docs: Move align-with example out of ports parameter box

Introduces a new "s-shape" wire style connecting two ports on opposite
cardinal sides (east<->west or north<->south) via 5 segments joined at
4 corners (u1-start, u1-end, u2-start, u2-end). The axis is auto-detected
from port anchors; when both endpoints share the same perpendicular
coordinate (single-block loopback) `s-ratio-mid` is reinterpreted as an
absolute signed offset so the crossbar can still be placed above or
below the endpoints.

Also adds `u-at` to the "u-shape" style, an anchor-based crossbar
placement analogous to `zigzag-at`. `u-depth` now defaults to
`auto` to allow clean mutual-exclusion with `u-at`.

Factors the shared placement normalizer into
`normalize-scalar-offset(at, axis)`; `normalize-zigzag-at` remains as
a thin backwards-compatible wrapper.

doc/examples.typ

@@ -534,3 +534,137 @@ wire.intersection("w1.zig")
   ```,
   vertical: true,
 )
+
+#let u-at = example(
+  ```
+  // `u-at` places the U-bend crossbar on the axis
+  // of a referenced anchor, overriding `u-depth`.
+  element.block(x: 0, y: 0,    w: 1.5, h: 1.5, id: "eA",
+    fill: util.colors.orange,
+    ports: (east: ((id: "o1"), (id: "o2"))))
+  element.block(x: 0, y: -3.5, w: 1.5, h: 1.5, id: "eB",
+    fill: util.colors.orange,
+    ports: (east: ((id: "i1"), (id: "i2"))))
+  element.block(x: 4, y: -2.25, w: 0.6, h: 0.6, id: "ref",
+    fill: util.colors.pink)
+  // Align one U crossbar with ref.east.
+  wire.wire("u1", ("eA-port-o1", "eB-port-i1"),
+            style: "u-shape",
+            u-at: "ref.east")
+  // Ergonomic scalar offset: 1 right of ref.east.
+  wire.wire("u2", ("eA-port-o2", "eB-port-i2"),
+            style: "u-shape", color: util.colors.blue,
+            u-at: (rel: 1, to: "ref.east"))
+  ```,
+  vertical: true,
+)
+
+#let s-shape-wire = example(
+  ```
+  // `s-shape` connects endpoints on opposite sides
+  // via 5 segments joined at 4 corners (u1-start,
+  // u1-end, u2-start, u2-end). Auto-detects axis
+  // from port anchors.
+  element.block(x: 0, y: 0, w: 1, h: 1, id: "A",
+    fill: util.colors.orange,
+    ports: (west: ((id: "out"),)))
+  element.block(x: 2.5, y: -1.75, w: 1, h: 1, id: "B",
+    fill: util.colors.orange,
+    ports: (east: ((id: "in"),)))
+  wire.wire("s1", ("A-port-out", "B-port-in"),
+            style: "s-shape")
+
+  // Anchor-based override of the crossbar position.
+  element.block(x: 5.5, y: 0, w: 1, h: 1, id: "C",
+    fill: util.colors.yellow,
+    ports: (west: ((id: "out"),)))
+  element.block(x: 8.5, y: -1.75, w: 1, h: 1, id: "D",
+    fill: util.colors.yellow,
+    ports: (east: ((id: "in"),)))
+  element.block(x: 7, y: -0.7, w: 0.5, h: 0.5, id: "ref",
+    fill: util.colors.pink)
+  wire.wire("s2", ("C-port-out", "D-port-in"),
+            style: "s-shape",
+            s-at-mid: "ref.south")
+
+  // C-shape degeneration: crossbar outside the
+  // endpoint span (s-ratio-mid > 100%).
