diff --git a/build.gradle b/build.gradle
index 41c2ab8b0b..5e0676d0a3 100644
--- a/build.gradle
+++ b/build.gradle
@@ -31,7 +31,7 @@ configure(subprojects.findAll { it.projectDir.toPath().resolve('sql').toFile().e
 
   // Remove distributed SQL as part of `clean` task
   task undoDistributeSql(type: Delete) {
-    doLast { // Explicity do last to avoid running during configuration step
+    doLast { // Explicitly do last to avoid running during configuration step
       file("${sp.projectDir}/sql").list().each {
         delete "$rootDir/deployment/postgres-init-db/sql/$it"
       }
diff --git a/constraints/build.gradle b/constraints/build.gradle
index 8a219a80a4..5daa876e15 100644
--- a/constraints/build.gradle
+++ b/constraints/build.gradle
@@ -12,6 +12,9 @@ java {
 
 test {
   useJUnitPlatform()
+  testLogging {
+    exceptionFormat = 'full'
+  }
 }
 
 jacocoTestReport {
diff --git a/contrib/build.gradle b/contrib/build.gradle
index ebb6146fb6..673231ed0f 100644
--- a/contrib/build.gradle
+++ b/contrib/build.gradle
@@ -15,6 +15,9 @@ java {
 
 test {
   useJUnitPlatform()
+  testLogging {
+    exceptionFormat = 'full'
+  }
 }
 
 jacocoTestReport {
diff --git a/db-tests/build.gradle b/db-tests/build.gradle
index 24d3960f58..c4420085f9 100644
--- a/db-tests/build.gradle
+++ b/db-tests/build.gradle
@@ -18,6 +18,9 @@ jacocoTestReport {
 
 task e2eTest(type: Test) {
   useJUnitPlatform()
+  testLogging {
+    exceptionFormat = 'full'
+  }
 }
 
 dependencies {
diff --git a/e2e-tests/build.gradle b/e2e-tests/build.gradle
index 33d5e47d01..68e0a9392e 100644
--- a/e2e-tests/build.gradle
+++ b/e2e-tests/build.gradle
@@ -43,10 +43,14 @@ task e2eTest(type: Test) {
   // Run the tests in parallel to improve performance
   maxParallelForks = Runtime.runtime.availableProcessors().intdiv(2) ?: 1
   useJUnitPlatform()
+
+  testLogging {
+    exceptionFormat = 'full'
+  }
 }
 
 dependencies {
-  testImplementation project(":timeline")
+  testImplementation project(":procedural:timeline")
   testImplementation "com.zaxxer:HikariCP:5.1.0"
   testImplementation("org.postgresql:postgresql:42.6.0")
   testImplementation project(':merlin-driver')
diff --git a/e2e-tests/src/test/java/gov/nasa/jpl/aerie/e2e/SchedulingTests.java b/e2e-tests/src/test/java/gov/nasa/jpl/aerie/e2e/SchedulingTests.java
index 2955842836..ada11145be 100644
--- a/e2e-tests/src/test/java/gov/nasa/jpl/aerie/e2e/SchedulingTests.java
+++ b/e2e-tests/src/test/java/gov/nasa/jpl/aerie/e2e/SchedulingTests.java
@@ -736,7 +736,7 @@ void beforeEach() throws IOException, InterruptedException {
       // Insert the Plan
       fooPlan = hasura.createPlan(
           fooId,
-          "Foo Plan - Simulation Tests",
+          "Foo Plan - Scheduling Tests",
           "720:00:00",
           planStartTimestamp);
 
diff --git a/examples/banananation/build.gradle b/examples/banananation/build.gradle
index 402c81ca9e..3637a0ecd4 100644
--- a/examples/banananation/build.gradle
+++ b/examples/banananation/build.gradle
@@ -12,6 +12,9 @@ java {
 
 test {
   useJUnitPlatform()
+  testLogging {
+    exceptionFormat = 'full'
+  }
 }
 
 jacocoTestReport {
diff --git a/examples/config-with-defaults/build.gradle b/examples/config-with-defaults/build.gradle
index 2fa0e7e215..1e745a759f 100644
--- a/examples/config-with-defaults/build.gradle
+++ b/examples/config-with-defaults/build.gradle
@@ -19,6 +19,9 @@ jar {
 
 test {
   useJUnitPlatform()
+  testLogging {
+    exceptionFormat = 'full'
+  }
 }
 
 jacocoTestReport {
diff --git a/examples/config-without-defaults/build.gradle b/examples/config-without-defaults/build.gradle
index 2fa0e7e215..1e745a759f 100644
--- a/examples/config-without-defaults/build.gradle
+++ b/examples/config-without-defaults/build.gradle
@@ -19,6 +19,9 @@ jar {
 
 test {
   useJUnitPlatform()
+  testLogging {
+    exceptionFormat = 'full'
+  }
 }
 
 jacocoTestReport {
diff --git a/examples/foo-missionmodel/build.gradle b/examples/foo-missionmodel/build.gradle
index 2fa0e7e215..1e745a759f 100644
--- a/examples/foo-missionmodel/build.gradle
+++ b/examples/foo-missionmodel/build.gradle
@@ -19,6 +19,9 @@ jar {
 
 test {
   useJUnitPlatform()
+  testLogging {
+    exceptionFormat = 'full'
+  }
 }
 
 jacocoTestReport {
diff --git a/examples/minimal-mission-model/build.gradle b/examples/minimal-mission-model/build.gradle
index 2fa0e7e215..1e745a759f 100644
--- a/examples/minimal-mission-model/build.gradle
+++ b/examples/minimal-mission-model/build.gradle
@@ -19,6 +19,9 @@ jar {
 
 test {
   useJUnitPlatform()
+  testLogging {
+    exceptionFormat = 'full'
+  }
 }
 
 jacocoTestReport {
diff --git a/examples/streamline-demo/build.gradle b/examples/streamline-demo/build.gradle
index b0679446c5..48afd9f8c3 100644
--- a/examples/streamline-demo/build.gradle
+++ b/examples/streamline-demo/build.gradle
@@ -19,6 +19,9 @@ jar {
 
 test {
   useJUnitPlatform()
+  testLogging {
+    exceptionFormat = 'full'
+  }
 }
 
 jacocoTestReport {
diff --git a/merlin-driver/build.gradle b/merlin-driver/build.gradle
index 76cbca76bb..acc07bd493 100644
--- a/merlin-driver/build.gradle
+++ b/merlin-driver/build.gradle
@@ -17,6 +17,9 @@ test {
   useJUnitPlatform {
     includeEngines 'jqwik', 'junit-jupiter'
   }
+  testLogging {
+    exceptionFormat = 'full'
+  }
 }
 
 jacocoTestReport {
diff --git a/merlin-driver/src/main/java/gov/nasa/jpl/aerie/merlin/driver/SimulationDriver.java b/merlin-driver/src/main/java/gov/nasa/jpl/aerie/merlin/driver/SimulationDriver.java
index 9608639f2d..bf11a8bac4 100644
--- a/merlin-driver/src/main/java/gov/nasa/jpl/aerie/merlin/driver/SimulationDriver.java
+++ b/merlin-driver/src/main/java/gov/nasa/jpl/aerie/merlin/driver/SimulationDriver.java
@@ -165,11 +165,11 @@ void simulateTask(final MissionModel<Model> missionModel, final TaskFactory<Retu
       }
 
       // Schedule all activities.
-      final var taskId = engine.scheduleTask(elapsedTime, task);
+      final var spanId = engine.scheduleTask(elapsedTime, task);
 
       // Drive the engine until we're out of time.
       // TERMINATION: Actually, we might never break if real time never progresses forward.
-      while (!engine.isTaskComplete(taskId)) {
+      while (!engine.getSpan(spanId).isComplete()) {
         final var batch = engine.extractNextJobs(Duration.MAX_VALUE);
 
         // Increment real time, if necessary.
@@ -233,9 +233,11 @@ private static <Model, Output> TaskFactory<Unit> makeTaskFactory(
   {
     // Emit the current activity (defined by directiveId)
     return executor -> scheduler0 -> TaskStatus.calling((TaskFactory<Output>) (executor1 -> scheduler1 -> {
+      scheduler1.pushSpan();
       scheduler1.emit(directiveId, activityTopic);
       return task.create(executor1).step(scheduler1);
     }), scheduler2 -> {
+      scheduler2.popSpan();
       // When the current activity finishes, get the list of the activities that needed this activity to finish to know their start time
       final List<Pair<ActivityDirectiveId, Duration>> dependents = resolved.get(directiveId) == null ? List.of() : resolved.get(directiveId);
       // Iterate over the dependents
diff --git a/merlin-driver/src/main/java/gov/nasa/jpl/aerie/merlin/driver/engine/SignalId.java b/merlin-driver/src/main/java/gov/nasa/jpl/aerie/merlin/driver/engine/SignalId.java
deleted file mode 100644
index da6057ea63..0000000000
--- a/merlin-driver/src/main/java/gov/nasa/jpl/aerie/merlin/driver/engine/SignalId.java
+++ /dev/null
@@ -1,18 +0,0 @@
-package gov.nasa.jpl.aerie.merlin.driver.engine;
-
-/** A typed wrapper for signal IDs. */
-public sealed interface SignalId {
-  /** A signal controlled by a task. */
-  record TaskSignalId(TaskId id) implements SignalId {}
-
-  /** A signal controlled by a condition. */
-  record ConditionSignalId(ConditionId id) implements SignalId {}
-
-  static TaskSignalId forTask(final TaskId task) {
-    return new TaskSignalId(task);
-  }
-
-  static ConditionSignalId forCondition(final ConditionId condition) {
-    return new ConditionSignalId(condition);
-  }
-}
diff --git a/merlin-driver/src/main/java/gov/nasa/jpl/aerie/merlin/driver/engine/SimulationEngine.java b/merlin-driver/src/main/java/gov/nasa/jpl/aerie/merlin/driver/engine/SimulationEngine.java
index efbddb54f2..e3df17dd47 100644
--- a/merlin-driver/src/main/java/gov/nasa/jpl/aerie/merlin/driver/engine/SimulationEngine.java
+++ b/merlin-driver/src/main/java/gov/nasa/jpl/aerie/merlin/driver/engine/SimulationEngine.java
@@ -25,6 +25,7 @@
 import gov.nasa.jpl.aerie.merlin.protocol.types.SerializedValue;
 import gov.nasa.jpl.aerie.merlin.protocol.types.TaskStatus;
 import gov.nasa.jpl.aerie.merlin.protocol.types.ValueSchema;
+import org.apache.commons.lang3.mutable.MutableInt;
 import org.apache.commons.lang3.tuple.Pair;
 import org.apache.commons.lang3.tuple.Triple;
 
@@ -35,6 +36,8 @@
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.LinkedHashSet;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
@@ -52,8 +55,10 @@
 public final class SimulationEngine implements AutoCloseable {
   /** The set of all jobs waiting for time to pass. */
   private final JobSchedule<JobId, SchedulingInstant> scheduledJobs = new JobSchedule<>();
-  /** The set of all jobs waiting on a given signal. */
-  private final Subscriptions<SignalId, TaskId> waitingTasks = new Subscriptions<>();
+  /** The set of all jobs waiting on a condition. */
+  private final Map<ConditionId, TaskId> waitingTasks = new HashMap<>();
+  /** The set of all tasks blocked on some number of subtasks. */
+  private final Map<TaskId, MutableInt> blockedTasks = new HashMap<>();
   /** The set of conditions depending on a given set of topics. */
   private final Subscriptions<Topic<?>, ConditionId> waitingConditions = new Subscriptions<>();
   /** The set of queries depending on a given set of topics. */
@@ -66,23 +71,27 @@ public final class SimulationEngine implements AutoCloseable {
   /** The profiling state for each tracked resource. */
   private final Map<ResourceId, ProfilingState<?>> resources = new HashMap<>();
 
