feat(ysync): lib_symbols travel + layout save-sync (miss 08), TS hot-path opts (12), diff-on-rebind adopt (13) — doc 18

Miss 08A: the binding stores wire-carried (lib_symbols …) definitions in
kdoc_libsymbols and prefixes them on apply wires — a joiner that never saw a
symbol adopts it WITH its definition (new e2e ysync-libsymbols.spec.ts).
Miss 08B: registerSaveHook gains onSavedText; WasmTool routes saved-file text
to syncLayoutToY (per sheet room via the manager's syncLayoutFromSave, or the
single-room doc) so title block / paper / setup edits converge instead of
drifting. Opt 12 (TS half): zod off the observer hot path (yToItemUnchecked),
children index built once per conversion. Opt 13: seed()'s adopt diffs the
editor snapshot against the doc view and applies only the doc-authoritative
difference — clean rebinds apply nothing, the adopt undo entry shrinks to the
real changed set. Opt 14 deliberately deferred (doc 18). All TS-side; no wasm
rebuild (the C++ blob/findLib sides already carried definitions).

Verified: shared 107, standalone 79 (+2 known pre-existing wasm-assets),
ysync e2e 21/21 chromium, collab regression 21/3-skip firefox.

Bumps: web/pcbjam-shared (lib_symbols channel + syncLayoutToY + opts).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JgThWXtdvrYLK47EDFoGdq

docs/features/ysync-review/00-overview.md

@@ -93,3 +93,4 @@ sending half emits NOTHING, not the bare removal the doc predicted).
 | 15 | [15-plan-repro-tests-and-v2-e2e.md](15-plan-repro-tests-and-v2-e2e.md) | The approved plan: repro tests for bugs 01–07 + the v2 e2e port |
 | 16 | [16-repro-suite-results-and-empirical-findings.md](16-repro-suite-results-and-empirical-findings.md) | Plan 15 executed (2026-07-03): suite map, verified failure sites, empirical findings F1–F4 |
 | 17 | [17-fixes-bugs-01-07.md](17-fixes-bugs-01-07.md) | Bugs 01–07 fixed & verified (2026-07-03); findings F5–F6; remaining follow-ups |
+| 18 | [18-miss08-opts-12-13.md](18-miss08-opts-12-13.md) | Miss 08 (lib_symbols + layout save-sync) + opts 12/13 implemented; opt 14 deferred (2026-07-03) |

docs/features/ysync-review/08-miss-layout-state-never-syncs.md

@@ -1,7 +1,7 @@
 # Design miss 08 — Non-item document state only syncs at seed; `lib_symbols` is a landmine for the symbol-libraries milestone
 
 **Severity:** design gap (silent divergence for settings edits; structural blocker later)
-**Status:** open decision
+**Status:** IMPLEMENTED 2026-07-03 — see [18](18-miss08-opts-12-13.md) (lib_symbols channel + coarse layout save-sync; nets stay seed-frozen by design)
 
 ## Where
 

docs/features/ysync-review/12-opt-hot-path-full-model-work.md

@@ -1,7 +1,7 @@
 # Optimization 12 — O(full-model) work on every edit, apply, and remote batch
 
 **Severity:** performance (fine on demo boards; seconds-per-edit territory at 5–10k items)
-**Status:** open
+**Status:** TS items DONE 2026-07-03 (zod off the observer path, children index once — see [18](18-miss08-opts-12-13.md)); C++ item 1 delivered by [17](17-fixes-bugs-01-07.md) batch 3 except the scalar-scan/legacy-wire retirement (goes with the legacy-wire removal)
 
 ## The costs, per hot path
 

docs/features/ysync-review/13-opt-parked-dirty-full-sheet-replace.md

@@ -1,7 +1,7 @@
 # Optimization 13 — Parked-dirty sheet rebind re-applies the entire sheet instead of the delta
 
 **Severity:** performance + UX (heavy on big sheets; creates the adopt undo-bomb)
-**Status:** open
+**Status:** FIXED 2026-07-03 — option 2 (diff on rebind) — see [18](18-miss08-opts-12-13.md)
 
 ## Where
 

docs/features/ysync-review/14-opt-item-granularity-bandwidth.md

@@ -1,7 +1,7 @@
 # Optimization 14 — Item-level body granularity: whole-item payloads per nudge, LWW drops concurrent property edits
 
 **Severity:** known/documented v1 tradeoff — recorded here so its costs are visible when prioritizing
-**Status:** open (deliberate design decision; revisit trigger below)
+**Status:** open (deliberate design decision; revisit trigger below — reaffirmed 2026-07-03, see [18](18-miss08-opts-12-13.md))
 
