fix(race): read result validity before Merge redeems it to the pool (#260)

validateRequiredDefinitions read red.IsValid() *after* res.Merge(red).
Merge redeems a result whose wantsRedeemOnMerge is set (true for any
pool-borrowed result) back into the process-global sync.Pool. Reading
red after that point races with a concurrent Spec() goroutine borrowing
the same *Result and calling cleared() on it.

This surfaced as a rare data race under -race in Test_ParallelPool:

  Write at ... Result.cleared() <- resultsPool.BorrowResult()
  Previous read ... Result.IsValid() <- validateRequiredDefinitions

Capture validity into a local before merging, matching the read-before-
merge pattern used everywhere else (e.g. validateRequiredProperties,
default/example validators).

Signed-off-by: Frederic BIDON <fredbi@yahoo.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: fredbi

spec.go

@@ -554,8 +554,12 @@ DEFINITIONS:
 		if schema.Required != nil { // Safeguard
 			for _, pn := range schema.Required {
 				red := s.validateRequiredProperties(pn, d, &schema) //#nosec
+				// NOTE: capture validity before merging: Merge may redeem `red` to the
+				// pool (wantsRedeemOnMerge), after which reading it races with a concurrent
+				// BorrowResult().cleared() in another goroutine sharing the global pool.
+				isValid := red.IsValid()
 				res.Merge(red)
-				if !red.IsValid() && !s.Options.ContinueOnErrors {
+				if !isValid && !s.Options.ContinueOnErrors {
 					break DEFINITIONS // there is an error, let's stop that bleeding
 				}
 			}