re: measure the boot-nav title gate — and withdraw my own diagnosis

Last iteration I said launch_mission died because skip_intro only tests for
the title on a static frame, gated at rmse <= 1500, and that run logged 1503
and 1549 just above the cut. I also said the fix was NOT to nudge 1500 but
to measure both signals through a boot first. Measured, and the diagnosis
does not survive.

boot_trace.sh logs the two signals skip_intro decides on -- frame-to-frame
RMSE and the is_title.py green-glyph count -- through a clean boot with no
presses at all. One run, 29 samples over 484 s:

  8 samples had rmse <= 1500, so the gate OPENED eight times
  0 samples had glyph > 0, so the title was never seen

At t=145 s the RMSE was 1205, comfortably inside the threshold, and the
glyph test was called and answered zero. A frame can be perfectly static
without being the title -- the intro movie has long quiet stretches, three
reading RMSE exactly 0. So 1503/1549 were almost certainly movie frames too,
and raising the constant would have admitted two more of them.

What is left is narrower and honest: the interactive title never appeared,
rather than appearing and being missed by a threshold.

The limitation is recorded rather than buried: the tracer intended 1 s
sampling and achieved 16.9 s, because each iteration forks two screenshots,
ImageMagick compare and a fresh Python. So this does NOT prove the title
never appeared -- only that it was absent from 29 samples. A window shorter
than ~17 s falls between them. The recorded next step is to make the tracer
sample at the rate it claims before concluding anything stronger.

Artifact: docs/re/captures/boot-signal-trace.tsv.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PMRJjbxLqZtsb5Vb7KunPE

tools/re-capture/boot_trace.sh

@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+# Log the two signals `skip_intro.sh` decides on, every second, through a whole
+# boot -- WITHOUT pressing anything.
+#
+# Why: skip_intro only runs the title test when the frame is static, gated at
+# `rmse <= 1500`. A 381 s run measured 1503 and 1549 -- just above the cut -- so
+# the title test was never called and the one allowed press was never spent.
+# The fix is NOT to nudge 1500; a threshold moved to make one run pass is fitted
+# to a single sample. This produces the distribution the gate should be chosen
+# from: for every second, the frame-to-frame RMSE and the green-glyph count,
+# which are independent measurements of "is this a static frame" and "is this
+# the interactive title".
+#
+# Output is TSV on stdout: seconds, rmse, glyph_px.
+set -u
+export HOME=/sylph-home/re
+DISP="${DISPLAY:-:98}"
+SD="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+alive(){ ps -o pid=,stat= -C xenia_canary 2>/dev/null | awk '$2 !~ /^Z/ {print $1}'; }
+
+until xdotool search --name "Xenia-canary" >/dev/null 2>&1; do
+  [ -n "$(alive)" ] || { echo "# EMULATOR GONE before the window appeared" >&2; exit 4; }
+  sleep 1
+done
+printf 'secs\trmse\tglyph\n'
+deadline=$(( SECONDS + ${1:-600} ))
+while [ $SECONDS -lt $deadline ]; do
+  rm -f /tmp/bt1.png /tmp/bt2.png
+  screenshot /tmp/bt1.png >/dev/null 2>&1; sleep 0.6
+  screenshot /tmp/bt2.png >/dev/null 2>&1
+  # Same liveness guard as skip_intro: two STALE files compare to a constant
+  # non-zero RMSE, which reads exactly like a playing movie.
+  if [ ! -s /tmp/bt1.png ] || [ ! -s /tmp/bt2.png ]; then
+    echo "# SCREENSHOT FAILED at ${SECONDS}s" >&2; exit 5
+  fi
+  [ -n "$(alive)" ] || { echo "# EMULATOR GONE at ${SECONDS}s" >&2; exit 4; }
+  d=$(compare -metric RMSE /tmp/bt1.png /tmp/bt2.png null: 2>&1 | sed 's/ .*//' | cut -d. -f1)
+  g=$(python3 "$SD/is_title.py" /tmp/bt2.png 400 2>/dev/null | sed 's/[^0-9]*\([0-9]*\).*/\1/')
+  printf '%s\t%s\t%s\n' "$SECONDS" "${d:-0}" "${g:-0}"
+  sleep 1
+done