feat: Add wire.breakout element for bus fan-out diagrams

Introduces wire.breakout: a 45° diagonal line of configurable length
(default 1em) that starts at a given (x, y) and exposes a port anchor
<id>-port-<id> at its end point so wires can attach to it as if it were
a block port. A synthesized <id>.center anchor is placed opposite the
configured port-side so wire.wire with style "u-shape" can auto-detect
the port's cardinal side.
- x/y accept number, (rel:, to:) and (from:) forms; (from:) sets the
  start point to the referenced anchor's coordinate.
- direction: one of north-east/north-west/south-east/south-west.
- Optional label positioned via name-pos (NE/NW/SE/SW); when name-pos is
  opposite to direction, the label falls back to the start point so it
  never covers the diagonal line. Label padding matches wire.wire (3pt).
Also adds three examples (breakout, breakout-label, breakout-wire) in
doc/examples.typ referenced from the docstring so tidy auto-renders
them in the manual, and a gallery entry (gallery/test_breakout.typ)
demonstrating orthogonal bus fan-out with breakouts in all four
directions.

doc/examples.typ

@@ -81,6 +81,81 @@ wire.stub("p", "south", name: "south", length: 15pt)
 wire.stub("p", "west", name: "west", length: 3em)
 ```)
 
+#let breakout = example(```
+// 16 breakouts: 4 directions × 4 label positions, laid out
+// two per row so the labels have room to breathe.
+let dirs = ("north-east", "north-west", "south-east", "south-west")
+let poss = ("north-east", "north-west", "south-east", "south-west")
+let short = (
+  "north-east": "NE", "north-west": "NW",
+  "south-east": "SE", "south-west": "SW",
+)
+let cols = 2
+let dx = 5
+let dy = 2
+for (i, dir) in dirs.enumerate() {
+  for (j, pos) in poss.enumerate() {
+    let n = i * poss.len() + j
+    let r = calc.floor(n / cols)
+    let c = calc.rem(n, cols)
+    draw.circle((c * dx, -r * dy), radius: .05)
+    wire.breakout("b" + str(n),
+      x: c * dx, y: -r * dy,
+      direction: dir,
+      port-side: if dir.ends-with("east") { "west" } else { "east" },
+      name: short.at(dir) + "/" + short.at(pos),
+      name-pos: pos)
+  }
+}
+```)
+
+#let breakout-label = example(```
+// name-pos matches direction → label sits at the end point.
+wire.breakout("b1", x: 0, y: 0, direction: "north-east",
+              port-side: "east",
+              name: "at end", name-pos: "north-east")
+
+// name-pos opposite to direction → label would cover the line, so
+// it falls back to the start point.
+wire.breakout("b2", x: 4, y: 0, direction: "north-east",
+              port-side: "east",
+              name: "at start", name-pos: "south-west")
+```, vertical: true)
+
+#let breakout-wire = example(```
+// Bus fan-out: a horizontal wire from the left block to the lower
+// right block carries the full 10-bit bus. A breakout in the middle
+// of that wire taps bits [9:5] and routes them to the upper right
+// block via an L-shaped zigzag (up, then right).
+element.block(x: 0, y: 0, w: 2, h: 2, id: "src",
+  fill: util.colors.blue,
+  ports: (east: ((id: "out"),)))
+element.block(x: 6, y: 0, w: 2, h: 2, id: "dstL",
+  fill: util.colors.green,
+  ports: (west: ((id: "in"),)))
+element.block(x: 6, y: 4, w: 2, h: 2, id: "dstU",
+  fill: util.colors.orange,
+  ports: (west: ((id: "in"),)))
+
+// Full bus wire, labelled "[9:0]" on the left.
+wire.wire("wbus", ("src-port-out", "dstL-port-in"),
+          name: "[9:0]", name-pos: "start")
+
+// Breakout tapped from the midpoint of the bus.
+wire.breakout("tap",
+  x: (rel: 2, to: "src-port-out"),
+  y: (from: "src-port-out"),
+  direction: "north-east",
+  port-side: "west",
+  name: "[9:5]", name-pos: "north-east")
+
+// L-shaped wire from the breakout up and then right to the upper
+// block's input.
+wire.wire("wtap", ("tap-port-tap", "dstU-port-in"),
+          style: "zigzag", zigzag-dir: "horizontal",
+          zigzag-ratio: 100%)
+```)
+
 #let gate-and = example(```
 gates.gate-and(x: 0, y: 0, w: 1.5, h: 1.5)
 gates.gate-and(x: 3, y: 0, w: 1.5, h: 1.5, inverted: "all")

gallery/test_breakout.typ

@@ -0,0 +1,117 @@
+// Demonstrates the wire.breakout element used to split off slices of a
+// bus that connects blocks. The main bus wires are always laid out
+// orthogonally; breakouts diagonally tap intermediate points on those
+// wires and route the sub-bus to another block via an L-shaped zigzag.
