Bridge warden-ui's debug channel out of the qemu VM

The rig could drive the UI and detect one outcome: the process died. Nothing
could ask the UI what page it was on or what a tap would land on, because
that channel is a FIFO inside the guest and the initramfs is busybox-only
with no sshd. Scenarios therefore asserted nothing and screenshots went
unread.

run.sh --ctl exposes a second pci-serial port as a unix socket, the same
device the RS485 bridge already rides, listed first so it is always ttyS0.
It also puts warden.ctl on the kernel command line, and init bridges only
when that marker is present: a VM launched with --rs485 alone has a ttyS0
too, and that one is the Modbus wire. The bridge relays one command line in
and the FIFO's reply out, then a sentinel so the reader needs no timeout.

qmp.py gains the channel verbs (nav, page, stats, hit, assert_page,
assert_hit), records every step to results.jsonl as ok/fail/fatal, continues
past an assertion mismatch so one run reports every broken expectation, and
checks the console after EVERY step for the stage-2 init's EXITED line so a
crash is pinned to the step that caused it. assert_hit matches the widget's
bounding box: an icon has no usable caption and two list rows share a class,
but the geometry the UI itself resolved is exact.

The vocabulary is what tools/warden-ctl already speaks over SSH to a real
panel, so a script that runs here runs there. Verified end to end on the rig
(11/11 verbs round-tripped) and against the bench panel, where the same
commands returned byte-identical results.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013aHKWzT5EF86RFKRMtAv9n

qemu/tests/ui-drive.sh

@@ -64,6 +64,7 @@ for _attempt in 1 2 3; do
   PORT=$((21000 + RANDOM % 20000))
   : > "$WORK/console.log"
   bash "$QDIR/run.sh" --kernel "$ZIMAGE" --display headless --qmp "$WORK/qmp.sock" \
+    --ctl "$WORK/ctl.sock" \
     --ssh-port "$PORT" --http-port $((PORT + 1)) --api-port $((PORT + 2)) \
     > "$WORK/console.log" 2>&1 &
   QEMU_PID=$!
@@ -118,15 +119,43 @@ done
   exit 1
 }
 
-echo "== driving $SCRIPT"
-python3 "$HERE/qmp.py" "$WORK/qmp.sock" drive "$SCRIPT" "$OUTDIR"
+# The control bridge (init -> warden-ui's debug FIFO, see run.sh --ctl) comes
+# up with the UI; a script's first `page`/`hit` must not race it. Bounded, and
+# fail-closed: a scenario that asserts on UI state needs the channel, and a
+# silently absent one would turn every assertion into an infrastructure error
+# dressed as a test result.
+echo "== waiting for the control bridge"
+deadline=$((SECONDS + 60))
+until grep -aq 'init: control bridge on' "$WORK/console.log"; do
+  [ $SECONDS -lt $deadline ] || {
+    echo "FATAL: the control bridge never announced itself (run.sh --ctl / init marker)" >&2
+    tail -25 "$WORK/console.log" >&2
+    exit 1
+  }
+  sleep 1
+done
 
-# The UI must still be alive: see the header. Checked AFTER the script so a
-# crash caused by the interaction is caught, which is the usual case.
+echo "== driving $SCRIPT"
+# Every step lands in results.jsonl (ok / fail / fatal); an assertion mismatch
+# is a `fail` and the run continues, so one run reports every broken
+# expectation. The driver's exit status is the verdict; capture it rather than
+# let `set -e` skip the backstop and the summary below.
+drive_rc=0
+python3 "$HERE/qmp.py" "$WORK/qmp.sock" drive "$SCRIPT" "$OUTDIR" \
+  --ctl "$WORK/ctl.sock" --console "$WORK/console.log" || drive_rc=$?
+
+# The UI must still be alive: see the header. The driver checks this after
+# every step and pins a crash to the step that caused it; this is the
+# backstop for a death after the last step, or a driver that itself fell over.
 if grep -aq 'warden-ui EXITED' "$WORK/console.log"; then
   echo "FATAL: warden-ui DIED during the run:" >&2
   grep -a -A22 'warden-ui EXITED' "$WORK/console.log" >&2
   exit 1
 fi
+if [ "$drive_rc" -ne 0 ]; then
+  echo "UI-DRIVE-FAIL: see $OUTDIR/results.jsonl" >&2
+  grep -E '"status": "(fail|fatal)"' "$OUTDIR/results.jsonl" >&2 || true
+  exit 1
+fi
 
-echo "UI-DRIVE-PASS (screenshots in $OUTDIR)"
+echo "UI-DRIVE-PASS (results in $OUTDIR/results.jsonl, screenshots in $OUTDIR)"