From 79fac9fda92ce4e732a4fa81f89f39730c00abb7 Mon Sep 17 00:00:00 2001
From: Vincent Koc <vincentkoc@ieee.org>
Date: Sun, 21 Jun 2026 22:26:22 +0800
Subject: [PATCH] fix(agents): cap new prompt projection output

---
 .../tool-result-truncation.test.ts            | 25 +++++++++++++
 .../tool-result-truncation.ts                 | 36 +++++++++++++++++++
 2 files changed, 61 insertions(+)

diff --git a/src/agents/embedded-agent-runner/tool-result-truncation.test.ts b/src/agents/embedded-agent-runner/tool-result-truncation.test.ts
index 4fb13ea3f2d5..6df2a8aa879c 100644
--- a/src/agents/embedded-agent-runner/tool-result-truncation.test.ts
+++ b/src/agents/embedded-agent-runner/tool-result-truncation.test.ts
@@ -496,6 +496,31 @@ describe("truncateOversizedToolResultsInMessages", () => {
     );
     expect(stableFirst.truncatedCount).toBe(0);
     expect(stableSecond.messages.slice(0, stableHistory.length)).toEqual(stableFirst.messages);
+    const stableThird = truncateOversizedToolResultsInMessages(
+      [
+        ...stableHistory,
+        makeToolResult("c".repeat(15_000), "stable_3"),
+        makeToolResult("d".repeat(15_000), "stable_4"),
+      ],
+      128_000,
+      12_000,
+      12_000,
+      stableState,
+    );
+    const stableFourth = truncateOversizedToolResultsInMessages(
+      [
+        ...stableHistory,
+        makeToolResult("c".repeat(15_000), "stable_3"),
+        makeToolResult("d".repeat(15_000), "stable_4"),
+        makeToolResult("e".repeat(15_000), "stable_5"),
+      ],
+      128_000,
+      12_000,
+      12_000,
+      stableState,
+    );
+    const lastText = stableFourth.messages.at(-1);
+    expect(lastText && getToolResultTextLength(lastText)).toBeLessThanOrEqual(12_000);
   });
 
   it("does not restore filtered image blocks when reusing a projection", () => {
diff --git a/src/agents/embedded-agent-runner/tool-result-truncation.ts b/src/agents/embedded-agent-runner/tool-result-truncation.ts
index 2c0bdef5f94d..f74f33d10878 100644
--- a/src/agents/embedded-agent-runner/tool-result-truncation.ts
+++ b/src/agents/embedded-agent-runner/tool-result-truncation.ts
@@ -588,9 +588,45 @@ function buildAggregateToolResultReplacements(params: {
     remainingReduction -= actualReduction;
   }
 
+  if (remainingReduction > 0) {
+    for (const candidate of candidates.filter((item) => item.aggregateEligible)) {
+      if (remainingReduction <= 0) {
+        break;
+      }
+      if (replacements.some((replacement) => replacement.entryId === candidate.entryId)) {
+        continue;
+      }
+      const emptyMessage = clearToolResultText(candidate.message);
+      const actualReduction = Math.max(
+        0,
+        candidate.textLength - getToolResultTextLength(emptyMessage),
+      );
+      if (actualReduction <= 0) {
+        continue;
+      }
+      replacements.push({ entryId: candidate.entryId, message: emptyMessage });
+      remainingReduction -= actualReduction;
+    }
+  }
+
   return replacements;
 }
 
+function clearToolResultText(message: AgentMessage): AgentMessage {
+  const content = (message as { content?: unknown }).content;
+  if (!Array.isArray(content)) {
+    return message;
+  }
+  return {
+    ...message,
+    content: content.map((block) =>
+      block && typeof block === "object" && (block as { type?: unknown }).type === "text"
+        ? { ...block, text: "" }
+        : block,
+    ),
+  } as AgentMessage;
+}
+
 function buildOversizedToolResultReplacements(params: {
   branch: ToolResultBranchEntry[];
   maxChars: number;