-  /** The task that spawned a given task (if any). */
-  private final Map<TaskId, TaskId> taskParent = new HashMap<>();
-  /** The set of children for each task (if any). */
-  @DerivedFrom("taskParent")
-  private final Map<TaskId, Set<TaskId>> taskChildren = new HashMap<>();
+  /** The set of all spans of work contributed to by modeled tasks. */
+  private final Map<SpanId, Span> spans = new HashMap<>();
+  /** A count of the direct contributors to each span, including child spans and tasks. */
+  private final Map<SpanId, MutableInt> spanContributorCount = new HashMap<>();
 
   /** A thread pool that modeled tasks can use to keep track of their state between steps. */
   private final ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor();
 
   /** Schedule a new task to be performed at the given time. */
-  public <Return> TaskId scheduleTask(final Duration startTime, final TaskFactory<Return> state) {
+  public <Output> SpanId scheduleTask(final Duration startTime, final TaskFactory<Output> state) {
     if (startTime.isNegative()) throw new IllegalArgumentException("Cannot schedule a task before the start time of the simulation");
 
+    final var span = SpanId.generate();
+    this.spans.put(span, new Span(Optional.empty(), startTime, Optional.empty()));
+
     final var task = TaskId.generate();
-    this.tasks.put(task, new ExecutionState.InProgress<>(startTime, state.create(this.executor)));
+    this.spanContributorCount.put(span, new MutableInt(1));
+    this.tasks.put(task, new ExecutionState<>(span, 0, Optional.empty(), state.create(this.executor)));
     this.scheduledJobs.schedule(JobId.forTask(task), SubInstant.Tasks.at(startTime));
-    return task;
+
+    return span;
   }
 
   /** Register a resource whose profile should be accumulated over time. */
@@ -105,7 +114,7 @@ public void invalidateTopic(final Topic<?> topic, final Duration invalidationTim
     for (final var condition : conditions) {
       // If we were going to signal tasks on this condition, well, don't do that.
       // Schedule the condition to be rechecked ASAP.
-      this.scheduledJobs.unschedule(JobId.forSignal(SignalId.forCondition(condition)));
+      this.scheduledJobs.unschedule(JobId.forSignal(condition));
       this.scheduledJobs.schedule(JobId.forCondition(condition), SubInstant.Conditions.at(invalidationTime));
     }
   }
@@ -119,8 +128,7 @@ public JobSchedule.Batch<JobId> extractNextJobs(final Duration maximumTime) {
     // that the condition depends on, in which case we might accidentally schedule an update for a condition
     // that no longer exists.
     for (final var job : batch.jobs()) {
-      if (!(job instanceof JobId.SignalJobId j)) continue;
-      if (!(j.id() instanceof SignalId.ConditionSignalId s)) continue;
+      if (!(job instanceof JobId.SignalJobId s)) continue;
 
       this.conditions.remove(s.id());
       this.waitingConditions.unsubscribeQuery(s.id());
@@ -156,7 +164,7 @@ public void performJob(
     if (job instanceof JobId.TaskJobId j) {
       this.stepTask(j.id(), frame, currentTime);
     } else if (job instanceof JobId.SignalJobId j) {
-      this.stepSignalledTasks(j.id(), frame);
+      this.stepTask(this.waitingTasks.remove(j.id()), frame, currentTime);
     } else if (job instanceof JobId.ConditionJobId j) {
       this.updateCondition(j.id(), frame, currentTime, maximumTime);
     } else if (job instanceof JobId.ResourceJobId j) {
@@ -168,108 +176,77 @@ public void performJob(
 
   /** Perform the next step of a modeled task. */
   public void stepTask(final TaskId task, final TaskFrame<JobId> frame, final Duration currentTime) {
-    // The handler for each individual task stage is responsible
-    //   for putting an updated lifecycle back into the task set.
-    var lifecycle = this.tasks.remove(task);
+    // The handler for the next status of the task is responsible
+    //   for putting an updated state back into the task set.
+    var state = this.tasks.remove(task);
 
-    stepTaskHelper(task, frame, currentTime, lifecycle);
-  }
-
-  private <Return> void stepTaskHelper(
-      final TaskId task,
-      final TaskFrame<JobId> frame,
-      final Duration currentTime,
-      final ExecutionState<Return> lifecycle)
-  {
-    // Extract the current modeling state.
-    if (lifecycle instanceof ExecutionState.InProgress<Return> e) {
-      stepEffectModel(task, e, frame, currentTime);
-    } else if (lifecycle instanceof ExecutionState.AwaitingChildren<Return> e) {
-      stepWaitingTask(task, e, frame, currentTime);
-    } else {
-      // TODO: Log this issue to somewhere more general than stderr.
-      System.err.println("Task %s is ready but in unexpected execution state %s".formatted(task, lifecycle));
-    }
+    stepEffectModel(task, state, frame, currentTime);
   }
 
   /** Make progress in a task by stepping its associated effect model forward. */
-  private <Return> void stepEffectModel(
+  private <Output> void stepEffectModel(
       final TaskId task,
-      final ExecutionState.InProgress<Return> progress,
+      final ExecutionState<Output> progress,
       final TaskFrame<JobId> frame,
       final Duration currentTime
   ) {
     // Step the modeling state forward.
-    final var scheduler = new EngineScheduler(currentTime, task, frame);
+    final var scheduler = new EngineScheduler(currentTime, progress.shadowedSpans(), progress.span(), progress.caller(), frame);
     final var status = progress.state().step(scheduler);
 
     // TODO: Report which topics this activity wrote to at this point in time. This is useful insight for any user.
     // TODO: Report which cells this activity read from at this point in time. This is useful insight for any user.
 
     // Based on the task's return status, update its execution state and schedule its resumption.
-    if (status instanceof TaskStatus.Completed<Return>) {
-      final var children = new LinkedList<>(this.taskChildren.getOrDefault(task, Collections.emptySet()));
-
-      this.tasks.put(task, progress.completedAt(currentTime, children));
-      this.scheduledJobs.schedule(JobId.forTask(task), SubInstant.Tasks.at(currentTime));
-    } else if (status instanceof TaskStatus.Delayed<Return> s) {
-      if (s.delay().isNegative()) throw new IllegalArgumentException("Cannot schedule a task in the past");
-
-      this.tasks.put(task, progress.continueWith(s.continuation()));
-      this.scheduledJobs.schedule(JobId.forTask(task), SubInstant.Tasks.at(currentTime.plus(s.delay())));
-    } else if (status instanceof TaskStatus.CallingTask<Return> s) {
-      final var target = TaskId.generate();
-      SimulationEngine.this.tasks.put(target, new ExecutionState.InProgress<>(currentTime, s.child().create(this.executor)));
-      SimulationEngine.this.taskParent.put(target, task);
-      SimulationEngine.this.taskChildren.computeIfAbsent(task, $ -> new HashSet<>()).add(target);
-      frame.signal(JobId.forTask(target));
-
-      this.tasks.put(task, progress.continueWith(s.continuation()));
-      this.waitingTasks.subscribeQuery(task, Set.of(SignalId.forTask(target)));
-    } else if (status instanceof TaskStatus.AwaitingCondition<Return> s) {
-      final var condition = ConditionId.generate();
-      this.conditions.put(condition, s.condition());
-      this.scheduledJobs.schedule(JobId.forCondition(condition), SubInstant.Conditions.at(currentTime));
-
-      this.tasks.put(task, progress.continueWith(s.continuation()));
-      this.waitingTasks.subscribeQuery(task, Set.of(SignalId.forCondition(condition)));
-    } else {
-      throw new IllegalArgumentException("Unknown subclass of %s: %s".formatted(TaskStatus.class, status));
-    }
-  }
+      switch (status) {
+        case TaskStatus.Completed<Output> s -> {
+          // Propagate completion up the span hierarchy.
+          // TERMINATION: The span hierarchy is a finite tree, so eventually we find a parentless span.
+          var span = scheduler.span;
+          while (true) {
+            if (this.spanContributorCount.get(span).decrementAndGet() > 0) break;
+            this.spanContributorCount.remove(span);
 
-  /** Make progress in a task by checking if all of the tasks it's waiting on have completed. */
-  private <Return> void stepWaitingTask(
-      final TaskId task,
-      final ExecutionState.AwaitingChildren<Return> awaiting,
-      final TaskFrame<JobId> frame,
-      final Duration currentTime
-  ) {
-    // TERMINATION: We break when there are no remaining children,
-    //   and we always remove one if we don't break for other reasons.
-    while (true) {
-      if (awaiting.remainingChildren().isEmpty()) {
-        this.tasks.put(task, awaiting.joinedAt(currentTime));
-        frame.signal(JobId.forSignal(SignalId.forTask(task)));
-        break;
-      }
+            this.spans.compute(span, (_id, $) -> $.close(currentTime));
 
-      final var nextChild = awaiting.remainingChildren().getFirst();
-      if (!(this.tasks.get(nextChild) instanceof ExecutionState.Terminated<?>)) {
-        this.tasks.put(task, awaiting);
-        this.waitingTasks.subscribeQuery(task, Set.of(SignalId.forTask(nextChild)));
-        break;
-      }
+            final var span$ = this.spans.get(span).parent;
+            if (span$.isEmpty()) break;
 
-      // This child is complete, so skip checking it next time; move to the next one.
-      awaiting.remainingChildren().removeFirst();
-    }
-  }
+            span = span$.get();
+          }
+
+          // Notify any blocked caller of our completion.
+          progress.caller().ifPresent($ -> {
+            if (this.blockedTasks.get($).decrementAndGet() == 0) {
+              this.blockedTasks.remove($);
+              this.scheduledJobs.schedule(JobId.forTask($), SubInstant.Tasks.at(currentTime));
+            }
+          });
+        }
+        case TaskStatus.Delayed<Output> s -> {
+          if (s.delay().isNegative()) throw new IllegalArgumentException("Cannot schedule a task in the past");
+
+          this.tasks.put(task, progress.continueWith(scheduler.span, scheduler.shadowedSpans, s.continuation()));
+          this.scheduledJobs.schedule(JobId.forTask(task), SubInstant.Tasks.at(currentTime.plus(s.delay())));
+        }
+        case TaskStatus.CallingTask<Output> s -> {
+          final var target = TaskId.generate();
+          SimulationEngine.this.spanContributorCount.get(scheduler.span).increment();
+          SimulationEngine.this.tasks.put(target, new ExecutionState<>(scheduler.span, 0, Optional.of(task), s.child().create(this.executor)));
+          SimulationEngine.this.blockedTasks.put(task, new MutableInt(1));
+          frame.signal(JobId.forTask(target));
+
+          this.tasks.put(task, progress.continueWith(scheduler.span, scheduler.shadowedSpans, s.continuation()));
+        }
+        case TaskStatus.AwaitingCondition<Output> s -> {
+          final var condition = ConditionId.generate();
+          this.conditions.put(condition, s.condition());
+          this.scheduledJobs.schedule(JobId.forCondition(condition), SubInstant.Conditions.at(currentTime));
 
