TeachChat: model selector, proxy routing fix, titan seed cleanup

- teach.py: use _proxy_model() + pass api_key/api_base from settings (fixes LiteLLM provider error for openrouter/bedrock models)
- teach.py: accept model_id in ChatRequest so frontend can select model
- main.py: remove titan-embed-v2 from general seed, auto-delete legacy entry on startup
- main.py: kill stale idle-in-transaction DB connections at startup to prevent DDL lock hangs
- main.py: set lock_timeout=10s on DDL connection as fast-fail safety net
- TeachChat.jsx: fetch /teach/models, show selector dropdown in header when >1 model available

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/main.py

@@ -7,7 +7,7 @@ from fastapi.staticfiles import StaticFiles
 
 from app.config import settings
 from app.database import engine, Base, SessionLocal
-from app.routers import auth, documents, quizzes, attempts, admin, tts, nextcloud, categories, questions, question_categories, favorites
+from app.routers import auth, documents, quizzes, attempts, admin, tts, nextcloud, categories, questions, question_categories, favorites, teach
 from app.utils.auth import get_password_hash
 from app.utils.scheduler import start_scheduler, stop_scheduler
 
@@ -65,11 +65,19 @@ def seed_default_models():
                 AIModelConfig(name="Claude Haiku 4.5", model_id="claude-haiku-4.5", task="extraction", is_active=True, is_default=True),
                 AIModelConfig(name="Claude Sonnet 4.6", model_id="claude-sonnet-4.6", task="extraction", is_active=True, is_default=False),
                 AIModelConfig(name="Gemini 2.5 Flash", model_id="gemini-2.5-flash", task="extraction", is_active=True, is_default=False),
-                AIModelConfig(name="Titan Embed v2 (Embedding)", model_id="titan-embed-v2", task="general", is_active=True, is_default=False),
             ]
             db.add_all(defaults)
             db.commit()
 
+        # Clean up legacy titan-embed-v2 "general" entry (was mistakenly seeded)
+        titan = db.query(AIModelConfig).filter(
+            AIModelConfig.model_id == "titan-embed-v2",
+            AIModelConfig.task == "general",
+        ).first()
+        if titan:
+            db.delete(titan)
+            db.commit()
+
         # Always ensure OpenAI TTS voice models exist (idempotent)
         tts_voices = [
             # OpenAI (work with OPENAI_API_KEY)
@@ -123,7 +131,23 @@ def setup_pgvector():
     from sqlalchemy import text
     # Import new models so create_all picks them up
     from app.models import quiz_category, quiz_question_link, question_category, favorite  # noqa
+
+    # Kill stale idle-in-transaction connections from previous killed startups.
+    # They hold DDL locks and cause ALTER TABLE below to hang indefinitely.
     with engine.connect() as conn:
+        conn.execute(text("""
+            SELECT pg_terminate_backend(pid)
+            FROM pg_stat_activity
+            WHERE datname = current_database()
+              AND state = 'idle in transaction'
+              AND query_start < NOW() - INTERVAL '30 seconds'
+              AND pid != pg_backend_pid()
+        """))
+        conn.commit()
+
+    with engine.connect() as conn:
+        # Fail fast instead of hanging if a lock can't be acquired within 10s.
+        conn.execute(text("SET lock_timeout = '10s'"))
         conn.execute(text("CREATE EXTENSION IF NOT EXISTS vector"))
         conn.execute(text("ALTER TABLE questions ADD COLUMN IF NOT EXISTS embedding vector(1024)"))
         conn.execute(text("""
@@ -292,6 +316,7 @@ app.include_router(categories.router, prefix="/api/categories", tags=["categorie
 app.include_router(questions.router, prefix="/api/questions", tags=["questions"])
 app.include_router(question_categories.router, prefix="/api/question-categories", tags=["question-categories"])
 app.include_router(favorites.router, prefix="/api/favorites", tags=["favorites"])
+app.include_router(teach.router, prefix="/api/teach", tags=["teach"])
 
 
 @app.get("/api/health")

backend/app/models/question.py

@@ -1,6 +1,6 @@
 from pgvector.sqlalchemy import Vector
 from sqlalchemy import Column, Integer, String, Text, JSON, ForeignKey
-from sqlalchemy.orm import relationship
+from sqlalchemy.orm import relationship, deferred
 
 from app.config import settings
 from app.database import Base
@@ -23,7 +23,7 @@ class Question(Base):
     explanation = Column(Text, nullable=True)
     page_reference = Column(Integer, nullable=True)
     image_path = Column(String, nullable=True)
-    embedding = Column(Vector(1024), nullable=True)  # semantic search vector
+    embedding = deferred(Column(Vector(1024), nullable=True))  # semantic search vector — deferred: not loaded in standard queries
 
     question_category = relationship("QuestionCategory", back_populates="questions",
                                      foreign_keys=[question_category_id])

backend/app/routers/admin.py

@@ -143,8 +143,8 @@ def create_model(
     db: Session = Depends(get_db),
     admin: User = Depends(require_admin),
 ):
-    if data.task not in ("extraction", "tts", "general"):
-        raise HTTPException(status_code=400, detail="Task must be extraction, tts, or general")
+    if data.task not in ("extraction", "tts", "general", "teach"):
+        raise HTTPException(status_code=400, detail="Task must be extraction, tts, general, or teach")
 
     if data.is_default:
         db.query(AIModelConfig).filter(
@@ -201,6 +201,124 @@ def delete_model(
     db.commit()
 
 
+@router.post("/models/{model_id}/test")
+def test_model(
+    model_id: int,
+    db: Session = Depends(get_db),
+    admin: User = Depends(require_admin),
+):
+    """Send a simple test completion to verify an LLM model is reachable.
+    TTS models are previewed via /tts/speak instead."""
+    model = db.query(AIModelConfig).filter(AIModelConfig.id == model_id).first()
+    if not model:
+        raise HTTPException(status_code=404, detail="Model config not found")
+
+    if model.task == "tts":
+        raise HTTPException(status_code=400, detail="Use the Preview button to test TTS voices — it plays audio directly.")
+
+    try:
+        import litellm
+        from app.services.ai_service import _proxy_model
+        use_model = _proxy_model(model.model_id)
+        kwargs = {
+            "model": use_model,
+            "messages": [{"role": "user", "content": "Reply with only the word: OK"}],
+            "max_tokens": 10,
+        }
+        if model.api_key:
+            kwargs["api_key"] = model.api_key
+        elif settings.LITELLM_API_KEY:
+            kwargs["api_key"] = settings.LITELLM_API_KEY
+        if settings.LITELLM_API_BASE:
+            kwargs["api_base"] = settings.LITELLM_API_BASE
+        response = litellm.completion(**kwargs)
+        reply = response.choices[0].message.content.strip()
+        return {"message": f"✓ {model.model_id} → {reply!r}"}
+    except Exception as e:
+        raise HTTPException(status_code=502, detail=str(e))
+
+
+@router.get("/tts/voices")
+def search_tts_voices(
+    provider: str,
+    api_key: str | None = None,
+    region: str | None = None,
+    admin: User = Depends(require_admin),
+):
+    """Discover available TTS voices from ElevenLabs, AWS Polly, or return OpenAI hardcoded list."""
+
+    if provider == "elevenlabs":
+        key = api_key or settings.ELEVENLABS_API_KEY
+        if not key:
+            raise HTTPException(status_code=400, detail="ElevenLabs API key required (set ELEVENLABS_API_KEY in .env or enter it above)")
+        try:
+            resp = httpx.get(
+                "https://api.elevenlabs.io/v1/voices",
+                headers={"xi-api-key": key},
+                timeout=15,
+            )
+            resp.raise_for_status()
+            voices = resp.json().get("voices", [])
+            return {"voices": [
+                {
+                    "model_id": f"elevenlabs/{v['voice_id']}",
+                    "name": v["name"],
+                    "labels": v.get("labels", {}),
+                }
+                for v in sorted(voices, key=lambda x: x["name"])
+            ]}
+        except HTTPException:
+            raise
+        except Exception as e:
+            raise HTTPException(status_code=400, detail=f"ElevenLabs API error: {e}")
+
+    elif provider == "polly":
+        access_key = api_key or settings.AWS_ACCESS_KEY_ID
+        secret_key = settings.AWS_SECRET_ACCESS_KEY
+        aws_region = region or settings.AWS_REGION or "us-east-1"
+        if not access_key or not secret_key:
+            raise HTTPException(
+                status_code=400,
+                detail="AWS credentials required — set AWS_ACCESS_KEY_ID / AWS_SECRET_ACCESS_KEY in .env",
+            )
+        try:
+            import boto3
+            polly = boto3.client(
+                "polly",
+                aws_access_key_id=access_key,
+                aws_secret_access_key=secret_key,
+                region_name=aws_region,
+            )
+            resp = polly.describe_voices(Engine="neural")
+            voices = resp.get("Voices", [])
+            return {"voices": [
+                {
+                    "model_id": f"polly/{v['Id']}",
+                    "name": f"{v['Name']} — {v['LanguageName']} ({v.get('Gender', '')})",
+                    "labels": {"gender": v.get("Gender", ""), "language": v.get("LanguageName", "")},
+                }
+                for v in sorted(voices, key=lambda x: x["Name"])
+            ]}
+        except HTTPException:
+            raise
+        except Exception as e:
+            raise HTTPException(status_code=400, detail=f"AWS Polly error: {e}")
+
+    elif provider == "openai":
+        voices = []
+        for model_name in ["tts-1", "tts-1-hd"]:
+            for voice in ["alloy", "ash", "coral", "echo", "fable", "nova", "onyx", "sage", "shimmer"]:
+                voices.append({
+                    "model_id": f"{model_name}:{voice}",
+                    "name": f"{model_name} · {voice}",
+                    "labels": {"model": model_name, "voice": voice},
+                })
+        return {"voices": voices}
+
+    else:
+        raise HTTPException(status_code=400, detail=f"Unknown provider '{provider}'. Valid: elevenlabs, polly, openai")
+
+
 # --- System Settings ---
 
