fix: Disable memfs for newly spawned subagents [LET-7975] (#1371)

src/agent/subagents/manager.ts

@@ -534,6 +534,9 @@ export function buildSubagentArgs(
     // Create new agent (original behavior)
     args.push("--new-agent", "--system", type);
     args.push("--tags", `type:${type}`);
+    // Default all newly spawned subagents to non-memfs mode.
+    // This avoids memfs startup overhead unless explicitly enabled elsewhere.
+    args.push("--no-memfs");
     if (model) {
       args.push("--model", model);
     }
@@ -575,9 +578,6 @@ export function buildSubagentArgs(
   if (!isDeployingExisting) {
     if (config.memoryBlocks === "none") {
       args.push("--init-blocks", "none");
-      if (config.mode === "stateless") {
-        args.push("--no-memfs");
-      }
     } else if (
       Array.isArray(config.memoryBlocks) &&
       config.memoryBlocks.length > 0

src/tests/agent/subagent-model-resolution.test.ts

@@ -121,7 +121,7 @@ describe("resolveSubagentLauncher", () => {
 });
 
 describe("buildSubagentArgs", () => {
-  const baseConfig: Omit<SubagentConfig, "mode"> = {
+  const baseConfig: SubagentConfig = {
     name: "test-subagent",
     description: "test",
     systemPrompt: "test prompt",
@@ -129,31 +129,28 @@ describe("buildSubagentArgs", () => {
     recommendedModel: "inherit",
     skills: [],
     memoryBlocks: "none",
+    mode: "stateful",
   };
 
-  test("adds --no-memfs for stateless subagents with memoryBlocks none", () => {
-    const args = buildSubagentArgs(
-      "test-subagent",
-      { ...baseConfig, mode: "stateless" },
-      null,
-      "hello",
-    );
+  test("adds --no-memfs for newly spawned subagents by default", () => {
+    const args = buildSubagentArgs("test-subagent", baseConfig, null, "hello");
 
     expect(args).toContain("--init-blocks");
     expect(args).toContain("none");
     expect(args).toContain("--no-memfs");
   });
 
-  test("does not add --no-memfs for stateful subagents with memoryBlocks none", () => {
+  test("does not force --no-memfs when deploying an existing subagent agent", () => {
     const args = buildSubagentArgs(
       "test-subagent",
-      { ...baseConfig, mode: "stateful" },
+      baseConfig,
       null,
       "hello",
+      "agent-existing",
     );
 
-    expect(args).toContain("--init-blocks");
-    expect(args).toContain("none");
+    expect(args).toContain("--agent");
+    expect(args).not.toContain("--new-agent");
     expect(args).not.toContain("--no-memfs");
   });
 });