+  element.block(x: 11, y: 0, w: 1, h: 1, id: "E",
+    fill: util.colors.green,
+    ports: (west: ((id: "out"),)))
+  element.block(x: 14, y: -0.75, w: 1, h: 1, id: "F",
+    fill: util.colors.green,
+    ports: (east: ((id: "in"),)))
+  wire.wire("s3", ("E-port-out", "F-port-in"),
+            style: "s-shape",
+            s-ratio-mid: 200%)
+  ```,
+  vertical: true,
+)
+
+#let s-shape-wire-vertical = example(
+  ```
+  // `s-shape` on the vertical axis (north <-> south):
+  // seg1 and seg5 are vertical, the crossbar is
+  // vertical, and the two horizontals connect them.
+  element.block(x: 0, y: 0, w: 1, h: 1, id: "A",
+    fill: util.colors.orange,
+    ports: (north: ((id: "out"),)))
+  element.block(x: 2, y: -3, w: 1, h: 1, id: "B",
+    fill: util.colors.orange,
+    ports: (south: ((id: "in"),)))
+  wire.wire("s1", ("A-port-out", "B-port-in"),
+            style: "s-shape")
+
+  // Anchor-based override of the vertical crossbar.
+  element.block(x: 5, y: 0, w: 1, h: 1, id: "C",
+    fill: util.colors.yellow,
+    ports: (north: ((id: "out"),)))
+  element.block(x: 7, y: -3, w: 1, h: 1, id: "D",
+    fill: util.colors.yellow,
+    ports: (south: ((id: "in"),)))
+  element.block(x: 6.25, y: -1.5, w: 0.5, h: 0.5, id: "vref",
+    fill: util.colors.pink)
+  wire.wire("s2", ("C-port-out", "D-port-in"),
+            style: "s-shape",
+            s-at-mid: "vref.east")
+  ```,
+  vertical: true,
+)
+
+#let s-shape-wire-loopback = example(
+  ```
+  // `s-shape` looping back on a single block that
+  // has a west output and an east input. The wire
+  // exits west, wraps around below the block via a
+  // C-shape, and enters from the east.
+  //
+  // Since both endpoints share the same y, the
+  // crossbar's position is set by `s-ratio-mid`
+  // as an absolute distance below the endpoint y.
+  element.block(x: 2, y: 0, w: 1.5, h: 1.5, id: "A",
+    fill: util.colors.orange,
+    ports: (
+      west: ((id: "out"),),
+      east: ((id: "in"),),
+    ))
+  wire.wire("s1", ("A-port-out", "A-port-in"),
+            style: "s-shape",
+            s-depth-1: 1.5, s-depth-2: 1.5,
+            s-ratio-mid: 150%)
+
+  // Negative `s-ratio-mid` routes the crossbar the
+  // other way (above the block).
+  element.block(x: 7, y: 0, w: 1.5, h: 1.5, id: "B",
+    fill: util.colors.yellow,
+    ports: (
+      west: ((id: "out"),),
+      east: ((id: "in"),),
+    ))
+  wire.wire("s2", ("B-port-out", "B-port-in"),
+            style: "s-shape",
+            s-depth-1: 1.5, s-depth-2: 1.5,
+            s-ratio-mid: -150%)
+  ```,
+  vertical: true,
+)

manual.typ

@@ -166,8 +166,24 @@ If you have installed Circuiteria directly in your project, import #link("src/li
 
 #pagebreak()
 
+#let element-scope = (
+  element: element,
+  circuit: circuit,
+  draw: draw,
+  wire: wire,
+  tidy: tidy,
+  examples: examples,
+  doc-ref: doc-ref
+)
+
+#let elmt-docs = tidy.parse-module(
+  read("src/elements/element.typ"),
+  name: "element",
+  old-syntax: true,
+  scope: element-scope
+)
+
 #let element-docs = tidy.parse-module(
-  read("src/elements/element.typ") + "\n" +
   read("src/elements/alu.typ") + "\n" +
   read("src/elements/block.typ") + "\n" +
   read("src/elements/extender.typ") + "\n" +
@@ -175,18 +191,19 @@ If you have installed Circuiteria directly in your project, import #link("src/li
   read("src/elements/group.typ"),
   name: "element",
   old-syntax: true,
-  scope: (
-    element: element,
-    circuit: circuit,
-    draw: draw,
-    wire: wire,
-    tidy: tidy,
-    examples: examples,
-    doc-ref: doc-ref
-  )
