[sleitor]

Fixes #703

Summary

Projects with exactOptionalPropertyTypes enabled couldn't forward a possibly-undefined value to <Streamdown>'s optional props (e.g. isAnimating={streaming} where streaming?: boolean) because they were declared as prop?: T rather than prop?: T | undefined.

This adds | undefined to the optional properties of the public types. It is types-only and a no-op for consumers without the flag.

• packages/streamdown/index.tsx: StreamdownProps, ControlsConfig / CopyControlConfig, LinkSafetyConfig, MermaidOptions, StreamdownContextType, BlockProps
• lib/plugin-types.ts, lib/shiki-types.ts: highlighter/plugin/theme types, PluginConfig, CustomRendererProps
• lib/markdown.ts (Options, Components), lib/animate.ts (AnimateOptions), lib/icon-context.tsx (IconComponent)
• packages/remend/src/index.ts: RemendOptions / RemendHandler (passed through the remend prop)

Type test

Adds packages/streamdown/type-tests/exact-optional-property-types.tsx plus tsconfig.exact-optional.json, run via pnpm check-types:exact-optional in packages/streamdown. It type-checks forwarding undefined to optional props against the built .d.ts with exactOptionalPropertyTypes: true.

Test plan

• pnpm biome check passes
• pnpm test passes (1310 tests)
• pnpm check-types:exact-optional passes
• Changeset added

[vercel]

@sleitor is attempting to deploy a commit to the Vercel Team on Vercel.

A member of the Team first needs to authorize it.

[farnabaz]

LGTM, Thanks