@@ -51,16 +51,16 @@ jobs:
       fail-fast: true
       matrix:
         include:
-          # stdio:  the subprocess transport (whole suite — the primary lane).
-          # launch: the whole suite over the AF_UNIX launcher transport.
+          # launch: the primary lane, over the reusable AF_UNIX launcher transport.
+          # stdio:  the subprocess compatibility lane (whole suite).
           # shm:    launch + the POSIX shared-memory side channel. Rides the
           #         launcher, not raw subprocess: stdio already covers the
           #         fork-per-connection path and spends most of its wall-clock
           #         doing it, so re-paying that cost to test shm is waste.
           # http:   the whole suite over the stateless HTTP transport.
+          - { lane: launch }
           - { lane: stdio }
           - { lane: shm, shm_bytes: '67108864' }
-          - { lane: launch }
           - { lane: http }
     name: integration (${{ matrix.lane }})
     steps:
 
@@ -45,10 +45,11 @@ suite against the Python worker (see the project `CLAUDE.md`).
 
 ## Transport lanes
 
-`run-integration.sh` honours `TRANSPORT=stdio|shm|launch|http` (the workflow
-runs them as a matrix):
+`run-integration.sh` honours `TRANSPORT=stdio|shm|launch|http` and defaults to
+`launch` when the variable is omitted (the workflow runs every lane explicitly
+as a matrix):
 
-- **`stdio`** — the subprocess transport (the primary lane); the whole suite.
+- **`stdio`** — the subprocess compatibility lane; the whole suite.
   Also boots the versioned and versioned-tables workers as background HTTP
   servers (`VGI_VERSIONED_HTTP_WORKER` / `VGI_VERSIONED_TABLES_HTTP_WORKER`) so
   the `attach/versioned_tables_*_http` and `versioning_http` tests run.
@@ -62,7 +63,7 @@ runs them as a matrix):
   via the `__transport_options__` handshake and carried in POSIX shm rather than
   in the pipe or socket — and engages identically over the launcher (verified:
   the same 18 `[shm]` transfers under `VGI_RPC_SHM_DEBUG=1` on both).
-- **`launch`** — the AF_UNIX launcher transport; the whole suite, with *every*
+- **`launch`** — the default and primary AF_UNIX launcher transport; the whole suite, with *every*
   `VGI_*_WORKER` fronted by `launch:` so traffic flows through the C++ launcher
   (`ResolveLauncherSocketPath` → AF_UNIX → `UnixSocketWorker`). Mirrors the vgi
   Makefile's `test_launcher`: the point is that the launcher path produces
 
@@ -8,8 +8,9 @@
 # Ported from vgi-go's harness. The Python differences:
 #   * The "worker binaries" are console scripts installed into the project venv
 #     by `uv sync --all-extras` (the vgi-fixtures workspace member); the C++
-#     client spawns them as subprocesses. We use their absolute .venv/bin paths
-#     so each spawn skips `uv run`'s resolve overhead.
+#     client launches them from their absolute .venv/bin paths. The default
+#     launcher transport keeps one warm process instead of paying Python startup
+#     for every DuckDB connection.
 #   * Every per-catalog worker is the same Python program with a different
 #     entrypoint; the base `WorkerClass.main()` understands stdin/stdout,
 #     `--http`, and the launcher's `--unix`, so one binary covers every lane.
@@ -27,7 +28,7 @@
 #   HAYBARN_UNITTEST  path to the haybarn-unittest binary
 # Optional:
 #   BIN_DIR           dir holding the fixture console scripts (default: $REPO/.venv/bin)
-#   TRANSPORT         stdio | shm | launch | http   (default: stdio)
+#   TRANSPORT         stdio | shm | launch | http   (default: launch)
 #   VGI_RPC_SHM_SIZE_BYTES  shm side-channel segment size (the shm lane)
 #   STAGE             scratch dir for the preprocessed test tree (default: mktemp)
 set -euo pipefail
@@ -39,7 +40,7 @@ HERE="$(cd "$(dirname "$0")" && pwd)"
 REPO="$(cd "$HERE/.." && pwd)"
 BIN_DIR="${BIN_DIR:-$REPO/.venv/bin}"
 STAGE="${STAGE:-$(mktemp -d)}"
-TRANSPORT="${TRANSPORT:-stdio}"
+TRANSPORT="${TRANSPORT:-launch}"
 INTEGRATION="$VGI_SRC/test/sql/integration"
 [ -d "$INTEGRATION" ] || { echo "::error::no test/sql/integration under VGI_SRC=$VGI_SRC"; exit 1; }
 
