feat: phase 5 of AI pipeline hardening — R42 retrieval & telemetry

- Add dependency-free TF-IDF retrieval (src/lib/retrieval.js) with NL+EN
  stopwords and a WeakMap-cached index.
- Rewrite buildKbContext to ship the top-K relevant topics + verbatim-
  mentioned ids only, filter relations to the included set, and append a
  [kb_hash: <8 hex>] suffix so the ephemeral prompt cache busts when the
  graph changes. Returns { context, retrievedTopics, allTopics }.
- Add LOOKUP_TOPIC_TOOL and drive useChat through callLLM directly with a
  multi-hop tool_result loop capped at 3 hops; preserve Anthropic-provided
  tool_use ids through callLLM so the loop can echo correct tool_use_id.
- Truncate R42 history to the last 12 turns and prepend a single
  "(earlier conversation truncated)" assistant message.
- Set R42 chat defaults: temperature 0.3, maxTokens 2048.
- Add pb_migrations/1780500002_created_llm_calls.js (the best-effort
  logger in callLLM was already wired) and a new Admin → Diagnostics
  view showing the last 100 calls with token usage, cache-hit rate, and
  USD cost from a local Anthropic price table.
- Finalize AI_PIPELINE_HARDENING_PLAN.md: mark Phases 1–5 shipped and
  Phase 6 (eval harness) explicitly out of scope.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/chat/useChat.js

@@ -1,17 +1,59 @@
 import { useCallback, useEffect, useRef, useState } from 'react';
 import { storage } from '../../lib/storage';
-import { anthropicApi } from '../../lib/api';
+import { callLLM } from '../../lib/llm';
+import * as db from '../../lib/db';
 import { buildKbContext, validateDelta, deltaKey } from './rag';
-import { buildSystemPrompt, PROPOSE_GRAPH_DELTA_TOOL, STRINGS } from './prompts';
+import {
+  buildSystemPrompt,
+  PROPOSE_GRAPH_DELTA_TOOL,
+  LOOKUP_TOPIC_TOOL,
+  STRINGS,
+} from './prompts';
 
 const MAX_HISTORY = 50;
+const VERBATIM_TURNS = 12;
+const MAX_LOOKUP_HOPS = 3;
+const TRUNCATION_NOTICE = '(earlier conversation truncated)';
+
+/** Trim API history to the last N turns and prepend a truncation notice. */
+function truncateApiMessages(history) {
+  if (history.length <= VERBATIM_TURNS) return history;
+  const tail = history.slice(-VERBATIM_TURNS);
+  return [{ role: 'assistant', content: TRUNCATION_NOTICE }, ...tail];
+}
+
+async function resolveLookupTopic(id, allTopics) {
+  const topic = allTopics.find(t => t.id === id);
+  if (!topic) {
+    return { ok: false, payload: `Geen topic gevonden met id "${id}".` };
+  }
+  const content = await db.getContent(id).catch(() => null);
+  let contentSnippet = null;
+  if (content) {
+    let raw;
+    if (typeof content === 'string') raw = content;
+    else if (content.article) raw = typeof content.article === 'string' ? content.article : JSON.stringify(content.article);
+    else raw = JSON.stringify(content);
+    contentSnippet = raw.replace(/\s+/g, ' ').trim().slice(0, 2400);
+  }
+  return {
+    ok: true,
+    payload: {
+      id: topic.id,
+      label: topic.label,
+      type: topic.type || 'concept',
+      description: topic.description || '',
+      learning_content: contentSnippet,
+    },
+  };
+}
 
 /**
  * Conversation hook for R42.
- * Owns the message list, persists to chat:thread:{userId}, calls Anthropic,
- * and surfaces validated graph delta suggestions inline.
- *
- * Note: buildKbContext is async (reads PocketBase), so send() is fully async.
+ * Owns the message list, persists to chat:thread:{userId}, calls Anthropic
+ * via the shared `callLLM` client (with a `lookup_topic` multi-hop loop and
+ * the `propose_graph_delta` tool), and surfaces validated graph delta
+ * suggestions inline.
  */
 export function useChat({ user, isAdmin }) {
   const threadKey = user ? `chat:thread:${user.id}` : null;
@@ -20,7 +62,6 @@ export function useChat({ user, isAdmin }) {
   const [errored, setErrored] = useState(false);
   const seenDeltaKeys = useRef(new Set());
 
