fix(solid-query): prevent lost updates when mounting cached queries

[2wheeh]

fixes #11384

🎯 Changes

Fixes a Solid Query timing issue where updates could be lost when a cached query refetched during mount.

Observer attachment is deferred until the conditional subtree is ready, while the optimistic fetch status remains available synchronously. Regression tests cover the behavior in both browser and semantic tests.

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Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-10T03:36:27.829358Z	9d49169	Draft marked ready

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