Add browser runtime, Emscripten build, and persistent submodule updates

[espmaniac]

Summary

• add an English-only os/main.c for the Emscripten browser target
• provide browser HAL functions using emscripten_get_now()
• expose task and runtime control functions to JavaScript
• add root-level build-browser.sh
• add .github/workflows/build-browser.yml
• generate os/wasm-rtos.js and os/wasm-rtos.wasm
• update os/wasm-rtos and nested wasm3 before every build
• persist an updated top-level os/wasm-rtos gitlink back to the current GitHub branch after a successful push-triggered build

Submodule update

The workflow runs:

git submodule sync --recursive
git submodule update --init --remote --recursive

This updates the top-level os/wasm-rtos checkout and the nested os/wasm-rtos/wasm3 checkout before Emscripten compilation.

Persistence on GitHub

After a successful push-triggered build, the workflow stages and persists the top-level gitlink:

git add os/wasm-rtos
git commit -m "Update wasm-rtos submodule"
git push origin "HEAD:$branch"

Pull-request-triggered runs do not push. This avoids duplicate writes and prevents write failures for forked pull requests.

wasm3 is owned by the wasm-rtos repository. A newer nested checkout is used for the current build, but its gitlink can only become permanent through a commit in wasm-rtos itself. The workflow emits a warning when the nested checkout differs from the gitlink recorded by wasm-rtos.

Build architecture

The Emscripten build compiles:

• os/main.c
• os/wasm-rtos/os.c
• every C source in os/wasm-rtos/wasm3/source

It does not compile os/wasm-rtos/hal.c, because os/main.c supplies the browser HAL implementation.

Outputs

The build creates and validates:

• os/wasm-rtos.js
• os/wasm-rtos.wasm

Both files are uploaded together as the wasm-rtos-browser workflow artifact and are not committed by the submodule persistence step.

Validation

Workflow run #11 successfully completed recursive submodule update, Emscripten installation, browser runtime compilation, output validation, and artifact upload. The persistence step is intentionally skipped on the pull-request run and executes on the corresponding push run.

Do not merge until the browser API and persistent top-level submodule update behavior are accepted.