Use PCSX2 RAM to recover the chunk loader's transformation

This is what RAM was needed for: nothing about the loader's transformation is
recoverable from the disc.

Anchor: a 32-byte probe from inside a chunk record in level 0's core_data, searched
in the level-0 savestate. It hits at 0x18538a8 and the record's first bytes at
0x185387e -- exactly chunk_base + record_offset, no rescaling. So the chunk payload
is copied VERBATIM; unlike collision and the shrub packet tables it is not expanded
or repacked.

Result 1: the offset table is rewritten to absolute EE addresses.
  disc: f000057c f00006b0 f00007e4 f0000914
  RAM:  0xf185387c 0xf18539b0 0xf1853ae4 0xf1853c14
The 0xf0000000|low24 tag becomes 0xf1850000|low24 -- tag replaced by the chunk's
load base, low 24 bits untouched. Consecutive deltas agree exactly (0x134, 0x134,
0x130), which is why the disc-side stride is approximate rather than constant.

Result 2: every record gains a constant 2-byte prefix 02 00, and the rewritten
table points at THAT rather than at the record data. Walking all 90 records from
the RAM dump: prefix 02 00 on 90 of 90; the disc's index bytes preserved unchanged
at +2/+3 on 90 of 90.

Result 3, the useful one: the byte at +2 takes exactly 0, 16, 32, ... 240 -- the
16 values index_rule predicts for step = 16, phase = 0. The mixed-radix record index
derived from the disc is corroborated on the running game's own copy of the chunk.
That is a disc-derived claim validated against the game, which is the strongest form
of check available here.

On disc a chunk is [16-byte header][10 zero bytes][tagged offset table][records].
In RAM it is [16-byte header][10 zero bytes][absolute-pointer table][records each
prefixed with 02 00]. The 02 00 is unexplained -- possibly a record type or an
alignment the loader needs -- but it is constant, so like the two index bytes it
carries no per-record information.

docs/plan/pcsx2-verification.md

@@ -726,3 +726,55 @@ coincidence inside a short run.
 **The collision lead in this file is disproved, not merely unproven.** Recorded
 here so it is not picked up again. Level 1's grid is 384 cells and nothing found
 so far counts to it.
+
+## The chunk container: what the loader does to it
+
+This is what RAM was needed for. Nothing about the loader's transformation is
+recoverable from the disc.
+
+**Anchor.** A 32-byte probe from inside a chunk record in level 0's `core_data`
+was searched in the level-0 savestate. It hits at `0x18538a8`, and the record's
+first bytes hit at `0x185387e` -- exactly `chunk_base + record_offset`, with no
+rescaling. So the chunk payload is copied **verbatim**; it is not expanded or
+repacked the way the collision payload and the shrub packet tables are.
+
+**Result 1 -- the offset table is rewritten to absolute EE addresses.**
+Disc, at chunk `0x100b302`:
+
+    offsets[0..3] = f000057c f00006b0 f00007e4 f0000914
+
+RAM, in a table at `0x185331c`:
+
+    0xf185387c  0xf18539b0  0xf1853ae4  0xf1853c14
+
+The tagged form `0xf0000000 | low24` becomes `0xf1850000 | low24`: the tag is
+replaced by the chunk's load base and the low 24 bits are untouched. The
+consecutive deltas agree exactly (`0x134, 0x134, 0x130`, which is why the
+disc-side `stride` is approximate rather than constant).
+
+**Result 2 -- every record gains a constant 2-byte prefix, and the table points
+at the prefix.** RAM at each record:
+
+    0x185387c  02 00 00 00 38 d3 4c 38 ...
+    0x18539b0  02 00 10 00 2f bb 4c 38 ...
+    0x1853ae4  02 00 20 00 20 8f 4c 38 ...
+    0x1853c14  02 00 30 00 14 6f 4c 38 ...
+
+Walked all **90** records of the chunk from the RAM dump:
+
+    2-byte prefix                          : 02 00 on 90 of 90
+    disc index bytes preserved at +2/+3    : 90 of 90
+    byte at +2, distinct values            : 0, 16, 32, ... 240 (16 values)
+
+**Result 3 -- the disc-side index finding is confirmed against live data.** The
+bytes at `+2` take exactly the 16 values `ResolvedChunk::index_rule` predicts for
+`step = 16, phase = 0`, stepping 0x00, 0x10, 0x20, ... That is the mixed-radix
+record index, measured on 2,430 records from the disc and now corroborated on the
+running game's own copy of one chunk.
+
+**What this means for the format.** On disc, a chunk is
+`[16-byte header][10 zero bytes][tagged offset table][records]`. In RAM it is
+`[16-byte header][10 zero bytes][absolute-pointer table][records each prefixed
+with 02 00]`. The `02 00` is unexplained -- it may be a record type or an
+alignment the loader needs -- but it is constant, so it carries no per-record
+information either.