 @router.get("/settings")
@@ -262,3 +380,13 @@ def test_embedding(admin: User = Depends(require_admin)):
     if result is None:
         raise HTTPException(status_code=500, detail=f"Embedding failed for model: {model}")
     return {"model": model, "dimensions": len(result), "status": "ok"}
+
+
+@router.post("/embedding/regenerate")
+def regenerate_embeddings(admin: User = Depends(require_admin)):
+    """Queue a background Celery task to regenerate all question embeddings."""
+    import uuid
+    from app.tasks.quiz_tasks import regenerate_embeddings as regen_task
+    job_id = str(uuid.uuid4())
+    regen_task.delay(job_id, admin.id)
+    return {"job_id": job_id, "message": "Regeneration started — progress visible in the Jobs badge."}

backend/app/routers/attempts.py

@@ -404,6 +404,7 @@ def get_quiz_history(
     for a in completed:
         pct = round((a.score / a.total_questions * 100) if a.total_questions > 0 else 0, 1)
         by_quiz[a.quiz_id].append({
+            "attempt_id": a.id,
             "date": a.completed_at.isoformat(),
             "percentage": pct,
             "score": a.score,

backend/app/routers/teach.py

@@ -0,0 +1,169 @@
+"""Teach chat endpoint — AI tutor for study mode questions."""
+from fastapi import APIRouter, Depends, HTTPException
+from pydantic import BaseModel
+from sqlalchemy.orm import Session
+
+from app.database import get_db
+from app.models.question import Question
+from app.models.ai_model_config import AIModelConfig
+from app.models.user import User
+from app.utils.auth import get_current_user
+
+router = APIRouter()
+
+
+class ChatMessage(BaseModel):
+    role: str  # "user" | "assistant"
+    content: str
+
+
+class ChatRequest(BaseModel):
+    question_id: int
+    messages: list[ChatMessage]
+    model_id: int | None = None  # AIModelConfig.id — if None, use default
+
+
+def _get_teach_model(db: Session, model_config_id: int | None = None):
+    """Return (model_id, api_key) for the requested (or default) teach model, or None."""
+    if model_config_id:
+        m = db.query(AIModelConfig).filter(
+            AIModelConfig.id == model_config_id,
+            AIModelConfig.task == "teach",
+            AIModelConfig.is_active == True,
+        ).first()
+        if m:
+            return (m.model_id, m.api_key or None)
+    # Fall back to default, then any active
+    m = db.query(AIModelConfig).filter(
+        AIModelConfig.task == "teach",
+        AIModelConfig.is_active == True,
+        AIModelConfig.is_default == True,
+    ).first()
+    if not m:
+        m = db.query(AIModelConfig).filter(
+            AIModelConfig.task == "teach",
+            AIModelConfig.is_active == True,
+        ).first()
+    return (m.model_id, m.api_key or None) if m else None
+
+
+def _find_similar_questions(db: Session, question: Question, limit: int = 4) -> list[Question]:
+    """Return up to `limit` questions with similar embeddings, excluding the current one."""
+    if question.embedding is None:
+        return []
+    try:
+        from sqlalchemy import text as sa_text
+        emb = question.embedding
+        emb_literal = "[" + ",".join(str(x) for x in emb) + "]"
+        rows = db.execute(sa_text(f"""
+            SELECT id, 1 - (embedding <=> '{emb_literal}'::vector) AS sim
+            FROM questions
+            WHERE embedding IS NOT NULL AND id != {question.id}
+            ORDER BY embedding <=> '{emb_literal}'::vector
+            LIMIT {limit}
+        """)).fetchall()
+        ids = [r.id for r in rows if float(r.sim) >= 0.35]
+        if not ids:
+            return []
+        return db.query(Question).filter(Question.id.in_(ids)).all()
+    except Exception:
+        return []
+
+
+def _build_system_prompt(question: Question, similar: list[Question]) -> str:
+    opts = ""
+    if question.options:
+        letters = "ABCDE"
+        opts = "\n".join(f"  {letters[i]}) {opt}" for i, opt in enumerate(question.options))
+
+    prompt = (
+        "You are a medical education tutor helping a student understand the following question. "
+        "Be accurate, educational, and concise. You may reveal and explain the correct answer.\n\n"
+        f"=== Current Question ===\n{question.question_text}\n"
+    )
+    if opts:
+        prompt += f"Options:\n{opts}\n"
+    if question.correct_answer:
+        prompt += f"Correct Answer: {question.correct_answer}\n"
+    if question.explanation:
+        prompt += f"Explanation: {question.explanation}\n"
+
+    if similar:
+        prompt += "\n=== Related Questions (for broader context) ===\n"
+        for i, sq in enumerate(similar, 1):
+            prompt += f"{i}. {sq.question_text}"
+            if sq.correct_answer:
+                prompt += f" → Answer: {sq.correct_answer}"
+            prompt += "\n"
+
+    prompt += (
+        "\nAnswer the student's questions about this topic. "
+        "If they ask why an option is wrong, explain the underlying concept. "
+        "Keep responses focused and under 200 words unless a longer explanation is needed."
+    )
+    return prompt
+
+
+@router.get("/models")
+def list_teach_models(
+    db: Session = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Return available teach models for the frontend to display."""
+    models = db.query(AIModelConfig).filter(
+        AIModelConfig.task == "teach",
+        AIModelConfig.is_active == True,
+    ).all()
+    return [{"id": m.id, "name": m.name, "model_id": m.model_id, "is_default": m.is_default} for m in models]
+
+
+@router.post("/chat")
+def chat(
+    req: ChatRequest,
+    db: Session = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Send a message to the teach AI with full question context."""
+    model_info = _get_teach_model(db, req.model_id)
+    if not model_info:
+        raise HTTPException(
+            status_code=503,
+            detail="No teaching AI model is configured. Ask an admin to add a model with task 'teach'.",
+        )
+    model_id, api_key = model_info
+
+    question = db.query(Question).filter(Question.id == req.question_id).first()
+    if not question:
+        raise HTTPException(status_code=404, detail="Question not found")
+
+    similar = _find_similar_questions(db, question)
+    system_prompt = _build_system_prompt(question, similar)
+
+    messages = [{"role": "system", "content": system_prompt}]
+    for msg in req.messages:
+        if msg.role not in ("user", "assistant"):
+            continue
+        messages.append({"role": msg.role, "content": msg.content})
+
+    try:
+        import litellm
+        from app.config import settings
+        from app.services.ai_service import _proxy_model
+        use_model = _proxy_model(model_id)
+        kwargs = {
+            "model": use_model,
+            "messages": messages,
+            "max_tokens": 600,
+            "temperature": 0.4,
+        }
+        if api_key:
+            kwargs["api_key"] = api_key
+        elif settings.LITELLM_API_KEY:
+            kwargs["api_key"] = settings.LITELLM_API_KEY
+        if settings.LITELLM_API_BASE:
+            kwargs["api_base"] = settings.LITELLM_API_BASE
+        response = litellm.completion(**kwargs)
+        reply = response.choices[0].message.content.strip()
+        return {"reply": reply}
+    except Exception as e:
+        raise HTTPException(status_code=502, detail=f"AI model error: {str(e)}")

