Drop SASI on capacity, then find the budget never had the disk in it

USER DECISION: drop the `sasi` profile. Not on bandwidth -- on capacity. A SASI
volume is 40 MB, and the 22.8 min of unique scene footage on the source Blu-ray
(streams 00000-00201, measured, not recalled) is 146 MiB at the LOWEST rate this
codec makes -- more than the machine's whole 4-unit SASI space. `scsi` is the
only profile now. FINDINGS 32.

Then the user asked whether we were drawing the wrong conclusions about PIO vs
DMA, and we were, more broadly than the question implied. Every CPU figure in
FINDINGS 24-34 is scored against the full 833,333 cycles/frame with nothing
subtracted for moving the bitstream off disk. Debiting the HD63450 cycle-steal
at the long-standing 8 clk/word ESTIMATE, "1 frame of 120 misses" becomes 84 of
120, median 112.4%. PIO at the span rate is 99.8% of the machine. Spans buy
cycles by spending bandwidth and the bandwidth returns as steal, so 31.6's "fits
completely" becomes a worst frame of 114.3%. 10 fps absorbs it: median 93.7%,
1/120. FINDINGS 35. `11_cpu_budget.py` takes --io dma|pio|none, defaults to dma,
and warns if asked for none.

Also landed:
- item 1 done: the cost model checked against the 68000 on a cost-aware
  container, -3.07% to +0.01%, whole-window mean -1.22%. FINDINGS 34.
- item 4 done: the container carries its own 4-byte record alignment (DLX2).
  94/120 record starts were on odd addresses -- an address error, not a slow
  read -- now 0/120 for 16 B/s. Re-encoding reproduces 31.1 exactly. FINDINGS 33.
- a `scsi` window does not fit the 2 MB machine the rig emulates (2.84 MB of
  stream past a 0x200000 ceiling). The gate now verifies 80 of 120 frames and
  SAYS so, and fails loudly when the pass does not complete, instead of
  reporting a phantom 49,005-pixel diff. FINDINGS 36.

Three near-misses this session had one shape: an unobservable run nearly
produced a false finding. stdbuf -oL on any MAME job that prints progress -- a
file is block-buffered too, and a run that is merely finishing looks exactly
like one that is wedged.

check.sh ALL GREEN.

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

tools/analysis/08_mode_map.py

@@ -16,7 +16,7 @@ the mode headers would exploit.
   RAW   16 literal palette indices -- the escape that makes lam=0 pixel-exact
 
 Usage: python3 tools/analysis/08_mode_map.py <frames_dir> <out.webm>
-           [--profile sasi|scsi] [--scale N] [--lossless] [--fixed-lam]
+           [--profile scsi] [--scale N] [--lossless] [--fixed-lam]
 
 --fixed-lam renders the pre-session-6 encoder (no rate control) instead.
 Output format follows the extension. Prefer .webm: GIF re-quantises to 256
@@ -45,7 +45,7 @@ def main():
     if "--scale" in sys.argv:
         SCALE = int(sys.argv[sys.argv.index("--scale")+1])
     prof = RC.PROFILES[sys.argv[sys.argv.index("--profile")+1]
-                       if "--profile" in sys.argv else "sasi"]
+                       if "--profile" in sys.argv else "scsi"]
     m   = H.build(src, k1=prof["k1"], k4=prof["k4"])
     # Rate-controlled by default, so the map shows the mode decisions that
     # actually ship. --fixed-lam renders the pre-session-6 encoder instead;