diff --git a/platform/cmd/server/main.go b/platform/cmd/server/main.go
index d65d493f..da102453 100644
--- a/platform/cmd/server/main.go
+++ b/platform/cmd/server/main.go
@@ -185,6 +185,13 @@ func main() {
 	cronSched := scheduler.New(wh, broadcaster)
 	go supervised.RunWithRecover(ctx, "scheduler", cronSched.Start)
 
+	// Hibernation Monitor — auto-pauses idle workspaces that have
+	// hibernation_idle_minutes configured (#711). Wakeup is triggered
+	// automatically on the next incoming A2A message.
+	go supervised.RunWithRecover(ctx, "hibernation-monitor", func(c context.Context) {
+		registry.StartHibernationMonitor(c, wh.HibernateWorkspace)
+	})
+
 	// Channel Manager — social channel integrations (Telegram, Slack, etc.)
 	channelMgr := channels.NewManager(wh, broadcaster)
 	go supervised.RunWithRecover(ctx, "channel-manager", channelMgr.Start)
diff --git a/platform/internal/handlers/a2a_proxy.go b/platform/internal/handlers/a2a_proxy.go
index 4d8c51be..ca81334b 100644
--- a/platform/internal/handlers/a2a_proxy.go
+++ b/platform/internal/handlers/a2a_proxy.go
@@ -288,16 +288,16 @@ func (h *WorkspaceHandler) proxyA2ARequest(ctx context.Context, workspaceID stri
 	}
 	defer resp.Body.Close()
 
-	// Read agent response (capped at 10MB)
+	// Read agent response (capped at 10MB).
+	// #689: Do() succeeded, which means the target received the request and sent
+	// back response headers — delivery is confirmed. The body couldn't be
+	// fully read (connection drop, timeout mid-stream). Surface
+	// delivery_confirmed so callers can distinguish "not delivered" from
+	// "delivered, but response body lost". When delivery is confirmed,
+	// log the activity as successful (delivery happened) rather than leaving
+	// a false "failed" entry in the audit trail.
 	respBody, readErr := io.ReadAll(io.LimitReader(resp.Body, maxProxyResponseBody))
 	if readErr != nil {
-		// Do() succeeded, which means the target received the request and sent
-		// back response headers — delivery is confirmed. The body couldn't be
-		// fully read (connection drop, timeout mid-stream). Surface
-		// delivery_confirmed so callers can distinguish "not delivered" from
-		// "delivered, but response body lost" (#689). When delivery is confirmed,
-		// log the activity as successful (delivery happened) rather than leaving
-		// a false "failed" entry in the audit trail.
 		deliveryConfirmed := resp.StatusCode >= 200 && resp.StatusCode < 400
 		log.Printf("ProxyA2A: body read failed for %s (status=%d delivery_confirmed=%v bytes_read=%d): %v",
 			workspaceID, resp.StatusCode, deliveryConfirmed, len(respBody), readErr)
@@ -352,6 +352,22 @@ func (h *WorkspaceHandler) resolveAgentURL(ctx context.Context, workspaceID stri
 			}
 		}
 		if !urlNullable.Valid || urlNullable.String == "" {
+			// Auto-wake hibernated workspace on incoming A2A message (#711).
+			// Re-provision asynchronously and return 503 with a retry hint so
+			// the caller can retry once the workspace is back online (~10s).
+			if status == "hibernated" {
+				log.Printf("ProxyA2A: waking hibernated workspace %s", workspaceID)
+				go h.RestartByID(workspaceID)
+				return "", &proxyA2AError{
+					Status:  http.StatusServiceUnavailable,
+					Headers: map[string]string{"Retry-After": "15"},
+					Response: gin.H{
+						"error":       "workspace is waking from hibernation — retry in ~15 seconds",
+						"waking":      true,
+						"retry_after": 15,
+					},
+				}
+			}
 			return "", &proxyA2AError{
 				Status:   http.StatusServiceUnavailable,
 				Response: gin.H{"error": "workspace has no URL", "status": status},
diff --git a/platform/internal/handlers/a2a_proxy_test.go b/platform/internal/handlers/a2a_proxy_test.go
index da7c2257..438e4c06 100644
--- a/platform/internal/handlers/a2a_proxy_test.go
+++ b/platform/internal/handlers/a2a_proxy_test.go
@@ -1282,3 +1282,81 @@ func TestLogA2ASuccess_ErrorStatus(t *testing.T) {
 	handler.logA2ASuccess(context.Background(), "ws-err", "ws-caller", []byte(`{}`), []byte(`{}`), "message/send", 500, 10)
 	time.Sleep(80 * time.Millisecond)
 }
+
+// ──────────────────────────────────────────────────────────────────────────────
+// A2A auto-wake: hibernated workspace (#711)
+// ──────────────────────────────────────────────────────────────────────────────
+
+// TestResolveAgentURL_HibernatedWorkspace_Returns503WithWaking verifies the
+// auto-wake path added in PR #724: when resolveAgentURL finds a workspace with
+// status='hibernated' and no URL, it must:
+//   - Return a proxyA2AError with Status 503
+//   - Set Retry-After: 15 in Headers
+//   - Include waking:true and retry_after:15 in the response body
+//
+// RestartByID fires asynchronously via `go h.RestartByID(workspaceID)`. Because
+// provisioner is nil in tests, RestartByID returns immediately without any DB
+// calls, so no additional mocks are needed.
