fix(session): turning off Restore State left the session file on disk

[PathGao]

The todo asked to finish a migration windowSession.svelte.ts:98-112 describes as unfinished. It isn't — that comment describes the endpoint, and the endpoint is reached. But auditing it turned up something the migration did leave behind.

The bug

restore()'s !shouldRestoreState() branch is what makes the "Restore State on Reopen" setting take effect. While the snapshot lived in localStorage, its two removeItem calls ended the session and its record together.

The snapshot moved to a file on the Rust side in #214. The branch was not updated. It now clears two keys nothing writes and leaves window-state-v2.json on disk — so the list of every document the user had open persists in the config directory indefinitely, for exactly the user who turned the setting off to stop it being kept. Nothing rewrites the file while the setting is off, so a later launch can also resurrect a stale session.

Fix is the existing discardPersistedState(), which already clears both stores. Net +1 line of code. Test written first against master's behaviour, confirmed failing.

Two things had to hold before adding a destructive call to a startup path, and both do: settings.restoreStateOnReopen is loaded synchronously in the SettingsStore constructor, before MarkdownViewer.init runs, so there is no async window where it reads as its default; and restore() returns on !isMainWindow above this branch, so secondary windows cannot reach it.

On the two localStorage keys

Every occurrence in production code is getItem or removeItem — zero setItem. Both are compat reads for a user upgrading over a pre-#214 (snapshot) or pre-#501 (breadcrumb) build.

Kept, not deleted. They cost four lines and buy that user a clean upgrade; deleting them silently drops their tabs. Added a test that drives the path end to end — pre-v2 records, an untitled entry, a HOME sentinel — so the compat path is asserted rather than assumed. Falsified by stubbing the legacy read to null.

Why this data is on the Rust side at all

Worth recording, because #638's rule does not decide it. Rust does not read either file — load_window_state and load_restore_progress are read_to_string handing bytes to the frontend unparsed. By #638's ownership test ("Rust owns it because Rust reads it", as with pinned_tags) this is not Rust's data.

It is there for a different and correct reason: setItem is an async message to the WebKit storage process, and both records exist specifically to survive the event that loses that message — the last window closing, or the process being killed. That is durability, not ownership — a third category neither precedent covers.

npm test 872 · vitest 305 · cargo test 148 · check 0 errors.

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