fix(gsd): detect concurrent event log growth during reconcile

Adds a pre-write guard in reconcileWorktreeLogs: re-reads the event
log before overwriting and retries if it grew since the initial read.
Prevents appendEvent calls between read and rewrite from being silently
dropped by the atomic overwrite.

src/resources/extensions/gsd/workflow-reconcile.ts

@@ -433,6 +433,14 @@ function _reconcileWorktreeLogsInner(
   const merged = indexed.map(({ e }) => e);
 
   // Step 7: Write merged event log FIRST (so crash recovery can re-derive DB state)
+  // Guard: detect concurrent appendEvent calls between our read (step 1) and
+  // this rewrite. If the log grew, re-read and retry to avoid dropping events.
+  const preWriteEvents = readEvents(mainLogPath);
+  if (preWriteEvents.length > mainEvents.length) {
+    logWarning("reconcile", `Event log grew during reconcile (${mainEvents.length} → ${preWriteEvents.length}), retrying with fresh read`);
+    return _reconcileWorktreeLogsInner(mainBasePath, worktreeBasePath);
+  }
+
   const baseEvents = mainEvents.slice(0, forkPoint + 1);
   const mergedLog = baseEvents.concat(merged);
   const logContent = mergedLog.map((e) => JSON.stringify(e)).join("\n") + (mergedLog.length > 0 ? "\n" : "");