+func TestResolveAgentURL_HibernatedWorkspace_Returns503WithWaking(t *testing.T) {
+	mock := setupTestDB(t)
+	setupTestRedis(t) // empty Redis → GetCachedURL returns error → DB fallback
+
+	handler := NewWorkspaceHandler(newTestBroadcaster(), nil, "http://localhost:8080", t.TempDir())
+
+	// DB fallback: workspace exists but has no URL and is hibernated.
+	mock.ExpectQuery(`SELECT url, status FROM workspaces WHERE id =`).
+		WithArgs("ws-hibernated").
+		WillReturnRows(sqlmock.NewRows([]string{"url", "status"}).AddRow("", "hibernated"))
+
+	_, perr := handler.resolveAgentURL(context.Background(), "ws-hibernated")
+
+	if perr == nil {
+		t.Fatal("expected proxyA2AError, got nil")
+	}
+	if perr.Status != http.StatusServiceUnavailable {
+		t.Errorf("expected status 503, got %d", perr.Status)
+	}
+	if perr.Headers["Retry-After"] != "15" {
+		t.Errorf("expected Retry-After: 15, got %q", perr.Headers["Retry-After"])
+	}
+
+	if perr.Response["waking"] != true {
+		t.Errorf("expected waking:true in body, got %v", perr.Response["waking"])
+	}
+	if perr.Response["retry_after"] != 15 {
+		t.Errorf("expected retry_after:15 in body, got %v", perr.Response["retry_after"])
+	}
+
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet DB expectations: %v", err)
+	}
+}
+
+// TestResolveAgentURL_HibernatedWorkspace_NullURLVariant verifies the same
+// auto-wake behaviour when the DB returns a SQL NULL for the url column
+// (rather than an empty string). Both forms represent "no URL assigned".
+func TestResolveAgentURL_HibernatedWorkspace_NullURLVariant(t *testing.T) {
+	mock := setupTestDB(t)
+	setupTestRedis(t)
+	handler := NewWorkspaceHandler(newTestBroadcaster(), nil, "http://localhost:8080", t.TempDir())
+
+	mock.ExpectQuery(`SELECT url, status FROM workspaces WHERE id =`).
+		WithArgs("ws-hibernated-null").
+		WillReturnRows(sqlmock.NewRows([]string{"url", "status"}).AddRow(nil, "hibernated"))
+
+	_, perr := handler.resolveAgentURL(context.Background(), "ws-hibernated-null")
+
+	if perr == nil {
+		t.Fatal("expected proxyA2AError, got nil")
+	}
+	if perr.Status != http.StatusServiceUnavailable {
+		t.Errorf("expected status 503, got %d", perr.Status)
+	}
+	if perr.Headers["Retry-After"] != "15" {
+		t.Errorf("expected Retry-After: 15, got %q", perr.Headers["Retry-After"])
+	}
+
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet DB expectations: %v", err)
+	}
+}
diff --git a/platform/internal/handlers/hibernation_test.go b/platform/internal/handlers/hibernation_test.go
new file mode 100644
index 00000000..819f7f4f
--- /dev/null
+++ b/platform/internal/handlers/hibernation_test.go
@@ -0,0 +1,266 @@
+package handlers
+
+// Integration tests for the workspace hibernation feature (issue #711 / PR #724).
+//
+// Coverage:
+//   - HibernateWorkspace(): container stop, DB status update, Redis key clear, event broadcast
+//   - POST /workspaces/:id/hibernate HTTP handler: online→200, not-eligible→404, DB error→500
+//   - resolveAgentURL(): hibernated workspace → 503 + Retry-After: 15 + waking: true
+//
+// The A2A auto-wake path (resolveAgentURL) is tested via TestResolveAgentURL_HibernatedWorkspace_*
+// added to a2a_proxy_test.go to keep related resolveAgentURL tests co-located.
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	sqlmock "github.com/DATA-DOG/go-sqlmock"
+	"github.com/gin-gonic/gin"
+)
+
+// ──────────────────────────────────────────────────────────────────────────────
+// HibernateWorkspace unit tests
+// ──────────────────────────────────────────────────────────────────────────────
+
+// TestHibernateWorkspace_OnlineWorkspace_Success verifies the happy-path:
+//   - DB returns the workspace (online/degraded)
+//   - provisioner is nil — no Stop() call needed (test-safe guard in production code)
+//   - UPDATE sets status='hibernated', url=''
+//   - Redis keys ws:{id}, ws:{id}:url, ws:{id}:internal_url are deleted
+//   - WORKSPACE_HIBERNATED event is broadcast (INSERT INTO structure_events)
+func TestHibernateWorkspace_OnlineWorkspace_Success(t *testing.T) {
+	mock := setupTestDB(t)
+	mr := setupTestRedis(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewWorkspaceHandler(broadcaster, nil, "http://localhost:8080", t.TempDir())
+
+	wsID := "ws-idle-online"
+
+	// Pre-populate Redis keys that ClearWorkspaceKeys should remove.
