fins: fins.js is the entry point; map web/fins/ in its header

Step 5 (last) of splitting fins.js. The header described the M4 fin that
stood beside the part, which is gone; it now says what buildFins builds,
keeps the horizontal-tine rationale prop/config.js cites, and maps
web/fins/. buildFins's opts.mode doc says 'stabilize' is an old name for
'auto'. Comments and docs that named fins.js for code now in web/fins/
(PAD.style, buildPad, seatingOf, unservedAfterWedges, the Onshape port's
section notes) point at the module that owns it.

No code change.

docs/FIN-SPEC.md

@@ -98,7 +98,7 @@ welts.
   tined side fins (the Onshape port's; the web tool no longer builds them) are never
   cut -- their tines anchor across the whole blade.
 
-## Bed pad styles — `PAD.style` in `web/fins.js`
+## Bed pad styles — `PAD.style` in `web/fins/pad.js`
 
 The pad goes under a part whose bed contact is under `padMinArea` (60 mm²), which is
 nearly every tilted part. **Printed, 2026-09-24:** a cube on its edge in **PETG** with

docs/IMPLEMENTATION-PLAN.md

@@ -80,7 +80,7 @@ change; re-run before believing it.
 
 - `hub_post_foot` at 0/25/40 — the part has **0.0 mm² of bed contact at every
   tilt from 0° to 165°**; it balances on the tip of its own tapered foot.
-  Nothing you add can hold it. `seatingOf()` in `fins.js` classifies this as
+  Nothing you add can hold it. `seatingOf()` in `fins/seating.js` classifies this as
   `point` and the UI says so. Not a bug.
 - `voron_drive_frame` at 0° — its only overhangs are two 25 mm² regions sitting
   0.5 mm off the plate with a 5.1 mm span. Correctly not worth a wall.

docs/PERFORMANCE-SPEC.md

@@ -11,7 +11,8 @@ Repo: `~/projects/support-fins` (product **Support Fins**). The generation engin
 is pure mesh math (no DOM/three.js), so it profiles and runs headless with Deno.
 
 - `web/fins.js` — `buildFins()` entry; auto mode recurses to `mode:'prop'`, then
-  adds wedges (`buildPerpFins`) and the bed pad (`buildPad`).
+  adds wedges (`buildPerpFins`, `web/fins/wedges.js`) and the bed pad (`buildPad`,
+  `web/fins/pad.js`).
 - `web/prop.js` — `buildProps()`, which drives the per-wall pipeline in `web/prop/`:
   `splitRegion`/`patchTracks` (tracks.js), `sweep` (sweep.js),
   `settleTop`/`contourTop`/`lowerSag` (contact.js), `stationIsClear`/`stationCertified`

plugins/onshape/supportFins.fs

@@ -225,7 +225,7 @@ const FIN_WIDE_AREA     = 1500 * millimeter ^ 2;
 const FIN_ROW_PITCH     = 55.0 * millimeter;
 const FIN_ROW_MAX       = 20;
 
-// Bed pad -- web/fins.js buildPad
+// Bed pad -- web/fins/pad.js buildPad
 const PAD_MARGIN        = 4.0 * millimeter;       // grip spread past the contact
 const PAD_MIN_AREA      = 60.0 * millimeter ^ 2;  // above this much bed contact no pad is needed
 const PAD_SEGS          = 48;
@@ -1856,7 +1856,7 @@ function buildFinAt(context is Context, fid is Id, env is map, s is map, win is
     return { "ok" : true, "tines" : count };
 }
 
-// ─── Bed pad (web/fins.js buildPad) ───────────────────────────────────────────
+// ─── Bed pad (web/fins/pad.js buildPad) ───────────────────────────────────────
 
 /**
  * A part tilted onto an edge has near-zero bed contact and peels before any fin

tests/unserved.test.js

@@ -1,7 +1,7 @@
 // UNSERVED must count dropped overhangs, not hide them. buildFins used to report
 // `unserved - wedged PATCHES`: a patch count off a region count (two different
 // segmentations), so wedges under one region hid others that nothing supports.
-// Credit is spatial now (fins.js unservedAfterWedges): a region is served when a
+// Credit is spatial now (fins/wedges.js unservedAfterWedges): a region is served when a
 // wall stands under it or a wedge vertex sits just under one of its faces.
 import { loadModel, analyze, fins, assert, rotX, rotY } from './_util.js';
 