backend/app/tasks/quiz_tasks.py

@@ -273,3 +273,44 @@ def extract_quiz(
         raise
     finally:
         db.close()
+
+
+@celery_app.task(name="regenerate_embeddings", bind=True)
+def regenerate_embeddings(self, job_id: str, user_id: int):
+    """Regenerate embeddings for all questions using the current embedding model."""
+    r = _redis()
+    r.set(f"extraction:status:{job_id}", "running", ex=EXPIRE_SECONDS)
+    r.set(f"extraction:job_title:{job_id}", "Regenerate Embeddings", ex=EXPIRE_SECONDS)
+    r.lpush(f"extraction:user_jobs:{user_id}", job_id)
+    r.expire(f"extraction:user_jobs:{user_id}", 86400)
+
+    db = SessionLocal()
+    try:
+        from app.models.question import Question
+        from app.services import embedding_service
+
+        questions = db.query(Question).all()
+        total = len(questions)
+        _push_step(r, job_id, "start", f"Regenerating embeddings for {total} questions…")
+
+        ok = 0
+        for i, q in enumerate(questions):
+            try:
+                if embedding_service.embed_question(q):
+                    ok += 1
+                if (i + 1) % 50 == 0:
+                    db.commit()
+                    _push_step(r, job_id, "progress", f"{i + 1}/{total} processed ({ok} embedded)")
+            except Exception as e:
+                logger.warning(f"Embedding failed for question {q.id}: {e}")
+
+        db.commit()
+        _push_step(r, job_id, "done", f"Done — {ok}/{total} questions re-embedded.")
+        r.set(f"extraction:status:{job_id}", "completed", ex=EXPIRE_SECONDS)
+    except Exception as e:
+        logger.exception(f"Embedding regeneration failed for job {job_id}")
+        _push_step(r, job_id, "error", f"Failed: {e}")
+        r.set(f"extraction:status:{job_id}", "failed", ex=EXPIRE_SECONDS)
+        raise
+    finally:
+        db.close()

frontend/nginx.conf

@@ -4,6 +4,13 @@ server {
     root /usr/share/nginx/html;
     index index.html;
 
+    # Gzip compression
+    gzip on;
+    gzip_types text/plain text/css application/json application/javascript text/xml application/xml text/javascript;
+    gzip_min_length 1024;
+    gzip_proxied any;
+    gzip_comp_level 6;
+
     # Security headers
     add_header X-Frame-Options "SAMEORIGIN" always;
     add_header X-Content-Type-Options "nosniff" always;

frontend/src/components/Dialog.jsx

@@ -0,0 +1,41 @@
+/**
+ * Dialog — styled modal that replaces window.confirm() and window.alert().
+ * Used via the useDialog() hook. Matches the Suspend Quiz popup style.
+ *
+ * Props:
+ *   open         — boolean
+ *   title        — string (optional)
+ *   message      — string
+ *   confirmLabel — string (default "OK")
+ *   cancelLabel  — string | null  (null = no cancel button → alert mode)
+ *   onConfirm    — () => void
+ *   onCancel     — () => void
+ *   danger       — boolean (makes confirm button red)
+ */
+export default function Dialog({ open, title, message, confirmLabel = 'OK', cancelLabel = null, onConfirm, onCancel, danger = false }) {
+  if (!open) return null
+
+  return (
+    <div
+      style={{ position: 'fixed', inset: 0, background: 'rgba(0,0,0,0.6)', zIndex: 1000, display: 'flex', alignItems: 'center', justifyContent: 'center', padding: 16 }}
+      onClick={e => { if (e.target === e.currentTarget && onCancel) onCancel() }}
+    >
+      <div style={{ background: 'var(--card-bg)', borderRadius: 14, padding: 28, maxWidth: 420, width: '100%', textAlign: 'center', boxShadow: '0 20px 60px rgba(0,0,0,0.3)' }}>
+        {title && <h2 style={{ marginBottom: 10, fontSize: '1.1rem' }}>{title}</h2>}
+        <p style={{ color: 'var(--text-muted)', fontSize: '0.9rem', marginBottom: 22, lineHeight: 1.5 }}>{message}</p>
+        <div style={{ display: 'flex', gap: 10, justifyContent: 'center' }}>
+          {cancelLabel && (
+            <button className="btn btn-secondary" onClick={onCancel}>{cancelLabel}</button>
+          )}
+          <button
+            className={`btn ${danger ? 'btn-danger' : 'btn-primary'}`}
+            onClick={onConfirm}
+            autoFocus
+          >
+            {confirmLabel}
+          </button>
+        </div>
+      </div>
+    </div>
+  )
+}

frontend/src/components/Navbar.jsx

@@ -3,29 +3,10 @@ import { Link, useLocation } from 'react-router-dom'
 import { useAuth } from '../context/AuthContext'
 import api from '../api/client'
 
-function JobsBadge() {
-  const [activeJobs, setActiveJobs] = useState([])
-  const [allJobs, setAllJobs] = useState([])
+function JobsBadge({ jobs }) {
   const [open, setOpen] = useState(false)
-
-  useEffect(() => {
-    let interval
-    const load = async () => {
-      try {
-        const res = await api.get('/quizzes/jobs')
-        const jobs = res.data || []
-        setAllJobs(jobs)
-        const running = jobs.filter(j => j.status === 'running' || j.status === 'pending')
-        setActiveJobs(running)
-        // Poll faster when jobs running, slower when idle
-        clearInterval(interval)
-        interval = setInterval(load, running.length > 0 ? 3000 : 30000)
-      } catch { }
-    }
-    load()
-    interval = setInterval(load, 30000)
-    return () => clearInterval(interval)
-  }, [])
+  const allJobs = jobs
+  const activeJobs = jobs.filter(j => j.status === 'running' || j.status === 'pending')
 
   if (allJobs.length === 0) return null
 
@@ -79,12 +60,32 @@ function JobsBadge() {
 export default function Navbar() {
   const { user, logout } = useAuth()
   const [menuOpen, setMenuOpen] = useState(false)
+  const [jobs, setJobs] = useState([])
   const location = useLocation()
   const isModerator = user?.role === 'admin' || user?.role === 'moderator'
 
   // Close menu on route change
   useEffect(() => { setMenuOpen(false) }, [location.pathname])
 
+  // Single job-polling instance for the whole navbar
+  useEffect(() => {
+    if (!user) return
+    let interval
+    const load = async () => {
+      try {
+        const res = await api.get('/quizzes/jobs')
+        const jobList = res.data || []
+        setJobs(jobList)
+        const running = jobList.filter(j => j.status === 'running' || j.status === 'pending')
+        clearInterval(interval)
+        interval = setInterval(load, running.length > 0 ? 3000 : 30000)
+      } catch { }
+    }
+    load()
+    interval = setInterval(load, 30000)
+    return () => clearInterval(interval)
+  }, [user])
+
 
   const navLinks = user ? [
     { to: '/', label: 'Dashboard' },
@@ -109,13 +110,13 @@ export default function Navbar() {
                   {l.label}
                 </Link>
               ))}
-              <JobsBadge />
+              <JobsBadge jobs={jobs} />
               <button onClick={logout}>Logout</button>
             </nav>
 
             {/* Mobile: jobs + hamburger */}
             <div className="nav-mobile-controls">
-              <JobsBadge />
+              <JobsBadge jobs={jobs} />
               <button
                 onClick={() => setMenuOpen(v => !v)}
                 aria-label="Menu"