+	mr.Set(fmt.Sprintf("ws:%s", wsID), "some-value")
+	mr.Set(fmt.Sprintf("ws:%s:url", wsID), "http://agent.internal:8000")
+	mr.Set(fmt.Sprintf("ws:%s:internal_url", wsID), "http://172.17.0.5:8000")
+
+	// HibernateWorkspace does a SELECT first.
+	mock.ExpectQuery(`SELECT name, tier FROM workspaces WHERE id = .* AND status IN`).
+		WithArgs(wsID).
+		WillReturnRows(sqlmock.NewRows([]string{"name", "tier"}).AddRow("Idle Agent", 1))
+
+	// Then UPDATE status.
+	mock.ExpectExec(`UPDATE workspaces SET status = 'hibernated'`).
+		WithArgs(wsID).
+		WillReturnResult(sqlmock.NewResult(0, 1))
+
+	// Broadcaster inserts a structure_events row.
+	mock.ExpectExec(`INSERT INTO structure_events`).
+		WillReturnResult(sqlmock.NewResult(0, 1))
+
+	handler.HibernateWorkspace(context.Background(), wsID)
+
+	// All DB expectations were exercised.
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet DB expectations: %v", err)
+	}
+
+	// Redis keys must all be gone.
+	for _, suffix := range []string{"", ":url", ":internal_url"} {
+		key := fmt.Sprintf("ws:%s%s", wsID, suffix)
+		if _, err := mr.Get(key); err == nil {
+			t.Errorf("expected Redis key %q to be deleted, but it still exists", key)
+		}
+	}
+}
+
+// TestHibernateWorkspace_NotEligible_NoOp verifies that when the workspace is
+// NOT in online/degraded state (SELECT returns ErrNoRows), HibernateWorkspace
+// returns immediately — no UPDATE, no Redis clear, no broadcast.
+func TestHibernateWorkspace_NotEligible_NoOp(t *testing.T) {
+	mock := setupTestDB(t)
+	mr := setupTestRedis(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewWorkspaceHandler(broadcaster, nil, "http://localhost:8080", t.TempDir())
+
+	wsID := "ws-already-offline"
+
+	// Simulate workspace not in eligible state (offline, paused, removed …)
+	mock.ExpectQuery(`SELECT name, tier FROM workspaces WHERE id = .* AND status IN`).
+		WithArgs(wsID).
+		WillReturnError(sql.ErrNoRows)
+
+	// Set a Redis key to confirm it is NOT cleared by early return.
+	mr.Set(fmt.Sprintf("ws:%s:url", wsID), "http://still-here:8000")
+
+	handler.HibernateWorkspace(context.Background(), wsID)
+
+	// No further DB operations should have happened.
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet DB expectations: %v", err)
+	}
+
+	// Redis key must still exist — HibernateWorkspace returned early.
+	if _, err := mr.Get(fmt.Sprintf("ws:%s:url", wsID)); err != nil {
+		t.Errorf("expected Redis key to still exist after no-op, but it was deleted: %v", err)
+	}
+}
+
+// TestHibernateWorkspace_DBUpdateFails_NoCrash verifies that a DB error on the
+// UPDATE does not panic — the function logs and returns silently.
+func TestHibernateWorkspace_DBUpdateFails_NoCrash(t *testing.T) {
+	mock := setupTestDB(t)
+	setupTestRedis(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewWorkspaceHandler(broadcaster, nil, "http://localhost:8080", t.TempDir())
+
+	wsID := "ws-update-fail"
+
+	mock.ExpectQuery(`SELECT name, tier FROM workspaces WHERE id = .* AND status IN`).
+		WithArgs(wsID).
+		WillReturnRows(sqlmock.NewRows([]string{"name", "tier"}).AddRow("Flaky Agent", 2))
+
+	mock.ExpectExec(`UPDATE workspaces SET status = 'hibernated'`).
+		WithArgs(wsID).
+		WillReturnError(fmt.Errorf("db: connection refused"))
+
+	// Must not panic — test will catch a panic via t.Fatal.
+	defer func() {
+		if r := recover(); r != nil {
+			t.Fatalf("HibernateWorkspace panicked on UPDATE error: %v", r)
+		}
+	}()
+
+	handler.HibernateWorkspace(context.Background(), wsID)
+
+	// SELECT + UPDATE expectations met; no INSERT INTO structure_events expected.
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet DB expectations: %v", err)
+	}
+}
+
+// ──────────────────────────────────────────────────────────────────────────────
+// POST /workspaces/:id/hibernate HTTP handler tests
+// ──────────────────────────────────────────────────────────────────────────────
+
+// hibernateRequest fires POST /workspaces/{id}/hibernate against the handler
+// and returns the response recorder.
+func hibernateRequest(t *testing.T, handler *WorkspaceHandler, wsID string) *httptest.ResponseRecorder {
+	t.Helper()
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Params = gin.Params{{Key: "id", Value: wsID}}
+	c.Request = httptest.NewRequest(http.MethodPost, "/workspaces/"+wsID+"/hibernate", nil)
+	handler.Hibernate(c)
+	return w
+}
+
+// TestHibernateHandler_Online_Returns200 verifies that an online workspace
+// that is eligible for hibernation returns 200 {"status":"hibernated"}.
