What is it?

• Bug

Description

When a component throws a promise on first client render (e.g. a library resolving QRLs by throwing, like formisch's useResolvedQrl) and the promise resolution writes a signal the component already subscribed to, the component is diffed a second time before its child component has rendered its <Slot />. At that point the child host has no children yet, so descend() flips $isCreationMode$ on, and the sticky flag leaks into the existing projection from the first pass. expectElement then blindly re-creates plain element children instead of matching them (components survive because expectComponent matches by hash), and a trailing component sibling jumps the cursor past the stale element so expectNoMore never cleans it up — leaving duplicated DOM.

Symptom in an app: form fields rendered twice on every first SPA navigation to a route, correct again when revisiting (cached QRLs resolve synchronously, so nothing throws).

The fix: a projection never inherits creation mode from the surrounding level — an existing projection keeps its children across re-renders, so they must be diffed against, never re-created; it is in creation mode only when new or empty. Handled in descend() via an isProjection param (replacing shouldExpectNoChildren, which was already projection-only). Regression tests cover default and named slots; both fail without the behavior change.

Checklist

• My code follows the developer guidelines of this project
• I performed a self-review of my own code
• I added a changeset with pnpm change
• I added new tests to cover the fix / functionality