fix(emulator): migrate to SDL3 and Linux graphics deps

[OGKevin]

Fedora/non-NixOS devenv could not create an SDL renderer because pkgs.SDL2 was sdl2-compat without GL/Wayland/X11 libs (#855).

• Replace sdl2 crate with sdl3 (default renderer, software fallback)
• Ship pkgs.sdl3 plus Linux graphics packages in devenv
• Update CI apt/brew and contributor docs

Closes: CAD-137

Change-Id: 9a9bbb96856f95728af6630851a39718
Change-Id-Short: qpqoooqtrutk

[OGKevin]

@cursoragent can you have a look at the failing ci 🙏🏾

[cursor]

I traced the Cargo failure and pushed a fix on ogkevin/push/qpqoooqtrutk (commit 74921e6b).

What failed

The required-cargo job is just a rollup — the real failure was cache-warmup → Warmup llvm-cov build:

rust-lld: error: unable to find library -lSDL3

The cache budget warnings are noise; they did not cause this failure.

Root cause

The PR switched apt from libsdl2-dev to libsdl3-dev, but Cargo CI still runs on ubuntu-latest (Ubuntu 24.04). libsdl3-dev does not exist on 24.04 (it landed in 25.10+).

The apt cache action requested libsdl3-dev, but the resolved install list had only 29 packages — SDL3 was silently skipped. That was enough for cargo check (no linking), but cargo llvm-cov nextest-archive links test binaries and failed on -lSDL3.

Fix pushed

1. Run SDL3-native Linux jobs on ubuntu-26.04 (matches .cursor/Dockerfile):
   • cache-warmup, build-kobo, build-kobo-test
2. Point the test/clippy Linux matrix at ubuntu-26.04 via CI_LINUX_OS in xtask
3. Install apt packages in clippy jobs (they link too, but previously had no apt step)
4. Bump apt cache version 1.1 → 1.2

All 16 matrix unit tests pass locally.

CI status

A new Cargo run is in progress: https://github.com/OGKevin/cadmus/actions/runs/31897736888

cache-warmup is running (it failed within ~16 minutes last time), which is a good early sign. Full Cargo still takes ~20 minutes — worth watching that the llvm-cov warmup step completes this time.

  

[github-actions]

🚫 [actionlint] _{reported by reviewdog 🐶}
label "ubuntu-26.04" is unknown. available labels are "windows-latest", "windows-latest-8-cores", "windows-2025", "windows-2025-vs2026", "windows-2022", "windows-11-arm", "ubuntu-slim", "ubuntu-latest", "ubuntu-latest-4-cores", "ubuntu-latest-8-cores", "ubuntu-latest-16-cores", "ubuntu-24.04", "ubuntu-24.04-arm", "ubuntu-22.04", "ubuntu-22.04-arm", "macos-latest", "macos-latest-xlarge", "macos-latest-large", "macos-26-intel", "macos-26-xlarge", "macos-26-large", "macos-26", "macos-15-intel", "macos-15-xlarge", "macos-15-large", "macos-15", "macos-14-xlarge", "macos-14-large", "macos-14", "self-hosted", "x64", "arm", "arm64", "linux", "macos", "windows". if it is a custom label for self-hosted runner, set list of labels in actionlint.yaml config file [runner-label]

[OGKevin]

@cursoragent can you explain this linter failure while the CI itself succeded. Is actionlint outdated?

[cursor]

Yes — this is essentially actionlint being behind GitHub, not your workflow being wrong.

What’s happening

These are two different checks:

Check	What it validates
Cargo CI	GitHub actually runs the job on a real runner
actionlint	Statically checks workflow YAML against a built-in list of known runs-on labels

You changed jobs to runs-on: ubuntu-26.04. GitHub added that runner in June 2026 (public preview), and your Cargo run proves it works: cache-warmup completed on ubuntu-26.04, and test/clippy matrix jobs are running on it too.

actionlint 1.7.12 (pinned in .github/workflows/actions-lint.yml) still has a hardcoded allowlist that includes things like ubuntu-24.04 and macos-26, but not ubuntu-26.04. So it reports:

label "ubuntu-26.04" is unknown

That’s a false positive relative to real GitHub behavior.

Is actionlint outdated?

Relative to GitHub: yes.
Relative to its own releases: it’s current — 1.7.12 is the latest released version, and upstream support for ubuntu-26.04 is still pending (rhysd/actionlint#682, PR #683).

So this isn’t “you’re using a deprecated runner”; it’s “the linter’s catalog hasn’t caught up with a new GitHub runner image yet.”

Why Cargo can pass while Actions lint fails

They’re separate required checks:

• Cargo → compiles/links/tests on real infrastructure
• Actions lint → runs actionlint on .github/workflows/** before anything executes

actionlint fails fast on the unknown label, which is why required-actions-lint fails even while Cargo is green/in progress.

How to silence it (when you want to)

Common options:

1. Add .github/actionlint.yaml and whitelist the label:

   self-hosted-runner:
     labels:
       - ubuntu-26.04

   (Despite the name, this is the standard way to teach actionlint about labels GitHub supports but actionlint doesn’t know yet.)

2. Ignore the specific error in .github/lint/actionlint-ignore.txt.

3. Upgrade actionlint once a release includes ubuntu-26.04 (PR chore(deps): use matchDepNames for mupdf Renovate group #683 merged/released).

Bottom line: CI succeeding on ubuntu-26.04 is the ground truth. actionlint is flagging a label GitHub already accepts but its static list hasn’t been updated for yet.