Support fixed-resolution KMS/GLES rendering and RGBA8 canvases

[brandonpayton]

Purpose

Support fixed-resolution native KMS/GLES applications in the browser presentation path without app-specific scaling or rendering behavior. The core feature is not LOVE-specific: Kandelo now lets a KMS consumer render at its intended connector mode while the browser UI stretches that scanout to the available canvas area, and the WebGL-backed GLES bridge exposes the render-target formats needed by native GLES renderers.

LOVE/BYTEPATH/SNKRX remain in this PR as consumers and regression fixtures. They are the applications that exposed the bug, but the runtime fixes are generic KMS/GLES behavior rather than a LOVE-only renderer path.

The immediate regression was BYTEPATH rendering its 480x270 game through RGBA4 canvases because Kandelo did not advertise RGBA8 render-target support on the GLES query path. BYTEPATH uses neutral 127-gray displacement maps for RGB glitch shaders; RGBA4 quantization moved that neutral value far enough to produce exaggerated red/green/blue copies. Advertising the equivalent GLES capability (GL_OES_rgb8_rgba8) keeps native renderers on RGBA8 targets and restores the intended small channel separation.

Changes

• Expose GL_OES_rgb8_rgba8 from the WebGL-backed GLES query path so native GLES renderers can use RGBA8 render targets.
• Make glReadPixels handle packed, 16-bit, and 32-bit formats with correct byte sizing and chunked reads under the GL query cap.
• Match browser readPixels destination typed arrays to packed GL types, including unaligned output spans.
• Replace the earlier KMS maxCssScale presentation knob with generic presentation.kms.fit: "contain" | "stretch" metadata.
• Let KMS demo metadata declare fixed target-resolution scanouts that the browser canvas can stretch, leaving user software at its original target resolution.
• Add a Chromium browser regression test that boots BYTEPATH gameplay through the native KMS/GLES path, captures the raw KMS canvas, and asserts full-pane fill plus bounded RGB channel separation.
• Keep the LOVE native package on the upstream renderer and document the browser presentation contract.

Why LOVE Is Still In The PR

This PR is non-LOVE-specific at the platform layer, but it still carries LOVE package and demo metadata because that is the current end-to-end proof. BYTEPATH and SNKRX exercise fixed-resolution KMS presentation, GLES render-target selection, shader-driven post-processing, and browser canvas scaling in a way the simpler framebuffer demos do not.

There is no Kandelo runtime branch that detects BYTEPATH, SNKRX, or LOVE to fake success. The LOVE-specific pieces are package/build inputs and demo metadata for real consumers of the generic KMS/GLES path.

Evidence

Check	Result
git diff --check	passed
scripts/dev-shell.sh bash scripts/build-gles-stubs.sh	passed
scripts/dev-shell.sh bash packages/registry/love/build-love.sh	passed; patch applies and love.wasm rebuilds
scripts/dev-shell.sh bash images/vfs/scripts/build-shell-vfs-image.sh	passed; shell VFS rebuilt with LOVE runtime
../scripts/dev-shell.sh npx vitest run test/webgl-bridge.test.ts from host/	passed: 25 tests
scripts/dev-shell.sh npx vitest run web-libs/kandelo-session/test/kandelo-session.test.ts	passed: 46 tests
../../scripts/dev-shell.sh env KANDELO_PLAYWRIGHT_PORT=5424 CI=1 npx playwright test test/kandelo-kms-gles-rendering.spec.ts --project=chromium from apps/browser-demos/	passed

Final BYTEPATH browser capture from the renamed Playwright run:

Capture	Backing store	CSS rect	Fill	RGB shift
10s gameplay	480x270	2048x1045	width=1, height=1	rg=1, rb=2
22s gameplay	480x270	2048x1045	width=1, height=1	rg=1, rb=2

The same browser run syslog showed the normal native renderer path only:

• love: using KMS/EGL/GLES presenter on /dev/dri/card0
• love: using upstream LÖVE OpenGL renderer on Kandelo KMS/EGL

Contract Notes

• Browser-facing KMS presentation behavior changed through image metadata.
• Host WebGL behavior changed for the browser KMS path. Node-visible POSIX behavior is unchanged.
• ABI was not changed.
• Package source/build inputs changed; local LOVE and shell VFS artifacts were rebuilt for validation, but binary release indexes were not published.

Not Run

• Full browser Playwright suite.
• POSIX/libc/Sortix conformance suites.
• Full ./run.sh browser end-to-end manual flow.

[github-actions]

Phase B-1 matrix build status — pr-843-staging

ABI v16. 67 built, 4 failed, 71 total.

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node-vfs	wasm32	failed	—
wordpress	wasm32	failed	—

_{Auto-generated; replaced on each push. Raw data in the publish-status workflow artifact.}