 ## Where
 

docs/features/ysync-review/18-miss08-opts-12-13.md

@@ -0,0 +1,102 @@
+# Miss 08 + opts 12/13 implemented; opt 14 deliberately deferred (2026-07-03)
+
+**Status:** miss [08](08-miss-layout-state-never-syncs.md) (both halves), opt
+[12](12-opt-hot-path-full-model-work.md)'s TS items, and opt
+[13](13-opt-parked-dirty-full-sheet-replace.md) implemented and verified. All
+TS/shared-side — the C++ already did its part (eeschema's `itemBlob` emits the
+`lib_symbols` context; `doApplyItems`' `findLib` was designed to prefer a
+blob-carried definition), so no WASM rebuild was needed.
+
+## 08A — lib_symbols channel
+
+- New `kdoc_libsymbols` Y.Map (lib id → `(symbol …)` definition text): concurrent
+  placements of DIFFERENT symbols merge per definition instead of LWW-clobbering
+  one layout slot.
+- `docToY` extracts the layout's `(lib_symbols …)` definitions into the map and
+  keeps the layout slot EMPTY (the injection point); `yToDoc` re-injects the
+  map's definitions sorted by lib id — the order KiCad's own writer emits, so
+  materialization matches editor saves.
+- Emit direction: `wireLibSymbols(wire)` recovers definitions from the
+  multi-form clipboard blob (`unwrapWireItem` still strips them from the ITEM
+  payload); the binding stores them in the same transaction as the item delta.
+- Apply direction: `deltaToItemsWire(delta, view, libDefs)` prefixes a root
+  item carrying `(lib_id …)` with its definition — exactly the multi-form shape
+  eeschema's paste path parses, so `findLib`'s first branch resolves it and a
+  peer that has never seen the symbol renders it correctly.
+- e2e: `tests/kicad/ysync-libsymbols.spec.ts` — a joiner whose cold copy lacks
+  the symbol adopts it WITH its definition (chromium two-tab; F2 applies).
+
+## 08B — coarse layout save-sync
+
+- New shared `syncLayoutToY(fileDoc, ydoc, origin)`: reconciles non-item layout
+  slots per HEAD KEYWORD group (title block, paper, setup, settings…) from a
+  just-saved file — a changed group is replaced wholesale (LWW at head
+  granularity; different heads merge). `{item}` slots are never touched.
+- Deliberate freezes: `net` (pcbnew's root net table — net-creating edits are
+  not possible in the standalone; repeated positional heads can't be reconciled
+  by name) stays seed-frozen; `lib_symbols` routes to the defs map ADDITIVELY
+  (a save can't know about a peer's not-yet-applied placement).
+- Wiring: `registerSaveHook` gained `onSavedText` (decoded saved text);
+  WasmTool routes it — eeschema per sheet via the manager's new
+  `syncLayoutFromSave` (parked rooms sync too; the dirty mark it causes costs
+  only the real delta now, see opt 13), pcbnew/pl_editor via the single-room
+  doc.
+- Known limitation (unchanged from the doc's "coarse but converging"): a peer's
+  EDITOR does not live-update non-item state — the room doc converges, so
+  materialization/reopen and drift-detect see it; live propagation into an open
+  editor's title block would need a C++ apply for non-item state.
+
+## Opt 12 — TS hot-path (items 2 + 4)
+
+- `yToItemUnchecked` (no zod) feeds the binding's `itemsView()` — both hot
+  directions (every local emit, every remote batch). zod stays at the trust
+  boundaries: wire parse, seed, materialize.
+- `itemsWireToDelta` builds the parent→children index ONCE per conversion
+  (was: full-scan `descendants()` per wire item and per removed id).
+- NOT taken from doc 12: retiring the C++ scalar scan + legacy emit (the scan
+  still feeds the legacy wire and covers eeschema's unreported post-Push
+  connectivity cleanup — retire it together with the legacy-wire removal,
+  miss 11 follow-up), and the lazy `deltaToItemsWire` view (item 3) — killing
+  zod removed the dominant cost; revisit if profiling says otherwise.
+
+## Opt 13 — diff-on-rebind adopt (option 2)
+
+`seed()`'s adopt no longer renders and re-applies EVERY doc root. It diffs the
+editor snapshot against the doc view (`itemsWireToDelta` + `wireItemUuids`) and
+applies only the doc-authoritative difference:
+
+- doc-only ROOTS → added (their sexprs embed descendants; a doc-only child makes
+  its shared parent differ and rides the parent's re-apply);
+- differing items → the DOC's version re-applied, lifted to their root (the C++
+  upsert replaces roots; a bare child apply would mis-parent);
+- editor-only ROOTS → removed (editor-only children vanish with their parent's
+  re-apply).
+
+An empty diff degrades to baseline-only — the parked-dirty rebind, the clean
+revisit, and the cold divergent adopt now share one code path, and the adopt's
+single commit (and undo entry — the miss-09 "adopt undo bomb") shrinks to the
+real changed set.
+
+## Opt 14 — deferred, on purpose
+
+The slot-level CRDT refinement is a meaningful rewrite of `kicad-y`'s write path
+plus the whole conversion layer, with real interleaving-anomaly risk. Doc 14's
+own revisit triggers (measured bandwidth/storage cost; concurrent same-item UX
+complaints) are unmet, and the flatten already gives per-child granularity.
+Nothing in this batch forecloses it — `body` stayed one JSON value.
+
+## Verification
+
+- pcbjam-shared: 107 (9 new in `test/layout-libsymbols-sync.test.ts`)
+- standalone: 79 + 2 known pre-existing wasm-assets fixture failures
+  (collab suite 42, incl. 3 new diff-adopt + 2 lib_symbols binding tests;
+  save-flow +2)
+- e2e (chromium): full ysync set + `ysync-libsymbols.spec.ts` green
+- No C++ changes; no WASM rebuild.
+
+## Remaining from the review
+
+Misses [09](09-miss-undo-not-collab-aware.md) (collab-aware undo — the adopt
+shrink here removes its worst case) and [10](10-miss-no-repair-path.md) (drift
+repair), opt 12's C++ retirement half (with the legacy-wire removal), opt 14
+(triggers above), and doc 17's carried-over follow-ups.

