diff --git a/harness/src/run-leaf.ts b/harness/src/run-leaf.ts
index 701478e..d4ece49 100644
--- a/harness/src/run-leaf.ts
+++ b/harness/src/run-leaf.ts
@@ -16,6 +16,7 @@ import { BufferedRedisBackend } from "./buffered-redis-backend.js";
 import { flushExtension } from "./flush-extension.js";
 import { checkpointExtension } from "./checkpoint-extension.js";
 import { submitVerdictExtension, VERDICT_ENTRY_TYPE, type VerdictCapture } from "./submit-verdict-tool.js";
+import { verdictTerminationExtension } from "./verdict-termination-extension.js";
 import { validateVerdict, type Verdict } from "./verdict.js";
 import type { GateCapture } from "./request-approval-tool.js";
 import { computeGateState, decideSeed, validateDecision, type Decision, GATE_DECISION_ENTRY_TYPE } from "./gate.js";
@@ -446,6 +447,7 @@ export const realProduceVerdict: ProduceVerdict = async (item, env, config, capt
         k8sSandboxExtension({ config: selected?.config ?? null, transport: selected?.transport }),
         flushExtension(backend),
         checkpointExtension(store, sessionManager),
+        verdictTerminationExtension(capture, { maxTurns: env.maxTurns }),
       ],
     });
     await resourceLoader.reload();
diff --git a/harness/src/submit-verdict-tool.ts b/harness/src/submit-verdict-tool.ts
index cd0f8f5..5a80f89 100644
--- a/harness/src/submit-verdict-tool.ts
+++ b/harness/src/submit-verdict-tool.ts
@@ -50,7 +50,11 @@ export function submitVerdictExtension(capture: VerdictCapture, sink?: VerdictSi
         }
         capture.verdict = r.value;
         sink?.appendCustomEntry(VERDICT_ENTRY_TYPE, r.value);
-        return { content: [{ type: "text", text: "Verdict recorded." }] };
+        // `terminate: true` tells agent-loop.ts to stop the turn loop after this tool call
+        // (AgentToolResult.terminate) — without it the model just keeps getting re-prompted
+        // and calls submit_verdict again, sometimes thousands of times, until something
+        // external kills the pod.
+        return { content: [{ type: "text", text: "Verdict recorded." }], terminate: true };
       },
     } as any);
   };
diff --git a/harness/src/verdict-termination-extension.ts b/harness/src/verdict-termination-extension.ts
new file mode 100644
index 0000000..773eb97
--- /dev/null
+++ b/harness/src/verdict-termination-extension.ts
@@ -0,0 +1,58 @@
+import type { ExtensionAPI, ExtensionFactory } from "@earendil-works/pi-coding-agent";
+import type { VerdictCapture } from "./submit-verdict-tool.js";
+
+export interface TurnCounter {
+  turns: number;
+}
+
+// Envelopes don't always set `maxTurns` (it's optional on LeafEnvelope), but the runaway-loop
+// bug this extension exists to prevent has no other guard — so fall back to a hard cap even when
+// the caller omits one, rather than silently skipping turn-limiting for those leaves.
+const DEFAULT_MAX_TURNS = 40;
+
+/**
+ * Backstop for the leaf agent loop: caps total turns even if a verdict is never submitted, and
+ * blocks any further tool calls once a verdict HAS been captured (in case the model tries to call
+ * more tools after submit_verdict, e.g. as part of a parallel batch that didn't all set
+ * `terminate`). The primary fix lives in submit-verdict-tool.ts, which now sets `terminate: true`
+ * on its own tool result — agent-loop.ts stops the turn loop as soon as every tool call in a batch
+ * sets that flag (AgentToolResult.terminate). This extension exists because that primary fix only
+ * covers the "model calls submit_verdict cleanly" path; without a cap, a model that never calls
+ * submit_verdict (or calls it alongside other tools that don't terminate) can still spin forever —
+ * one observed leaf called submit_verdict ~1,269 times before an external pod kill stopped it.
+ *
+ * `tool_call`'s `block` result is the only extension hook that can halt execution here —
+ * `tool_result`/`turn_end` results carry no loop-control field (AgentSession.afterToolCall drops
+ * any `terminate` an extension tries to set on `tool_result`). Blocking still costs one turn (the
+ * model sees a "blocked" tool error and gets re-prompted) rather than stopping instantly, so this
+ * is a safety net, not the fast path. `runLeaf` already treats a leaf with no captured verdict as
+ * `no_verdict` (a normal, already-handled failure outcome), so hitting the turn cap without a
+ * verdict fails cleanly instead of hanging the queue message forever.
+ */
+export function verdictTerminationExtension(
+  capture: VerdictCapture,
+  opts: { maxTurns?: number } = {},
+): ExtensionFactory {
+  const counter: TurnCounter = { turns: 0 };
+  // Treat a missing OR non-positive maxTurns as "use the default" — a nullish-coalesce alone would
+  // let an explicit 0 (or negative) through, which then fails the `> 0` guard below and silently
+  // DISABLES the cap (unbounded), the opposite of what a caller passing 0 would expect.
