Figured out trace syntax and passing context bounds to lambdas.

modules/api-definition/src/main/scala/gs/test/v0/definition/TestGroup.scala

@@ -1,12 +1,10 @@
 package gs.test.v0.definition
 
 import cats.data.EitherT
-import cats.data.Kleisli
 import cats.effect.Async
 import cats.syntax.all.*
 import gs.test.v0.definition.pos.SourcePosition
 import java.util.concurrent.ConcurrentHashMap
-import natchez.Span
 import scala.collection.mutable.ListBuffer
 import scala.jdk.CollectionConverters.*
 
@@ -266,15 +264,16 @@ object TestGroup:
       *   The function this test will execute.
       */
     def pure(unitOfWork: => Either[TestFailure, Unit]): Unit =
-      effectful(Kleisli(_ => Async[F].pure(unitOfWork)))
+      effectful(Async[F].pure(unitOfWork))
 
     /** Finalize and register this test with an effectful unit of work.
       *
       * @param unitOfWork
       *   The function this test will execute.
       */
-    def effectful(unitOfWork: => Kleisli[F, Span[F], Either[TestFailure, Any]])
-      : Unit =
+    def effectful(
+      unitOfWork: natchez.Trace[F] ?=> F[Either[TestFailure, Any]]
+    ): Unit =
       registry.register(
         new TestDefinition[F](
           name = name,
@@ -288,16 +287,14 @@ object TestGroup:
         )
       )
 
-    /** Helper type for representing `span => EitherT[F, TestFailure, Any]`
-      */
-    type ET[A] = EitherT[F, TestFailure, A]
-
     /** Finalize and register this test with an effectful unit of work.
       *
       * @param unitOfWork
       *   The function this test will execute.
       */
-    def apply(unitOfWork: => Kleisli[ET, Span[F], Any]): Unit =
+    def apply(
+      unitOfWork: natchez.Trace[F] ?=> EitherT[F, TestFailure, Any]
+    ): Unit =
       registry.register(
         new TestDefinition[F](
           name = name,
@@ -306,7 +303,7 @@ object TestGroup:
           tags = tags.distinct.toList,
           markers = markers.distinct.toList,
           iterations = iterations,
-          unitOfWork = UnitOfWork[F].apply(unitOfWork.mapF(_.value)),
+          unitOfWork = UnitOfWork.applyT(unitOfWork),
           sourcePosition = pos
         )
       )
@@ -406,7 +403,20 @@ object TestGroup:
       *   The function this test will execute.
       */
     def pure(unitOfWork: Input => Either[TestFailure, Unit]): Unit =
-      effectful(input => Kleisli(_ => Async[F].pure(unitOfWork(input))))
+      registry.register(
+        new TestDefinition[F](
+          name = name,
+          permanentId = permanentId,
+          documentation = documentation,
+          tags = tags.distinct.toList,
+          markers = markers.distinct.toList,
+          iterations = iterations,
+          unitOfWork = UnitOfWork.apply(
+            inputFunction.map(input => unitOfWork(input))
+          ),
+          sourcePosition = pos
+        )
+      )
 
     /** Finalize and register this test with an effectful unit of work.
       *
@@ -414,7 +424,7 @@ object TestGroup:
       *   The function this test will execute.
       */
     def effectful(
-      unitOfWork: Input => Kleisli[F, Span[F], Either[TestFailure, Any]]
+      unitOfWork: natchez.Trace[F] ?=> Input => F[Either[TestFailure, Any]]
     ): Unit =
       registry.register(
         new TestDefinition[F](
@@ -425,24 +435,20 @@ object TestGroup:
           markers = markers.distinct.toList,
           iterations = iterations,
           unitOfWork = UnitOfWork.apply(
-            Kleisli(span =>
-              inputFunction.flatMap(input => unitOfWork(input).run(span))
-            )
+            inputFunction.flatMap(input => unitOfWork(input))
           ),
           sourcePosition = pos
         )
       )
 
