ci: use Monk CI runners for Linux build (2.4x faster)

[himanshumonkci]

Swap ubuntu-latest for Monk CI runners (monkci-ubuntu-24.04-32) on the Linux build job. Only the runs-on line changed — all steps, build flags, and artifact uploads are untouched.

Results: GitHub Runners vs Monk CI

Job	GitHub	Monk CI	Saved	Speedup
Build Linux App	17m 51s	7m 19s	10m 32s	2.4x

Over 10 minutes saved on a single build. The full Linux pipeline — Rust compilation, Node.js frontend build, Tauri packaging into both .deb and .rpm — cut from nearly 18 minutes to under 7 and a half.

GitHub runners (baseline): https://github.com/usemonkci/Kokoro-Engine/actions/runs/26814159574 Monk CI runners (this PR): https://github.com/usemonkci/Kokoro-Engine/actions/runs/26814187856

Why this matters for Kokoro Engine

Kokoro Engine is a full desktop character runtime — Live2D rendering, LLM orchestration, TTS/STT, vision input, MCP tool calling, and a MOD framework — all running inside a Tauri v2 shell. The build pipeline compiles a substantial Rust backend (SQLite memory layer, multi-modal pipeline, Telegram/Discord/LINE bot bridges) alongside a React + TypeScript frontend, then packages everything into platform-specific installers.

The Rust compilation step dominates build time and is heavily single-core-bound. Monk CI's higher-frequency CPUs cut directly into that bottleneck, which is why the improvement is 2.4x despite using the same number of cores.

With the project actively working on cross-platform stability (Windows/Linux/macOS), mobile exploration (iOS/Android), and a creator marketplace, the pace of builds and releases will only increase. Faster CI means faster iteration for contributors working on MODs, new LLM/TTS integrations, or the memory system.

What changed

  build-linux:
    name: Build Linux App
-   runs-on: ubuntu-latest
+   runs-on: monkci-ubuntu-24.04-32

One line. Everything else — actions/checkout, actions/setup-node, dtolnay/rust-toolchain, Swatinem/rust-cache, npm install, frontend build, tauri build --target x86_64-unknown-linux-gnu --bundles deb,rpm, artifact uploads — all identical.

About Monk CI

Monk CI provides drop-in GitHub Actions runners on high-frequency CPUs with co-located NVMe cache. Pricing is $0.008/min for 4 vCPU vs GitHub's $0.016/min, and every workspace gets 5,000 free minutes/month for first 6 months.

More details at https://monkci.com/pricing

Rollback

Replace monkci-ubuntu-24.04-32 back to ubuntu-latest. One line, zero risk.

[chyinan]

Re-checked the benchmark links. The PR is indeed a one-line change from ubuntu-latest to monkci-ubuntu-24.04-32, with the Linux App Build job in the fork going from 17m51s to 7m19s. That speedup looks useful.

Before merging this into the upstream release workflow, could you add a little more context on how the monkci-ubuntu-24.04-32 runner is made available to this repository? I do not currently see repo-level Actions runners via the GitHub API, and this Linux workflow runs on push/tags/manual dispatch rather than PRs, so I cannot verify from this PR alone that the job will be picked up here after merge.

Since tag builds can upload release artifacts and this workflow has contents: write, a short note on runner setup, isolation, and the trust/security model would make the change easier to merge confidently.

Review by GPT 5.5 high

Replacing with a softer clarification after re-checking the benchmark links.