feat: add FAST template converter CLI

[janechu]

Pull Request

📖 Description

Adds fast convert to @microsoft/fast-build so FAST declarative .html templates can be converted to WebUI prerelease HTML or FAST v3 TypeScript. This includes the new microsoft-fast-convert Rust crate, Node CLI/config integration, fixture validation, docs, package build/packaging updates, and release/version-sync support for the bundled converter crate.

👩‍💻 Reviewer Notes

Please review the converter's intentionally limited expression grammar and the packaging changes that include converter WASM files under wasm/convert/.

📑 Test Plan

• cargo fmt --manifest-path crates/microsoft-fast-convert/Cargo.toml -- --check
• cargo check --manifest-path crates/microsoft-fast-convert/Cargo.toml
• cargo test --manifest-path crates/microsoft-fast-convert/Cargo.toml
• cargo test --manifest-path crates/microsoft-fast-build/Cargo.toml
• npm run build -w @microsoft/fast-build
• npm run test:node -w @microsoft/fast-build
• npm run checkchange
• npm run biome:check
• Targeted npx biome check --no-errors-on-unmatched ... for changed JS/JSON files
• npm pack --dry-run --json -w @microsoft/fast-build verified converter WASM files are included

✅ Checklist

General

• I have included a change request file using $ npm run change
• I have added tests for my changes.
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation and followed the standards for this project.

Agents

• I have linked to an existing issue in this project that this change addresses
• I have read the skills
• I have read the DESIGN.md file(s) in packages relevent to my changes
• I have updated the DESIGN.md file(s) in packages relevent to my changes

[Copilot]

Pull request overview

Adds a new fast convert subcommand to @microsoft/fast-build, backed by a new microsoft-fast-convert Rust/WASM module, to convert FAST declarative .html templates into either WebUI prerelease HTML or FAST v3 TypeScript output. This extends the existing fast-build CLI/WASM integration model and updates packaging + release/version-sync tooling to treat the converter crate as a bundled asset of the fast-build release.

Changes:

• Added fast convert CLI subcommand with config loading, path/output validation, and converter WASM dispatch.
• Introduced the microsoft-fast-convert crate (Rust API + wasm-bindgen export) with conversion + validation tests.
• Updated packaging, docs, CI Rust validation, and release scripts to include/sync the bundled converter crate and WASM outputs.

Reviewed changes

Copilot reviewed 35 out of 39 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
packages/fast-build/wasm/convert/.npmignore	Packaging ignore override for converter wasm directory.
packages/fast-build/wasm/.npmignore	Packaging ignore override for wasm directory.
packages/fast-build/test/wasm-stub.cjs	Test preload stub extended to intercept converter WASM module.
packages/fast-build/test/fixtures/convert/validation/unsupported-f-attribute/template.html	Fixture input for unsupported f-* attribute validation.
packages/fast-build/test/fixtures/convert/validation/unsupported-f-attribute/fast-convert.config.json	Fixture config for unsupported f-* attribute case.
packages/fast-build/test/fixtures/convert/validation/missing-inner-template/template.html	Fixture input for missing inner <template> validation.
packages/fast-build/test/fixtures/convert/validation/missing-inner-template/fast-convert.config.json	Fixture config for missing inner <template> case.
packages/fast-build/test/fixtures/convert/validation/invalid-repeat/template.html	Fixture input for invalid repeat expression validation.
packages/fast-build/test/fixtures/convert/validation/invalid-repeat/fast-convert.config.json	Fixture config for invalid repeat expression case.
packages/fast-build/test/fixtures/convert/supported.html	Supported conversion fixture covering directives/attrs/bindings.
packages/fast-build/test/fixtures/convert/fast-convert.config.json	Default fixture config used to validate config discovery + output patterns.
packages/fast-build/test/fixtures/convert/convert-fixtures.test.js	End-to-end fixture tests for fast convert output + validation errors.
packages/fast-build/test/config.test.js	CLI tests extended for convert, help output, and stubbed converter WASM.
packages/fast-build/README.md	User-facing documentation for fast convert usage/config/fixtures.
packages/fast-build/package.json	Exports/files/scripts updated to include converter WASM and tests.
packages/fast-build/DESIGN.md	Architecture docs updated for convert command and bundled WASM/module map.
packages/fast-build/build-wasm.cjs	New build helper to build both build and convert WASM artifacts.
packages/fast-build/bin/fast.js	CLI updated to dispatch build vs convert, config validation, convert path rules.
crates/microsoft-fast-convert/tests/errors.rs	Rust tests for converter validation/unsupported cases.
crates/microsoft-fast-convert/tests/conversions.rs	Rust tests for expected conversions for both targets.
crates/microsoft-fast-convert/src/wasm.rs	wasm-bindgen export for convert_template.
crates/microsoft-fast-convert/src/syntax/webui.rs	WebUI prerelease conversion pass for directives + attribute validation.
crates/microsoft-fast-convert/src/syntax/mod.rs	Shared directive parsing/validation helpers for syntax backends.
crates/microsoft-fast-convert/src/syntax/fast_v3_ts.rs	FAST v3 TS conversion pass, escaping, and helper import selection.
crates/microsoft-fast-convert/src/lib.rs	Public Rust API surface and module wiring.
crates/microsoft-fast-convert/src/html.rs	Hand-scanner for tags/attrs and <f-template>/inner <template> extraction.
crates/microsoft-fast-convert/src/expression.rs	Limited expression grammar conversion + repeat/event scope handling.
crates/microsoft-fast-convert/src/error.rs	Converter error model + contextual error formatting.
crates/microsoft-fast-convert/src/converter.rs	Syntax selection and dispatch after shared template validation.
crates/microsoft-fast-convert/README.md	Crate-level docs for Rust and WASM usage + validation scope.
crates/microsoft-fast-convert/DESIGN.md	Design doc for converter pipeline/modules/targets.
crates/microsoft-fast-convert/Cargo.toml	New crate manifest (bundled with fast-build release).
crates/microsoft-fast-convert/Cargo.lock	New lockfile for converter crate dependencies.
change/@microsoft-fast-build-40280b6e-6a6e-4d63-92ce-3158204cb0e0.json	Beachball change file for @microsoft/fast-build minor feature.
build/scripts/download-github-releases.mjs	Release validation updated to support bundled crate pairing for fast-build.
build/scripts/create-github-releases.mjs	GitHub release creation updated to attach multiple crate assets per package.
beachball.config.js	Version sync updated to bump multiple paired crates for one npm package.
.github/workflows/README.md	Docs updated for bundled fast-build release assets (npm + multiple crates).
.github/workflows/ci-validate-rust.yml	CI updated to run Rust tests for both fast-build and fast-convert crates.