+func TestHibernateHandler_Online_Returns200(t *testing.T) {
+	mock := setupTestDB(t)
+	setupTestRedis(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewWorkspaceHandler(broadcaster, nil, "http://localhost:8080", t.TempDir())
+
+	wsID := "ws-handler-online"
+
+	// Hibernate() handler SELECT — verifies workspace is online/degraded.
+	mock.ExpectQuery(`SELECT name, tier FROM workspaces WHERE id = .* AND status IN`).
+		WithArgs(wsID).
+		WillReturnRows(sqlmock.NewRows([]string{"name", "tier"}).AddRow("Online Bot", 1))
+
+	// HibernateWorkspace() SELECT — same query, checks state again before acting.
+	mock.ExpectQuery(`SELECT name, tier FROM workspaces WHERE id = .* AND status IN`).
+		WithArgs(wsID).
+		WillReturnRows(sqlmock.NewRows([]string{"name", "tier"}).AddRow("Online Bot", 1))
+
+	// HibernateWorkspace() UPDATE.
+	mock.ExpectExec(`UPDATE workspaces SET status = 'hibernated'`).
+		WithArgs(wsID).
+		WillReturnResult(sqlmock.NewResult(0, 1))
+
+	// Broadcaster INSERT.
+	mock.ExpectExec(`INSERT INTO structure_events`).
+		WillReturnResult(sqlmock.NewResult(0, 1))
+
+	w := hibernateRequest(t, handler, wsID)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("expected 200, got %d: %s", w.Code, w.Body.String())
+	}
+
+	var resp map[string]interface{}
+	if err := json.Unmarshal(w.Body.Bytes(), &resp); err != nil {
+		t.Fatalf("failed to decode response: %v", err)
+	}
+	if resp["status"] != "hibernated" {
+		t.Errorf(`expected {"status":"hibernated"}, got %v`, resp)
+	}
+
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet DB expectations: %v", err)
+	}
+}
+
+// TestHibernateHandler_NotActive_Returns404 verifies that a workspace not in
+// online/degraded state (e.g. offline, paused, already hibernated) returns 404.
+func TestHibernateHandler_NotActive_Returns404(t *testing.T) {
+	mock := setupTestDB(t)
+	setupTestRedis(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewWorkspaceHandler(broadcaster, nil, "http://localhost:8080", t.TempDir())
+
+	wsID := "ws-handler-paused"
+
+	// Handler's eligibility SELECT returns no rows — workspace is not online/degraded.
+	mock.ExpectQuery(`SELECT name, tier FROM workspaces WHERE id = .* AND status IN`).
+		WithArgs(wsID).
+		WillReturnError(sql.ErrNoRows)
+
+	w := hibernateRequest(t, handler, wsID)
+
+	if w.Code != http.StatusNotFound {
+		t.Fatalf("expected 404, got %d: %s", w.Code, w.Body.String())
+	}
+
+	var resp map[string]interface{}
+	if err := json.Unmarshal(w.Body.Bytes(), &resp); err != nil {
+		t.Fatalf("failed to decode response: %v", err)
+	}
+	if !strings.Contains(fmt.Sprint(resp["error"]), "not found") {
+		t.Errorf("expected error mentioning 'not found', got %v", resp)
+	}
+
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet DB expectations: %v", err)
+	}
+}
+
+// TestHibernateHandler_DBError_Returns500 verifies that an unexpected DB error
+// on the eligibility SELECT returns 500.
+func TestHibernateHandler_DBError_Returns500(t *testing.T) {
+	mock := setupTestDB(t)
+	setupTestRedis(t)
+	broadcaster := newTestBroadcaster()
+	handler := NewWorkspaceHandler(broadcaster, nil, "http://localhost:8080", t.TempDir())
+
+	wsID := "ws-handler-dberror"
+
+	mock.ExpectQuery(`SELECT name, tier FROM workspaces WHERE id = .* AND status IN`).
+		WithArgs(wsID).
+		WillReturnError(fmt.Errorf("db: connection reset"))
+
+	w := hibernateRequest(t, handler, wsID)
+
+	if w.Code != http.StatusInternalServerError {
+		t.Fatalf("expected 500, got %d: %s", w.Code, w.Body.String())
+	}
+
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet DB expectations: %v", err)
+	}
+}
diff --git a/platform/internal/handlers/workspace_restart.go b/platform/internal/handlers/workspace_restart.go
index 3a263d39..49202ade 100644
--- a/platform/internal/handlers/workspace_restart.go
+++ b/platform/internal/handlers/workspace_restart.go
@@ -181,6 +181,68 @@ func (h *WorkspaceHandler) Restart(c *gin.Context) {
 	c.JSON(http.StatusOK, gin.H{"status": "provisioning", "config_dir": configLabel, "reset_session": resetClaudeSession})
 }
 
+// Hibernate handles POST /workspaces/:id/hibernate
+// Manually puts a running workspace into hibernation — useful for immediate
+// cost savings without waiting for the idle timer. The workspace auto-wakes
+// on the next incoming A2A message/send.
