diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4c9c1efc235..6b0876596fd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -105,6 +105,7 @@ Docs: https://docs.openclaw.ai
 - Agents/usage tracking: stop forcing `supportsUsageInStreaming: false` on non-native OpenAI-completions providers so compatible backends report token usage and cost again instead of showing all zeros. (#46500) Fixes #46142. Thanks @ademczuk.
 - Plugins/subagents: preserve gateway-owned plugin subagent access across runtime, tool, and embedded-runner load paths so gateway plugin tools and context engines can still spawn and manage subagents after the loader cache split. (#46648) Thanks @jalehman.
 - Control UI/overview: keep the language dropdown aligned with the persisted locale during dashboard startup so refreshing the page does not fall back to English before locale hydration completes. (#48019) Thanks @git-jxj.
+- Agents/compaction: rerun transcript repair after `session.compact()` so orphaned `tool_result` blocks cannot survive compaction and break later Anthropic requests. (#16095) thanks @claw-sylphx.
 
 ## 2026.3.13
 
diff --git a/src/agents/pi-embedded-runner/compact.ts b/src/agents/pi-embedded-runner/compact.ts
index ba001a6746a..ea6bc0c5299 100644
--- a/src/agents/pi-embedded-runner/compact.ts
+++ b/src/agents/pi-embedded-runner/compact.ts
@@ -64,7 +64,10 @@ import { ensureRuntimePluginsLoaded } from "../runtime-plugins.js";
 import { resolveSandboxContext } from "../sandbox.js";
 import { repairSessionFileIfNeeded } from "../session-file-repair.js";
 import { guardSessionManager } from "../session-tool-result-guard-wrapper.js";
-import { sanitizeToolUseResultPairing } from "../session-transcript-repair.js";
+import {
+  repairToolUseResultPairing,
+  sanitizeToolUseResultPairing,
+} from "../session-transcript-repair.js";
 import {
   acquireSessionWriteLock,
   resolveSessionLockMaxHoldFromTimeout,
@@ -954,6 +957,22 @@ export async function compactEmbeddedPiSessionDirect(
             },
           },
         );
+        // Re-run tool_use/tool_result pairing repair after compaction.
+        // Compaction can remove assistant messages containing tool_use blocks
+        // while leaving orphaned tool_result blocks behind, which causes
+        // Anthropic API 400 errors: "unexpected tool_use_id found in tool_result blocks".
+        // See: https://github.com/openclaw/openclaw/issues/15691
+        if (transcriptPolicy.repairToolUseResultPairing) {
+          const postCompactRepair = repairToolUseResultPairing(session.messages);
+          if (postCompactRepair.droppedOrphanCount > 0 || postCompactRepair.moved) {
+            session.agent.replaceMessages(postCompactRepair.messages);
+            log.info(
+              `[compaction] post-compact repair: dropped ${postCompactRepair.droppedOrphanCount} orphaned tool_result(s), ` +
+                `${postCompactRepair.droppedDuplicateCount} duplicate(s) ` +
+                `(sessionKey=${params.sessionKey ?? params.sessionId})`,
+            );
+          }
+        }
         await runPostCompactionSideEffects({
           config: params.config,
           sessionKey: params.sessionKey,
diff --git a/src/agents/session-transcript-repair.test.ts b/src/agents/session-transcript-repair.test.ts
index eea82268d7d..6ed5fdedb73 100644
--- a/src/agents/session-transcript-repair.test.ts
+++ b/src/agents/session-transcript-repair.test.ts
@@ -488,3 +488,143 @@ describe("stripToolResultDetails", () => {
     expect(out).toBe(input);
   });
 });
+
+describe("post-compaction orphaned tool_result removal (#15691)", () => {
+  it("drops orphaned tool_result blocks left after compaction removes tool_use messages", () => {
+    const input = castAgentMessages([
+      {
+        role: "assistant",
+        content: [{ type: "text", text: "Here is a summary of our earlier conversation..." }],
+      },
+      {
+        role: "toolResult",
+        toolCallId: "toolu_compacted_1",
+        toolName: "Read",
+        content: [{ type: "text", text: "file contents" }],
+        isError: false,
