Headless dumps and captures

What it does

Tui::shot draws the app at any size after a list of keys, dump::text and dump::ansi print it, Tui::bench times every screen, and capture::capture and capture::compare record every cell of every screen before a big change and report each cell that moved after it.

Time comes from the run, never the wall clock: drawing reads the loop's moment, and Tui::advance moves the run's clock, so the same app gives the same frames. The app wires them to its own flags, as the demo does with --dump, --keys, --bench, --capture and --compare.

• A dump at any size

  One key, a 72x14 dump, printed as text.

  $ cargo run --release --example demo -- --dump 72x14 --keys "tab"
   ──────────────────────────────── demo ──────────────── workspace one ─
                      1 Home  2 What to do next  3 Log
                                  5 steps
   ─ What to do next ────────────────────────────────────────────────────
      Step                        How
    ▌ Replace this screen         Home and Next are two Screen types; s…
      Set your accent             Tui::new takes one colour, or Palette…
      Add your first command      a key in Screen::key, its work in Cx:…
      Load real data              Screen::load returns the read; Screen…
      Wire the headless flags     --dump, --keys, --at, --bench, --capt…
  
   ──────────────────────────────────────────────────────────────────────
   ↑↓ move · enter open · / filter · ctrl+k go to · ctrl+c twice quit

• Frames before and after

  capture::capture walks every screen, and the app's key scripts for deeper states, at a list of sizes, and saves every cell, its symbol, colours and modifiers. capture::compare walks the same again and reports each cell that differs, by screen, size and position. Capture, change, compare, and delete the captures.

• A bench in the box

  Tui::bench draws each screen 1,000 times into an in-memory terminal, the whole shell each time, moving the clock a frame at a time. It is how the frame times on the Speed page were taken.

• No commands spawned

  Headless runs never spawn a command, and a stop there marks a queued one stopped, so a dump never starts real work.