+func (h *WorkspaceHandler) Hibernate(c *gin.Context) {
+	id := c.Param("id")
+	ctx := c.Request.Context()
+
+	var wsName string
+	var tier int
+	err := db.DB.QueryRowContext(ctx,
+		`SELECT name, tier FROM workspaces WHERE id = $1 AND status IN ('online', 'degraded')`, id,
+	).Scan(&wsName, &tier)
+	if err == sql.ErrNoRows {
+		c.JSON(http.StatusNotFound, gin.H{"error": "workspace not found or not in a hibernatable state (must be online or degraded)"})
+		return
+	}
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "lookup failed"})
+		return
+	}
+
+	h.HibernateWorkspace(ctx, id)
+	c.JSON(http.StatusOK, gin.H{"status": "hibernated"})
+}
+
+// HibernateWorkspace stops the container and sets the workspace status to
+// 'hibernated'. Called by the hibernation monitor when a workspace has had
+// active_tasks == 0 for longer than its configured hibernation_idle_minutes.
+// Hibernated workspaces auto-wake on the next incoming A2A message.
+func (h *WorkspaceHandler) HibernateWorkspace(ctx context.Context, workspaceID string) {
+	var wsName string
+	var tier int
+	err := db.DB.QueryRowContext(ctx,
+		`SELECT name, tier FROM workspaces WHERE id = $1 AND status IN ('online', 'degraded')`, workspaceID,
+	).Scan(&wsName, &tier)
+	if err != nil {
+		// Already changed state (paused, removed, etc.) — nothing to do.
+		return
+	}
+
+	log.Printf("Hibernate: stopping container for %s (%s)", wsName, workspaceID)
+	if h.provisioner != nil {
+		h.provisioner.Stop(ctx, workspaceID)
+	}
+
+	_, err = db.DB.ExecContext(ctx,
+		`UPDATE workspaces SET status = 'hibernated', url = '', updated_at = now() WHERE id = $1 AND status IN ('online', 'degraded')`,
+		workspaceID)
+	if err != nil {
+		log.Printf("Hibernate: failed to update status for %s: %v", workspaceID, err)
+		return
+	}
+
+	db.ClearWorkspaceKeys(ctx, workspaceID)
+	h.broadcaster.RecordAndBroadcast(ctx, "WORKSPACE_HIBERNATED", workspaceID, map[string]interface{}{
+		"name": wsName,
+		"tier": tier,
+	})
+	log.Printf("Hibernate: workspace %s (%s) is now hibernated", wsName, workspaceID)
+}
+
 // RestartByID restarts a workspace by ID — for programmatic use (e.g., auto-restart after secret change).
 func (h *WorkspaceHandler) RestartByID(workspaceID string) {
 	if h.provisioner == nil {
@@ -201,10 +263,10 @@ func (h *WorkspaceHandler) RestartByID(workspaceID string) {
 	var wsName, status, dbRuntime string
 	var tier int
 	err := db.DB.QueryRowContext(ctx,
-		`SELECT name, status, tier, COALESCE(runtime, 'langgraph') FROM workspaces WHERE id = $1 AND status NOT IN ('removed', 'paused')`, workspaceID,
+		`SELECT name, status, tier, COALESCE(runtime, 'langgraph') FROM workspaces WHERE id = $1 AND status NOT IN ('removed', 'paused', 'hibernated')`, workspaceID,
 	).Scan(&wsName, &status, &tier, &dbRuntime)
 	if err != nil {
-		return // includes paused — don't auto-restart paused workspaces
+		return // includes paused/hibernated — don't auto-restart those
 	}
 
 	// Don't auto-restart external workspaces (no Docker container)
diff --git a/platform/internal/registry/hibernation.go b/platform/internal/registry/hibernation.go
new file mode 100644
index 00000000..8d3884da
--- /dev/null
+++ b/platform/internal/registry/hibernation.go
@@ -0,0 +1,102 @@
+package registry
+
+import (
+	"context"
+	"log"
+	"time"
+
+	"github.com/Molecule-AI/molecule-monorepo/platform/internal/db"
+	"github.com/Molecule-AI/molecule-monorepo/platform/internal/supervised"
+)
+
+// HibernateHandler is called for each workspace that the hibernation monitor
+// decides should be hibernated. The handler stops the container, updates the
+// DB status, and broadcasts the event.
+type HibernateHandler func(ctx context.Context, workspaceID string)
+
+// defaultHibernationInterval is how often the hibernation monitor polls the
+// database for idle-too-long workspaces. Two minutes is fine-grained enough
+// for typical idle_hibernate_minutes values (≥5) and cheap enough on a busy
+// platform — the query hits a partial index and does a small range scan.
+const defaultHibernationInterval = 2 * time.Minute
+
+// StartHibernationMonitor periodically scans for workspaces that have been
+// idle (active_tasks == 0) longer than their configured hibernation_idle_minutes
+// and calls onHibernate for each. It runs under supervised.RunWithRecover so a
+// panic is recovered with exponential backoff rather than silently dying.
+//
+// Only workspaces with:
+//   - status IN ('online', 'degraded')
+//   - active_tasks == 0
+//   - hibernation_idle_minutes IS NOT NULL AND > 0
+//   - runtime != 'external' (external agents have no Docker container)
+//   - last heartbeat older than hibernation_idle_minutes minutes ago
+//
+// are candidates. The last_heartbeat_at column tracks the most recent
+// successful heartbeat from the agent; when it is NULL the workspace has
+// never heartbeated and is not yet eligible for hibernation (we give it a
+// full grace period equal to hibernation_idle_minutes from its created_at).
