[PathGao]

What this is

Follows #990. Windows are now equal, and each one's session is recorded as it changes rather than only at quit:

• After a crash or kill -9, every window comes back with its own tabs, its own unsaved tabs (feat(editor): keep unsaved changes when quitting #962), and its own position and size. Before, the window list was only written on quit, and unsaved tabs from other windows landed in the launch window.
• Nothing treats the window labelled main specially any more, except that it is the window Tauri creates at launch.
• The two restore settings are renamed in parallel, one for windows and one for content: Restore windows on launch ("Reopens your last windows and tabs. File contents are read from disk.") and Restore unsaved changes on launch ("Quitting won't ask to save. Tabs with unsaved changes come back next time."). They now sit next to each other in Settings → Files. Setting keys are unchanged.

Mechanism

Continuous session. Each window writes its own window-state/<label>.json within 500 ms of a change to its tabs, active tab, view mode, split, tag or sidebar folder. It uses #962's bounded, serialized writer, renamed createBoundedWriter. Scroll and cursor positions don't trigger writes; they ride along with the next write, and are also written on blur, when the window is hidden, on close and on quit. The set of snapshot files is the window list. Window geometry is saved through the window-state plugin 500 ms after a move or resize (coalesced), because the plugin itself only saves on exit.

Remember or forget is unchanged from #990, with two gaps closed:

• An updater restart no longer brings other windows back stale, since they are already current.
• If a quit is cancelled partway, the windows it had already closed are forgotten. The quit state is now Mutex<Option<Vec<label>>> instead of a bool, and set_quitting(false) drops their snapshots. Their unsaved backups become orphans.

Former main-window privileges:

Privilege	Now
Crash guard	Per label, the same code in every window
Orphan unsaved backups	Handed out by Rust (claim_unsaved_recovery), once each, to whichever window asks first
Sidebar folder	Stored in each window's own snapshot. The global folder.lastRoot key is migrated once
Startup file (argv, or macOS Opened before ready)	Answered once, to the launch window
Files opened while running	Focused window, else last focused, else the launch window
Legacy localStorage snapshot	Read and removed once by the launch window

scripts/windowsAreEqual.test.ts fails if the frontend compares against 'main' or mentions isMain. In Rust non-test code, "main" appears only as LAUNCH_LABEL.

Startup adoption. A small plugin runs before the window-state plugin loads. If the launch window has no snapshot of its own but other windows are remembered, it adopts the first of them: snapshot, crash guard, unsaved backup and geometry. So a relaunch after closing the launch window opens no extra empty window. The snapshot is moved last, so a kill midway re-adopts the same window. An existing launch-window backup is never overwritten; the adopted one becomes an orphan instead.

Behaviour changes

• With "Restore windows on launch" off, the sidebar folder is no longer reopened, because it is part of window state now. Unsaved changes are governed by the other setting and still come back, into the launch window.
• An empty window open at quit comes back, as in VS Code.

Scope

• The window-state plugin writes its file with fs::write, not an atomic rename. A kill during that write loses every window's geometry once. Tabs and unsaved changes are unaffected. This is marked ponytail: in the code.
• In the first ~500 ms after launch, before the first snapshot, a crash loses the sidebar folder.
• Windows and Linux were not run.

Tests

• Bounded writer: nothing is written before restore, writes are bounded at 500 ms with the latest state winning, a forget isn't undone by a queued write, and dispose waits for an in-flight write. Each was confirmed to fail with the code broken.
• Rust: cancelled quit forgets windows already closed; orphans are claimed once; the adoption decision (a pure function); adoption moves files and geometry without overwriting the launch window's backup; last-focused routing; geometry is saved on move and resize with the same flags as the plugin.
• Folder: restored per window, the old key migrated once, a window's own folder wins.
• Tests that assumed main-only restore were updated. The new-window test (feat(windows): open a new empty window with Cmd+Shift+N #991) no longer passes the removed isMainWindow option.

Verification

npm run check 0 errors, npm test 1142 pass, npx vitest run 523 pass, cargo test 206 pass, cargo fmt --check and cargo clippy --all-targets -- -D warnings clean.

macOS 27, release test bundle:

• Two windows, each with an unsaved untitled tab. After kill -9, both came back, each with its own tab and text.
• Two windows moved to an external display and resized (80,-1150 760×560 and 700,-950 900×651). After kill -9, both reopened at exactly those positions and sizes.
• Closing the launch window asked and was discarded, then Quit. On relaunch, one window opened at the other window's position and size with its tab, and its files had been adopted. No empty window appeared.