diff --git a/packages/ai/CHANGELOG.md b/packages/ai/CHANGELOG.md
index 59a7fae0..132ef082 100644
--- a/packages/ai/CHANGELOG.md
+++ b/packages/ai/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+- Fixed OpenAI Responses replay for foreign tool-call item IDs by hashing foreign `function_call.id` values into bounded `fc_<hash>` IDs instead of preserving backend-specific normalized shapes that OpenAI Codex rejects.
+
 ## [0.61.1] - 2026-03-20
 
 ### Changed
diff --git a/packages/ai/src/providers/openai-responses-shared.ts b/packages/ai/src/providers/openai-responses-shared.ts
index e74e6d13..63858536 100644
--- a/packages/ai/src/providers/openai-responses-shared.ts
+++ b/packages/ai/src/providers/openai-responses-shared.ts
@@ -97,14 +97,20 @@ export function convertResponsesMessages<TApi extends Api>(
 		return normalized.replace(/_+$/, "");
 	};
 
-	const normalizeToolCallId = (id: string): string => {
+	const buildForeignResponsesItemId = (itemId: string): string => {
+		const normalized = `fc_${shortHash(itemId)}`;
+		return normalized.length > 64 ? normalized.slice(0, 64) : normalized;
+	};
+
+	const normalizeToolCallId = (id: string, _targetModel: Model<TApi>, source: AssistantMessage): string => {
 		if (!allowedToolCallProviders.has(model.provider)) return normalizeIdPart(id);
 		if (!id.includes("|")) return normalizeIdPart(id);
 		const [callId, itemId] = id.split("|");
 		const normalizedCallId = normalizeIdPart(callId);
-		let normalizedItemId = normalizeIdPart(itemId);
+		const isForeignToolCall = source.provider !== model.provider || source.api !== model.api;
+		let normalizedItemId = isForeignToolCall ? buildForeignResponsesItemId(itemId) : normalizeIdPart(itemId);
 		// OpenAI Responses API requires item id to start with "fc"
-		if (!normalizedItemId.startsWith("fc")) {
+		if (!normalizedItemId.startsWith("fc_")) {
 			normalizedItemId = normalizeIdPart(`fc_${normalizedItemId}`);
 		}
 		return `${normalizedCallId}|${normalizedItemId}`;
diff --git a/packages/ai/test/openai-responses-foreign-toolcall-id.test.ts b/packages/ai/test/openai-responses-foreign-toolcall-id.test.ts
new file mode 100644
index 00000000..c50fcc88
--- /dev/null
+++ b/packages/ai/test/openai-responses-foreign-toolcall-id.test.ts
@@ -0,0 +1,66 @@
+import { describe, expect, it } from "vitest";
+import { getModel } from "../src/models.js";
+import { convertResponsesMessages } from "../src/providers/openai-responses-shared.js";
+import type { AssistantMessage, Context, ToolResultMessage, Usage } from "../src/types.js";
+import { shortHash } from "../src/utils/hash.js";
+
+const COPILOT_RAW_TOOL_CALL_ID =
+	"call_4VnzVawQXPB9MgYib7CiQFEY|I9b95oN1wD/cHXKTw3PpRkL6KkCtzTJhUxMouMWYwHeTo2j3htzfSk7YPx2vifiIM4g3A8XXyOj8q4Bt6SLUG7gqY1E3ELkrkVQNHglRfUmWj84lqxJY+Puieb3VKyX0FB+83TUzn91cDMF/4gzt990IzqVrc+nIb9RRscRD070Du16q1glydVjWR0SBJsE6TbY/esOjFpqplogQqrajm1eI++f3eLi73R6q7hVusY0QbeFySVxABCjhN0lXB04caBe1rzHjYzul6MAXj7uq+0r17VLq+yrtyYhN12wkmFqHeqTyEei6EFPbMy24Nc+IbJlkP0OCg02W+gOnyBFcbi2ctvJFSOhSjt1CqBdqCnnhwUqXjbWiT0wh3DmLScRgTHmGkaI+oAcQQjfic65nxj+TnEkReA==";
+
+const usage: Usage = {
+	input: 0,
+	output: 0,
+	cacheRead: 0,
+	cacheWrite: 0,
+	totalTokens: 0,
+	cost: { input: 0, output: 0, cacheRead: 0, cacheWrite: 0, total: 0 },
+};
+
+describe("OpenAI Responses foreign tool call ID normalization", () => {
+	it("hashes foreign Copilot tool item IDs into a bounded Codex-safe fc_<hash> shape", () => {
+		const model = getModel("openai-codex", "gpt-5.3-codex");
+		const assistant: AssistantMessage = {
+			role: "assistant",
+			content: [
+				{
+					type: "toolCall",
+					id: COPILOT_RAW_TOOL_CALL_ID,
+					name: "edit",
+					arguments: { path: "src/styles/app.css" },
+				},
+			],
+			api: "openai-responses",
+			provider: "github-copilot",
+			model: "gpt-5.3-codex",
+			usage,
+			stopReason: "toolUse",
+			timestamp: Date.now() - 2000,
+		};
+		const toolResult: ToolResultMessage = {
+			role: "toolResult",
+			toolCallId: COPILOT_RAW_TOOL_CALL_ID,
+			toolName: "edit",
+			content: [{ type: "text", text: "ok" }],
+			isError: false,
+			timestamp: Date.now() - 1000,
+		};
+		const context: Context = {
+			systemPrompt: "You are concise.",
+			messages: [{ role: "user", content: "Use the tool.", timestamp: Date.now() - 3000 }, assistant, toolResult],
+		};
+
+		const input = convertResponsesMessages(model, context, new Set(["openai", "openai-codex", "opencode"]));
+		const functionCall = input.find((item) => item.type === "function_call");
+
+		expect(functionCall).toBeDefined();
+		expect(functionCall?.type).toBe("function_call");
+		if (!functionCall || functionCall.type !== "function_call") {
+			throw new Error("Expected function_call item");
+		}
+
+		const expectedItemId = `fc_${shortHash(COPILOT_RAW_TOOL_CALL_ID.split("|")[1]!)}`;
+		expect(functionCall.id).toBe(expectedItemId);
+		expect(functionCall.id?.length ?? 0).toBeLessThanOrEqual(64);
+		expect(functionCall.id).toMatch(/^fc_[A-Za-z0-9]+$/);
+	});
+});