frontend/src/components/TeachChat.jsx

@@ -0,0 +1,276 @@
+import { useState, useEffect, useRef } from 'react'
+import api from '../api/client'
+
+/**
+ * TeachChat — slide-in AI tutor drawer for study mode.
+ *
+ * Props:
+ *   question  — current question object (id, question_text, options, correct_answer, explanation)
+ *
+ * Layout:
+ *   Mobile  — bottom sheet, 70vh
+ *   Desktop — right-side panel inside quiz-layout, 320px wide
+ */
+export default function TeachChat({ question }) {
+  const [open, setOpen] = useState(false)
+  const [messages, setMessages] = useState([])   // {role, content}
+  const [input, setInput] = useState('')
+  const [loading, setLoading] = useState(false)
+  const [noModel, setNoModel] = useState(false)
+  const [models, setModels] = useState([])
+  const [selectedModelId, setSelectedModelId] = useState(null) // AIModelConfig.id
+  const bottomRef = useRef(null)
+  const inputRef = useRef(null)
+
+  // Load available teach models once
+  useEffect(() => {
+    api.get('/teach/models').then(res => {
+      setModels(res.data)
+      const def = res.data.find(m => m.is_default) || res.data[0]
+      if (def) setSelectedModelId(def.id)
+    }).catch(() => {})
+  }, [])
+
+  // Clear chat when question changes
+  useEffect(() => {
+    setMessages([])
+    setInput('')
+    setNoModel(false)
+  }, [question?.id])
+
+  // Scroll to bottom when messages change
+  useEffect(() => {
+    bottomRef.current?.scrollIntoView({ behavior: 'smooth' })
+  }, [messages])
+
+  // Focus input when drawer opens
+  useEffect(() => {
+    if (open) setTimeout(() => inputRef.current?.focus(), 150)
+  }, [open])
+
+  const send = async () => {
+    const text = input.trim()
+    if (!text || loading) return
+
+    const userMsg = { role: 'user', content: text }
+    const next = [...messages, userMsg]
+    setMessages(next)
+    setInput('')
+    setLoading(true)
+
+    try {
+      const res = await api.post('/teach/chat', {
+        question_id: question.id,
+        messages: next,
+        model_id: selectedModelId || null,
+      })
+      setMessages(m => [...m, { role: 'assistant', content: res.data.reply }])
+    } catch (err) {
+      const detail = err.response?.data?.detail || 'AI error'
+      if (err.response?.status === 503) setNoModel(true)
+      setMessages(m => [...m, { role: 'assistant', content: `⚠️ ${detail}` }])
+    } finally {
+      setLoading(false)
+    }
+  }
+
+  const onKey = (e) => {
+    if (e.key === 'Enter' && !e.shiftKey) { e.preventDefault(); send() }
+  }
+
+  // ── Floating button (always visible in study mode) ──────────────────────
+  const fabStyle = {
+    position: 'fixed',
+    bottom: 80,
+    right: 18,
+    zIndex: 400,
+    width: 48,
+    height: 48,
+    borderRadius: '50%',
+    background: open ? 'var(--primary)' : '#1e3a5f',
+    color: 'white',
+    border: 'none',
+    cursor: 'pointer',
+    fontSize: '1.3rem',
+    display: 'flex',
+    alignItems: 'center',
+    justifyContent: 'center',
+    boxShadow: '0 4px 16px rgba(0,0,0,0.25)',
+    transition: 'background 0.2s, transform 0.15s',
+  }
+
+  // ── Drawer shell ────────────────────────────────────────────────────────
+  // Mobile: fixed bottom sheet. Desktop (≥768px): right panel via CSS class.
+  const drawerMobile = {
+    position: 'fixed',
+    bottom: 0,
+    left: 0,
+    right: 0,
+    height: '70vh',
+    background: 'var(--card-bg)',
+    borderTop: '2px solid var(--primary)',
+    borderRadius: '16px 16px 0 0',
+    zIndex: 390,
+    display: 'flex',
+    flexDirection: 'column',
+    boxShadow: '0 -8px 32px rgba(0,0,0,0.18)',
+    animation: 'slideUp 0.22s ease',
+  }
+
+  return (
+    <>
+      {/* Floating button */}
+      <button
+        style={fabStyle}
+        onClick={() => setOpen(v => !v)}
+        title={open ? 'Close AI tutor' : 'Ask AI tutor'}
+        onMouseEnter={e => e.currentTarget.style.transform = 'scale(1.1)'}
+        onMouseLeave={e => e.currentTarget.style.transform = 'none'}
+      >
+        {open ? '✕' : '🎓'}
+      </button>
+
+      {/* Backdrop on mobile */}
+      {open && (
+        <div
+          className="teach-chat-backdrop"
+          onClick={() => setOpen(false)}
+          style={{ position: 'fixed', inset: 0, zIndex: 380, background: 'rgba(0,0,0,0.3)' }}
+        />
+      )}
+
+      {/* Drawer */}
+      {open && (
+        <div className="teach-chat-drawer" style={drawerMobile}>
+          {/* Header */}
+          <div style={{
+            display: 'flex', alignItems: 'center', justifyContent: 'space-between',
+            padding: '10px 16px', borderBottom: '1px solid var(--border)', flexShrink: 0, gap: 8,
+          }}>
+            <span style={{ fontWeight: 700, fontSize: '0.9rem', flexShrink: 0 }}>🎓 AI Tutor</span>
+            {models.length > 1 && (
+              <select
+                value={selectedModelId || ''}
+                onChange={e => { setSelectedModelId(Number(e.target.value)); setMessages([]); }}
+                style={{
+                  flex: 1, fontSize: '0.78rem', padding: '3px 6px', borderRadius: 6,
+                  border: '1px solid var(--border)', background: 'var(--input-bg)', color: 'var(--text)',
+                  minWidth: 0,
+                }}
+              >
+                {models.map(m => <option key={m.id} value={m.id}>{m.name}</option>)}
+              </select>
+            )}
+            <button onClick={() => setOpen(false)} style={{ background: 'none', border: 'none', cursor: 'pointer', color: 'var(--text-muted)', fontSize: '1.1rem', lineHeight: 1, flexShrink: 0 }}>✕</button>
+          </div>
+
+          {/* Question context chip */}
+          <div style={{
+            padding: '8px 16px', background: 'var(--bg)', borderBottom: '1px solid var(--border)',
+            fontSize: '0.78rem', color: 'var(--text-muted)', flexShrink: 0,
+            overflow: 'hidden', textOverflow: 'ellipsis', whiteSpace: 'nowrap',
+          }}>
+            📋 {question.question_text?.slice(0, 100)}{question.question_text?.length > 100 ? '…' : ''}
+          </div>
+
+          {/* Messages */}
+          <div style={{ flex: 1, overflowY: 'auto', padding: '12px 16px', display: 'flex', flexDirection: 'column', gap: 10 }}>
+            {messages.length === 0 && !noModel && (
+              <div style={{ color: 'var(--text-muted)', fontSize: '0.83rem', textAlign: 'center', marginTop: 24 }}>
+                Ask the AI tutor anything about this question — why an answer is wrong, the underlying concept, related topics, etc.
+              </div>
+            )}
+            {noModel && (
+              <div className="alert alert-error" style={{ fontSize: '0.82rem' }}>
+                No teaching AI is configured. Ask an admin to add a model with task <strong>teach</strong> in the Admin Dashboard.
+              </div>
+            )}
+            {messages.map((m, i) => (
+              <div key={i} style={{
+                alignSelf: m.role === 'user' ? 'flex-end' : 'flex-start',
+                maxWidth: '85%',
+                background: m.role === 'user' ? 'var(--primary)' : 'var(--bg)',
+                color: m.role === 'user' ? 'white' : 'var(--text)',
+                padding: '8px 12px',
+                borderRadius: m.role === 'user' ? '12px 12px 2px 12px' : '12px 12px 12px 2px',
+                fontSize: '0.85rem',
+                lineHeight: 1.55,
+                border: m.role === 'assistant' ? '1px solid var(--border)' : 'none',
+                whiteSpace: 'pre-wrap',
+              }}>
+                {m.content}
+              </div>
+            ))}
+            {loading && (
+              <div style={{
+                alignSelf: 'flex-start', background: 'var(--bg)', border: '1px solid var(--border)',
+                borderRadius: '12px 12px 12px 2px', padding: '8px 14px', fontSize: '0.82rem', color: 'var(--text-muted)',
+              }}>
+                <span style={{ display: 'inline-flex', gap: 4 }}>
+                  <span className="spinner" style={{ width: 12, height: 12, borderWidth: 2 }} /> Thinking…
+                </span>
+              </div>
+            )}
+            <div ref={bottomRef} />
+          </div>
+
+          {/* Input */}
+          <div style={{
+            padding: '10px 12px', borderTop: '1px solid var(--border)', flexShrink: 0,
+            display: 'flex', gap: 8,
+          }}>
+            <textarea
+              ref={inputRef}
+              value={input}
+              onChange={e => setInput(e.target.value)}
+              onKeyDown={onKey}
+              placeholder="Ask a question… (Enter to send)"
+              rows={2}
+              style={{
+                flex: 1, resize: 'none', padding: '8px 10px',
+                border: '1px solid var(--border)', borderRadius: 8,
+                fontSize: '0.875rem', background: 'var(--input-bg)', color: 'var(--text)',
+                fontFamily: 'inherit', lineHeight: 1.4,
+              }}
+            />
+            <button
+              onClick={send}
+              disabled={loading || !input.trim()}
+              className="btn btn-primary btn-sm"
+              style={{ alignSelf: 'flex-end', padding: '8px 14px' }}
+            >
+              Send
+            </button>
+          </div>
+        </div>
+      )}
+
+      <style>{`
+        @keyframes slideUp {
+          from { transform: translateY(100%); opacity: 0; }
+          to   { transform: translateY(0);    opacity: 1; }
+        }
+        @media (min-width: 768px) {
+          .teach-chat-backdrop { display: none !important; }
+          .teach-chat-drawer {
+            position: fixed !important;
+            bottom: 0 !important;
+            right: 0 !important;
+            left: auto !important;
+            top: 0 !important;
+            width: 340px !important;
+            height: 100vh !important;
+            border-radius: 0 !important;
+            border-top: none !important;
+            border-left: 2px solid var(--primary) !important;
+            animation: slideRight 0.22s ease !important;
+          }
+        }
+        @keyframes slideRight {
+          from { transform: translateX(100%); opacity: 0; }
+          to   { transform: translateX(0);    opacity: 1; }
+        }
+      `}</style>
+    </>
+  )
+}

