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app/instructor/page.tsx

@@ -8,6 +8,8 @@ import ExercisesTable from './ExercisesTable';
 import AnalyticsPanel from './AnalyticsPanel';
 import Navbar from '@/app/components/Navbar';
 import { Radio, Users } from 'lucide-react';
+import { getAllHistoryResults, type HistorySession } from '@/lib/history-db';
+import { formatWAT } from '@/lib/format';
 
 interface Exercise {
   id: string;
@@ -161,8 +163,81 @@ export default async function InstructorDashboard() {
             </div>
             <LiveMonitor />
           </div>
+
+          {/* Past Cohorts History */}
+          <PastCohorts />
         </div>
       </main>
     </div>
   );
 }
+
+async function PastCohorts() {
+  const history = await getAllHistoryResults().catch(() => []);
+  if (history.length === 0) return null;
+
+  // Group by cohort
+  const cohorts = new Map<string, Array<HistorySession & { username: string }>>();
+  for (const h of history) {
+    if (!cohorts.has(h.cohort)) cohorts.set(h.cohort, []);
+    cohorts.get(h.cohort)!.push(h);
+  }
+
+  return (
+    <div style={{ marginTop: '2rem' }}>
+      <div className="section-header">
+        <span className="section-title">Past Recoding</span>
+      </div>
+      {Array.from(cohorts.entries()).map(([cohort, rows]) => {
+        const passed = rows.filter((r) => r.passed === true).length;
+        const failed = rows.filter((r) => r.passed === false).length;
+        return (
+          <div key={cohort} className="card" style={{ marginBottom: '1rem' }}>
+            <div className="card-header">
+              <span className="card-title">{cohort}</span>
+              <div style={{ display: 'flex', gap: '0.5rem' }}>
+                <span className="badge badge-green">{passed} passed</span>
+                <span className="badge badge-red">{failed} failed</span>
+                <span className="badge badge-gray">{rows.length} total</span>
+              </div>
+            </div>
+            <div className="table-wrap">
+              <table>
+                <thead>
+                  <tr>
+                    <th>Participant</th>
+                    <th>Exercise</th>
+                    <th>Score</th>
+                    <th>Result</th>
+                    <th>Questions</th>
+                    <th>Completed</th>
+                  </tr>
+                </thead>
+                <tbody>
+                  {rows.map((r, i) => (
+                    <tr key={i}>
+                      <td style={{ fontWeight: 600 }}>{r.username}</td>
+                      <td>{r.exercise_title}</td>
+                      <td style={{ fontVariantNumeric: 'tabular-nums' }}>
+                        {r.score !== null ? `${Number(r.score).toFixed(1)}%` : '—'}
+                      </td>
+                      <td>
+                        {r.passed === true
+                          ? <span className="badge badge-green">Pass</span>
+                          : r.passed === false
+                            ? <span className="badge badge-red">Fail</span>
+                            : <span className="badge badge-gray">—</span>}
+                      </td>
+                      <td style={{ color: 'var(--text2)' }}>{r.final_count}/{r.question_count}</td>
+                      <td style={{ color: 'var(--text3)' }}>{r.closed_at ? formatWAT(r.closed_at) : '—'}</td>
+                    </tr>
+                  ))}
+                </tbody>
+              </table>
+            </div>
+          </div>
+        );
+      })}
+    </div>
+  );
+}

app/participant/page.tsx

@@ -5,6 +5,8 @@ import { sql } from '@/lib/db';
 import Link from 'next/link';
 import Navbar from '@/app/components/Navbar';
 import { InboxIcon } from 'lucide-react';
+import { getParticipantHistory } from '@/lib/history-db';
+import { formatWAT } from '@/lib/format';
 
 export const dynamic = 'force-dynamic';
 
@@ -49,8 +51,7 @@ export default async function ExerciseCataloguePage() {
     console.error('[participant/page] Failed to load exercises:', err);
   }
 
-  if (!fetchError && exercises.length > 0) {
-    try {
+  if (!fetchError && exercises.length > 0) {    try {
       const ids = exercises.map((e) => e.id);
       const sessions = await sql`
         SELECT exercise_id, closed_at, score, passed,
@@ -97,6 +98,9 @@ export default async function ExerciseCataloguePage() {
     }
   }
 
