P1: Add concurrency governor for streaming and agent spawning

[galic1987]

Source

ChatGPT architecture review feedback

Problem

No global backpressure mechanism for streaming responses or multi-agent spawning. Unbounded task spawning with concurrent streaming can cause:

• Resource exhaustion under heavy swarm workloads
• Flaky behavior when many agents stream simultaneously
• No structured cancellation on session end

Proposal

1. Global semaphore (MAX_INFLIGHT_STREAMS) to cap concurrent LLM streaming responses
2. Per-agent semaphore to limit tool execution concurrency within each agent
3. Structured cancellation — when a session ends or ESC is pressed, all spawned tasks are cancelled cleanly via CancellationToken (tokio-util) rather than just setting an AtomicBool
4. Backpressure on tool results — if an agent's result queue is full, slow down rather than drop

Relevant Code

• src/agent/mod.rs — cancelled: Arc<AtomicBool> (current cancellation)
• src/agent/execution.rs — tool execution spawning
• src/orchestration/parallel.rs — parallel orchestration

Priority

P1 — stability under load