v0.9.0 — a 2D query lifecycle, WAL that responds, and a tour that stops burying the city

The city reached the top of Hacker News. This is what the thread asked for.

Added

• A 2D query lifecycle view, at observability/. The city answers what
  PostgreSQL is made of and the 3D trace answers what happens when you run
  something — but a camera can only point at one place at a time. This shows the
  whole journey at once, from client to commit, with your position marked and
  the stops a statement skips struck through rather than hidden. The plan tree is
  finally drawn as a tree: BackendSim.plan has carried per-node rows, cost and
  timing since the beginning with nothing rendering it. SVG rather than canvas,
  so a keyboard and a screen reader can follow it.
• Measurement. The largest traffic event in this project's history was
  invisible. Cookieless, no consent banner, no fingerprinting, no personal data —
  aggregate counts plus outbound clicks tagged by the panel they came from.

Fixed

• WAL responds to the workload again. Watching the city at one transaction
  per second showed the wal_buffers ring racing. Two defects: the buffer filled
  under load and never drained once demand stopped, and ten times the transaction
  rate produced only 1.4 times the WAL. That second one broke the causal chain
  the city exists to teach, since write volume is what drives checkpoint
  frequency. Three rounds of expert review missed both, because both are visible
  only when something changes.
• The tour stops burying the city. Three people said so independently.
  Measuring showed the narration card was not the problem — a scrim draining
  contrast from the whole scene was, along with spotlight cones rendering as flat
  diagonal slabs at the quality tier most visitors get. Attention is directed
  additively now: the target is marked and everything else is left alone.

Changed

• The dependency rule said "no telemetry, no analytics". It was written against
  surveillance rather than measurement, so it now states what is actually true
  instead of a blanket denial the software no longer honours.