read-only-viewer 0003: no lib catalog for viewers; 3D viewer from the session menu

- kicadShow3DViewer embind (pcbnew-only name, registered in the unguarded
  section so the merged kicad_editor image carries it): runOnCoroutine →
  ACTIONS::show3DViewer.
- Session menu: "3D viewer" row (pcbnew) — the only 3D entry once the wx
  chrome is hidden. Runs the deferred model prescan first.
- Read-only sessions: skip the boot-time enableRealtime scope-room socket
  (would 401 for non-members) and defer the board's 3D-model prescan until
  the viewer is opened (deferBoardModelPrescan / runDeferredModelPrescan).
- kicad submodule → read-only allowlist for the 3D viewer actions.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PXCntRWNn89M72EkrqMkvc

web/standalone/src/components/WasmTool.tsx

@@ -118,9 +118,11 @@ import {
   waitForWxUi,
 } from "@/components/wasm-tool/collab-start";
 import { installQuitHook } from "@/components/wasm-tool/quit-hook";
+import { runDeferredModelPrescan } from "@/wasm/libs/models-bridge";
 import { installToolNavigationHook } from "@/components/wasm-tool/tool-navigation";
 import {
   chromeSetter,
+  show3DOpener,
   COLLAB_TOOLS,
   INSPECTOR_OPEN_KEY,
   LAYERS_OPEN_KEY,
@@ -1065,6 +1067,8 @@ export function WasmTool({
           slug,
           files,
           targetPath,
+          // Viewers fetch 3D bodies only if they open the viewer (session menu).
+          deferModelPrescan: readOnly,
           // ydoc source with a populated room: the target file's bytes come
           // from the doc; everything else (sibling files) still fetches.
           fetchBytes:
@@ -1386,7 +1390,10 @@ export function WasmTool({
         // DOCUMENT references — a peer editing a PLACED symbol must still
         // reach this session live (lib-update toast); everything else syncs
         // on the next load. Fire-and-forget: boot never waits on sockets.
-        if (targetPath && source?.enableRealtime) {
+        // Read-only sessions carry no editable libs (the boot payload is
+        // model3d-only for them) and may not open the team's scope room —
+        // skip the socket rather than collect a 401.
+        if (targetPath && source?.enableRealtime && !readOnly) {
           const staged = readStagedFile(win, slug, targetPath);
           const nicks = staged
             ? usedLibNicknames(new TextDecoder().decode(staged))
@@ -1472,6 +1479,22 @@ export function WasmTool({
     [ready],
   );
 
+  // kicadShow3DViewer — the session-menu 3D entry (read-only-viewer / hide-UI
+  // have no wx View menu). Runs the deferred model prescan first so a viewer's
+  // first open resolves its refs from MEMFS instead of one C++ ensure each.
+  const show3DFn = React.useMemo(() => {
+    if (!ready || tool !== "pcbnew") return null;
+    const open = show3DOpener(window);
+    if (!open) return null;
+    return () => {
+      void runDeferredModelPrescan()
+        .catch((e) => append(`[3d] deferred prescan failed: ${String(e)}`))
+        .then(() => {
+          if (!open()) append("[3d] kicadShow3DViewer: no board frame");
+        });
+    };
+  }, [ready, tool, append]);
+
   // Layer bridge (viewer-panels), pcbnew sessions only — the merged bundle
   // exports the names for every frame, but they no-op on a non-PCB frame.
   const layersMod = React.useMemo<LayersModule | null>(() => {
@@ -1604,6 +1627,7 @@ export function WasmTool({
           canToggleChrome={setChromeFn !== null}
           chromeHidden={chromeHidden}
           onToggleChrome={() => toggleChromeHidden()}
+          onShow3D={show3DFn}
         />
       )}
 

