fix: fit an opened map to the window it is opened in

[Azgaar]

The bug

A map opened on a screen that is not the one it was made on no longer fills the window. 1.152.0 changed two things at once in fitMapToScreen():

setViewport(Math.min(graph.width, wanted.width), Math.min(graph.height, wanted.height));
setZoomExtent(Math.max(options.app.zoomExtent.min, coverMin), max);

Each half breaks one direction:

• Map smaller than the window — the #map svg is sized to the map's extent, so the map sits in the top-left with dead canvas right and bottom.
• Map larger than the window — the cover scale is below 1, but the default zoomExtent.min of 1 wins, so the map can never be zoomed out to fit.

Reproduced with 1.108.12.map (extent 1440×778) at 1600×900 and at 1000×600, and confirmed against a build of d00e3311^.

What it used to do

public/modules/ui/options.js sized the svg from the user's canvas request (which follows the window), and the floor was the derived cover value, which also overwrote the control:

svgWidth = Math.min(+mapWidthInput.value, window.innerWidth);
const zoomMin = rn(Math.max(svgWidth / graphWidth, svgHeight / graphHeight), 3);
zoomExtentMin.value = zoomMin;
setZoomExtent(zoomMin, +zoomExtentMax.value);

The fix

• canvas.ts — the viewport follows the window (or the viewport the user pinned); the extent no longer bounds it. The zoom floor is max(viewport / extent), rounded up — rounding to nearest can leave a sub-pixel strip of canvas, which makes d3's constrain centre the map instead of pinning it. It is written to app.zoomExtent.min and into the panel, so the control shows the limit the canvas enforces.
• zoom.ts — new constrainZoom() re-applies the current transform through the behavior, because d3 enforces scaleExtent/translateExtent on gestures only; a raised floor otherwise did nothing until the user touched the map. resetZoom() targets the floor rather than a bare identity, and skips the transition at duration 0 (Submap and Transform call resetZoom(0) right after a fit).
• load.ts — fitMapToScreen() runs before focusOn() (matching the generation path, so a ?scale=/?burg= deep link still wins), followed by resetZoom(0) so an opened map opens at the fitted view.
• options-tab.ts — a hand-set floor applies as typed and stands until the next fit re-derives it, as before. "Restore default zoom extent" re-derives the floor instead of forcing 1, which would have re-broken the invariant.

Verified

1.108.12.map, extent 1440×778:

Window	#map svg	Zoom floor	Opens at
1000×600 (smaller)	1000×600	0.772	0.772 — whole map fitted
1600×900 (bigger)	1600×900	1.157	1.157 — scaled up, no bands

setMapZoom(0.1) clamps to the floor; zooming to 4 and then resizing keeps k=4 and only re-derives the floor, so a resize never yanks the user's view; regenerating resets the extent to the window with floor 1.

942 unit tests, tsc and biome check src/ pass. tests/e2e/canvas-size.spec.ts covers both directions; per the repo rule Playwright was not run locally, so CI is the first run.

Notes

• app.zoomExtent.min is now a derived value the canvas writes rather than a stored preference — that is what 1.151 did, and docs/architecture/configuration.md is updated to say so, but it sits slightly against that file's "preferences are what the user asked for" framing. Worth a second opinion.
• The version bump to 1.152.1 was already in the working tree; the sync-version pre-commit hook pulls package.json and the lockfile along with it.

🤖 Generated with Claude Code

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