ROADMAP #133: Blocked-state subphase contract — implement §6.5

Adds BlockedSubphase enum with 7 variants for structured blocked-state reporting:
- blocked.trust_prompt — trust gate blockers
- blocked.prompt_delivery — prompt misdelivery
- blocked.plugin_init — plugin startup failures
- blocked.mcp_handshake — MCP connection issues
- blocked.branch_freshness — stale branch blockers
- blocked.test_hang — test timeout/hang
- blocked.report_pending — report generation stuck

LaneEventBlocker now carries optional subphase field that gets serialized
into LaneEvent data. Enables clawhip to route recovery without pane scraping.

Updates:
- lane_events.rs: BlockedSubphase enum, LaneEventBlocker.subphase field
- lane_events.rs: blocked()/failed() constructors with subphase serialization
- lib.rs: Export BlockedSubphase
- tools/src/lib.rs: classify_lane_blocker() with subphase: None
- Test imports and fixtures updated

Backward-compatible: subphase is Option<>, existing events continue to work.

ROADMAP.md

@@ -803,7 +803,12 @@ Acceptance:
 - channel status updates stay short and machine-grounded
 - claws stop inferring state from raw build spam
 
-### 6.5. Blocked-state subphase contract
+### 133. Blocked-state subphase contract (was §6.5)
+**Filed:** 2026-04-20 from dogfood cycle — previous cycle identified §4.44.5 provenance gap, this cycle targets §6.5 implementation.
+
+**Problem:** Currently `lane.blocked` is a single opaque state. Recovery recipes cannot distinguish trust-gate blockers from MCP handshake failures, branch freshness issues, or test hangs. All blocked lanes look the same, forcing pane-scrape triage.
+
+**Concrete implementation:
 When a lane is `blocked`, also expose the exact subphase where progress stopped, rather than forcing claws to infer from logs.
 
 Subphases should include at least: