feat(gate): drop the reasoning field from selection → ~1.5s (comfortable margin)

Even "<=8 words" was ignored — the model wrote a full-sentence reasoning, pushing
begin_session to ~7s (thin under the 8s budget). The gate only needs the names, so
request just {"selectedNames":[...]}. Validated live vs vllm-current
(glm-4.6-reap-fast): 1.5s, valid JSON. (reasoning defaults to '' in extractSelection.)

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

src/mcplocal/src/gate/llm-selector.ts

@@ -95,11 +95,11 @@ export class LlmPromptSelector {
   ): Promise<LlmSelectionResult> {
     const { getSystemPromptFn, signal, serverInfer } = opts;
 
-    // Keep the answer SHORT: latency is proportional to output length (a
-    // no-think model runs ~10-13 tok/s), and a verbose reasoning field pushes a
-    // selection past the gate's responsiveness budget. Ask for compact JSON with
-    // a <=8-word reasoning — ~2s vs ~9s for a prose reasoning.
-    const DEFAULT_SYSTEM_PROMPT = `You are a context selection assistant. Given a developer's task keywords and available project prompts, select the relevant ones. Return ONLY compact JSON: {"selectedNames":[...],"reasoning":"<=8 words"}. No prose outside the JSON. Priority 10 prompts must always be included.`;
+    // Keep the answer as SHORT as possible: latency is proportional to output
+    // length (a no-think model runs ~10-18 tok/s). Even an "<=8 words" reasoning
+    // got ignored (models write a full sentence → ~7s). Drop the reasoning field
+    // entirely — the gate only needs the names → just {selectedNames} → ~1-2s.
+    const DEFAULT_SYSTEM_PROMPT = `You are a context selection assistant. Given a developer's task keywords and available project prompts, select the relevant ones. Return ONLY this JSON and nothing else: {"selectedNames":[...]}. No reasoning, no prose, no explanation. Priority 10 prompts must always be included.`;
     const systemPrompt = getSystemPromptFn
       ? await getSystemPromptFn('llm-gate-context-selector', DEFAULT_SYSTEM_PROMPT)
       : DEFAULT_SYSTEM_PROMPT;
@@ -109,7 +109,7 @@ export class LlmPromptSelector {
 Available prompts:
 ${promptIndex.map((p) => `- ${p.name} (priority: ${p.priority}): ${p.summary ?? 'No summary'}${p.chapters?.length ? `\n  Chapters: ${p.chapters.join(', ')}` : ''}`).join('\n')}
 
-Select the relevant prompts. Return JSON: { "selectedNames": [...], "reasoning": "..." }`;
+Select the relevant prompts. Return ONLY: {"selectedNames":[...]}`;
 
     const messages: ChatMessage[] = [
       { role: 'system', content: systemPrompt },