fix(standalone): never let the boot-time default-lib create blank the lib tables

Anonymous open of a public project (read-only viewer): boot saw no writable
lib, POSTed createLib("My Symbols"), the session gate 401'd, and the throw
escaped the listLibs try/catch — both sym/fp lib tables were seeded EMPTY for
the session (staging: /tg44/projects/arduino/... Arduino Leonardo.kicad_sch).

- ensureWritableLib(): skipped for readOnly sessions; a failed create is
  logged and swallowed, never propagated (the listed libs stay seeded).
- WasmTool passes readOnly through to boot.
- unit tests for the skip / create / already-writable / rejected-create paths.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CtN6ASBvMGNbjPqY5boycg

web/standalone/src/components/WasmTool.tsx

@@ -997,6 +997,10 @@ export function WasmTool({
           // frame token tells its single_top launcher which editor frame to open.
           frame: TOOL_FRAME[tool],
           mobile: mobileUi,
+          // Viewers can't write: skip the boot-time default-lib create (a
+          // session-gated POST that 401s anonymously and used to blank the
+          // lib tables — anonymous public-schematic open on staging).
+          readOnly,
         });
         // Identity must be settled before the doc session / presence binds
         // below — effectively instant, it raced the multi-second wasm boot.

web/standalone/src/wasm/boot.test.ts

@@ -1,5 +1,6 @@
 import { afterEach, describe, expect, it, vi } from "vitest";
 import {
+  ensureWritableLib,
   hasWritableLib,
   installPthreadWorkerRedirect,
   pthreadWorkerScript,
@@ -28,6 +29,57 @@ describe("hasWritableLib", () => {
   });
 });
 
+/**
+ * Boot-time default-lib create. Regression: an anonymous viewer of a public
+ * project has no writable lib, so boot POSTed createLib, the session gate
+ * 401'd, and the throw escaped the caller's try — seeding EMPTY lib tables.
+ */
+describe("ensureWritableLib", () => {
+  const log = () => {};
+
+  it("skips the create entirely for read-only sessions", async () => {
+    const createLib = vi.fn(async () => lib("org"));
+    const lists = [[lib("origin")]];
+    expect(await ensureWritableLib({ createLib }, lists, { readOnly: true, log })).toBeNull();
+    expect(createLib).not.toHaveBeenCalled();
+    expect(lists[0]).toHaveLength(1);
+  });
+
+  it("creates once and joins every per-kind list when nothing writable is listed", async () => {
+    const created = lib("org");
+    const createLib = vi.fn(async () => created);
+    const sym = [lib("origin")];
+    const fp = [lib("mirror")];
+    expect(await ensureWritableLib({ createLib }, [sym, fp], { log })).toBe(created);
+    expect(createLib).toHaveBeenCalledWith("My Symbols");
+    expect(sym).toContain(created);
+    expect(fp).toContain(created);
+  });
+
+  it("does nothing when a writable lib already exists", async () => {
+    const createLib = vi.fn(async () => lib("org"));
+    await ensureWritableLib({ createLib }, [[lib("user")]], { log });
+    expect(createLib).not.toHaveBeenCalled();
+  });
+
+  it("swallows a rejected create (401) and leaves the listed libs intact", async () => {
+    const createLib = vi.fn(async () => {
+      throw new Error("401");
+    });
+    const logs: string[] = [];
+    const sym = [lib("origin"), lib("mirror")];
+    await expect(
+      ensureWritableLib({ createLib }, [sym], { log: (m) => logs.push(m) }),
+    ).resolves.toBeNull();
+    expect(sym).toHaveLength(2);
+    expect(logs.some((m) => /non-fatal/.test(m))).toBe(true);
+  });
+
+  it("is a no-op for sources without createLib", async () => {
+    expect(await ensureWritableLib({}, [[lib("origin")]], { log })).toBeNull();
+  });
+});
+
 /**
  * Cross-origin (CDN) pthread spawn fix — doc-23 §7 KNOWN GAP. Emscripten
  * spawns pthread workers from the glue's absolute URL; when that URL is the

web/standalone/src/wasm/boot.ts

@@ -41,6 +41,38 @@ export function hasWritableLib(lists: Iterable<LibInfo[]>): boolean {
   );
 }
 
