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

docs/re/BACKLOG.md

@@ -1033,25 +1033,31 @@ premise was wrong.**
   Candidates: the **7 `.embsec_` sections** (VAs 0x84D0000–0x86AC000, ~129 KB
   total, executable) or a hashed record in `hidden/MiscBin.pak`. **Finding it
   gives the actual per-phase clear condition for every stage.**
-* 🚧 **(2026-08-25) BLOCKED — the live test of the `reset_phase_threads` rename
-  never got to run, because boot-nav cannot reach the title.** The experiment is
-  ready and worth doing: built-in 100 clears the trigger container and frees
-  every thread but the caller, so at a phase terminator **both**
-  `[phase+272+20]` (triggers queued) and `[phase+216+8]` (coroutines alive)
-  should collapse; if they climb straight through a phase boundary instead, the
-  reading is wrong. `tools/re-capture/phase_watch.py` now prints both counters —
-  **written this session but never yet exercised against a live guest.**
-  **The blocker, measured:** `skip_intro.sh` only tests for the title when the
-  frame is static, gated at `rmse <= 1500`. A 381 s run produced 18 "waiting it
-  out" samples, and two of them — **1503 at 104 s and 1549 at 139 s** — sat just
-  above the cut, so `is_title.py` was never even called and the single allowed
-  press was never spent. The attract loop then restarts and the wait never ends.
-  ▶️ **First step, and it is NOT "raise the constant":** log `rmse` *and* the
-  `is_title.py` glyph count every second through a boot, so the true-title and
-  attract-demo distributions can be seen; only then decide the gate. Tuning 1500
-  to make one run pass would be fitting to a single sample. Note the surrounding
-  comments are emphatic that tapping through the movies is what breaks the
-  title, so the press budget really is one.
+* ❌ **(2026-08-25) My own boot-nav diagnosis, MEASURED AND WITHDRAWN.** I said
+  the run died because `skip_intro.sh` gates the title test at `rmse <= 1500`
+  and the run logged 1503/1549, just above the cut. Measured over a clean
+  no-press boot ([`boot-nav-title-gate.md`](boot-nav-title-gate.md),
+  `captures/boot-signal-trace.tsv`): the gate **opened eight times** in 29
+  samples, and at `t=145 s` the RMSE was **1205** — inside the threshold — with
+  `is_title.py` answering **0 glyph pixels**. The glyph count was 0 in *all* 29
+  samples over 484 s. A static frame is not the title; the intro movie has long
+  quiet stretches, three of them reading RMSE exactly 0. So the gate is not what
+  stopped it, and raising the constant would have admitted two more movie frames.
+  🟡 Narrowed: **the interactive title never appeared**, rather than appearing and
+  being missed. ❔ **But the run does not prove that** — the tracer intended 1 s
+  sampling and achieved **16.9 s** (two screenshots + ImageMagick `compare` + a
+  fresh Python per iteration), so a title window under ~17 s falls between
+  samples. ▶️ First step: make the tracer sample at the rate it claims — one
+  long-lived Python process computing both signals — then re-run. Second: check
+  whether the fast 2026-08-25 run had a warm shader cache that this one, started
+  after `rm -f /dev/shm/xenia_*`, did not.
+* 🚧 **(2026-08-25) STILL UNRUN — the live test of the `reset_phase_threads`
+  rename.** Built-in 100 clears the trigger container and frees every thread but
+  the caller, so at a phase terminator **both** `[phase+272+20]` (triggers
+  queued) and `[phase+216+8]` (coroutines alive) should collapse; if they climb
+  straight through a phase boundary instead, the reading is wrong.
+  `tools/re-capture/phase_watch.py` prints both — **written, still never
+  exercised against a live guest.** Blocked behind the boot-nav item above.
 * 🟡 **(2026-08-25) The legacy IDXD string-pool reader is wrong far more often
   than assumed** — now measurable for the first time, since the record table gives
   a ground truth. Verified by hand: `FCSRange` (the module doc's own canonical