tests/kicad/ysync-libsymbols.spec.ts

@@ -0,0 +1,195 @@
+import * as path from "path";
+import type { Page } from "@playwright/test";
+import { test, expect } from "./fixtures";
+
+/**
+ * Miss 08A e2e — embedded library definitions travel the v2 wire.
+ *
+ * A schematic symbol is only renderable with its `(lib_symbols …)` definition.
+ * The TS layer used to strip that envelope ("sender context") so a peer that
+ * had never seen the symbol received a definition-less instance and the room's
+ * materialization referenced a lib id it didn't contain. Now definitions live
+ * in `kdoc_libsymbols` and are re-prefixed on every apply wire.
+ *
+ * Two kicad_editor instances → Firefox's per-process wasm budget (finding F2):
+ * chromium only, like the other two-tab specs.
+ */
+
+const SYM1 = "44444444-0000-0000-0000-000000000001";
+const WIRE1 = "22222222-0000-0000-0000-000000000001";
+
+const SCH_WITH_SYMBOL = `(kicad_sch
+\t(version 20250114)
+\t(generator "eeschema")
+\t(generator_version "9.0")
+\t(uuid "11111111-1111-1111-1111-111111111111")
+\t(paper "A4")
+\t(lib_symbols
+\t\t(symbol "Device:R" (pin_numbers (hide yes)) (pin_names (offset 0)) (exclude_from_sim no) (in_bom yes) (on_board yes)
+\t\t\t(property "Reference" "R" (at 2.032 0 90) (effects (font (size 1.27 1.27))))
+\t\t\t(property "Value" "R" (at 0 0 90) (effects (font (size 1.27 1.27))))
+\t\t\t(symbol "R_0_1"
+\t\t\t\t(rectangle (start -1.016 -2.54) (end 1.016 2.54) (stroke (width 0.254) (type default)) (fill (type none)))
+\t\t\t)
+\t\t\t(symbol "R_1_1"
+\t\t\t\t(pin passive line (at 0 3.81 270) (length 1.27) (name "~" (effects (font (size 1.27 1.27)))) (number "1" (effects (font (size 1.27 1.27)))))
+\t\t\t\t(pin passive line (at 0 -3.81 90) (length 1.27) (name "~" (effects (font (size 1.27 1.27)))) (number "2" (effects (font (size 1.27 1.27)))))
+\t\t\t)
+\t\t)
+\t)
+\t(wire (pts (xy 50.8 50.8) (xy 101.6 50.8)) (stroke (width 0) (type default)) (uuid "${WIRE1}"))
+\t(symbol (lib_id "Device:R") (at 63.5 63.5 0) (unit 1) (exclude_from_sim no) (in_bom yes) (on_board yes) (dnp no)
+\t\t(uuid "${SYM1}")
+\t\t(property "Reference" "R1" (at 66.04 62.23 0) (effects (font (size 1.27 1.27)) (justify left)))
+\t\t(property "Value" "10k" (at 66.04 64.77 0) (effects (font (size 1.27 1.27)) (justify left)))
+\t\t(property "Footprint" "" (at 0 0 0) (effects (font (size 1.27 1.27)) (hide yes)))
+\t\t(property "Datasheet" "" (at 0 0 0) (effects (font (size 1.27 1.27)) (hide yes)))
+\t\t(pin "1" (uuid "44444444-0000-0000-0000-0000000000a1"))
+\t\t(pin "2" (uuid "44444444-0000-0000-0000-0000000000a2"))
+\t\t(instances (project "rt" (path "/11111111-1111-1111-1111-111111111111" (reference "R1") (unit 1))))
+\t)
+\t(sheet_instances (path "/" (page "1")))
+)
+`;
+
+// B's cold copy: the same sheet BEFORE the symbol was placed — no instance, no
+// definition. The adopt must deliver both.
+const SCH_WITHOUT_SYMBOL = `(kicad_sch
+\t(version 20250114)
+\t(generator "eeschema")
+\t(generator_version "9.0")
+\t(uuid "11111111-1111-1111-1111-111111111111")
+\t(paper "A4")
+\t(lib_symbols)
+\t(wire (pts (xy 50.8 50.8) (xy 101.6 50.8)) (stroke (width 0) (type default)) (uuid "${WIRE1}"))
+\t(sheet_instances (path "/" (page "1")))
+)
+`;
+
+type FS = {
+  mkdirTree(p: string): void;
+  writeFile(p: string, d: string): void;
+  readFile(p: string, o: { encoding: "utf8" }): string;
+};
+type Mod = {
+  kicadOpenFile(p: string): unknown;
+  kicadCollabSnapshotItems(): string;
+  kicadCollabApplyItems(j: string): unknown;
+  kicadSaveSchematic(p: string): unknown;
+};
+
+const BOOT_TIMEOUT = 150000;
+const BUNDLE = path.resolve(__dirname, "../apps/kicad/collab-bundle-v2.js");
+
+function hasAbort(l: { consoleLogs: string[]; errors: string[] }): boolean {
