diff --git a/.changeset/green-ducks-applaud.md b/.changeset/green-ducks-applaud.md
new file mode 100644
index 0000000000..35a6e70ba0
--- /dev/null
+++ b/.changeset/green-ducks-applaud.md
@@ -0,0 +1,5 @@
+---
+"cline": patch
+---
+
+Canonicalize `attempt_completion` tool args by mapping `response` to `result` in the central tool executor to prevent intermittent missing-parameter retries with native parallel tool calling.
diff --git a/src/core/task/ToolExecutor.ts b/src/core/task/ToolExecutor.ts
index a9e0253627..ba38b594f1 100644
--- a/src/core/task/ToolExecutor.ts
+++ b/src/core/task/ToolExecutor.ts
@@ -54,6 +54,15 @@ import { createUIHelpers } from "./tools/types/UIHelpers"
 import { ToolDisplayUtils } from "./tools/utils/ToolDisplayUtils"
 import { ToolResultUtils } from "./tools/utils/ToolResultUtils"
 
+export function canonicalizeAttemptCompletionParams(block: ToolUse): boolean {
+	if (block.name === ClineDefaultTool.ATTEMPT && !block.params?.result && typeof block.params?.response === "string") {
+		block.params.result = block.params.response
+		return true
+	}
+
+	return false
+}
+
 export class ToolExecutor {
 	private autoApprover: AutoApprove
 	private coordinator: ToolExecutorCoordinator
@@ -360,6 +369,7 @@ export class ToolExecutor {
 		if (!this.coordinator.has(block.name)) {
 			return false // Tool not handled by coordinator
 		}
+		canonicalizeAttemptCompletionParams(block)
 
 		const config = this.asToolConfig()
 
diff --git a/src/core/task/__tests__/ToolExecutor.canonicalization.test.ts b/src/core/task/__tests__/ToolExecutor.canonicalization.test.ts
new file mode 100644
index 0000000000..2de3d3c019
--- /dev/null
+++ b/src/core/task/__tests__/ToolExecutor.canonicalization.test.ts
@@ -0,0 +1,58 @@
+import { strict as assert } from "node:assert"
+import { ClineDefaultTool } from "@shared/tools"
+import { describe, it } from "mocha"
+import type { ToolUse } from "../../assistant-message"
+import { canonicalizeAttemptCompletionParams } from "../ToolExecutor"
+
+describe("ToolExecutor canonicalization", () => {
+	it("canonicalizes attempt_completion response into result", () => {
+		const block: ToolUse = {
+			type: "tool_use",
+			name: ClineDefaultTool.ATTEMPT,
+			params: {
+				response: "final answer from response field",
+				task_progress: "- [x] done",
+			},
+			partial: false,
+		}
+
+		const didCanonicalize = canonicalizeAttemptCompletionParams(block)
+
+		assert.equal(didCanonicalize, true)
+		assert.equal(block.params.result, "final answer from response field")
+		assert.equal(block.params.response, "final answer from response field")
+	})
+
+	it("does not canonicalize when attempt_completion already has result", () => {
+		const block: ToolUse = {
+			type: "tool_use",
+			name: ClineDefaultTool.ATTEMPT,
+			params: {
+				result: "already canonical",
+				response: "extra text",
+			},
+			partial: false,
+		}
+
+		const didCanonicalize = canonicalizeAttemptCompletionParams(block)
+
+		assert.equal(didCanonicalize, false)
+		assert.equal(block.params.result, "already canonical")
+	})
+
+	it("does not canonicalize non-attempt tools", () => {
+		const block: ToolUse = {
+			type: "tool_use",
+			name: ClineDefaultTool.ACT_MODE,
+			params: {
+				response: "act mode response",
+			},
+			partial: false,
+		}
+
+		const didCanonicalize = canonicalizeAttemptCompletionParams(block)
+
+		assert.equal(didCanonicalize, false)
+		assert.equal(block.params.result, undefined)
+	})
+})