phase 6: performance review playbook in TESTING.md + UDP-vs-TCP rationale in stream_server

Two pieces of documentation, neither changes behavior:

1. TESTING.md gains a "Performance review playbook" section: per-
   session capture commands for firmware serial + /state poll +
   Scrypted console, an annotated walkthrough of what each log
   shape means, an investigation-threshold table mapping
   user-facing symptoms to likely causes and the first thing to
   check, and a one-line tools list. Replaces the implicit "ask the
   maintainer how to debug" loop with a reproducible workflow.

2. stream_server.c gains a "Why TCP and not UDP" header comment
   documenting the analysis from the design phase. JPEGs are ~123
   IP datagrams at 1500 MTU; on hardwired Gigabit LAN switch-fabric
   loss is < 1e-9/packet → per-frame corruption ≈ 1.2e-7. UDP's
   theoretical wins (no Nagle, latest-wins semantics) don't apply
   because TCP_NODELAY is on, socket.write p50 < 1ms, and the
   FIONREAD trick already implements latest-wins on the receive
   side. UDP's costs (200-400 LOC of app-layer fragmentation, loss
   of nc/curl debug, FIONREAD trick stops working under
   fragmentation) are real. Documented as reference so a future
   contributor doesn't re-derive the analysis from scratch.

0 files changed, 0 insertions, 0 deletions