frontend/src/hooks/useDialog.js

@@ -0,0 +1,49 @@
+import { useState } from 'react'
+
+/**
+ * useDialog — Promise-based hook for confirm and alert dialogs.
+ *
+ * Usage:
+ *   const { dialogProps, openConfirm, openAlert } = useDialog()
+ *
+ *   // In JSX: <Dialog {...dialogProps} />
+ *
+ *   // Confirm (returns true/false):
+ *   const ok = await openConfirm('Delete this item?', { title: 'Delete', confirmLabel: 'Delete', danger: true })
+ *   if (!ok) return
+ *
+ *   // Alert (acknowledgement only):
+ *   await openAlert('Something went wrong.')
+ */
+export function useDialog() {
+  const [dialog, setDialog] = useState(null)
+
+  const openConfirm = (message, { title, confirmLabel = 'Confirm', cancelLabel = 'Cancel', danger = false } = {}) =>
+    new Promise(resolve => {
+      setDialog({ message, title, confirmLabel, cancelLabel, danger, resolve })
+    })
+
+  const openAlert = (message, { title } = {}) =>
+    new Promise(resolve => {
+      setDialog({ message, title, confirmLabel: 'OK', cancelLabel: null, danger: false, resolve })
+    })
+
+  const close = (result) => {
+    setDialog(d => { d?.resolve(result); return null })
+  }
+
+  const dialogProps = dialog
+    ? {
+        open: true,
+        title: dialog.title,
+        message: dialog.message,
+        confirmLabel: dialog.confirmLabel,
+        cancelLabel: dialog.cancelLabel,
+        danger: dialog.danger,
+        onConfirm: () => close(true),
+        onCancel: () => close(false),
+      }
+    : { open: false }
+
+  return { dialogProps, openConfirm, openAlert }
+}

frontend/src/pages/AdminPage.jsx

@@ -2,12 +2,15 @@ import { useState, useEffect } from 'react'
 import { useNavigate } from 'react-router-dom'
 import { useAuth } from '../context/AuthContext'
 import api from '../api/client'
+import Dialog from '../components/Dialog'
+import { useDialog } from '../hooks/useDialog'
 
-const TASKS = ['extraction', 'tts', 'general']
+const TASKS = ['extraction', 'tts', 'general', 'teach']
 
 export default function AdminPage() {
   const { user } = useAuth()
   const navigate = useNavigate()
+  const { dialogProps, openConfirm } = useDialog()
   const [tab, setTab] = useState('models')
   const [users, setUsers] = useState([])
   const [models, setModels] = useState([])
@@ -26,6 +29,18 @@ export default function AdminPage() {
   const [searchLoading, setSearchLoading] = useState(false)
   const [searchError, setSearchError] = useState('')
   const [searchFilter, setSearchFilter] = useState('')
+  const [searchTaskHint, setSearchTaskHint] = useState('extraction')
+
+  // TTS voice discovery state
+  const [ttsProvider, setTtsProvider] = useState('elevenlabs')
+  const [ttsSearchKey, setTtsSearchKey] = useState('')
+  const [ttsVoices, setTtsVoices] = useState([])
+  const [ttsVoicesLoading, setTtsVoicesLoading] = useState(false)
+  const [ttsVoicesError, setTtsVoicesError] = useState('')
+  const [ttsVoicesFilter, setTtsVoicesFilter] = useState('')
+
+  // TTS preview state per model db id: {text, loading, error, audioUrl}
+  const [ttsPreviews, setTtsPreviews] = useState({})
 
   // Embedding model search state (in settings tab)
   const [embedSearchResults, setEmbedSearchResults] = useState([])
@@ -34,6 +49,9 @@ export default function AdminPage() {
   const [embedSearchFilter, setEmbedSearchFilter] = useState('')
   const [embedTestResult, setEmbedTestResult] = useState(null)
   const [embedTestLoading, setEmbedTestLoading] = useState(false)
+  const [originalEmbedModel, setOriginalEmbedModel] = useState(null)
+  const [embedModelChanged, setEmbedModelChanged] = useState(false)
+  const [regenLoading, setRegenLoading] = useState(false)
 
   useEffect(() => {
     if (!user?.role || user.role !== 'admin') { navigate('/'); return }
@@ -51,6 +69,7 @@ export default function AdminPage() {
       setUsers(usersRes.data)
       setModels(modelsRes.data)
       setSettings(settingsRes.data)
+      setOriginalEmbedModel(settingsRes.data.embedding_model || '')
     } catch (err) {
       setError(err.response?.data?.detail || 'Failed to load data')
     } finally {
@@ -101,7 +120,8 @@ export default function AdminPage() {
   }
 
   const deleteModel = async (modelId) => {
-    if (!confirm('Delete this model config?')) return
+    const ok = await openConfirm('Remove this model configuration?', { title: 'Remove Model', confirmLabel: 'Remove', danger: true })
+    if (!ok) return
     try {
       await api.delete(`/admin/models/${modelId}`)
       loadData()
@@ -110,6 +130,22 @@ export default function AdminPage() {
     }
   }
 
+  const [testResults, setTestResults] = useState({})
+  const [testingModel, setTestingModel] = useState(null)
+
+  const testModel = async (model) => {
+    setTestingModel(model.id)
+    setTestResults(r => ({ ...r, [model.id]: null }))
+    try {
+      const res = await api.post(`/admin/models/${model.id}/test`)
+      setTestResults(r => ({ ...r, [model.id]: { ok: true, message: res.data.message || 'OK' } }))
+    } catch (err) {
+      setTestResults(r => ({ ...r, [model.id]: { ok: false, message: err.response?.data?.detail || 'Test failed' } }))
+    } finally {
+      setTestingModel(null)
+    }
+  }
+
   const searchLiteLLM = async () => {
     setSearchError('')
     setSearchResults([])
@@ -162,18 +198,76 @@ export default function AdminPage() {
       setSettings(s => ({ ...s, embedding_model: modelId }))
       setEmbedSearchResults([])
       setSuccess(`Embedding model set to: ${modelId}`)
+      if (originalEmbedModel && modelId !== originalEmbedModel) {
+        setEmbedModelChanged(true)
+      }
     } catch (err) {
       setError(err.response?.data?.detail || 'Failed to save embedding model')
     }
   }
 
+  const startRegeneration = async () => {
+    setRegenLoading(true)
+    try {
+      await api.post('/admin/embedding/regenerate')
+      setEmbedModelChanged(false)
+      setSuccess('Regeneration started — watch the Jobs badge for progress.')
+    } catch (err) {
+      setError(err.response?.data?.detail || 'Failed to start regeneration')
+    } finally {
+      setRegenLoading(false)
+    }
+  }
+
   const addFromSearch = (modelId) => {
-    setNewModel(m => ({ ...m, model_id: modelId, name: modelId }))
+    setNewModel(m => ({ ...m, model_id: modelId, name: modelId, task: searchTaskHint }))
     setSearchResults([])
-    // scroll to add form
     document.getElementById('add-model-form')?.scrollIntoView({ behavior: 'smooth' })
   }
 
+  // ── TTS voice discovery ─────────────────────────────────────────
+  const searchTtsVoices = async () => {
+    setTtsVoicesError('')
+    setTtsVoices([])
+    setTtsVoicesLoading(true)
+    try {
+      const params = new URLSearchParams({ provider: ttsProvider })
+      if (ttsSearchKey) params.set('api_key', ttsSearchKey)
+      const res = await api.get(`/admin/tts/voices?${params}`)
+      setTtsVoices(res.data.voices)
+    } catch (err) {
+      setTtsVoicesError(err.response?.data?.detail || 'Failed to fetch voices')
+    } finally {
+      setTtsVoicesLoading(false)
+    }
+  }
+
+  const addTtsFromSearch = (voice) => {
+    setNewModel(m => ({ ...m, model_id: voice.model_id, name: voice.name, task: 'tts' }))
+    setTtsVoices([])
+    document.getElementById('add-model-form')?.scrollIntoView({ behavior: 'smooth' })
+  }
+
+  // ── TTS preview (calls /tts/speak directly) ─────────────────────
+  const setPreview = (id, patch) =>
+    setTtsPreviews(p => ({ ...p, [id]: { text: 'Hello, this is a voice preview.', ...p[id], ...patch } }))
+
+  const playTtsPreview = async (model) => {
+    const state = ttsPreviews[model.id] || {}
+    const text = state.text || 'Hello, this is a voice preview.'
+    setPreview(model.id, { loading: true, error: null })
+    try {
+      const res = await api.post('/tts/speak', { text, voice: model.model_id }, { responseType: 'blob' })
+      const url = URL.createObjectURL(res.data)
+      const audio = new Audio(url)
+      audio.onended = () => URL.revokeObjectURL(url)
+      audio.play()
+      setPreview(model.id, { loading: false })
+    } catch (err) {
+      setPreview(model.id, { loading: false, error: err.response?.data?.detail || 'Playback failed' })
+    }
+  }
+
   if (loading) return <div className="loading"><div className="spinner"></div> Loading...</div>
 
   const modelsByTask = TASKS.reduce((acc, t) => {
@@ -187,6 +281,7 @@ export default function AdminPage() {
 
   return (
     <div>
+      <Dialog {...dialogProps} />
       <div className="card">
         <h2>Admin Dashboard</h2>
         <div style={{ display: 'flex', gap: 8, marginTop: 12 }}>
@@ -203,20 +298,20 @@ export default function AdminPage() {
 
