.
• Concurrent tasks per agent: Removed the single-task-per-agent restriction. Each execution gets a unique task_id and its own JSON file ({agent}_{task_id}.json).
• Inline notifications: When a subagent finishes, the user sees an inline status message on stderr without disrupting the model stream.
• Context injection: Completed agent summaries are queued as pending_additional_context and included in the next user prompt.
• tokio::select!: The response stream loop now uses tokio::select! to concurrently monitor subagent completions alongside the model response stream.

Files changed

File	Summary
crates/chat-cli/src/cli/chat/mod.rs	Add completion channel to ChatSession, use tokio::select! in response loop
crates/chat-cli/src/cli/chat/tools/delegate.rs	Concurrent task support, completion channel plumbing, updated file storage
crates/chat-cli/src/cli/chat/tools/mod.rs	Thread completion_tx through Tool::invoke

Testing

cargo test — 326 passed, 0 failed, 13 ignored (CI-only).

References

• Feature request: Feat: Async/non-blocking subagent delegation q-command-line-discussions#318

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.