+  scope: element-scope
 )
 
-#tidy.show-module(element-docs, sort-functions: false)
+#tidy.show-module(elmt-docs, sort-functions: false, show-module-name: true)
+
+#figure(
+  examples.align-with-ports,
+  caption: [Example of the `align-with` port field (see #doc-ref("element.elmt")).],
+  kind: "example",
+  supplement: [Example],
+) <elmt-align-with-example>
+
+#tidy.show-module(element-docs, sort-functions: false, show-module-name: false)
 
 #pagebreak()
 

src/elements/element.typ

@@ -38,7 +38,7 @@
 ///   - `name` (`str`): Optional name displayed *in* the block
 ///   - `clock` (`bool`): Whether it is a clock port (triangle symbol)
 ///   - `vertical` (`bool`): Whether the name should be drawn vertically
-///   - `align-with` (`str`, `dictionary`): Optional. Reuse another port's placement coordinate (east/west: y, north/south: x). Accepted forms: `"<local-id>"` (same-element port; axis must match, transitively resolved, cycles panic), `(element: "<id>", port: "<id>")` (cross-element; axis not validated; target element must be drawn first), or `"<raw-anchor>"` (any unrecognised string is used as a CeTZ anchor name). See #examples.align-with-ports
+///   - `align-with` (`str`, `dictionary`): Optional. Reuse another port's placement coordinate (east/west: y, north/south: x). Accepted forms: `"<local-id>"` (same-element port; axis must match, transitively resolved, cycles panic), `(element: "<id>", port: "<id>")` (cross-element; axis not validated; target element must be drawn first), or `"<raw-anchor>"` (any unrecognised string is used as a CeTZ anchor name). See @elmt-align-with-example.
 ///   - `x` (length, ratio, function): Optional. North/south ports only. Explicit x-offset override measured from the left corner of the side. A `ratio` is used as a percentage along the side; a length/number is used as an absolute offset; a function is called with the element width and must return a length/number. Panics if used together with `align-with` or on an east/west port.
 ///   - `y` (length, ratio, function): Optional. East/west ports only. Analogous to `x`, measured from the top corner of the side and called with the element height when a function is passed.
 ///   - `shape` (`none`, `str`): Optional. Per-port override of the element-level `port-shape` (e.g. `"pentagon"`). Lets a single port on a block or group opt into (or out of) a shape independently of the element default. See the `port-shape` parameter below.

src/wire.typ

@@ -6,7 +6,22 @@
 ///
 /// The `"u-shape"` style connects two ports that face the same cardinal side.
 /// #examples.u-shape-wire
-#let wire-styles = ("direct", "zigzag", "dodge", "guided", "u-shape")
+///
+/// The `"u-shape"` crossbar can also be aligned to an anchor via `u-at`
+/// (analogous to `zigzag-at`).
+/// #examples.u-at
+///
+/// The `"s-shape"` style connects two ports that face opposite cardinal sides
+/// (east↔west or north↔south) via 5 segments.
+/// #examples.s-shape-wire
+///
+/// The `"s-shape"` style also supports the vertical axis (north↔south):
+/// #examples.s-shape-wire-vertical
+///
+/// The `"s-shape"` style can also loop a single block's output back to its
+/// own input by wrapping around above (or below) via a C-shape:
+/// #examples.s-shape-wire-loopback
+#let wire-styles = ("direct", "zigzag", "dodge", "guided", "u-shape", "s-shape")
 #let signal-width = 1pt
 #let bus-width = 1.5pt
 
@@ -27,24 +42,31 @@
   return (pts, anchors)
 }
 
-// Normalize a `zigzag-at` value.
+// Normalize an anchor-based placement value used by `zigzag-at`, `u-at`, and
+// the `s-at-*` family.
