Bring the headless rig into the repository

A rendering claim about iris was verified by hand from another checkout,
because the compositor script and the input replay lived in ai-app's
submodule and not here.

`scripts/run-headless.sh` starts a headless sway on its own socket, runs
an example against it and screenshots the result. `rig-input`'s
`replay-touch` drives a recorded gesture in through Wayland's virtual
pointer, since a headless compositor has no input device to move.

`iris::harness` gains the `.touch` parser, so a recording means the same
thing replayed into a harness as into a window rather than being read
twice by two parsers.

The ai-app copy's `--phone` became `--mode`, since which phone is not
iris's business; its `IRIS_SCALE` has nothing to hand a density to here,
so it waits for one.

src/harness.rs

@@ -37,6 +37,81 @@ macro_rules! assert_corners {
 }
 pub use crate::assert_corners;
 
+/// One replayed pointer sample, cut down to what a window delivers: where the
+/// pointer is, and whether the button changed.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum TouchAction {
+    Down,
+    Move,
+    Up,
+}
+
+impl TouchAction {
+    fn parse(word: &str) -> Option<Self> {
+        match word {
+            "down" => Some(Self::Down),
+            "move" => Some(Self::Move),
+            "up" => Some(Self::Up),
+            _ => None,
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug)]
+pub struct TouchSample {
+    pub t_ms: u64,
+    pub action: TouchAction,
+    pub pos: Vec2,
+}
+
+/// A recorded gesture, in the output's own pixels: `<ms> down|move|up <x> <y>`
+/// a line, `#` to end of line ignored.
+///
+/// One parser for both ways of replaying a recording -- into a harness, and
+/// into a real window -- so the two cannot read the same file differently.
+pub struct TouchScript {
+    pub samples: Vec<TouchSample>,
+}
+
+impl TouchScript {
+    pub fn parse(text: &str) -> Result<Self, String> {
+        let mut samples: Vec<TouchSample> = Vec::new();
+        for (i, line) in text.lines().enumerate() {
+            let line = line.split('#').next().unwrap_or("").trim();
+            if line.is_empty() {
+                continue;
+            }
+            let at = |what: &str| format!("touch script line {}: {what}: {line:?}", i + 1);
+            let mut words = line.split_whitespace();
+            let (Some(t), Some(action), Some(x), Some(y), None) = (
+                words.next(),
+                words.next(),
+                words.next(),
+                words.next(),
+                words.next(),
+            ) else {
+                return Err(at("expected `t_ms action x y`"));
+            };
+            let t_ms: u64 = t.parse().map_err(|_| at("t_ms is not a whole number"))?;
+            let action =
+                TouchAction::parse(action).ok_or_else(|| at("action is not down/move/up"))?;
+            let x: f32 = x.parse().map_err(|_| at("x is not a number"))?;
+            let y: f32 = y.parse().map_err(|_| at("y is not a number"))?;
+            if let Some(last) = samples.last()
+                && t_ms < last.t_ms
+            {
+                return Err(at("samples must be in time order"));
+            }
+            samples.push(TouchSample {
+                t_ms,
+                action,
+                pos: Vec2::new(x, y),
+            });
+        }
+        Ok(Self { samples })
+    }
+}
+
 #[derive(Default)]
 pub struct HarnessState {
     pub root: Option<StrongWidget>,
@@ -160,6 +235,23 @@ impl Harness {
         self.release(CursorButton::Left);
     }
 
+    /// Drives a recorded gesture through the harness.
+    pub fn replay(&mut self, script: &TouchScript) {
+        for sample in &script.samples {
+            match sample.action {
+                TouchAction::Down => {
+                    self.move_to(sample.pos);
+                    self.press(CursorButton::Left);
+                }
+                TouchAction::Move => self.move_to(sample.pos),
+                TouchAction::Up => {
+                    self.move_to(sample.pos);
+                    self.release(CursorButton::Left);
+                }
+            }
+        }
+    }
+
     fn button(&mut self, button: CursorButton) -> &mut ActivationState {
         let buttons = &mut self.cursor.buttons;
         match button {
@@ -178,3 +270,51 @@ impl Harness {
         self.cursor.end_frame();
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn parse(text: &str) -> Result<Vec<(u64, TouchAction, f32, f32)>, String> {
+        Ok(TouchScript::parse(text)?
+            .samples
+            .iter()
+            .map(|s| (s.t_ms, s.action, s.pos.x, s.pos.y))
+            .collect())
+    }
+
+    #[test]
+    fn a_recording_is_time_action_and_a_point() {
+        assert_eq!(
+            parse("0 down 10 20\n16 move 10.5 24\n32 up 10.5 24").unwrap(),
+            [
+                (0, TouchAction::Down, 10.0, 20.0),
+                (16, TouchAction::Move, 10.5, 24.0),
+                (32, TouchAction::Up, 10.5, 24.0),
+            ]
+        );
+    }
+
+    #[test]
+    fn blank_lines_and_comments_are_not_samples() {
+        assert_eq!(
+            parse("# a flick\n\n 0 down 1 2   # the finger lands\n\n").unwrap(),
+            [(0, TouchAction::Down, 1.0, 2.0)]
+        );
+    }
+
+    #[test]
+    fn a_recording_that_goes_backwards_is_rejected() {
+        // Replay waits out the gap between samples, so time running backwards
+        // would silently become no wait at all.
+        let err = parse("16 down 1 2\n0 up 1 2").unwrap_err();
+        assert!(err.contains("time order"), "{err}");
+    }
+
+    #[test]
+    fn a_line_that_is_not_a_sample_says_which_line() {
+        let err = parse("0 down 1 2\n16 wiggle 1 2").unwrap_err();
+        assert!(err.contains("line 2"), "{err}");
+        assert!(err.contains("down/move/up"), "{err}");
+    }
+}