@@ -232,7 +233,7 @@ export VGI_SIMPLE_WRITABLE_WORKER="${LAUNCH_PREFIX}${SIMPLE_WRITABLE}"
 
 case "$TRANSPORT" in
   stdio)
-    # Subprocess transport (the primary lane) — the only lane that spawns a
+    # Subprocess transport — the only lane that spawns a
     # fresh worker process per DuckDB connection, and so the only one that can
     # host the crash / pool-recovery tests below.
     export VGI_TEST_WORKER="$WORKER"
 
@@ -19,12 +19,16 @@
 #   --integration-only   skip pytest
 #   --quiet              don't print summaries to stdout
 #   --show               print cached summaries WITHOUT re-running
+#
+# Environment:
+#   VGI_INTEGRATION_TRANSPORT  launch (default) | stdio
 set -uo pipefail
 
 # Repo locations (override for non-default checkouts).
 REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
 VGI_PYTHON_DIR="${VGI_PYTHON_DIR:-$REPO_ROOT}"
 VGI_CPP_DIR="${VGI_CPP_DIR:-$HOME/Development/vgi}"
+VGI_INTEGRATION_TRANSPORT="${VGI_INTEGRATION_TRANSPORT:-launch}"
 
 CACHE=/tmp/vgi-test-cache
 mkdir -p "$CACHE"
@@ -46,7 +50,7 @@ for arg in "$@"; do
     --integration-only) run_pytest=0 ;;
     --quiet) quiet=1 ;;
     --show) show_only=1 ;;
-    -h|--help) sed -n '2,22p' "$0"; exit 0 ;;
+    -h|--help) sed -n '2,26p' "$0"; exit 0 ;;
     *) echo "unknown flag: $arg" >&2; exit 2 ;;
   esac
 done
@@ -186,11 +190,25 @@ run_pytest_job() {
 
 run_integration_job() {
   cd "$VGI_CPP_DIR" || exit 99
-  # `~[.]` excludes Catch2-hidden tests, i.e. `*.test_slow` files. These
-  # tend to assert best-effort behavior (e.g. `on_cancel` firing) that
-  # gets flaky under -j 8 contention; run them manually when needed.
-  VGI_TEST_WORKER="uv run --project $VGI_PYTHON_DIR vgi-fixture-worker" \
-    timeout 600 ./build/release/test/unittest -j 8 "test/sql/integration/*" "~[.]" >"$INT_LOG" 2>&1
+  local worker="uv run --project $VGI_PYTHON_DIR vgi-fixture-worker"
+  case "$VGI_INTEGRATION_TRANSPORT" in
+    launch)
+      worker="launch:$worker"
+      export VGI_REQUIRE_LAUNCHER_TRANSPORT=1
+      ;;
+    stdio)
+      unset VGI_REQUIRE_LAUNCHER_TRANSPORT
+      ;;
+    *)
+      echo "unsupported VGI_INTEGRATION_TRANSPORT=$VGI_INTEGRATION_TRANSPORT (expected launch or stdio)" >&2
+      return 2
+      ;;
+  esac
+  # `~[.]` excludes Catch2-hidden tests, i.e. `*.test_slow` files. The
+  # launcher keeps one Python worker warm while unittest advances serially,
+  # avoiding both repeated startup and cross-test state contention.
+  VGI_TEST_WORKER="$worker" \
+    timeout 600 ./build/release/test/unittest "test/sql/integration/*" "~[.]" >"$INT_LOG" 2>&1
   local rc=$?
   summarize_integration "$INT_LOG" "$INT_SUMMARY" "$INT_FAILURES"
   echo "exit=$rc" >>"$INT_SUMMARY"
@@ -206,10 +224,15 @@ if [[ "$run_integration" == 1 ]]; then
   pids+=($!)
 fi
 
+exit_code=0
 for pid in "${pids[@]}"; do
-  wait "$pid"
+  if ! wait "$pid"; then
+    exit_code=1
+  fi
 done
 
 if [[ "$quiet" == 0 ]]; then
   print_summary
 fi
+
+exit "$exit_code"