+  return [...l.consoleLogs, ...l.errors].some((s) => s.includes("Aborted("));
+}
+
+async function bootOpen(page: Page, content: string, name: string): Promise<void> {
+  await page.goto("/kicad/eeschema.html");
+  await expect(page.locator("#canvas")).toBeVisible({ timeout: BOOT_TIMEOUT });
+  await page.waitForFunction(
+    () => {
+      const m = (window as unknown as { Module?: Mod }).Module;
+      return (
+        !!m &&
+        typeof m.kicadOpenFile === "function" &&
+        typeof m.kicadCollabSnapshotItems === "function" &&
+        typeof m.kicadSaveSchematic === "function"
+      );
+    },
+    null,
+    { timeout: BOOT_TIMEOUT },
+  );
+  await page.waitForFunction(
+    () =>
+      !!window.wxElementRegistry &&
+      window.wxElementRegistry
+        .findAll({ visible: true })
+        .some((e) => /Frame$/.test(e.typeName) || (e.name || "").endsWith("Frame")),
+    null,
+    { timeout: BOOT_TIMEOUT },
+  );
+  await page.evaluate(
+    ({ content, name }) => {
+      const w = window as unknown as { FS: FS; Module: Mod };
+      try {
+        w.FS.mkdirTree("/home/kicad/documents");
+      } catch {
+        /* exists */
+      }
+      const p = `/home/kicad/documents/${name}.kicad_sch`;
+      w.FS.writeFile(p, content);
+      w.Module.kicadOpenFile(p);
+    },
+    { content, name },
+  );
+  await expect.poll(() => page.title(), { timeout: 30000 }).toMatch(new RegExp(name, "i"));
+  await page.addScriptTag({ path: BUNDLE });
+}
+
+function startV2(
+  page: Page,
+  opts: { room: string; settleMs?: number; seedText?: string },
+): Promise<void> {
+  return page.evaluate(async (o) => {
+    const w = window as unknown as {
+      KicadCollabV2: { start: (m: unknown, win: unknown, o: unknown) => Promise<void> };
+      Module: unknown;
+    };
+    await w.KicadCollabV2.start(w.Module, window, o);
+  }, opts);
+}
+
+function saveText(page: Page): Promise<string> {
+  return page.evaluate(() => {
+    const w = window as unknown as { FS: FS; Module: Mod };
+    const out = "/home/kicad/documents/_dump.kicad_sch";
+    w.Module.kicadSaveSchematic(out);
+    return w.FS.readFile(out, { encoding: "utf8" });
+  });
+}
+
+test.describe("v2 items wire — lib_symbols travel (miss 08A)", () => {
+  test.describe.configure({ timeout: 420000 });
+
+  test("a joiner that never saw the symbol adopts it WITH its definition", async ({
+    context,
+    testLogger,
+  }) => {
+    test.skip(
+      test.info().project.name === "firefox",
+      "two kicad_editor tabs exceed Firefox's per-process wasm budget",
+    );
+
+    const room = `ysync-libsym-${test.info().workerIndex}`;
+    const tabA = await context.newPage();
+    const tabB = await context.newPage();
+    await bootOpen(tabA, SCH_WITH_SYMBOL, "tabA");
+    await bootOpen(tabB, SCH_WITHOUT_SYMBOL, "tabB");
+
+    await startV2(tabA, { room, seedText: SCH_WITH_SYMBOL }); // fresh → file-seed
+    await startV2(tabB, { room }); // joins → diff-adopt (doc authority)
+
+    // The adopt delivered the INSTANCE…
+    await expect
+      .poll(async () => (await saveText(tabB)).includes(SYM1), {
+        timeout: 20000,
+        intervals: [400],
+      })
+      .toBe(true);
+    // …AND its DEFINITION (findLib resolved it from the wire's lib_symbols
+    // context; before miss 08A the peer kept an empty lib_symbols and the
+    // instance rendered broken / materialized as an invalid file).
+    const saved = await saveText(tabB);
+    expect(saved).toContain(`(symbol "Device:R"`);
+    expect(saved).toContain(`(lib_id "Device:R")`);
+
+    // The untouched wire survived the diff-adopt (only the difference applied).
+    expect(saved).toContain(WIRE1);
+
+    expect(hasAbort(testLogger), "no WASM abort").toBe(false);
+    await tabA.close();
+    await tabB.close();
+  });
+});

