Find the sustained action sequence: it breaks both profiles

The open risk since session 2 was "a sustained action sequence could still
break the bitrate", with every clip measured so far being 1.2-1.7 s. Closed by
measurement rather than by sampling clips by hand.

07_motion_survey.py scans a whole stream at 96x72 for the hottest sliding
window of inter-frame difference. On 00223 the spread between the quietest and
hottest sustained 10 s windows is 10.6x, which is the argument for not eyeballing
it. Hottest is t=539.4s, the Singe endgame.

There, with the fixed lam the CLI uses, sasi overshoots 110 -> 129.6 KB/s (+18%)
and scsi 280 -> 373.8 KB/s (+34%). Rate control moves from "insurance, not a
fix" to required, and is promoted above the full-disc survey. The bus is not
broken -- 381.6 KB/s still fits the 488 KB/s figure -- so FINDINGS 21 survives,
at 78% of the pipe instead of a comfortable margin.

Three further corrections fall out:

- The two largest streams on the disc are bonus material. 00216 is the feature
  with a burned-in commentary PiP; 00215 is the commentary. 00223 is the clean
  9.4 min. A size-ranked survey would have encoded live action.
- On hard content the 256-colour scene palette (31.33 dB) binds well before the
  X68000 display (40.81 dB); scsi is already within 0.51 dB of it.
- FINDINGS 24.5's architecture question resolves to "both paths, chosen per
  frame": 30-53% of frames sit above the 70% crossover. Picking per frame costs
  a median 37.0% of the frame budget and caps at 53.6%. Reporting for this is
  wired into encode.py, which previously only printed a mean over all frames --
  the one statistic that cannot answer a per-frame question.

extract.py takes optional start/dur; 08_mode_map.py renders source | decoded |
block-mode map to .webm.

Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6

README.md

@@ -26,8 +26,13 @@ docs/            findings, status, hardware reference
 tools/analysis/  measurement scripts, numbered in the order they were written
                  (01/02 marked BROKEN deliberately, kept as regression refs).
                  Run from the repo root — they import from tools/encoder/.
+                 07 finds the hottest sustained window in a stream; 08 renders
+                 source | decoded | block-mode map as .webm.
 tools/bench/     MAME Lua injection harness + 68000 benchmark sources.
                  `check.sh` re-runs both display regression tests (~40 s).
+                 `blit.s`/`blit.lua` time the full-frame GVRAM blit on the
+                 68000 itself (FINDINGS 24) — not part of check.sh, because
+                 wall timings would make the green-light check host-sensitive.
                  `crtc_mode.lua` is the single source of truth for CRTC R00-R08
                  and R20 — do not write CRTC values anywhere else.
 tools/vasm/      vasm m68k assembler (built from source)
@@ -62,3 +67,8 @@ python3 tools/encoder/profile_gen.py --bw-mbps 4 --name scsi
 > pointing to the correction — heed those, especially 18 (reversed by 21).
 
 Source media (`DRAGONS_LAIR.iso`) and ROMs are gitignored — supply your own.
+
+**Not every large stream is game footage.** `00216` is the feature with a
+burned-in commentary picture-in-picture and `00215` is the commentary itself —
+the two largest files on the disc. The clean 9.4-minute animation is **`00223`**.
+See FINDINGS 25.1 before running any size-ranked survey.