refactor: normalize branch name handling and enhance auto mode settings merging

- Updated branch name normalization to align with UI conventions, treating "main" as null for consistency.
- Implemented deep merging of `autoModeByWorktree` settings to preserve existing entries during updates.
- Enhanced the BoardView component to persist max concurrency settings to the server, ensuring accurate capacity checks.
- Added error handling for feature rollback persistence in useBoardActions.

These changes improve the reliability and consistency of auto mode settings across the application.

apps/server/src/services/auto-mode-service.ts

@@ -534,7 +534,11 @@ export class AutoModeService {
       const autoModeByWorktree = settings.autoModeByWorktree;
 
       if (projectId && autoModeByWorktree && typeof autoModeByWorktree === 'object') {
-        const key = `${projectId}::${branchName ?? '__main__'}`;
+        // Normalize branch name to match UI convention:
+        // - null or "main" -> "__main__" (UI treats "main" as the main worktree)
+        // This ensures consistency with how the UI stores worktree settings
+        const normalizedBranch = branchName === 'main' ? null : branchName;
+        const key = `${projectId}::${normalizedBranch ?? '__main__'}`;
         const entry = autoModeByWorktree[key];
         if (entry && typeof entry.maxConcurrency === 'number') {
           return entry.maxConcurrency;
@@ -1039,7 +1043,9 @@ export class AutoModeService {
   }> {
     // Load feature to get branchName
     const feature = await this.loadFeature(projectPath, featureId);
-    const branchName = feature?.branchName ?? null;
+    const rawBranchName = feature?.branchName ?? null;
+    // Normalize "main" to null to match UI convention for main worktree
+    const branchName = rawBranchName === 'main' ? null : rawBranchName;
 
     // Get per-worktree limit
     const maxAgents = await this.resolveMaxConcurrency(projectPath, branchName);

apps/server/src/services/settings-service.ts

@@ -621,6 +621,21 @@ export class SettingsService {
       };
     }
 
+    // Deep merge autoModeByWorktree if provided (preserves other worktree entries)
+    if (sanitizedUpdates.autoModeByWorktree) {
+      type WorktreeEntry = { maxConcurrency: number; branchName: string | null };
+      const mergedAutoModeByWorktree: Record<string, WorktreeEntry> = {
+        ...current.autoModeByWorktree,
+      };
+      for (const [key, value] of Object.entries(sanitizedUpdates.autoModeByWorktree)) {
+        mergedAutoModeByWorktree[key] = {
+          ...mergedAutoModeByWorktree[key],
+          ...value,
+        };
+      }
+      updated.autoModeByWorktree = mergedAutoModeByWorktree;
+    }
+
     await writeSettingsJson(settingsPath, updated);
     logger.info('Global settings updated');