+//
+// `axis` selects which cartesian component the offset applies to:
+//   - `"x"` → offset in x (used when the placement fixes an x coordinate, e.g.
+//             a vertical bend line for horizontal wire flow).
+//   - `"y"` → offset in y (used when the placement fixes a y coordinate).
 //
 // Accepted forms:
-//   - `none`                              → unset; ratio-based placement is used.
+//   - `none`                              → unset; caller falls back to
+//                                           depth/ratio-based placement.
 //   - `str` / tuple / native CeTZ dict    → passed through as a CeTZ coordinate.
 //   - `(rel: <length>, to: <coord>)` with a *scalar* `rel`
 //                                         → ergonomic axial offset, rewritten
 //                                           to `(rel: (rel, 0), to: to)` for
-//                                           `dir == "vertical"` or
+//                                           `axis == "x"` or
 //                                           `(rel: (0, rel), to: to)` for
-//                                           `dir == "horizontal"`. If `rel` is
-//                                           already an array/tuple, the value
-//                                           is passed through unchanged.
-#let normalize-zigzag-at(at, dir) = {
+//                                           `axis == "y"`. If `rel` is already
+//                                           an array/tuple, the value is
+//                                           passed through unchanged.
+#let normalize-scalar-offset(at, axis) = {
   if at == none { return none }
   if type(at) == dictionary and "rel" in at and "to" in at and type(at.rel) != array {
     let r = at.rel
-    if dir == "vertical" {
+    if axis == "x" {
       return (rel: (r, 0), to: at.to)
     } else {
       return (rel: (0, r), to: at.to)
@@ -53,6 +75,14 @@
   return at
 }
 
+// Backwards-compatible wrapper: translates the old `dir` vocabulary
+// (`"vertical"` / `"horizontal"`) to the `axis` vocabulary used by
+// `normalize-scalar-offset`.
+#let normalize-zigzag-at(at, dir) = {
+  let axis = if dir == "vertical" { "x" } else { "y" }
+  return normalize-scalar-offset(at, axis)
+}
+
 #let get-zigzag-wire(pts, ratio, dir, at: none) = {
   let start = pts.first()
   let end = pts.last()
@@ -193,7 +223,7 @@
   }
 }
 
-#let get-u-shape-wire(pts, u-depth, u-side, ctx) = {
+#let get-u-shape-wire(pts, u-depth, u-side, u-at, ctx) = {
   let start = pts.first()
   let end = pts.last()
 
@@ -227,22 +257,33 @@
   let (sx, sy, ..) = s
   let (ex, ey, ..) = e
 
+  // If `u-at` is set, resolve its coordinate and extract the relevant axis
+  // component; use it as the crossbar position instead of computing from
+  // `u-depth`.
+  let bar-at = none
+  if u-at != none {
+    let axis = if side == "east" or side == "west" { "x" } else { "y" }
+    let at-norm = normalize-scalar-offset(u-at, axis)
+    let (ctx2, r) = coordinate.resolve(ctx, at-norm)
+    bar-at = if axis == "x" { r.first() } else { r.at(1) }
+  }
+
   let p1
   let p2
   if side == "east" {
-    let bx = calc.max(sx, ex) + u-depth
+    let bx = if bar-at != none { bar-at } else { calc.max(sx, ex) + u-depth }
     p1 = (bx, sy, 0)
     p2 = (bx, ey, 0)
   } else if side == "west" {
-    let bx = calc.min(sx, ex) - u-depth
+    let bx = if bar-at != none { bar-at } else { calc.min(sx, ex) - u-depth }
     p1 = (bx, sy, 0)
     p2 = (bx, ey, 0)
   } else if side == "north" {
-    let by = calc.max(sy, ey) + u-depth
+    let by = if bar-at != none { bar-at } else { calc.max(sy, ey) + u-depth }
     p1 = (sx, by, 0)
     p2 = (ex, by, 0)
   } else if side == "south" {
-    let by = calc.min(sy, ey) - u-depth
+    let by = if bar-at != none { bar-at } else { calc.min(sy, ey) - u-depth }
     p1 = (sx, by, 0)
     p2 = (ex, by, 0)
   }
@@ -257,6 +298,210 @@
   return (points, anchors)
 }
 
+// Valid combinations of endpoint sides for an S-shape wire.
