diff --git a/src/sync/diskMirror.ts b/src/sync/diskMirror.ts
index 684378a3..a5d2f695 100644
--- a/src/sync/diskMirror.ts
+++ b/src/sync/diskMirror.ts
@@ -11,6 +11,7 @@ import {
 	type FrontmatterValidationResult,
 } from "./frontmatterGuard";
 import { isLocalOrigin } from "./origins";
+import { isMarkdownConflictArtifactPath } from "./markdownConflictArtifact";
 import { contentBaselineHash } from "./diskIndex";
 import { PreservedUnresolvedRegistry, type PreservedUnresolvedEntry, type PreservedUnresolvedReason } from "./preservedUnresolved";
 export { isLocalOrigin };
@@ -502,6 +503,11 @@ export class DiskMirror {
 
 	async flushWrite(path: string, force = false): Promise<void> {
 		path = normalizePath(path);
+		// Older clients admitted safety copies into the shared document. The
+		// upload filter alone cannot protect a user deleting one locally: its
+		// CRDT entry survives, so reconciliation or a remote edit can recreate
+		// it. Enforce locality on every writeback, including forced writes.
+		if (isMarkdownConflictArtifactPath(path)) return;
 		return this.runPathWriteLocked(path, () => this.flushWriteUnlocked(path, force));
 	}
 
diff --git a/src/sync/markdownConflictArtifact.ts b/src/sync/markdownConflictArtifact.ts
index 4a5f56cd..d620f57c 100644
--- a/src/sync/markdownConflictArtifact.ts
+++ b/src/sync/markdownConflictArtifact.ts
@@ -10,7 +10,7 @@
  * Stamp is ISO-8601 with `:` replaced by `-`.
  */
 const MARKDOWN_CONFLICT_ARTIFACT_RE =
-	/ \(YAOS conflict(?: - (?:crdt|disk|editor))? from .+ \d{4}-\d{2}-\d{2}T\d{2}-\d{2}-\d{2}Z\)(?: \d+)?\.md$/u;
+	/ \(YAOS conflict(?: - (?:crdt|disk|editor))? from .+ \d{4}-\d{2}-\d{2}T\d{2}-\d{2}-\d{2}Z\)(?: \d+)?\.[mM][dD]$/u;
 
 export function isMarkdownConflictArtifactPath(path: string): boolean {
 	const normalized = path.replace(/\\/g, "/");
diff --git a/src/sync/vaultSync.ts b/src/sync/vaultSync.ts
index cae78e91..7842e108 100644
--- a/src/sync/vaultSync.ts
+++ b/src/sync/vaultSync.ts
@@ -1,4 +1,5 @@
 import * as Y from "yjs";
+import { isMarkdownConflictArtifactPath } from "./markdownConflictArtifact";
 import YSyncProvider from "y-partyserver/provider";
 import { IndexeddbPersistence } from "y-indexeddb";
 import { normalizePath } from "obsidian";
@@ -1191,7 +1192,11 @@ export class VaultSync {
 		let skipped = 0;
 
 		this.ensurePathIndexes();
-		const crdtPaths = new Set<string>(this._pathIndex.keys());
+		// Keep legacy synced artifacts in the document for recovery, but never
+		// plan disk creates/overwrites for these now-local-only safety copies.
+		const crdtPaths = new Set<string>(
+			[...this._pathIndex.keys()].filter((path) => !isMarkdownConflictArtifactPath(path)),
+		);
 
 		// CRDT files not on disk → create on disk
 		// IMPORTANT: use diskPresentPaths (all known disk paths), not
@@ -1221,6 +1226,7 @@ export class VaultSync {
 