+  const maxTurns = typeof opts.maxTurns === "number" && opts.maxTurns > 0 ? opts.maxTurns : DEFAULT_MAX_TURNS;
+  return (pi: ExtensionAPI) => {
+    pi.on("turn_start", () => {
+      counter.turns += 1;
+    });
+    pi.on("tool_call", (event) => {
+      if (capture.verdict) {
+        return { block: true, reason: "Verdict already submitted for this item — task complete." };
+      }
+      if (typeof maxTurns === "number" && maxTurns > 0 && counter.turns > maxTurns) {
+        return {
+          block: true,
+          reason: `Turn limit (${maxTurns}) reached without a submitted verdict — stopping.`,
+        };
+      }
+      return {};
+    });
+  };
+}
diff --git a/harness/test/submit-verdict-tool.test.ts b/harness/test/submit-verdict-tool.test.ts
index 43a6e8a..3785d0c 100644
--- a/harness/test/submit-verdict-tool.test.ts
+++ b/harness/test/submit-verdict-tool.test.ts
@@ -25,6 +25,22 @@ describe("submitVerdictExtension", () => {
     expect(res.isError).toBeFalsy();
   });
 
+  it("sets terminate: true on a successful verdict, so agent-loop.ts stops the turn loop", async () => {
+    const capture: VerdictCapture = {};
+    const { api, tools } = fakePi();
+    submitVerdictExtension(capture)(api);
+    const res = await tools[0].execute("call-1", { item_id: "i1", verdict: "CLEAR", reason: "r" }, undefined, undefined, {} as any);
+    expect(res.terminate).toBe(true);
+  });
+
+  it("does not set terminate on an invalid verdict (agent should retry, not stop)", async () => {
+    const capture: VerdictCapture = {};
+    const { api, tools } = fakePi();
+    submitVerdictExtension(capture)(api);
+    const res = await tools[0].execute("call-1", { item_id: "i1", verdict: "MAYBE", reason: "r" }, undefined, undefined, {} as any);
+    expect(res.terminate).toBeFalsy();
+  });
+
   it("rejects an invalid verdict and does not capture", async () => {
     const capture: VerdictCapture = {};
     const { api, tools } = fakePi();
diff --git a/harness/test/verdict-termination-extension.test.ts b/harness/test/verdict-termination-extension.test.ts
new file mode 100644
index 0000000..55073a4
--- /dev/null
+++ b/harness/test/verdict-termination-extension.test.ts
@@ -0,0 +1,72 @@
+import { describe, it, expect } from "vitest";
+import { verdictTerminationExtension } from "../src/verdict-termination-extension";
+import type { VerdictCapture } from "../src/submit-verdict-tool";
+
+function fakePi() {
+  const handlers: Record<string, Function> = {};
+  const pi = { on: (ev: string, h: Function) => { handlers[ev] = h; } };
+  return { pi: pi as any, handlers };
+}
+
+describe("verdictTerminationExtension", () => {
+  it("does not block tool calls before a verdict is captured and under the turn cap", () => {
+    const capture: VerdictCapture = {};
+    const { pi, handlers } = fakePi();
+    verdictTerminationExtension(capture, { maxTurns: 5 })(pi);
+    const result = handlers["tool_call"]({});
+    expect(result).toEqual({});
+  });
+
+  it("blocks tool calls once a verdict has already been captured", () => {
+    const capture: VerdictCapture = { verdict: { item_id: "i1", verdict: "CLEAR", reason: "r" } };
+    const { pi, handlers } = fakePi();
+    verdictTerminationExtension(capture, { maxTurns: 5 })(pi);
+    const result = handlers["tool_call"]({});
+    expect(result.block).toBe(true);
+    expect(result.reason).toMatch(/verdict already submitted/i);
+  });
+
+  it("blocks tool calls once maxTurns is exceeded without a verdict", () => {
+    const capture: VerdictCapture = {};
+    const { pi, handlers } = fakePi();
+    verdictTerminationExtension(capture, { maxTurns: 2 })(pi);
+    // turn_start fires once per turn; simulate 3 turns (exceeds cap of 2)
+    handlers["turn_start"]();
+    handlers["turn_start"]();
+    handlers["turn_start"]();
+    const result = handlers["tool_call"]({});
+    expect(result.block).toBe(true);
+    expect(result.reason).toMatch(/turn limit/i);
+  });
+
+  it("does not block at exactly the turn cap (only after exceeding it)", () => {
+    const capture: VerdictCapture = {};
+    const { pi, handlers } = fakePi();
+    verdictTerminationExtension(capture, { maxTurns: 2 })(pi);
+    handlers["turn_start"]();
+    handlers["turn_start"]();
+    const result = handlers["tool_call"]({});
+    expect(result).toEqual({});
+  });
+
+  it("applies a default turn cap when maxTurns is omitted (never leaves the loop unbounded)", () => {
+    const capture: VerdictCapture = {};
+    const { pi, handlers } = fakePi();
+    verdictTerminationExtension(capture)(pi);
+    for (let i = 0; i < 41; i++) handlers["turn_start"]();
+    const result = handlers["tool_call"]({});
+    expect(result.block).toBe(true);
+    expect(result.reason).toMatch(/turn limit/i);
+  });
+
+  it("treats maxTurns: 0 as 'use default' rather than disabling the cap", () => {
+    const capture: VerdictCapture = {};
+    const { pi, handlers } = fakePi();
+    verdictTerminationExtension(capture, { maxTurns: 0 })(pi);
+    // 0 must NOT mean unbounded — it should fall back to the default cap and still block.
+    for (let i = 0; i < 41; i++) handlers["turn_start"]();
+    const result = handlers["tool_call"]({});
+    expect(result.block).toBe(true);
+    expect(result.reason).toMatch(/turn limit/i);
+  });
+});