+// Keyed by (sorted) pair; value is the wire axis.
+#let _s-axis-from-sides(a, b) = {
+  if a == none or b == none { return none }
+  let pair = (a, b)
+  if ("east" in pair) and ("west" in pair) { return "horizontal" }
+  if ("north" in pair) and ("south" in pair) { return "vertical" }
+  return none
+}
+
+// S-shape wire: 5 segments, 4 corners; connects endpoints on opposite sides.
+//
+// Horizontal axis (east ↔ west): sequence exits/enters through horizontal
+// segments; two vertical segments join them via a horizontal crossbar.
+//
+// Corner layout (horizontal axis):
+//   start ── c1
+//            │
+//            c2 ─────────── c3
+//                           │
+//                           c4 ── end
+//
+// (or mirrored, depending on which endpoint faces east vs west, and on the
+// relative y of the endpoints; when y_mid is outside the endpoint span the
+// shape degenerates into a C-shape.)
+#let get-s-shape-wire(
+  pts,
+  s-axis,
+  s-depth-1,
+  s-ratio-mid,
+  s-depth-2,
+  s-at-1,
+  s-at-mid,
+  s-at-2,
+  strict,
+  ctx,
+) = {
+  let start = pts.first()
+  let end = pts.last()
+
+  // Detect endpoint sides
+  let side-start = _u-detect-side(start, ctx)
+  let side-end = _u-detect-side(end, ctx)
+
+  // Resolve (auto|explicit) axis
+  let axis = s-axis
+  if axis == auto {
+    let detected = _s-axis-from-sides(side-start, side-end)
+    if detected == none {
+      panic(
+        "s-shape: could not auto-detect s-axis; endpoints must be port anchors "
+        + "facing opposite sides on the same axis (east+west or north+south). "
+        + "Detected start='" + repr(side-start) + "', end='" + repr(side-end)
+        + "'. Set s-axis explicitly to \"horizontal\" or \"vertical\"."
+      )
+    }
+    axis = detected
+  }
+  if axis != "horizontal" and axis != "vertical" {
+    panic("s-shape: invalid s-axis '" + repr(axis) + "'; must be \"horizontal\" or \"vertical\"")
+  }
+
+  // Effective depth/ratio (auto → defaults)
+  let depth-1 = if s-depth-1 == auto { 0.5 } else { s-depth-1 }
+  let depth-2 = if s-depth-2 == auto { 0.5 } else { s-depth-2 }
+  let ratio-mid-raw = if s-ratio-mid == auto { 50% } else { s-ratio-mid }
+  let ratio-mid = ratio-mid-raw / 100%
+
+  let (ctx, s) = coordinate.resolve(ctx, start)
+  let (ctx, e) = coordinate.resolve(ctx, end)
+  let (sx, sy, ..) = s
+  let (ex, ey, ..) = e
+
+  // Determine outward directions from each port
+  let outward(side) = {
+    if side == "east" { return (1, 0) }
+    if side == "west" { return (-1, 0) }
+    if side == "north" { return (0, 1) }
+    if side == "south" { return (0, -1) }
+    return none
+  }
+  let out-s = outward(side-start)
+  let out-e = outward(side-end)
+  // Fallback when a port side isn't known (e.g. non-port endpoint): infer from
+  // the axis, assuming the wire flows toward the far endpoint.
