Summary

Add reconnect reconciliation to ensure Hostlink and Rails reconcile task state after WebSocket reconnect before Rails sends new tasks.

Hostlink

• HelloPayload, HelloAckPayload, and typed snapshot structs in wsprotocol message.go
• buildHelloPayload() builds reconnect snapshot from localtaskstore.Snapshot() including running task, received-not-started attempts, unacked finals, output ranges, spool status, and client version
• applyHelloAckLocalState() applies final ACKs and discard directives from hello-ack before marking session active
• replayRequestedOutput() replays only the output ranges Rails requested from a given next sequence
• Snapshot() now returns running task metadata, received attempts, unacked finals with parsed status, unacked output ranges, and spool status
• DiscardReceived() deletes received-but-not-started attempts (safe for running/final)
• UnackedMessagesFrom() supports targeted output replay by stream and sequence

Tests

• wsprotocol: HelloPayload/HelloAckPayload shape and validation tests
• localtaskstore: snapshot includes reconnect-safe state, discard safety, interrupted startup recovery
• wsclient: hello payload includes snapshot, hello-ack directives applied correctly, discard does not erase running work

Dependencies

This change builds on PR #184 (hostlink-runner-refactor). The wsclient, localtaskstore, and wsprotocol files extend interfaces/types introduced there.