[dviejokfs]

What

Adds Provider::Acp and providers::acp::Acp (default feature acp): one adapter for any agent that speaks the Agent Client Protocol over stdio, such as Gemini CLI (gemini --acp), GitHub Copilot (copilot --acp) and Cursor (cursor-agent acp).

• Agents live in a shared, updatable AcpAgents registry. A turn selects one with the agent harness option, advertised as a HarnessControlKind::Agent control.
• A turn runs initialize, session/new (or session/resume, else session/load without its replay), optional mode and model selection, then session/prompt.
• session/request_permission reaches the interaction handler unless AcceptEdits/FullAccess decide it. Cancellation sends session/cancel; -32000 fails as an authentication error before the prompt.
• Acp::probe_agent runs the handshake to report capabilities and sign-in state.
• New TurnEvent::PlanUpdated (PlanEntry/PlanEntryStatus) and AgentAdapter::terminal_exit_grace.

Docs: docs/how-to/run-acp-agents.md, docs/reference/events.md. End-to-end tests in tests/acp_stdio.rs use a scripted POSIX-shell ACP agent.

Why

Lets Temps Fleet run ACP agents through the same runtime as Claude, Codex and OpenCode. Fleet's ACP code sits behind cfg(fleet_acp_runtime) until this merges and its pin moves.

Verification

cargo fmt --check, cargo clippy --locked --all-targets --all-features -- -D warnings and cargo test --all-features --lib (442 passed) are clean locally. CI runs a newer clippy than my local toolchain, so its first run may report lints I could not reproduce.

🤖 Generated with Claude Code

[greptile-apps]

Confidence Score: 5/5

[High impact] The PR appears safe to merge; the previous stderr-reader finding is fixed and no new blocking issues remain.

Summary

Adds an ACP adapter that runs registered agents over stdio, handles permissions, and streams tool results and plans.

• ACP agents run through the runtime one turn at a time.
• Runtime discovery lists the installed ACP agents.
• ACP plan updates arrive as complete runtime events.
• Finished turns stop waiting on lingering agents and stderr pipes.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  A[Start agent and stderr reader] --> B[Run turn]
  B --> C[Early error or timeout]
  C --> D[Drop capture and stop reader]
  B --> E[Provider exits]
  E --> F{Preserve descendants?}
  F -->|Yes| G[Disarm process cleanup and detach reader]
  F -->|No| H[Keep reader attached]
  G --> I[Wait briefly for stderr]
  H --> I
  I --> J[Return result]

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_{Reviews (8) · Last reviewed commit: "fix(runtime): detach a turn's stderr rea..." · Reviewed by Greptile}