+  if out-s == none {
+    if axis == "horizontal" { out-s = (if ex > sx { 1 } else { -1 }, 0) }
+    else { out-s = (0, if ey > sy { 1 } else { -1 }) }
+  }
+  if out-e == none {
+    if axis == "horizontal" { out-e = (if sx > ex { 1 } else { -1 }, 0) }
+    else { out-e = (0, if sy > ey { 1 } else { -1 }) }
+  }
+
+  // Resolve the three placement overrides
+  let resolve-axial(at, ax) = {
+    if at == none { return none }
+    let at-norm = normalize-scalar-offset(at, ax)
+    let (_, r) = coordinate.resolve(ctx, at-norm)
+    return if ax == "x" { r.first() } else { r.at(1) }
+  }
+
+  let c1x
+  let c1y
+  let c2x
+  let c2y
+  let c3x
+  let c3y
+  let c4x
+  let c4y
+
+  if axis == "horizontal" {
+    // seg1 and seg5 are horizontal; the two verticals sit at x = x1 and x = x2.
+    let x1-at = resolve-axial(s-at-1, "x")
+    let x2-at = resolve-axial(s-at-2, "x")
+    let y-mid-at = resolve-axial(s-at-mid, "y")
+
+    let x1 = if x1-at != none { x1-at } else { sx + out-s.at(0) * depth-1 }
+    let x2 = if x2-at != none { x2-at } else { ex + out-e.at(0) * depth-2 }
+    // When the endpoints share the same y (degenerate span), the ratio-based
+    // formula collapses to sy. Fall back to a unit offset scaled by ratio-mid
+    // so the crossbar can still be pushed away from the endpoint axis
+    // (e.g. for single-block loopbacks). Direction defaults to "down" (-y).
+    let y-mid = if y-mid-at != none {
+      y-mid-at
+    } else if ey == sy {
+      sy - ratio-mid
+    } else {
+      sy + ratio-mid * (ey - sy)
+    }
+
+    c1x = x1; c1y = sy
+    c2x = x1; c2y = y-mid
+    c3x = x2; c3y = y-mid
+    c4x = x2; c4y = ey
+
+    // Sanity checks (strict-only)
+    if strict {
+      // seg1 must extend outward: sign(x1 - sx) should match out-s.x
+      if (x1 - sx) * out-s.at(0) <= 0 {
+        panic("s-shape: seg1 does not extend outward from start port "
+          + "(x1=" + str(x1) + ", start.x=" + str(sx) + ", outward.x="
+          + str(out-s.at(0)) + "). Adjust s-depth-1 or s-at-1.")
+      }
+      if (x2 - ex) * out-e.at(0) <= 0 {
+        panic("s-shape: seg5 does not extend outward from end port "
+          + "(x2=" + str(x2) + ", end.x=" + str(ex) + ", outward.x="
+          + str(out-e.at(0)) + "). Adjust s-depth-2 or s-at-2.")
+      }
+    }
+  } else {
+    // vertical axis: seg1 and seg5 are vertical; the two horizontals sit at
+    // y = y1 and y = y2; the middle crossbar is vertical at x = x-mid.
+    let y1-at = resolve-axial(s-at-1, "y")
+    let y2-at = resolve-axial(s-at-2, "y")
+    let x-mid-at = resolve-axial(s-at-mid, "x")
+
+    let y1 = if y1-at != none { y1-at } else { sy + out-s.at(1) * depth-1 }
+    let y2 = if y2-at != none { y2-at } else { ey + out-e.at(1) * depth-2 }
+    // Degenerate-span fallback: see comment in the horizontal branch.
+    let x-mid = if x-mid-at != none {
+      x-mid-at
+    } else if ex == sx {
+      sx + ratio-mid
+    } else {
+      sx + ratio-mid * (ex - sx)
+    }
+
+    c1x = sx; c1y = y1
+    c2x = x-mid; c2y = y1
+    c3x = x-mid; c3y = y2
+    c4x = ex; c4y = y2
+
+    if strict {
+      if (y1 - sy) * out-s.at(1) <= 0 {
+        panic("s-shape: seg1 does not extend outward from start port "
+          + "(y1=" + str(y1) + ", start.y=" + str(sy) + ", outward.y="
+          + str(out-s.at(1)) + "). Adjust s-depth-1 or s-at-1.")
