Add biscuit board laser ablation essentials guide

docs/elements/board.mdx

@@ -86,7 +86,8 @@ Usually you'll want to use an autorouter preset:
 - `autorouter="auto"` - Uses the [platform configuration](../guides/running-tscircuit/platform-configuration.md). For tscircuit.com this defaults to `sequential-trace`.
 - `autorouter="sequential-trace"` - Iterate over each trace and use tscircuit's fast built-in autorouter. This method is fast and deterministic but often fails with over 50 traces.
 - `autorouter="auto-local"` - Use the platform configuration, but only route locally (do not make API calls)
-- `autorouter="auto-cloud"` - Use the platform configuration for 
+- `autorouter="auto-cloud"` - Use the platform configuration for
+- `autorouter="laser_prefab"` - Reserve prefabricated vias that can be reassigned during routing. Ideal for rapid-turn PCBs produced with laser ablation and mechanical drilling templates. See the [Biscuit Board Laser Ablation guide](../guides/tscircuit-essentials/biscuit-board-laser-ablation.mdx) for a complete walkthrough.
 
 For complex boards with over 50 traces, you should use `autorouter="auto-cloud"`
 to take advantage of tscircuit's cloud autorouters, which internally use the popular

docs/elements/via.mdx

@@ -42,3 +42,4 @@ import CircuitPreview from "@site/src/components/CircuitPreview"
 | outerDiameter | number \| string | "0.8mm" | Outer diameter of the copper annular ring |
 | pcbX | number | 0 | PCB X position of the via |
 | pcbY | number | 0 | PCB Y position of the via |
+| netIsAssignable | boolean | `false` | Marks the via as prefabricated so autorouters like `laser_prefab` can claim it for any compatible net. For a full workflow, see the [Biscuit Board Laser Ablation guide](../guides/tscircuit-essentials/biscuit-board-laser-ablation.mdx). |

