docs(tailordb): document hook _newValue/_oldValue and _newData/_oldData

[toiroakr]

Summary

Documents the new TailorDB hook variables that expose this request's raw input and the pre-operation value, so update hooks can tell what the user actually sent apart from the existing record.

• _newValue / _oldValue — this field's raw input / previous value (JS + CEL)
• _newData.{field} / _oldData.{field} — sibling fields of the request input / previous record (CEL only)

_value / _data are unchanged (still the merged state). Backed by platform-core-services#12177.

⚠️ Draft — blocked on SDK support

This is intentionally a draft. Right now the new variables are only usable via the raw expression string forms (Terraform .tf, CUE, CEL *_expr), which is what the examples here use, because those map directly to the backend script runtime.

The TypeScript SDK callback form is not yet supported: @tailor-platform/sdk's HookFn currently only destructures { value, data, user } (packages/sdk/src/configure/services/tailordb/types.ts). Before this page can show .ts examples like ({ newValue, oldValue }) => ..., the SDK needs a matching change (extend HookFn + the hook→script compiler). Tracking that as a prerequisite follow-up.

Open items before un-drafting

• tailor-platform/sdk: expose newValue / oldValue / newData / oldData in the hook callback context, then add .ts examples to mirror the .tf ones here
• Decide whether to also document type-level hooks / type validate (_input / _newData / _oldData / _oldData on type validate), which are currently undocumented on this page

🤖 Generated with Claude Code

[toiroakr]

Not needed for now: hook reference docs are synced from the SDK repo (docs/sdk/ via sdk-docs-sync). The new variables should be documented in tailor-platform/sdk alongside the HookFn change, which then syncs over. Closing; will fold into the SDK change.