diff --git a/src/agents/pi-extensions/compaction-safeguard.test.ts b/src/agents/pi-extensions/compaction-safeguard.test.ts
index b6256554c52..ef294a4f4c9 100644
--- a/src/agents/pi-extensions/compaction-safeguard.test.ts
+++ b/src/agents/pi-extensions/compaction-safeguard.test.ts
@@ -417,6 +417,48 @@ describe("compaction-safeguard recent-turn preservation", () => {
     );
   });
 
+  it("drops orphaned tool results from preserved assistant turns", () => {
+    const messages: AgentMessage[] = [
+      { role: "user", content: "older ask", timestamp: 1 },
+      {
+        role: "assistant",
+        content: [{ type: "toolCall", id: "call_old", name: "read", arguments: {} }],
+        timestamp: 2,
+      } as unknown as AgentMessage,
+      {
+        role: "toolResult",
+        toolCallId: "call_old",
+        toolName: "read",
+        content: [{ type: "text", text: "old result" }],
+        timestamp: 3,
+      } as unknown as AgentMessage,
+      { role: "user", content: "recent ask", timestamp: 4 },
+      {
+        role: "assistant",
+        content: [{ type: "toolCall", id: "call_recent", name: "read", arguments: {} }],
+        timestamp: 5,
+      } as unknown as AgentMessage,
+      {
+        role: "toolResult",
+        toolCallId: "call_recent",
+        toolName: "read",
+        content: [{ type: "text", text: "recent result" }],
+        timestamp: 6,
+      } as unknown as AgentMessage,
+    ];
+
+    const split = splitPreservedRecentTurns({
+      messages,
+      recentTurnsPreserve: 1,
+    });
+
+    const summarizableToolResultIds = split.summarizableMessages
+      .filter((msg) => msg.role === "toolResult")
+      .map((msg) => (msg as { toolCallId?: unknown }).toolCallId);
+    expect(summarizableToolResultIds).toContain("call_old");
+    expect(summarizableToolResultIds).not.toContain("call_recent");
+  });
+
   it("clamps preserve count into a safe range", () => {
     expect(resolveRecentTurnsPreserve(undefined)).toBe(3);
     expect(resolveRecentTurnsPreserve(-1)).toBe(0);
diff --git a/src/agents/pi-extensions/compaction-safeguard.ts b/src/agents/pi-extensions/compaction-safeguard.ts
index 0c492b26a15..a801fb800f6 100644
--- a/src/agents/pi-extensions/compaction-safeguard.ts
+++ b/src/agents/pi-extensions/compaction-safeguard.ts
@@ -18,6 +18,7 @@ import {
   summarizeInStages,
 } from "../compaction.js";
 import { collectTextContentBlocks } from "../content-blocks.js";
+import { repairToolUseResultPairing } from "../session-transcript-repair.js";
 import { getCompactionSafeguardRuntime } from "./compaction-safeguard-runtime.js";
 
 const log = createSubsystemLogger("compaction-safeguard");
@@ -222,13 +223,16 @@ function splitPreservedRecentTurns(params: {
   }
   const preservedIndexSet = new Set(candidateIndexes);
   const summarizableMessages = params.messages.filter((_, idx) => !preservedIndexSet.has(idx));
+  // Preserving recent assistant turns can orphan downstream toolResult messages.
+  // Repair pairings here so compaction summarization doesn't trip strict providers.
+  const repairedSummarizableMessages = repairToolUseResultPairing(summarizableMessages).messages;
   const preservedMessages = params.messages
     .filter((_, idx) => preservedIndexSet.has(idx))
     .filter((msg) => {
       const role = (msg as { role?: unknown }).role;
       return role === "user" || role === "assistant";
     });
-  return { summarizableMessages, preservedMessages };
+  return { summarizableMessages: repairedSummarizableMessages, preservedMessages };
 }
 
 function formatPreservedTurnsSection(messages: AgentMessage[]): string {