web/pcbjam-shared

@@ -1 +1 @@
-Subproject commit f12d9af9595c915bb17a31bb59d156d38b256cbf
+Subproject commit 2387cecba80221e463fde02636d9ce4c3c24a044

web/standalone/src/components/WasmTool.tsx

@@ -9,6 +9,7 @@ import {
   projectToolPath,
   toolSchema,
   ydocHasState,
+  syncLayoutToY,
   yToDoc,
   type KicadDoc,
   type Tool,
@@ -570,6 +571,9 @@ export function WasmTool({
   const startedRef = React.useRef(false);
   const driftRef = React.useRef<{ stop(): void } | null>(null);
   const sheetManagerRef = React.useRef<SheetCollabManager | null>(null);
+  // The single-room collab doc (pcbnew/pl_editor), for the layout save-sync
+  // (miss 08B); eeschema routes per sheet through the manager instead.
+  const collabDocRef = React.useRef<import("yjs").Doc | null>(null);
   const [status, setStatus] = React.useState("Loading tool…");
   const [logs, setLogs] = React.useState<string[]>([]);
   const [showLog, setShowLog] = React.useState(false);
@@ -795,6 +799,21 @@ export function WasmTool({
           onSaved: (relPath) => {
             if (relPath.endsWith(".kicad_sch")) void sheetManagerRef.current?.onboard(relPath);
           },
+          // Non-item document state (title block, paper, setup…) only reaches the
+          // room at seed time; reconcile it from every save (miss 08B).
+          onSavedText: (relPath, text) => {
+            if (sheetManagerRef.current) {
+              sheetManagerRef.current.syncLayoutFromSave(relPath, text);
+              return;
+            }
+            if (collabDocRef.current && relPath === targetPath) {
+              try {
+                syncLayoutToY(fileToDoc(text), collabDocRef.current, "layout-save");
+              } catch (err) {
+                append(`[save] layout sync failed: ${String(err)}`);
+              }
+            }
+          },
         });
         const { session, targetBytes } = await maybeConnectDocSession(win, {
           docSource,
@@ -865,6 +884,7 @@ export function WasmTool({
             log: append,
             onStatus: setStatus,
           });
+          collabDocRef.current = collabHandle?.doc ?? null;
           if (collabHandle && targetPath && COLLAB_TOOLS.has(tool)) {
             driftRef.current = startDriftDetection({
               doc: collabHandle.doc,
@@ -897,6 +917,7 @@ export function WasmTool({
       // onActiveChange(null).
       sheetManagerRef.current?.destroy();
       sheetManagerRef.current = null;
+      collabDocRef.current = null;
       oom.stop();
     };
     // Boot is one-shot per mount; deps intentionally exclude files/targetPath so

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

@@ -4,6 +4,7 @@ import {
   docToFile,
   fileToDoc,
   itemsWireToDelta,
+  kicadLibSymbolsMap,
   parseItemsWireDelta,
   renderItem,
   sexprToItems,
@@ -244,4 +245,100 @@ describe("bindKicadCollab — two editors over relayed Y.Docs", () => {
       sexprToItems(`(pad "1" smd (at 0 0) (uuid "pad-1"))`, "fp-1").items["pad-1"]!.body,
     );
   });
+
+  it("adopt applies only the DIFFERENCE (opt 13) — identical items cost nothing", () => {
+    const { edA, edB, bindA, bindB } = setup();
+    const SEG = `(segment (start 0 0) (end 1 1) (uuid "seg-1"))`;
+    seedEditor(edA, FP);
+    seedEditor(edA, SEG);
+    bindA.seed();
+
+    // B's editor already holds the IDENTICAL footprint but not the segment.
+    seedEditor(edB, FP);
+    bindB.seed();
+
+    expect(edB.store["seg-1"]).toBeDefined(); // caught up
+    expect(edB.applied).toHaveLength(1);
+    const wire = parseItemsWireDelta(edB.applied[0]!);
+    // Only the missing segment travelled — the matching footprint did not.
+    expect(wire.added).toHaveLength(1);
+    expect(wire.added[0]!.sexpr).toContain("seg-1");
+    expect(wire.changed).toHaveLength(0);
+    expect(wire.removed).toHaveLength(0);
+  });
+
+  it("adopt with a fully matching editor applies NOTHING (clean rebind)", () => {
+    const { edA, edB, bindA, bindB } = setup();
+    seedEditor(edA, FP);
+    bindA.seed();
+    seedEditor(edB, FP);
+    bindB.seed();
+    expect(edB.applied).toHaveLength(0);
+  });
+
+  it("adopt re-applies a differing item's DOC version, lifted to its root", () => {
+    const { edA, edB, bindA, bindB } = setup();
+    seedEditor(edA, FP);
+    bindA.seed();
+
+    // B holds the same footprint but its pad drifted (never-synced local state).
+    seedEditor(edB, FP.replace(`(pad "1" smd (at 0 0)`, `(pad "1" smd (at 9 9)`));
+    bindB.seed();
+
+    // Doc authority: B's editor converges on the doc's pad, via ONE root re-apply.
+    expect(edB.store["pad-1"]!.body).toEqual(
+      sexprToItems(`(pad "1" smd (at 0 0) (uuid "pad-1"))`, "fp-1").items["pad-1"]!.body,
+    );
+    expect(edB.applied).toHaveLength(1);
+    const wire = parseItemsWireDelta(edB.applied[0]!);
+    expect(wire.changed).toHaveLength(1);
+    expect(wire.changed[0]!.sexpr).toContain(`(uuid "fp-1")`); // the root, not the bare pad
+  });
+});
+
+describe("lib_symbols flow through the binding (miss 08A)", () => {
+  const DEF = `(symbol "Device:R" (property "Reference" "R" (at 2 0 90)))`;
+  const INSTANCE = `(symbol (lib_id "Device:R") (at 100 50 0) (uuid "sym-1"))`;
+
+  it("an emitted placement's definition is stored and re-rendered for the peer", () => {
+    const { a, b } = pair();
+    const edA = new FakeEditor();
+    const edB = new FakeEditor();
+    bindKicadCollab(a, edA).seed();
+    bindKicadCollab(b, edB).seed();
+
+    // A places a symbol: the eeschema blob is multi-form (definition + instance).
+    edA.localUpsert(`(lib_symbols ${DEF}) ${INSTANCE}`, null, "added");
+
+    // B's editor received the instance WITH its definition prefixed (findLib's
+    // first branch), even though B has never seen this symbol.
+    expect(edB.store["sym-1"]).toBeDefined();
+    const applied = edB.applied.map((j) => parseItemsWireDelta(j));
+    const symWire = applied
+      .flatMap((w) => [...w.added, ...w.changed])
+      .find((w) => w.sexpr.includes("sym-1"));
+    expect(symWire, "the symbol reached B").toBeTruthy();
+    expect(symWire!.sexpr).toMatch(/^\(lib_symbols \(symbol "Device:R"/);
+
+    // And the definition landed in the room's defs map on BOTH sides
+    // (materialization injection is covered by the shared-lib tests — this
+    // room was editor-snapshot-seeded, which carries no layout/meta).
+    expect(kicadLibSymbolsMap(b).get("Device:R")).toContain(`"Device:R"`);
+    expect(kicadLibSymbolsMap(a).get("Device:R")).toContain(`"Device:R"`);
+  });
+
+  it("adopt of a doc holding a symbol carries the definition too", () => {
+    const { a, b } = pair();
+    const edA = new FakeEditor();
+    const edB = new FakeEditor();
+    bindKicadCollab(a, edA).seed();
+    edA.localUpsert(`(lib_symbols ${DEF}) ${INSTANCE}`, null, "added");
+
+    // B joins with an empty editor → adopts the doc.
+    bindKicadCollab(b, edB).seed();
+    expect(edB.store["sym-1"]).toBeDefined();
+    const wire = parseItemsWireDelta(edB.applied[0]!);
+    const symWire = [...wire.added, ...wire.changed].find((w) => w.sexpr.includes("sym-1"));
+    expect(symWire!.sexpr).toMatch(/^\(lib_symbols \(symbol "Device:R"/);
+  });
 });