+      }
+      if (y2 - ey) * out-e.at(1) <= 0 {
+        panic("s-shape: seg5 does not extend outward from end port "
+          + "(y2=" + str(y2) + ", end.y=" + str(ey) + ", outward.y="
+          + str(out-e.at(1)) + "). Adjust s-depth-2 or s-at-2.")
+      }
+    }
+  }
+
+  let c1 = (c1x, c1y, 0)
+  let c2 = (c2x, c2y, 0)
+  let c3 = (c3x, c3y, 0)
+  let c4 = (c4x, c4y, 0)
+
+  let points = (start, c1, c2, c3, c4, end)
+  let anchors = (
+    "start": start,
+    "u1-start": c1,
+    "u1-end": c2,
+    "u2-start": c3,
+    "u2-end": c4,
+    "end": end,
+  )
+  return (points, anchors)
+}
+
 #let get-guided-wire(pts, margins, sides, center-guides, ctx) = {
   let start = pts.first()
   let end = pts.last()
@@ -362,7 +607,16 @@
 /// - guided-margins (array): the start and end of guided margins of the wire (only with style "guided")
 /// - guided-sides (array): the side of start and end array (must be either "north", "south", "west", "east") (only work with style "guided")
 /// - u-side (auto, str): The cardinal side both endpoints face (one of "east", "west", "north", "south"). If `auto`, it is deduced from the endpoints when they are port anchors of the form `<elmt-id>-port-<port-id>` by comparing each port's position with its element's `.center` anchor. Auto-detection panics if the two endpoints resolve to different sides, or if neither endpoint is a port anchor (only with style "u-shape")
-/// - u-depth (number): Distance between the outermost endpoint (in the `u-side` direction) and the U-bend line (only with style "u-shape")
+/// - u-depth (auto, number): Distance between the outermost endpoint (in the `u-side` direction) and the U-bend line (only with style "u-shape"). Defaults to `auto`, which resolves to `0.5`. Panics if combined with an explicitly set `u-at`.
+/// - u-at (none, str, array, dictionary): Optional. Anchor-based placement of the U-bend crossbar (only with style "u-shape"). When set, overrides `u-depth` (which must be left at its default `auto`). The crossbar sits on the axis extracted from the given coordinate: `x` for `u-side` in `("east", "west")`, `y` for `("north", "south")`. Accepted forms mirror `zigzag-at`: raw CeTZ anchor name string, any native CeTZ coordinate, or the ergonomic scalar-offset form `(rel: <length>, to: <coord>)`, which is rewritten to `(dx, 0)` for east/west and `(0, dy)` for north/south.
+/// - s-axis (auto, str): The s-shape wire axis, one of "horizontal" or "vertical" (only with style "s-shape"). If `auto`, it is deduced from the endpoint port anchors: opposite east/west ports yield `"horizontal"`, opposite north/south ports yield `"vertical"`. Auto-detection panics on same-side, cross-axis, or non-port endpoints.
+/// - s-depth-1 (auto, number): Distance seg1 (the first outward segment) extends from the start port (only with style "s-shape"). Defaults to `auto`, which resolves to `0.5`. Panics if combined with an explicit `s-at-1`.
+/// - s-ratio-mid (auto, ratio): Position of the s-shape crossbar between the endpoints along the axis perpendicular to `s-axis` (only with style "s-shape"). Defaults to `auto`, which resolves to `50%`. Values outside `0%..100%` are allowed and yield a C-shape variant. When the two endpoints share the same perpendicular coordinate (e.g. a single-block loopback where both ports are at the same y), the endpoint span is zero and `s-ratio-mid` is instead interpreted as an absolute offset from that shared coordinate: the crossbar sits `s-ratio-mid` units below the endpoints for horizontal S, or `s-ratio-mid` units right for vertical S (using `1` = ratio unit). Panics if combined with an explicit `s-at-mid`.
+/// - s-depth-2 (auto, number): Distance seg5 (the last inward segment) extends from the end port (only with style "s-shape"). Defaults to `auto`, which resolves to `0.5`. Panics if combined with an explicit `s-at-2`.