+      },
+      {
+        role: "toolResult",
+        toolCallId: "toolu_compacted_2",
+        toolName: "exec",
+        content: [{ type: "text", text: "command output" }],
+        isError: false,
+      },
+      { role: "user", content: "now do something else" },
+      {
+        role: "assistant",
+        content: [
+          { type: "text", text: "I'll read that file" },
+          { type: "toolCall", id: "toolu_active_1", name: "Read", arguments: { path: "foo.ts" } },
+        ],
+      },
+      {
+        role: "toolResult",
+        toolCallId: "toolu_active_1",
+        toolName: "Read",
+        content: [{ type: "text", text: "actual content" }],
+        isError: false,
+      },
+    ]);
+
+    const result = repairToolUseResultPairing(input);
+
+    expect(result.droppedOrphanCount).toBe(2);
+    const toolResults = result.messages.filter((message) => message.role === "toolResult");
+    expect(toolResults).toHaveLength(1);
+    expect((toolResults[0] as { toolCallId?: string }).toolCallId).toBe("toolu_active_1");
+    expect(result.messages.map((message) => message.role)).toEqual([
+      "assistant",
+      "user",
+      "assistant",
+      "toolResult",
+    ]);
+  });
+
+  it("handles synthetic tool_result from interrupted request after compaction", () => {
+    const input = castAgentMessages([
+      {
+        role: "assistant",
+        content: [{ type: "text", text: "Compaction summary of previous conversation." }],
+      },
+      {
+        role: "toolResult",
+        toolCallId: "toolu_interrupted",
+        toolName: "unknown",
+        content: [
+          {
+            type: "text",
+            text: "[openclaw] missing tool result in session history; inserted synthetic error result for transcript repair.",
+          },
+        ],
+        isError: true,
+      },
+      { role: "user", content: "continue please" },
+    ]);
+
+    const result = repairToolUseResultPairing(input);
+
+    expect(result.droppedOrphanCount).toBe(1);
+    expect(result.messages.some((message) => message.role === "toolResult")).toBe(false);
+    expect(result.messages.map((message) => message.role)).toEqual(["assistant", "user"]);
+  });
+
+  it("preserves valid tool_use/tool_result pairs while removing orphans", () => {
+    const input = castAgentMessages([
+      {
+        role: "assistant",
+        content: [
+          { type: "toolCall", id: "toolu_valid", name: "Read", arguments: { path: "a.ts" } },
+        ],
+      },
+      {
+        role: "toolResult",
+        toolCallId: "toolu_valid",
+        toolName: "Read",
+        content: [{ type: "text", text: "content of a.ts" }],
+        isError: false,
+      },
+      { role: "user", content: "thanks, what about b.ts?" },
+      {
+        role: "toolResult",
+        toolCallId: "toolu_gone",
+        toolName: "Read",
+        content: [{ type: "text", text: "content of old file" }],
+        isError: false,
+      },
+      {
+        role: "assistant",
+        content: [{ type: "text", text: "Let me check b.ts" }],
+      },
+    ]);
+
+    const result = repairToolUseResultPairing(input);
+
+    expect(result.droppedOrphanCount).toBe(1);
+    const toolResults = result.messages.filter((message) => message.role === "toolResult");
+    expect(toolResults).toHaveLength(1);
+    expect((toolResults[0] as { toolCallId?: string }).toolCallId).toBe("toolu_valid");
+  });
+
+  it("returns original array when no orphans exist", () => {
+    const input = castAgentMessages([
+      {
+        role: "assistant",
+        content: [{ type: "toolCall", id: "toolu_1", name: "Read", arguments: { path: "x.ts" } }],
+      },
+      {
+        role: "toolResult",
+        toolCallId: "toolu_1",
+        toolName: "Read",
+        content: [{ type: "text", text: "ok" }],
+        isError: false,
+      },
+      { role: "user", content: "good" },
+    ]);
+
+    const result = repairToolUseResultPairing(input);
+
+    expect(result.droppedOrphanCount).toBe(0);
+    expect(result.messages).toStrictEqual(input);
+  });
+});