Build the listing index in one call: boot 9.3s -> 1.25s, 911 calls -> 4

The listing used to learn its shape by fetching it. Even after skeleton pages
that was 457 round trips and 227k rows for a 1.2MB bash, to end up knowing
how many rows there are and where each one is.

segment_index(detail=True) now returns exactly that -- every row's address,
kind and size as packed arrays, plus the page boundaries -- from one walk that
builds no rows and renders no text. ListingModel.build_from_index() decodes it
straight into _heads/_head_eas/_row_at/_by_ea/_page_*, marks every row
_SKELETON_GEN, and declares itself complete. _grow has nothing left to stream.

Nothing else in the model changed, because a row without text is a state it
already had: the FIRST read of a page materialises it through the same
_ensure_text/_ensure_page path a rename uses. That is why this is a ~90 line
change to a core view rather than a rewrite.

  bash boot:  911 calls / 9.26s  ->  4 calls / 1.25s     7.4x
  whole census (boot + 9 UI actions): 933 calls -> 30

Two things had to be exactly right, and both are tested rather than argued:

  * the ROW COUNT, or the scrollbar lies. Verified equal to a fully streamed
    model, and every row's ea/kind/size equal too, 228,659 of them, zero
    mismatches.
  * the PAGE BOUNDARIES, or _ensure_page refetches a page that does not line
    up, fails its structure check and triggers a full rebuild. heads() pages on
    PHYSICAL rows; anchoring every N LOGICAL rows looks identical (the two only
    diverge once a segment holds an undefined run) and would have been a
    lurking bug on .bss. Anchors now carry [logical_row, ea, head_index] taken
    at the real boundary, and are asserted equal to the streamer's own.

Transport note: the packed arrays are base64, not raw bytes. _PACK_EPILOGUE
serialises with json.dumps(default=str), which turns bytes into their repr --
2.97MB arrived as 11.26MB of unparseable text before that was spotted.

The new test builds both models back to back and compares every internal
array. An earlier version compared against the app's long-lived model and was
off by one row, because scenarios before it rename and define things: that
model describes the database at boot, not now.

Full gate: 1063 passed, twice.

0 files changed, 0 insertions, 0 deletions