feat: protocol-aware execution wave — phase gate for live WAL shipping

Add host-side protocol state seam that derives per-replica execution
state from V2 sender/session snapshots and blocks live-tail WAL
shipping while an active recovery session is in progress.

New file: weed/server/block_protocol_state.go
  - replicaProtocolExecutionState derived from engine snapshots
  - LiveEligible=false during active catch-up/rebuild sessions
  - bindProtocolExecutionPolicy wires policy into BlockVol
  - syncProtocolExecutionState called after assignments + core events

Data plane changes:
  - WALShipper.Ship() checks liveShippingPolicy before dial/send
  - BlockVol.SetLiveShippingPolicy persists across shipper group rebuilds
  - ShipperGroup propagates policy to all shippers

Design contract: sw-block/design/v2-protocol-aware-execution.md

Scope: WAL-first rollout only. Prevents illegal live-tail delivery
during active recovery. Does not change snapshot/build behavior or
move backlog. Next wave: bounded WAL catch-up under same contract.

Tests: 4 unit/component tests for phase gate behavior, plus bootstrap
seam tests that confirmed the two pre-existing bugs locally.

13 files changed, 900 insertions, 69 deletions.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

weed/server/master_block_assignment_queue.go

@@ -119,6 +119,16 @@ func assignmentConfirmedByHeartbeat(a blockvol.BlockVolumeAssignment, infos []bl
 			return true
 		}
 		if info.ReplicaDataAddr == expectedData && info.ReplicaCtrlAddr == expectedCtrl {
+			// A primary refresh assignment that carries replica transport should not
+			// be confirmed while the local V2 core still projects allocated_only.
+			// Otherwise the master can drop the refresh based only on legacy
+			// transport fields before the VS actually re-applies the assignment to
+			// the core and grows replica membership.
+			if blockvol.RoleFromWire(a.Role) == blockvol.RolePrimary &&
+				info.EngineProjectionMode != "" &&
+				info.EngineProjectionMode == "allocated_only" {
+				return false
+			}
 			return true
 		}
 	}