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Multi Window Spec

Status

v1 shipped (2026-04-23) — single-process, per-window state. Every window is a Tauri WebviewWindow inside the same OS process; the former global AppState was split so a process-wide AppState container maps a window label to a per-window WorkspaceState (workspace root, file index, watcher handle, gitignore matcher, pending-open queue, settings layer). IPC handlers look up the calling window's state via webview.label() and emit events back via handle.emit_to(&label, ...) so two windows hosting different workspaces never cross-talk. Opening a workspace from the sidebar switcher, welcome screen, command palette, or a cross-workspace dock/drag-drop builds a new window with a UUID label and pre-queues a pending-open payload; the new window hydrates onto it during its normal startup flow. If a window already hosts the requested workspace it's focused rather than duplicated. The window close event removes the state, which drops the watcher and cancels FSEvents/inotify subscriptions. tauri-plugin-single-instance is registered with a handler that opens a new window for secondary launches.

Known limitations:

  • Recent-workspaces and session JSON files live in app data and are shared across windows; concurrent writes from two windows race at the filesystem layer.
  • Global settings are loaded into each window's Settings independently, so a global-setting change in window A is not reflected in window B until B's Settings reload.
  • No macOS Window menu entries, no session-restore of multiple windows at quit, no tab tear-off — these are tracked as future work in TODOS.md.

Summary

Allow Writer to open multiple workspace windows at once. Today the app is single-window; opening a second workspace replaces the current one.

Goals

  • File > New Window and Cmd+Shift+N open a fresh workspace window.
  • Each window has independent state: workspace, tabs, sidebar, history.
  • Closing one window does not affect the others.
  • Restoring a session restores every window that was open at quit.
  • Cross-window communication is minimal in v1: just shared workspace data on disk.

Non-Goals

  • Tab tear-off (drag a tab to a new window).
  • Cross-window drag and drop in v1.
  • Window-to-window state syncing beyond what the filesystem already provides.

Architectural Implications

This is a significant architectural change because much of the current app assumes a single global Zustand store and a single Rust workspace state.

Decisions for v1:

  • The Rust side adopts a per-window state map keyed by Tauri window label. Workspace root, file index, and watcher handle move from state.rs global state into per-window slots.
  • The frontend continues to use Zustand stores but each window mounts its own store instance scoped to that window's React tree.
  • Tauri commands learn to look up state by the originating window label.

UX Decisions

  • New windows default to the welcome screen unless they were restored from session.
  • The macOS Window menu lists open Writer windows.
  • The Dock badge / app icon does not change.
  • Each window has its own command palette, sidebar, and tab strip.

Conflict Behavior

  • If two windows have the same file open and the user edits it in one and saves, the other window's open buffer should reload (or prompt) just like the existing watcher-driven reload path.
  • Two unsaved divergent edits to the same file from two windows: surface a conflict warning before save in the second window.

Files Expected To Change

  • apps/desktop/src-tauri/src/state.rs (per-window state map)
  • every command in apps/desktop/src-tauri/src/commands/ (accept window label or tauri::Window)
  • apps/desktop/src-tauri/src/lib.rs (window creation API + event handling)
  • apps/desktop/src/stores/* (per-window store boundaries)
  • apps/desktop/src/App.tsx
  • new apps/desktop/src/hooks/use-window-id.ts
  • session restore logic
  • comprehensive Rust and frontend tests

Acceptance Criteria

  • The user can open multiple Writer windows simultaneously, each with its own workspace and tabs.
  • Closing one window does not impact others.
  • Quitting and relaunching restores all previously open windows.
  • Conflicting edits between windows are detected and surfaced rather than silently lost.