fix(schema): widen explanation.maxLength to 2000 (was 1000)

CHANGELOG.md

@@ -25,9 +25,10 @@ A fifth language-learning exercise idea surfaced a gap the existing "extra
 text" fields do not cover: `hint` is shown on demand before/during answering,
 `examples` are worked examples shown before answering that must not spoil it,
 and neither fits "explain the French word-order rule AFTER the learner
-answers". `Exercise` gains an optional `explanation` (Markdown, max 1000
-chars, mirrors `hint`'s shape) - not restricted to any exercise type, like
-`hint` itself.
+answers". `Exercise` gains an optional `explanation` (Markdown, max 2000
+chars - twice `hint`'s 1000, since Markdown structure eats characters
+faster than a single-line nudge) - not restricted to any exercise type,
+like `hint` itself.
 
 `x-schema-version` `1.12` -> `1.13` in both schemas (lesson + content-manifest
 move in lockstep, established convention). Additive: content without the new

docs/lesson-format.md

@@ -243,7 +243,7 @@ see [Stable identity](#stable-identity-stable_id)).
 
 ### Explanation (post-answer)
 
-`explanation` (string \| null, max 1000 chars, schema v1.13) is Markdown
+`explanation` (string \| null, max 2000 chars, schema v1.13) is Markdown
 explaining WHY the answer/grammar is what it is - a French word-order rule, a
 grammatical case, a spelling exception. Timing is what distinguishes it from
 the other three "extra text" fields:

schema/lesson.schema.json

@@ -412,15 +412,15 @@
         "explanation": {
           "anyOf": [
             {
-              "maxLength": 1000,
+              "maxLength": 2000,
               "type": "string"
             },
             {
               "type": "null"
             }
           ],
           "default": null,
-          "description": "Optional Markdown explanation of WHY the answer/grammar is what it is (e.g. word order, a grammatical case), shown AFTER the learner answers - regardless of correct or incorrect - unlike ``hint`` (on demand, before/during answering) and ``examples`` (worked examples shown before answering, must not spoil it). Not restricted to any exercise type. Additive; schema_version 1.13.",
+          "description": "Optional Markdown explanation of WHY the answer/grammar is what it is (e.g. word order, a grammatical case), shown AFTER the learner answers - regardless of correct or incorrect - unlike ``hint`` (on demand, before/during answering) and ``examples`` (worked examples shown before answering, must not spoil it). 2000 chars, twice ``hint``'s 1000: Markdown structure (a short list, bold terms) eats characters faster than a single-line nudge, and a real \"why\" often runs longer than a hint. Not restricted to any exercise type. Additive; schema_version 1.13.",
           "title": "Explanation"
         },
         "ext_payload": {

src/__fixtures__/schema-baseline/lesson.schema.json

@@ -412,15 +412,15 @@
         "explanation": {
           "anyOf": [
             {
-              "maxLength": 1000,
+              "maxLength": 2000,
               "type": "string"
             },
             {
               "type": "null"
             }
           ],
           "default": null,
-          "description": "Optional Markdown explanation of WHY the answer/grammar is what it is (e.g. word order, a grammatical case), shown AFTER the learner answers - regardless of correct or incorrect - unlike ``hint`` (on demand, before/during answering) and ``examples`` (worked examples shown before answering, must not spoil it). Not restricted to any exercise type. Additive; schema_version 1.13.",
+          "description": "Optional Markdown explanation of WHY the answer/grammar is what it is (e.g. word order, a grammatical case), shown AFTER the learner answers - regardless of correct or incorrect - unlike ``hint`` (on demand, before/during answering) and ``examples`` (worked examples shown before answering, must not spoil it). 2000 chars, twice ``hint``'s 1000: Markdown structure (a short list, bold terms) eats characters faster than a single-line nudge, and a real \"why\" often runs longer than a hint. Not restricted to any exercise type. Additive; schema_version 1.13.",
           "title": "Explanation"
         },
         "ext_payload": {

src/types/lesson-schema.generated.ts

@@ -216,7 +216,7 @@ export type Distractors = string[];
  */
 export type Examples1 = InlineExample[] | null;
 /**
- * Optional Markdown explanation of WHY the answer/grammar is what it is (e.g. word order, a grammatical case), shown AFTER the learner answers - regardless of correct or incorrect - unlike ``hint`` (on demand, before/during answering) and ``examples`` (worked examples shown before answering, must not spoil it). Not restricted to any exercise type. Additive; schema_version 1.13.
+ * Optional Markdown explanation of WHY the answer/grammar is what it is (e.g. word order, a grammatical case), shown AFTER the learner answers - regardless of correct or incorrect - unlike ``hint`` (on demand, before/during answering) and ``examples`` (worked examples shown before answering, must not spoil it). 2000 chars, twice ``hint``'s 1000: Markdown structure (a short list, bold terms) eats characters faster than a single-line nudge, and a real "why" often runs longer than a hint. Not restricted to any exercise type. Additive; schema_version 1.13.
  */
 export type Explanation = string | null;
 /**

src/validate.test.ts

@@ -458,12 +458,12 @@ describe("schema 1.13 — explanation on exercises (idea 5: post-answer 'why')",
     expect(validateLesson(lessonWithExplanation(null)).valid).toBe(true);
   });
 
-  it("boundary: rejects an explanation longer than 1000 characters", () => {
-    expect(validateLesson(lessonWithExplanation("x".repeat(1001))).valid).toBe(false);
+  it("boundary: rejects an explanation longer than 2000 characters", () => {
+    expect(validateLesson(lessonWithExplanation("x".repeat(2001))).valid).toBe(false);
   });
 
-  it("boundary: accepts an explanation at exactly 1000 characters", () => {
-    expect(validateLesson(lessonWithExplanation("x".repeat(1000))).valid).toBe(true);
+  it("boundary: accepts an explanation at exactly 2000 characters", () => {
+    expect(validateLesson(lessonWithExplanation("x".repeat(2000))).valid).toBe(true);
   });
 
   it("is not restricted to one exercise type: a matching exercise may carry it too", () => {