+  // Fetch history from past exam DBs
+  const history = await getParticipantHistory(session.user.name ?? '').catch(() => []);
+
   return (
     <div className="page">
       <Navbar username={session.user.name ?? undefined} role="participant" />
@@ -178,6 +182,38 @@ export default async function ExerciseCataloguePage() {
               );
             })}
           </div>
+
+          {/* Past Recoding History */}
+          {history.length > 0 && (
+            <div style={{ marginTop: '2rem' }}>
+              <div className="page-header" style={{ marginBottom: '1rem' }}>
+                <h2 style={{ fontSize: '1.1rem', fontWeight: 700, color: 'var(--text)' }}>Past Recoding</h2>
+                <p className="page-sub">Your results from previous recoding sessions.</p>
+              </div>
+              <div style={{ display: 'flex', flexDirection: 'column', gap: '0.75rem' }}>
+                {history.map((h, i) => (
+                  <div key={i} className="exercise-card" style={{ cursor: 'default' }}>
+                    <div className="exercise-card-info">
+                      <div className="exercise-card-title">{h.exercise_title}</div>
+                      <div className="exercise-card-meta" style={{ display: 'flex', gap: '0.75rem', flexWrap: 'wrap' }}>
+                        <span>{h.cohort}</span>
+                        {h.closed_at && <span>{formatWAT(h.closed_at)}</span>}
+                        <span>{h.final_count}/{h.question_count} questions submitted</span>
+                      </div>
+                    </div>
+                    <div style={{ display: 'flex', alignItems: 'center', gap: '0.5rem', flexWrap: 'wrap', justifyContent: 'flex-end' }}>
+                      {h.score !== null && (
+                        <span className={`badge ${h.passed === false ? 'badge-red' : h.passed === true ? 'badge-green' : 'badge-gray'}`} style={{ fontSize: 11 }}>
+                          {Number(h.score).toFixed(1)}%{h.passed === true ? ' ✓ Pass' : h.passed === false ? ' ✗ Fail' : ''}
+                        </span>
+                      )}
+                      <span className="badge badge-gray" style={{ fontSize: 11 }}>Completed</span>
+                    </div>
+                  </div>
+                ))}
+              </div>
+            </div>
+          )}
         </div>
       </main>
     </div>

