diff --git a/package.json b/package.json
index c1578fc5..0c43b448 100644
--- a/package.json
+++ b/package.json
@@ -4,7 +4,6 @@
   "private": true,
   "type": "module",
   "scripts": {
-    "validate": "node scripts/validate-plugins.mjs"
+    "validate": "node scripts/validate-plugins.mjs && node --test plugins/agents-squad/schema-portability.test.mjs"
   }
 }
-
diff --git a/plugins/agents-squad/index.ts b/plugins/agents-squad/index.ts
index 4894905e..7117423e 100644
--- a/plugins/agents-squad/index.ts
+++ b/plugins/agents-squad/index.ts
@@ -5,7 +5,7 @@ import {
 	readFileSync,
 	writeFileSync,
 } from "node:fs";
-import { dirname, join, resolve } from "node:path";
+import { dirname, isAbsolute, join, relative, resolve, sep } from "node:path";
 import { fileURLToPath } from "node:url";
 import {
 	type AgentPlugin,
@@ -90,6 +90,8 @@ const GLOBAL_SKILLS_DIR = join(resolveClineDataDirPath(), "settings", "skills");
 
 /** Safe identifier pattern for conversation IDs used in filesystem paths. */
 const SAFE_ID_RE = /^[A-Za-z0-9_-]+$/;
+const HANDOFF_PATH_ALLOWED_RE = /^[A-Za-z0-9._/-]+$/;
+const HANDOFF_PATH_MAX_LENGTH = 240;
 
 const envOr = (key: string, fallback: string): string =>
 	process.env[key]?.trim() || fallback;
@@ -298,14 +300,45 @@ function resolveHandoffPath(
 	ctx: AgentToolContext,
 	relativePath: string,
 ): string {
+	const handoffPath = validateHandoffRelativePath(relativePath);
 	const dir = handoffsDir(ctx);
-	const resolved = resolve(dir, relativePath);
-	if (!resolved.startsWith(`${dir}/`)) {
+	const resolved = resolve(dir, handoffPath);
+	const pathFromHandoffsDir = relative(dir, resolved);
+	if (
+		!pathFromHandoffsDir ||
+		pathFromHandoffsDir === ".." ||
+		pathFromHandoffsDir.startsWith(`..${sep}`) ||
+		isAbsolute(pathFromHandoffsDir)
+	) {
 		throw new Error(`Handoff path escapes directory: ${relativePath}`);
 	}
 	return resolved;
 }
 
+function validateHandoffRelativePath(relativePath: string): string {
+	const trimmed = relativePath.trim();
+	if (!trimmed) {
+		throw new Error("Handoff path must not be empty");
+	}
+	if (trimmed.length > HANDOFF_PATH_MAX_LENGTH) {
+		throw new Error(
+			`Handoff path must be ${HANDOFF_PATH_MAX_LENGTH} characters or fewer`,
+		);
+	}
+	if (trimmed.startsWith("/")) {
+		throw new Error(`Handoff path must be relative: ${relativePath}`);
+	}
+	if (!HANDOFF_PATH_ALLOWED_RE.test(trimmed)) {
+		throw new Error(
+			"Use a relative file path with letters, numbers, '.', '_', '-', or '/'.",
+		);
+	}
+	if (trimmed.split("/").includes("..")) {
+		throw new Error(`Handoff path must not contain '..': ${relativePath}`);
+	}
+	return trimmed;
+}
+
 function emitSteer(sessionId: string | undefined, prompt: string): void {
 	if (sessionId && prompt.trim()) {
 		globalThis.__clinePluginHost?.emitEvent?.("steer_message", {
@@ -407,9 +440,8 @@ const HandoffPathInput = z
 	.trim()
 	.min(1)
 	.max(240)
-	.regex(
-		/^(?!\/)(?!.*(?:^|\/)\.\.(?:\/|$))[A-Za-z0-9._/-]+$/,
-		"Use a relative file path with letters, numbers, '.', '_', '-', or '/'.",
+	.describe(
+		"Relative file path using letters, numbers, '.', '_', '-', or '/'. Must not be absolute or contain '..' segments.",
 	);
 
 const StartSubagentInput = z
diff --git a/plugins/agents-squad/schema-portability.test.mjs b/plugins/agents-squad/schema-portability.test.mjs
new file mode 100644
index 00000000..c5e2faef
--- /dev/null
+++ b/plugins/agents-squad/schema-portability.test.mjs
@@ -0,0 +1,52 @@
+import assert from "node:assert/strict";
+import { readFile } from "node:fs/promises";
+import { test } from "node:test";
+
+const pluginSource = await readFile(new URL("./index.ts", import.meta.url), "utf8");
+
+function containsZodRegexLookaround(source) {
+	for (const match of source.matchAll(/\.regex\(\s*\//g)) {
+		let escaped = false;
+		let inCharacterClass = false;
+		for (let index = match.index + match[0].length; index < source.length; index++) {
+			const character = source[index];
+			if (escaped) {
+				escaped = false;
+				continue;
+			}
+			if (character === "\\") {
+				escaped = true;
+				continue;
+			}
+			if (character === "[") {
+				inCharacterClass = true;
+				continue;
+			}
+			if (character === "]" && inCharacterClass) {
+				inCharacterClass = false;
+				continue;
+			}
+			if (character === "/" && !inCharacterClass) break;
+			if (character !== "(" || inCharacterClass || source[index + 1] !== "?") continue;
+			const marker = source.slice(index + 2, index + 4);
+			if (marker[0] === "=" || marker[0] === "!" || marker === "<=" || marker === "<!") {
+				return true;
+			}
+		}
+	}
+	return false;
+}
+
+test("model-facing handoff schemas avoid regex lookarounds", () => {
+	assert.equal(
+		containsZodRegexLookaround(pluginSource),
+		false,
+		"OpenAI-compatible providers reject regex lookarounds in tool JSON Schemas",
+	);
+});
+
+test("schema detector distinguishes lookarounds from literal text", () => {
+	assert.equal(containsZodRegexLookaround("z.string().regex(/^(?!\\/).+$/)"), true);
+	assert.equal(containsZodRegexLookaround(String.raw`z.string().regex(/\(?!literal/)`), false);
+	assert.equal(containsZodRegexLookaround("z.string().regex(/[(?!)]/ )"), false);
+});