-  /** Cause any tasks waiting on the given signal to be resumed concurrently with other jobs in the current frame. */
-  public void stepSignalledTasks(final SignalId signal, final TaskFrame<JobId> frame) {
-    final var tasks = this.waitingTasks.invalidateTopic(signal);
-    for (final var task : tasks) frame.signal(JobId.forTask(task));
+          this.tasks.put(task, progress.continueWith(scheduler.span, scheduler.shadowedSpans, s.continuation()));
+          this.waitingTasks.put(condition, task);
+        }
+      }
   }
 
   /** Determine when a condition is next true, and schedule a signal to be raised at that time. */
@@ -289,7 +266,7 @@ public void updateCondition(
 
     final var expiry = querier.expiry.map(currentTime::plus);
     if (prediction.isPresent() && (expiry.isEmpty() || prediction.get().shorterThan(expiry.get()))) {
-      this.scheduledJobs.schedule(JobId.forSignal(SignalId.forCondition(condition)), SubInstant.Tasks.at(prediction.get()));
+      this.scheduledJobs.schedule(JobId.forSignal(condition), SubInstant.Tasks.at(prediction.get()));
     } else {
       // Try checking again later -- where "later" is in some non-zero amount of time!
       final var nextCheckTime = Duration.max(expiry.orElse(horizonTime), currentTime.plus(Duration.EPSILON));
@@ -318,85 +295,91 @@ public void updateResource(
   @Override
   public void close() {
     for (final var task : this.tasks.values()) {
-      if (task instanceof ExecutionState.InProgress r) {
-        r.state.release();
-      }
+      task.state().release();
     }
 
     this.executor.shutdownNow();
   }
 
-  /** Determine if a given task has fully completed. */
-  public boolean isTaskComplete(final TaskId task) {
-    return (this.tasks.get(task) instanceof ExecutionState.Terminated);
-  }
-
-  private record TaskInfo(
-      Map<String, ActivityDirectiveId> taskToPlannedDirective,
-      Map<String, SerializedActivity> input,
-      Map<String, SerializedValue> output
+  private record SpanInfo(
+      Map<SpanId, ActivityDirectiveId> spanToPlannedDirective,
+      Map<SpanId, SerializedActivity> input,
+      Map<SpanId, SerializedValue> output
   ) {
-    public TaskInfo() {
+    public SpanInfo() {
       this(new HashMap<>(), new HashMap<>(), new HashMap<>());
     }
 
-    public boolean isActivity(final TaskId id) {
-      return this.input.containsKey(id.id());
+    public boolean isActivity(final SpanId id) {
+      return this.input.containsKey(id);
+    }
+
+    public boolean isDirective(SpanId id) {
+      return this.spanToPlannedDirective.containsKey(id);
+    }
+
+    public ActivityDirectiveId getDirective(SpanId id) {
+      return this.spanToPlannedDirective.get(id);
     }
 
-    public record Trait(Iterable<SerializableTopic<?>> topics, Topic<ActivityDirectiveId> activityTopic) implements EffectTrait<Consumer<TaskInfo>> {
+    public record Trait(Iterable<SerializableTopic<?>> topics, Topic<ActivityDirectiveId> activityTopic) implements EffectTrait<Consumer<SpanInfo>> {
       @Override
-      public Consumer<TaskInfo> empty() {
-        return taskInfo -> {};
+      public Consumer<SpanInfo> empty() {
+        return spanInfo -> {};
       }
 
       @Override
-      public Consumer<TaskInfo> sequentially(final Consumer<TaskInfo> prefix, final Consumer<TaskInfo> suffix) {
-        return taskInfo -> { prefix.accept(taskInfo); suffix.accept(taskInfo); };
+      public Consumer<SpanInfo> sequentially(final Consumer<SpanInfo> prefix, final Consumer<SpanInfo> suffix) {
+        return spanInfo -> { prefix.accept(spanInfo); suffix.accept(spanInfo); };
       }
 
       @Override
-      public Consumer<TaskInfo> concurrently(final Consumer<TaskInfo> left, final Consumer<TaskInfo> right) {
-        // SAFETY: For each task, `left` commutes with `right`, because no task runs concurrently with itself.
-        return taskInfo -> { left.accept(taskInfo); right.accept(taskInfo); };
+      public Consumer<SpanInfo> concurrently(final Consumer<SpanInfo> left, final Consumer<SpanInfo> right) {
+        // SAFETY: `left` and `right` should commute. HOWEVER, if a span happens to directly contain two activities
+        //   -- that is, two activities both contribute events under the same span's provenance -- then this
+        //   does not actually commute.
+        //   Arguably, this is a model-specific analysis anyway, since we're looking for specific events
+        //   and inferring model structure from them, and at this time we're only working with models
+        //   for which every activity has a span to itself.
+        return spanInfo -> { left.accept(spanInfo); right.accept(spanInfo); };
       }
 
-      public Consumer<TaskInfo> atom(final Event ev) {
-        return taskInfo -> {
+      public Consumer<SpanInfo> atom(final Event ev) {
+        return spanInfo -> {
           // Identify activities.
           ev.extract(this.activityTopic)
-            .ifPresent(directiveId -> taskInfo.taskToPlannedDirective.put(ev.provenance().id(), directiveId));
+            .ifPresent(directiveId -> spanInfo.spanToPlannedDirective.put(ev.provenance(), directiveId));
 
           for (final var topic : this.topics) {
             // Identify activity inputs.
-            extractInput(topic, ev, taskInfo);
+            extractInput(topic, ev, spanInfo);
 
             // Identify activity outputs.
-            extractOutput(topic, ev, taskInfo);
+            extractOutput(topic, ev, spanInfo);
           }
         };
       }
 
       private static <T>
-      void extractInput(final SerializableTopic<T> topic, final Event ev, final TaskInfo taskInfo) {
+      void extractInput(final SerializableTopic<T> topic, final Event ev, final SpanInfo spanInfo) {
         if (!topic.name().startsWith("ActivityType.Input.")) return;
 
         ev.extract(topic.topic()).ifPresent(input -> {
           final var activityType = topic.name().substring("ActivityType.Input.".length());
 
-          taskInfo.input.put(
-              ev.provenance().id(),
+          spanInfo.input.put(
+              ev.provenance(),
               new SerializedActivity(activityType, topic.outputType().serialize(input).asMap().orElseThrow()));
         });
       }
 
       private static <T>
-      void extractOutput(final SerializableTopic<T> topic, final Event ev, final TaskInfo taskInfo) {
+      void extractOutput(final SerializableTopic<T> topic, final Event ev, final SpanInfo spanInfo) {
         if (!topic.name().startsWith("ActivityType.Output.")) return;
 
         ev.extract(topic.topic()).ifPresent(output -> {
-          taskInfo.output.put(
-              ev.provenance().id(),
+          spanInfo.output.put(
+              ev.provenance(),
               topic.outputType().serialize(output));
         });
       }
@@ -418,14 +401,14 @@ public static SimulationResults computeResults(
       final TemporalEventSource timeline,
       final Iterable<SerializableTopic<?>> serializableTopics
   ) {
-    // Collect per-task information from the event graph.
-    final var taskInfo = new TaskInfo();
+    // Collect per-span information from the event graph.
+    final var spanInfo = new SpanInfo();
 
     for (final var point : timeline) {
       if (!(point instanceof TemporalEventSource.TimePoint.Commit p)) continue;
 
-      final var trait = new TaskInfo.Trait(serializableTopics, activityTopic);
-      p.events().evaluate(trait, trait::atom).accept(taskInfo);
+      final var trait = new SpanInfo.Trait(serializableTopics, activityTopic);
+      p.events().evaluate(trait, trait::atom).accept(spanInfo);
     }
 
     // Extract profiles for every resource.
@@ -458,87 +441,79 @@ public static SimulationResults computeResults(
       }
     }
 
+    // Identify the nearest ancestor *activity* (excluding intermediate anonymous tasks).
+    final var activityParents = new HashMap<SpanId, SpanId>();
+    final var activityDirectiveIds = new HashMap<SpanId, ActivityDirectiveId>();
+    engine.spans.forEach((span, state) -> {
+      if (!spanInfo.isActivity(span)) return;
+
+      var parent = state.parent();
+      while (parent.isPresent() && !spanInfo.isActivity(parent.get()) && !spanInfo.isDirective(parent.get())) {
+        parent = engine.spans.get(parent.get()).parent();
+      }
+
+      if (parent.isPresent()) {
+        if (spanInfo.isActivity(parent.get())) {
+          activityParents.put(span, parent.get());
+        } else if (spanInfo.isDirective(parent.get())) {
+          activityDirectiveIds.put(span, spanInfo.getDirective(parent.get()));
+        }
+      }
+    });
+
+    final var activityChildren = new HashMap<SpanId, List<SpanId>>();
+    activityParents.forEach((activity, parent) -> {
+      activityChildren.computeIfAbsent(parent, $ -> new LinkedList<>()).add(activity);
+    });
 
     // Give every task corresponding to a child activity an ID that doesn't conflict with any root activity.
-    final var taskToSimulatedActivityId = new HashMap<String, SimulatedActivityId>(taskInfo.taskToPlannedDirective.size());
+    final var spanToSimulatedActivityId = new HashMap<SpanId, SimulatedActivityId>(activityDirectiveIds.size());
     final var usedSimulatedActivityIds = new HashSet<>();
-    for (final var entry : taskInfo.taskToPlannedDirective.entrySet()) {
-      taskToSimulatedActivityId.put(entry.getKey(), new SimulatedActivityId(entry.getValue().id()));
+    for (final var entry : activityDirectiveIds.entrySet()) {
+      spanToSimulatedActivityId.put(entry.getKey(), new SimulatedActivityId(entry.getValue().id()));
       usedSimulatedActivityIds.add(entry.getValue().id());
     }
     long counter = 1L;
-    for (final var task : engine.tasks.keySet()) {
-      if (!taskInfo.isActivity(task)) continue;
-      if (taskToSimulatedActivityId.containsKey(task.id())) continue;
+    for (final var span : engine.spans.keySet()) {
+      if (!spanInfo.isActivity(span)) continue;
+      if (spanToSimulatedActivityId.containsKey(span)) continue;
 
       while (usedSimulatedActivityIds.contains(counter)) counter++;
-      taskToSimulatedActivityId.put(task.id(), new SimulatedActivityId(counter++));
+      spanToSimulatedActivityId.put(span, new SimulatedActivityId(counter++));
     }
 
-    // Identify the nearest ancestor *activity* (excluding intermediate anonymous tasks).
-    final var activityParents = new HashMap<SimulatedActivityId, SimulatedActivityId>();
-    engine.tasks.forEach((task, state) -> {
-      if (!taskInfo.isActivity(task)) return;
-
-      var parent = engine.taskParent.get(task);
-      while (parent != null && !taskInfo.isActivity(parent)) {
-        parent = engine.taskParent.get(parent);
-      }
-
-      if (parent != null) {
-        activityParents.put(taskToSimulatedActivityId.get(task.id()), taskToSimulatedActivityId.get(parent.id()));
-      }
-    });
-
-    final var activityChildren = new HashMap<SimulatedActivityId, List<SimulatedActivityId>>();
-    activityParents.forEach((task, parent) -> {
-      activityChildren.computeIfAbsent(parent, $ -> new LinkedList<>()).add(task);
-    });
-
     final var simulatedActivities = new HashMap<SimulatedActivityId, SimulatedActivity>();
     final var unfinishedActivities = new HashMap<SimulatedActivityId, UnfinishedActivity>();
-    engine.tasks.forEach((task, state) -> {
-      if (!taskInfo.isActivity(task)) return;
+    engine.spans.forEach((span, state) -> {
+      if (!spanInfo.isActivity(span)) return;
 