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

@@ -7,13 +7,16 @@ import {
   isEmptyKicadDelta,
   itemsWireToDelta,
   kicadItemsMap,
+  kicadLibSymbolsMap,
   parseItemsWireDelta,
-  renderItem,
   seedDocToY,
+  upsertLibSymbolsToY,
+  wireItemUuids,
+  wireLibSymbols,
   Y_KDOC_META,
   Y_KDOC_SEED_NONCE,
   ydocHasState,
-  yToItem,
+  yToItemUnchecked,
   type ItemsWireDelta,
   type KicadDoc,
   type KicadItem,
@@ -87,15 +90,24 @@ export function bindKicadCollab(doc: Y.Doc, bridge: KicadItemsBridge): KicadBind
   // Concurrent double-seed arbitration cleanup (bug 06); set by the file-seed branch.
   let detachSeedArbitration: (() => void) | undefined;
 
-  /** Plain snapshot of the Y items (the `current`/`view` the conversions need). */
+  /**
+   * Plain snapshot of the Y items (the `current`/`view` the conversions need).
+   * Unchecked reads (opt 12): this runs on every local emit AND every remote
+   * batch; the zod walk of each body tree dominated at scale. The wire parse
+   * zod-validates at the trust boundary; seed/materialize keep checked reads.
+   */
   const itemsView = (): Record<string, KicadItem> => {
     const view: Record<string, KicadItem> = {};
     items.forEach((ym, uuid) => {
-      view[uuid] = yToItem(ym);
+      view[uuid] = yToItemUnchecked(ym);
     });
     return view;
   };
 
+  /** kdoc_libsymbols reader for the apply direction (miss 08). */
+  const libDefs = (libId: string): string | undefined =>
+    kicadLibSymbolsMap(doc).get(libId);
+
   // DOWN: local editor change → Y.Doc
   bridge.onItems((json: string) => {
     if (destroyed) return; // stale hook (bug 07) — a destroyed binding is inert
@@ -107,13 +119,19 @@ export function bindKicadCollab(doc: Y.Doc, bridge: KicadItemsBridge): KicadBind
       return;
     }
     const delta = itemsWireToDelta(wire, itemsView());
-    if (isEmptyKicadDelta(delta)) return;
+    // Library definitions the blob carried (a placed symbol's lib_symbols
+    // context — miss 08): store them alongside the items, same transaction.
+    const defs = wireLibSymbols(wire);
+    if (isEmptyKicadDelta(delta) && Object.keys(defs).length === 0) return;
     clog("⬇ onItems (local edit):", {
       added: delta.added.length,
       updated: delta.updated.length,
       removed: delta.removed.length,
     });
-    applyDeltaToY(doc, delta, ORIGIN);
+    doc.transact(() => {
+      applyDeltaToY(doc, delta, ORIGIN);
+      upsertLibSymbolsToY(doc, defs, ORIGIN);
+    }, ORIGIN);
   });
 
