docs(skills): state which record each validation rule type is judged against (#15046)

The rule-type table in skills/objectstack-data/rules/validation.md said what
each type is for and when it fails, but never which record the predicate is
evaluated on -- and the answer is not uniform across the six. An author who
generalises "validations[] holds invariants" reaches for `format` to guard
stored data and silently gets a write gate instead.

Adds one column, "Judged against", each cell measured from evaluateRule's
dispatch in packages/objectql/src/validation/rule-validator.ts:

- script / cross_field  -> ctx.merged, the prior row overlaid with the write
- format / json_schema  -> ctx.data, the write payload, behind a
                           `field in data` guard, so an omitted field is
                           never judged
- state_machine         -> ctx.data value against ctx.previous, same guard;
                           the insert leg checks initialStates instead
- conditional           -> its `when` on ctx.merged, then the nested rule
                           re-dispatched through the same switch

Table only: no prose, heading, example or tool-choice changes. Net lines 0.


Claude-Session: https://claude.ai/code/session_019RfFHiRCSs3JXLK4cwcfox

Co-authored-by: Claude <noreply@anthropic.com>

Author: claude[bot]

skills/objectstack-data/rules/validation.md

@@ -6,14 +6,14 @@ Comprehensive guide for implementing validation rules in ObjectStack.
 
 The **complete** set of `type` discriminators accepted by `ValidationRuleSchema`:
 
-| Type | Purpose | When Validation Fails |
-|:-----|:--------|:---------------------|
-| `script` | CEL predicate over the record | When predicate evaluates to `true` |
-| `state_machine` | Legal state transitions | When transition not allowed |
-| `format` | Regex or built-in format | When format doesn't match |
-| `cross_field` | CEL predicate comparing fields | When predicate evaluates to `true` |
-| `json_schema` | Validate JSON field | When JSON doesn't match schema |
-| `conditional` | Apply nested rule when a predicate holds | When nested rule fails |
+| Type | Purpose | When Validation Fails | Judged against |
+|:-----|:--------|:---------------------|:---------------|
+| `script` | CEL predicate over the record | When predicate evaluates to `true` | Merged record — prior row plus this write |
+| `state_machine` | Legal state transitions | When transition not allowed | Written value vs the prior row's, only when the write sets the field (insert: `initialStates`) |
+| `format` | Regex or built-in format | When format doesn't match | Write payload only — an omitted field is never judged |
+| `cross_field` | CEL predicate comparing fields | When predicate evaluates to `true` | Merged record — prior row plus this write |
+| `json_schema` | Validate JSON field | When JSON doesn't match schema | Write payload only — an omitted field is never judged |
+| `conditional` | Apply nested rule when a predicate holds | When nested rule fails | Its `when` on the merged record; the nested rule as its own type |
 
 There is no other type. In particular: