Mdviewer

Highlights — macOS double-click reliability

This release fixes the hang that occurred when opening a second markdown file from Finder, and the issue where launching with multiple files only showed the first window.

Fixes

• Double-click second file no longer hangs the app. Tauri 2 holds the plugin-store mutex for the duration of RunEvent::Opened plugin dispatch, and WebviewWindowBuilder::build() re-acquires the same mutex via window_created — self-deadlock. The handler now hops to a tokio worker via tauri::async_runtime::spawn before calling run_on_main_thread, so window creation runs in a later event-loop iteration after the lock is released.
• Multiple-file launches now show every window. Windows created back-to-back during startup landed at identical coordinates because AppKit's auto-cascade did not engage — the second window was hidden behind the first. New cascade_position(window_index) helper assigns a distinct (x, y) to each window with monotonic offsets.
• Replaced homemade single-instance scheme with tauri-plugin-single-instance. The previous polling thread called WebviewWindowBuilder::build() from a non-main thread, which is unsound on macOS (AppKit/WebKit init must run on the main thread). The plugin handles single-instance correctly cross-platform; on macOS its callback runs on a tokio task, so dispatching back to the main thread via run_on_main_thread works as expected.

Documented for future maintainers

See docs/plans/2026-05-01-macos-file-open-deadlock-fix.md for the architectural map, the reasoning, the regression-test recipe, and a list of "don'ts" — including: do not install the bundle to /Applications/ by dragging from the DMG. Use bin/install.sh.

Tests

38 unit tests pass, clippy is clean with -D warnings. Three new tests pin cascade_position behavior.