onPageRendered: page.html is undefined for some pages during alloy dev initial build

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Description

During alloy dev initial build, some pages arrive at onPageRendered with page.html set to undefined (JavaScript) instead of an empty string or the rendered HTML.

Steps to reproduce

1. Register an onPageRendered hook with the v0.6.0 object API:

   alloy.hook("onPageRendered", {}, (page) => {
     // page.html is undefined for some pages
     if (page.html.includes('something')) { ... }
   });

2. Run alloy dev on a site with many pages (e.g., RHDS with 820 pages)
3. The initial build fails with:

   TypeError: cannot read property 'includes' of undefined
       at <anonymous> (01-transforms.js:7:36)
   

Expected behavior

page.html should always be a string (empty "" is fine, undefined is not). The HookRenderedPayload struct uses json:"html" without omitempty, so Go should always serialize the field.

Workaround

Guard against undefined:

alloy.hook("onPageRendered", {}, (page) => {
  if (!page.html) return page;
  // ... transform page.html
});

Notes

• alloy build works fine — the issue only appears during alloy dev initial build
• The error occurs on "item 0" suggesting it may affect the first page in the batch
• buildPageRenderedPayload() calls page.HTML() which returns empty string for nil RenderedBody — so the Go side should be sending "", not omitting the field

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Investigation: Bug cannot exist in current codebase

Traced every code path from page rendering through hook dispatch to JavaScript runtime delivery. The described bug is not plausible.

Every link in the chain guarantees html is a string

Step	Code location	What happens	Result
1. Page rendering	content/page.go:55-60	page.HTML() returns p.renderedStr; when RenderedBody is nil, returns "" (Go zero value)	Always string
2. Payload construction	pipeline/hooks.go:521-533	buildPageRenderedPayload() sets HTML: page.HTML()	Always string
3. Struct definition	plugin/payload.go:27-32	HookRenderedPayload uses json:"html" — no omitempty	Key always serialized
4. JSON serialization	sonic Marshal()	"" serializes to "html":"" in JSON	Key always present
5. JS deserialization	JSON.parse(...) in QuickJS/Node	{"html":""} parses to {html: ""}	Always string in JS

No architectural difference between build and dev

The claim that "only alloy dev is affected" doesn't hold:

• alloy dev initial build calls the same pipeline.Build() function
• Build() creates its own internal plugin registry, runs the full pipeline, dispatches onPageRendered hooks, then defers registry.Close() — identical lifecycle to alloy build
• The only difference is SkipSSR: true, which doesn't affect rendered-page hook dispatch

No race conditions

• Payloads are built after all rendering workers finish (worker pool awaited at build.go:878-885, hooks dispatched at line 889)
• ReleaseRenderedBody() happens after dispatchPostRenderHooks() returns
• Batch dispatch in Node distributes across goroutines but each operates on separate indices

Possible explanation: HookPagePayload confusion

HookPagePayload (used for onPagesReady/onContentLoaded, not onPageRendered) does have json:"html,omitempty" — which omits the key for empty strings, producing undefined in JS. If the reporter confused which hook was being called, or if their plugin registers for onPagesReady and accesses page.html there, that would explain the behavior.

Recommendation

This needs a minimal reproduction to proceed. The reporter may be hitting a plugin-side bug, or confusing onPagesReady (which uses omitempty and legitimately produces undefined for empty HTML) with onPageRendered (which doesn't).