docs(wiki): correct the architecture the diagrams describe, and add the no-blocking-DB page
The wiki described two things that are not the system.
First, the three Kafka topics between order-management and execution. Those
legs became direct in-process calls through ShardedOrderDispatcher when the two
services merged, and execution-service was deleted as a module - no directory,
no entry in the parent pom, port 8087 unused. Seven pages still drew those
topics as live flow and two still gave execution a port and a deployment
command. The service count was still eight; it is seven.
Second, and worse: Architecture-and-Order-Flow and Exchange-Core-Integration
showed the API gateway calling venue.submit(order).join() in-process, straight
into the exchange-core ring. That topology was never built. The gateway proxies
to order-management-service over HTTP, and the matching engine is reached from
the writer thread inside that service. Commit 5fd980c removed the unverified
throughput figures attached to this flow but left the flow itself, so the pages
read as though they had been checked. Both now carry an explicit note saying
what was wrong rather than quietly showing something different, because a
reader who saw the old diagram deserves to know it was replaced and why.
Adds No-Blocking-DB-Hot-Path, which states the rule the order path holds -
nothing on the single writer thread blocks on PostgreSQL - with the five
mechanisms behind it, the measurements, and the three constraints accepted in
exchange: one instance may accept orders, a lost durable write is silent, and
the write-ahead log recovers process death but not machine loss. The
constraints get equal space to the mechanisms on purpose.
Every class, metric and script named was checked against the source. Figures
come from CONFIGURATION.md; the crash behaviour is cited as the scripts that
assert it rather than as a number, since no run of it is recorded.