feat(acp): session/resume, set_mode, set_config_option

[rohitg00]

Summary

PR #63 shipped 8 client→agent methods. ACP defines three more that fell to METHOD_NOT_FOUND until now. This PR implements all of them and updates the method table to be exhaustive so the deferred surface is fully visible.

Methods added

Method	Behaviour
session/resume	Like session/load but skips history replay. Refreshes cwd + mcpServers on the session record, claims ownership so subsequent agent::events route here. Per ACP: "useful for agents that can resume sessions but don't implement full session loading."
session/set_mode	Persists modeId on the session record. Brain workers can read it on the next prompt turn (system-prompt suffix, per-mode tool gating, etc.). Catalog validation is the brain's concern.
session/set_config_option	Persists configId / value pairs in config_options on the session record. Same split: persistence here, semantics in the brain.

Implementation notes

• SessionRecord gains:
  • mode: Option<String> (skip_serializing_if = "Option::is_none" — backward-compatible with pre-existing records)
  • config_options: serde_json::Map<String, Value> (default empty)
• New update_session_record helper does a read-modify-write of one record under the per-session history mutex that already serializes append_history. No parallel lock map.
• agentCapabilities.sessionCapabilities now advertises { list: {}, close: {}, resume: {} } — matches the ACP schema slots in this version. set_mode / set_config_option ship without an explicit capability flag because the in-repo schema doesn't include those slots yet; clients that try them succeed, clients that don't try are unaffected.

README

Method table is now exhaustive. The misleading "deferred to v0.2" line is replaced with explicit rows for every method:

• Implemented: initialize, authenticate, session/{new,load,resume,list,prompt,cancel,close,set_mode,set_config_option}, session/update
• Deferred (reverse-RPC, agents use iii primitives directly): session/request_permission, fs/{read,write}_text_file, terminal/{create,kill,output,release,wait_for_exit}

Validation

• 17 lib + 10 protocol envelope tests pass (3 new round-trip tests for the new param shapes)
• cargo clippy --all-targets -- -D warnings clean
• Live smoke against the 7-worker brain stack:
  • sessionCapabilities advertises {close, list, resume} on initialize
  • session/set_mode persists modeId="code" (verified via state::get)
  • session/set_config_option persists configId="thinking" value "high"
  • session/resume refreshes cwd to "/new"
  • All three return {} on success, INVALID_PARAMS (-32602) on missing sessionId
  • Full canonical brain flow (real Claude streaming through agent::events) still passes

Test plan

• cargo test — 17 lib + 10 protocol envelope tests pass
• cargo clippy --all-targets -- -D warnings clean
• Live smoke covering all 3 new methods + missing-session error path
• Canonical brain flow regression smoke (session/prompt streaming)
• Post-merge: trigger acp release if version bumped in a follow-up

Follow-ups

Reverse-RPC paths remain deferred — they need a JSON-RPC framer that can originate requests from the agent side. Internal iii brains today use iii primitives directly for filesystem and terminal access. Lands as a separate PR when an external ACP agent (consumed via future acp-client) needs the editor to act on its behalf.

Summary by CodeRabbit

• New Features

  • Added session resumption capability with environment state preservation and history handling
  • Introduced per-session configuration management and mode settings
  • Extended ACP session lifecycle operations and capabilities

• Documentation

  • Expanded ACP session management documentation with new operation details and capability information

[coderabbitai]

Caution

Review failed

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📝 Walkthrough

Walkthrough

This PR extends the ACP session management with three new capabilities: session resume (restoring environment state without history replay), session mode configuration, and per-session configuration options. Supporting types, handler methods, session record fields, and tests are added across the codebase.

Changes

ACP Session Lifecycle Extension

Layer / File(s)	Summary
Data Shape & Types acp/src/types.rs, acp/src/session.rs	Three new parameter structs added (SessionResumeParams, SessionSetModeParams, SessionSetConfigOptionParams). SessionRecord extended with mode (optional string) and config_options (map) fields.
Core Session Management acp/src/handler.rs	Three new handler methods implemented: session_resume (updates cwd and mcp_servers without history replay), session_set_mode (stores mode_id on session), and session_set_config_option (stores config key-value pairs). Initialize response extended with sessionCapabilities: [list, close, resume].
Documentation acp/README.md	Methods table expanded with entries for session/resume, session/set_mode, session/set_config_option, session/list, session/cancel, session/close, and session/update. Narrative added on capability advertising, deferred permissions, and brain contract negotiation.
Tests acp/tests/protocol.rs	Three JSON round-trip tests validate deserialization of the new parameter types and assert key field presence (session_id, cwd, mcp_servers; mode_id; config_id and value).

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• iii-hq/workers#63: Extends the same ACP session management codebase with session/resume and configuration APIs.

Poem

🐰 A rabbit hops through sessions new,
Resume and modes now in the queue!
Config options, safely stored,
Session state is now restored.
Hopping forward, smooth and clean—
Best ACP flow we've ever seen! 🥕

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'feat(acp): session/resume, set_mode, set_config_option' directly and concisely summarizes the three main methods added in the PR, which is the primary focus of the changeset.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/acp-additional-methods

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