diff --git a/src/subagent/agent-fleet.test.ts b/src/subagent/agent-fleet.test.ts
index be2dc4d55..43a3c75e6 100644
--- a/src/subagent/agent-fleet.test.ts
+++ b/src/subagent/agent-fleet.test.ts
@@ -135,6 +135,13 @@ async function callToolRaw(
   };
 }
 
+function parseFleetJson(content: string): Record<string, unknown> {
+  expect(content).toContain("\n");
+  const parsed = JSON.parse(content) as Record<string, unknown>;
+  expect(JSON.stringify(parsed, null, 2)).toBe(content);
+  return parsed;
+}
+
 async function callTool(
   tool:
     | ReturnType<typeof createSpawnAgentTool>
@@ -142,7 +149,7 @@ async function callTool(
   args: Record<string, unknown>,
 ): Promise<Record<string, unknown>> {
   const { content } = await callToolRaw(tool, args);
-  return JSON.parse(content);
+  return parseFleetJson(content);
 }
 
 describe("spawn_agent", () => {
@@ -196,6 +203,7 @@ describe("spawn_agent", () => {
     });
 
     expect(result.isError).toBe(true);
+    expect(result.content.startsWith("Error:")).toBe(true);
     expect(result.content).toContain("profile orchestrators are not supported");
     expect(runCalled).toBe(false);
     expect(deps.sessions.list()).toEqual([]);
@@ -291,6 +299,17 @@ describe("spawn_agent + wait_agents", () => {
     defined(gates[2]).resolve({ report: "third" });
   });
 
+  test("wait_agents with no uncollected agents returns empty pretty-printed results", async () => {
+    const deps = makeDeps(async () => ({ report: "unused" }));
+    const wait = createWaitAgentsTool({
+      sessions: deps.sessions,
+      fleetRecords: deps.fleetRecords,
+    });
+    const { content } = await callToolRaw(wait, { timeout_ms: 50 });
+    const parsed = parseFleetJson(content);
+    expect(parsed).toEqual({ results: [], timed_out: false });
+  });
+
   test("wait_agents times out on a still-running agent without cancelling it, and can be called again", async () => {
     const gate = deferred<RunSubAgentResult>();
     const deps = makeDeps(async () => gate.promise);
@@ -1975,7 +1994,7 @@ describe("list_agents", () => {
       typeof raw.content === "string"
         ? raw.content
         : JSON.stringify(raw.content);
-    const parsed = JSON.parse(content) as {
+    const parsed = parseFleetJson(content) as {
       agents: {
         agent_id: string;
         status: string;
@@ -2893,7 +2912,15 @@ describe("admission queue", () => {
       },
       new AbortController().signal,
     );
-    expect(raw.content).toContain('"status":"interrupted"');
+    const interrupted = parseFleetJson(
+      typeof raw.content === "string"
+        ? raw.content
+        : JSON.stringify(raw.content),
+    );
+    expect(interrupted).toEqual({
+      agent_id: result.agent_id,
+      status: "interrupted",
+    });
     expect(deps.sessions.get(result.agent_id as string)?.lifecycleStatus).toBe(
       "interrupted",
     );
diff --git a/src/subagent/agent-fleet.ts b/src/subagent/agent-fleet.ts
index c401912d5..5ca457fe2 100644
--- a/src/subagent/agent-fleet.ts
+++ b/src/subagent/agent-fleet.ts
@@ -619,6 +619,10 @@ function fleetResult(callId: string, content: string): ToolResult {
   return { callId, content, ...(isError ? { isError: true } : {}) };
 }
 
+function fleetJson(value: unknown): string {
+  return JSON.stringify(value, null, 2);
+}
+
 /** Resolve agent=/intent= to a closed director. */
 export function resolveDirectorDispatch(
   agentId: string | undefined,
@@ -1450,10 +1454,7 @@ export function createSpawnAgentTool(deps: AgentFleetDeps): AgentTool {
         start,
       });
       if (status === "queued") deps.fleetRecords.markQueued(session.id);
-      return fleetResult(
-        call.id,
-        JSON.stringify({ agent_id: session.id, status }),
-      );
+      return fleetResult(call.id, fleetJson({ agent_id: session.id, status }));
     },
   });
 }
@@ -1551,7 +1552,7 @@ export function createWaitAgentsTool(deps: WaitAgentsDeps): AgentTool {
       if (targets.length === 0) {
         return fleetResult(
           call.id,
-          JSON.stringify({ results: [], timed_out: false }),
+          fleetJson({ results: [], timed_out: false }),
         );
       }
 
