feat(mcp+lifecycle): MCP degraded-startup reporting, lane event schema, lane completion hardening

Add MCP structured degraded-startup classification (P2.10):
- classify MCP failures as startup/handshake/config/partial
- expose failed_servers + recovery_recommendations in tool output
- add mcp_degraded output field with server_name, failure_mode, recoverable

Canonical lane event schema (P2.7):
- add LaneEventName variants for all lifecycle states
- wire LaneEvent::new with full 3-arg signature (event, status, emitted_at)
- emit typed events for Started, Blocked, Failed, Finished

Fix let mut executor for search test binary
Fix lane_completion unused import warnings

Note: mcp_stdio::manager_discovery_report test has pre-existing failure on clean main, unrelated to this commit.

rust/crates/runtime/src/lib.rs

@@ -8,6 +8,7 @@ mod file_ops;
 pub mod green_contract;
 mod hooks;
 mod json;
+mod lane_events;
 pub mod lsp_client;
 mod mcp;
 mod mcp_client;
@@ -62,6 +63,9 @@ pub use file_ops::{
 pub use hooks::{
     HookAbortSignal, HookEvent, HookProgressEvent, HookProgressReporter, HookRunResult, HookRunner,
 };
+pub use lane_events::{
+    LaneEvent, LaneEventBlocker, LaneEventName, LaneEventStatus, LaneFailureClass,
+};
 pub use mcp::{
     mcp_server_signature, mcp_tool_name, mcp_tool_prefix, normalize_name_for_mcp,
     scoped_mcp_config_hash, unwrap_ccr_proxy_url,