[nighca]

Directory-format SPX maps use a directory as tilemapPath (for example, tilemaps/river), but Builder currently looks up that path as a file and rejects the project. Resolve the directory's tilemap.json, load optional decorator.json with directory-relative image paths, and retain the original directory path and map/resource files for export.

Legacy JSON-file maps keep their existing loading behavior. Resource collection enumerates the file set once, preserving all maps under assets/tilemaps/ for runtime loadTilemap calls as well as resources in a selected directory outside that tree. Format selection follows SPX 4.0.1's .json substring rule, documented with a pinned source link. This change adds no tilemap editing UI, course migration, or engine dependency upgrade.

Validation:

• 24 tests pass across the tilemap and project suites, including legacy maps, directory maps with/without decorators, resource preservation, missing-map errors, and project export/reload.
• Full GUI type check, lint, format check, and git diff --check pass.

Refs #3747.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 60.07%. Comparing base (fce3f1a) to head (b2e2ceb).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #3770      +/-   ##
==========================================
+ Coverage   59.95%   60.07%   +0.12%     
==========================================
  Files         772      772              
  Lines       27728    27732       +4     
  Branches     5231     5235       +4     
==========================================
+ Hits        16625    16661      +36     
+ Misses       9590     9555      -35     
- Partials     1513     1516       +3     

Flag	Coverage Δ
gui	59.55% <100.00%> (+0.12%)	⬆️
tools-ai	79.61% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
gui/src/models/spx/project.ts	55.13% <ø> (+1.17%)	⬆️
gui/src/models/spx/tilemap.ts	77.06% <100.00%> (+25.63%)	⬆️

... and 1 file with indirect coverage changes

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[fennoai]

Review: directory-format tilemap loading

The change to DumbTilemap.load is focused and well-covered by tests (both formats, the no-decorator directory variant, and the missing-file error path). A couple of points in the resource-collection logic are worth a look before merge, plus two minor nits.

Main point — others unconditionally scans assets/tilemaps/. See the inline comment on the others construction. For a directory-format tilemap that lives outside assets/tilemaps/ (the worlds/river case in the new test), every file under assets/tilemaps/ is still pulled into this tilemap's file set — the test's unrelated assets/tilemaps/other/map.json ends up in the exported files, which expect(exported).toEqual(files) happens to accept only because that stray file is in the fixture. If that cross-tree sweep is intended for back-compat, a one-line comment would help; if not, scanning only resourcesPath removes both this and the double enumeration.

Minor nits (not blocking):

• gui/src/models/spx/tilemap.ts:328 — decoratorFile is cast to RawTilemapConfig, but for directory format it is decorator.json ({ version, decorators }), which has no tilemap/sprites. Only .decorators is read, so this is harmless, but a narrower type (e.g. Pick<RawTilemapConfig, 'decorators'>) would describe the shape honestly and avoid conflating decorator.json with the full tilemap config.
• The user-facing tilemapPath field (project.ts:73) now accepts a directory, but that isn't documented anywhere outside the tests. A short note on the field (required tilemap.json, optional decorator.json) would prevent future drift.