From b3bf49f826b78b02bef089252df8159eafcc3990 Mon Sep 17 00:00:00 2001
From: RSI smoke <rsi-smoke@example.invalid>
Date: Tue, 13 Oct 2026 21:13:41 -0600
Subject: [PATCH] Sanitize malformed tool-call arguments before echoing history
 (#11)

A truncated or empty arguments string echoed back in conversation
history makes Meta 400 the next request ('arguments must be valid
JSON'), fail-closing the pilot. Replace unparseable arguments with {}
on the wire; the journal keeps the raw response and the run continues
through the designed error-nudge path.
---
 scripts/monitor-pilot/live-runner.ts         | 15 ++++++++++++++-
 src/monitoring/__tests__/live-runner.test.ts | 20 ++++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/scripts/monitor-pilot/live-runner.ts b/scripts/monitor-pilot/live-runner.ts
index 9f814eb..8a5f62b 100644
--- a/scripts/monitor-pilot/live-runner.ts
+++ b/scripts/monitor-pilot/live-runner.ts
@@ -282,7 +282,20 @@ function parseArgs(call: { readonly id: string; readonly function: { readonly na
 }
 
 function toolCallMessage(response: LlmResponse): ChatMessage {
-	return response.message
+	const toolCalls = response.message.tool_calls?.map((call) => {
+		if (isJsonObjectArguments(call.function.arguments)) return call
+		return { ...call, function: { ...call.function, arguments: "{}" } }
+	})
+	return { ...response.message, tool_calls: toolCalls }
+}
+
+function isJsonObjectArguments(raw: string): boolean {
+	try {
+		const parsed: unknown = JSON.parse(raw)
+		return parsed !== null && typeof parsed === "object" && !Array.isArray(parsed)
+	} catch {
+		return false
+	}
 }
 
 function stableCallBatchSignature(calls: readonly PilotToolCall[]): string {
diff --git a/src/monitoring/__tests__/live-runner.test.ts b/src/monitoring/__tests__/live-runner.test.ts
index 79029cb..87d3755 100644
--- a/src/monitoring/__tests__/live-runner.test.ts
+++ b/src/monitoring/__tests__/live-runner.test.ts
@@ -456,6 +456,25 @@ async function testReasoningHeavyNativeOverrunIsAccepted(): Promise<void> {
 	} finally { await fs.rm(directory, { recursive: true, force: true }) }
 }
 
+async function testMalformedArgumentsAreSanitizedOnEcho(): Promise<void> {
+	const directory = await scratch()
+	try {
+		const broken = { name: "apply_diff", args: "{\"content\":\"truncated" }
+		const done = { name: "attempt_completion",
+			args: JSON.stringify({ result: "done" }) }
+		const client = new MockBillingClient([broken, done])
+		const summary = await collectLiveDevelopment({ outputDir: directory, client })
+		assert.equal(summary.abortedAttempts, 0)
+		assert.equal(summary.completedRuns, 32)
+		const history = client.requests[1]?.messages ?? []
+		const calls = history.filter((message) => {
+			return (message.tool_calls?.length ?? 0) > 0
+		})
+		const echoed = calls[0]?.tool_calls?.[0]?.function.arguments
+		assert.equal(echoed, "{}")
+	} finally { await fs.rm(directory, { recursive: true, force: true }) }
+}
+
 async function testHeldoutCannotStartWithoutQualifiedDevelopment(): Promise<void> {
 	const directory = await scratch()
 	try {
@@ -537,6 +556,7 @@ await testCopiedGlobalLedgerEpochsDoNotBlockResume()
 await testKnownPerRunAdmissionStopCompletesAndSettlesTrajectory()
 await testCompletionOverrunIsJournaledBeforeAnyToolDispatch()
 await testReasoningHeavyNativeOverrunIsAccepted()
+await testMalformedArgumentsAreSanitizedOnEcho()
 await testHeldoutCannotStartWithoutQualifiedDevelopment()
 await testHeldoutRejectsDifferentFrozenOutputCapBeforeInference()
 await testStorageRootSymlinkIsRejectedBeforeInference()