session: both transports for every integration test, and the mid-step pause written into step-v1

Review found two Memory-only tests behind a README claim that every integration test runs
twice. Both are now generated by both_transports!: the one-agent composition, and the
old-epoch refusal, which is one of the three tests the old-worker-replies row cites. The
README says which single test walks both transports inside itself instead, because it
compares their traces against each other.

step-v1 section 2 gains the mid-step pause line and a dated amendment saying why it is not
a new edge: a pause requested during a transition is the ordinary
Committing(k) -> Ready(k+1) edge followed by Ready(k+1) -> Paused(k+1), because section 6
requires the transition to finish first, so the only boundary such a pause can land on is
the one the transition just committed.

docs/design/session-framework/step-v1.md

@@ -30,6 +30,7 @@ Starting → Ready(k) → Preparing(k) → Applying(k) → Observing(k+1)
 
 Ready(k) → Paused(k) → Ready(k)
 Ready(k) / Paused(k) → Capturing(k) → same boundary
+pause requested mid-step → Committing(k) → Ready(k+1) → Paused(k+1)
 any unresolved partial failure → Failed → Restoring(new epoch) → Paused(k)
 terminal episode → Paused(k) → Resetting(new epoch) → Ready(0)
 ```
@@ -38,6 +39,12 @@ terminal episode → Paused(k) → Resetting(new epoch) → Ready(0)
 transition carry `scope.step=k`; result fields identify `nextStep=k+1` where applicable.
 Do not send Agent.Commit with step `k+1` merely because the observation is newer.
 
+**Amendment, 2026-09-22.** The mid-step pause line above adds no new edge: a pause requested
+during a transition is served by the ordinary `Committing(k) → Ready(k+1)` edge followed by
+`Ready(k+1) → Paused(k+1)`. It is written into the machine because section 6 requires the
+transition to finish first, so the only boundary such a pause can land on is the one the
+transition just committed.
+
 ## 3. Transaction sequence
 
 ### Phase A: prepare all agents concurrently

services/flysim/crates/fly-session/README.md

@@ -114,7 +114,9 @@ harness.shutdown().await;
   libraries, so their types live here rather than in the payload contract. An intent is a
   `PortControl` without its port, and only the coordinator adds the port.
 - **The phase machine.** `step-v1` section 2 is this crate's, not the contract crate's; the
-  trace's phase path is recorded beside the contract's `TransitionTrace`.
+  trace's phase path is recorded beside the contract's `TransitionTrace`. The mid-step pause
+  it takes -- the transition finishes, then the session pauses at the boundary it just
+  committed -- is now written into the section 2 machine as a dated amendment.
 
 ## Limitations
 
@@ -136,8 +138,10 @@ cargo test -p fly-session                                    # unit + both integ
 cargo run -p fly-session --example session                   # the runnable synthetic session
 ```
 
-Every integration test runs twice, once over the in-memory transport and once over a Unix
-socket, through the same router code:
+Every integration test runs over both transports, through the same router code: all but one
+are generated twice by `both_transports!`, and
+`sequential_concurrent_and_reversed_orders_agree` walks both transports inside one test
+because it compares their behaviour traces against each other.
 
 - `tests/session.rs`: one world advance per complete batch; every agent Prepared before the
   advance; one task evaluation per transition; every agent committed before the next Prepare or

services/flysim/crates/fly-session/tests/failures.rs

@@ -12,7 +12,7 @@ use common::{Fixture, at, fly_a, fly_b, within};
 use fly_session::agent::AgentFaults;
 use fly_session::coordinator::Injections;
 use fly_session::environment::EnvironmentFaults;
-use fly_session::harness::{HarnessConfig, SessionHarness, Via};
+use fly_session::harness::{HarnessConfig, Via};
 use fly_session::phase::Phase;
 use fly_session::types::*;
 
@@ -27,6 +27,7 @@ both_transports!(
     a_reply_from_another_incarnation_is_rejected,
     a_world_that_advanced_without_sensory_data_fails_the_transition,
     an_exact_duplicate_of_a_running_operation_is_in_progress,
+    an_old_epoch_operation_is_refused_with_stale_epoch,
 );
 
 const STEPS: u64 = 4;
@@ -338,13 +339,10 @@ async fn an_exact_duplicate_of_a_running_operation_is_in_progress(via: Via) {
     f.shutdown().await;
 }
 
-/// A restarted worker under a new epoch refuses an operation from the old one.
-#[tokio::test(flavor = "multi_thread", worker_threads = 4)]
-async fn an_old_epoch_operation_is_refused_with_stale_epoch() {
-    let dir = tempfile::tempdir().unwrap();
-    let mut harness = SessionHarness::start(Via::Memory, dir.path(), HarnessConfig::default())
-        .await
-        .unwrap();
+/// A live worker under this epoch refuses an operation naming another one.
+async fn an_old_epoch_operation_is_refused_with_stale_epoch(via: Via) {
+    let mut f = clean_fixture(via).await;
+    let harness = &mut f.harness;
     within("bootstrap", harness.coordinator.bootstrap()).await.unwrap();
     within("step", harness.coordinator.step()).await.unwrap();
 
@@ -371,6 +369,5 @@ async fn an_old_epoch_operation_is_refused_with_stale_epoch() {
     .expect_err("an old epoch cannot mutate this worker");
     assert_eq!(err.code, ErrorCode::StaleEpoch);
     assert_eq!(harness.coordinator.stats().advances, 1);
-    harness.shutdown().await;
-    drop(dir);
+    f.shutdown().await;
 }

services/flysim/crates/fly-session/tests/session.rs

@@ -26,6 +26,7 @@ both_transports!(
     a_terminal_episode_pauses_at_its_own_boundary,
     status_answers_with_the_committed_boundary,
     a_worker_refuses_a_second_initialize,
+    a_single_agent_composition_runs_the_same_transaction,
 );
 
 const STEPS: u64 = 3;
@@ -376,8 +377,7 @@ async fn sequential_concurrent_and_reversed_orders_agree() {
 
 /// A one-agent composition still runs the same transaction, so the barrier is not two-agent
 /// specific.
-#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
-async fn a_single_agent_composition_runs_the_same_transaction() {
+async fn a_single_agent_composition_runs_the_same_transaction(via: Via) {
     let config = HarnessConfig {
         agents: vec![AgentSpec {
             agent_id: id("fly-a"),
@@ -387,7 +387,7 @@ async fn a_single_agent_composition_runs_the_same_transaction() {
         }],
         ..HarnessConfig::default()
     };
-    let mut f: Fixture = fixture(Via::Memory, config).await;
+    let mut f: Fixture = fixture(via, config).await;
     within("bootstrap", f.harness.coordinator.bootstrap()).await.unwrap();
     within("run", f.harness.coordinator.run(3)).await.unwrap();
     assert_eq!(f.harness.coordinator.stats().advances, 3);