docs/re: boot time refuted as the gate on (A); the flag correlates with no mechanism

An interleaved A/B (arms alternating in one series, so cache warming cannot pose
as either variable) breaks the confound the last entry flagged — and not in the
direction the first table suggested. The LATEST title of every run recorded,
268 s, accepted (A); a 232 s title refused. "The title arrived late" is dead.

That leaves --log_ui_draws correlating at 0 of 7 against 4 of 5, with no
mechanism available: the cvar is read only when F10 arms a capture, F10 was never
pressed in those runs, the per-draw hook is one relaxed atomic load, and the two
arms' startup config dumps are byte-identical across 246 settings. A correlation
with no mechanism — and an arm that failed once — is not a finding; it is a
variable to remove. Removed: F10 now arms the capture unconditionally.

Also recorded: three boots this session ended on a permanent black screen, two of
them with no input at all. Not the pad, not the cache-flush crash, about one boot
in five.

Five candidate explanations for the (A) gate are now eliminated or refuted. The
next step is the guest's own state machine in sylpheed.db, not another guess from
outside.

docs/re/BACKLOG.md

@@ -171,10 +171,14 @@ available in the container.
 **And a second screen is NO LONGER BLOCKED, but it is not routine either.** The
 main menu has been reached (screenshot in
 [`canary-scripted-input-traps.md`](canary-scripted-input-traps.md)), so the
-"Ⓐ is dead" reading is withdrawn. **Not routine after all** — see the 2026-08-19 table in
-[`canary-scripted-input-traps.md`](canary-scripted-input-traps.md): 3 of 3
-successes without `--log_ui_draws` and 0 of 5 with it, perfectly confounded with
-how long the boot took (every success ≤147 s, every failure ≥177 s). Until that
+"Ⓐ is dead" reading is withdrawn. **Not routine after all** — see the 2026-08-19 tables in
+[`canary-scripted-input-traps.md`](canary-scripted-input-traps.md): 4 of 5
+successes without `--log_ui_draws`, 0 of 7 with it. An interleaved series
+**refuted the boot-time confound** (the latest title of all, 268 s, accepted Ⓐ;
+a 232 s title refused), and no mechanism exists for the flag — it is read only
+when F10 arms a capture, and F10 was never pressed. The variable has been removed
+rather than believed: F10 now arms the capture unconditionally, so navigation
+runs need no flag. Until that
 is separated, capturing a screen *and* navigating to it in the same run is not
 dependable. The earlier claim, kept: the title that ends the boot sequence
 accepts a single Ⓐ (2 of 2 at the time); the title the attract loop returns to