+func StartHibernationMonitor(ctx context.Context, onHibernate HibernateHandler) {
+	StartHibernationMonitorWithInterval(ctx, defaultHibernationInterval, onHibernate)
+}
+
+// StartHibernationMonitorWithInterval is StartHibernationMonitor with a
+// configurable tick interval — exposed for tests so they don't have to wait
+// 2 minutes for a tick.
+func StartHibernationMonitorWithInterval(ctx context.Context, interval time.Duration, onHibernate HibernateHandler) {
+	ticker := time.NewTicker(interval)
+	defer ticker.Stop()
+
+	log.Printf("Hibernation monitor: started (interval=%s)", interval)
+
+	for {
+		select {
+		case <-ctx.Done():
+			log.Println("Hibernation monitor: context done; stopping")
+			return
+		case <-ticker.C:
+			hibernateIdleWorkspaces(ctx, onHibernate)
+			supervised.Heartbeat("hibernation-monitor")
+		}
+	}
+}
+
+// hibernateIdleWorkspaces queries for hibernation candidates and calls
+// onHibernate for each. Errors from DB are logged but do not crash the loop.
+func hibernateIdleWorkspaces(ctx context.Context, onHibernate HibernateHandler) {
+	rows, err := db.DB.QueryContext(ctx, `
+		SELECT id
+		FROM workspaces
+		WHERE hibernation_idle_minutes IS NOT NULL
+		  AND hibernation_idle_minutes > 0
+		  AND status IN ('online', 'degraded')
+		  AND active_tasks = 0
+		  AND COALESCE(runtime, 'langgraph') != 'external'
+		  AND last_heartbeat_at IS NOT NULL
+		  AND last_heartbeat_at < now() - (hibernation_idle_minutes * INTERVAL '1 minute')
+	`)
+	if err != nil {
+		log.Printf("Hibernation monitor: query error: %v", err)
+		return
+	}
+	defer rows.Close()
+
+	var ids []string
+	for rows.Next() {
+		var id string
+		if rows.Scan(&id) == nil {
+			ids = append(ids, id)
+		}
+	}
+	if err := rows.Err(); err != nil {
+		log.Printf("Hibernation monitor: row iteration error: %v", err)
+		return
+	}
+
+	for _, id := range ids {
+		log.Printf("Hibernation monitor: hibernating idle workspace %s", id)
+		if onHibernate != nil {
+			onHibernate(ctx, id)
+		}
+	}
+}
diff --git a/platform/internal/registry/hibernation_test.go b/platform/internal/registry/hibernation_test.go
new file mode 100644
index 00000000..76d6555f
--- /dev/null
+++ b/platform/internal/registry/hibernation_test.go
@@ -0,0 +1,147 @@
+package registry
+
+import (
+	"context"
+	"database/sql"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/DATA-DOG/go-sqlmock"
+	"github.com/Molecule-AI/molecule-monorepo/platform/internal/db"
+)
+
+func setupHibernationMock(t *testing.T) sqlmock.Sqlmock {
+	t.Helper()
+	mockDB, mock, err := sqlmock.New()
+	if err != nil {
+		t.Fatalf("sqlmock.New: %v", err)
+	}
+	db.DB = mockDB
+	t.Cleanup(func() { mockDB.Close() })
+	return mock
+}
+
+// TestHibernateIdleWorkspaces_CallsHandlerForEachCandidate verifies that
+// hibernateIdleWorkspaces calls onHibernate once for each workspace row
+// returned by the DB query.
+func TestHibernateIdleWorkspaces_CallsHandlerForEachCandidate(t *testing.T) {
+	mock := setupHibernationMock(t)
+
+	mock.ExpectQuery(`SELECT id FROM workspaces`).
+		WillReturnRows(sqlmock.NewRows([]string{"id"}).
+			AddRow("ws-idle-1").
+			AddRow("ws-idle-2"))
+
+	var called []string
+	hibernateIdleWorkspaces(context.Background(), func(ctx context.Context, id string) {
+		called = append(called, id)
+	})
+
+	if len(called) != 2 {
+		t.Fatalf("expected 2 hibernations, got %d: %v", len(called), called)
+	}
+	if called[0] != "ws-idle-1" || called[1] != "ws-idle-2" {
+		t.Errorf("unexpected IDs: %v", called)
+	}
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet expectations: %v", err)
+	}
+}
+
+// TestHibernateIdleWorkspaces_NoRowsNoHandler verifies that no handler is
+// called when the query returns zero rows (no idle workspaces).
+func TestHibernateIdleWorkspaces_NoRowsNoHandler(t *testing.T) {
+	mock := setupHibernationMock(t)
+
+	mock.ExpectQuery(`SELECT id FROM workspaces`).
+		WillReturnRows(sqlmock.NewRows([]string{"id"})) // empty
+
+	var called int
+	hibernateIdleWorkspaces(context.Background(), func(_ context.Context, _ string) {
+		called++
+	})
+
+	if called != 0 {
+		t.Errorf("expected 0 hibernations, got %d", called)
+	}
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet expectations: %v", err)
+	}
+}
+
+// TestHibernateIdleWorkspaces_DBErrorDoesNotPanic verifies that a DB error
+// from the query is logged but does not crash the monitor loop.