-    /** Helper type for representing `span => EitherT[F, TestFailure, Any]`
-      */
-    type ET[A] = EitherT[F, TestFailure, A]
-
     /** Finalize and register this test with an effectful unit of work.
       *
       * @param unitOfWork
       *   The function this test will execute.
       */
-    def apply(unitOfWork: => Input => Kleisli[ET, Span[F], Any]): Unit =
+    def apply(
+      unitOfWork: natchez.Trace[F] ?=> Input => EitherT[F, TestFailure, Any]
+    ): Unit =
       registry.register(
         new TestDefinition[F](
           name = name,
@@ -451,12 +457,8 @@ object TestGroup:
           tags = tags.distinct.toList,
           markers = markers.distinct.toList,
           iterations = iterations,
-          unitOfWork = UnitOfWork[F].apply(
-            Kleisli(span =>
-              inputFunction.flatMap { input =>
-                unitOfWork(input).mapF(_.value).run(span)
-              }
-            )
+          unitOfWork = UnitOfWork.applyT(
+            EitherT.liftF(inputFunction).flatMap(unitOfWork)
           ),
           sourcePosition = pos
         )

modules/api-definition/src/main/scala/gs/test/v0/definition/UnitOfWork.scala

@@ -1,9 +1,17 @@
 package gs.test.v0.definition
 
-import cats.data.Kleisli
-import natchez.Span
+import cats.~>
+import cats.Applicative
+import cats.data.EitherT
+import cats.effect.kernel.Async
+import cats.effect.kernel.Ref
+import cats.effect.kernel.Resource
+import cats.effect.syntax.all.*
+import cats.syntax.all.*
+import java.net.URI
+import natchez.*
 
-trait UnitOfWork[F[_]]:
+sealed trait UnitOfWork[F[_]]:
 
   def work(
     span: Span[F]
@@ -11,6 +19,10 @@ trait UnitOfWork[F[_]]:
 
 object UnitOfWork:
 
+  type Traced[F[_]] = natchez.Trace[F] ?=> F[Either[TestFailure, Any]]
+
+  type TracedT[F[_]] = natchez.Trace[F] ?=> EitherT[F, TestFailure, Any]
+
   /** Instantiate a new [[UnitOfWork]] with the given function that requires a
     * `Span[F]` as input.
     *
@@ -19,13 +31,96 @@ object UnitOfWork:
     * @return
     *   The new [[UnitOfWork]] instance.
     */
-  def apply[F[_]](
-    uow: Kleisli[F, Span[F], Either[TestFailure, Any]]
-  ): UnitOfWork[F] = new UnitOfWork[F] {
+  def apply[F[_]: Async](
+    unitOfWork: Traced[F]
+  ): UnitOfWork[F] =
+    new UnitOfWork[F] {
 
       override def work(span: Span[F]): F[Either[TestFailure, Any]] =
-      uow.apply(span)
+        makeInternalTrace[F](span).flatMap { trace =>
+          given Trace[F] = trace
+          unitOfWork
+        }
 
     }
 
+  def applyT[F[_]: Async](
+    unitOfWork: TracedT[F]
+  ): UnitOfWork[F] =
+    new UnitOfWork[F] {
+
+      override def work(span: Span[F]): F[Either[TestFailure, Any]] =
+        makeInternalTrace[F](span).flatMap { trace =>
+          given Trace[F] = trace
+          unitOfWork.value
+        }
+
+    }
+
+  private def makeInternalTrace[F[_]: Async](sourceSpan: Span[F])
+    : F[natchez.Trace[F]] =
+    Ref.of[F, Span[F]](sourceSpan).map(src => new InternalTrace[F](src))
+
+  // Copied from the Natchez ioTrace
+  private class InternalTrace[F[_]: Async](
+    val src: Ref[F, Span[F]]
+  ) extends natchez.Trace[F]:
+
+    def put(fields: (String, TraceValue)*): F[Unit] =
+      src.get.flatMap(_.put(fields*))
+
+    def log(fields: (String, TraceValue)*): F[Unit] =
+      src.get.flatMap(_.log(fields*))
+
+    def log(event: String): F[Unit] =
+      src.get.flatMap(_.log(event))
+
+    def attachError(
+      err: Throwable,
+      fields: (String, TraceValue)*
+    ): F[Unit] =
+      src.get.flatMap(_.attachError(err, fields*))
+
+    def kernel: F[Kernel] = src.get.flatMap(_.kernel)
+
+    def spanR(
+      name: String,
+      options: Span.Options = Span.Options.Defaults
+    ): Resource[F, F ~> F] =
+      for {
+        parent <- Resource.eval(src.get)
+        child  <- parent.span(name, options)
+      } yield new (F ~> F) {
+        def apply[A](fa: F[A]): F[A] =
+          src.get.flatMap { old =>
+            src
+              .set(child)
+              .bracket(_ => fa.onError { case e => child.attachError(e) })(_ =>
+                src.set(old)
+              )
+          }
+
+      }
+
+    def span[A](
+      name: String,
+      options: Span.Options = Span.Options.Defaults
+    )(
+      k: F[A]
+    ): F[A] =
+      spanR(name, options).use(_(k))
+
+    def traceId: F[Option[String]] =
+      src.get.flatMap(_.traceId)
+
+    override def spanId(
+      implicit
+      F: Applicative[F]
+    ): F[Option[String]] =
+      src.get.flatMap(_.spanId)
+
+    override def traceUri: F[Option[URI]] = src.get.flatMap(_.traceUri)
+
+  end InternalTrace
+
 end UnitOfWork

modules/api-definition/src/test/scala/gs/test/v0/definition/GroupImplementationTests.scala