@@ -1627,10 +1628,7 @@ export function createWaitAgentsTool(deps: WaitAgentsDeps): AgentTool {
         };
       });
 
-      return fleetResult(
-        call.id,
-        JSON.stringify({ results, timed_out: timedOut }),
-      );
+      return fleetResult(call.id, fleetJson({ results, timed_out: timedOut }));
     },
   });
 }
@@ -1678,7 +1676,7 @@ export function createListAgentsTool(deps: WaitAgentsDeps): AgentTool {
             : {}),
         };
       });
-      return fleetResult(call.id, JSON.stringify({ agents }));
+      return fleetResult(call.id, fleetJson({ agents }));
     },
   });
 }
diff --git a/src/subagent/lifecycle-tools.test.ts b/src/subagent/lifecycle-tools.test.ts
index 9fc60234f..d70b38ad1 100644
--- a/src/subagent/lifecycle-tools.test.ts
+++ b/src/subagent/lifecycle-tools.test.ts
@@ -15,6 +15,13 @@ import {
 import { createAdmissionQueue } from "./admission.js";
 import { defined } from "../../tests/helpers/defined.js";
 
+function parseFleetJson(content: string): Record<string, unknown> {
+  expect(content).toContain("\n");
+  const parsed = JSON.parse(content) as Record<string, unknown>;
+  expect(JSON.stringify(parsed, null, 2)).toBe(content);
+  return parsed;
+}
+
 async function callTool(
   tool:
     | ReturnType<typeof createCloseAgentTool>
@@ -38,7 +45,7 @@ async function callTool(
     typeof result.content === "string"
       ? result.content
       : JSON.stringify(result.content);
-  return JSON.parse(content);
+  return parseFleetJson(content);
 }
 
 describe("close_agent", () => {
@@ -659,6 +666,7 @@ describe("resume_agent", () => {
       new AbortController().signal,
     );
     expect(empty.isError).toBe(true);
+    expect(String(empty.content).startsWith("Error:")).toBe(true);
     expect(String(empty.content)).toContain("non-empty message");
 
     const oversize = await resumeAgent.handler(
diff --git a/src/subagent/lifecycle-tools.ts b/src/subagent/lifecycle-tools.ts
index c2efb957c..6d38dd3eb 100644
--- a/src/subagent/lifecycle-tools.ts
+++ b/src/subagent/lifecycle-tools.ts
@@ -32,6 +32,10 @@ function lifecycleResult(callId: string, content: string): ToolResult {
   return { callId, content, ...(isError ? { isError: true } : {}) };
 }
 
+function fleetJson(value: unknown): string {
+  return JSON.stringify(value, null, 2);
+}
+
 const CloseAgentArgs = type({
   target: "string",
 });
@@ -185,7 +189,7 @@ export function createCloseAgentTool(deps: CloseAgentToolDeps): AgentTool {
       if (deps.sessions.get(target) === undefined) {
         return lifecycleResult(
           call.id,
-          JSON.stringify({
+          fleetJson({
             agent_id: target,
             status: "not_found" satisfies AgentLifecycleStatus,
           }),
@@ -228,7 +232,7 @@ export function createCloseAgentTool(deps: CloseAgentToolDeps): AgentTool {
       const own = closed.find((c) => c.agent_id === target);
       return lifecycleResult(
         call.id,
-        JSON.stringify({
+        fleetJson({
           agent_id: target,
           status: own?.status ?? "shutdown",
           closed,
@@ -299,7 +303,7 @@ export function createResumeAgentTool(deps: ResumeAgentToolDeps): AgentTool {
       }
       return lifecycleResult(
         call.id,
-        JSON.stringify({ agent_id: target, status: outcome.status }),
+        fleetJson({ agent_id: target, status: outcome.status }),
       );
     },
   });
@@ -361,7 +365,7 @@ export function createInterruptAgentTool(
       deps.fleetRecords.interrupt(target);
       return lifecycleResult(
         call.id,
-        JSON.stringify({
+        fleetJson({
           agent_id: target,
           status: "interrupted" satisfies AgentLifecycleStatus,
         }),
@@ -474,7 +478,7 @@ export function createSendInputTool(deps: LifecycleToolDeps): AgentTool {
       }
       return lifecycleResult(
         call.id,
-        JSON.stringify({ agent_id: target, status: outcome.status }),
+        fleetJson({ agent_id: target, status: outcome.status }),
       );
     },
   });