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Rich Harris 2287ad005a fix: detect and error on non-idempotent each block keys in dev mode (#17732 ) ## Summary Fixes #17721 In dev mode, detect when a keyed each block has a key function that returns different values when called multiple times for the same item (non-idempotent). This catches the common mistake of using array literals like `[thing.group, thing.id]` as keys, which creates a new array object each time and will never match by reference. - Adds new `each_key_volatile` error with helpful message explaining the issue - Checks key idempotency in the each block loop during dev mode - Provides a clear error instead of the cryptic "Cannot read properties of undefined" that occurred previously --------- Co-authored-by: 7nik <kifiranet@gmail.com>	2 days ago
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docs	fix: detect and error on non-idempotent each block keys in dev mode (#17732 )	2 days ago

fix: detect and error on non-idempotent each block keys in dev mode (#17732 )

## Summary

Fixes #17721

In dev mode, detect when a keyed each block has a key function that
returns different values when called multiple times for the same item
(non-idempotent). This catches the common mistake of using array
literals like `[thing.group, thing.id]` as keys, which creates a new
array object each time and will never match by reference.

- Adds new `each_key_volatile` error with helpful message explaining the
issue
- Checks key idempotency in the each block loop during dev mode
- Provides a clear error instead of the cryptic "Cannot read properties
of undefined" that occurred previously

---------

Co-authored-by: 7nik <kifiranet@gmail.com>

docs

fix: detect and error on non-idempotent each block keys in dev mode (#17732 )