diff --git a/frontend/src/lib/components/agentTrace.test.ts b/frontend/src/lib/components/agentTrace.test.ts
index d2df80107a..2cca3177ee 100644
--- a/frontend/src/lib/components/agentTrace.test.ts
+++ b/frontend/src/lib/components/agentTrace.test.ts
@@ -144,3 +144,17 @@ describe('the max-iterations path', () => {
 		])
 	})
 })
+
+// A result is whatever a script returned, so every nested field is arbitrary even
+// once the messages have roles. A throw in here takes down the whole result
+// viewer, including the ordinary error such a payload usually rides on.
+describe('a malformed message that still has a role', () => {
+	it.each([
+		['tool_calls that are not a list', { role: 'assistant', tool_calls: {} }],
+		['annotations that are not a list', { role: 'assistant', content: 'hi', annotations: 'abc' }],
+		['a content object', { role: 'assistant', content: { text: 'hi' } }],
+		['an agent_action that is not an object', { role: 'tool', agent_action: 'tool_call' }]
+	])('survives %s', (_label, message) => {
+		expect(() => buildAgentTrace([message as never])).not.toThrow()
+	})
+})
diff --git a/frontend/src/lib/components/agentTrace.ts b/frontend/src/lib/components/agentTrace.ts
index 2f7827df61..a30bb1c4cf 100644
--- a/frontend/src/lib/components/agentTrace.ts
+++ b/frontend/src/lib/components/agentTrace.ts
@@ -46,7 +46,7 @@ function contentText(content: unknown): string {
 
 function sourcesOf(message: AgentMessage): WebSearchSource[] | undefined {
 	const annotations = message.annotations
-	if (!annotations?.length) {
+	if (!Array.isArray(annotations) || annotations.length === 0) {
 		return undefined
 	}
 	const sources = annotations
@@ -61,7 +61,14 @@ export function buildAgentTrace(messages: AgentMessage[]): AgentTraceEntry[] {
 	// the two are joined by `tool_call_id`.
 	const argsByCallId = new Map<string, string>()
 	for (const message of messages) {
-		for (const call of message.tool_calls ?? []) {
+		// A job result is whatever its script returned, and the shape check that got
+		// us here only proves each message has a `role`. Anything nested is still
+		// arbitrary, and a throw here would take the whole result viewer down with
+		// it — including the plain error a lookalike payload is usually attached to.
+		if (!Array.isArray(message.tool_calls)) {
+			continue
+		}
+		for (const call of message.tool_calls) {
 			if (call.id && typeof call.function?.arguments === 'string') {
 				argsByCallId.set(call.id, call.function.arguments)
 			}