diff --git a/src/smt/smt_parallel.cpp b/src/smt/smt_parallel.cpp
index 8a3910590..b28d7d2d0 100644
--- a/src/smt/smt_parallel.cpp
+++ b/src/smt/smt_parallel.cpp
@@ -559,7 +559,7 @@ namespace smt {
             if (m_ablate_backtracking) {
                 // Ablation: for each target, pass the entire path from root to that node
                 for (auto const& target : targets) {
-                    if (m_search_tree.is_lease_canceled(target.leased_node, target.cancel_epoch))
+                    if (m_search_tree.is_lease_canceled(target.leased_node))
                         continue;
                     
                     // Reconstruct the full path from root to this target node
@@ -1135,7 +1135,7 @@ namespace smt {
             
             // only cancel workers that currently hold a lease, whose lease is canceled,
             // and haven't already been signaled (prevents multiple inc_cancel() for same lease)
-            if (lease.leased_node && !lease.cancel_signaled && m_search_tree.is_lease_canceled(lease.leased_node, lease.cancel_epoch)) {
+            if (lease.leased_node && !lease.cancel_signaled && m_search_tree.is_lease_canceled(lease.leased_node)) {
                 p.m_workers[worker_id]->cancel_lease();
                 m_worker_leases[worker_id].cancel_signaled = true;
             }
@@ -1190,14 +1190,13 @@ namespace smt {
 
         unsigned best_idx = select_best_core_min_job_unlocked();
         m_core_min_jobs.swap(best_idx, m_core_min_jobs.size() - 1);
-        core_min_job* job = m_core_min_jobs.detach_back();
+        scoped_ptr<core_min_job> job = m_core_min_jobs.detach_back();
         m_core_min_jobs.pop_back();
         SASSERT(job);
         source = job->source;
         core.reset();
         for (expr* c : job->core)
             core.push_back(g2l(c));
-        dealloc(job);
         return source != nullptr;
     }
 
@@ -1288,7 +1287,7 @@ namespace smt {
         if (!g_core.empty()) {
             collect_matching_targets_unlocked(source, g_core[0].get(), g_core, targets);
             for (auto const& target : targets) {
-                if (!m_search_tree.is_lease_canceled(target.leased_node, target.cancel_epoch))
+                if (!m_search_tree.is_lease_canceled(target.leased_node))
                     m_search_tree.backtrack(target.leased_node, g_core);
             }
         }
@@ -1342,7 +1341,7 @@ namespace smt {
         for (node* t : matches) {
             if (!t || t == source)
                 continue;
-            if (m_search_tree.is_lease_canceled(t, t->get_cancel_epoch()))
+            if (m_search_tree.is_lease_canceled(t))
                 continue;
 
             // When source is provided, keep only external matches. Nodes in the
@@ -1369,7 +1368,7 @@ namespace smt {
             if (!is_highest_ancestor)
                 continue;
 
-            targets.push_back({ t, t->get_cancel_epoch() });
+            targets.push_back({ t });
         }
     }
 
@@ -1385,7 +1384,7 @@ namespace smt {
         SASSERT(lease != nullptr || targets != nullptr);
         bool did_backtrack = false;
 
-        if (lease && !m_search_tree.is_lease_canceled(lease->leased_node, lease->cancel_epoch)) {
+        if (lease && !m_search_tree.is_lease_canceled(lease->leased_node)) {
             // we close/backtrack regardless of whether this lease is stale or not, as long as the lease isn't canceled
             // i.e. worker 1 splits this node, but then worker 2 determines UNSAT --> worker 2 is stale but we still close this node and backtrack
             did_backtrack = true;
@@ -1395,7 +1394,7 @@ namespace smt {
         }
         if (targets) {
             for (auto const& target : *targets) {
-                if (m_search_tree.is_lease_canceled(target.leased_node, target.cancel_epoch))
+                if (m_search_tree.is_lease_canceled(target.leased_node))
                     continue;
 
                 did_backtrack = true;
@@ -1427,13 +1426,13 @@ namespace smt {
         if (m_state != state::is_running)
             return;
 
-        if (m_search_tree.is_lease_canceled(lease.leased_node, lease.cancel_epoch))
+        if (m_search_tree.is_lease_canceled(lease.leased_node))
             return;
 
         expr_ref lit(m), nlit(m);
         lit = l2g(atom);
         nlit = mk_not(m, lit);
-        bool did_split = m_search_tree.try_split(lease.leased_node, lease.cancel_epoch, lit, nlit, effort);
+        bool did_split = m_search_tree.try_split(lease.leased_node, lit, nlit, effort);
 
         release_lease_unlocked(worker_id, lease.leased_node);
 
