feat: consume the boot payload (load-path-rework 0001 §6, client)

useProjectBoot: the tool page tries the ONE composed boot round-trip first —
its project half is the getProject shape — and falls back to the active
source's getProject on any miss (older backend, local-store slug, static
gallery), so downstream behavior without a payload is exactly pre-boot.

With a payload: seedSessionIdentity makes the /api/me flight a resolved
no-op; the synced libs source is constructed with the preloaded listing
(kind-filtered client-side by kindCounts — the same org/mirror-always +
libHasKind rule the server applies) and the batch-resolved stacks, and every
INTERNAL listing (syncState, presync, enableRealtime name-mapping) rides the
preload too; the fresh project-sync digest threads into staging so a warm
restage affirms with zero HTTP.

Measured warm load (Arduino repo-as-project): total API traffic = 1 boot
request + the ydoc-backed per-file set — /api/me, /libs, sync-stacks and
/sync/manifest all at zero.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VLSht9cadprtT2mhynawWu

web/standalone/src/lib/config.ts

@@ -311,7 +311,19 @@ export function modelsSourceConfig(): Model3dSource | null {
     : null;
 }
 
-export function libsSourceConfig(projectId?: string): LibsSource | null {
+/** The boot payload's lib hand-over (see wasm/libs/synced-source.ts). */
+export interface LibsBootPreload {
+  libs: import("@/wasm/libs/synced-source").PreloadedLibDto[];
+  stacks: Record<
+    string,
+    import("@pcbjam/shared").SyncStackDescriptor | null
+  >;
+}
+
+export function libsSourceConfig(
+  projectId?: string,
+  preload?: LibsBootPreload,
+): LibsSource | null {
   const kind = import.meta.env.VITE_LIBS_SOURCE ?? "remote";
   // "local" is the placeholder id for launches with no real backend project
   // (local folder, tool grid, lib-scoped open). It is NOT a project on the
@@ -338,6 +350,7 @@ export function libsSourceConfig(projectId?: string): LibsSource | null {
                   scope: currentScope(),
                   user: userSlug(),
                   project,
+                  preloaded: preload,
                   log: (m) => console.log(m),
                 },
               )