+#import "/src/lib.typ": circuit, element, util, wire
+
+#set page(width: auto, height: auto, margin: .5cm)
+
+#circuit({
+  // ---- Source block on the left, main sink on the right ----
+  element.block(x: 0, y: 0, w: 2, h: 2, id: "src", fill: util.colors.blue, ports: (
+    east: ((id: "out"),),
+  ))
+
+  element.block(x: 15, y: 0, w: 2, h: 2, id: "dstMain", fill: util.colors.green, ports: (
+    west: ((id: "in"),),
+  ))
+
+  // Full bus from src to dstMain, labelled [15:0] at the start.
+  wire.wire("wbus", ("src-port-out", "dstMain-port-in"), name: "[15:0]", name-pos: "start")
+
+  // ---- Upper-left sink: taps bits [11:8] via NW breakout ----
+  element.block(x: 0, y: 4, w: 2, h: 2, id: "dstNW", fill: util.colors.yellow, ports: (
+    east: ((id: "in"),),
+  ))
+
+  wire.breakout(
+    "tapNE",
+    x: (rel: 3, to: "src-port-out"),
+    y: (from: "src-port-out"),
+    direction: "north-east",
+    port-side: "west",
+    name: "[15:12]",
+    name-pos: "north-east",
+  )
+
+  // L-shape: up first, then left into dstNW.
+  wire.wire(
+    "wNW",
+    ("tapNE-port-tapNE", "dstNW-port-in"),
+    style: "zigzag",
+    zigzag-dir: "horizontal",
+    zigzag-ratio: 100%,
+  )
+
+  // ---- Upper-right sink: taps bits [15:12] via NE breakout ----
+  element.block(x: 15, y: 4, w: 2, h: 2, id: "dstNE", fill: util.colors.orange, ports: (
+    west: ((id: "in"),),
+  ))
+
+  wire.breakout(
+    "tapNW",
+    x: (rel: 7, to: "src-port-out"),
+    y: (from: "src-port-out"),
+    direction: "north-west",
+    port-side: "east",
+    name: "[11:8]",
+    name-pos: "north-east",
+  )
+
+  // L-shape: up first, then right into dstNE.
+  wire.wire(
+    "wNE",
+    ("tapNW-port-tapNW", "dstNE-port-in"),
+    style: "zigzag",
+    zigzag-dir: "horizontal",
+    zigzag-ratio: 100%,
+  )
+
+  // ---- Lower-left sink: taps bits [3:0] via SW breakout ----
+  element.block(x: 0, y: -4, w: 2, h: 2, id: "dstSW", fill: util.colors.purple, ports: (
+    east: ((id: "in"),),
+  ))
+
+  wire.breakout(
+    "tapSE",
+    x: (rel: 5, to: "src-port-out"),
+    y: (from: "src-port-out"),
+    direction: "south-east",
+    port-side: "west",
+    name: "[7:4]",
+    name-pos: "south-east",
+  )
+
+  // L-shape: down first, then left into dstSW.
+  wire.wire(
+    "wSW",
+    ("tapSE-port-tapSE", "dstSW-port-in"),
+    style: "zigzag",
+    zigzag-dir: "horizontal",
+    zigzag-ratio: 100%,
+  )
+
+  // ---- Lower-right sink: taps bits [7:4] via SE breakout ----
+  element.block(x: 15, y: -4, w: 2, h: 2, id: "dstSE", fill: util.colors.pink, ports: (
+    west: ((id: "in"),),
+  ))
+
+  wire.breakout(
+    "tapSW",
+    x: (rel: 11, to: "src-port-out"),
+    y: (from: "src-port-out"),
+    direction: "south-west",
+    port-side: "east",
+    name: "[3:0]",
+    name-pos: "south-west",
+  )
+
+  // L-shape: down first, then right into dstSE.
+  wire.wire(
+    "wSE",
+    ("tapSW-port-tapSW", "dstSE-port-in"),
+    style: "zigzag",
+    zigzag-dir: "horizontal",
+    zigzag-ratio: 100%,
+  )
+})

src/wire.typ

@@ -1,5 +1,5 @@
 #import "/src/cetz.typ": draw, coordinate
-#import "util.typ": opposite-anchor, normalize-coord
+#import "util.typ": opposite-anchor, normalize-coord, resolve-rel-coord
 
 /// List of valid wire styles
 /// #examples.wires
@@ -511,3 +511,141 @@
     )
   }
 }
+
+/// Draws a wire breakout: a 45° diagonal line starting at (x, y) and
+/// ending 1 unit away in one of the four diagonal directions. The end
+/// point exposes a port anchor named `<id>-port-<id>` so wires can attach
+/// to it as if it were a block port. A synthesized `<id>.center` anchor
+/// is placed opposite `port-side` so #doc-ref("wire.wire") with
+/// `style: "u-shape"` can auto-detect the port side.
+///
+/// #examples.breakout
+///
+/// Label positions are anchored so that the label sits neatly next to the
+/// end point of the breakout. When the label direction matches the
+/// breakout direction (which would overlap the line) the label is
+/// automatically placed at the start point instead so the text does not
+/// cover the line.
