Updates you can undo, a panel that tells you why nothing happened, and four-player chess that finishes its own promotions. The largest release since self-updating landed.
Which download?
| Archive | Size | Use it when |
|---|---|---|
mephisto-3.1.217.zip |
585 MB | First install — everything, engines included |
mephisto-3.1.217-update.zip |
6 MB | You already have Mephisto — extract over your existing folder |
⚠️ Extract the update over your existing install, never into an empty folder — without the engines it cannot run. Extract in place: Chrome derives an unpacked extension's id from its folder path, so a new folder means a new id and re-running the native-host installer.
On 3.1.215 or later with automatic updates set up? Neither archive. Click the panel's "click to install", or Settings → Updates → Install Update.
Every update is undoable now
Before anything is overwritten, the new version is written to a staging folder and the files it replaces are copied to a backup.
- Roll Back appears in Settings when there is something to go back to, labelled with the version. Files the update added are recorded separately, so rolling back removes them instead of leaving two builds mixed together.
- Finish Interrupted Update appears if a staging folder is left behind — the bytes are already on disk and already checked, so it is a copy, not a second download.
- What changed is shown once in the panel after an install: "Updated to v3.1.218 — …", taken from the release's own first sentence.
True atomicity is not available — the extension id comes from the folder path, so the folder cannot be swapped out from under itself. Recoverable is the honest word, and it is what this is.
Verified on a real filesystem against the published archive: staging leaves the install untouched, the backup holds the old bytes and never the engines, and rolling back leaves the folder byte-identical to before the update.
The panel says why nothing happened
Every path that ended in "no move" used to end in silence, which is indistinguishable from a bug — and was reported as one three times.
- A reason line under the readout for the things you cannot otherwise see: a four-player board that is not playable, a move the board cannot understand, a square not on screen, a position that moved on mid-search. Deliberately not used for anything that happens in ordinary play.
- Copy Diagnostics (panel → Engine tab, or D) puts version, browser, bundled assets, connected hosts, granted permissions, what was detected, why the last move was or was not played, the active toggles and the last 200 trace lines on your clipboard. No addresses, no query strings, no extension id — it is meant to go straight into a bug report.
- Verbose Logging in Settings → Diagnostics. The trace is quiet while the game tab is focused unless Premove happens to be on; that default hid the cause of a four-player bug for three sessions, so it now has a switch instead of an incantation.
- A scrape watchdog: above 60 scrapes a second — a rate real play never reaches — scraping backs off and says so once.
Four-player chess
- Promotions are played in full. The picker is found by its shape — four pieces in two rows over the board — not by a class name, since every class there is generated. If nothing matches that shape it leaves the piece to you rather than guessing, because a wrong guess would be a wrong piece.
- Elimination was wrong, not just untested. The turn came from counting filled cells and taking
count % 4. Chess.com lays that table out as four columns in seat order, so once a seat is out its column stops filling, every later round holds three moves instead of four, and the modulo drifts a seat further out per round. Reading the position of the last filled cell is correct either way. - Multiple lines, on the page board, the panel's own 14×14 board, and a colour-matched list of scores beneath it. Tetrarch has always had MultiPV; nothing had asked for it.
- Autoplay works on the analysis board, not only in a game.
The floating panel
- 79% smaller payload. It was shipping all three board textures — 784 KB of base64 in a 973 KB payload — to use at most one. On a flat-colour theme it now carries none. First open after a cold start went 145 ms → 82 ms.
- It can no longer open into silence. A frame appears before anything is awaited, says more if the worker is slow, and times out rather than hanging — reported as ten seconds of nothing after a browser restart.
- Tetrarch no longer offers an Elo slider; it has no
UCI_Eloto cap.
Known limits
The ten-second stall that prompted the startup work is not explained. It is now visible and survivable, and the trace ring will capture it next time — that is all this release claims about it.
No real game has been seen past an elimination, so that path is pinned by synthetic positions. The promotion picker is confirmed for a seat at the bottom of the board; whether Chess.com rotates that picker per seat is untested, and is noted in the code where the order is declared.