Add changeset for Zod union deduplication fix

Co-authored-by: mrlubos <[email protected]>

Author: Copilot

.changeset/fix-zod-union-deduplication.md

@@ -0,0 +1,13 @@
+---
+"@hey-api/openapi-ts": patch
+---
+
+Fix Zod schema union deduplication by including validation constraints in type ID
+
+The Zod plugin was incorrectly deduplicating schemas with different validation constraints when using `anyOf`, resulting in incomplete union schemas. This fix ensures that schemas with different validation constraints (like `minLength`, `maxLength`, `minimum`, `maximum`, `pattern`, etc.) are properly preserved in unions.
+
+For example, with an `anyOf` containing strings with different length constraints:
+- Before: `z.string().length(5)` (incorrect - only one constraint)
+- After: `z.union([z.string().length(5), z.string().length(2)])` (correct - proper union)
+
+Fixes issue where the `deduplicateSchema` function was only considering `$ref`, `type`, `const`, and `format` when creating type identifiers, but ignored validation constraints.