-  // Load persisted thread + seed greeting
   useEffect(() => {
     if (!user) return;
     const stored = storage.get(threadKey, null);
@@ -41,7 +82,6 @@ export function useChat({ user, isAdmin }) {
     }
   }, [user, threadKey]);
 
-  // Persist on change
   useEffect(() => {
     if (!threadKey) return;
     const capped = messages.slice(-MAX_HISTORY);
@@ -68,29 +108,43 @@ export function useChat({ user, isAdmin }) {
     setErrored(false);
 
     try {
-      const { context: kbContext, topics: kbTopics } = await buildKbContext(trimmed);
+      const { context: kbContext, allTopics } = await buildKbContext(trimmed);
       const systemPrompt = buildSystemPrompt({
         userName: user.name || 'daar',
         isAdmin,
         kbContext,
       });
 
-      // Strip UI-only fields before sending to Anthropic
-      const apiMessages = next
+      const historyMessages = next
         .filter(m => m.role === 'user' || m.role === 'assistant')
         .map(m => ({ role: m.role, content: m.content }));
 
-      const response = await anthropicApi.chat(systemPrompt, apiMessages, {
-        tools: [PROPOSE_GRAPH_DELTA_TOOL],
-      });
+      const apiMessages = truncateApiMessages(historyMessages);
 
       let textOut = '';
       let suggestion = null;
-      for (const block of response.content || []) {
-        if (block.type === 'text') {
-          textOut += (textOut ? '\n' : '') + (block.text || '');
-        } else if (block.type === 'tool_use' && block.name === PROPOSE_GRAPH_DELTA_TOOL.name) {
-          const validated = validateDelta(block.input, kbTopics);
+      let hops = 0;
+
+      while (true) {
+        const response = await callLLM({
+          task: 'chat.r42',
+          tier: 'standard',
+          system: systemPrompt,
+          messages: apiMessages,
+          tools: [LOOKUP_TOPIC_TOOL, PROPOSE_GRAPH_DELTA_TOOL],
+          maxTokens: 2048,
+          temperature: 0.3,
+        });
+
+        if (response.text) {
+          textOut += (textOut ? '\n' : '') + response.text;
+        }
+
+        const lookupCalls = response.toolUses.filter(tu => tu.name === LOOKUP_TOPIC_TOOL.name);
+        const deltaCall = response.toolUses.find(tu => tu.name === PROPOSE_GRAPH_DELTA_TOOL.name);
+
+        if (deltaCall && !suggestion) {
+          const validated = validateDelta(deltaCall.input, allTopics);
           if (validated) {
             const key = deltaKey(validated);
             if (!seenDeltaKeys.current.has(key)) {
@@ -99,6 +153,33 @@ export function useChat({ user, isAdmin }) {
             }
           }
         }
+
+        if (lookupCalls.length === 0 || hops >= MAX_LOOKUP_HOPS) break;
+        hops++;
+
+        const assistantBlocks = [];
+        if (response.text) assistantBlocks.push({ type: 'text', text: response.text });
+        for (const tu of response.toolUses) {
+          if (!tu.id) continue;
+          assistantBlocks.push({ type: 'tool_use', id: tu.id, name: tu.name, input: tu.input });
+        }
+        apiMessages.push({ role: 'assistant', content: assistantBlocks });
+
+        const toolResults = [];
+        for (const tu of lookupCalls) {
+          if (!tu.id) continue;
+          const topicId = String(tu.input?.id || '').trim();
+          const resolved = await resolveLookupTopic(topicId, allTopics);
+          toolResults.push({
+            type: 'tool_result',
+            tool_use_id: tu.id,
+            content: typeof resolved.payload === 'string'
+              ? resolved.payload
+              : JSON.stringify(resolved.payload),
+            ...(resolved.ok ? {} : { is_error: true }),
+          });
+        }
+        apiMessages.push({ role: 'user', content: toolResults });
       }
 
       const assistantMsg = {