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## High-level PR Summary
This PR adds support for custom `metadata` to inline products in the
payments system. The change allows developers to attach arbitrary
metadata to products created inline (without pre-configuration), which
Stack Auth will store and return with the product. This enables
applications to associate custom data such as feature flags, reference
IDs, or other application-specific attributes with products. The
implementation adds a new `productSchemaWithMetadata` schema, updates
the product type handling in the backend, and includes comprehensive e2e
tests verifying metadata is persisted and returned correctly through
purchase creation, validation, and listing endpoints.
⏱️ Estimated Review Time: 15-30 minutes
<details>
<summary>💡 Review Order Suggestion</summary>
| Order | File Path |
|-------|-----------|
| 1 | `packages/stack-shared/src/schema-fields.ts` |
| 2 | `apps/backend/src/lib/payments.tsx` |
| 3 |
`apps/e2e/tests/backend/endpoints/api/v1/payments/purchase-session.test.ts`
|
| 4 |
`apps/e2e/tests/backend/endpoints/api/v1/payments/create-purchase-url.test.ts`
|
| 5 |
`apps/e2e/tests/backend/endpoints/api/v1/payments/products.test.ts` |
</details>
[](https://discord.gg/n3SsVDAW6U)
[
<!-- RECURSEML_SUMMARY:END -->
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **New Features**
* Products now support custom metadata (client, client read-only, and
server) and expose these fields in inline product representations.
* Metadata is preserved and propagated through purchase creation,
validation, grants, and owned-product listings so it’s available after
purchase.
* **Tests**
* Added end-to-end tests verifying metadata is accepted, persisted, and
returned in purchase creation, validation, grant, and listing flows.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
<!-- ELLIPSIS_HIDDEN -->
----
> [!IMPORTANT]
> Adds support for custom metadata in inline products, updating schemas
and functions to handle metadata, with comprehensive tests verifying the
changes.
>
> - **Behavior**:
> - Adds support for custom metadata in inline products, allowing
arbitrary metadata attachment.
> - Updates `ensureProductIdOrInlineProduct()` and
`productToInlineProduct()` in `payments.tsx` to handle metadata.
> - Metadata is preserved and returned in purchase creation, validation,
and listing endpoints.
> - **Schemas**:
> - Adds `productSchemaWithMetadata` in `schema-fields.ts` to include
`clientMetadata`, `clientReadOnlyMetadata`, and `serverMetadata`.
> - Updates `inlineProductSchema` to support metadata fields.
> - **Tests**:
> - Adds e2e tests in `purchase-session.test.ts`,
`create-purchase-url.test.ts`, and `products.test.ts` to verify metadata
handling.
>
> <sup>This description was created by </sup>[<img alt="Ellipsis"
src="https://img.shields.io/badge/Ellipsis-blue?color=175173">](https://www.ellipsis.dev?ref=stack-auth%2Fstack-auth&utm_source=github&utm_medium=referral)<sup>
for 1b5601c991. You can
[customize](https://app.ellipsis.dev/stack-auth/settings/summaries) this
summary. It will automatically update as commits are pushed.</sup>
<!-- ELLIPSIS_HIDDEN -->
---------
Co-authored-by: Konsti Wohlwend <n2d4xc@gmail.com>
6d9c2b1fea