+/**
+ * Ensure the owner has at least one writable lib to save items into, creating
+ * the default one when none is listed. A writable lib holds either kind, so a
+ * created lib joins every per-kind list (mutated in place).
+ *
+ * Skipped outright for read-only sessions (anonymous viewer of a public
+ * project, read-only-viewer): they cannot write, so there is nothing to save
+ * into — and the create is a session-gated POST that 401s for them. Best-effort
+ * either way: a failed create (401/403, backend without the route, a network
+ * blip) is logged and swallowed, NEVER propagated — an exception here used to
+ * escape the caller's listLibs try/catch and seed EMPTY lib tables for the
+ * whole session (observed on staging: anonymous open of a public schematic).
+ */
+export async function ensureWritableLib(
+  source: Pick<LibsSource, "createLib">,
+  listsByKind: Iterable<LibInfo[]>,
+  opts: { readOnly?: boolean; log: (msg: string) => void; name?: string },
+): Promise<LibInfo | null> {
+  const lists = [...listsByKind];
+  if (opts.readOnly || !source.createLib || hasWritableLib(lists)) return null;
+  try {
+    const created = await source.createLib(opts.name ?? DEFAULT_USER_LIB_NAME);
+    if (!created) return null;
+    for (const libs of lists) libs.push(created);
+    opts.log(`[libs] created default user lib "${created.name}"`);
+    return created;
+  } catch (e) {
+    opts.log(`[libs] default user lib create failed (non-fatal): ${String(e)}`);
+    return null;
+  }
+}
+
 /**
  * Boot a KiCad tool directly in the main React document — no iframe.
  *
@@ -116,6 +148,9 @@ export interface BootOptions {
    *  only — chrome visibility is owned by the shell's chrome-visibility store
    *  (WasmTool applies it via kicadSetChrome). */
   mobile?: boolean;
+  /** Read-only session (anonymous/public viewer): never attempt writes at
+   *  boot — in particular no default-user-lib create (see ensureWritableLib). */
+  readOnly?: boolean;
 }
 
 let booted: { tool: Tool; promise: Promise<void> } | null = null;
@@ -363,6 +398,7 @@ async function doBoot(opts: BootOptions): Promise<void> {
     libsSource,
     modelsSource,
     enumerateGate,
+    readOnly,
   } = opts;
   // Truthful fetch label: a warm start (download-completion marker present)
   // reads from the HTTP cache, so "Downloading" would be a lie — and vice versa.
@@ -436,15 +472,9 @@ async function doBoot(opts: BootOptions): Promise<void> {
       // kind-agnostic containers and appear in every list).
       const listsByKind = new Map<"symbol" | "footprint", LibInfo[]>();
       for (const k of libKinds) listsByKind.set(k, await libsSource.listLibs(k));
-      // Ensure the owner has at least one writable lib to save items into.
+      // Ensure the owner has at least one writable lib to save items into
-      // A writable lib holds either kind, so the created lib joins every table.
+      // (skipped read-only; never throws — a failure must not empty the tables).
-      if (libsSource.createLib && !hasWritableLib(listsByKind.values())) {
+      await ensureWritableLib(libsSource, listsByKind.values(), { readOnly, log });
-        const created = await libsSource.createLib(DEFAULT_USER_LIB_NAME);
-        if (created) {
-          for (const libs of listsByKind.values()) libs.push(created);
-          log(`[libs] created default user lib "${created.name}"`);
-        }
-      }
       const symList = listsByKind.get("symbol");
       const fpList = listsByKind.get("footprint");
       if (symList) {