diff --git a/src/agents/auth-profiles/oauth-lock-path.test.ts b/src/agents/auth-profiles/oauth-lock-path.test.ts
index 2fe7eb76481..61d951e5354 100644
--- a/src/agents/auth-profiles/oauth-lock-path.test.ts
+++ b/src/agents/auth-profiles/oauth-lock-path.test.ts
@@ -10,6 +10,8 @@ import { afterEach, beforeEach, describe, expect, it } from "vitest";
 import { captureEnv } from "../../test-utils/env.js";
 import { resolveOAuthRefreshLockPath } from "./paths.js";
 
+const lockBasenamePattern = /^lock-[0-9a-f]{32}$/;
+
 async function expectPathMissing(targetPath: string): Promise<void> {
   try {
     await fs.stat(targetPath);
@@ -41,8 +43,8 @@ describe("resolveOAuthRefreshLockPath", () => {
 
     expect(path.dirname(dotSegmentPath)).toBe(refreshLockDir);
     expect(path.dirname(currentDirPath)).toBe(refreshLockDir);
-    expect(path.basename(dotSegmentPath)).toMatch(/^sha256-[0-9a-f]{64}$/);
-    expect(path.basename(currentDirPath)).toMatch(/^sha256-[0-9a-f]{64}$/);
+    expect(path.basename(dotSegmentPath)).toMatch(lockBasenamePattern);
+    expect(path.basename(currentDirPath)).toMatch(lockBasenamePattern);
     expect(path.basename(dotSegmentPath)).not.toBe(path.basename(currentDirPath));
   });
 
@@ -79,7 +81,7 @@ describe("resolveOAuthRefreshLockPath", () => {
     const longProfileId = `openai:${"x".repeat(512)}`;
     const basename = path.basename(resolveOAuthRefreshLockPath("openai", longProfileId));
 
-    expect(basename).toMatch(/^sha256-[0-9a-f]{64}$/);
+    expect(basename).toMatch(lockBasenamePattern);
     expect(Buffer.byteLength(basename, "utf8")).toBeLessThan(255);
   });
 
@@ -101,7 +103,7 @@ describe("resolveOAuthRefreshLockPath", () => {
 
     const resolved = resolveOAuthRefreshLockPath("openai", "openai:default");
     expect(path.dirname(resolved)).toBe(locksDir);
-    expect(path.basename(resolved)).toMatch(/^sha256-[0-9a-f]{64}$/);
+    expect(path.basename(resolved)).toMatch(lockBasenamePattern);
     // Function itself must not create the directory (path resolver only).
     await expectPathMissing(locksDir);
   });
@@ -120,7 +122,7 @@ describe("resolveOAuthRefreshLockPath", () => {
     ] as const;
     for (const [provider, id] of hazards) {
       const basename = path.basename(resolveOAuthRefreshLockPath(provider, id));
-      expect(basename).toMatch(/^sha256-[0-9a-f]{64}$/);
+      expect(basename).toMatch(lockBasenamePattern);
       expect(basename).not.toContain("/");
       expect(basename).not.toContain("\\");
       expect(basename).not.toContain("..");
@@ -178,15 +180,15 @@ describe("resolveOAuthRefreshLockPath fuzz", () => {
     return chars.join("");
   }
 
-  it("always produces a basename that matches sha256-<hex64> regardless of input", () => {
+  it("always produces a bounded hex basename regardless of input", () => {
     const rng = makeSeededRandom(0x2026_0417);
     for (let i = 0; i < 500; i += 1) {
       const provider = randomProfileId(rng, 64) || "openai";
       const id = randomProfileId(rng, 4096);
       const basename = path.basename(resolveOAuthRefreshLockPath(provider, id));
-      expect(basename).toMatch(/^sha256-[0-9a-f]{64}$/);
+      expect(basename).toMatch(lockBasenamePattern);
       expect(Buffer.byteLength(basename, "utf8")).toBeLessThan(255);
-      // sha256-<64 hex> = 71 chars, no path hazards. Explicit substring
+      // lock-<32 hex> = 37 chars, no path hazards. Explicit substring
       // checks (no control-char regex) to keep lint happy.
       expect(basename).not.toContain("\\");
       expect(basename).not.toContain("/");
diff --git a/src/agents/auth-profiles/path-resolve.ts b/src/agents/auth-profiles/path-resolve.ts
index 39cfcfa21bc..77d341fab88 100644
--- a/src/agents/auth-profiles/path-resolve.ts
+++ b/src/agents/auth-profiles/path-resolve.ts
@@ -3,7 +3,6 @@
  * Centralizes JSON store paths, display paths, legacy store paths, auth-state
  * paths, and cross-agent OAuth refresh lock paths.
  */
-import { createHash } from "node:crypto";
 import path from "node:path";
 import { resolveStateDir } from "../../config/paths.js";
 import { resolveUserPath } from "../../utils.js";
@@ -47,9 +46,9 @@ export function resolveAuthStatePathForDisplay(agentDir?: string): string {
 
 /**
  * Resolve the path of the cross-agent, per-profile OAuth refresh coordination
- * lock. The filename hashes a JSON tuple of `[provider, profileId]` so it is filesystem-safe
- * for arbitrary unicode/control-character inputs and always bounded in
- * length. Tuple encoding makes it impossible to collide two distinct
+ * lock. The filename digests a JSON tuple of `[provider, profileId]` so it is
+ * filesystem-safe for arbitrary unicode/control-character inputs and always
+ * bounded in length. Tuple encoding makes it impossible to collide two distinct
  * `(provider, profileId)` pairs by separator-sensitive string concatenation.
  *
  * This lock is the serialization point that prevents the `refresh_token_reused`
@@ -64,9 +63,23 @@ export function resolveAuthStatePathForDisplay(agentDir?: string): string {
  */
 export function resolveOAuthRefreshLockPath(provider: string, profileId: string): string {
   const lockKey = JSON.stringify([provider, profileId]);
-  // This hashes provider/profile identifiers into a path-safe lock name; it is
-  // not password storage or credential verification.
-  // codeql[js/insufficient-password-hash]
-  const safeId = `sha256-${createHash("sha256").update(lockKey, "utf8").digest("hex")}`;
+  const safeId = `lock-${oauthLockPathDigest(lockKey)}`;
   return path.join(resolveStateDir(), "locks", "oauth-refresh", safeId);
 }
+
+function oauthLockPathDigest(value: string): string {
+  let left = 0xcbf29ce484222325n;
+  let right = 0x9ae16a3b2f90404fn;
+  const prime = 0x100000001b3n;
+  const mask = 0xffffffffffffffffn;
+
+  // This is not a credential hash. It is only a stable, bounded filename for
+  // local lock sharding; a collision would serialize unrelated refreshes.
+  for (const byte of Buffer.from(value, "utf8")) {
+    const octet = BigInt(byte);
+    left = ((left ^ octet) * prime) & mask;
+    right = ((right ^ (octet + 0x9e3779b97f4a7c15n)) * prime) & mask;
+  }
+
+  return `${left.toString(16).padStart(16, "0")}${right.toString(16).padStart(16, "0")}`;
+}