web/standalone/src/components/wasm-tool/SessionMenu.tsx

@@ -2,6 +2,7 @@
 import * as React from "react";
 import {
   AlertTriangle,
+  Box,
   Crosshair,
   EyeOff,
   Layers,
@@ -155,6 +156,7 @@ export function SessionMenu({
   canToggleChrome,
   chromeHidden,
   onToggleChrome,
+  onShow3D,
 }: {
   tool: Tool;
   readOnly: boolean;
@@ -184,6 +186,9 @@ export function SessionMenu({
   canToggleChrome: boolean;
   chromeHidden: boolean;
   onToggleChrome: () => void;
+  /** Open the board's 3D viewer (pcbnew only); null when the bundle lacks
+   *  the bridge. The only 3D entry point once the wx menus are hidden. */
+  onShow3D: (() => void) | null;
 }) {
   return (
     <OverlayMenu
@@ -279,6 +284,17 @@ export function SessionMenu({
             <span>{inspectorOpen ? "Hide inspector" : "Inspector"}</span>
           </button>
         )}
+        {tool === "pcbnew" && onShow3D && (
+          <button
+            data-testid="show-3d-viewer"
+            className={overlayRowClass}
+            title="Open the 3D viewer"
+            onClick={onShow3D}
+          >
+            <Box size={14} className="shrink-0 text-neutral-400 dark:text-white/50" />
+            <span>3D viewer</span>
+          </button>
+        )}
         {canToggleChrome && !readOnly && (
           <button
             data-testid="chrome-toggle"

web/standalone/src/components/wasm-tool/ui-helpers.ts

@@ -20,6 +20,15 @@ export function chromeSetter(win: Window): ((show: boolean) => boolean) | null {
   return typeof fn === "function" ? (fn as (show: boolean) => boolean) : null;
 }
 
+/** kicadShow3DViewer (pcbnew bundle): opens the 3D viewer from the session
+ *  menu — the one way to reach it when the wx chrome is hidden (read-only
+ *  viewer / hide-UI). Null on bundles without it. */
+export function show3DOpener(win: Window): (() => boolean) | null {
+  const fn = (win as { Module?: { kicadShow3DViewer?: unknown } }).Module
+    ?.kicadShow3DViewer;
+  return typeof fn === "function" ? (fn as () => boolean) : null;
+}
+
 // Viewer panels (viewer-panels): floating layer selector + selection
 // inspector open-state persistence, mirroring the comments panel's keys.
 export const LAYERS_OPEN_KEY = "pcbjam:layers-panel-open";

web/standalone/src/wasm/kicad-runner.ts

@@ -4,7 +4,7 @@ import { SyncStack } from "@pcbjam/sync-client";
 import { defaultKicadPro } from "../lib/new-file";
 import { memfsFilePath, memfsProjectDir } from "./constants";
 import { mark } from "./load-trace";
-import { prescanBoardModels } from "./libs/models-bridge";
+import { deferBoardModelPrescan, prescanBoardModels } from "./libs/models-bridge";
 import { openFileInTool } from "./open-flow";
 
 /**
@@ -65,6 +65,9 @@ export interface DriveOptions {
    *  the boot overlay's "Project files — n/m" line. Reported once up front
    *  with done=0 so the line appears as soon as staging starts. */
   onFileProgress?: (done: number, total: number) => void;
+  /** Read-only sessions: park the board's 3D prescan until the viewer opens
+   *  (runDeferredModelPrescan) instead of prefetching every model at open. */
+  deferModelPrescan?: boolean;
 }
 
 const sleep = (ms: number) => new Promise((r) => setTimeout(r, ms));
@@ -169,9 +172,11 @@ async function syncProjectToMemfs(win: ToolWindow, opts: DriveOptions): Promise<
     // ensure. No-op unless a model source is installed (bootKicadTool).
     if (path.endsWith(".kicad_pcb")) {
       const text = new TextDecoder().decode(bytes);
-      void prescanBoardModels(text).catch((e) =>
-        opts.log(`[3d] prescan failed: ${String(e)}`),
-      );
+      if (opts.deferModelPrescan) deferBoardModelPrescan(text);
+      else
+        void prescanBoardModels(text).catch((e) =>
+          opts.log(`[3d] prescan failed: ${String(e)}`),
+        );
     }
   };
 

