Click-to-revert and where your data lives

What it does

The History panel is now interactive. Each entry carries an explicit, always-visible "Restore" button (Google Sheets Version History's "Restore this version" pattern — discoverable without hovering, keyboard-accessible); pressing it non-destructively restores the document to that state — it records a new version at the top of the timeline and keeps every prior version, so nothing is lost (undo the restore to step back out of it). Hovering an entry previews it: the cells it touched light up on the grid (a transient amber highlight that clears when you move away), and the entry shows what changed — a before → after for a single value edit (e.g. 10 → 20), or a short summary for a formatting change ("fill color") or a multi-cell edit ("3 cells"). Consecutive identical operations on the same cell (the 8× repeated date-format on C5 seen in dogfooding) collapse into a single row with a ×N badge, so the timeline stays legible. Timestamps are human-readable — "just now", "2 min ago", "Today 3:45 PM", "Yesterday", then a date like "Jul 14" for older entries — with the exact absolute time available on hover.

The chrome now also tells you, at a glance, where the current document and its history actually live. A footer strip states this in plain words; the History panel header carries the matching note; and while the workbook is in the browser-only local mode (the default — see persistent-history), the tab-close warning stays off, since the document and its history are already saved.

Deferred to

(persistent history — autosave + restore across reload, in THIS browser) has shipped; see persistent-history. What's still deferred is the account half:

• Cross-device version history — the same non-destructive restore, but with versions saved server-side so they survive not just a reload but a different device too, rather than being scoped to this one browser.
• Account-saved history, the account indicator state going live, and the "Sign in to save" upgrade CTA from standalone.

Verified behavior

Matches Google Sheets: Restoring to a past state matches Google Sheets File → Version history: picking a version and clicking "Restore this version" does NOT discard the versions in between — it makes a NEW current version equal to the chosen one and keeps the full history intact, and the restore is itself undoable. The standalone restore here is exactly that (non-destructive, create-a-new-version), driven from the timeline. The undo/redo of individual edits follows Sheets' Ctrl+Z — whole-edit steps, and a fresh edit clears the redo branch. The "where your data lives" signaling has no direct Sheets cell-behavior to replicate: Sheets always runs in one persistent, Drive-saved mode ("All changes saved in Drive") and never exposes a browser-only/at-risk mode, so the mode indicator + data-loss guard are a TrueCalc-original response to the playground being client-side with no account (a light oracle pass — this is Studio UX, not a cell computation).

Undo steps back through edits and a new edit clears the redo branch (the restore substrate)

Given

• A1 = 1

When I type 2 into A1, then type 3 into A1, then undo, then undo, then type 9 into A1, then redo

Then

• A1 shows 9

The chrome states where the workbook currently lives

Given

• A1 = 1

When I click A1

Then

• [aria-label="Storage status"] is visible containing "Saved in this browser"