docs/guides/tscircuit-essentials/biscuit-board-laser-ablation.mdx

@@ -0,0 +1,123 @@
+---
+title: Biscuit Board Laser Ablation
+description: Learn how to route PCBs against a prefabricated via template using the laser_prefab autorouter and the netIsAssignable via property.
+---
+
+import CircuitPreview from "@site/src/components/CircuitPreview"
+
+# Biscuit Board Laser Ablation
+
+The **laser_prefab** autorouter pairs tscircuit with a fabrication process that
+combines laser ablation and a "biscuit" carrier board. Fabricators pre-drill a
+matrix of vias into an inexpensive substrate—the biscuit—then laminate thin
+copper to the top and bottom. A UV or IR laser ablates the copper, defining the
+traces while leaving the via barrels intact. Because the vias are prefabricated,
+you route against a known template instead of drilling new holes for every
+board.
+
+This guide walks through designing for that workflow. You'll learn how to:
+
+1. Build a reusable via template (the biscuit board).
+2. Place that template, route with `autorouter="laser_prefab"`, and confirm the results match the prefabricated geometry.
+
+## 1. Build a reusable via template (a biscuit board)
+
+Create a component for your biscuit template that contains every via location
+available on the board. Mark each via with `netIsAssignable` so it is treated as
+an assignable via when the router runs. The vias can optionally include default
+net names to serve as documentation for repeated layouts.
+
+```tsx title="src/biscuit-template.tsx"
+import { Fragment } from "react"
+
+export const BiscuitTemplate = () => (
+  <Fragment>
+    <via name="B1" pcbX={-4} pcbY={6} fromLayer="top" toLayer="bottom" netIsAssignable />
+    <via name="B2" pcbX={0} pcbY={6} fromLayer="top" toLayer="bottom" netIsAssignable />
+    <via name="B3" pcbX={4} pcbY={6} fromLayer="top" toLayer="bottom" netIsAssignable />
+    <via name="B4" pcbX={-4} pcbY={0} fromLayer="top" toLayer="bottom" netIsAssignable />
+    <via name="B5" pcbX={0} pcbY={0} fromLayer="top" toLayer="bottom" netIsAssignable />
+    <via name="B6" pcbX={4} pcbY={0} fromLayer="top" toLayer="bottom" netIsAssignable />
+  </Fragment>
+)
+```
+
+Keep the template focused on the vias themselves. Copper features such as
+fiducials or alignment marks should live in their own components so you can swap
+templates without affecting the mechanical stackup.
+
+## 2. Place the biscuit template, route, and validate
+
+Include the template inside your `<board />` before adding components. Because
+the vias are already drilled in the physical biscuit, avoid translating or
+rotating the template in a way that misaligns the coordinates.
+
+<CircuitPreview
+  defaultView="pcb"
+  code={`export default () => (
+  <board width="20mm" height="20mm" autorouter="laser_prefab">
+    <group name="biscuit" pcbX={0} pcbY={0}>
+      <via name="B1" pcbX={-4} pcbY={6} fromLayer="top" toLayer="bottom" netIsAssignable />
+      <via name="B2" pcbX={0} pcbY={6} fromLayer="top" toLayer="bottom" netIsAssignable />
+      <via name="B3" pcbX={4} pcbY={6} fromLayer="top" toLayer="bottom" netIsAssignable />
+      <via name="B4" pcbX={-4} pcbY={0} fromLayer="top" toLayer="bottom" netIsAssignable />
+      <via name="B5" pcbX={0} pcbY={0} fromLayer="top" toLayer="bottom" netIsAssignable />
+      <via name="B6" pcbX={4} pcbY={0} fromLayer="top" toLayer="bottom" netIsAssignable />
+    </group>
+
+    <testpoint name="TP_TOP" footprintVariant="pad" pcbX={0} pcbY={9} layer="top" />
+    <testpoint name="TP_BOTTOM" footprintVariant="pad" pcbX={0} pcbY={-9} layer="bottom" />
+  </board>
+)`}
+/>
+
+Keep the board outline slightly inside the biscuit's usable area so the laser
+can clear debris without hitting the rails.
+
+Once the template is in place, add traces exactly as you would for a conventional
+board. The router treats assignable vias as neutral territory: any net can claim
+them provided both layers are available and no design rules are violated.
+
+```tsx title="src/laser-prefab-example.tsx"
+<board width="20mm" height="20mm" autorouter="laser_prefab">
+  <BiscuitTemplate />
+
+  <chip
+    name="U1"
+    footprint="soic8"
+    pcbX={-6}
+    pcbY={0}
+    connections={{ pin1: "R1.pin1", pin8: "B6.top" }}
+  />
+  <resistor name="R1" resistance="1k" footprint="0402" pcbX={6} pcbY={0} />
+
+  <trace from="TP_TOP.pin1" to="B2.top" />
+  <trace from="B2.bottom" to="TP_BOTTOM.pin1" />
+</board>
+```
+
+After generating manufacturing data (Gerber or ODB++ exports) or reviewing the
+PCB preview, confirm that:
+
+- Every claimed via matches a real location on the biscuit template.
+- Unused vias remain isolated and keep their original net names.
+- Trace clearances respect your fabrication limits.
+
+<CircuitPreview
+  defaultView="pcb"
+  code={`export default () => (
+  <board width="20mm" height="20mm" autorouter="laser_prefab">
+    <group name="biscuit">
+      <via name="B2" pcbX={0} pcbY={6} fromLayer="top" toLayer="bottom" netIsAssignable />
+      <via name="B5" pcbX={0} pcbY={0} fromLayer="top" toLayer="bottom" netIsAssignable />
+    </group>
+
+    <testpoint name="TP_TOP" footprintVariant="pad" pcbX={0} pcbY={9} layer="top" />
+    <testpoint name="TP_BOTTOM" footprintVariant="pad" pcbX={0} pcbY={-9} layer="bottom" />
+
+    <trace from="TP_TOP.pin1" to="B2.top" />
+    <trace from="B2.bottom" to="B5.top" />
+    <trace from="B5.bottom" to="TP_BOTTOM.pin1" />
+  </board>
+)`}
+/>