@@ -1451,7 +1450,7 @@ namespace smt {
 
     bool parallel::batch_manager::lease_canceled(node_lease const &lease) {
         std::scoped_lock lock(mux);
-        return m_state == state::is_running && m_search_tree.is_lease_canceled(lease.leased_node, lease.cancel_epoch);
+        return m_state == state::is_running && m_search_tree.is_lease_canceled(lease.leased_node);
     }
 
     void parallel::batch_manager::collect_clause(ast_translation &l2g, unsigned source_worker_id, expr *clause) {
@@ -1763,7 +1762,6 @@ namespace smt {
         IF_VERBOSE(2, m_search_tree.display(verbose_stream()); verbose_stream() << "\n";);
         
         lease.leased_node = t;
-        lease.cancel_epoch = t->get_cancel_epoch();
         if (id >= m_worker_leases.size())
             m_worker_leases.resize(id + 1);
         m_worker_leases[id] = lease;
diff --git a/src/smt/smt_parallel.h b/src/smt/smt_parallel.h
index 79b326889..f1ebfcd0c 100644
--- a/src/smt/smt_parallel.h
+++ b/src/smt/smt_parallel.h
@@ -64,12 +64,6 @@ namespace smt {
         struct node_lease {
             node* leased_node = nullptr;
 
-            // Cancellation generation counter for this node/subtree.
-            // Incremented when the node is closed; used to signal that all
-            // workers holding leases on this node (or its descendants)
-            // must abandon work immediately.
-            unsigned cancel_epoch = 0;
-
             // Guards against multiple inc_cancel() calls for the same lease.
             // Set when cancel_lease() is signaled; cleared when a new lease is assigned.
             bool cancel_signaled = false;
diff --git a/src/solver/parallel_tactical2.cpp b/src/solver/parallel_tactical2.cpp
index ec27f176f..c7eddb4d8 100644
--- a/src/solver/parallel_tactical2.cpp
+++ b/src/solver/parallel_tactical2.cpp
@@ -127,12 +127,6 @@ class parallel_solver {
     struct node_lease {
         search_tree::node<solver_cube_config>* leased_node = nullptr;
 
-        // Cancellation generation counter for this node/subtree.
-        // Incremented when the node is closed; used to signal that all
-        // workers holding leases on this node (or its descendants)
-        // must abandon work immediately.
-        unsigned cancel_epoch = 0;
-
         // Guards against multiple inc_cancel() calls for the same lease.
         // Set when cancel_lease() is signaled; cleared when a new lease is assigned.
         bool cancel_signaled  = false;
@@ -218,7 +212,7 @@ class parallel_solver {
         expr_ref_vector m_unsat_core;
 
         // called from batch manager to cancel other workers if we've reached a verdict
-        void cancel_workers_unlocked() {
+        void cancel_background_threads() {
             IF_VERBOSE(1, verbose_stream() << "Canceling workers\n");
             for (auto* w : p.m_workers)
                 w->cancel();
@@ -248,7 +242,7 @@ class parallel_solver {
                 if (id == source_worker_id) continue;
                 auto const& lease = m_worker_leases[id];
                 if (lease.leased_node && !lease.cancel_signaled &&
-                    m_search_tree.is_lease_canceled(lease.leased_node, lease.cancel_epoch)) {
+                    m_search_tree.is_lease_canceled(lease.leased_node)) {
                     p.m_workers[id]->cancel_lease();
                     m_worker_leases[id].cancel_signaled = true;
                 }
@@ -316,7 +310,7 @@ class parallel_solver {
             for (auto* t : matches) {
                 if (!t || t == source)
                     continue;
-                if (m_search_tree.is_lease_canceled(t, t->get_cancel_epoch()))
+                if (m_search_tree.is_lease_canceled(t))
                     continue;
 
                 // When source is provided, keep only external matches. Nodes in the
@@ -343,7 +337,7 @@ class parallel_solver {
                 if (!is_highest_ancestor)
                     continue;
 
-                targets.push_back({ t, t->get_cancel_epoch() });
+                targets.push_back({ t });
             }
         }
 
@@ -405,7 +399,7 @@ class parallel_solver {
             SASSERT(lease != nullptr || targets != nullptr);
             bool did_backtrack = false;
 