+///
+/// #examples.breakout-label
+///
+/// The port anchor makes it easy to fan out a bus:
+///
+/// #examples.breakout-wire
+///
+/// - id (str): The breakout id (also used as the port id)
+/// - x (number, dictionary): The starting x position (same forms as `element.block`)
+/// - y (number, dictionary): The starting y position (same forms as `element.block`)
+/// - direction (str): One of `"north-east"`, `"north-west"`, `"south-east"`, `"south-west"`
+/// - length (length, number): The diagonal length (default `1em`, matches port size)
+/// - port-side (str): Cardinal side used for wire-attach behavior (`"north"`, `"east"`, `"south"`, `"west"`)
+/// - stroke (stroke): Line stroke (paint + thickness)
+/// - name (none, str): Optional label displayed near the breakout
+/// - name-pos (none, str): Label position, one of `"north-west"`, `"north-east"`, `"south-west"`, `"south-east"`
+/// - debug (bool): If true, shows a red dot at the port anchor
+#let breakout(
+  id,
+  x: none, y: none,
+  direction: "north-east",
+  length: 1em,
+  port-side: "east",
+  stroke: black + 1pt,
+  name: none,
+  name-pos: none,
+  debug: false,
+) = draw.get-ctx(ctx => {
+  if x == none { panic("breakout: parameter x must be set") }
+  if y == none { panic("breakout: parameter y must be set") }
+
+  let valid-directions = ("north-east", "north-west", "south-east", "south-west")
+  if not direction in valid-directions {
+    panic("breakout: invalid direction '" + repr(direction)
+          + "'; must be one of " + repr(valid-directions))
+  }
+  let valid-sides = ("north", "east", "south", "west")
+  if not port-side in valid-sides {
+    panic("breakout: invalid port-side '" + repr(port-side)
+          + "'; must be one of " + repr(valid-sides))
+  }
+
+  // Diagonal component: length / sqrt(2). Resolve to a canvas-space
+  // number so we can do arithmetic with anchor coordinates.
+  let d-raw = length / calc.sqrt(2)
+  let (_, d-vec) = coordinate.resolve(ctx, (d-raw, 0, 0))
+  let d = d-vec.at(0)
+
+  // Direction sign vector for (dx, dy).
+  let sx = if direction.ends-with("east") { 1 } else { -1 }
+  let sy = if direction.starts-with("north") { 1 } else { -1 }
+
+  // Resolve x.
+  let sx0 = x
+  if type(x) == dictionary {
+    if "rel" in x {
+      sx0 = resolve-rel-coord(ctx, x, 0)
+    } else if "from" in x {
+      let (_, from-pos) = coordinate.resolve(ctx, x.from)
+      sx0 = from-pos.at(0)
+    } else {
+      panic("breakout: unsupported x dictionary: " + repr(x))
+    }
+  }
+  // Resolve y.
+  let sy0 = y
+  if type(y) == dictionary {
+    if "rel" in y {
+      sy0 = resolve-rel-coord(ctx, y, 1)
+    } else if "from" in y {
+      let (_, from-pos) = coordinate.resolve(ctx, y.from)
+      sy0 = from-pos.at(1)
+    } else {
+      panic("breakout: unsupported y dictionary: " + repr(y))
+    }
+  }
+
+  let start = (sx0, sy0)
+  let end = (rel: (sx * d, sy * d), to: start)
+
+  // Offset used for the synthesized center anchor: opposite of port-side.
+  let center-offset = (
+    "north": (0, -1em),
+    "east":  (-1em, 0),
+    "south": (0, 1em),
+    "west":  (1em, 0),
+  ).at(port-side)
+
+  let port-anchor-name = id + "-port-" + id
+
+  draw.group(name: id, {
+    draw.line(start, end, stroke: stroke)
+    draw.anchor("start", start)
+    draw.anchor("end", end)
+    draw.anchor("center", (rel: center-offset, to: end))
+
+    if name != none and name-pos != none {
+      let label-anchor = (
+        "north-west": "south-east",
+        "north-east": "south-west",
+        "south-west": "north-east",
+        "south-east": "north-west",
+      ).at(name-pos)
+
+      // Overlap case: label direction is opposite to breakout direction,
+      // so the label at the end point would extend back over the line.
+      // Anchor it at the start point instead.
+      let label-pos = if name-pos == opposite-anchor(direction) { start } else { end }
+
+      draw.content(label-pos, anchor: label-anchor, padding: 3pt, name)
+    }
+  })
+
+  // Port anchor emitted at top level so it can be referenced by its
+  // bare name (mirrors add-port's approach in ports.typ).
+  if debug {
+    draw.circle(end, name: port-anchor-name,
+                radius: .1, stroke: none, fill: red)
+  } else {
+    draw.hide(draw.circle(end, name: port-anchor-name,
+                          radius: 0, stroke: none))
+  }
+})