Explain the possible frame rate in the performance overlay (#275)

- Concepts: what the Possible line shows and why it is an upper bound
- Architecture: how possibleFps is computed
- Development: the e2e total is 1602

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Architecture.md

@@ -363,7 +363,8 @@ ticks with `performance.now()`; `PlaySession` sorts them into behaviors, physics
 `GameViewport` adds up what its `redraw` takes, and `ui/render.ts` keeps what the last
 `app.render()` took (`lastRenderTime`). Both together are *Drawing*. `Editor.tick` times itself;
 what is left of that once the systems and the game's redraw are taken off is *Editor*. The meter
-averages per frame over 0.5 s, the window of the fps readout. The released game leaves
+averages per frame over 0.5 s, the window of the fps readout. *Possible* on top is
+`possibleFps`: 1000 ms over the sum of the five areas, rounded down. The released game leaves
 `timeSystem` unset, so the world runs untimed there. Browsers round `performance.now()` (Chromium
 to 0.1 ms without cross-origin isolation), which the average over some 30 frames smooths out.
 

Concepts.md

@@ -109,6 +109,11 @@ averaged over half a second:
 | **Drawing** | Building the game's picture and handing the frame to the GPU |
 | **Editor** | Everything else the editor does in the frame: writing the run into the model, the panels, the console |
 
+The top line, **Possible**, is the frame rate the measured time would allow if nothing waited for
+the display: a second divided by the five times added up. The frame rate below it stops at the
+display's rate (60 on most screens), this one does not. Because the GPU's time is not in it, it is
+an upper bound, and the editor's share is in it, so a released game can do a little better.
+
 A dash stands for what has not been measured yet, in the first half second of a run. The numbers
 are what the main thread spends; the GPU works on after that, and its time is not in them. The
 switch is not saved and stays as it is until the page is loaded again. A released game has no

Development.md

@@ -18,7 +18,7 @@ php tests/php/accounts.test.php                               # the API's accoun
                                                               #   has and the web server's container has not (SKIP there)
 php tests/php/snapshots.test.php                              # the snapshot store (#231), the same way
 php tests/php/releases.test.php                               # the release store (#266), the same way
-node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1601 editor checks, screenshots in /tmp/gm-e2e-*.png
+node tools/seed-e2e.mjs && node tools/e2e.mjs                 # 1602 editor checks, screenshots in /tmp/gm-e2e-*.png
 GM_STEPS=20 node tools/e2e.mjs                                # or 1-12, or 6,20 — a subset while working on one step
 ./e2e.sh start [GM_STEPS]                                     # the same run detached, see below
 ./e2e.sh status                                               # live progress, or the last run's result