diff --git a/packages/coding-agent/src/internal-urls/local-protocol.ts b/packages/coding-agent/src/internal-urls/local-protocol.ts
index a8f1fe1d0..75eadd6d9 100644
--- a/packages/coding-agent/src/internal-urls/local-protocol.ts
+++ b/packages/coding-agent/src/internal-urls/local-protocol.ts
@@ -34,9 +34,11 @@ function safeSessionId(options: LocalProtocolOptions): string {
 	return safe.length > 0 ? safe : "session";
 }
 
-function shortLocalRoot(candidate: string, options: LocalProtocolOptions): string {
-	const hash = Bun.hash(candidate).toString(36);
-	return path.join(os.tmpdir(), "omp-local", `${safeSessionId(options)}-${hash}`);
+function shortLocalRoot(options: LocalProtocolOptions): string {
+	// Derive the short root from the stable session id, never the artifact path,
+	// so `SessionManager.moveTo()` and the resume-after-move flow keep finding
+	// the same `local://` directory the session wrote pre-move.
+	return path.join(os.tmpdir(), "omp-local", safeSessionId(options));
 }
 
 function getContentType(filePath: string): InternalResource["contentType"] {
@@ -126,7 +128,7 @@ export function resolveLocalRoot(options: LocalProtocolOptions, platform: NodeJS
 	if (artifactsDir) {
 		const candidate = path.resolve(artifactsDir, "local");
 		if (platform === "win32" && candidate.length >= WINDOWS_LOCAL_ROOT_MAX_CHARS) {
-			return shortLocalRoot(candidate, options);
+			return shortLocalRoot(options);
 		}
 		return candidate;
 	}
diff --git a/packages/coding-agent/test/internal-urls/local-protocol.test.ts b/packages/coding-agent/test/internal-urls/local-protocol.test.ts
index 6876a2ecc..7b8891686 100644
--- a/packages/coding-agent/test/internal-urls/local-protocol.test.ts
+++ b/packages/coding-agent/test/internal-urls/local-protocol.test.ts
@@ -90,8 +90,9 @@ describe("LocalProtocolHandler", () => {
 		);
 	});
 
-	it("uses a short temp root for long Windows artifact paths", async () => {
+	it("uses a stable short temp root for long Windows artifact paths", async () => {
 		const longArtifactsDir = path.join(os.tmpdir(), "a".repeat(220), "artifacts");
+		const expectedRoot = path.join(os.tmpdir(), "omp-local", "session_long");
 		const options = {
 			getArtifactsDir: () => longArtifactsDir,
 			getSessionId: () => "session:long",
@@ -99,10 +100,17 @@ describe("LocalProtocolHandler", () => {
 		const root = resolveLocalRoot(options, "win32");
 		const resolved = resolveLocalUrlToPath("local://memo.txt", options, "win32");
 
-		expect(root).toContain(path.join("omp-local", "session_long-"));
-		expect(root).not.toContain(longArtifactsDir);
-		expect(root.length).toBeLessThan(path.join(longArtifactsDir, "local").length);
-		expect(resolved).toBe(path.join(root, "memo.txt"));
+		expect(root).toBe(expectedRoot);
+		expect(resolved).toBe(path.join(expectedRoot, "memo.txt"));
+
+		// The short root must survive moves of the artifact directory so
+		// `local://PLAN.md` and handoff files written pre-move stay reachable
+		// after `SessionManager.moveTo()` updates `getArtifactsDir()`.
+		const movedOptions = {
+			getArtifactsDir: () => path.join(os.tmpdir(), "b".repeat(220), "artifacts"),
+			getSessionId: () => "session:long",
+		};
+		expect(resolveLocalRoot(movedOptions, "win32")).toBe(expectedRoot);
 	});
 
 	it("blocks symlink escapes outside local root", async () => {