kicad-validity B3+C+S: revert toast, corpus lint, .kicad_mod tier

B3 (editor): kicad-binding observes kdoc_meta.revertNonce (deduped, like
seedNonce) → DOC_REVERTED_EVENT → WasmTool doc-reverted-toast (15 s,
data-testid for the deferred e2e check).
C: tests/tools/corpus-lint.ts (npm run corpus:lint) — kicad_tools --lint
over the fixture corpora raw + shared-codec round-trips
(docToFile(fileToDoc(x))); the E3/wrapInBoardEnvelope-class gate. Skips
when output/kicad_tools.js isn't built; CI step lands when kicad_tools
joins the CI app set. 7 fixtures / 7 round-trips green.
S: --lint + --resave gain the .kicad_mod tier (pcbToolsLintFootprint /
pcbToolsResaveFootprint; writer needs CTL_FOR_LIBRARY or the board flags
strip the (version) header). Verified: qa footprint round-trip lints
clean, resave stamps 20260206, garbage exits 1. Also bumps pcbjam-shared
(mergeYUpdates for the bisect pass).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HLua64PCVwkQ1hpWdaf1Gm

web/standalone/src/components/WasmTool.tsx

@@ -67,6 +67,7 @@ import {
   type FollowTarget,
 } from "@/wasm/collab/follow-user";
 import { startCrossAppPresence, type CrossAppHandle } from "@/wasm/collab/cross-app";
+import { DOC_REVERTED_EVENT } from "@/wasm/collab/kicad-binding";
 import {
   createComments,
   hasCommentsBridge,
@@ -790,6 +791,9 @@ export function WasmTool({
   // A collaborator updated library items that are PLACED in the open document
   // (LIB_ITEM_UPDATED_EVENT) — placed copies keep the previous version, so warn.
   const [libUpdate, setLibUpdate] = React.useState<string | null>(null);
+  // The backend rolled this document back to its last valid state
+  // (kicad-validity 0001 — DOC_REVERTED_EVENT from the collab binding).
+  const [docReverted, setDocReverted] = React.useState<string | null>(null);
   // Eager whole-library idb→wasm load in flight (the ~tens-of-seconds fat-load on
   // first chooser/editor open). Drives a full-cover overlay so the freeze reads as
   // "loading, just slow" rather than a hang. Null when idle; `done/total` count the
@@ -856,14 +860,23 @@ export function WasmTool({
           `placed copies keep the previous version until updated from the library.`,
       );
     };
+    const onDocReverted = (e: Event) => {
+      const d = (e as CustomEvent<{ reason?: string; at?: string }>).detail;
+      setDocReverted(
+        `This document was rolled back to its last valid state — invalid content ` +
+          `was detected${d?.reason ? ` (${d.reason})` : ""}. Recent edits may have been undone.`,
+      );
+    };
     window.addEventListener(LIB_BUSY_EVENT, onBusy);
     window.addEventListener(LIB_ERROR_EVENT, onError);
     window.addEventListener(LIB_ITEM_UPDATED_EVENT, onItemUpdated);
+    window.addEventListener(DOC_REVERTED_EVENT, onDocReverted);
     return () => {
       clearTimeout(busyTimer);
       window.removeEventListener(LIB_BUSY_EVENT, onBusy);
       window.removeEventListener(LIB_ERROR_EVENT, onError);
       window.removeEventListener(LIB_ITEM_UPDATED_EVENT, onItemUpdated);
+      window.removeEventListener(DOC_REVERTED_EVENT, onDocReverted);
     };
   }, []);
 
@@ -881,6 +894,13 @@ export function WasmTool({
     return () => clearTimeout(t);
   }, [libUpdate]);
 