docs/re/boot-nav-title-gate.md

@@ -0,0 +1,85 @@
+# The boot-nav title gate — my own diagnosis, measured and withdrawn
+
+Status: ❌ **the previous diagnosis is WITHDRAWN.** 🟡 the real failure is
+narrowed but not settled. ❔ the measurement has a limitation that matters, and
+it is stated below rather than buried.
+
+## What I claimed last iteration
+
+`launch_mission.sh` failed to reach the mission: 381 s of `skip_intro.sh`
+printing "movie … waiting it out", 18 times, and the ready room never arrived.
+`skip_intro.sh` only tests for the interactive title when the frame is **static**,
+gated at `rmse <= 1500`, and that run logged **1503 at 104 s** and **1549 at
+139 s** — just above the cut. I wrote that the gate had therefore blocked the
+title test and eaten the run.
+
+I also wrote, correctly, that the fix was *not* to nudge 1500, and that the first
+step was to measure both signals through a whole boot. That is what this is.
+
+## The measurement
+
+`tools/re-capture/boot_trace.sh` logs, without pressing anything, the two signals
+`skip_intro.sh` decides on: the frame-to-frame RMSE (two grabs 0.6 s apart) and
+the green-glyph pixel count from `is_title.py` — independent tests for "is this
+static" and "is this the interactive title".
+
+One clean boot, no input at any point:
+[`captures/boot-signal-trace.tsv`](captures/boot-signal-trace.tsv).
+
+```
+29 samples spanning 484 s
+ 8 samples with rmse <= 1500   (the gate OPENED eight times)
+ 0 samples with glyph > 0      (the title was never seen)
+```
+
+The eight low-RMSE samples: `t=12, 29, 62` (rmse 0), `t=99` (1486), `t=115`
+(1350), `t=145` (**1205**), `t=316` (0), `t=484` (0).
+
+## ❌ Why the old diagnosis is wrong
+
+The gate is not what stopped it. It **opened eight times**, and at `t=145` the
+RMSE was **1205** — comfortably inside the threshold — so `is_title.py` was
+called and answered **0 glyph pixels**. A frame can be perfectly static and still
+not be the title; the intro movie has long quiet stretches, and three samples
+read an RMSE of exactly 0.
+
+So `1503`/`1549` in the failing run were almost certainly *also* not the title,
+and raising the threshold to admit them would have admitted two more movie
+frames, not the title. The instinct to leave the constant alone was right; the
+reason I gave for it was wrong.
+
+## 🟡 What the failure actually is
+
+Narrowed, not settled: **the interactive title never appeared at all** in 484 s
+of a no-press boot — not "appeared and was missed by the gate". The glyph count
+was 0 in all 29 samples, including the last one at 484 s where the frame was
+completely static (rmse 0).
+
+A static frame with no glyph at 484 s is consistent with the attract loop having
+returned to a title that, per `menu_draw_capture.sh`, "accepts nothing at all" —
+but this run never pressed anything, so nothing can have broken it. That points
+at the boot itself, not at the navigation.
+
+## ❔ The limitation, stated plainly
+
+**The intended sampling rate was 1 s; the achieved rate was 16.9 s.** Each
+iteration takes two screenshots, runs ImageMagick `compare` and starts a Python
+interpreter, and that costs ~15 s per loop in this container. So 29 samples cover
+484 s with big gaps between them.
+
+That means this run does **not** prove the title never appeared — only that it
+was absent from every one of 29 samples. A title window shorter than ~17 s could
+fall between two samples. Before concluding anything stronger, the tracer needs
+to get cheap enough to sample at the rate it claims: keep one Python process
+alive and compute the RMSE and the glyph count in it, instead of forking
+`compare` and a fresh interpreter every second.
+
+## What this does not settle
+
+* Whether the title ever appears on this boot path at all.
+* Whether the earlier "readyroom at 9 s, IN FLIGHT at 37 s" run (recorded
+  2026-08-25 in `BACKLOG.md`) used a warm shader cache that this run lacked —
+  this one was started after `rm -f /dev/shm/xenia_*`, which the fast run may not
+  have been.
+* The live test this was all for — whether the trigger container and the
+  coroutine list both collapse at a phase terminator — remains unrun.

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

@@ -0,0 +1,30 @@
+secs	rmse	glyph
+12	0	0
+29	0	0
+47	11264	0
+62	0	0
+80	3250	0
+99	1486	0
+115	1350	0
+130	1512	0
+145	1205	0
+159	2714	0
+171	2712	0
+189	34429	0
+201	30721	0
+218	10379	0
+234	12487	0
+252	14940	0
+273	23650	0
+293	12200	0
+308	35782	0
+316	0	0
+332	8713	0
+351	21680	0
+369	7567	0
+386	4642	0
+412	9647	0
+436	6524	0
+458	18867	0
+476	11594	0
+484	0	0

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