v0.9.0

Negotiate protocolVersion at init time and emit v1 or v2
session/update payloads accordingly. Same code base, dispatch by
version. The implementation adds:

• protocol::ProtocolVersion enum (V1, V2, LATEST) and the
  Session::protocol_version field for defense-in-depth and future
  per-session routing.
• AppState::protocol_version (set by run_acp_loop from the negotiated
  value) so every emit helper branches on the same source of truth.
  AppState: Clone is hand-written; sessions are wrapped in
  Arc<RwLock<...>> so the clone shares the map.
• acp::notify_*_for(version, …) dispatchers that route to the v1 or
  v2 implementation. The plain (no-suffix) notify_* functions stay
  as the v1 shortcut for code paths that have not migrated.
• acp::notify_state_idle_for() for v2-only state_update (IdleState).
• negotiate_protocol_version(params) in main.rs — implements the
  ACP spec's "pick the highest version we both support" rule.
  Clients that omit protocolVersion fall back to v1 (conservative
  default). Clients requesting a version > 2 fall back to v2 with a
  warning.
• v2-shaped InitializeResponse: unified info + capabilities
  (role-agnostic), with capabilities.session.prompt.image expressed
  as {} (capability marker) when supported.
• v2-shaped session/update discriminators:
  • agent_message_chunk, agent_thought_chunk (chunk variants)
  • tool_call_update (instead of v1's tool_call)
  • plan_update with plan: { type: "items", planId, entries[] }
• v2 baseline session/close (alias for v1's session/end) and
  session/list (returns active sessions as
  {sessions: [{sessionId, cwd}], nextCursor: null}).
• v2 graceful rejects for session/delete, session/resume,
  session/load: -32601 not_implemented / -32001
no_persistence with stable data.reason.
• LlmConfig.build_body is now backend-aware: OpenAI-compatible gets
  top-level temperature / max_tokens; Ollama native gets them
  inside options (temperature + num_predict). The previous
  top-level-only shape meant every Ollama native request silently used
  the model's defaults for sampling.

Tests

9 new tests in tests/clients/protocol_version.rs:

• v2_initialize_returns_unified_capabilities_shape
• v2_tool_call_uses_tool_call_update_not_tool_call
• v2_plan_uses_plan_update_with_plan_id
• v2_emits_state_update_at_end_of_turn
• v2_does_not_emit_state_update_for_v1_clients
• v1_client_gets_legacy_shapes_unchanged
• inspector_style_session_list_returns_empty_array_with_no_sessions
  (updated from the pre-0.9.0 negative-test now that session/list
  is implemented)
• inspector_style_session_close_succeeds_and_variants (updated
  similarly)

168 tests passing; cargo fmt --check and
cargo clippy --all-targets -- -D warnings clean.

Migration

• v1 Clients see no behavior change. The plain notify_* functions
  still emit v1, and every emit site in main.rs was migrated to
  use the _for(version, …) helpers that branch on the negotiated
  version.
• Existing inspector_style_session_list_returns_method_not_found_gracefully
  and inspector_style_session_close_returns_method_not_found_gracefully
  tests were renamed and rewritten as positive tests. The original
  intent of those tests (probe capability, get clear error) is
  preserved — session/close now returns -32001 UnknownSession
  instead of -32601 MethodNotFound when called on a non-existent
  session, and session/list returns {sessions: []} with no
  sessions open.

Co-Authored-By: Claude noreply@anthropic.com

Full Changelog: v0.8.2...v0.9.0