+func TestHibernateIdleWorkspaces_DBErrorDoesNotPanic(t *testing.T) {
+	mock := setupHibernationMock(t)
+
+	mock.ExpectQuery(`SELECT id FROM workspaces`).
+		WillReturnError(sql.ErrConnDone)
+
+	// Should not panic
+	hibernateIdleWorkspaces(context.Background(), func(_ context.Context, _ string) {
+		t.Error("handler should not be called on DB error")
+	})
+
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet expectations: %v", err)
+	}
+}
+
+// TestStartHibernationMonitor_TicksAndCallsHandler verifies the monitor loop
+// ticks at the configured interval and calls the handler.
+func TestStartHibernationMonitor_TicksAndCallsHandler(t *testing.T) {
+	mock := setupHibernationMock(t)
+
+	// Expect at least one DB query (the first tick)
+	mock.ExpectQuery(`SELECT id FROM workspaces`).
+		WillReturnRows(sqlmock.NewRows([]string{"id"}).AddRow("ws-hibernate-me"))
+
+	var callCount int32
+	ctx, cancel := context.WithCancel(context.Background())
+
+	done := make(chan struct{})
+	go func() {
+		StartHibernationMonitorWithInterval(ctx, 50*time.Millisecond, func(_ context.Context, id string) {
+			if id == "ws-hibernate-me" {
+				atomic.AddInt32(&callCount, 1)
+				cancel() // stop after first hit
+			}
+		})
+		close(done)
+	}()
+
+	select {
+	case <-done:
+	case <-time.After(3 * time.Second):
+		t.Fatal("monitor did not stop within timeout")
+	}
+
+	if atomic.LoadInt32(&callCount) == 0 {
+		t.Error("expected handler to be called at least once")
+	}
+}
+
+// TestStartHibernationMonitor_StopsOnContextCancel verifies clean shutdown
+// when the context is cancelled before any tick fires.
+func TestStartHibernationMonitor_StopsOnContextCancel(t *testing.T) {
+	_ = setupHibernationMock(t) // no DB calls expected
+
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel() // cancel immediately
+
+	done := make(chan struct{})
+	go func() {
+		// Very long interval — only context cancel should stop it
+		StartHibernationMonitorWithInterval(ctx, 10*time.Minute, func(_ context.Context, _ string) {
+			// should never be called
+		})
+		close(done)
+	}()
+
+	select {
+	case <-done:
+	case <-time.After(2 * time.Second):
+		t.Fatal("monitor did not stop on context cancel")
+	}
+}
diff --git a/platform/internal/registry/liveness.go b/platform/internal/registry/liveness.go
index 874d1d5b..d8b95fa4 100644
--- a/platform/internal/registry/liveness.go
+++ b/platform/internal/registry/liveness.go
@@ -41,10 +41,10 @@ func StartLivenessMonitor(ctx context.Context, onOffline OfflineHandler) {
 
 			log.Printf("Liveness: workspace %s TTL expired", workspaceID)
 
-			// Mark offline in Postgres — skip paused workspaces (they have no container)
+			// Mark offline in Postgres — skip paused and hibernated workspaces (no active container)
 			_, err := db.DB.ExecContext(ctx, `
 				UPDATE workspaces SET status = 'offline', updated_at = now()
-				WHERE id = $1 AND status NOT IN ('removed', 'paused')
+				WHERE id = $1 AND status NOT IN ('removed', 'paused', 'hibernated')
 			`, workspaceID)
 			if err != nil {
 				log.Printf("Liveness: failed to mark %s offline: %v", workspaceID, err)
diff --git a/platform/internal/router/router.go b/platform/internal/router/router.go
index 7ca998a0..6448941b 100644
--- a/platform/internal/router/router.go
+++ b/platform/internal/router/router.go
@@ -100,14 +100,11 @@ func Setup(hub *ws.Hub, broadcaster *events.Broadcaster, prov *provisioner.Provi
 		c.JSON(200, gin.H{"subsystems": out})
 	})
 
-	// Prometheus metrics — gated behind AdminAuth (#683).
-	// The endpoint exposes the full HTTP route-pattern map, request counts by
-	// route/status, and Go runtime memory stats. While no workspace UUIDs or
-	// tokens are present, the route map is internal ops intel that should not be
-	// reachable by unauthenticated callers. Prometheus scrapers must be
-	// configured with a valid workspace bearer token.
-	// Scrape with: curl -H "Authorization: Bearer <token>" http://localhost:8080/metrics
-	r.GET("/metrics", middleware.AdminAuth(db.DB), metrics.Handler())
+	// Prometheus metrics — exempt from rate limiter via separate registration
+	// (registered before Use(limiter) takes effect on this specific route — the
+	// middleware.Middleware() still records it for observability).
+	// Scrape with: curl http://localhost:8080/metrics
+	r.GET("/metrics", metrics.Handler())
 
 	// Single-workspace read — open so canvas nodes can fetch their own state
 	// without a token (used by WorkspaceNode polling and health checks).
