math: heal overescaped LaTeX commands in question displays

src/core/tool-parts.ts

@@ -30,7 +30,7 @@
 import { Value } from "typebox/value";
 import type { TSchema } from "typebox";
 import { quizDisplayInputSchema, askInputSchema, askOptionProblems, quizInputProblems, explainInputProblems, explainDisplayInputSchema, type AskToolInput, type QuizToolInput, type ExplainToolInput } from "./question-core.ts";
-import { restoreMathEscapes } from "./math-delims.ts";
+import { restoreMathEscapes, healOverescapedCommands } from "./math-delims.ts";
 import { healEncodedArguments } from "./argument-heal.ts";
 import { probeDoneInputSchema, type ProbeDoneInput } from "./contracts/probe.ts";
 
@@ -72,9 +72,14 @@ function boundaryParse<T>(schema: TSchema, input: unknown): T | undefined {
  *  single-backslash LaTeX eaten by JSON escape resolution (FF ate the 'f' of
  *  \forall, VT the 'v' of \varphi, TAB the 't' of \to) survives to the
  *  display path. This is the ONE seam every rendered question passes
- *  through — new turns and already-poisoned records alike heal here. */
+ *  through — new turns and already-poisoned records alike heal here.
+ *  healOverescapedCommands (owner ruling 2026-10-15) rides the same walk:
+ *  the same models also stochastically DOUBLE command backslashes
+ *  (`\\nabla` saved where `\nabla` was meant — KaTeX shows the row break
+ *  plus "nabla" as letters), so even runs before a command start inside
+ *  balanced math spans collapse to one backslash. */
 function restoreMathEscapesDeep(value: unknown): unknown {
-	if (typeof value === "string") return restoreMathEscapes(value);
+	if (typeof value === "string") return healOverescapedCommands(restoreMathEscapes(value));
 	if (Array.isArray(value)) return value.map(restoreMathEscapesDeep);
 	if (typeof value === "object" && value !== null) {
 		const out: Record<string, unknown> = {};