v0.4.0 — the buildings start telling the truth

The buildings start telling the truth, and the elephant comes back.

Fixed — the geometry

The prose in this city had been through two rounds of expert review. The
geometry had been through none. A geometry-truth audit — four PostgreSQL
specialists auditing buildings, adjacencies, animations and scale as claims
rather than reading the text beside them — found the city contradicting its own
documentation in places where a reader would believe the building.

• The xmin horizon blade floated above every active backend. It was computed
  independently of the PGPROC pillars it cuts through, so fourteen backends
  could all sit below the "oldest transaction ID anyone can still see" plane —
  arithmetically impossible, and an inversion of the single lesson that
  structure exists to teach.
• The OS page cache was drawn inside the excavation, below a line the city's
  own signage says separates memory from durable storage. It is volatile kernel
  memory outside PostgreSQL's address space. pg_wal broke the same line in the
  other direction — printed on the pit floor as a data-directory subdirectory
  while built as a surface vault outside the cut.
• archive_command was built twice, with archived WAL parked in two stores
  in series, teaching a two-stage archive pipeline PostgreSQL does not have.
• TOAST sliced before it compressed. PostgreSQL compresses first and slices
  only what still does not fit.
• Index maintenance flew from the index into the heap, and the
  buffer-mapping probe ran backwards.
• The LSN ruler displayed an equation its own rows failed to satisfy — the
  lag bar spanned standby-flush→replay while the byte count beside it was
  computed from primary-flush→replay.
• Cumulative statistics was a rolling sixty-bar time series. PostgreSQL
  keeps monotonic counters and no history whatsoever.

Fixed — the plate

• The Slonik plate is the real mark again. v0.3.0 built the outline from the
  blue fill path of the genuine PostgreSQL SVG. The commit that followed it —
  titled "trace the plate from the real PostgreSQL logo artwork" — replaced that
  vector data with hand-authored control points, which is the opposite of what
  its message claims. Four later passes then edited the hand drawing, each
  widening it slightly to satisfy the containment audit, until the trunk was 3%
  of the plate's height and the silhouette was a rounded blob. The vector data
  is restored: front-on head, both ears, both tusks, trunk down the centreline.

Added

• Sound. The audio engine had existed for some time as 505 lines that
  nothing imported. It is now driven from the walk controller, so footstep
  cadence comes from distance travelled and surfaces are read from what the
  collision layer says is underfoot. Off by default.
• Swimming in the buffer pool (shared_buffers). The plaza is 1,024 page
  frames whose height is their clock-sweep usage_count and whose colour is
  their state. You can now be inside it, at the scale of the pages.
• Walking and swimming on a phone. Pointer lock does not exist on iOS
  Safari, so first person was unreachable on mobile. There are now thumb
  controls: a stick that appears where the thumb lands, and look-by-drag with
  sensitivity in degrees per centimetre so it feels the same on any screen.
• tools/plot-plate.mjs — prints the plate's silhouette, bounding box and
  trunk proportion straight from the source in about two seconds. Five attempts
  at the shape had been judged through a seventy-second software render with the
  side panels covering two thirds of the frame, which is why none of them could
  iterate.
• The page-anatomy and data-directory views now open from where their question
  arises, rather than from a tab strip pinned to a corner.

Changed

• The panel design drops the coloured accent bars, and then the corner brackets
  that briefly replaced them. Both are generated-interface clichés; the fix was
  to subtract rather than to substitute.

Known issues

• Cache hit ratio settles near 87% where a healthy production system sits at
  98–99%.
• The plate's containment audit still constrains the silhouette; the shape holds
  the city, and the city was not laid out to be an elephant.
• iOS Safari differs from Chrome's mobile emulation in touch handling and
  viewport units. The touch controls have not been tested on a real device.