-            if (lease && !m_search_tree.is_lease_canceled(lease->leased_node, lease->cancel_epoch)) {
+            if (lease && !m_search_tree.is_lease_canceled(lease->leased_node)) {
                 // we close/backtrack regardless of whether this lease is stale or not, as long as the lease isn't canceled
                 // i.e. worker 1 splits this node, but then worker 2 determines UNSAT --> worker 2 is stale but we still close this node and backtrack
                 did_backtrack = true;
@@ -414,7 +408,7 @@ class parallel_solver {
             }
             if (targets) {
                 for (auto const& target : *targets) {
-                    if (m_search_tree.is_lease_canceled(target.leased_node, target.cancel_epoch))
+                    if (m_search_tree.is_lease_canceled(target.leased_node))
                         continue;
                     did_backtrack = true;
                     m_search_tree.backtrack(target.leased_node, g_core);
@@ -438,7 +432,7 @@ class parallel_solver {
                 SASSERT(m_unsat_core.empty());
                 for (auto& e : m_search_tree.get_core_from_root())
                     m_unsat_core.push_back(e.get());
-                cancel_workers_unlocked();
+                cancel_background_threads();
             }
         }
 
@@ -477,14 +471,14 @@ class parallel_solver {
             if (m_state != state::is_running) return;
             m_state = state::is_sat;
             m_model = mdl.translate(l2g);
-            cancel_workers_unlocked();
+            cancel_background_threads();
         }
 
         void set_cancel() {
             std::scoped_lock lock(mux);
             if (m_state != state::is_running)
                 return;
-            cancel_workers_unlocked();
+            cancel_background_threads();
         }
 
         void set_unsat(ast_translation& l2g,
@@ -496,7 +490,7 @@ class parallel_solver {
             SASSERT(m_unsat_core.empty());
             for (expr* c : core)
                 m_unsat_core.push_back(l2g(c));
-            cancel_workers_unlocked();
+            cancel_background_threads();
         }
 
         void set_exception(std::string const& msg) {
@@ -505,7 +499,7 @@ class parallel_solver {
             if (m_state != state::is_running) return;
             m_state = state::is_exception_msg;
             m_exception_msg = msg;
-            cancel_workers_unlocked();
+            cancel_background_threads();
         }
 
         void set_exception(unsigned error_code) {
@@ -514,7 +508,7 @@ class parallel_solver {
             if (m_state != state::is_running) return;
             m_state = state::is_exception_code;
             m_exception_code = error_code;
-            cancel_workers_unlocked();
+            cancel_background_threads();
         }
 
         bool get_cube(ast_translation& g2l, unsigned id,
@@ -531,7 +525,6 @@ class parallel_solver {
             if (!t) return false;
 
             lease.leased_node  = t;
-            lease.cancel_epoch = t->get_cancel_epoch();
             if (id >= m_worker_leases.size())
                 m_worker_leases.resize(id + 1);
             m_worker_leases[id] = lease;
@@ -638,7 +631,7 @@ class parallel_solver {
                     m_unsat_core.push_back(l2g(e));
                 ++m_stats.m_core_min_jobs_published;
                 ++m_stats.m_core_min_global_unsat;
-                cancel_workers_unlocked();
+                cancel_background_threads();
                 return;
             }
 
@@ -651,7 +644,7 @@ class parallel_solver {
             if (!g_core.empty()) {
                 collect_matching_targets_unlocked(source, g_core[0].get(), g_core, targets);
                 for (auto const& target : targets) {
-                    if (!m_search_tree.is_lease_canceled(target.leased_node, target.cancel_epoch))
+                    if (!m_search_tree.is_lease_canceled(target.leased_node))
                         m_search_tree.backtrack(target.leased_node, g_core);
                 }
             }
@@ -672,7 +665,7 @@ class parallel_solver {
                 SASSERT(m_unsat_core.empty());
                 for (auto& e : m_search_tree.get_core_from_root())
                     m_unsat_core.push_back(e.get());
-                cancel_workers_unlocked();
+                cancel_background_threads();
             }
         }
 
@@ -682,7 +675,7 @@ class parallel_solver {
                 return false;
             if (m_state != state::is_running)
                 return false;
-            if (m_search_tree.is_lease_canceled(lease.leased_node, lease.cancel_epoch))
+            if (m_search_tree.is_lease_canceled(lease.leased_node))
                 return false;
 
             expr_ref _atom(l2g(atom), m);            
@@ -694,8 +687,7 @@ class parallel_solver {
                        expr* atom, unsigned effort) {
             std::scoped_lock lock(mux);
             if (m_state != state::is_running) return;
-            if (m_search_tree.is_lease_canceled(
-                    lease.leased_node, lease.cancel_epoch)) return;
+            if (m_search_tree.is_lease_canceled(lease.leased_node)) return;
 
             expr_ref lit(m), nlit(m);
             lit  = l2g(atom);
@@ -704,8 +696,7 @@ class parallel_solver {
             VERIFY(!lease.leased_node->path_contains_atom(nlit));
 
             bool did_split = m_search_tree.try_split(
-                lease.leased_node, lease.cancel_epoch,
-                lit, nlit, effort);
+                lease.leased_node, lit, nlit, effort);
 
             release_lease_unlocked(worker_id, lease.leased_node);
 