-      final var activityId = taskToSimulatedActivityId.get(task.id());
-      final var directiveId = taskInfo.taskToPlannedDirective.get(task.id()); // will be null for non-directives
+      final var activityId = spanToSimulatedActivityId.get(span);
+      final var directiveId = activityDirectiveIds.get(span);
 
-      if (state instanceof ExecutionState.Terminated<?> e) {
-        final var inputAttributes = taskInfo.input().get(task.id());
-        final var outputAttributes = taskInfo.output().get(task.id());
+      if (state.endOffset().isPresent()) {
+        final var inputAttributes = spanInfo.input().get(span);
+        final var outputAttributes = spanInfo.output().get(span);
 
         simulatedActivities.put(activityId, new SimulatedActivity(
             inputAttributes.getTypeName(),
             inputAttributes.getArguments(),
-            startTime.plus(e.startOffset().in(Duration.MICROSECONDS), ChronoUnit.MICROS),
-            e.joinOffset().minus(e.startOffset()),
-            activityParents.get(activityId),
-            activityChildren.getOrDefault(activityId, Collections.emptyList()),
-            (activityParents.containsKey(activityId)) ? Optional.empty() : Optional.of(directiveId),
+            startTime.plus(state.startOffset().in(Duration.MICROSECONDS), ChronoUnit.MICROS),
+            state.endOffset().get().minus(state.startOffset()),
+            spanToSimulatedActivityId.get(activityParents.get(span)),
+            activityChildren.getOrDefault(span, Collections.emptyList()).stream().map(spanToSimulatedActivityId::get).toList(),
+            (activityParents.containsKey(span)) ? Optional.empty() : Optional.of(directiveId),
             outputAttributes
         ));
-      } else if (state instanceof ExecutionState.InProgress<?> e){
-        final var inputAttributes = taskInfo.input().get(task.id());
-        unfinishedActivities.put(activityId, new UnfinishedActivity(
-            inputAttributes.getTypeName(),
-            inputAttributes.getArguments(),
-            startTime.plus(e.startOffset().in(Duration.MICROSECONDS), ChronoUnit.MICROS),
-            activityParents.get(activityId),
-            activityChildren.getOrDefault(activityId, Collections.emptyList()),
-            (activityParents.containsKey(activityId)) ? Optional.empty() : Optional.of(directiveId)
-        ));
-      } else if (state instanceof ExecutionState.AwaitingChildren<?> e){
-        final var inputAttributes = taskInfo.input().get(task.id());
+      } else {
+        final var inputAttributes = spanInfo.input().get(span);
         unfinishedActivities.put(activityId, new UnfinishedActivity(
             inputAttributes.getTypeName(),
             inputAttributes.getArguments(),
-            startTime.plus(e.startOffset().in(Duration.MICROSECONDS), ChronoUnit.MICROS),
-            activityParents.get(activityId),
-            activityChildren.getOrDefault(activityId, Collections.emptyList()),
-            (activityParents.containsKey(activityId)) ? Optional.empty() : Optional.of(directiveId)
+            startTime.plus(state.startOffset().in(Duration.MICROSECONDS), ChronoUnit.MICROS),
+            spanToSimulatedActivityId.get(activityParents.get(span)),
+            activityChildren.getOrDefault(span, Collections.emptyList()).stream().map(spanToSimulatedActivityId::get).toList(),
+            (activityParents.containsKey(span)) ? Optional.empty() : Optional.of(directiveId)
         ));
-      } else {
-        throw new Error("Unexpected subtype of %s: %s".formatted(ExecutionState.class, state.getClass()));
       }
     });
 
@@ -585,12 +560,8 @@ public static SimulationResults computeResults(
                                  serializedTimeline);
   }
 
-  public Optional<Duration> getTaskDuration(TaskId taskId){
-    final var state = tasks.get(taskId);
-    if (state instanceof ExecutionState.Terminated e) {
-      return Optional.of(e.joinOffset().minus(e.startOffset()));
-    }
-    return Optional.empty();
+  public Span getSpan(SpanId spanId) {
+    return this.spans.get(spanId);
   }
 
 
@@ -680,12 +651,22 @@ private static Optional<Duration> min(final Optional<Duration> a, final Optional
   /** A handle for processing requests and effects from a modeled task. */
   private final class EngineScheduler implements Scheduler {
     private final Duration currentTime;
-    private final TaskId activeTask;
+    private int shadowedSpans;
+    private SpanId span;
+    private final Optional<TaskId> caller;
     private final TaskFrame<JobId> frame;
 
-    public EngineScheduler(final Duration currentTime, final TaskId activeTask, final TaskFrame<JobId> frame) {
+    public EngineScheduler(
+        final Duration currentTime,
+        final int shadowedSpans,
+        final SpanId span,
+        final Optional<TaskId> caller,
+        final TaskFrame<JobId> frame)
+    {
       this.currentTime = Objects.requireNonNull(currentTime);
-      this.activeTask = Objects.requireNonNull(activeTask);
+      this.shadowedSpans = shadowedSpans;
+      this.span = Objects.requireNonNull(span);
+      this.caller = Objects.requireNonNull(caller);
       this.frame = Objects.requireNonNull(frame);
     }
 
@@ -704,7 +685,7 @@ public <State> State get(final CellId<State> token) {
     @Override
     public <EventType> void emit(final EventType event, final Topic<EventType> topic) {
       // Append this event to the timeline.
-      this.frame.emit(Event.create(topic, event, this.activeTask));
+      this.frame.emit(Event.create(topic, event, this.span));
 
       SimulationEngine.this.invalidateTopic(topic, this.currentTime);
     }
@@ -712,11 +693,44 @@ public <EventType> void emit(final EventType event, final Topic<EventType> topic
     @Override
     public void spawn(final TaskFactory<?> state) {
       final var task = TaskId.generate();
-      SimulationEngine.this.tasks.put(task, new ExecutionState.InProgress<>(this.currentTime, state.create(SimulationEngine.this.executor)));
-      SimulationEngine.this.taskParent.put(task, this.activeTask);
-      SimulationEngine.this.taskChildren.computeIfAbsent(this.activeTask, $ -> new HashSet<>()).add(task);
+      SimulationEngine.this.spanContributorCount.get(this.span).increment();
+      SimulationEngine.this.tasks.put(task, new ExecutionState<>(this.span, 0, this.caller, state.create(SimulationEngine.this.executor)));
+      this.caller.ifPresent($ -> SimulationEngine.this.blockedTasks.get($).increment());
       this.frame.signal(JobId.forTask(task));
     }
+
+    @Override
+    public void pushSpan() {
+      final var parentSpan = this.span;
+      this.shadowedSpans += 1;
+      this.span = SpanId.generate();
+
+      SimulationEngine.this.spans.put(this.span, new Span(Optional.of(parentSpan), this.currentTime, Optional.empty()));
+      SimulationEngine.this.spanContributorCount.put(this.span, new MutableInt(1));
+    }
+
+    @Override
+    public void popSpan() {
+      // TODO: Do we want to throw an error instead?
+      if (this.shadowedSpans == 0) return;
+      final SpanId parentSpan = SimulationEngine.this.spans.get(this.span).parent().orElseThrow();
+
+      if (SimulationEngine.this.spanContributorCount.get(this.span).decrementAndGet() == 0) {
+        SimulationEngine.this.spanContributorCount.remove(this.span);
+        SimulationEngine.this.spans.compute(this.span, (_id, $) -> $.close(currentTime));
+        // Parent span contributor count remains constant, because this.span is removed, and this task is added
+      } else {
+        // Parent span contributor count increases by one, because this task is added without removing this.span
+        SimulationEngine.this.spanContributorCount.get(parentSpan).increment();
+      }
+
+      // NOTE: We don't need to propagate completion any further, because the next shadowed span
+      // has by definition not been completed: this task may still contribute to it, and this task
+      // has not terminated.
+
+      this.shadowedSpans -= 1;
+      this.span = parentSpan;
+    }
   }
 
   /** A representation of a job processable by the {@link SimulationEngine}. */
@@ -724,8 +738,8 @@ public sealed interface JobId {
     /** A job to step a task. */
     record TaskJobId(TaskId id) implements JobId {}
 
-    /** A job to step all tasks waiting on a signal. */
-    record SignalJobId(SignalId id) implements JobId {}
+    /** A job to resume a task blocked on a condition. */
+    record SignalJobId(ConditionId id) implements JobId {}
 
     /** A job to query a resource. */
     record ResourceJobId(ResourceId id) implements JobId {}
@@ -737,7 +751,7 @@ static TaskJobId forTask(final TaskId task) {
       return new TaskJobId(task);
     }
 
-    static SignalJobId forSignal(final SignalId signal) {
+    static SignalJobId forSignal(final ConditionId signal) {
       return new SignalJobId(signal);
     }
 
@@ -750,40 +764,27 @@ static ConditionJobId forCondition(final ConditionId condition) {
     }
   }
 
-  /** The lifecycle stages every task passes through. */
-  private sealed interface ExecutionState<Return> {
-    /** The task is in its primary operational phase. */
-    record InProgress<Return>(Duration startOffset, Task<Return> state)
-        implements ExecutionState<Return>
-    {
-      public AwaitingChildren<Return> completedAt(
-          final Duration endOffset,
-          final LinkedList<TaskId> remainingChildren) {
-        return new AwaitingChildren<>(this.startOffset, endOffset, remainingChildren);
-      }
+  /** The state of an executing task. */
+  private record ExecutionState<Output>(SpanId span, int shadowedSpans, Optional<TaskId> caller, Task<Output> state) {
+    public ExecutionState<Output> continueWith(final SpanId span, final int shadowedSpans, final Task<Output> newState) {
+      return new ExecutionState<>(span, shadowedSpans, this.caller, newState);
+    }
+  }
 
-      public InProgress<Return> continueWith(final Task<Return> newState) {
-        return new InProgress<>(this.startOffset, newState);
-      }
+  /** The span of time over which a subtree of tasks has acted. */
+  public record Span(Optional<SpanId> parent, Duration startOffset, Optional<Duration> endOffset) {
+    /** Close out a span, marking it as inactive past the given time. */
+    public Span close(final Duration endOffset) {
+      if (this.endOffset.isPresent()) throw new Error("Attempt to close an already-closed span");
+      return new Span(this.parent, this.startOffset, Optional.of(endOffset));
     }
 
-    /** The task has completed its primary operation, but has unfinished children. */
-    record AwaitingChildren<Return>(
-        Duration startOffset,
-        Duration endOffset,
-        LinkedList<TaskId> remainingChildren
-    ) implements ExecutionState<Return>
-    {
-      public Terminated<Return> joinedAt(final Duration joinOffset) {
-        return new Terminated<>(this.startOffset, this.endOffset, joinOffset);
-      }
+    public Optional<Duration> duration() {
+      return this.endOffset.map($ -> $.minus(this.startOffset));
     }
 