lib/history-db.ts

@@ -0,0 +1,160 @@
+/**
+ * History database connections — read-only connections to past exam DBs.
+ * Configure via env vars: HISTORY_DB_1_URL, HISTORY_DB_1_LABEL, etc.
+ */
+
+import { neon } from '@neondatabase/serverless';
+
+export interface HistoryDb {
+  index: number;
+  label: string;
+  sql: ReturnType<typeof neon>;
+}
+
+let _cache: HistoryDb[] | null = null;
+
+export function getHistoryDbs(): HistoryDb[] {
+  if (_cache) return _cache;
+
+  const dbs: HistoryDb[] = [];
+  let i = 1;
+
+  while (true) {
+    const url = process.env[`HISTORY_DB_${i}_URL`];
+    if (!url) break;
+
+    const label = process.env[`HISTORY_DB_${i}_LABEL`] ?? `Cohort ${i}`;
+    dbs.push({ index: i, label, sql: neon(url) });
+    i++;
+  }
+
+  _cache = dbs;
+  return dbs;
+}
+
+export interface HistorySession {
+  cohort: string;
+  cohortIndex: number;
+  exercise_title: string;
+  exercise_slug: string;
+  score: number | null;
+  passed: boolean | null;
+  closed_at: string | null;
+  question_count: number;
+  final_count: number;
+}
+
+/**
+ * Fetch past session results for a participant across all history DBs.
+ * Matches by username since user IDs may differ across DBs.
+ */
+export async function getParticipantHistory(username: string): Promise<HistorySession[]> {
+  const dbs = getHistoryDbs();
+  if (dbs.length === 0) return [];
+
+  const results: HistorySession[] = [];
+
+  await Promise.all(
+    dbs.map(async (db) => {
+      try {
+        const rows = await db.sql`
+          SELECT
+            e.title        AS exercise_title,
+            e.slug         AS exercise_slug,
+            e.question_count,
+            s.score,
+            s.passed,
+            s.closed_at,
+            (SELECT COUNT(*)::int FROM submissions sub
+             WHERE sub.session_id = s.id AND sub.is_final = true) AS final_count
+          FROM sessions s
+          JOIN exercises e ON e.id = s.exercise_id
+          JOIN users u ON u.id = s.user_id
+          WHERE u.username = ${username}
+            AND s.closed_at IS NOT NULL
+          ORDER BY s.closed_at DESC
+        ` as Record<string, unknown>[];
+
+        for (const row of rows) {
+          results.push({
+            cohort: db.label,
+            cohortIndex: db.index,
+            exercise_title: row.exercise_title as string,
+            exercise_slug: row.exercise_slug as string,
+            score: row.score as number | null,
+            passed: row.passed as boolean | null,
+            closed_at: row.closed_at as string | null,
+            question_count: row.question_count as number,
+            final_count: row.final_count as number,
+          });
+        }
+      } catch (err) {
+        console.error(`[history-db] Failed to query cohort "${db.label}":`, err);
+      }
+    })
+  );
+
+  // Sort by closed_at descending across all cohorts
+  return results.sort((a, b) => {
+    if (!a.closed_at) return 1;
+    if (!b.closed_at) return -1;
+    return new Date(b.closed_at).getTime() - new Date(a.closed_at).getTime();
+  });
+}
+
+/**
+ * Fetch all past results across all history DBs for instructor view.
+ */
+export async function getAllHistoryResults(): Promise<Array<HistorySession & { username: string }>> {
+  const dbs = getHistoryDbs();
+  if (dbs.length === 0) return [];
+
+  const results: Array<HistorySession & { username: string }> = [];
+
+  await Promise.all(
+    dbs.map(async (db) => {
+      try {
+        const rows = await db.sql`
+          SELECT
+            u.username,
+            e.title        AS exercise_title,
+            e.slug         AS exercise_slug,
+            e.question_count,
+            s.score,
+            s.passed,
+            s.closed_at,
+            (SELECT COUNT(*)::int FROM submissions sub
+             WHERE sub.session_id = s.id AND sub.is_final = true) AS final_count
+          FROM sessions s
+          JOIN exercises e ON e.id = s.exercise_id
+          JOIN users u ON u.id = s.user_id
+          WHERE s.closed_at IS NOT NULL
+          ORDER BY u.username, s.closed_at DESC
+        ` as Record<string, unknown>[];
+
+        for (const row of rows) {
+          results.push({
+            username: row.username as string,
+            cohort: db.label,
+            cohortIndex: db.index,
+            exercise_title: row.exercise_title as string,
+            exercise_slug: row.exercise_slug as string,
+            score: row.score as number | null,
+            passed: row.passed as boolean | null,
+            closed_at: row.closed_at as string | null,
+            question_count: row.question_count as number,
+            final_count: row.final_count as number,
+          });
+        }
+      } catch (err) {
+        console.error(`[history-db] Failed to query cohort "${db.label}":`, err);
+      }
+    })
+  );
+
+  return results.sort((a, b) => {
+    if (!a.closed_at) return 1;
+    if (!b.closed_at) return -1;
+    return new Date(b.closed_at).getTime() - new Date(a.closed_at).getTime();
+  });
+}

migrations/reset_keep_users.sql

@@ -0,0 +1,20 @@
+-- ============================================================
+-- Reset script — wipes all session/exercise data, keeps users
+-- Safe to run between exam cohorts.
+-- Run with: psql $DATABASE_URL -f migrations/reset_keep_users.sql
+-- ============================================================
+
+-- Delete in dependency order
+TRUNCATE TABLE
+  audit_log,
+  autosave_history,
+  edit_events,
+  paste_events,
+  focus_events,
+  submissions,
+  sessions,
+  exercise_assignments,
+  questions,
+  exercises,
+  feedback
+RESTART IDENTITY CASCADE;

package.json

@@ -9,6 +9,7 @@
     "lint": "next lint",
     "test": "vitest run",
     "migrate": "psql $DATABASE_URL -f migrations/run_all.sql",
+    "db:reset": "psql $DATABASE_URL -f migrations/reset_keep_users.sql",
     "test:watch": "vitest",
     "migrate:fresh": "tsx scripts/migrate.ts fresh && tsx scripts/seed.ts && tsx scripts/import-questions.ts",
     "seed": "tsx scripts/seed.ts",