@@ -726,8 +717,7 @@ class parallel_solver {
         bool lease_canceled(node_lease const& lease) {
             std::scoped_lock lock(mux);
             return m_state == state::is_running &&
-                   m_search_tree.is_lease_canceled(
-                       lease.leased_node, lease.cancel_epoch);
+                   m_search_tree.is_lease_canceled(lease.leased_node);
         }
 
         void collect_clause(ast_translation& l2g,
@@ -1630,8 +1620,6 @@ class parallel_solver {
 
                 curr_batch.reset();
             }
-            if (!m.inc())
-                b.set_cancel();
         }
 
     public:
@@ -1831,8 +1819,7 @@ class parallel_solver {
                 if (minimized.size() < original_size)
                     b.publish_minimized_core(m_l2g, asms, source, original_size, minimized);
             }
-            if (!m.inc())
-                b.set_cancel();
+            b.set_cancel();
         }
 
         void cancel() {
@@ -1892,8 +1879,6 @@ public:
             static_cast<unsigned>(std::thread::hardware_concurrency()),
             pp.threads_max());
         bool core_minimize = pp.core_minimize();
-        if (pp.ablate_backtracking())
-            core_minimize = false;
         unsigned num_bb_threads = pp.num_bb_threads();
         if (num_bb_threads > 2)
             throw default_exception("parallel.num_bb_threads must be 0, 1, or 2");
@@ -1941,7 +1926,7 @@ public:
 
         m_batch_manager.initialize(num_bb_threads);
 
-        auto safe_run = [&](std::function<void()> run_fn, reslimit& lim) {
+        auto safe_run = [&](auto&& run_fn, reslimit& lim) {
             try {
                 run_fn();
                 if (lim.is_canceled())
@@ -1960,11 +1945,12 @@ public:
                     m_batch_manager.set_cancel();
             }
         };
+
         /* Launch threads. */
         vector<std::thread> threads;
         for (auto *w : m_workers)
             threads.push_back(std::thread([w, &safe_run]() {
-                 safe_run([w]() { w->run(); }, w->limit());
+                safe_run([w]() { w->run(); }, w->limit());
             }));
         if (m_core_minimizer_worker)
             threads.push_back(std::thread([this, &safe_run]() {
diff --git a/src/util/search_tree.h b/src/util/search_tree.h
index 701c2fe8d..9b9f15064 100644
--- a/src/util/search_tree.h
+++ b/src/util/search_tree.h
@@ -50,7 +50,6 @@ namespace search_tree {
         unsigned m_effort_spent = 0;
         unsigned m_round_max_effort = 0;
         unsigned m_active_workers = 0;
-        unsigned m_cancel_epoch = 0;
 
     public:
         node(literal const &l, node *parent) : m_literal(l), m_parent(parent), m_status(status::open) {}
@@ -156,12 +155,6 @@ namespace search_tree {
             m_round_max_effort = effort;
             m_effort_spent += m_round_max_effort;
         }
-        unsigned get_cancel_epoch() const {
-            return m_cancel_epoch;
-        }
-        void inc_cancel_epoch() {
-            ++m_cancel_epoch;
-        }
     };
 
     template <typename Config> class tree {
@@ -348,7 +341,6 @@ namespace search_tree {
         void close(node<Config> *n, vector<literal> const &C) {
             if (!n || n->get_status() == status::closed)
                 return;
-            n->inc_cancel_epoch();
             n->set_status(status::closed);
             n->set_core(C);
             close(n->left(), C);
@@ -452,8 +444,8 @@ namespace search_tree {
 
         // On timeout, either expand the current leaf or reopen the node for a
         // later revisit, depending on the tree-expansion heuristic.
-        bool try_split(node<Config> *n, unsigned cancel_epoch, literal const &a, literal const &b, unsigned effort) {
-            if (is_lease_canceled(n, cancel_epoch))
+        bool try_split(node<Config> *n, literal const &a, literal const &b, unsigned effort) {
+            if (is_lease_canceled(n))
                 return false;
 
             // Record at most one effort contribution per concurrent round on this node.
@@ -552,8 +544,8 @@ namespace search_tree {
             n->dec_active_workers();
         }
 
-        bool is_lease_canceled(node<Config>* n, unsigned cancel_epoch) const {
-            return !n || n->get_status() == status::closed || n->get_cancel_epoch() != cancel_epoch;
+        bool is_lease_canceled(node<Config>* n) const {
+            return !n || n->get_status() == status::closed;
         }
 
         vector<literal> const &get_core_from_root() const {