-    /** The task and all its delegated children have completed. */
-    record Terminated<Return>(
-        Duration startOffset,
-        Duration endOffset,
-        Duration joinOffset
-    ) implements ExecutionState<Return> {}
+    public boolean isComplete() {
+      return this.endOffset.isPresent();
+    }
   }
 }
diff --git a/merlin-driver/src/main/java/gov/nasa/jpl/aerie/merlin/driver/engine/SpanId.java b/merlin-driver/src/main/java/gov/nasa/jpl/aerie/merlin/driver/engine/SpanId.java
new file mode 100644
index 0000000000..96f5795b0c
--- /dev/null
+++ b/merlin-driver/src/main/java/gov/nasa/jpl/aerie/merlin/driver/engine/SpanId.java
@@ -0,0 +1,10 @@
+package gov.nasa.jpl.aerie.merlin.driver.engine;
+
+import java.util.UUID;
+
+/** A typed wrapper for span IDs. */
+public record SpanId(String id) {
+  public static SpanId generate() {
+    return new SpanId(UUID.randomUUID().toString());
+  }
+}
diff --git a/merlin-driver/src/main/java/gov/nasa/jpl/aerie/merlin/driver/timeline/Event.java b/merlin-driver/src/main/java/gov/nasa/jpl/aerie/merlin/driver/timeline/Event.java
index e9f334a7da..7fd8840319 100644
--- a/merlin-driver/src/main/java/gov/nasa/jpl/aerie/merlin/driver/timeline/Event.java
+++ b/merlin-driver/src/main/java/gov/nasa/jpl/aerie/merlin/driver/timeline/Event.java
@@ -1,6 +1,6 @@
 package gov.nasa.jpl.aerie.merlin.driver.timeline;
 
-import gov.nasa.jpl.aerie.merlin.driver.engine.TaskId;
+import gov.nasa.jpl.aerie.merlin.driver.engine.SpanId;
 import gov.nasa.jpl.aerie.merlin.protocol.driver.Topic;
 
 import java.util.Objects;
@@ -16,7 +16,7 @@ private Event(final Event.GenericEvent<?> inner) {
   }
 
   public static <EventType>
-  Event create(final Topic<EventType> topic, final EventType event, final TaskId provenance) {
+  Event create(final Topic<EventType> topic, final EventType event, final SpanId provenance) {
     return new Event(new Event.GenericEvent<>(topic, event, provenance));
   }
 
@@ -34,7 +34,7 @@ public Topic<?> topic() {
     return this.inner.topic();
   }
 
-  public TaskId provenance() {
+  public SpanId provenance() {
     return this.inner.provenance();
   }
 
@@ -43,7 +43,7 @@ public String toString() {
     return "<@%s, %s>".formatted(System.identityHashCode(this.inner.topic), this.inner.event);
   }
 
-  private record GenericEvent<EventType>(Topic<EventType> topic, EventType event, TaskId provenance) {
+  private record GenericEvent<EventType>(Topic<EventType> topic, EventType event, SpanId provenance) {
     private GenericEvent {
       Objects.requireNonNull(topic);
       Objects.requireNonNull(event);
diff --git a/merlin-driver/src/test/java/gov/nasa/jpl/aerie/merlin/driver/AnchorSimulationTest.java b/merlin-driver/src/test/java/gov/nasa/jpl/aerie/merlin/driver/AnchorSimulationTest.java
index fac9709efb..748256a98b 100644
--- a/merlin-driver/src/test/java/gov/nasa/jpl/aerie/merlin/driver/AnchorSimulationTest.java
+++ b/merlin-driver/src/test/java/gov/nasa/jpl/aerie/merlin/driver/AnchorSimulationTest.java
@@ -1083,6 +1083,7 @@ public OutputType<Object> getOutputType() {
       @Override
       public TaskFactory<Object> getTaskFactory(final Object o, final Object o2) {
         return executor -> $ -> {
+          $.pushSpan();
           $.emit(this, delayedActivityDirectiveInputTopic);
           return TaskStatus.delayed(oneMinute, $$ -> {
             $$.emit(Unit.UNIT, delayedActivityDirectiveOutputTopic);
@@ -1108,6 +1109,7 @@ public OutputType<Object> getOutputType() {
       @Override
       public TaskFactory<Object> getTaskFactory(final Object o, final Object o2) {
         return executor -> scheduler -> {
+          scheduler.pushSpan();
           scheduler.emit(this, decomposingActivityDirectiveInputTopic);
           return TaskStatus.delayed(
               Duration.ZERO,
diff --git a/merlin-driver/src/test/java/gov/nasa/jpl/aerie/merlin/driver/engine/TaskFrameTest.java b/merlin-driver/src/test/java/gov/nasa/jpl/aerie/merlin/driver/engine/TaskFrameTest.java
index 44e8cbed5e..1b435dfbce 100644
--- a/merlin-driver/src/test/java/gov/nasa/jpl/aerie/merlin/driver/engine/TaskFrameTest.java
+++ b/merlin-driver/src/test/java/gov/nasa/jpl/aerie/merlin/driver/engine/TaskFrameTest.java
@@ -28,7 +28,7 @@
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
 public final class TaskFrameTest {
-  private static final TaskId ORIGIN = TaskId.generate();
+  private static final SpanId ORIGIN = SpanId.generate();
 
   // This regression test identified a bug in the LiveCells-chain-avoidance optimization in TaskFrame.
   @Test
diff --git a/merlin-framework-processor/src/main/java/gov/nasa/jpl/aerie/merlin/processor/generator/MissionModelGenerator.java b/merlin-framework-processor/src/main/java/gov/nasa/jpl/aerie/merlin/processor/generator/MissionModelGenerator.java
index be17603c33..08af87e754 100644
--- a/merlin-framework-processor/src/main/java/gov/nasa/jpl/aerie/merlin/processor/generator/MissionModelGenerator.java
+++ b/merlin-framework-processor/src/main/java/gov/nasa/jpl/aerie/merlin/processor/generator/MissionModelGenerator.java
@@ -808,12 +808,14 @@ public Optional<JavaFile> generateActivityMapper(final MissionModelRecord missio
                         .map(effectModel -> CodeBlock
                             .builder()
                             .add(
-                                "return $T.$L(() -> {$>\n$L$<});\n",
+                                "return $T.$L(() -> $T.$L(() -> {$>\n$L$<}));\n",
                                 ModelActions.class,
                                 switch (effectModel.executor()) {
                                   case Threaded -> "threaded";
                                   case Replaying -> "replaying";
                                 },
+                                ModelActions.class,
+                                "scoped",
                                 effectModel.returnType()
                                     .map(returnType -> CodeBlock
                                         .builder()
@@ -835,6 +837,7 @@ public Optional<JavaFile> generateActivityMapper(final MissionModelRecord missio
                             .add(
                                 "return executor -> scheduler -> {$>\n$L$<};\n",
                                 CodeBlock.builder()
+                                    .addStatement("scheduler.pushSpan()")
                                     .addStatement("scheduler.emit($L, this.$L)", "activity", "inputTopic")
                                     .addStatement("scheduler.emit($T.UNIT, this.$L)", Unit.class, "outputTopic")
                                     .addStatement("return $T.completed($T.UNIT)", TaskStatus.class, Unit.class)
diff --git a/merlin-framework/build.gradle b/merlin-framework/build.gradle
index a52dde0379..66a07a16c6 100644
--- a/merlin-framework/build.gradle
+++ b/merlin-framework/build.gradle
@@ -15,6 +15,9 @@ java {
 
 test {
   useJUnitPlatform()
+  testLogging {
+    exceptionFormat = 'full'
+  }
 }
 
 jacocoTestReport {
diff --git a/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/Context.java b/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/Context.java
index 6738237a37..65a457d1b4 100644
--- a/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/Context.java
+++ b/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/Context.java
@@ -31,6 +31,8 @@ enum ContextType { Initializing, Reacting, Querying }
 
   void spawn(TaskFactory<?> task);
   <Return> void call(TaskFactory<Return> task);
+  void pushSpan();
+  void popSpan();
 
   void delay(Duration duration);
   void waitUntil(Condition condition);
diff --git a/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/InitializationContext.java b/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/InitializationContext.java
index 9615830a69..5529a6dd6d 100644
--- a/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/InitializationContext.java
+++ b/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/InitializationContext.java
@@ -61,6 +61,16 @@ public <Return> void call(final TaskFactory<Return> task) {
     throw new IllegalStateException("Cannot yield during initialization");
   }
 
+  @Override
+  public void pushSpan() {
+    // Do nothing.
+  }
+
+  @Override
+  public void popSpan() {
+    // Do nothing.
+  }
+
   @Override
   public void delay(final Duration duration) {
     throw new IllegalStateException("Cannot yield during initialization");
diff --git a/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/ModelActions.java b/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/ModelActions.java
index 1c9019f328..bdbbabd3db 100644
--- a/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/ModelActions.java
+++ b/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/ModelActions.java
@@ -36,6 +36,22 @@ public static TaskFactory<Unit> replaying(final Runnable task) {
     });
   }
 
+  public static <T> T scoped(final Supplier<T> block) {
+    context.get().pushSpan();
+    try {
+      return block.get();
+    } finally {
+      context.get().popSpan();
+    }
+  }
+
+  public static void scoped(final Runnable block) {
+    scoped(() -> {
+      block.run();
+      return Unit.UNIT;
+    });
+  }
+
 
   public static <T> void emit(final T event, final Topic<T> topic) {
     context.get().emit(event, topic);
diff --git a/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/QueryContext.java b/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/QueryContext.java
index 2425a9ab77..e2c0bf169f 100644
--- a/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/QueryContext.java
+++ b/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/QueryContext.java
@@ -52,6 +52,16 @@ public <Return> void call(final TaskFactory<Return> task) {
     throw new IllegalStateException("Cannot schedule tasks in a query-only context");
   }
 
+  @Override
+  public void pushSpan() {
+    // Do nothing.
+  }
+
+  @Override
+  public void popSpan() {
+    // Do nothing.
+  }
+
   @Override
   public void delay(final Duration duration) {
     throw new IllegalStateException("Cannot yield in a query-only context");
diff --git a/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/ReplayingReactionContext.java b/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/ReplayingReactionContext.java
index e9998ff256..e6e8d5bbfb 100644
--- a/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/ReplayingReactionContext.java
+++ b/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/ReplayingReactionContext.java
@@ -78,6 +78,20 @@ public <T> void call(final TaskFactory<T> task) {
     });
   }
 
+  @Override
+  public void pushSpan() {
+    this.memory.doOnce(() -> {
+      this.scheduler.pushSpan();
+    });
+  }
+
+  @Override
+  public void popSpan() {
+    this.memory.doOnce(() -> {
+      this.scheduler.popSpan();
+    });
+  }
+
   @Override
   public void delay(final Duration duration) {
     this.memory.doOnce(() -> {
diff --git a/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/ThreadedReactionContext.java b/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/ThreadedReactionContext.java
index 3edd568d9e..0a4984bda0 100644
--- a/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/ThreadedReactionContext.java
+++ b/merlin-framework/src/main/java/gov/nasa/jpl/aerie/merlin/framework/ThreadedReactionContext.java
@@ -63,6 +63,16 @@ public <T> void call(final TaskFactory<T> task) {
     this.scheduler = this.handle.call(task);
   }
 
