[Preview NG] Replace deprecated ChangeHandler with typed onChange signatures

[jeremywiebe]

Summary:

This PR is part of a series building a typed, hook-based preview system for the Perseus editor. The new system replaces the untyped window.iframeDataStore + raw postMessage(string) communication with structured, validated message passing via usePreviewController and usePreviewPresenter hooks. The new system is being built alongside the old one — no existing behavior changes until the final PR in the series flips the switch.

Previous PRs in this series:

• [Preview NG] Type findWidgets functions and add JSDoc to HintRenderer props #3464
• [Preview NG] Remove unused bold support from hint preview #3467
• [Preview NG] Add typed preview message protocol with validators #3474
• [Preview NG] Add functions to sanitize objects for sending to Preview #3492
• [Preview NG] Introduce hooks to manage preview communication #3495
• [Preview NG] Export preview system hooks from @khanacademy/perseus-editor #3499
• [Preview NG] Add PreviewWithIframe component #3578
• [Preview NG] Migrate Perseus to the new preview system #3581

--

Editor and ArticleEditor were using ChangeHandler (and Changeable.ChangeableProps), a deprecated signature whose callback and silent parameters were dead code throughout the codebase. This replaces both with concrete typed signatures so they are accurate and don't include data that the editor doesn't actually dispatch.

Note: This change ripples in a few places worth flagging in review. Inside ArticleEditor, removing Changeable.ChangeableProps lets us drop the local RendererProps shim type that existed only to widen the parameter; the affected helpers (_updateIssues, _sections, _handleEditorChange, _apiOptionsForSection, getSaveWarnings) now use PerseusRenderer / PerseusArticle directly. In editor.tsx, two props.onChange call sites previously used the trailing callback parameter to position the cursor after a synchronous text replacement; that side-effect is dropped here because no caller actually wired it through, and the cursor positioning code wasn't reachable in practice.

Issue: LEMS-3741

Test plan:

• pnpm tsc
• pnpm test
• pnpm lint

[github-actions]

🗄️ Schema Change: No Changes ✅

[github-actions]

npm Snapshot: Published

Good news!! We've packaged up the latest commit from this PR (69a91a1) and published it to npm. You
can install it using the tag PR3588.

Example:

pnpm add @khanacademy/perseus@PR3588

If you are working in Khan Academy's frontend, you can run the below command.

./dev/tools/bump_perseus_version.ts -t PR3588

If you are working in Khan Academy's webapp, you can run the below command.

./dev/tools/bump_perseus_version.js -t PR3588

[github-actions]

Size Change: -76 B (-0.02%)

Total Size: 503 kB

📦 View Changed

Filename	Size	Change
packages/perseus-editor/dist/es/index.js	104 kB	-76 B (-0.07%)

ℹ️ View Unchanged

Filename	Size
packages/kas/dist/es/index.js	20.6 kB
packages/keypad-context/dist/es/index.js	1 kB
packages/kmath/dist/es/index.js	6.31 kB
packages/math-input/dist/es/index.js	98.5 kB
packages/math-input/dist/es/strings.js	1.61 kB
packages/perseus-core/dist/es/index.item-splitting.js	12 kB
packages/perseus-core/dist/es/index.js	25.5 kB
packages/perseus-linter/dist/es/index.js	9.41 kB
packages/perseus-score/dist/es/index.js	9.78 kB
packages/perseus-utils/dist/es/index.js	403 B
packages/perseus/dist/es/index.js	198 kB
packages/perseus/dist/es/strings.js	8.5 kB
packages/pure-markdown/dist/es/index.js	1.39 kB
packages/simple-markdown/dist/es/index.js	6.71 kB

_{compressed-size-action}

[github-actions]

🛠️ Item Splitting: No Changes ✅

[claude]

Claude Code Review

This repository is configured for manual code reviews. Comment @claude review to trigger a review and subscribe this PR to future pushes, or @claude review once for a one-time review.

_{Tip: disable this comment in your organization's Code Review settings.}