web/fins.js

@@ -1,14 +1,9 @@
 /**
- * Fin generation -- M4. The fin stands BESIDE the part on a flat upright face,
- * held off by a standoff, and horizontal tines fuse across that gap into the
- * part. See planes.js for why M3's sweep-under-the-overhang geometry had to be
- * abandoned, and docs/FIN-SPEC.md for where every number below comes from.
- *
- * A fin is three kinds of solid that overlap and get unioned by the slicer -- no
- * boolean kernel anywhere, the same approach the rest of the project uses:
- *   1. the WALL, a thin round-topped blade standing off the part face;
- *   2. the BASE, a wide flat ellipse that keeps the wall stuck to the plate;
- *   3. the TINES, tiny horizontal nubs bridging the standoff into the part.
+ * Combined support -- the entry point the app, the Worker and the plugins call.
+ * `buildFins` builds the tined breakaway walls (prop.js) under the overhangs,
+ * adds angled wedges under the broad downward faces no wall reached, lays a bed
+ * pad under a part that barely touches the plate, and runs sway braces last.
+ * docs/FIN-SPEC.md is where every number comes from.
  *
  * The tines are the point. A wall with only a gap constrains the part in one
  * direction and it falls away sideways -- Slant3D demos a cube doing exactly
@@ -21,10 +16,17 @@
  * a retraction each. Horizontal tines also lie in the plane of the layer lines,
  * which is what lets you BEND them to snap clean instead of tearing them out.
  *
- * Everything about the wall is built in the patch's frame (planes.js), so a fin
- * serving a leaning face leans with it. The tines are the exception: they are
- * built in world axes, because a tine must occupy ONE layer, and a box that is
- * flat in a leaning frame is not flat in z.
+ * LAYOUT. This file is the entry point: `buildFins`, `buildFinsCore` (auto and
+ * prop), `applyTunables`, `coverPitch`, and re-exports of everything app.js,
+ * orient.js, finworker.js, ui/, the plugins and the tests import. The pieces
+ * live in web/fins/:
+ *
+ *   config.js     FIN, the tine, pad and coverage numbers the UI shares
+ *   seating.js    how the part sits on the plate: contact, face/edge/point
+ *   pad.js        PAD and the bed pad (conforming oval, or the brim-style one)
+ *   wedges.js     angled wedges where no wall reaches; gripPatches for Draw
+ *
+ * Each module imports only modules above it in this list and never fins.js.
  */
 import { findWallPatches } from './planes.js';
 import { buildProps, noProps, PROP } from './prop.js';
@@ -90,9 +92,9 @@ export function applyTunables(t) {
  * Generate supports for the part in its current orientation.
  *
  * @param opts.mode     'prop' (the default: a vertical breakaway wall under
- *                      each overhang), 'stabilize' (the Brace: a tined fin
- *                      against toppling; docs/FIN-SPEC.md), or 'auto' (props for
- *                      the overhangs PLUS bracing fins if the part would topple)
+ *                      each overhang, no tines) or 'auto' (tined walls PLUS
+ *                      wedges under the faces no wall reached). 'stabilize' is
+ *                      an old name for 'auto'; any other mode builds 'prop'.
  * @param opts.bedPad   add the pad when bed contact is too small to hold
  */
 export function buildFins(topo, result, rot, opts = {}) {

web/index.html

@@ -223,7 +223,7 @@
        is exposed. Support gap = clearance between a support top and the part (bigger
        = cleaner surface / easier to remove, too big = stops holding the overhang).
        Bed pad = the pad under a part that barely touches the plate (PAD.style in
-       fins.js): Auto (default) picks Light, or Sure hold on a small foot, and
+       fins/pad.js): Auto (default) picks Light, or Sure hold on a small foot, and
        its option text shows which. Light is one layer standing 0.12mm off the part, like a slicer
        brim; Sure hold is the thicker pad tacked into the part; Custom exposes
        every pad number and is the only style that shows them. -->

web/ui/finbuild.js

@@ -220,8 +220,8 @@ export function refreshFins() {
 // reply and the inline fallback. buildFins runs in BOTH modes: in Suggest it
 // places the walls; in Draw it is called only for the bed pad + seating verdict
 // (a tilted part rests on an edge and needs a pad however its walls are placed,
-// and that logic lives in fins.js), so Draw ignores the suggested walls and shows
-// the hand-drawn ones instead.
+// and that logic lives in fins/pad.js + fins/seating.js), so Draw ignores the
+// suggested walls and shows the hand-drawn ones instead.
 function applyBuilt(built) {
   finBusy = false;
   clearSpinner();

web/ui/readout.js

@@ -207,7 +207,7 @@ function updateDrawReadout(built, ms) {
 
 /**
  * The Light pad grips by first-layer squish along the part's first-layer outline.
- * A part on a point or a small round foot has only a few mm of it, so fins.js
+ * A part on a point or a small round foot has only a few mm of it, so fins/pad.js
  * builds Sure hold there instead (pad.autoSure) -- say so, since the user picked
  * Light. A Custom pad with a gap on such a foot gets a warning instead of a swap.
  */

web/ui/settings.js

@@ -55,7 +55,7 @@ el('fin-mode').addEventListener('change', (e) => {
   setGizmo();
   refreshFins();
 });
-// Bed pad style (PAD.style in fins.js). Only Custom shows the pad's numbers; the
+// Bed pad style (PAD.style in fins/pad.js). Only Custom shows the pad's numbers; the
 // presets keep theirs fixed (Sure hold's follow the material profile). Switching
 // to Custom starts it from whichever preset was showing, so a tweak begins from
 // numbers that are known to print rather than from blanks.