fix(sync): avoid double export when uncommitted JSONL detected (bd-uuo9)

Add alreadyExported flag to skip redundant export. When
gitHasUncommittedBeadsChanges() detects uncommitted changes, we export
at line 175. The flag prevents the normal flow from exporting again
at line 293.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/sync.go

@@ -166,6 +166,8 @@ Use --merge to merge the sync branch back to main branch.`,
 		// GH#885: Preflight check for uncommitted JSONL changes
 		// This detects when a previous sync exported but failed before commit,
 		// leaving the JSONL in an inconsistent state across worktrees.
+		// Track if we already exported during pre-flight to avoid redundant export later.
+		alreadyExported := false
 		if hasUncommitted, err := gitHasUncommittedBeadsChanges(ctx); err != nil {
 			fmt.Fprintf(os.Stderr, "Warning: failed to check for uncommitted changes: %v\n", err)
 		} else if hasUncommitted {
@@ -176,6 +178,7 @@ Use --merge to merge the sync branch back to main branch.`,
 				FatalError("re-exporting to reconcile state: %v", err)
 			}
 			fmt.Println("✓ State reconciled")
+			alreadyExported = true
 		}
 
 		// GH#638: Check sync.branch BEFORE upstream check
@@ -287,7 +290,7 @@ Use --merge to merge the sync branch back to main branch.`,
 				}
 			}
 
-			if !skipExport {
+			if !skipExport && !alreadyExported {
 				// Pre-export integrity checks
 				if err := ensureStoreActive(); err == nil && store != nil {
 					if err := validatePreExport(ctx, store, jsonlPath); err != nil {