Fix site editor crash when query loop has multiple post-templates

[mattheu]

Problem

Opening any template in the site editor that contains a pattern with a core/query block having two or more core/post-template children crashes the editor with a TypeError. The AGBI opinion archive template reproduces this via the editors-pick-opinion pattern, which uses a two-column layout (1 featured card + 4 grid cards) inside a single query.

Root cause

withQueryLoopContextProvider populates UsedPostsContext by calling:

return childPostTemplatesClientIds.map( getBlock );

getBlock() can transiently return null in the site editor when a pattern block's inner blocks are registered in the block-name index before their full record is written to byClientId (the two store structures are updated in separate microtasks during initial block-tree construction). This leaves null values in the postTemplates array.

Both withPostTemplateStyles and withPostTemplateInspectorControls then iterate postTemplates and access postTemplate.clientId without a null guard — throwing TypeError: Cannot read properties of null (reading 'clientId') and crashing the editor.

This was masked in ≤ 0.4.x because withUniqueQueryId always called setAttributes on first render, forcing a store update + re-render cycle that resolved the transient null state before any consumer ran. The 0.7.0 fix (preserve unique queryIds) eliminated that forced re-render, exposing the latent race.

Fix

1. Filter nulls from getBlock() results in withQueryLoopContextProvider so consumers always receive valid block objects:

   return childPostTemplatesClientIds.map( getBlock ).filter( Boolean );

2. Guard the hideAfterLimit CSS rule against perPage = undefined: without a perPage limit the expression offset + undefined + 2 evaluates to NaN, producing the invalid selector nth-of-type(n+NaN). Suppress the rule entirely when no limit is set (correct behaviour — if there's no limit, no posts should be hidden).

Testing

• Open the site editor and edit a template that embeds a pattern containing a core/query with two core/post-template children
• Editor should load without crashing
• Inspector controls for each post-template should show correctly
• Post-template CSS offset/limiting should still function for templates where perPage is set

🤖 Generated with Claude Code

[github-actions]

Playwright test results

 19 passed

Details

 19 tests across 6 suites
 1 minute, 18 seconds
 9603440