+/// - s-at-1 (none, str, array, dictionary): Optional. Anchor-based placement overriding `s-depth-1` (only with style "s-shape"). Fixes the x (horizontal S) or y (vertical S) of the first vertical bend line. Accepted forms mirror `zigzag-at`.
+/// - s-at-mid (none, str, array, dictionary): Optional. Anchor-based placement overriding `s-ratio-mid` (only with style "s-shape"). Fixes the y (horizontal S) or x (vertical S) of the crossbar. Accepted forms mirror `zigzag-at`.
+/// - s-at-2 (none, str, array, dictionary): Optional. Anchor-based placement overriding `s-depth-2` (only with style "s-shape"). Fixes the x (horizontal S) or y (vertical S) of the second vertical bend line. Accepted forms mirror `zigzag-at`.
+/// - strict (bool): If true, s-shape performs sanity checks and panics when seg1/seg5 do not extend outward from their port (only with style "s-shape"). Defaults to `false`.
 #let wire(
   id, pts,
   bus: false,
@@ -385,7 +639,16 @@
   dodge-sides: ("east", "west"),
   dodge-margins: (5%, 5%),
   u-side: auto,
-  u-depth: 0.5,
+  u-depth: auto,
+  u-at: none,
+  s-axis: auto,
+  s-depth-1: auto,
+  s-ratio-mid: auto,
+  s-depth-2: auto,
+  s-at-1: none,
+  s-at-mid: none,
+  s-at-2: none,
+  strict: false,
 ) = draw.get-ctx(ctx => {
   if not style in wire-styles {
     panic("Invalid wire style '" + style + "'")
@@ -408,6 +671,39 @@
   }
   let zigzag-ratio-effective = if zigzag-ratio == auto { 50% } else { zigzag-ratio }
 
+  // `u-at` validation.
+  if u-at != none {
+    if style != "u-shape" {
+      panic("wire '" + id + "': `u-at` requires style: \"u-shape\" (got \""
+        + style + "\")")
+    }
+    if u-depth != auto {
+      panic("wire '" + id
+        + "': cannot combine `u-at` with an explicit `u-depth`")
+    }
+  }
+  let u-depth-effective = if u-depth == auto { 0.5 } else { u-depth }
+
+  // `s-at-*` validation.
+  let s-params-set = (
+    s-axis != auto or s-depth-1 != auto or s-ratio-mid != auto
+    or s-depth-2 != auto or s-at-1 != none or s-at-mid != none
+    or s-at-2 != none
+  )
+  if s-params-set and style != "s-shape" {
+    panic("wire '" + id + "': `s-*` parameters require style: \"s-shape\" (got \""
+      + style + "\")")
+  }
+  if s-at-1 != none and s-depth-1 != auto {
+    panic("wire '" + id + "': cannot combine `s-at-1` with an explicit `s-depth-1`")
+  }
+  if s-at-mid != none and s-ratio-mid != auto {
+    panic("wire '" + id + "': cannot combine `s-at-mid` with an explicit `s-ratio-mid`")
+  }
+  if s-at-2 != none and s-depth-2 != auto {
+    panic("wire '" + id + "': cannot combine `s-at-2` with an explicit `s-depth-2`")
+  }
+
   // Normalize user-provided coordinates: (x, y) -> (x, y, 0)
   let pts = pts.map(normalize-coord)
   
@@ -468,10 +764,24 @@
   } else if style == "u-shape" {
     (points, anchors) = get-u-shape-wire(
       pts,
-      u-depth,
+      u-depth-effective,
       u-side,
+      u-at,
       ctx
     )
+  } else if style == "s-shape" {
+    (points, anchors) = get-s-shape-wire(
+      pts,
+      s-axis,
+      s-depth-1,
+      s-ratio-mid,
+      s-depth-2,
+      s-at-1,
+      s-at-mid,
+      s-at-2,
+      strict,
+      ctx,
+    )
   }
 
   let mark = (fill: color)