       {tab === 'models' && (
         <>
-          {/* LiteLLM search */}
+          {/* LiteLLM / OpenAI-compatible search — for extraction, teach, general */}
           <div className="card">
-            <h2>Search Models from LiteLLM</h2>
+            <h2>Search LLM Models</h2>
             <p style={{ color: '#64748b', fontSize: '0.85rem', marginBottom: 16 }}>
-              Query an OpenAI-compatible API (or your LiteLLM proxy) to see available models, then click one to add it.
+              Query your LiteLLM proxy or any OpenAI-compatible API. Works for <strong>extraction</strong>, <strong>teach</strong>, and <strong>general</strong> tasks.
             </p>
             <div className="grid-2">
               <div className="form-group">
-                <label>API Base URL (optional)</label>
+                <label>API Base URL (optional — uses .env if blank)</label>
                 <input
                   type="text"
                   value={searchApiBase}
                   onChange={e => setSearchApiBase(e.target.value)}
-                  placeholder="e.g. https://api.openai.com or LiteLLM proxy URL"
+                  placeholder="e.g. https://litellm.myserver.com"
                 />
               </div>
               <div className="form-group">
@@ -228,6 +323,12 @@ export default function AdminPage() {
                   placeholder="sk-..."
                 />
               </div>
+              <div className="form-group">
+                <label>Adding model for task</label>
+                <select value={searchTaskHint} onChange={e => setSearchTaskHint(e.target.value)}>
+                  {['extraction', 'teach', 'general'].map(t => <option key={t} value={t}>{t}</option>)}
+                </select>
+              </div>
             </div>
             <button className="btn btn-primary" onClick={searchLiteLLM} disabled={searchLoading}>
               {searchLoading ? 'Searching...' : 'Search Models'}
@@ -280,29 +381,123 @@ export default function AdminPage() {
                 <span style={{ fontSize: '0.75rem', color: '#64748b', marginLeft: 8, fontWeight: 400 }}>
                   {task === 'extraction' ? '— AI that extracts questions from PDFs' :
                    task === 'tts' ? '— Text-to-speech voices' :
+                   task === 'teach' ? '— AI tutor shown in study mode chat' :
                    '— General purpose AI'}
                 </span>
               </h2>
+
+              {/* TTS voice discovery — only in the tts card */}
+              {task === 'tts' && (
+                <div style={{ marginBottom: 16, padding: '12px 14px', background: 'var(--bg)', borderRadius: 8, border: '1px solid var(--border)' }}>
+                  <div style={{ fontWeight: 600, fontSize: '0.85rem', marginBottom: 8 }}>Discover Voices</div>
+                  <div style={{ display: 'flex', gap: 8, flexWrap: 'wrap', marginBottom: 8 }}>
+                    <select value={ttsProvider} onChange={e => { setTtsProvider(e.target.value); setTtsVoices([]) }}
+                      style={{ padding: '5px 10px', borderRadius: 6, border: '1px solid var(--border)', fontSize: '0.85rem', background: 'var(--input-bg)', color: 'var(--text)' }}>
+                      <option value="elevenlabs">ElevenLabs</option>
+                      <option value="polly">AWS Polly (Neural)</option>
+                      <option value="openai">OpenAI TTS</option>
+                    </select>
+                    <input type="password" value={ttsSearchKey} onChange={e => setTtsSearchKey(e.target.value)}
+                      placeholder="API key (uses .env if blank)"
+                      style={{ flex: 1, minWidth: 140, padding: '5px 10px', borderRadius: 6, border: '1px solid var(--border)', fontSize: '0.85rem', background: 'var(--input-bg)', color: 'var(--text)' }} />
+                    <button className="btn btn-primary btn-sm" onClick={searchTtsVoices} disabled={ttsVoicesLoading}>
+                      {ttsVoicesLoading ? 'Searching...' : 'Search'}
+                    </button>
+                  </div>
+                  {ttsVoicesError && <div className="alert alert-error" style={{ fontSize: '0.82rem', padding: '6px 12px' }}>{ttsVoicesError}</div>}
+                  {ttsVoices.length > 0 && (
+                    <div>
+                      <div style={{ display: 'flex', justifyContent: 'space-between', alignItems: 'center', marginBottom: 6 }}>
+                        <span style={{ fontSize: '0.82rem', color: 'var(--text-muted)' }}>{ttsVoices.length} voices — click to add</span>
+                        <input type="text" placeholder="Filter..." value={ttsVoicesFilter} onChange={e => setTtsVoicesFilter(e.target.value)}
+                          style={{ padding: '3px 8px', borderRadius: 6, border: '1px solid var(--border)', fontSize: '0.82rem', width: 160, background: 'var(--input-bg)', color: 'var(--text)' }} />
+                      </div>
+                      <div style={{ maxHeight: 220, overflowY: 'auto', border: '1px solid var(--border)', borderRadius: 8 }}>
+                        {ttsVoices
+                          .filter(v => !ttsVoicesFilter || v.name.toLowerCase().includes(ttsVoicesFilter.toLowerCase()) || v.model_id.toLowerCase().includes(ttsVoicesFilter.toLowerCase()))
+                          .map(v => (
+                            <div key={v.model_id} style={{ display: 'flex', justifyContent: 'space-between', alignItems: 'center', padding: '7px 12px', borderBottom: '1px solid var(--border)', fontSize: '0.83rem' }}>
+                              <div>
+                                <span style={{ fontWeight: 500 }}>{v.name}</span>
+                                {v.labels && Object.keys(v.labels).length > 0 && (
+                                  <span style={{ color: 'var(--text-muted)', marginLeft: 8, fontSize: '0.75rem' }}>
+                                    {Object.values(v.labels).filter(Boolean).join(' · ')}
+                                  </span>
+                                )}
+                                <div style={{ fontFamily: 'monospace', fontSize: '0.75rem', color: 'var(--text-muted)' }}>{v.model_id}</div>
+                              </div>
+                              <button className="btn btn-primary btn-sm" onClick={() => addTtsFromSearch(v)}>+ Add</button>
+                            </div>
+                          ))}
+                      </div>
+                    </div>
+                  )}
+                </div>
+              )}
+
               {modelsByTask[task].length === 0 ? (
                 <div className="empty-state" style={{ padding: 16 }}>No models configured</div>
               ) : (
                 modelsByTask[task].map(m => (
-                  <div className="section-item" key={m.id}>
-                    <div style={{ minWidth: 0 }}>
-                      <strong>{m.name}</strong>
-                      <div style={{ fontSize: '0.82rem', color: '#64748b', fontFamily: 'monospace', overflow: 'hidden', textOverflow: 'ellipsis', whiteSpace: 'nowrap' }}>{m.model_id}</div>
-                    </div>
-                    <div style={{ display: 'flex', gap: 6, alignItems: 'center', flexShrink: 0 }}>
-                      {m.is_default && <span className="badge badge-ready">Default</span>}
-                      {!m.is_default && (
-                        <button className="btn btn-secondary btn-sm" onClick={() => setDefault(m.id)}>Set Default</button>
-                      )}
-                      <button
-                        className={`btn btn-sm ${m.is_active ? 'btn-secondary' : 'btn-primary'}`}
-                        onClick={() => toggleActive(m)}
-                      >{m.is_active ? 'Disable' : 'Enable'}</button>
-                      <button className="btn btn-danger btn-sm" onClick={() => deleteModel(m.id)}>Remove</button>
+                  <div key={m.id}>
+                    <div className="section-item">
+                      <div style={{ minWidth: 0 }}>
+                        <strong>{m.name}</strong>
+                        <div style={{ fontSize: '0.82rem', color: '#64748b', fontFamily: 'monospace', overflow: 'hidden', textOverflow: 'ellipsis', whiteSpace: 'nowrap' }}>{m.model_id}</div>
+                      </div>
+                      <div style={{ display: 'flex', gap: 6, alignItems: 'center', flexShrink: 0 }}>
+                        {m.is_default && <span className="badge badge-ready">Default</span>}
+                        {!m.is_default && (
+                          <button className="btn btn-secondary btn-sm" onClick={() => setDefault(m.id)}>Set Default</button>
+                        )}
+                        {task === 'tts' ? (
+                          <button
+                            className="btn btn-secondary btn-sm"
+                            onClick={() => setPreview(m.id, { open: !(ttsPreviews[m.id]?.open) })}
+                          >Preview</button>
+                        ) : (
+                          <button
+                            className="btn btn-secondary btn-sm"
+                            onClick={() => testModel(m)}
+                            disabled={testingModel === m.id}
+                          >{testingModel === m.id ? 'Testing...' : 'Test'}</button>
+                        )}
+                        <button
+                          className={`btn btn-sm ${m.is_active ? 'btn-secondary' : 'btn-primary'}`}
+                          onClick={() => toggleActive(m)}
+                        >{m.is_active ? 'Disable' : 'Enable'}</button>
+                        <button className="btn btn-danger btn-sm" onClick={() => deleteModel(m.id)}>Remove</button>
+                      </div>
                     </div>
+
+                    {/* LLM test result */}
+                    {testResults[m.id] && (
+                      <div className={`alert ${testResults[m.id].ok ? 'alert-success' : 'alert-error'}`} style={{ marginTop: 6, marginBottom: 0, padding: '6px 12px', fontSize: '0.82rem' }}>
+                        {testResults[m.id].ok ? '✓ ' : '✗ '}{testResults[m.id].message}
+                      </div>
+                    )}
+
+                    {/* TTS preview */}
+                    {task === 'tts' && ttsPreviews[m.id]?.open && (
+                      <div style={{ marginTop: 6, padding: '10px 12px', background: 'var(--bg)', borderRadius: 8, display: 'flex', gap: 8, flexWrap: 'wrap', alignItems: 'flex-start' }}>
+                        <textarea
+                          value={ttsPreviews[m.id]?.text ?? 'Hello, this is a voice preview.'}
+                          onChange={e => setPreview(m.id, { text: e.target.value })}
+                          rows={2}
+                          style={{ flex: 1, minWidth: 160, padding: '6px 10px', borderRadius: 6, border: '1px solid var(--border)', fontSize: '0.85rem', resize: 'none', background: 'var(--input-bg)', color: 'var(--text)', fontFamily: 'inherit' }}
+                        />
+                        <button className="btn btn-primary btn-sm" style={{ alignSelf: 'flex-end' }}
+                          onClick={() => playTtsPreview(m)}
+                          disabled={ttsPreviews[m.id]?.loading}>
+                          {ttsPreviews[m.id]?.loading ? '⏳' : '▶ Play'}
+                        </button>
+                        {ttsPreviews[m.id]?.error && (
+                          <div className="alert alert-error" style={{ width: '100%', marginTop: 4, padding: '5px 10px', fontSize: '0.82rem' }}>
+                            {ttsPreviews[m.id].error}
+                          </div>
+                        )}
+                      </div>
+                    )}
                   </div>
                 ))
               )}
@@ -470,6 +665,27 @@ export default function AdminPage() {
               </label>
             </div>
 
