State the current app model in the checkpoint and README

The checkpoint's table still said the document and scalar apps were not
one authorable model, and that equivalent-server latency was unproven.
A new section records what has been checked since: one app model (aup to
module format v5), persistence, Vega's surfaces and hot swap, apps as
HTTP services, and the measurements against axum and drogon, with what
remains. The README opens with the same in brief.

1 files changed, 9 insertions, 0 deletions

diff --git a/README.md b/README.md
index 25a02e7..f880a97 100644
--- a/README.md
+++ b/README.md
@@ -1,5 +1,14 @@
 # Pure
 
+**Current app model (2026-09-26).** Apps are written in [aup](/srv/git/aup.git) and run as Pure modules
+([format v5](docs/design/008-module-format.md)), verified completely before they execute: declared states persist
+in Pure's tree store, every event is a transaction, views are pure functions of state. The same spec becomes a
+terminal UI, a CLI, spoken sentences and a web page through [Vega](/srv/git/vega.git), and an HTTP service through
+`pure-serve` (views are GETs, inputs are POSTs with JSON bodies; answers are durable). Measurements against axum and
+drogon on a Raspberry Pi 5 are in [075](docs/research/075-http-host-against-axum.md) and
+[077](docs/research/077-apps-as-http-services.md); the status table is [CHECKPOINT.md](CHECKPOINT.md). The text below
+records the earlier document runtime this grew from.
+
 A standalone native micro runtime being designed as a small operating
 system. Pure owns the application model for execution, memory, protection,
 resource lifetimes, storage, and communication. Efficient connections between