jsonschema: pre-compile regexps

This is the first CL that deals with the process of preparing a schema for validation.

Perform some basic checks on the scheme. Along the way, compile regexps and store
them in the schema for use during validation.

Change-Id: I0e5e6ce28656dcecb6d2d4b2fdc98998fa05b6f1
Reviewed-on: https://go-review.googlesource.com/c/tools/+/669696
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Alan Donovan <adonovan@google.com>

internal/jsonschema/resolve_test.go

@@ -0,0 +1,37 @@
+// Copyright 2025 The Go MCP SDK Authors. All rights reserved.
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file.
+
+package jsonschema
+
+import (
+	"regexp"
+	"testing"
+)
+
+func TestCheckLocal(t *testing.T) {
+	for _, tt := range []struct {
+		s    *Schema
+		want string // error must be non-nil and match this regexp
+	}{
+		{nil, "nil"},
+		{
+			&Schema{Pattern: "]["},
+			"regexp",
+		},
+		{
+			&Schema{PatternProperties: map[string]*Schema{"*": nil}},
+			"regexp",
+		},
+	} {
+		_, err := tt.s.Resolve()
+		if err == nil {
+			t.Errorf("%s: unexpectedly passed", tt.s.json())
+			continue
+		}
+		if !regexp.MustCompile(tt.want).MatchString(err.Error()) {
+			t.Errorf("%s: did not match\nerror: %s\nregexp: %s",
+				tt.s.json(), err, tt.want)
+		}
+	}
+}