diff --git a/platform/api/migrations/015_scenario_attempts_abandonment.sql b/platform/api/migrations/015_scenario_attempts_abandonment.sql
new file mode 100644
index 0000000..32db14a
--- /dev/null
+++ b/platform/api/migrations/015_scenario_attempts_abandonment.sql
@@ -0,0 +1,20 @@
+-- Abandoned/interrupted attempt handling — Phase 4.1, docs/PHASE4_1_PREPRODUCTION_HARDENING.md
+-- §13. 'abandoned' was already a valid scenario_attempts.status value (migration 012's CHECK
+-- constraint) but nothing ever set it — an attempt left open when a Lab was reaped, an
+-- environment destroyed, a session ended, or a student moved on to a different scenario just
+-- stayed 'in_progress' forever, an honest but incomplete signal. This is NOT an academic
+-- failure marker — an abandoned attempt has no `result`, doesn't count against the student,
+-- and the row is never deleted (see src/attempts.js abandonAttempt for the enforcement of
+-- that). It exists so instructor views and needs-attention logic can tell "still working" from
+-- "stopped, for a reason we know."
+
+ALTER TABLE scenario_attempts ADD COLUMN IF NOT EXISTS abandoned_at TIMESTAMPTZ;
+ALTER TABLE scenario_attempts ADD COLUMN IF NOT EXISTS abandoned_reason TEXT;
+
+DO $$ BEGIN
+  ALTER TABLE scenario_attempts ADD CONSTRAINT scenario_attempts_abandoned_reason_check
+    CHECK (abandoned_reason IS NULL OR abandoned_reason IN
+      ('environment_destroyed', 'session_ended', 'scenario_switched'));
+EXCEPTION
+  WHEN duplicate_object THEN NULL;
+END $$;
diff --git a/platform/api/src/attempts.js b/platform/api/src/attempts.js
index 036ba4a..b782aaa 100644
--- a/platform/api/src/attempts.js
+++ b/platform/api/src/attempts.js
@@ -2,11 +2,55 @@
 // session on a scenario (not per validation click, see migrations/012). Every mutation here
 // updates that one row in place; nothing is ever inserted twice for the same open attempt.
 //
-// Deliberately does NOT try to detect "abandoned" attempts automatically (e.g. on Lab destroy)
-// — that would need a reaper-style background job wired to Provisioner environment_events,
-// which is more machinery than the instructional-visibility goal here needs. An attempt just
-// stays 'in_progress' if the student never returns to finish it; instructors can already see
-// "in_progress, N failed validations" as a real signal. Documented as a known limitation.
+// Phase 4.1 (docs/PHASE4_1_PREPRODUCTION_HARDENING.md §13) added real abandonment handling —
+// see abandonAttempt/abandonOpenAttemptsFor* below and their call sites (environment
+// destroy/reset in server.js and admin-routes.js, logout in server.js, the session sweeper in
+// sessions.js, and the "different scenario" transition inline in getOrCreateOpenAttempt just
+// below). Still deliberately NOT a new standalone background job — every trigger either rides
+// an existing request handler or the session sweeper that already runs periodically.
+
+// An attempt is never silently deleted or marked as a failure by abandonment — result stays
+// NULL, the row stays queryable, instructors see "abandoned (reason)" as a real, honest status
+// rather than a punitive one. No-op (and does not overwrite an existing abandoned_reason) if
+// the attempt is already terminal.
+async function abandonAttempt(pool, attemptId, reason) {
+  const { rows } = await pool.query(
+    `UPDATE scenario_attempts SET status = 'abandoned', abandoned_at = now(), abandoned_reason = $2
+     WHERE attempt_id = $1 AND status = 'in_progress' RETURNING *`,
+    [attemptId, reason]
+  );
+  return rows[0] || null;
+}
+
+// Trigger: environment destroyed (idle reaper, student reset, admin reset/destroy — see
+// server.js's student reset route and admin-routes.js's reset/destroy routes, all of which
+// call this right after telling the Provisioner to tear the environment down). A reset creates
+// a fresh environment_id in some flows and reuses the same one in others (see
+// provisioner lifecycle.js's reset — same environment_id, fresh container) — either way, any
+// attempt still open against the OLD container state is honestly "not going to be resumed as
+// the same working session," so it's abandoned rather than left open indefinitely.
+async function abandonOpenAttemptsForEnvironment(pool, environmentId) {
+  const { rows } = await pool.query(
+    `UPDATE scenario_attempts SET status = 'abandoned', abandoned_at = now(), abandoned_reason = 'environment_destroyed'
+     WHERE environment_id = $1 AND status = 'in_progress' RETURNING attempt_id`,
+    [environmentId]
+  );
+  return rows.length;
+}
+
+// Trigger: logout (server.js POST /api/logout) and the session sweeper's periodic pass for
+// students whose sessions have all expired (sessions.js). Deliberately student-scoped, not
+// environment-scoped — a student can log out while their Lab keeps running (it isn't
+// destroyed until reaped or explicitly ended), but the WORKING SESSION on whatever scenario
+// they had open is over the moment they're no longer authenticated to record more progress on it.
+async function abandonOpenAttemptsForStudent(pool, studentId) {
+  const { rows } = await pool.query(
+    `UPDATE scenario_attempts SET status = 'abandoned', abandoned_at = now(), abandoned_reason = 'session_ended'
+     WHERE student_id = $1 AND status = 'in_progress' RETURNING attempt_id`,
+    [studentId]
+  );
+  return rows.length;
+}
 