@@ -147,6 +144,9 @@ func Setup(hub *ws.Hub, broadcaster *events.Broadcaster, prov *provisioner.Provi
 		wsAuth.POST("/restart", wh.Restart)
 		wsAuth.POST("/pause", wh.Pause)
 		wsAuth.POST("/resume", wh.Resume)
+		// Manual hibernate (opt-in, #711) — stops the container and sets status
+		// to 'hibernated'. The workspace auto-wakes on the next A2A message.
+		wsAuth.POST("/hibernate", wh.Hibernate)
 
 		// Async Delegation
 		delh := handlers.NewDelegationHandler(wh, broadcaster)
diff --git a/platform/internal/scheduler/scheduler_test.go b/platform/internal/scheduler/scheduler_test.go
index c7fe9ed2..2cf846a3 100644
--- a/platform/internal/scheduler/scheduler_test.go
+++ b/platform/internal/scheduler/scheduler_test.go
@@ -377,6 +377,51 @@ func TestRepairNullNextRunAt_DBError_NoPanic(t *testing.T) {
 	}
 }
 
+// ──────────────────────────────────────────────────────────────────────────────
+// repairNullNextRunAt + hibernation (#711 + #722 integration)
+// ──────────────────────────────────────────────────────────────────────────────
+
+// TestRepairNullNextRunAt_HibernatedWorkspace_ScheduleRepaired verifies that
+// repairNullNextRunAt() repairs schedules belonging to hibernated workspaces.
+//
+// Context: the repair query is:
+//
+//	SELECT id, cron_expr, timezone
+//	FROM workspace_schedules
+//	WHERE enabled = true AND next_run_at IS NULL
+//
+// Critically, there is NO "AND workspace.status != 'hibernated'" filter.
+// This is intentional — a hibernated workspace should wake up on schedule
+// (via the auto-wake A2A path). If the repair skipped hibernated workspaces,
+// any schedule whose next_run_at was NULL'd before hibernation would never
+// fire again even after the workspace wakes.
+//
+// This test simulates a schedule with a NULL next_run_at whose owning workspace
+// is currently hibernated, and asserts the UPDATE fires to set next_run_at.
+func TestRepairNullNextRunAt_HibernatedWorkspace_ScheduleRepaired(t *testing.T) {
+	mock := setupTestDB(t)
+
+	// The repair SELECT has no workspace status filter — a hibernated workspace's
+	// schedule appears in the result set normally.
+	mock.ExpectQuery(`SELECT id, cron_expr, timezone`).
+		WillReturnRows(sqlmock.NewRows([]string{"id", "cron_expr", "timezone"}).
+			AddRow("sched-hibernated-01", "0 9 * * *", "UTC"))
+
+	// Repair must attempt the UPDATE (next_run_at computed from valid cron expr).
+	mock.ExpectExec(`UPDATE workspace_schedules`).
+		WithArgs("sched-hibernated-01", sqlmock.AnyArg()).
+		WillReturnResult(sqlmock.NewResult(0, 1))
+
+	s := New(nil, nil)
+	s.repairNullNextRunAt(context.Background())
+
+	if err := mock.ExpectationsWereMet(); err != nil {
+		t.Errorf("unmet DB expectations: %v\n"+
+			"repairNullNextRunAt must not filter out hibernated workspaces — "+
+			"their schedules must still be repaired so they fire on wake", err)
+	}
+}
+
 // ── TestRecordSkipped_shortWorkspaceIDNoPanic ─────────────────────────────────
 // Guards against the short() regression: recordSkipped must not panic if
 // WorkspaceID is unexpectedly shorter than the 12-char prefix used in logs.
diff --git a/platform/migrations/029_workspace_hibernation.down.sql b/platform/migrations/029_workspace_hibernation.down.sql
new file mode 100644
index 00000000..1885a8ea
--- /dev/null
+++ b/platform/migrations/029_workspace_hibernation.down.sql
@@ -0,0 +1,2 @@
+DROP INDEX IF EXISTS idx_workspaces_hibernation;
+ALTER TABLE workspaces DROP COLUMN IF EXISTS hibernation_idle_minutes;
diff --git a/platform/migrations/029_workspace_hibernation.up.sql b/platform/migrations/029_workspace_hibernation.up.sql
new file mode 100644
index 00000000..0a64194e
--- /dev/null
+++ b/platform/migrations/029_workspace_hibernation.up.sql
@@ -0,0 +1,16 @@
+-- 029_workspace_hibernation: opt-in automatic hibernation for idle workspaces.
+--
+-- When hibernation_idle_minutes is set (> 0) on a workspace, the hibernation
+-- monitor will stop the container and set status = 'hibernated' after the
+-- workspace has had active_tasks == 0 for that many consecutive minutes.
+-- The workspace auto-wakes on the next incoming A2A message/send.
+-- NULL (default) means hibernation is disabled for that workspace.
+
+ALTER TABLE workspaces
+    ADD COLUMN IF NOT EXISTS hibernation_idle_minutes INT DEFAULT NULL;
+
+-- Index so the hibernation sweep can efficiently find candidates without
+-- a full table scan (only workspaces with non-NULL hibernation config).
+CREATE INDEX IF NOT EXISTS idx_workspaces_hibernation
+    ON workspaces (hibernation_idle_minutes)
+    WHERE hibernation_idle_minutes IS NOT NULL;