docs/re: the mission path measured end to end — the cache crash is the blocker

Driving menu -> NEW GAME -> DIFFICULTY -> SELECT DATA -> slot 01 with plain flags
gets further than any run so far: SELECT DATA is reached with ZERO crashes (the
screen is alive — a log_ui_draws probe there records 140 draws over 8 frames),
and then choosing a slot lets the game proceed into a cinematic or load, where it
crashes at 0x82307128 — the same cache-flush std::map erase.

So the crash is intermittent in WHERE it fires, not whether: boot, SELECT DATA,
and now after slot selection. There is no safe path through the menus to be found
by choosing different options.

And it is the blocker for every mission-side experiment — the second capital-ship
capture included. Navigation is not the obstacle any more; it is scripted and
works.

Not settled and said so: how to get past it. --mem_watch=false does not (twice).
--eh_dispatch is still untested because no run with it on has reached a throw.
The black-screen hang is a separate intermittent failure with no diagnosis. A fix
is emulator guest-race work, not RE.

docs/re/title-crash-stl-tree.md

@@ -222,3 +222,37 @@ Not settled: whether a warm cache prevents *this* firing the way it prevents the
 boot-time one. The cache was warm here (the 6-file `aab216c3` restored earlier),
 so the answer looks like **no** — but that is one run, and the cold/warm A/B was
 only ever run against the boot-time throw.
+
+## Standing blocker: the mission path, measured end to end (2026-08-19)
+
+Driving `menu → NEW GAME → DIFFICULTY → SELECT DATA → pick slot 01` with plain
+flags (`--mem_watch=false`, no EH knobs) gets **further than any run so far** and
+still ends the same way:
+
+| step | outcome |
+|---|---|
+| main menu → NEW GAME | **DIFFICULTY** |
+| DIFFICULTY → Ⓐ | **SELECT DATA**, and this time with **0 crashes** ([capture](captures/select-data-reached-no-crash.png)) — the screen is alive, a `log_ui_draws` probe there records **140 draws over 8 frames** |
+| slot 01 → Ⓐ | the game proceeds — several changing frames, a cinematic or load — and then **crashes at `0x82307128`**, the same cache-flush `std::map` erase |
+
+Two things this settles, and one it does not.
+
+**Settled: the crash is intermittent in *where* it fires, not whether.** It has
+now been seen at boot, at `SELECT DATA`, and after the save slot is chosen. The
+same run reached `SELECT DATA` cleanly and died one screen later. So there is no
+"safe path" through the menus to be found by picking different options — the
+flush throws whenever it next runs.
+
+**Settled: this is the blocker for every mission-side experiment.** The second
+capital-ship capture, in-flight probes, mission-outcome work: all of them are
+behind this, and navigation is no longer the obstacle — that part is scripted and
+works (`tools/re-capture/newgame_path.sh`, `blackscreen_probe.sh`).
+
+**Not settled: how to get past it.** `--mem_watch=false` does not (measured
+twice). `--eh_dispatch` remains untested because no run with it on has reached a
+throw. And the black-screen hang is a *separate* intermittent failure that takes
+some runs out earlier — it is not the crash, and it has no diagnosis yet.
+
+The cheap trigger from the top of this note (an incomplete on-disc cache) still
+stands as the fastest way to reproduce the throw for bisection; what is missing
+is a fix, and that is guest-race work in the emulator, not RE.

tools/re-capture/blackscreen_probe.sh

@@ -0,0 +1,62 @@
+#!/usr/bin/env bash
+# Drive into the black-screen hang and ask what the guest is still doing.
+#
+# Three questions, three cheap probes, all taken WHILE the screen is black:
+#   * is it still presenting frames?  -> F10 arms the UI draw capture, whose
+#     header records the frame numbers it covered and how many draws it saw
+#   * is it still doing file I/O?     -> count ResolvePath lines before/after
+#   * is it still running at all?     -> the emulator's own MEM-WATCH/thread log
+set -u
+export HOME=/sylph-home/re SDL_AUDIODRIVER=dummy DISPLAY=:98
+SD="$(cd "$(dirname "$0")" && pwd)"
+OUT="${1:-/sylph-home/re/blackprobe}"
+mkdir -p "$OUT"; rm -f "$OUT"/xenia_re_ui_draws_*.log
+shot(){ screenshot "$1" >/dev/null 2>&1; }
+screen(){ shot /tmp/bp.png; python3 "$SD/screen_id.py" /tmp/bp.png | awk '{print $1}'; }
+alive(){ ps -o pid=,stat= -C xenia_canary 2>/dev/null | awk '$2 !~ /^Z/ {print $1}'; }
+resolves(){ grep -c "ResolvePath" "$OUT/canary.stdout" 2>/dev/null || echo 0; }
+
+for attempt in $(seq 1 "${ATTEMPTS:-3}"); do
+echo "=== attempt $attempt"
+pkill -9 -x xenia_canary 2>/dev/null; sleep 3
+( cd "$OUT" && nohup run-canary --mem_watch=false \
+    --ui_draw_capture_frames=8 --ui_draw_capture_max=4000 \
+    --logged_profile_slot_0_xuid=B13EBABEBABEBABE >"$OUT/canary.stdout" 2>&1 & )
+sleep 8
+until xdotool search --name "Xenia-canary" >/dev/null 2>&1; do
+  [ -n "$(alive)" ] || { echo "EMULATOR GONE"; exit 4; }; sleep 1
+done
+win="$(xdotool search --name "Xenia-canary" | tail -1)"
+
+s=""; deadline=$(( SECONDS + 420 ))
+while [ $SECONDS -lt $deadline ]; do s="$(screen)"; [ "$s" = "title" ] && break; sleep 2; done
+[ "$s" = "title" ] || { echo "NO TITLE"; continue; }
+python3 "$SD/pad.py" tap A 0.3
+for _ in 1 2 3 4 5 6 7 8; do sleep 3; s="$(screen)"; [ "$s" = "menu" ] && break; done
+[ "$s" = "menu" ] || { echo "(A) refused; rebooting"; continue; }
+echo "menu -> A (NEW GAME) -> A (difficulty)"
+python3 "$SD/pad.py" tap A 0.3; sleep 10
+python3 "$SD/pad.py" tap A 0.3
+
+# wait for black
+for i in $(seq 1 20); do
+  sleep 6; s="$(screen)"
+  mean=$(identify -format "%[fx:mean]" /tmp/bp.png 2>/dev/null)
+  echo "  t+$((i*6))s $s mean=$mean"
+  case "$mean" in 0|0.0*) break ;; esac
+done
+shot "$OUT/black.png"
+echo "--- probing the black screen"
+r1=$(resolves); sleep 20; r2=$(resolves)
+echo "ResolvePath lines: $r1 -> $r2 (delta $((r2-r1)))"
+xdotool windowactivate --sync "$win"; sleep 1
+xdotool key F10; sleep 4; xdotool mousemove 900 400 click 1; sleep 3
+grep -i "UI-CAP" "$OUT/canary.stdout" | tail -3
+head -2 "$OUT"/xenia_re_ui_draws_*.log 2>/dev/null
+echo "log lines now: $(wc -l < "$OUT/canary.stdout")"
+sleep 20
+echo "log lines +20s: $(wc -l < "$OUT/canary.stdout")"
+echo "BLACK PROBE DONE"
+exit 0
+done
+echo "GAVE UP"