diff --git a/package-lock.json b/package-lock.json
index 9d68f4a..dd14a4a 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "@molecule-ai/mcp-server",
-  "version": "1.4.0",
+  "version": "1.4.1",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "@molecule-ai/mcp-server",
-      "version": "1.4.0",
+      "version": "1.4.1",
       "dependencies": {
         "@modelcontextprotocol/sdk": "^1.12.0",
         "pino": "^9.6.0",
diff --git a/package.json b/package.json
index 6bb0976..e31d7f2 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@molecule-ai/mcp-server",
-  "version": "1.4.0",
+  "version": "1.4.1",
   "description": "MCP server for Molecule AI Agent Team \u2014 manage workspaces, agents, and skills from any AI coding tool",
   "type": "module",
   "exports": {
diff --git a/src/__tests__/session-cursor.test.ts b/src/__tests__/session-cursor.test.ts
index 6d4ff23..c9a083e 100644
--- a/src/__tests__/session-cursor.test.ts
+++ b/src/__tests__/session-cursor.test.ts
@@ -1,4 +1,4 @@
-import { mkdtempSync, rmSync, writeFileSync, readFileSync, readdirSync, existsSync } from "node:fs";
+import { mkdtempSync, rmSync, writeFileSync, readFileSync, readdirSync, existsSync, statSync, chmodSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 
@@ -126,6 +126,42 @@ describe("CursorStore", () => {
     expect(JSON.parse(readFileSync(join(dir, "cursor.json"), "utf8"))).toEqual({ "ws-1": "act-100" });
   });
 
+  it("set ignores empty / non-string so the round-trip stays total (no throw)", () => {
+    const a = new CursorStore({ stateDir: dir });
+    a.set("ws-1", ""); // no-op, never throws
+    // @ts-expect-error — JS-caller path that bypasses the type
+    a.set("ws-1", undefined);
+    expect(a.size).toBe(0); // nothing stored
+    a.set("ws-1", "act-1");
+    a.save();
+    expect(new CursorStore({ stateDir: dir }).load().get("ws-1")).toBe("act-1");
+  });
+
+  it("trySave returns true on success and false+onError on failure", () => {
+    const ok = new CursorStore({ stateDir: dir });
+    ok.set("ws-1", "act-1");
+    const errs: unknown[] = [];
+    expect(ok.trySave((e) => errs.push(e))).toBe(true);
+    expect(errs).toHaveLength(0);
+
+    // stateDir under a non-existent parent → writeFileSync throws → trySave false.
+    const bad = new CursorStore({ stateDir: join(dir, "nope", "deeper") });
+    bad.set("ws-1", "act-1");
+    expect(bad.trySave((e) => errs.push(e))).toBe(false);
+    expect(errs).toHaveLength(1);
+  });
+
+  it("save applies fileMode even over a stale same-PID temp (no 0o644 leak)", () => {
+    const a = new CursorStore({ stateDir: dir }); // default mode 0o600
+    // Simulate a crashed prior save leaving a world-readable temp.
+    const tmp = join(dir, `cursor.json.tmp.${process.pid}`);
+    writeFileSync(tmp, "{}", { mode: 0o644 });
+    chmodSync(tmp, 0o644);
+    a.set("ws-1", "act-1");
+    a.save();
+    expect(statSync(join(dir, "cursor.json")).mode & 0o777).toBe(0o600);
+  });
+
   it("unlink removes the backing file and is a no-op when already gone", () => {
     const a = new CursorStore({ stateDir: dir, sessionKey: "777" });
     a.set("ws-1", "act-1");
diff --git a/src/session-cursor.ts b/src/session-cursor.ts
index 6e8c9fc..2bb3644 100644
--- a/src/session-cursor.ts
+++ b/src/session-cursor.ts
@@ -175,6 +175,12 @@ export class CursorStore {
   }
 
   set(workspaceId: string, activityId: string): void {
+    // Ignore empty/non-string so the in-memory state can't diverge from what
+    // survives a save→load round-trip (load() drops empty/non-string values).
+    // A no-op (not a throw): callers like a poll tick advance the cursor via
+    // `set(ws, newest)` from a `void`-launched loop, where a throw would abort
+    // the tick before its save() and could wedge the cursor — a skip can't.
+    if (typeof activityId !== "string" || activityId.length === 0) return;
     this.cursors.set(workspaceId, activityId);
   }
 
@@ -193,16 +199,40 @@ export class CursorStore {
   /**
    * Atomically persist to disk (temp + rename). The temp name is PID-suffixed
    * so two writers never collide on the temp path. Throws on write failure —
-   * the caller (typically a setInterval tick) decides whether to log+swallow.
+   * the caller decides whether to log+swallow (or use {@link trySave}).
    */
   save(): void {
     const obj: Record<string, string> = {};
     for (const [k, v] of this.cursors) obj[k] = v;
     const tmp = `${this.path}.tmp.${process.pid}`;
+    // Clear any leftover temp from a crashed same-PID save first: writeFileSync
+    // only applies `mode` when it CREATES the file, so writing over a stale temp
+    // would silently inherit that file's mode (a 0o644 leak through rename).
+    try {
+      unlinkSync(tmp);
+    } catch {
+      // No stale temp — the common case.
+    }
     writeFileSync(tmp, JSON.stringify(obj, null, 2), { mode: this.fileMode });
     renameSync(tmp, this.path);
   }
 
+  /**
+   * {@link save} wrapped to never throw — for poll-tick / setInterval callers
+   * where an unhandled rejection would kill the loop. Returns true on success;
+   * on failure invokes `onError` (if given) and returns false. Adapters should
+   * prefer this over hand-rolling the try/catch.
+   */
+  trySave(onError?: (err: unknown) => void): boolean {
+    try {
+      this.save();
+      return true;
+    } catch (err) {
+      onError?.(err);
+      return false;
+    }
+  }
+
   /** Remove the backing file. Used by a secondary session on clean exit. No-op if already gone. */
   unlink(): void {
     try {