merge(478): WebSocket CRDT sync layer (manual squash from feature/story-478)

Manual squash-merge of feature/story-478_… into master after the in-pipeline
mergemaster runs failed silently. The 478 agent did substantial real work
across multiple respawn cycles before being interrupted; commits on the
feature branch were intact and verified high-quality but never merged via
the normal pipeline path due to compounding bugs:

- The first mergemaster attempt ran ($0.82 in tokens) and exited "Done"
  cleanly but didn't push anything to master — likely the worktree was
  briefly on master rather than the feature branch when the merge_agent_work
  MCP tool ran, so it found nothing to merge.
- Subsequent timer fires defaulted to spawning coders instead of resuming
  mergemaster, burning more tokens for no progress.
- Bug 510 (split-brain shadows yanking done stories back to current) and
  bug 501 (timers don't cancel on stop/completion) compounded the cost.

What this commit lands:
- server/src/crdt_sync.rs (new, ~518 lines): GET /crdt-sync WebSocket
  handler that subscribes to locally-applied SignedOps and streams them as
  binary frames. Per-peer bounded queue (256 ops) drops slow peers.
- server/src/crdt_state.rs: new public functions subscribe_ops(),
  all_ops_json(), apply_remote_op() backing the sync handler. Adds the
  CRDT_OP_TX broadcast channel (capacity 1024).
- server/src/main.rs: wires up the sync subsystem at startup.
- server/src/http/mod.rs: registers the new endpoint.
- server/src/config.rs: adds optional rendezvous field for outbound peers.
- server/src/worktree.rs: minor changes from the original branch.
- server/Cargo.toml: cfg lint suppression for CrdtNode derive.
- crates/bft-json-crdt/src/debug.rs: fix unused-variable warnings.

Resolved a trivial test-mod merge conflict in crdt_state.rs (both 478 and
503 added new tests at the end of the test module — kept both sets).

Note: this is the squash of the original 478 work that the user explicitly
authorized landing. The earlier rogue commit ac9f3ecf — which added a
DIFFERENT, broken implementation of the same feature directly to master
under the user's identity without consent — was reverted earlier in this
session. The forensic tags rogue-commit-2026-04-09-ac9f3ecf and
pre-502-reset-2026-04-09 still exist for incident audit.

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

server/src/config.rs

@@ -47,6 +47,12 @@ pub struct ProjectConfig {
     /// of the container/host local time.  Falls back to `chrono::Local` when absent.
     #[serde(default)]
     pub timezone: Option<String>,
+    /// WebSocket URL of a remote huskies node to sync CRDT state with.
+    /// Example: `rendezvous = "ws://server:3001/crdt-sync"`
+    /// When set, this node connects to the remote and exchanges CRDT ops
+    /// so both machines see the same pipeline state in real-time.
+    #[serde(default)]
+    pub rendezvous: Option<String>,
 }
 
 /// Configuration for the filesystem watcher's sweep behaviour.
@@ -220,6 +226,7 @@ impl Default for ProjectConfig {
             base_branch: None,
             rate_limit_notifications: default_rate_limit_notifications(),
             timezone: None,
+            rendezvous: None,
         }
     }
 }
@@ -295,6 +302,7 @@ impl ProjectConfig {
                             base_branch: legacy.base_branch,
                             rate_limit_notifications: legacy.rate_limit_notifications,
                             timezone: legacy.timezone,
+                            rendezvous: None,
                         };
                         validate_agents(&config.agent)?;
                         return Ok(config);
@@ -322,6 +330,7 @@ impl ProjectConfig {
                         base_branch: legacy.base_branch,
                         rate_limit_notifications: legacy.rate_limit_notifications,
                         timezone: legacy.timezone,
+                        rendezvous: None,
                     };
                     validate_agents(&config.agent)?;
                     Ok(config)
@@ -337,6 +346,7 @@ impl ProjectConfig {
                         base_branch: legacy.base_branch,
                         rate_limit_notifications: legacy.rate_limit_notifications,
                         timezone: legacy.timezone,
+                        rendezvous: None,
                     })
                 }
             }