feat(ai): scope persistence, parallel tools, Prometheus token/cache counters

C2 full scope persistence:
- getRecentConversationContext now returns per-turn guildId/channelId
- processMessage merges historical scope when current request is unscoped
- chatbot remembers server context across all 8 history exchanges (not just 3)

A4+Metrics:
- Add incrementCounterBy(name, delta, labels) to gateway-metrics
- Token-usage counters: llm_tokens_total{model, type, label} per batch
- Cache hit counters: moderation_cache_hits{type} exact/semantic-qdrant/semantic-pg
- Cache miss counters: moderation_cache_misses per batch
- Prometheus /metrics now exposes cost + cache hit-rate for dashboards

Performance:
- Parallel tool execution within each chatbot round (Promise.all)
- All tool results collected before sending to model (ordering preserved)
- Tool failure now logged with structured warning (chatbot.tools.ts)

Verified: backend tsc+biome 37/37, discord-gateway tsc+biome 210/210

services/discord-gateway/src/modules/ai-moderation/llmCaller.ts

@@ -14,6 +14,7 @@ import type { ChatCompletion } from "openai/resources/chat/completions";
 import { createChildLogger } from "@/shared/logger/index";
 import { delay, retryWithBackoff } from "@/shared/utils/index";
 import { config } from "../../shared/config/config.js";
+import { incrementCounterBy } from "../gateway-metrics/index.js";
 import type { AnalysisResult } from "../message-capture/types.js";
 import { llmChat } from "./llmClient.js";
 import { parseModerationResponse } from "./moderationResponseParser.js";
@@ -170,6 +171,23 @@ export async function callModerationLLM(
     // so cost per channel/guild can be tracked (routers bill per token).
     const usage = result?.usage;
     if (usage && (usage.prompt_tokens || usage.completion_tokens)) {
+      // Prometheus token-usage counters for cost tracking per model + phase.
+      // Counters accumulate across scrapes so total spend per model/label is
+      // queryable (rate(...) dashboards).
+      if (usage.prompt_tokens) {
+        incrementCounterBy("llm_tokens_total", usage.prompt_tokens, {
+          model: config.AI_LLM_MODEL,
+          type: "prompt",
+          label,
+        });
+      }
+      if (usage.completion_tokens) {
+        incrementCounterBy("llm_tokens_total", usage.completion_tokens, {
+          model: config.AI_LLM_MODEL,
+          type: "completion",
+          label,
+        });
+      }
       log.info(
         {
           label,

services/discord-gateway/src/modules/ai-moderation/moderationOrchestrator.ts

@@ -8,6 +8,7 @@
 import { LRUCache } from "lru-cache";
 import { createChildLogger } from "@/shared/logger/index";
 import { config } from "../../shared/config/config.js";
+import { incrementCounterBy } from "../gateway-metrics/index.js";
 import { extractMessageMediaEvidence } from "../message-capture/messageMetadata.js";
 import type {
   AnalysisResult,
@@ -243,10 +244,12 @@ export async function runModerationAnalysis(
     const representative = hitByKey.get(candidate.scopedKey);
     if (representative) {
       cacheHits.push({ ...representative, messageId: candidate.target.id });
+      incrementCounterBy("moderation_cache_hits", 1, { type: "exact" });
     } else {
       uncachedTargets.push(candidate.target);
     }
   }
+  incrementCounterBy("moderation_cache_misses", uncachedTargets.length);
 
   // ── Phase 2: semantic cache — batched (one embed call + one Qdrant
   //    batch search for ALL uncached text targets) ─────────────────────────
@@ -321,6 +324,9 @@ export async function runModerationAnalysis(
             hitByKey.set(cacheKey, hit);
             servedCacheKeys.add(cacheKey); // bump hit_count for metrics
             logCacheEvent("hit", cacheKey, "text");
+            incrementCounterBy("moderation_cache_hits", 1, {
+              type: "semantic-qdrant",
+            });
           }
         } else {
           // Legacy Postgres fallback path (no Qdrant): per-candidate scan.
@@ -360,6 +366,9 @@ export async function runModerationAnalysis(
             hitByKey.set(cacheKey, hit);
             servedCacheKeys.add(cacheKey); // bump hit_count for metrics
             logCacheEvent("hit", cacheKey, "text");
+            incrementCounterBy("moderation_cache_hits", 1, {
+              type: "semantic-pg",
+            });
           }
         }
 

services/discord-gateway/src/modules/gateway-metrics/index.ts

@@ -1,5 +1,6 @@
 export {
   incrementCounter,
+  incrementCounterBy,
   registerCollector,
   setGauge,
   startMetricsServer,

services/discord-gateway/src/modules/gateway-metrics/metrics.ts

@@ -37,16 +37,25 @@ export function registerCollector(fn: () => void): void {
 export function incrementCounter(
   name: string,
   labels?: Record<string, string>,
+): void {
+  incrementCounterBy(name, 1, labels);
+}
+
+/** Increment a counter by an explicit delta (e.g. token counts per batch). */
+export function incrementCounterBy(
+  name: string,
+  delta: number,
+  labels?: Record<string, string>,
 ): void {
   const k = key(`bete_${name}`, labels);
   const existing = metrics.get(k);
   if (existing) {
-    existing.value += 1;
+    existing.value += delta;
   } else {
     metrics.set(k, {
       help: `Counter: ${name}`,
       type: "counter",
-      value: 1,
+      value: delta,
       labels: labels ? { ...labels } : undefined,
     });
   }