   // UP: remote Y change → editor. The subscription + origin policy live HERE
@@ -123,7 +141,7 @@ export function bindKicadCollab(doc: Y.Doc, bridge: KicadItemsBridge): KicadBind
     if (!seeded) return; // pre-seed state sync — seed()'s adopt covers it
     const delta = deltaFromYEvents(items, events);
     if (isEmptyKicadDelta(delta)) return;
-    const wire = deltaToItemsWire(delta, itemsView());
+    const wire = deltaToItemsWire(delta, itemsView(), libDefs);
     if (isEmptyItemsWireDelta(wire)) return;
     clog("⬆ remote Y change → apply to editor:", {
       added: wire.added.length,
@@ -203,32 +221,69 @@ export function bindKicadCollab(doc: Y.Doc, bridge: KicadItemsBridge): KicadBind
       cwarn("seed: snapshotItems unparseable", err);
       return;
     }
-    const local = itemsWireToDelta(wire, {});
 
     const hasState = ydocHasState(doc);
-    clog(
-      `seed: doc has ${items.size} item(s), editor has ${local.added.length} →`,
-      hasState ? "ADOPTING doc (joining)" : "SEEDING doc (first tab)",
-    );
 
     if (!hasState) {
       // First tab, no file source: seed the shared doc from the editor model.
-      applyDeltaToY(doc, local, ORIGIN);
+      const local = itemsWireToDelta(wire, {});
+      clog(`seed: doc empty → SEEDING from editor snapshot (${local.added.length} item(s))`);
+      doc.transact(() => {
+        applyDeltaToY(doc, local, ORIGIN);
+        upsertLibSymbolsToY(doc, wireLibSymbols(wire), ORIGIN);
+      }, ORIGIN);
       return;
     }
 
     // Joining a populated doc: the editor adopts it (seed-once authority, same
     // rationale as the scalar reconciler §2 — divergent local uuids from a
-    // never-saved cold open must yield to the doc's identity). Apply the doc's
+    // never-saved cold open must yield to the doc's identity). Diff the editor
-    // ROOT items (their sexprs embed all descendants) and remove local-only roots.
+    // snapshot against the doc VIEW and apply only the DIFFERENCE (opt 13):
+    // identical items cost nothing, the apply commit (and its undo entry — the
+    // adopt undo-bomb, miss 09) shrinks to the real changed set, and a clean
+    // rebind degrades to baseline-only.
     const view = itemsView();
-    const docRoots = Object.entries(view)
+    const editorDelta = itemsWireToDelta(wire, view); // editor state vs doc view
-      .filter(([, item]) => item.parent === null)
+    const editorUuids = wireItemUuids(wire);
-      .map(([uuid]) => ({ sexpr: renderItem({ items: view }, uuid), parent: null }));
+
-    const removed = local.added
+    // Doc authority, inverted per class:
+    //  - doc-only ROOTS → add to the editor (their sexprs embed descendants;
+    //    a doc-only CHILD makes its shared parent's body differ → covered below);
+    //  - items that DIFFER → re-apply the doc's version, lifted to their root
+    //    (the C++ upsert replaces roots; a bare child apply would mis-parent);
+    //  - editor-only ROOTS → remove (editor-only children disappear with their
+    //    parent's re-apply).
+    const liftToRoot = (uuid: string): string => {
+      let cur = uuid;
+      while (view[cur]?.parent != null) cur = view[cur]!.parent!;
+      return cur;
+    };
+    const docOnly = Object.entries(view)
+      .filter(([uuid, it]) => it.parent === null && !editorUuids.has(uuid))
+      .map(([uuid, it]) => ({ uuid, ...it }));
+    const changedRoots = [
+      ...new Set(
+        editorDelta.updated.filter((it) => it.uuid in view).map((it) => liftToRoot(it.uuid)),
+      ),
+    ]
+      .filter((uuid) => !docOnly.some((it) => it.uuid === uuid))
+      .map((uuid) => ({ uuid, ...view[uuid]! }));
+    const removed = editorDelta.added
       .filter((it) => it.parent === null && !(it.uuid in view))
       .map((it) => it.uuid);
-    bridge.applyItems(JSON.stringify({ added: docRoots, changed: [], removed }));
+
+    const adoptWire = deltaToItemsWire(
+      { added: docOnly, updated: changedRoots, removed },
+      view,
+      libDefs,
+    );
+
+    clog(
+      `seed: doc has ${items.size} item(s) → ADOPTING diff:`,
+      `+${adoptWire.added.length} ~${adoptWire.changed.length} -${adoptWire.removed.length}`,
+    );
+    if (isEmptyItemsWireDelta(adoptWire)) return; // editor already matches — baseline only
+    bridge.applyItems(JSON.stringify(adoptWire));
   }
 
