MAESTRO: Add FilePreviewTab type and unified tab system foundation

Phase 1 of file preview tabs feature:
- Add FilePreviewTab interface with id, path, name, extension, scrollTop,
  searchQuery, editMode, editContent, and createdAt fields
- Add UnifiedTabRef type for tab ordering across types
- Add filePreviewTabs, activeFileTabId, and unifiedTabOrder to Session
- Update all 13 session creation locations with new fields
- Update session restoration to hydrate new fields from persistence

This establishes the data model for coexisting AI tabs, file preview tabs,
and future terminal tabs in a unified tab bar.

src/renderer/App.tsx

@@ -1111,6 +1111,9 @@ function MaestroConsoleInner() {
 						},
 					],
 					activeTabId: defaultTabId,
+					filePreviewTabs: [],
+					activeFileTabId: null,
+					unifiedTabOrder: [{ type: 'ai' as const, id: defaultTabId }],
 				};
 			}
 
@@ -1235,6 +1238,12 @@ function MaestroConsoleInner() {
 					agentError: undefined,
 					agentErrorPaused: false,
 					closedTabHistory: [], // Runtime-only, reset on load
+					// File preview tabs - initialize from persisted data or empty
+					filePreviewTabs: correctedSession.filePreviewTabs || [],
+					activeFileTabId: correctedSession.activeFileTabId ?? null,
+					unifiedTabOrder:
+						correctedSession.unifiedTabOrder ||
+						resetAiTabs.map((tab) => ({ type: 'ai' as const, id: tab.id })),
 				};
 			} else {
 				// Process spawn failed
@@ -1652,6 +1661,9 @@ function MaestroConsoleInner() {
 							aiTabs: [initialTab],
 							activeTabId: initialTabId,
 							closedTabHistory: [],
+							filePreviewTabs: [],
+							activeFileTabId: null,
+							unifiedTabOrder: [{ type: 'ai' as const, id: initialTabId }],
 							customPath: parentSession.customPath,
 							customArgs: parentSession.customArgs,
 							customEnvVars: parentSession.customEnvVars,
@@ -7287,6 +7299,9 @@ You are taking over this conversation. Based on the context above, provide a bri
 				aiTabs: [initialTab],
 				activeTabId: initialTabId,
 				closedTabHistory: [],
+				filePreviewTabs: [],
+				activeFileTabId: null,
+				unifiedTabOrder: [{ type: 'ai' as const, id: initialTabId }],
 				customPath: parentSession.customPath,
 				customArgs: parentSession.customArgs,
 				customEnvVars: parentSession.customEnvVars,
@@ -7468,6 +7483,9 @@ You are taking over this conversation. Based on the context above, provide a bri
 								aiTabs: [initialTab],
 								activeTabId: initialTabId,
 								closedTabHistory: [],
+								filePreviewTabs: [],
+								activeFileTabId: null,
+								unifiedTabOrder: [{ type: 'ai' as const, id: initialTabId }],
 								customPath: session.customPath,
 								customArgs: session.customArgs,
 								customEnvVars: session.customEnvVars,
@@ -8756,6 +8774,10 @@ You are taking over this conversation. Based on the context above, provide a bri
 				aiTabs: [initialTab],
 				activeTabId: initialTabId,
 				closedTabHistory: [],
+				// File preview tabs - start empty, unified tab order starts with initial AI tab
+				filePreviewTabs: [],
+				activeFileTabId: null,
+				unifiedTabOrder: [{ type: 'ai' as const, id: initialTabId }],
 				// Nudge message - appended to every interactive user message
 				nudgeMessage,
 				// Per-agent config (path, args, env vars, model)
@@ -8922,6 +8944,9 @@ You are taking over this conversation. Based on the context above, provide a bri
 				aiTabs: [initialTab],
 				activeTabId: initialTabId,
 				closedTabHistory: [],
+				filePreviewTabs: [],
+				activeFileTabId: null,
+				unifiedTabOrder: [{ type: 'ai' as const, id: initialTabId }],
 				// Auto Run configuration from wizard
 				autoRunFolderPath,
 				autoRunSelectedFile,
@@ -10958,6 +10983,9 @@ You are taking over this conversation. Based on the context above, provide a bri
 							aiTabs: [initialTab],
 							activeTabId: initialTabId,
 							closedTabHistory: [],
+							filePreviewTabs: [],
+							activeFileTabId: null,
+							unifiedTabOrder: [{ type: 'ai' as const, id: initialTabId }],
 							customPath: activeSession.customPath,
 							customArgs: activeSession.customArgs,
 							customEnvVars: activeSession.customEnvVars,
@@ -11133,6 +11161,9 @@ You are taking over this conversation. Based on the context above, provide a bri
 					aiTabs: [initialTab],
 					activeTabId: initialTabId,
 					closedTabHistory: [],
+					filePreviewTabs: [],
+					activeFileTabId: null,
+					unifiedTabOrder: [{ type: 'ai' as const, id: initialTabId }],
 					customPath: activeSession.customPath,
 					customArgs: activeSession.customArgs,
 					customEnvVars: activeSession.customEnvVars,
@@ -11282,6 +11313,9 @@ You are taking over this conversation. Based on the context above, provide a bri
 				aiTabs: [initialTab],
 				activeTabId: initialTabId,
 				closedTabHistory: [],
+				filePreviewTabs: [],
+				activeFileTabId: null,
+				unifiedTabOrder: [{ type: 'ai' as const, id: initialTabId }],
 				customPath: createWorktreeSession.customPath,
 				customArgs: createWorktreeSession.customArgs,
 				customEnvVars: createWorktreeSession.customEnvVars,
@@ -13215,6 +13249,9 @@ You are taking over this conversation. Based on the context above, provide a bri
 							aiTabs: [initialTab],
 							activeTabId: initialTabId,
 							closedTabHistory: [],
+							filePreviewTabs: [],
+							activeFileTabId: null,
+							unifiedTabOrder: [{ type: 'ai' as const, id: initialTabId }],
 							// Custom agent config
 							customPath: data.customPath,
 							customArgs: data.customArgs,

