xtask: add record-demo subcommand (v0)

[whme]

Summary

The README's demo/csshw.gif is currently re-recorded by hand each
time it drifts from the product, requiring a developer to manually
configure their workstation (wallpaper, fake SSH hosts, keystroke
overlay, ScreenToGif). This PR turns that artifact into a
reproducible build output.

This is v0 of a four-stage plan: a typed Rust DSL + driver +
local env that produces target/demo/csshw.gif on the developer's
own desktop. Requires ffmpeg and gifski on PATH. v1 (Windows
Sandbox provider, vendored SHA-pinned binaries, Carnac overlay,
visual normalisation) is in a separate stacked PR. v2 (CI workflows

• append-only demo-assets orphan branch) and v3 (Press(Chord)
  primitive + full canonical scene) are out of scope.

The PRs are stacked Gerrit-style: the v1 PR currently contains v0+v1
commits and targets main; once this PR merges, the v1 PR will be
rebased on main so only v1 changes remain.

v0 highlights

• DemoSystem trait + RealSystem behind which all side effects
  (Windows input synthesis, fs, subprocess) sit so unit tests
  exercise the driver via mockall with zero real-system effects.
• Closed Step enum + Script builder validating capture pairing
  and regex compilation at build time, so a typo in the script
  fails cargo check rather than a half-completed recording.
• Driver interprets steps via the trait; the in-flight ffmpeg
  capture is cleaned up even when a step errors mid-script.
• config_override writes target/demo/csshw-config.toml, a
  dispatcher.bat that strips an optional user@ prefix from
  csshw's USERNAME_AT_HOST substitution, and per-host
  enter.bat scripts with curated home directories.
• env/local.rs copies csshw.exe into target/demo/ so
  csshw's startup set_current_dir(exe_dir) lands on our config.
• terminate_csshw kills the daemon child and best-effort kills
  any CREATE_NEW_CONSOLE-detached client csshw.exe instances.

Test plan

• cargo build -p xtask clean (no warnings)
• cargo fmt clean
• cargo lint clean
• cargo test (all green)
• cargo doc-tests clean
• cargo xtask check-typography clean
• Manual: cargo xtask record-demo --env local produces a
  playable target/demo/csshw.gif

The full plan lives at
C:/Users/whme/.claude/plans/tranquil-hopping-karp.md.

[github-actions]

🤖 News Fragment Check

✅ Success! This PR meets the news fragment requirements.

[github-actions]

🤖 Diff Coverage Check

✅ Success!

Diff Coverage

Diff: origin/main...HEAD, staged and unstaged changes

No lines with coverage information in this diff.

[github-actions]

🤖 Coverage Check
Total Coverage: 61.78%

Filename	Stmts	Miss	Cover	Missing
src\protocol\serialization.rs	30	0	100.00%
src\protocol\deserialization.rs	53	0	100.00%
src\utils\windows.rs	120	14	88.33%	293, 516-518, 1004-1005, 1027-1031, 1177-1182
src\utils\config.rs	80	0	100.00%
src\client\mod.rs	223	146	34.53%	169-251, 310, 314, 319-323, 341-506
src\lib.rs	113	19	83.19%	257-265, 325-327, 345-354
src\cli.rs	314	57	81.85%	100-276
src\daemon\workspace.rs	21	0	100.00%
src\daemon\mod.rs	709	583	17.77%	188-190, 216-816, 877-1033, 1064-1065, 1108, 1138, 1182-1183, 1189-1191, 1204-1208, 1240, 1249-1253, 1272-1533
xtask\src\coverage.rs	55	3	94.55%	185, 199, 213
xtask\src\typography.rs	91	1	98.90%	259
xtask\src\changelog.rs	29	0	100.00%
xtask\src\readme.rs	72	1	98.61%	123
xtask\src\release.rs	144	15	89.58%	27, 492-502, 505, 509, 615
xtask\src\inject_agent_token.rs	48	0	100.00%
xtask\src\social_preview.rs	101	3	97.03%	259, 262, 265
TOTAL	2203	842	61.78%

[Copilot]

Pull request overview

Introduces a new cargo xtask record-demo subcommand that records a reproducible “demo as code” GIF via a typed Rust DSL, a mockable driver (DemoSystem), and a v0 local environment implementation.

Changes:

• Add record-demo CLI subcommand wiring in xtask, plus a new xtask::demo module with DSL, driver, script, and environment scaffolding.
• Implement v0 local demo environment: generates a demo-only csshw-config.toml + fake-host filesystem, launches csshw, and orchestrates ffmpeg→gifski recording.
• Add unit tests for DSL validation, driver semantics, config override output, and canonical script structure.

Reviewed changes

Copilot reviewed 16 out of 17 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
xtask/src/main.rs	Adds RecordDemo subcommand and dispatches into demo::record_demo.
xtask/src/demo/mod.rs	Defines DemoSystem abstraction + RealSystem and the record_demo entrypoint.
xtask/src/demo/dsl.rs	Adds typed Step enum + Script builder with compile-time-ish validation via build().
xtask/src/demo/driver.rs	Implements step interpreter, capture lifecycle, and window wait/focus/type primitives.
xtask/src/demo/script.rs	Defines canonical v0 demo script builder.
xtask/src/demo/config_override.rs	Writes demo-only config, dispatcher, and fake host home trees.
xtask/src/demo/recorder.rs	Implements ffmpeg capture + frame extraction + gifski encoding pipeline.
xtask/src/demo/windows_input.rs	Wraps Win32 window enumeration + input injection with non-Windows stubs.
xtask/src/demo/env/mod.rs	Introduces env module namespace (v0: local only).
xtask/src/demo/env/local.rs	v0 local provider: prepares demo tree, copies csshw.exe, runs driver, cleans up.
xtask/src/tests/test_demo_dsl.rs	Tests DSL ordering, defaults, and validation failures.
xtask/src/tests/test_demo_driver.rs	Tests driver behavior with a mock DemoSystem.
xtask/src/tests/test_demo_config_override.rs	Tests config/dispatcher/fakehost generation via mock writes.
xtask/src/tests/test_demo_script.rs	Sanity-checks canonical v0 script build and expected step shape.
xtask/src/tests/test_demo_mod.rs	Smoke-tests demo module public surface types.
xtask/Cargo.toml	Adds regex dependency and Windows-only windows dependency/features for demo input APIs.
Cargo.lock	Locks new dependencies (regex and transitive crates).

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