fix: hydrate strict event arguments in repeat scopes

[Mohamed Mansour (mohamedmansour)]

Summary

• Tighten WebUI event handler argument parsing so malformed calls fail at compile time instead of being silently normalized.
• Align @microsoft/webui-framework with the new strict event metadata contract: argSpecs arrays only, event target paths embedded in e[], and no legacy needsEvent / el[] compatibility path.
• Fix SSR hydration for scoped event arguments in repeated blocks, including multi-root repeat bodies and initially empty text bindings.
• Update DESIGN.md, docs/, and framework docs to describe the new event hydration and argument-resolution behavior.

Why

PR #317 added support for passing repeat-scope values to event handlers. Since that change is already merged to main and backward compatibility is not required, this follow-up locks down the new contract, rejects ambiguous handler syntax, and ensures SSR hydration wires scoped event handlers consistently.

Validation

• cargo test -p microsoft-webui-parser
• cd packages/webui-framework && pnpm test:unit && pnpm typecheck:e2e && pnpm exec playwright test tests/fixtures/list/list.spec.ts
• cd docs && pnpm build
• cargo xtask check

[Copilot]

Pull request overview

This PR tightens the cross-layer event binding contract (parser output → template metadata types → framework hydration) by making event handler arguments strictly parsed and consistently encoded, and by improving SSR hydration for repeat-scope event arguments and tricky repeat bodies.

Changes:

• Enforce strict event handler syntax in the Rust compiler (reject trailing tokens, invalid handler names, malformed args) and emit argSpecs as arrays consistently.
• Remove legacy event metadata shapes in the framework types/docs and embed event target paths directly in e[] entries.
• Fix SSR hydration edge cases: repeat-scoped event argument wiring in repeat blocks (including multi-root repeat bodies) and initially-empty text bindings.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
packages/webui-framework/src/template.ts	Removes mention of legacy el event-target table from template meta docs.
packages/webui-framework/src/template-types.ts	Makes CompiledEventArgs strictly an array shape (drops number legacy encoding).
packages/webui-framework/src/element.ts	Updates SSR hydration logic (text-node fallback insertion, repeat multi-root hydration path) and optimizes event listener wiring for common arg shapes.
packages/webui-framework/RENDERING.md	Updates runtime metadata documentation to reflect e[] carrying both args and target paths.
packages/webui-framework/README.md	Updates public docs/examples to the new strict event-call syntax and event metadata encoding.
docs/guide/concepts/interactivity.md	Documents repeat-scope values and supported event handler argument forms.
docs/guide/concepts/how-it-works.md	Notes that events are attached with compiled argument scopes during hydration.
docs/ai.md	Updates AI reference examples and guidance for event handler arguments and repeat-scope support.
DESIGN.md	Updates the specification to match the new event metadata and hydration behavior.
crates/webui-parser/src/plugin/webui.rs	Implements strict event handler parsing, validates handler/path grammar, updates root-event encoding, and adds regression tests.