Fix combat advisor schema mismatch — accept "creatures" alias for add

The real cause of the advisor falling back to deterministic: DeepSeek returns
the additions array under the key "creatures" (nudged by the prompt wording
"the creatures to add"), but the schema requires "add" — so safeParse failed.

- Spell out the exact JSON keys in the prompt ("add", not "creatures"/"monsters").
- Normalize creatures/monsters/additions aliases to "add" before validation, so
  a correct suggestion isn't discarded over a key-name synonym.
- Regression test using DeepSeek's exact wild payload.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/assistant/prompts.test.ts

@@ -49,4 +49,17 @@ describe('balanceSuggestionSchema', () => {
     expect(r.success).toBe(true);
     if (r.success) expect(r.data.add[0]!.count).toBe(2);
   });
+  it('accepts the "creatures" alias some models use for the add array', () => {
+    // Exact shape DeepSeek returned in the wild — array keyed "creatures", not "add".
+    const r = balanceSuggestionSchema.safeParse({
+      creatures: [{ name: 'Berserker', count: 1 }],
+      reasoning: 'Adding one CR 2 Berserker makes this deadly for a lone level 1 paladin.',
+      targetDifficulty: 'deadly',
+    });
+    expect(r.success).toBe(true);
+    if (r.success) {
+      expect(r.data.add).toHaveLength(1);
+      expect(r.data.add[0]!.name).toBe('Berserker');
+    }
+  });
 });

src/lib/assistant/prompts.ts

@@ -7,7 +7,23 @@ import type { CampaignContext, CreatureCandidate } from './context';
 // over-eager suggestion is accepted rather than rejecting the whole response.
 const monsterCount = z.coerce.number().int().min(1).max(12);
 
-export const balanceSuggestionSchema = z.object({
+/**
+ * Models sometimes name the additions array "creatures"/"monsters" instead of the
+ * expected "add" (DeepSeek does this). Normalize those synonyms before validation
+ * so a correct suggestion isn't discarded over a key-name mismatch.
+ */
+function normalizeBalanceShape(raw: unknown): unknown {
+  if (!raw || typeof raw !== 'object' || Array.isArray(raw)) return raw;
+  const o = { ...(raw as Record<string, unknown>) };
+  if (o.add === undefined) {
+    for (const alias of ['creatures', 'monsters', 'additions', 'addCreatures', 'add_creatures']) {
+      if (Array.isArray(o[alias])) { o.add = o[alias]; break; }
+    }
+  }
+  return o;
+}
+
+export const balanceSuggestionSchema = z.preprocess(normalizeBalanceShape, z.object({
   reasoning: z.string(),
   add: z.array(z.object({
     name: z.string(),
@@ -20,7 +36,7 @@ export const balanceSuggestionSchema = z.object({
     count: monsterCount,
   })).optional(),
   targetDifficulty: z.string(),
-});
+}));
 export type BalanceSuggestion = z.infer<typeof balanceSuggestionSchema>;
 
 function partyLine(ctx: CampaignContext): string {
@@ -38,10 +54,14 @@ export function buildBalancePrompt(
   const system =
     `${ctx.systemConstraint}\n\n` +
     `You are an encounter-balancing assistant for a ${ctx.systemLabel} game master. ` +
-    `Recommend which creatures to ADD to the current encounter to bring it to roughly "${current.targetDifficulty}" difficulty. ` +
+    `Recommend which creatures to add to the current encounter to bring it to roughly "${current.targetDifficulty}" difficulty. ` +
     `You MUST choose only from the provided candidate creatures (by exact name). Do not invent creatures or use any from another system. ` +
-    `Prefer 1–3 distinct creatures with sensible counts. Keep the reasoning to one or two sentences. ` +
-    `Each "count" must be a plain integer (e.g. 2, not "2"). Always include "reasoning" and "targetDifficulty".`;
+    `Prefer 1–3 distinct creatures with sensible counts.\n\n` +
+    `Respond with a JSON object with EXACTLY these keys:\n` +
+    `  "add": array of objects, each { "name": <exact candidate name>, "count": <integer ≥ 1> }\n` +
+    `  "reasoning": a one or two sentence string\n` +
+    `  "targetDifficulty": the target difficulty as a string\n` +
+    `Name the array "add" — not "creatures" or "monsters". Counts are plain integers (2, not "2").`;
 
   const candidateList = current.candidates
     .map((c) => `- ${c.name} (rating ${c.rating}${c.hp ? `, hp ${c.hp}` : ''}${c.ac ? `, ac ${c.ac}` : ''})`)
@@ -52,7 +72,7 @@ export function buildBalancePrompt(
     `Current encounter difficulty: ${current.difficulty}.\n` +
     `Target difficulty: ${current.targetDifficulty}.\n\n` +
     `Candidate creatures (choose only from these):\n${candidateList}\n\n` +
-    `Respond with the creatures to add (name + count), a short reasoning, and the targetDifficulty.`;
+    `Return the JSON object described above (keys: "add", "reasoning", "targetDifficulty").`;
 
   return { system, user };
 }