@@ -6,7 +6,6 @@ import cats.effect.IO
 import gs.test.v0.definition.{Tag => GsTag}
 import munit.*
 import natchez.Span
-import natchez.Trace
 
 class GroupImplementationTests extends FunSuite:
   import GroupImplementationTests.*
@@ -90,15 +89,16 @@ object GroupImplementationTests:
     val T1: PermanentId = pid"t1"
     val T2: PermanentId = pid"t2"
     val T3: PermanentId = pid"t3"
+    val T4: PermanentId = pid"t4"
 
   end Ids
 
-  class G1[F[_]: Async: Trace] extends TestGroup[F]:
+  class G1[F[_]: Async] extends TestGroup[F]:
     override def name: String = "G1"
     test(Ids.T1, "simple").pure(Right(()))
   end G1
 
-  class G2[F[_]: Async: Trace] extends TestGroup[F]:
+  class G2[F[_]: Async] extends TestGroup[F]:
 
     override def name: String =
       "G2"
@@ -120,7 +120,7 @@ object GroupImplementationTests:
     test(Ids.T2, "inherit from group").pure(Right(()))
   end G2
 
-  class G3[F[_]: Async: Trace] extends TestGroup[F]:
+  class G3[F[_]: Async] extends TestGroup[F]:
     override def name: String = "G3"
 
     test(Ids.T3, "configure test")
@@ -132,4 +132,12 @@ object GroupImplementationTests:
 
   end G3
 
+  class G4[F[_]: Async] extends TestGroup[F]:
+    override def name: String = "G4"
+
+    // TODO: Make test entrypoint and test Trace[F]
+    test(Ids.T4, "Effectful test").effectful {
+      ???
+    }
+
 end GroupImplementationTests

modules/api-definition/src/test/scala/gs/test/v0/definition/pos/SourcePositionTests.scala

@@ -1,6 +1,5 @@
 package gs.test.v0.definition.pos
 
-import cats.data.Kleisli
 import cats.effect.IO
 import cats.effect.kernel.Resource
 import gs.test.v0.IOSuite
@@ -10,8 +9,6 @@ import natchez.EntryPoint
 import natchez.Kernel
 import natchez.Span
 import natchez.Span.Options
-import natchez.Trace
-import natchez.Trace.Implicits.noop
 
 /** These tests are sensitive to changes, even in formatting! They are looking
   * for specific line numbers in this source code, so any sort of newline that
@@ -45,15 +42,15 @@ class SourcePositionTests extends IOSuite:
   }
 
   test("should provide the source position of a failed check") {
-    lookForSourcePosition(new G1, 73)
+    lookForSourcePosition(new G1, 81)
   }
 
   test("should provide the source position of an explicit failure") {
-    lookForSourcePosition(new G2, 82)
+    lookForSourcePosition(new G2, 90)
   }
 
   private def lookForSourcePosition(
-    groupDef: TestGroup[TracedIO],
+    groupDef: TestGroup[IO],
     line: Int
   ): Unit =
     val group = groupDef.compile()
@@ -61,7 +58,7 @@ class SourcePositionTests extends IOSuite:
       case t1 :: Nil =>
         ep.root("unit-test")
           .use { span =>
-            t1.unitOfWork.run(span).map {
+            t1.unitOfWork.work(span).map {
               case Left(TestFailure.AssertionFailed(_, _, _, pos)) =>
                 assertEquals(pos.file.endsWith(SourceFileName), true)
                 assertEquals(pos.line, line)
@@ -77,9 +74,7 @@ class SourcePositionTests extends IOSuite:
 
 object SourcePositionTests:
 
-  type TracedIO[A] = Kleisli[IO, Span[IO], A]
-
-  class G1 extends TestGroup[TracedIO]:
+  class G1 extends TestGroup[IO]:
     override def name: String = "G1"
 
     test(pid"t1", "pos").pure {
@@ -88,7 +83,7 @@ object SourcePositionTests:
 
   end G1
 
-  class G2 extends TestGroup[TracedIO]:
+  class G2 extends TestGroup[IO]:
     override def name: String = "G2"
 
     test(pid"t2", "pos").pure {