+  @Override
+  public void pushSpan() {
+    this.scheduler.pushSpan();
+  }
+
+  @Override
+  public void popSpan() {
+    this.scheduler.popSpan();
+  }
+
   @Override
   public void delay(final Duration duration) {
     this.scheduler = null;  // Relinquish the current scheduler before yielding, in case an exception is thrown.
diff --git a/merlin-framework/src/test/java/gov/nasa/jpl/aerie/merlin/framework/ThreadedTaskTest.java b/merlin-framework/src/test/java/gov/nasa/jpl/aerie/merlin/framework/ThreadedTaskTest.java
index ac3942dcd0..b961a41be8 100644
--- a/merlin-framework/src/test/java/gov/nasa/jpl/aerie/merlin/framework/ThreadedTaskTest.java
+++ b/merlin-framework/src/test/java/gov/nasa/jpl/aerie/merlin/framework/ThreadedTaskTest.java
@@ -31,6 +31,16 @@ public <Event> void emit(final Event event, final Topic<Event> topic) {
       public void spawn(final TaskFactory<?> task) {
         throw new UnsupportedOperationException();
       }
+
+      @Override
+      public void pushSpan() {
+        throw new UnsupportedOperationException();
+      }
+
+      @Override
+      public void popSpan() {
+        throw new UnsupportedOperationException();
+      }
     };
 
     final var pool = Executors.newCachedThreadPool();
diff --git a/merlin-sdk/build.gradle b/merlin-sdk/build.gradle
index 908b26fad7..15cd7aa7bc 100644
--- a/merlin-sdk/build.gradle
+++ b/merlin-sdk/build.gradle
@@ -15,6 +15,9 @@ java {
 
 test {
   useJUnitPlatform()
+  testLogging {
+    exceptionFormat = 'full'
+  }
 }
 
 jacocoTestReport {
diff --git a/merlin-sdk/src/main/java/gov/nasa/jpl/aerie/merlin/protocol/driver/Scheduler.java b/merlin-sdk/src/main/java/gov/nasa/jpl/aerie/merlin/protocol/driver/Scheduler.java
index 035658c136..c788a508d5 100644
--- a/merlin-sdk/src/main/java/gov/nasa/jpl/aerie/merlin/protocol/driver/Scheduler.java
+++ b/merlin-sdk/src/main/java/gov/nasa/jpl/aerie/merlin/protocol/driver/Scheduler.java
@@ -8,4 +8,8 @@ public interface Scheduler {
   <Event> void emit(Event event, Topic<Event> topic);
 
   void spawn(TaskFactory<?> task);
+
+  void pushSpan();
+
+  void popSpan();
 }
diff --git a/merlin-server/build.gradle b/merlin-server/build.gradle
index 7e4557f5b6..d13902ecff 100644
--- a/merlin-server/build.gradle
+++ b/merlin-server/build.gradle
@@ -60,6 +60,10 @@ test {
 
   environment "CONSTRAINTS_DSL_COMPILER_ROOT", projectDir.toPath().resolve('constraints-dsl-compiler')
   environment "CONSTRAINTS_DSL_COMPILER_COMMAND", './build/main.js'
+
+  testLogging {
+    exceptionFormat = 'full'
+  }
 }
 
 jacocoTestReport {
diff --git a/parsing-utilities/build.gradle b/parsing-utilities/build.gradle
index 3eaa311b8b..cb2790ca01 100644
--- a/parsing-utilities/build.gradle
+++ b/parsing-utilities/build.gradle
@@ -12,6 +12,9 @@ java {
 
 test {
   useJUnitPlatform()
+  testLogging {
+    exceptionFormat = 'full'
+  }
 }
 
 jacocoTestReport {
diff --git a/procedural/README.md b/procedural/README.md
new file mode 100644
index 0000000000..a17cee1523
--- /dev/null
+++ b/procedural/README.md
@@ -0,0 +1,7 @@
+# Procedural post-simulation libraries
+
+This subproject holds the libraries provided to the users for procedural scheduling / constraints / conditions.
+
+## Documentation
+
+To generate the unified docs, run `./gradlew :procedural:dokkaHtmlMultiModule`. It will be available in `procedural/build/dokka/htmlMultiModule/index.html`. To view it locally, you'll need a static file server to avoid CORS problems. In IntelliJ, you can right-click on `index.html` and select `Open In -> Browser -> ...` and this will start a server for you.
diff --git a/procedural/build.gradle b/procedural/build.gradle
new file mode 100644
index 0000000000..65061f0d89
--- /dev/null
+++ b/procedural/build.gradle
@@ -0,0 +1,8 @@
+plugins {
+  id "org.jetbrains.kotlin.jvm" version "1.9.22"
+  id 'org.jetbrains.dokka' version '1.9.10'
+}
+
+repositories {
+  mavenCentral()
+}
diff --git a/procedural/constraints/MODULE_DOCS.md b/procedural/constraints/MODULE_DOCS.md
new file mode 100644
index 0000000000..76386e400a
--- /dev/null
+++ b/procedural/constraints/MODULE_DOCS.md
@@ -0,0 +1,6 @@
+# Module Constraints
+
+This library provides basic tools for creating constraints, based on the timeline library.
+To define a constraint, just create a class that implements the Constraint interface.
+Then, follow the tutorial documentation (TODO: link to tutorial documentation once written)
+to package and upload your constraint to Aerie.
diff --git a/procedural/constraints/README.md b/procedural/constraints/README.md
new file mode 100644
index 0000000000..700351caff
--- /dev/null
+++ b/procedural/constraints/README.md
@@ -0,0 +1,9 @@
+# Constraints
+
+This library provides the `Constraint` interface and `Violations` timeline type, for users to create procedural constraints.
+
+- Building and testing: `./gradlew :procedural:constraints:build`
+- Generating a jar for local experimentation: `./gradlew :procedural:constraints:shadowJar`
+  - jar will be available at `procedural/constraints/build/libs/constraints-all.jar`
+
+See `/procedural/README.md` for instructions on generating viewing documentation.
diff --git a/procedural/constraints/build.gradle b/procedural/constraints/build.gradle
new file mode 100644
index 0000000000..80bce8c81c
--- /dev/null
+++ b/procedural/constraints/build.gradle
@@ -0,0 +1,54 @@
+import org.jetbrains.kotlin.gradle.dsl.jvm.JvmTargetValidationMode
+import org.jetbrains.kotlin.gradle.tasks.KotlinJvmCompile
+
+plugins {
+  id 'com.github.johnrengelman.shadow' version '8.1.1'
+  id "org.jetbrains.kotlin.jvm" version "1.9.22"
+  id 'java-library'
+  id 'org.jetbrains.dokka' version '1.9.10'
+}
+
+repositories {
+  mavenCentral()
+}
+
+dependencies {
+  implementation project(':procedural:timeline')
+
+  testImplementation 'org.junit.jupiter:junit-jupiter-engine:5.10.0'
+  testImplementation 'org.jetbrains.kotlin:kotlin-test-junit5'
+  testRuntimeOnly("org.junit.platform:junit-platform-launcher")
+}
+
+tasks.withType(KotlinJvmCompile.class).configureEach {
+  jvmTargetValidationMode = JvmTargetValidationMode.WARNING
+}
+
+tasks.named('test') {
+  useJUnitPlatform()
+}
+
+kotlin {
+  jvmToolchain(21)
+}
+
+var timelineSource = "${project(":procedural:timeline").projectDir}/src/main/kotlin"
+
+dokkaHtmlPartial.configure {
+  dokkaSourceSets {
+    configureEach {
+      // used as project name in the header
+      moduleName.set("Constraints")
+
+      reportUndocumented.set(true)
+      failOnWarning.set(true)
+
+      // contains descriptions for the module and the packages
+      includes.from("MODULE_DOCS.md")
+
+      sourceRoots.from(timelineSource)
+      suppressedFiles.from(timelineSource)
+    }
+  }
+}
+
diff --git a/procedural/constraints/src/main/kotlin/gov/nasa/jpl/aerie/procedural/constraints/ActivityId.kt b/procedural/constraints/src/main/kotlin/gov/nasa/jpl/aerie/procedural/constraints/ActivityId.kt
new file mode 100644
index 0000000000..337df89065
--- /dev/null
+++ b/procedural/constraints/src/main/kotlin/gov/nasa/jpl/aerie/procedural/constraints/ActivityId.kt
@@ -0,0 +1,7 @@
+package gov.nasa.jpl.aerie.procedural.constraints
+
+/** An activity ID, referencing either a directive or instance. */
+sealed interface ActivityId {
+  /***/ data class InstanceId(/***/ val id: Long): ActivityId
+  /***/ data class DirectiveId(/***/ val id: Long): ActivityId
+}
diff --git a/procedural/constraints/src/main/kotlin/gov/nasa/jpl/aerie/procedural/constraints/Constraint.kt b/procedural/constraints/src/main/kotlin/gov/nasa/jpl/aerie/procedural/constraints/Constraint.kt
new file mode 100644
index 0000000000..2fbd717b9b
--- /dev/null
+++ b/procedural/constraints/src/main/kotlin/gov/nasa/jpl/aerie/procedural/constraints/Constraint.kt
@@ -0,0 +1,18 @@
+package gov.nasa.jpl.aerie.procedural.constraints
+
+import gov.nasa.jpl.aerie.timeline.CollectOptions
+import gov.nasa.jpl.aerie.timeline.plan.Plan
+
+/** The interface that all constraints must satisfy. */
+interface Constraint {
+  /**
+   * Run the constraint on a plan.
+   *
+   * The provided collect options are the options that the [Violations] result will be collected on after
+   * the constraint is run. The constraint does not need to use the options unless it collects a timeline prematurely.
+   *
+   * @param plan the plan to check the constraint on
+   * @param options the [CollectOptions] that the result will be collected with
+   */
+  fun run(plan: Plan, options: CollectOptions): Violations
+}
diff --git a/procedural/constraints/src/main/kotlin/gov/nasa/jpl/aerie/procedural/constraints/Violation.kt b/procedural/constraints/src/main/kotlin/gov/nasa/jpl/aerie/procedural/constraints/Violation.kt
new file mode 100644
index 0000000000..9e51a81e08
--- /dev/null
+++ b/procedural/constraints/src/main/kotlin/gov/nasa/jpl/aerie/procedural/constraints/Violation.kt
@@ -0,0 +1,22 @@
+package gov.nasa.jpl.aerie.procedural.constraints
+
+import gov.nasa.jpl.aerie.timeline.Interval
+import gov.nasa.jpl.aerie.timeline.payloads.IntervalLike
+
+/** A single violation of a constraint. */
+data class Violation(
+    /** Interval on which the violation occurs. */
+    override val interval: Interval,
+
+    /** List of associated activities (directives or instances) that are related to the violation. */
+    val ids: List<ActivityId> = listOf()
+) : IntervalLike<Violation> {
+
+  override fun withNewInterval(i: Interval) = Violation(i, ids)
+
+  /** Constructs a violation on the same interval with a different list of ids. */
+  fun withNewIds(vararg id: ActivityId) = Violation(interval, id.asList())
+
+  /** Constructs a violation on the same interval with a different list of ids. */
+  fun withNewIds(ids: List<ActivityId>) = Violation(interval, ids)
+}
diff --git a/procedural/constraints/src/main/kotlin/gov/nasa/jpl/aerie/procedural/constraints/Violations.kt b/procedural/constraints/src/main/kotlin/gov/nasa/jpl/aerie/procedural/constraints/Violations.kt
new file mode 100644
index 0000000000..43af1ee4ac
--- /dev/null
+++ b/procedural/constraints/src/main/kotlin/gov/nasa/jpl/aerie/procedural/constraints/Violations.kt
@@ -0,0 +1,82 @@
+package gov.nasa.jpl.aerie.procedural.constraints
+
+import gov.nasa.jpl.aerie.procedural.constraints.ActivityId.DirectiveId
+import gov.nasa.jpl.aerie.procedural.constraints.ActivityId.InstanceId
+import gov.nasa.jpl.aerie.timeline.BaseTimeline
+import gov.nasa.jpl.aerie.timeline.BoundsTransformer
+import gov.nasa.jpl.aerie.timeline.Timeline
+import gov.nasa.jpl.aerie.timeline.collections.Intervals
+import gov.nasa.jpl.aerie.timeline.collections.Windows
+import gov.nasa.jpl.aerie.timeline.collections.profiles.Real
+import gov.nasa.jpl.aerie.timeline.ops.*
+import gov.nasa.jpl.aerie.timeline.ops.coalesce.CoalesceNoOp
+import gov.nasa.jpl.aerie.timeline.payloads.IntervalLike
+import gov.nasa.jpl.aerie.timeline.payloads.activities.Directive
+import gov.nasa.jpl.aerie.timeline.payloads.activities.Instance
+import gov.nasa.jpl.aerie.timeline.util.preprocessList
+
+/** A timeline of [Violations][Violation]. */
+data class Violations(private val timeline: Timeline<Violation, Violations>):
+    Timeline<Violation, Violations> by timeline,
+    ParallelOps<Violation, Violations>,
+    NonZeroDurationOps<Violation, Violations>,
+    CoalesceNoOp<Violation, Violations>
+{
+  constructor(vararg violation: Violation): this(violation.asList())
+  constructor(violations: List<Violation>): this(BaseTimeline(::Violations, preprocessList(violations, null)))
+
+  /**
+   * Maps the list of associated activity ids on each violation.
+   *
+   * @param f a function which takes a [Violation] and returns a new list of ids.
+   */
+  fun mapIds(f: (Violation) -> List<ActivityId>) = unsafeMap(BoundsTransformer.IDENTITY, false) { it.withNewIds(f(it)) }
+
+  /***/ companion object {
+    /** Creates a [Violations] object that violates when this profile equals a given value. */
+    @JvmStatic fun <V: Any> SerialConstantOps<V, *>.violateOn(v: V) = isolateEqualTo(v).violations()
+
+    /** Creates a [Violations] object that violates when this profile equals a given value. */
+    @JvmStatic fun Real.violateOn(n: Number) = equalTo(n).violateOn(true)
+
+    /**
+     * Creates a [Violations] object that violates on every object in the timeline.
+     *
+     * If the object is an activity, it will record the directive or instance id.
+     */
+    @JvmStatic fun <I: IntervalLike<I>> ParallelOps<I, *>.violations() =
+        unsafeMap(::Violations, BoundsTransformer.IDENTITY, false) {
+          Violation(
+              it.interval,
+              listOfNotNull(it.getActivityId())
+          )
+        }
+
+    /** Creates a [Violations] object that violates inside each interval. */
+    @JvmStatic fun Windows.violateInside() = unsafeCast(::Intervals).violations()
+    /** Creates a [Violations] object that violates outside each interval. */
+    @JvmStatic fun Windows.violateOutside() = complement().violateInside()
+
+    /**
+     * Creates a [Violations] object from two timelines, that violates whenever they have overlap.
+     *
+     * If either object is an activity, it will record the directive or instance id.
+     */
+    @JvmStatic infix fun <V: IntervalLike<V>, W: IntervalLike<W>> GeneralOps<V, *>.mutex(other: GeneralOps<W, *>) =
+        unsafeMap2(::Violations, other) { l, r, i -> Violation(
+            i,
+            listOfNotNull(
+                l.getActivityId(),
+                r.getActivityId()
+            )
+        )}
+
+    private fun <V: IntervalLike<V>> V.getActivityId() = when (this) {
+      is Instance<*> -> InstanceId(id)
+      is Directive<*> -> DirectiveId(id)
+      else -> null
+    }
+  }
+}
+
+
diff --git a/timeline/MODULE_DOCS.md b/procedural/timeline/MODULE_DOCS.md
similarity index 100%
rename from timeline/MODULE_DOCS.md
rename to procedural/timeline/MODULE_DOCS.md
diff --git a/procedural/timeline/README.md b/procedural/timeline/README.md
new file mode 100644
index 0000000000..3ad47c0cf3
--- /dev/null
+++ b/procedural/timeline/README.md
@@ -0,0 +1,27 @@
+# Timelines
+
+This library provides tools for querying and manipulating "timelines" from an Aerie plan or set of
+simulation results. This includes things like resource profiles, activity instances, and activity directives,
+but can be extended to support more kinds if needed.
+
+See [MODULE_DOCS.md](./MODULE_DOCS.md) for a description of the architecture and design of the library.
+
+- Building and testing: `./gradlew :procedural:timeline:build`
+- Generating a jar for local experimentation: `./gradlew :procedural:timeline:shadowJar`
+  - jar will be available at `procedural/timeline/build/libs/timeline-all.jar`
+
+See `/procedural/README.md` for instructions on generating viewing documentation.
+
+## Potential future optimizations
+
+- **caching/memoization:** currently collecting a timeline twice will result in it being
+  computed twice. Automatically memoizing the results has potential for unsoundness,
+  but to be fair, so does the entire concept of evaluating on restricted bounds. But if
+  we do it right, it could give theoretically unbounded speedup for complex timelines.
+- **inlining durations:** Turn the Duration class into an `inline value` class. This speeds
+  up the entire library by about 20%, based on a rudimentary benchmark. On the downside,
+  it makes the interface in Java use a bunch of longs instead of duration objects. Should
+  be possible to do cleanly, but will take some cleverness.
+- **streaming:** rework the core to be create streams instead of lists. It should be somewhat faster,
+  but I don't know how much. The main utility is that with segment streaming from simulation,
+  you could evaluate timelines in parallel with simulation.
diff --git a/timeline/build.gradle b/procedural/timeline/build.gradle
similarity index 91%
rename from timeline/build.gradle
rename to procedural/timeline/build.gradle
index 13ed1a2a17..5869350d05 100644
--- a/timeline/build.gradle
+++ b/procedural/timeline/build.gradle
@@ -35,9 +35,9 @@ kotlin {
   jvmToolchain(21)
 }
 
