feat(acp): add editor protocol server

[yan-ad]

Summary

• Add crabcode acp [--cwd PATH], a stdio Agent Client Protocol server backed by the Rust ACP SDK.
• Implement persisted ACP session lifecycle: create, list, load, resume, close, fork, prompt streaming, cancellation, mode selection, tool updates, and permission forwarding.
• Expose selectable Crabcode models to ACP clients with validated, session-local provider/model changes.
• Add crabcode models [provider] for non-interactive model discovery using the same credentials, custom providers, free models, runtime models, and effective catalog as Crabcode.
• Make configuration and history initialization workspace-aware for ACP sessions.
• Document Zed setup and add an ACP capability matrix with supported behavior, limitations, and follow-up work.

Editor Validation

The crabcode acp command was tested successfully with Zed IDE:

• Zed version: 1.13.1
• Zed commit: 00bd72e7838f4b875a913cd112b47a0ebe1ca62b
• Full version: 1.13.1+stable.332.00bd72e7838f4b875a913cd112b47a0ebe1ca62b

Validation

• cargo build
• cargo fmt --check
• cargo test acp::service::tests --bin crabcode
• cargo test parses_acp_command_with_workspace --bin crabcode
• cargo test parses_models_command_with_optional_provider --bin crabcode
• cargo test model::catalog::tests --bin crabcode
• cargo test config::configuration --bin crabcode
• git diff --check

Notes

• ACP model choices use canonical provider/model identifiers and remain session-local.
• The capability matrix intentionally documents unsupported image/audio ACP prompts, client-supplied MCP overlays, terminal embedding, reasoning-effort selection, and authoritative usage updates instead of advertising them.

[Blankeos]

Was thinking of this for a while now. Thanks for adding! Will review asap