+            {/* Embedding model change warning */}
+            {embedModelChanged && (
+              <div style={{ padding: '12px 16px', background: '#fef3c7', border: '1px solid #f59e0b', borderRadius: 8, marginBottom: 0, marginTop: 8 }}>
+                <strong style={{ color: '#92400e', display: 'block', marginBottom: 6 }}>
+                  ⚠️ Embedding model changed
+                </strong>
+                <span style={{ fontSize: '0.85rem', color: '#78350f' }}>
+                  Existing question embeddings were generated with the previous model and may produce inaccurate semantic search results.
+                  Regenerate them to restore full search quality.
+                </span>
+                <div style={{ marginTop: 10 }}>
+                  <button className="btn btn-primary btn-sm" onClick={startRegeneration} disabled={regenLoading}>
+                    {regenLoading ? 'Starting…' : 'Regenerate All Embeddings'}
+                  </button>
+                  <button className="btn btn-secondary btn-sm" style={{ marginLeft: 8 }} onClick={() => setEmbedModelChanged(false)}>
+                    Dismiss
+                  </button>
+                </div>
+              </div>
+            )}
+
             {/* Embedding Model */}
             <div style={{ padding: '16px 0' }}>
               <strong style={{ display: 'block', marginBottom: 4 }}>Embedding Model</strong>
@@ -492,6 +708,9 @@ export default function AdminPage() {
                 <button className="btn btn-secondary btn-sm" onClick={testEmbedding} disabled={embedTestLoading}>
                   {embedTestLoading ? 'Testing...' : 'Test'}
                 </button>
+                <button className="btn btn-secondary btn-sm" onClick={startRegeneration} disabled={regenLoading} title="Regenerate embeddings for all questions">
+                  {regenLoading ? 'Starting…' : 'Regenerate All'}
+                </button>
               </div>
               {embedTestResult && (
                 <div className={`alert ${embedTestResult.ok ? 'alert-success' : 'alert-error'}`} style={{ marginBottom: 8 }}>

frontend/src/pages/JobsPage.jsx

@@ -1,11 +1,14 @@
 import { useState, useEffect, useRef } from 'react'
 import { Link, useNavigate } from 'react-router-dom'
 import api from '../api/client'
+import Dialog from '../components/Dialog'
+import { useDialog } from '../hooks/useDialog'
 
 function JobDetail({ job }) {
   const [steps, setSteps] = useState([])
   const [expanded, setExpanded] = useState(false)
   const [quizData, setQuizData] = useState(null)
+  const { dialogProps, openAlert } = useDialog()
   const pollRef = useRef(null)
   const navigate = useNavigate()
 
@@ -41,6 +44,7 @@ function JobDetail({ job }) {
 
   return (
     <div className="card" style={{ marginBottom: 12 }}>
+      <Dialog {...dialogProps} />
       <div style={{ display: 'flex', justifyContent: 'space-between', alignItems: 'flex-start', gap: 12 }}>
         <div style={{ flex: 1 }}>
           <div style={{ display: 'flex', gap: 10, alignItems: 'center', marginBottom: 4, flexWrap: 'wrap' }}>
@@ -70,7 +74,7 @@ function JobDetail({ job }) {
                 job.status = 'cancelled'
                 load()
               } catch (e) {
-                alert(e.response?.data?.detail || 'Failed to cancel')
+                await openAlert(e.response?.data?.detail || 'Failed to cancel', { title: 'Error' })
               }
             }}>Cancel</button>
           )}

frontend/src/pages/QuestionBankPage.jsx

@@ -2,6 +2,8 @@ import { useState, useEffect, useRef } from 'react'
 import { useNavigate } from 'react-router-dom'
 import { useAuth } from '../context/AuthContext'
 import api from '../api/client'
+import Dialog from '../components/Dialog'
+import { useDialog } from '../hooks/useDialog'
 
 function QuestionStudyModal({ question, onClose }) {
   const [answered, setAnswered] = useState(null)
@@ -219,6 +221,7 @@ function QuestionEditModal({ question, categories, onSaved, onClose }) {
 }
 
 export default function QuestionBankPage() {
+  const { dialogProps, openAlert } = useDialog()
   const [questions, setQuestions] = useState([])
   const [total, setTotal] = useState(0)
   const [loading, setLoading] = useState(false)
@@ -317,7 +320,7 @@ export default function QuestionBankPage() {
       const res = await api.post('/question-categories/', { name: newCatName.trim() })
       setCategories(prev => [...prev, res.data])
       setNewCatName(''); setShowCatForm(false)
-    } catch (err) { alert(err.response?.data?.detail || 'Failed') }
+    } catch (err) { await openAlert(err.response?.data?.detail || 'Failed', { title: 'Error' }) }
   }
 
   const [deletingCatId, setDeletingCatId] = useState(null)
@@ -351,12 +354,13 @@ export default function QuestionBankPage() {
         setFavorites(prev => [...prev, questionId])
       }
     } catch (err) {
-      alert(err.response?.data?.detail || 'Failed to update favorite')
+      await openAlert(err.response?.data?.detail || 'Failed to update favorite', { title: 'Error' })
     }
   }
 
   return (
     <div>
+      <Dialog {...dialogProps} />
       {/* Delete category dialog */}
       {deletingCatId && (() => {
         const cat = categories.find(c => c.id === deletingCatId)

frontend/src/pages/QuizPage.jsx

@@ -1,8 +1,10 @@
-import { useState, useEffect, useRef, useCallback } from 'react'
+import { useState, useEffect, useRef, useCallback, lazy, Suspense } from 'react'
 import { useParams, useNavigate, Link } from 'react-router-dom'
 import { useAuth } from '../context/AuthContext'
 import api from '../api/client'
 
