Terminal Fabricate

Terminal Fabricate

One idea drives everything: termctrl already renders terminals to images and video - you only author its two input formats, and never run the real program. The rendering, theming, and encoding are bought (the terminal-control skill / termctrl binary owns them). This skill owns only the authoring of a session that never actually happened.

Boundary: to drive or record a real program, use the terminal-control skill. This one begins where that ends - when the session is invented, not captured.

Two paths, pick by output

Still from ANSI

Write the screen as ANSI bytes, then render - no session:

termctrl save --input frame.ansi --cols 80 --rows 24 --format svg --format png --out out
termctrl show --input frame.ansi --cols 80 --rows 24   # visible-text preview

--input - reads ANSI from stdin. --cols/--rows set the geometry for ANSI input (default 80x24); size them to the content or the screen clips.

Motion via a .termctrl timeline

Don't hand-encode the format. Author a small steps file and build it with the bundled script (EXECUTE):

scripts/build-termctrl.py --in steps.json --out run.termctrl
termctrl video run.termctrl --out run.mp4          # basic export, no edit plan
termctrl show --recording run.termctrl             # final-frame preview

steps.json (ESC is written \\e - double backslash, because JSON rejects a bare \e; \\x1b and \\033 also work, as does the standard JSON escape \u001b):

{ "cols": 80, "rows": 24, "steps": [
  { "at_ms": 0,    "text": "\\e[1;32m$\\e[0m claude \"summarise my day\"\n" },
  { "at_ms": 600,  "text": "\\e[2m* Thinking...\\e[0m\n" },
  { "at_ms": 1200, "text": "You have 3 meetings today.\n" }
] }

For anything beyond a couple of lines, generate steps.json from a short python3 heredoc rather than hand-writing escapes - it sidesteps the backslash-and-quote footguns entirely.

For a polished clip with captions/markers/speed, hand off to the terminal-control skill's record/mark/video --edit flow - the timeline format is identical, so a fabricated run.termctrl drops straight in.

Load-bearing gotchas

• Line breaks must be CRLF (\r\n), not \n. termctrl feeds a real VT parser, so a lone \n line-feeds without a carriage return and text staircases down the screen. build-termctrl.py converts \n to \r\n for you; when writing .ansi by hand, use \r\n explicitly.
• .termctrl bytes are integer arrays, not strings ({"type":"output","at_ms":600,"bytes":[27,91,...]}). That is the only reason the script exists - never encode them by eye.
• Always render and look before trusting it. Save a txt (or view the png) and read it back; a wrong escape or geometry is invisible in the source but obvious in the render.

Faking coding-agent chrome

For a convincing Claude Code / Codex TUI (boxes, spinner, * thinking, tool calls, diffs), read references/agent-chrome.md - the highest-fidelity route is to capture the real agent once and edit its ANSI, with hand-authored building blocks as the fallback.

Requires

termctrl (the terminal-control skill's binary; here it is nix-managed via packages/terminal-control.nix). If command -v termctrl fails, rebuild (drs on macOS, hms on Linux) rather than cargo install.

Motion export (termctrl video) additionally needs ffmpeg - install via nix, not brew, if command -v ffmpeg fails. Stills (PNG/SVG/text) need only termctrl.