src/renderer/types/index.ts

@@ -442,6 +442,29 @@ export interface ClosedTab {
 	closedAt: number; // Timestamp when closed
 }
 
+/**
+ * File Preview Tab for in-tab file viewing.
+ * Designed to coexist with AITab and future terminal tabs in the unified tab system.
+ * File tabs persist across session switches and app restarts.
+ */
+export interface FilePreviewTab {
+	id: string; // Unique tab ID (UUID)
+	path: string; // Full file path
+	name: string; // Filename without extension (displayed as tab name)
+	extension: string; // File extension with dot (e.g., '.md', '.ts') - shown as badge
+	scrollTop: number; // Saved scroll position
+	searchQuery: string; // Preserved search query
+	editMode: boolean; // Whether tab was in edit mode
+	editContent: string | undefined; // Unsaved edit content (undefined if no pending changes)
+	createdAt: number; // Timestamp for ordering
+}
+
+/**
+ * Reference to any tab in the unified tab system.
+ * Used for unified tab ordering across different tab types.
+ */
+export type UnifiedTabRef = { type: 'ai' | 'file'; id: string };
+
 export interface Session {
 	id: string;
 	groupId?: string;
@@ -559,6 +582,15 @@ export interface Session {
 	activeTabId: string;
 	// Stack of recently closed tabs for undo (max 25, runtime-only, not persisted)
 	closedTabHistory: ClosedTab[];
+
+	// File Preview Tabs - in-tab file viewing (coexists with AI tabs and future terminal tabs)
+	// Tabs are interspersed visually but stored separately for type safety
+	filePreviewTabs: FilePreviewTab[];
+	// Currently active file tab ID (null if an AI tab is active)
+	activeFileTabId: string | null;
+	// Unified tab ordering - determines visual order of all tabs (AI and file)
+	unifiedTabOrder: UnifiedTabRef[];
+
 	// Saved scroll position for terminal/shell output view
 	terminalScrollTop?: number;
 	// Draft input for terminal mode (persisted across session switches)

src/renderer/utils/tabHelpers.ts

@@ -893,6 +893,9 @@ export function createMergedSession(
 		aiTabs: [mergedTab],
 		activeTabId: tabId,
 		closedTabHistory: [],
+		filePreviewTabs: [],
+		activeFileTabId: null,
+		unifiedTabOrder: [{ type: 'ai' as const, id: tabId }],
 	};
 
 	return { session, tabId };