svelte

This is a follow-up to #17852. I was expecting it to resolve an issue that manifests in production, but somehow between my initial debugging and the merged fix something diverged and the issue still reproduces. Video of issue that prompted the original pr as well as this one: Before: https://github.com/user-attachments/assets/00847fe1-ed69-42ce-825f-700cbcd50e26 With this fix: https://github.com/user-attachments/assets/1932d049-82a6-4bd8-805a-2aed474b67f0 AI Explanation** When a branch effect (, ) is destroyed, deriveds inside it must not re-evaluate — the branch scope is gone and computed values will be stale or throw. The immediate trigger was bind:this teardown: destroying a component with bind:this schedules a microtask that calls get_value on the element binding. If the bound element was inside a child component rendered from a derived in an block that just became false, the derived would re-run with undefined and crash (e.g. calling on undefined). Root cause: returns null for destroyed parent effects, so sees and proceeds to re-evaluate. The fix walks the .parent chain directly to detect whether the nearest non-derived ancestor is a that has been , and returns the cached value instead. Tests: adds a component integration test (runtime-runes) that exercises the exact pattern, and a low-level signal unit test that directly sets up the block → branch → derived teardown sequence to confirm no re-evaluation occurs after destruction. Before submitting the PR, please make sure you do the following [ ] It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs [x] Prefix your PR title with , , , or . [x] This message body should clearly illustrate what problems it solves. [x] Ideally, include a test that fails without this PR but passes with it. [x] If this PR changes code within , add a changeset (). Tests and linting [x] Run the tests with and lint the project with