 		// Disk files not in CRDT
 		for (const path of diskPresentPaths) {
+			if (isMarkdownConflictArtifactPath(path)) continue;
 			const classification = classifyDiskPathForReconcile(
 				path,
 				crdtPaths.has(path),
diff --git a/tests/client/legacy-conflict-writeback.ts b/tests/client/legacy-conflict-writeback.ts
new file mode 100644
index 00000000..1c0c9948
--- /dev/null
+++ b/tests/client/legacy-conflict-writeback.ts
@@ -0,0 +1,71 @@
+import { webcrypto } from "node:crypto";
+import { TFile, type App } from "obsidian";
+import * as Y from "yjs";
+import { DiskMirror } from "../../src/sync/diskMirror";
+import { VaultSync } from "../../src/sync/vaultSync";
+import type { EditorBindingManager } from "../../src/sync/editorBinding";
+import { isMarkdownSyncable } from "../../src/types";
+import { partialOf } from "../mocks/productFixture";
+import { suite } from "../harness";
+
+const s = suite("legacy-conflict-writeback");
+Object.defineProperty(globalThis, "window", { value: { crypto: webcrypto }, configurable: true });
+
+const artifact = "note (YAOS conflict - crdt from Laptop 2026-08-27T11-05-00Z).md";
+const paths = [artifact, artifact.replace(/\.md$/, ".MD"), "note.md"];
+
+for (const path of paths) {
+	s.test(`writeback respects local-only policy: ${path}`, async () => {
+		const doc = new Y.Doc();
+		const text = doc.getText("body");
+		text.insert(0, "remote content");
+		const disk = new Map<string, string>();
+		const errors: unknown[] = [];
+		const app = partialOf<App>({
+			vault: {
+				getAbstractFileByPath: (p) => disk.has(p) ? Object.assign(new TFile(), { path: p }) : null,
+				read: async (file) => disk.get(file.path)!,
+				create: async (p, content) => { disk.set(p, content); return Object.assign(new TFile(), { path: p }); },
+				modify: async (file, content) => { disk.set(file.path, content); },
+			},
+		});
+		const mirror = new DiskMirror(app, partialOf<VaultSync>({ getTextForPath: () => text }),
+			partialOf<EditorBindingManager>({}), false, undefined, () => false);
+		mirror.setFlightEventHandler((event) => { if (event.kind === "disk.write.failed") errors.push(event); });
+		try {
+			const localOnly = path !== "note.md";
+			s.check(isMarkdownSyncable(path, [], ".obsidian") === !localOnly, "admission matches artifact policy");
+			await mirror.flushWrite(path);
+			s.check(disk.has(path) === !localOnly, "legacy CRDT artifact is not materialized; normal note is");
+			disk.delete(path);
+			await mirror.flushWrite(path, true);
+			s.check(disk.has(path) === !localOnly, "forced write cannot resurrect a deleted local artifact");
+			disk.set(path, "local safety copy");
+			await mirror.flushWrite(path, true);
+			s.check(disk.get(path) === (localOnly ? "local safety copy" : "remote content"), "existing artifact is not overwritten");
+			s.check(errors.length === 0, "no hidden write errors");
+		} finally { doc.destroy(); }
+	});
+}
+
+s.test("reconcile does not plan writes for previously synced conflict artifacts", () => {
+	const doc = new Y.Doc();
+	const sync: VaultSync = Object.assign(Object.create(VaultSync.prototype), {
+		_pathIndexesDirty: false,
+		_pathIndex: new Map(paths.map((p) => [p, p])),
+		_deletedPathIndex: new Set(),
+		_eventRing: [],
+		sys: doc.getMap("sys"),
+		debug: false,
+		getTextForPath: () => doc.getText("body"),
+	});
+	doc.getText("body").insert(0, "remote");
+	try {
+		const absent = sync.reconcileVault(new Map(), new Set(), "authoritative");
+		s.check(JSON.stringify(absent.createdOnDisk) === JSON.stringify(["note.md"]), "only normal missing notes are scheduled for creation");
+		const present = sync.reconcileVault(new Map(paths.map((p) => [p, "local"])), new Set(paths), "authoritative");
+		s.check(JSON.stringify(present.updatedOnDisk) === JSON.stringify(["note.md"]), "only normal existing notes are scheduled for overwrite");
+	} finally { doc.destroy(); }
+});
+
+await s.done();