diff --git a/src/agents/claude-cli-runner.test.ts b/src/agents/claude-cli-runner.test.ts
new file mode 100644
index 000000000..cfdccdd0e
--- /dev/null
+++ b/src/agents/claude-cli-runner.test.ts
@@ -0,0 +1,68 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+import { runClaudeCliAgent } from "./claude-cli-runner.js";
+
+const runCommandWithTimeoutMock = vi.fn();
+
+vi.mock("../process/exec.js", () => ({
+  runCommandWithTimeout: (...args: unknown[]) => runCommandWithTimeoutMock(...args),
+}));
+
+describe("runClaudeCliAgent", () => {
+  beforeEach(() => {
+    runCommandWithTimeoutMock.mockReset();
+  });
+
+  it("starts a new session without --session-id when no resume id", async () => {
+    runCommandWithTimeoutMock.mockResolvedValueOnce({
+      stdout: JSON.stringify({ message: "ok", session_id: "sid-1" }),
+      stderr: "",
+      code: 0,
+      signal: null,
+      killed: false,
+    });
+
+    await runClaudeCliAgent({
+      sessionId: "clawdbot-session",
+      sessionFile: "/tmp/session.jsonl",
+      workspaceDir: "/tmp",
+      prompt: "hi",
+      model: "opus",
+      timeoutMs: 1_000,
+      runId: "run-1",
+    });
+
+    expect(runCommandWithTimeoutMock).toHaveBeenCalledTimes(1);
+    const argv = runCommandWithTimeoutMock.mock.calls[0]?.[0] as string[];
+    expect(argv).toContain("claude");
+    expect(argv).not.toContain("--session-id");
+    expect(argv).not.toContain("--resume");
+  });
+
+  it("uses --resume when a resume session id is provided", async () => {
+    runCommandWithTimeoutMock.mockResolvedValueOnce({
+      stdout: JSON.stringify({ message: "ok", session_id: "sid-2" }),
+      stderr: "",
+      code: 0,
+      signal: null,
+      killed: false,
+    });
+
+    await runClaudeCliAgent({
+      sessionId: "clawdbot-session",
+      sessionFile: "/tmp/session.jsonl",
+      workspaceDir: "/tmp",
+      prompt: "hi",
+      model: "opus",
+      timeoutMs: 1_000,
+      runId: "run-2",
+      resumeSessionId: "sid-1",
+    });
+
+    expect(runCommandWithTimeoutMock).toHaveBeenCalledTimes(1);
+    const argv = runCommandWithTimeoutMock.mock.calls[0]?.[0] as string[];
+    expect(argv).toContain("--resume");
+    expect(argv).toContain("sid-1");
+    expect(argv).not.toContain("--session-id");
+  });
+});
diff --git a/src/agents/claude-cli-runner.ts b/src/agents/claude-cli-runner.ts
index 29eb7b13f..50b9081d2 100644
--- a/src/agents/claude-cli-runner.ts
+++ b/src/agents/claude-cli-runner.ts
@@ -208,7 +208,6 @@ async function runClaudeCliOnce(params: {
   systemPrompt: string;
   timeoutMs: number;
   resumeSessionId?: string;
-  sessionId?: string;
 }): Promise<ClaudeCliOutput> {
   const args = [
     "-p",
@@ -226,8 +225,6 @@ async function runClaudeCliOnce(params: {
   ];
   if (params.resumeSessionId) {
     args.push("--resume", params.resumeSessionId);
-  } else if (params.sessionId) {
-    args.push("--session-id", params.sessionId);
   }
   args.push(params.prompt);
 
@@ -297,12 +294,11 @@ export async function runClaudeCliAgent(params: {
       systemPrompt,
       timeoutMs: params.timeoutMs,
       resumeSessionId: params.resumeSessionId,
-      sessionId: params.sessionId,
     });
   } catch (err) {
     if (!params.resumeSessionId) throw err;
     log.warn(
-      `claude-cli resume failed for ${params.resumeSessionId}; retrying with --session-id (${params.sessionId})`,
+      `claude-cli resume failed for ${params.resumeSessionId}; retrying without resume`,
     );
     output = await runClaudeCliOnce({
       prompt: params.prompt,
@@ -310,7 +306,6 @@ export async function runClaudeCliAgent(params: {
       modelId,
       systemPrompt,
       timeoutMs: params.timeoutMs,
-      sessionId: params.sessionId,
     });
   }