-dokkaHtml.configure {
+dokkaHtmlPartial.configure {
   dokkaSourceSets {
-    named("main") {
+     configureEach {
       // used as project name in the header
       moduleName.set("Timeline")
 
@@ -49,10 +49,10 @@ dokkaHtml.configure {
 
       // adds source links that lead to this repository, allowing readers
       // to easily find source code for inspected declarations
-      sourceLink.configure {
+      sourceLink {
         localDirectory.set(file("timeline/src/main/kotlin"))
-        remoteUrl.set(URL(
-            "https://github.com/NASA-AMMOS/aerie/blob/feat/java-timeline-library/timeline/src/main/kotlin"
+        remoteUrl.set(new URL(
+            "https://github.com/NASA-AMMOS/aerie/blob/feat/java-timeline-library/timeline/src/main/kotlin/"
         ))
         remoteLineSuffix.set("#L")
       }
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/BaseTimeline.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/BaseTimeline.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/BaseTimeline.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/BaseTimeline.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/BoundsTransformer.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/BoundsTransformer.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/BoundsTransformer.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/BoundsTransformer.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/CollectOptions.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/CollectOptions.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/CollectOptions.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/CollectOptions.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/Duration.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/Duration.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/Duration.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/Duration.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/Interval.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/Interval.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/Interval.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/Interval.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/NullBinaryOperation.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/NullBinaryOperation.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/NullBinaryOperation.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/NullBinaryOperation.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/Timeline.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/Timeline.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/Timeline.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/Timeline.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/Directives.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/Directives.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/Directives.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/Directives.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/Instances.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/Instances.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/Instances.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/Instances.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/Intervals.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/Intervals.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/Intervals.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/Intervals.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/Windows.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/Windows.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/Windows.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/Windows.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/Booleans.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/Booleans.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/Booleans.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/Booleans.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/Constants.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/Constants.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/Constants.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/Constants.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/Numbers.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/Numbers.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/Numbers.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/Numbers.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/Real.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/Real.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/Real.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/Real.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/ActivityOps.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/ActivityOps.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/ActivityOps.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/ActivityOps.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/BooleanOps.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/BooleanOps.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/BooleanOps.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/BooleanOps.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/ConstantOps.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/ConstantOps.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/ConstantOps.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/ConstantOps.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/GeneralOps.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/GeneralOps.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/GeneralOps.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/GeneralOps.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/NonZeroDurationOps.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/NonZeroDurationOps.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/NonZeroDurationOps.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/NonZeroDurationOps.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/ParallelOps.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/ParallelOps.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/ParallelOps.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/ParallelOps.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/SegmentOps.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/SegmentOps.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/SegmentOps.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/SegmentOps.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialConstantOps.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialConstantOps.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialConstantOps.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialConstantOps.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialOps.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialOps.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialOps.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialOps.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialSegmentOps.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialSegmentOps.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialSegmentOps.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialSegmentOps.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/coalesce/CoalesceIntervalsOp.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/coalesce/CoalesceIntervalsOp.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/coalesce/CoalesceIntervalsOp.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/coalesce/CoalesceIntervalsOp.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/coalesce/CoalesceNoOp.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/coalesce/CoalesceNoOp.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/coalesce/CoalesceNoOp.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/coalesce/CoalesceNoOp.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/coalesce/CoalesceSegmentsOp.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/coalesce/CoalesceSegmentsOp.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/coalesce/CoalesceSegmentsOp.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/coalesce/CoalesceSegmentsOp.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/LinearOps.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/LinearOps.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/LinearOps.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/LinearOps.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/NumericOps.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/NumericOps.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/NumericOps.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/NumericOps.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/PrimitiveNumberOps.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/PrimitiveNumberOps.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/PrimitiveNumberOps.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/PrimitiveNumberOps.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/SerialNumericOps.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/SerialNumericOps.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/SerialNumericOps.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/SerialNumericOps.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/Connection.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/Connection.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/Connection.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/Connection.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/IntervalLike.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/IntervalLike.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/IntervalLike.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/IntervalLike.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/LinearEquation.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/LinearEquation.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/LinearEquation.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/LinearEquation.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/Segment.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/Segment.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/Segment.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/Segment.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/Activity.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/Activity.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/Activity.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/Activity.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/AnyDirective.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/AnyDirective.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/AnyDirective.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/AnyDirective.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/AnyInstance.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/AnyInstance.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/AnyInstance.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/AnyInstance.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/Directive.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/Directive.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/Directive.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/Directive.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/Instance.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/Instance.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/Instance.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/payloads/activities/Instance.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/plan/AeriePostgresPlan.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/plan/AeriePostgresPlan.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/plan/AeriePostgresPlan.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/plan/AeriePostgresPlan.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/plan/Plan.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/plan/Plan.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/plan/Plan.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/plan/Plan.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/util/Coalesce.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/util/Coalesce.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/util/Coalesce.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/util/Coalesce.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/util/ListUtils.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/util/ListUtils.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/util/ListUtils.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/util/ListUtils.kt
diff --git a/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/util/Map2.kt b/procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/util/Map2.kt
similarity index 100%
rename from timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/util/Map2.kt
rename to procedural/timeline/src/main/kotlin/gov/nasa/jpl/aerie/timeline/util/Map2.kt
diff --git a/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/BoundsTransformerTest.kt b/procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/BoundsTransformerTest.kt
similarity index 100%
rename from timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/BoundsTransformerTest.kt
rename to procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/BoundsTransformerTest.kt
diff --git a/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/IntervalTest.kt b/procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/IntervalTest.kt
similarity index 100%
rename from timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/IntervalTest.kt
rename to procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/IntervalTest.kt
diff --git a/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/SegmentTest.kt b/procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/SegmentTest.kt
similarity index 100%
rename from timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/SegmentTest.kt
rename to procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/SegmentTest.kt
diff --git a/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/collections/WindowsTest.kt b/procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/collections/WindowsTest.kt
similarity index 100%
rename from timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/collections/WindowsTest.kt
rename to procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/collections/WindowsTest.kt
diff --git a/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/BooleansTest.kt b/procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/BooleansTest.kt
similarity index 100%
rename from timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/BooleansTest.kt
rename to procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/BooleansTest.kt
diff --git a/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/NumbersTest.kt b/procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/NumbersTest.kt
similarity index 100%
rename from timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/NumbersTest.kt
rename to procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/NumbersTest.kt
diff --git a/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/RealTest.kt b/procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/RealTest.kt
similarity index 100%
rename from timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/RealTest.kt
rename to procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/collections/profiles/RealTest.kt
diff --git a/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/GeneralOpsTest.kt b/procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/GeneralOpsTest.kt
similarity index 100%
rename from timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/GeneralOpsTest.kt
rename to procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/GeneralOpsTest.kt
diff --git a/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/NonZeroDurationOpsTest.kt b/procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/NonZeroDurationOpsTest.kt
similarity index 100%
rename from timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/NonZeroDurationOpsTest.kt
rename to procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/NonZeroDurationOpsTest.kt
diff --git a/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/ParallelOpsTest.kt b/procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/ParallelOpsTest.kt
similarity index 100%
rename from timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/ParallelOpsTest.kt
rename to procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/ParallelOpsTest.kt
diff --git a/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialConstantTest.kt b/procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialConstantTest.kt
similarity index 100%
rename from timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialConstantTest.kt
rename to procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialConstantTest.kt
diff --git a/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialSegmentOpsTest.kt b/procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialSegmentOpsTest.kt
similarity index 100%
rename from timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialSegmentOpsTest.kt
rename to procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/SerialSegmentOpsTest.kt
diff --git a/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/LinearOpsTest.kt b/procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/LinearOpsTest.kt
similarity index 100%
rename from timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/LinearOpsTest.kt
rename to procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/LinearOpsTest.kt
diff --git a/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/PrimitiveNumberOpsTest.kt b/procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/PrimitiveNumberOpsTest.kt
similarity index 100%
rename from timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/PrimitiveNumberOpsTest.kt
rename to procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/PrimitiveNumberOpsTest.kt
diff --git a/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/SerialNumericOpsTest.kt b/procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/SerialNumericOpsTest.kt
similarity index 100%
rename from timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/SerialNumericOpsTest.kt
rename to procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/ops/numeric/SerialNumericOpsTest.kt
diff --git a/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/util/CoalesceTest.kt b/procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/util/CoalesceTest.kt
similarity index 100%
rename from timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/util/CoalesceTest.kt
rename to procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/util/CoalesceTest.kt
diff --git a/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/util/LinearEquationTest.kt b/procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/util/LinearEquationTest.kt
similarity index 100%
rename from timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/util/LinearEquationTest.kt
rename to procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/util/LinearEquationTest.kt
diff --git a/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/util/ListCollectorTest.kt b/procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/util/ListCollectorTest.kt
similarity index 100%
rename from timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/util/ListCollectorTest.kt
rename to procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/util/ListCollectorTest.kt
diff --git a/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/util/Map2Test.kt b/procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/util/Map2Test.kt
similarity index 100%
rename from timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/util/Map2Test.kt
rename to procedural/timeline/src/test/kotlin/gov/nasa/jpl/aerie/timeline/util/Map2Test.kt
diff --git a/scheduler-driver/build.gradle b/scheduler-driver/build.gradle
index fef5cca0f9..77686981ed 100644
--- a/scheduler-driver/build.gradle
+++ b/scheduler-driver/build.gradle
@@ -12,6 +12,9 @@ java {
 