   return {

web/standalone/src/wasm/collab/sheet-manager.ts

@@ -1,5 +1,5 @@
 import type * as Y from "yjs";
-import { collabRoomId, type KicadDoc } from "@pcbjam/shared";
+import { collabRoomId, fileToDoc, syncLayoutToY, type KicadDoc } from "@pcbjam/shared";
 import { connectKicadDoc, type KicadDocSession } from "./index";
 import {
   bindKicadCollab,
@@ -40,6 +40,12 @@ export interface SheetCollabManager {
   switchTo(sheetPath: string): Promise<void>;
   /** Warm a sheet created mid-session (driven by the save hook on an unknown path). */
   onboard(sheetPath: string): Promise<void>;
+  /**
+   * Coarse non-item layout sync from a just-saved sheet file (miss 08B): title
+   * block / paper / settings edits reconcile into the sheet's room doc, which
+   * otherwise only carries them from seed time. No-op for unknown sheets.
+   */
+  syncLayoutFromSave(sheetPath: string, fileText: string): void;
   /** The currently-bound sheet, for drift-detection wiring (null before first switch). */
   active(): { sheetPath: string; doc: Y.Doc } | null;
   /** Tear down ALL bindings + providers + docs (session end / unmount). */
@@ -251,6 +257,20 @@ export function createSheetCollabManager(opts: SheetManagerOptions): SheetCollab
     }
   }
 
+  function syncLayoutFromSave(sheetPath: string, fileText: string): void {
+    const room = rooms.get(sheetPath);
+    if (!room) return; // not a collab sheet (or still onboarding) — nothing to sync
+    try {
+      // Writing to a PARKED room's doc marks it dirty via startWatch — fine:
+      // the diff-on-rebind adopt makes the catch-up cost the real delta only.
+      if (syncLayoutToY(fileToDoc(fileText), room.doc, "layout-save")) {
+        clog(`[sheet] layout save-sync: ${sheetPath} updated`);
+      }
+    } catch (err) {
+      cwarn(`[sheet] layout save-sync failed for ${sheetPath}`, err);
+    }
+  }
+
   async function connectAll(sheetPaths: string[]): Promise<void> {
     await Promise.all(
       sheetPaths.map((p) =>
@@ -289,7 +309,7 @@ export function createSheetCollabManager(opts: SheetManagerOptions): SheetCollab
     opts.onActiveChange?.(null);
   }
 
-  return { connectAll, switchTo, onboard, active, destroy };
+  return { connectAll, switchTo, onboard, syncLayoutFromSave, active, destroy };
 }
 
 export interface SheetChangedWindow {

web/standalone/src/wasm/save-flow.test.ts

@@ -45,4 +45,39 @@ describe("registerSaveHook path routing", () => {
     expect(onSaved).not.toHaveBeenCalled();
     expect(saveBytes).not.toHaveBeenCalled();
   });
+
+  it("onSavedText receives the decoded file text (layout save-sync, miss 08B)", () => {
+    const onSavedText = vi.fn();
+    const win: SaveHookWindow = {
+      FS: {
+        readFile: () => new TextEncoder().encode("(kicad_sch (version 1))"),
+      } as unknown as SaveHookWindow["FS"],
+      kicadCollab: {},
+    };
+    registerSaveHook(win, {
+      slug: SLUG,
+      onSavedText,
+      log: () => {},
+      onStatus: () => {},
+    });
+    win.kicadCollab!.onSave!(`${PROJ}/sheet.kicad_sch`);
+    expect(onSavedText).toHaveBeenCalledWith("sheet.kicad_sch", "(kicad_sch (version 1))");
+  });
+
+  it("an onSavedText read failure is logged, not thrown", () => {
+    const onSavedText = vi.fn();
+    const log = vi.fn();
+    const win: SaveHookWindow = {
+      FS: {
+        readFile: () => {
+          throw new Error("gone");
+        },
+      } as unknown as SaveHookWindow["FS"],
+      kicadCollab: {},
+    };
+    registerSaveHook(win, { slug: SLUG, onSavedText, log, onStatus: () => {} });
+    win.kicadCollab!.onSave!(`${PROJ}/sheet.kicad_sch`);
+    expect(onSavedText).not.toHaveBeenCalled();
+    expect(log).toHaveBeenCalledWith(expect.stringContaining("onSavedText read failed"));
+  });
 });

web/standalone/src/wasm/save-flow.ts

@@ -35,6 +35,12 @@ export function registerSaveHook(
      * ("Add Sheet"), which the page-load file list can't contain.
      */
     onSaved?: (relPath: string) => void;
+    /**
+     * Like `onSaved` but with the saved file's TEXT (read back from MEMFS).
+     * The collab layout save-sync (miss 08B) uses it to reconcile non-item
+     * document state (title block, paper, setup…) into the room doc.
+     */
+    onSavedText?: (relPath: string, text: string) => void;
   },
 ): void {
   const projectPrefix = `${memfsProjectDir(opts.slug)}/`;
@@ -64,6 +70,17 @@ export function registerSaveHook(
 
     opts.onSaved?.(relPath);
 
+    if (opts.onSavedText) {
+      try {
+        const data = win.FS?.readFile(absPath);
+        if (data instanceof Uint8Array) {
+          opts.onSavedText(relPath, new TextDecoder().decode(data));
+        }
+      } catch (err) {
+        opts.log(`[save] onSavedText read failed for ${relPath}: ${String(err)}`);
+      }
+    }
+
     if (!opts.saveBytes) {
       opts.log(`[save] ${relPath} saved in MEMFS (no external save target)`);
       return;