Use structured JSON output for local model classification

Bouncer/src/background/local-model.ts

@@ -26,6 +26,19 @@ const DOWNLOAD_RETRY_DELAY_MS = 2000;
 // Keys that belong on the ModelRecord (appConfig), not chatOpts.
 const MODEL_RECORD_KEYS = new Set(['model', 'model_lib', 'model_type']);
 
+/** JSON schema for structured classification output from local models. */
+const CLASSIFICATION_RESPONSE_FORMAT = {
+  type: 'json_object' as const,
+  schema: JSON.stringify({
+    type: 'object',
+    properties: {
+      reasoning: { type: 'string' },
+      match: { type: ['string', 'null'] },
+    },
+    required: ['reasoning', 'match'],
+  }),
+};
+
 // ==================== Pure helpers ====================
 
 // Build both the appConfig (ModelRecord for CreateMLCEngine) and chatOpts
@@ -63,6 +76,22 @@ export function parseLocalModelResponse(rawResponse: string | null): { shouldHid
     return { shouldHide: false, reasoning: 'Empty model response — model returned no output' };
   }
 
+  // Try JSON structured output first
+  try {
+    const parsed = JSON.parse(rawResponse);
+    if (typeof parsed === 'object' && parsed !== null && 'reasoning' in parsed) {
+      const match = parsed.match;
+      const shouldHide = typeof match === 'string' && match.length > 0 && match !== 'null';
+      const reasoning = shouldHide
+        ? `${parsed.reasoning} (Matched: ${match})`
+        : String(parsed.reasoning);
+      return { shouldHide, reasoning };
+    }
+  } catch {
+    // Not JSON — fall through to regex parsing
+  }
+
+  // Fallback: freeform text parsing (backward compatibility)
   let reasoning = rawResponse;
   let shouldHide = false;
 
@@ -324,9 +353,10 @@ export class LocalEngine {
   async generate(
     messages: ChatMessage[],
     maxTokens: number,
-    { priority = 0, temperature, onStart }: { priority?: number; temperature?: number; onStart?: () => void } = {}
+    { priority = 0, temperature, onStart, responseFormat }: { priority?: number; temperature?: number; onStart?: () => void; responseFormat?: Record<string, unknown> } = {}
   ): Promise<string> {
     const requestOpts: Record<string, unknown> = { messages, max_tokens: maxTokens };
+    if (responseFormat) requestOpts.response_format = responseFormat;
     if (temperature !== undefined) requestOpts.temperature = temperature;
     const request = buildInferenceRequest(this._modelConfig || ({} as Record<string, never>), requestOpts);
 
@@ -674,7 +704,7 @@ export async function callLocalInference(
 
   let rawResponse: string;
   try {
-    rawResponse = await localEngine.generate(messages, 40, { priority, onStart });
+    rawResponse = await localEngine.generate(messages, 40, { priority, onStart, responseFormat: CLASSIFICATION_RESPONSE_FORMAT });
   } catch (imgError) {
     if ((imgError as Error).message === 'Inference preempted') throw imgError;
     if (useImages) {
@@ -684,7 +714,7 @@ export async function callLocalInference(
         { role: "system", content: LOCAL_SYSTEM_PROMPT },
         { role: "user", content: textOnlyContent }
       ];
-      rawResponse = await localEngine.generate(textMessages, 40, { priority, onStart });
+      rawResponse = await localEngine.generate(textMessages, 40, { priority, onStart, responseFormat: CLASSIFICATION_RESPONSE_FORMAT });
     } else {
       throw imgError;
     }

Bouncer/src/shared/prompts.ts

@@ -3,25 +3,9 @@
 import type { ChatMessage, EvaluationPostData } from '../types';
 
 // System prompt for local models processing one post at a time
-export const LOCAL_SYSTEM_PROMPT = `You filter posts. Write 10-15 words identifying what the post is about, then state if it matches a filter category.
+export const LOCAL_SYSTEM_PROMPT = `You filter posts. Classify whether a post matches any of the given filter categories.
 
-Example outputs (NOTE: you may not be filtering on these categories!):
-
-<example>
-<filter_categories>sports</filter_categories>
-<post>The Lakers won last night against the Bucks!</post>
-Post about NBA basketball game results, which is sports content. Matches sports.
-</example>
-
-<example>
-<filter_categories>politics</filter_categories>
-<post>I love cooking dinner each night with my husband</post>
-Post about making dinner at home, which is Food/lifestyle content, not politics content. No match.
-</example>
-
-You will be provided with a post (<post>) and a list of filter categories (<filter_categories>).
-Assess whether the topic of the post relates to any of the topics in the filter categories list.
-Your reasoning must be AT MOST 15 words, and MUST end with a statement of "Matches <topic>" or "No match".
+Respond with JSON: {"reasoning": "<10-15 words about what the post is about>", "match": "<matched category or null>"}
 
 Be precise in your judgment; only match posts that clearly and directly relate to the filter categories.`;
 

Bouncer/tests/background/local-model.test.ts

@@ -677,6 +677,47 @@ describe('parseLocalModelResponse', () => {
   });
 });
 
+describe('parseLocalModelResponse — structured JSON output', () => {
+  it('parses a JSON match response', () => {
+    const raw = '{"reasoning":"NBA game results, sports content","match":"sports"}';
+    const result = parseLocalModelResponse(raw);
+    expect(result.shouldHide).toBe(true);
+    expect(result.reasoning).toContain('sports');
+  });
+
+  it('parses a JSON no-match response', () => {
+    const raw = '{"reasoning":"Cooking dinner at home, lifestyle content","match":null}';
+    const result = parseLocalModelResponse(raw);
+    expect(result.shouldHide).toBe(false);
+    expect(result.reasoning).toContain('Cooking');
+  });
+
+  it('parses JSON with match as empty string as no-match', () => {
+    const raw = '{"reasoning":"General lifestyle post","match":""}';
+    const result = parseLocalModelResponse(raw);
+    expect(result.shouldHide).toBe(false);
+  });
+
+  it('falls back to regex parsing for non-JSON freeform output', () => {
+    const raw = 'Post about basketball game results. Matches sports.';
+    const result = parseLocalModelResponse(raw);
+    expect(result.shouldHide).toBe(true);
+    expect(result.reasoning).toContain('sports');
+  });
+
+  it('falls back to regex for malformed JSON', () => {
+    const raw = '{"reasoning": broken json Matches politics.';
+    const result = parseLocalModelResponse(raw);
+    expect(result.shouldHide).toBe(true);
+  });
+
+  it('treats match:"null" string as no-match', () => {
+    const raw = '{"reasoning":"Not related","match":"null"}';
+    const result = parseLocalModelResponse(raw);
+    expect(result.shouldHide).toBe(false);
+  });
+});
+
 // ==================== LocalEngine.generate / preempt / ensureLoaded / teardown ====================
 
 describe('LocalEngine generate + preempt + lifecycle', () => {