+const TeachChat = lazy(() => import('../components/TeachChat'))
+
 function TTSButton({ text, voice, onActiveChange }) {
   const [state, setState] = useState('idle') // idle | loading | playing
   const audioRef = useRef(null)
@@ -139,6 +141,7 @@ export default function QuizPage() {
   const [answers, setAnswers] = useState({})
   const [currentIdx, setCurrentIdx] = useState(0)
   const [loading, setLoading] = useState(true)
+  const [starting, setStarting] = useState(false)
   const [submitting, setSubmitting] = useState(false)
   const [attemptId, setAttemptId] = useState(null)
   const [timeLeft, setTimeLeft] = useState(null)
@@ -237,15 +240,22 @@ export default function QuizPage() {
     if (hasStarted.current) return
     hasStarted.current = true
     setSelectedVoice(voice)
+    setStarting(true)
     // DON'T set quizMode yet — wait for data to load first
     // (prevents mobile race condition where quiz renders without correct_answer)
 
     try {
-      const quizRes = await api.get(`/quizzes/${id}${mode === 'study' ? '?study=true' : ''}`)
-      setQuiz(quizRes.data)
+      let quizData = quiz
+      if (mode === 'study') {
+        // Need answers/explanations — fetch the full study version
+        const quizRes = await api.get(`/quizzes/${id}?study=true`)
+        quizData = quizRes.data
+        setQuiz(quizData)
+      }
+      // Exam mode reuses the already-loaded quiz (no answers needed)
       const attemptRes = await api.post(`/attempts/start?quiz_id=${id}`)
       setAttemptId(attemptRes.data.id)
-      const mins = timerMinutes || quizRes.data.time_limit_minutes
+      const mins = timerMinutes || quizData.time_limit_minutes
       const now = new Date().toISOString()
       setStartedAt(now)
       if (mode === 'exam' && mins) {
@@ -255,6 +265,7 @@ export default function QuizPage() {
       // NOW set mode — quiz data is fully loaded, safe to render
       setQuizMode(mode)
     } catch { navigate('/') }
+    finally { setStarting(false) }
   }
 
 useEffect(() => {
@@ -309,7 +320,7 @@ useEffect(() => {
       const res = await api.post(`/attempts/${attemptId}/submit`, submission)
       navigate(`/results/${attemptId}`, { state: { result: res.data } })
     } catch (err) {
-      if (!autoSubmit) alert(err.response?.data?.detail || 'Submission failed')
+      if (!autoSubmit) showToast(err.response?.data?.detail || 'Submission failed')
     } finally { setSubmitting(false) }
   }, [attemptId, answers, submitting])
 
@@ -323,7 +334,14 @@ useEffect(() => {
           <Link to={`/quizzes/${id}/edit`} className="btn btn-secondary btn-sm">✏️ Edit Questions</Link>
         </div>
       )}
-      <ModeSelectScreen quiz={quiz} voices={voices} onStart={startQuiz} />
+      {starting ? (
+        <div style={{ textAlign: 'center', padding: '60px 0' }}>
+          <div className="spinner" style={{ margin: '0 auto 16px' }} />
+          <div style={{ color: 'var(--text-muted)', fontSize: '0.95rem' }}>Loading quiz…</div>
+        </div>
+      ) : (
+        <ModeSelectScreen quiz={quiz} voices={voices} onStart={startQuiz} />
+      )}
     </div>
   )
 
@@ -591,6 +609,13 @@ useEffect(() => {
           </div>
         </div>
       </div>
+
+      {/* AI tutor — only in study mode, lazy-loaded */}
+      {isStudy && current && (
+        <Suspense fallback={null}>
+          <TeachChat question={current} />
+        </Suspense>
+      )}
     </div>
   )
 }

frontend/src/pages/QuizzesPage.jsx

@@ -3,6 +3,8 @@ import { useNavigate, Link } from 'react-router-dom'
 import { useAuth } from '../context/AuthContext'
 import api from '../api/client'
 import ConfirmButton from '../components/ConfirmButton'
+import Dialog from '../components/Dialog'
+import { useDialog } from '../hooks/useDialog'
 
 function InProgressSection() {
   const [inProgress, setInProgress] = useState([])
@@ -50,6 +52,73 @@ function InProgressSection() {
   )
 }
 
+function PastAttemptsSection() {
+  const [open, setOpen] = useState(false)
+  const [history, setHistory] = useState(null)
+  const [loading, setLoading] = useState(false)
+
+  const load = async () => {
+    if (history !== null) { setOpen(v => !v); return }
+    setLoading(true)
+    try {
+      const res = await api.get('/attempts/history')
+      setHistory(res.data)
+    } catch { setHistory([]) }
+    finally { setLoading(false); setOpen(true) }
+  }
+
+  const totalCompleted = history?.reduce((s, q) => s + q.attempts.length, 0) ?? 0
+
+  return (
+    <div className="card" style={{ marginBottom: 16 }}>
+      <button onClick={load} style={{
+        display: 'flex', justifyContent: 'space-between', alignItems: 'center',
+        width: '100%', background: 'none', border: 'none', cursor: 'pointer',
+        padding: 0, textAlign: 'left',
+      }}>
+        <h2 style={{ fontSize: '1rem', color: 'var(--text)', margin: 0 }}>
+          ✅ Past Attempts {history !== null && `(${totalCompleted})`}
+        </h2>
+        <span style={{ color: 'var(--text-muted)', fontSize: '0.8rem' }}>
+          {loading ? 'Loading...' : open ? '▲ Hide' : '▼ Show'}
+        </span>
+      </button>
+
+      {open && history !== null && (
+        <div style={{ marginTop: 12 }}>
+          {history.length === 0 ? (
+            <div style={{ color: 'var(--text-muted)', fontSize: '0.875rem' }}>No completed attempts yet.</div>
+          ) : history.map(quiz => (
+            <div key={quiz.quiz_id} style={{ marginBottom: 14 }}>
+              <div style={{ fontWeight: 600, fontSize: '0.88rem', marginBottom: 6 }}>{quiz.title}</div>
+              <div style={{ display: 'flex', flexDirection: 'column', gap: 5 }}>
+                {quiz.attempts.map((a, i) => (
+                  <div key={a.attempt_id} style={{
+                    display: 'flex', justifyContent: 'space-between', alignItems: 'center',
+                    padding: '7px 12px', background: 'var(--bg)', borderRadius: 8,
+                    fontSize: '0.82rem', gap: 8,
+                  }}>
+                    <span style={{ color: 'var(--text-muted)' }}>
+                      {new Date(a.date).toLocaleDateString()} — {a.score}/{a.total}
+                    </span>
+                    <span style={{
+                      fontWeight: 700, fontSize: '0.85rem',
+                      color: a.percentage >= 80 ? 'var(--correct-fg)' : a.percentage >= 50 ? '#d97706' : 'var(--wrong-fg)',
+                    }}>{a.percentage}%</span>
+                    <a href={`/results/${a.attempt_id}`} style={{ color: 'var(--primary)', fontSize: '0.78rem', textDecoration: 'none', flexShrink: 0 }}>
+                      Review →
+                    </a>
+                  </div>
+                ))}
+              </div>
+            </div>
+          ))}
+        </div>
+      )}
+    </div>
+  )
+}
+
 function HighlightText({ text, query }) {
   if (!query || !text) return <span>{text}</span>
   const idx = text.toLowerCase().indexOf(query.toLowerCase())
@@ -204,6 +273,7 @@ export default function QuizzesPage() {
   const [studyQuestion, setStudyQuestion] = useState(null)
   const [newCatName, setNewCatName] = useState('')
   const [addingCat, setAddingCat] = useState(false)
+  const { dialogProps, openAlert } = useDialog()
   const debounceRef = useRef(null)
   const { user } = useAuth()
   const navigate = useNavigate()
@@ -256,7 +326,7 @@ export default function QuizzesPage() {
       setCategories(prev => [...prev, res.data])
       setNewCatName('')
       setAddingCat(false)
-    } catch (err) { alert(err.response?.data?.detail || 'Failed to create category') }
+    } catch (err) { await openAlert(err.response?.data?.detail || 'Failed to create category', { title: 'Error' }) }
   }
 
   const deleteCategory = async (catId) => {
@@ -283,6 +353,7 @@ export default function QuizzesPage() {
 
   return (
     <div>
+      <Dialog {...dialogProps} />
       {studyQuestion && (
         <QuestionStudyModal question={studyQuestion} query={searchQuery} onClose={() => setStudyQuestion(null)} />
       )}
@@ -374,6 +445,9 @@ export default function QuizzesPage() {
       {/* In-progress quizzes */}
       {!isSearching && <InProgressSection />}
 
+      {/* Past attempts (loads on demand) */}
+      {!isSearching && <PastAttemptsSection />}
+
       {/* Normal quiz grid */}
       {!isSearching && (
         <>

frontend/src/pages/SettingsPage.jsx

@@ -203,7 +203,7 @@ function AdminSection() {
     <Section title="Administration">
       <div style={{ display: 'grid', gridTemplateColumns: 'repeat(auto-fill, minmax(180px, 1fr))', gap: 12 }}>
         {[
-          { to: '/admin', icon: '👥', label: 'User Management', desc: 'Manage accounts and roles' },
+          { to: '/admin', icon: '⚙️', label: 'Admin Dashboard', desc: 'Models, users, and settings' },
           { to: '/upload', icon: '📄', label: 'Upload PDF', desc: 'Add new documents' },
           { to: '/trash', icon: '🗑️', label: 'Trash', desc: 'Restore deleted quizzes' },
           { to: '/jobs', icon: '📋', label: 'Extraction Jobs', desc: 'View extraction history' },