 test {
   useJUnitPlatform()
+  testLogging {
+    exceptionFormat = 'full'
+  }
 }
 
 jacocoTestReport {
diff --git a/scheduler-driver/src/main/java/gov/nasa/jpl/aerie/scheduler/simulation/ResumableSimulationDriver.java b/scheduler-driver/src/main/java/gov/nasa/jpl/aerie/scheduler/simulation/ResumableSimulationDriver.java
index 2cf23d0897..5c6112af55 100644
--- a/scheduler-driver/src/main/java/gov/nasa/jpl/aerie/scheduler/simulation/ResumableSimulationDriver.java
+++ b/scheduler-driver/src/main/java/gov/nasa/jpl/aerie/scheduler/simulation/ResumableSimulationDriver.java
@@ -8,7 +8,7 @@
 import gov.nasa.jpl.aerie.merlin.driver.StartOffsetReducer;
 import gov.nasa.jpl.aerie.merlin.driver.engine.JobSchedule;
 import gov.nasa.jpl.aerie.merlin.driver.engine.SimulationEngine;
-import gov.nasa.jpl.aerie.merlin.driver.engine.TaskId;
+import gov.nasa.jpl.aerie.merlin.driver.engine.SpanId;
 import gov.nasa.jpl.aerie.merlin.driver.timeline.LiveCells;
 import gov.nasa.jpl.aerie.merlin.driver.timeline.TemporalEventSource;
 import gov.nasa.jpl.aerie.merlin.protocol.driver.Topic;
@@ -52,10 +52,10 @@ public class ResumableSimulationDriver<Model> implements AutoCloseable {
   private final Topic<ActivityDirectiveId> activityTopic = new Topic<>();
 
   //mapping each activity name to its task id (in String form) in the simulation engine
-  private final Map<ActivityDirectiveId, TaskId> plannedDirectiveToTask;
+  private final Map<ActivityDirectiveId, SpanId> plannedDirectiveToTask;
 
   //subset of plannedDirectiveToTask to check for scheduling dependent tasks
-  private final Map<ActivityDirectiveId, TaskId> toCheckForDependencyScheduling;
+  private final Map<ActivityDirectiveId, SpanId> toCheckForDependencyScheduling;
 
   //simulation results so far
   private SimulationResults lastSimResults;
@@ -317,7 +317,7 @@ private void simulateSchedule(final Map<ActivityDirectiveId, ActivityDirective>
       if (!plannedDirectiveToTask.isEmpty() && plannedDirectiveToTask
           .values()
           .stream()
-          .allMatch(engine::isTaskComplete)) {
+          .allMatch($ -> engine.getSpan($).isComplete())) {
         allTaskFinished = true;
       }
 
@@ -340,7 +340,7 @@ private void simulateSchedule(final Map<ActivityDirectiveId, ActivityDirective>
   public Optional<Duration> getActivityDuration(ActivityDirectiveId activityDirectiveId){
     //potential cause of non presence: (1) activity is outside plan bounds (2) activity has not been simulated yet
     if(!plannedDirectiveToTask.containsKey(activityDirectiveId)) return Optional.empty();
-    return engine.getTaskDuration(plannedDirectiveToTask.get(activityDirectiveId));
+    return engine.getSpan(plannedDirectiveToTask.get(activityDirectiveId)).duration();
   }
 
   private Set<ActivityDirectiveId> getSuccessorsToSchedule(final SimulationEngine engine) {
@@ -348,7 +348,7 @@ private Set<ActivityDirectiveId> getSuccessorsToSchedule(final SimulationEngine
     final var iterator = toCheckForDependencyScheduling.entrySet().iterator();
     while(iterator.hasNext()){
       final var taskToCheck = iterator.next();
-      if(engine.isTaskComplete(taskToCheck.getValue())){
+      if(engine.getSpan(taskToCheck.getValue()).isComplete()){
         toSchedule.add(taskToCheck.getKey());
         iterator.remove();
       }
@@ -395,6 +395,7 @@ private static <Output> TaskFactory<Output> makeTaskFactory(
       final TaskFactory<Output> task,
       final Topic<ActivityDirectiveId> activityTopic) {
     return executor -> scheduler -> {
+      scheduler.pushSpan();
       scheduler.emit(directiveId, activityTopic);
       return task.create(executor).step(scheduler);
     };
diff --git a/scheduler-driver/src/test/java/gov/nasa/jpl/aerie/scheduler/simulation/AnchorSchedulerTest.java b/scheduler-driver/src/test/java/gov/nasa/jpl/aerie/scheduler/simulation/AnchorSchedulerTest.java
index 24f668ef9f..c419caedd3 100644
--- a/scheduler-driver/src/test/java/gov/nasa/jpl/aerie/scheduler/simulation/AnchorSchedulerTest.java
+++ b/scheduler-driver/src/test/java/gov/nasa/jpl/aerie/scheduler/simulation/AnchorSchedulerTest.java
@@ -666,6 +666,7 @@ public OutputType<Object> getOutputType() {
     @Override
     public TaskFactory<Object> getTaskFactory(final Object o, final Object o2) {
       return executor -> $ -> {
+        $.pushSpan();
         $.emit(this, delayedActivityDirectiveInputTopic);
         return TaskStatus.delayed(oneMinute, $$ -> {
           $$.emit(Unit.UNIT, delayedActivityDirectiveOutputTopic);
@@ -691,6 +692,7 @@ public OutputType<Object> getOutputType() {
     @Override
     public TaskFactory<Object> getTaskFactory(final Object o, final Object o2) {
       return executor -> scheduler -> {
+        scheduler.pushSpan();
         scheduler.emit(this, decomposingActivityDirectiveInputTopic);
         return TaskStatus.delayed(
             Duration.ZERO,
diff --git a/settings.gradle b/settings.gradle
index 95d0c6ce7e..e8d8c7311b 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -11,7 +11,10 @@ include 'contrib'
 // Service support
 include 'parsing-utilities'
 include 'permissions'
-include 'timeline'
+
+// Procedural post-simulation libraries
+include 'procedural:timeline'
+include 'procedural:constraints'
 
 // Services for deployment within the Aerie infrastructure
 include 'merlin-server'
diff --git a/timeline/README.md b/timeline/README.md
deleted file mode 100644
index 128439d7d1..0000000000
--- a/timeline/README.md
+++ /dev/null
@@ -1,13 +0,0 @@
-# Timelines
-
-This library provides tools for querying and manipulating "timelines" from an Aerie plan or set of
-simulation results. This includes things like resource profiles, activity instances, and activity directives,
-but can be extended to support more kinds if needed.
-
-See [MODULE_DOCS.md](./MODULE_DOCS.md) for a description of the architecture and design of the library.
-
-- Building and testing: `./gradlew :timeline:build`
-- Generating a jar for local experimentation: `./gradlew :timeline:shadowJar`
-  - jar will be available at `timeline/build/libs/timeline-all.jar`
-- Generating documentation: `./gradlew :timeline:dokkaHtml`
-  - docs will be available at `timeline/build/dokka/html/index.html`