 async function getOrCreateOpenAttempt(pool, { studentId, scenarioId, environmentId, cohortId, curriculumStage, assessmentSessionId }) {
   const { rows: existing } = await pool.query(
@@ -17,6 +61,17 @@ async function getOrCreateOpenAttempt(pool, { studentId, scenarioId, environment
   );
   if (existing[0]) return existing[0];
 
+  // Trigger: student starts a different scenario while a previous one is still open (started
+  // via /start or implicitly via /validate, never finished). Only one scenario is "the one
+  // currently being worked on" per student+environment at a time from the app's own UX, so an
+  // open attempt on ANY OTHER scenario in this same environment is abandoned before the new
+  // one is created — never silently left as a phantom "still in progress" row.
+  await pool.query(
+    `UPDATE scenario_attempts SET status = 'abandoned', abandoned_at = now(), abandoned_reason = 'scenario_switched'
+     WHERE student_id = $1 AND environment_id = $2 AND scenario_id != $3 AND status = 'in_progress'`,
+    [studentId, environmentId, scenarioId]
+  );
+
   const { rows } = await pool.query(
     `INSERT INTO scenario_attempts
        (student_id, scenario_id, environment_id, cohort_id, curriculum_stage, started_at, status, assessment_session_id)
@@ -80,4 +135,7 @@ async function getAttemptSummary(pool, { studentId, scenarioId, environmentId })
   return rows[0] || null;
 }
 
-module.exports = { getOrCreateOpenAttempt, recordValidation, recordHintReveal, getAttemptSummary };
+module.exports = {
+  getOrCreateOpenAttempt, recordValidation, recordHintReveal, getAttemptSummary,
+  abandonAttempt, abandonOpenAttemptsForEnvironment, abandonOpenAttemptsForStudent,
+};
diff --git a/platform/api/src/sessions.js b/platform/api/src/sessions.js
index 0eeac60..cc0bd52 100644
--- a/platform/api/src/sessions.js
+++ b/platform/api/src/sessions.js
@@ -104,11 +104,28 @@ async function listInstructorSessions(pool, instructorId) {
 
 // Periodic cleanup of long-dead rows so the table doesn't grow forever — cosmetic/storage only,
 // not a security control (expired/revoked rows already fail resolveSession's WHERE clause).
+//
+// Phase 4.1 §13 also piggybacks the "session expires" abandonment trigger onto this same
+// existing interval, rather than adding a new background job: any scenario_attempts row still
+// 'in_progress' for a student with NO live session left (every session expired, idle-timed-out,
+// or revoked, not just deleted by the sweep above) gets abandoned. Deliberately does the
+// attempts update in the SAME pool.query call — one round trip, no separate job to keep in sync.
 function startSessionSweeper(pool) {
   setInterval(() => {
     pool.query(`DELETE FROM sessions WHERE expires_at < now() - interval '7 days'`).catch((e) => {
       console.error('[session sweep] failed:', e.message);
     });
+    pool.query(`
+      UPDATE scenario_attempts SET status = 'abandoned', abandoned_at = now(), abandoned_reason = 'session_ended'
+      WHERE status = 'in_progress'
+        AND NOT EXISTS (
+          SELECT 1 FROM sessions
+          WHERE sessions.student_id = scenario_attempts.student_id
+            AND sessions.revoked_at IS NULL AND sessions.expires_at > now() AND sessions.idle_expires_at > now()
+        )
+    `).catch((e) => {
+      console.error('[session sweep] attempt abandonment failed:', e.message);
+    });
   }, 60 * 60 * 1000).unref();
 }