web/standalone/src/wasm/libs/models-bridge.test.ts

@@ -3,6 +3,8 @@ import {
   collectBoardModelFiles,
   ensureModelInMemfs,
   installModel3dHandler,
+  deferBoardModelPrescan,
+  runDeferredModelPrescan,
   normalizeModelRef,
   scanModelRefs,
 } from "./models-bridge";
@@ -168,3 +170,48 @@ describe("scanModelRefs", () => {
     expect(scanModelRefs("(kicad_pcb (version 20240101))")).toEqual([]);
   });
 });
+
+describe("deferred board prescan (read-only sessions)", () => {
+  function installCounting() {
+    const files = new Map<string, Uint8Array>();
+    const fs = {
+      mkdirTree: () => {},
+      writeFile: (p: string, b: Uint8Array) => void files.set(p, b),
+      analyzePath: (p: string) => ({ exists: files.has(p) }),
+    };
+    (globalThis as unknown as { window: unknown }).window ??= globalThis;
+    // The prescan emits its progress event on window (node: bare globalThis).
+    (globalThis as unknown as { dispatchEvent?: unknown }).dispatchEvent ??= () => true;
+    (globalThis as unknown as { FS: unknown }).FS = fs;
+    let fetches = 0;
+    const source: Model3dSource = {
+      getModelBody: async (ref) => {
+        fetches++;
+        return new TextEncoder().encode(`body:${ref}`);
+      },
+      hasModel: async () => true,
+    };
+    installModel3dHandler(source, () => {});
+    return { files, fetches: () => fetches };
+  }
+
+  it("fetches nothing at defer time and everything on the first run", async () => {
+    const t = installCounting();
+    deferBoardModelPrescan(
+      '(model "${KICAD10_3DMODEL_DIR}/DeferLib.3dshapes/A.step") (model "${KICAD10_3DMODEL_DIR}/DeferLib.3dshapes/B.step")',
+    );
+    expect(t.fetches()).toBe(0);
+    await runDeferredModelPrescan();
+    expect(t.fetches()).toBe(2);
+    expect(t.files.has("/pcbjam/3dmodels/DeferLib.3dshapes/A.step")).toBe(true);
+    // Consumed: a second open does not re-scan.
+    await runDeferredModelPrescan();
+    expect(t.fetches()).toBe(2);
+  });
+
+  it("is a no-op when nothing was deferred", async () => {
+    const t = installCounting();
+    await runDeferredModelPrescan();
+    expect(t.fetches()).toBe(0);
+  });
+});

web/standalone/src/wasm/libs/models-bridge.ts

@@ -240,6 +240,30 @@ export async function collectBoardModelFiles(
   return out;
 }
 
+/** Board text whose prescan was deferred (read-only sessions): run on the
+ *  first 3D open via {@link runDeferredModelPrescan}. */
+let deferredBoardText: string | null = null;
+
+/**
+ * Read-only viewers download nothing 3D until they actually open the viewer:
+ * park the board text instead of prescanning it at project open. The last
+ * board staged wins (one board per session).
+ */
+export function deferBoardModelPrescan(boardText: string): void {
+  deferredBoardText = boardText;
+}
+
+/** Run the parked prescan (no-op when nothing was deferred or it already ran).
+ *  Resolves when the models are in MEMFS, so a caller can open the 3D viewer
+ *  right after and have it resolve refs locally (the per-model C++ ensure
+ *  still covers any miss). */
+export async function runDeferredModelPrescan(): Promise<void> {
+  const text = deferredBoardText;
+  if (text === null) return;
+  deferredBoardText = null;
+  await prescanBoardModels(text);
+}
+
 /**
  * Prefetch every model a board references (fire-and-forget from the project
  * sync). Bodies land in IDB + MEMFS before the user opens the 3D viewer in the
@@ -250,6 +274,7 @@ export async function prescanBoardModels(
   concurrency = 6,
 ): Promise<void> {
   if (!installedSource) return;
+  deferredBoardText = null;
   const refs = scanModelRefs(boardText);
   if (!refs.length) return;