+  // Auto-dismiss the doc-reverted toast (longest — the user should see it).
+  React.useEffect(() => {
+    if (!docReverted) return;
+    const t = setTimeout(() => setDocReverted(null), 15_000);
+    return () => clearTimeout(t);
+  }, [docReverted]);
+
   // Full-library eager load overlay. The fat-load fires one loading:true/false
   // pair PER library (222 on the full set), and between them the C++ side parses
   // with the main thread blocked. Show immediately on `true`, and only hide after
@@ -1647,6 +1667,18 @@ export function WasmTool({
         </button>
       )}
 
+      {/* Backend rolled this doc back to the last valid state (kicad-validity). */}
+      {docReverted && (
+        <button
+          data-testid="doc-reverted-toast"
+          className="absolute left-1/2 top-3 z-40 max-w-md -translate-x-1/2 rounded bg-orange-950/95 px-3 py-2 text-center text-xs text-orange-100 shadow-lg ring-1 ring-orange-500/40"
+          onClick={() => setDocReverted(null)}
+          title="Dismiss"
+        >
+          {docReverted}
+        </button>
+      )}
+
       {!effectiveChromeHidden && (
         <div className="absolute bottom-0 left-0 right-0 z-20">
           <button

web/standalone/src/wasm/collab/kicad-binding.ts

@@ -15,6 +15,9 @@ import {
   wireItemUuids,
   wireLibSymbols,
   Y_KDOC_META,
+  Y_KDOC_REVERT_AT,
+  Y_KDOC_REVERT_NONCE,
+  Y_KDOC_REVERT_REASON,
   Y_KDOC_SEED_NONCE,
   ydocHasState,
   ydocSexprVersion,
@@ -44,6 +47,12 @@ import { clog, cwarn } from "./debug";
  * fake editor bridge (kicad-binding.test.ts).
  */
 
+/**
+ * Window event fired when the backend rolled this doc back to its last valid
+ * state (kicad-validity 0001 B3). detail: { reason?: string; at?: string }.
+ */
+export const DOC_REVERTED_EVENT = "pcbjam:doc-reverted";
+
 /** The v2 per-item s-expr bridge (Stage C C++ contract), runtime-adapted. */
 export interface KicadItemsBridge {
   /** Full current model as an all-`added` ItemsWireDelta JSON. */
@@ -192,6 +201,31 @@ export function bindKicadCollab(
   };
   items.observeDeep(observer);
 
+  // Validity-revert notice (kicad-validity 0001 B3): the backend stamps
+  // kdoc_meta.revertNonce when it rolls the doc back to the last valid state
+  // (the content itself arrives through the normal item sync above). Watched
+  // like seedNonce; surfaced as a window event for the shell's toast. The
+  // nonce is deduped so a reconnect replaying the same marker stays silent.
+  const revMeta = doc.getMap(Y_KDOC_META);
+  let lastRevertNonce = revMeta.get(Y_KDOC_REVERT_NONCE);
+  const onRevertMeta = () => {
+    const nonce = revMeta.get(Y_KDOC_REVERT_NONCE);
+    if (nonce === undefined || nonce === lastRevertNonce) return;
+    lastRevertNonce = nonce;
+    clog("doc reverted by backend:", revMeta.get(Y_KDOC_REVERT_REASON));
+    if (typeof window !== "undefined") {
+      window.dispatchEvent(
+        new CustomEvent(DOC_REVERTED_EVENT, {
+          detail: {
+            reason: revMeta.get(Y_KDOC_REVERT_REASON),
+            at: revMeta.get(Y_KDOC_REVERT_AT),
+          },
+        }),
+      );
+    }
+  };
+  revMeta.observe(onRevertMeta);
+
   function seed(seedDoc?: KicadDoc, opts?: { editorMatchesDoc?: boolean }): void {
     seeded = true; // open the UP gate; everything below runs synchronously
     // `ydocHasState` (meta + layout + items), NOT `items.size`: a populated
@@ -344,6 +378,7 @@ export function bindKicadCollab(
       detachSeedArbitration?.();
       detachSeedArbitration = undefined;
       items.unobserveDeep(observer);
+      revMeta.unobserve(onRevertMeta);
     },
     items,
   };