fix(opencode): keep stderr tails on character boundaries

plugins/opencode/src/command.ts

@@ -71,7 +71,10 @@ export function rpc(executable: string, request: object, signal: AbortSignal): P
     // Hook output only reaches the host through these messages, and hook
     // failures arrive as structured errors from a zero exit.
     const describe = (message: string) => {
-      const detail = tail.toString().trim()
+      // Skip UTF-8 continuation bytes left by cutting the tail mid-character.
+      let start = 0
+      while ((tail[start] & 0xc0) === 0x80) start++
+      const detail = tail.subarray(start).toString().trim()
       return detail ? `${message}: ${detail}` : message
     }
     child.on("error", (error) => finish(() => reject(error)))

plugins/opencode/test/command.test.ts

@@ -39,7 +39,7 @@ const timer = setInterval(() => {
   await writeFile(join(temp, "runner.ts"), `
 import { rpc } from ${JSON.stringify(fileURLToPath(new URL("../src/command.ts", import.meta.url)))}
 for (let index = 0; index < 3; index++) {
-  console.log(await rpc(${JSON.stringify(executable)}, {}, AbortSignal.timeout(1500)))
+  console.log(await rpc(${JSON.stringify(executable)}, {}, AbortSignal.timeout(3000)))
 }
 `)
   try {
@@ -58,7 +58,7 @@ for (let index = 0; index < 3; index++) {
   } finally {
     await rm(temp, { recursive: true, force: true })
   }
-})
+}, 15_000)
 
 test("failed RPCs include a bounded stderr tail", async () => {
   const temp = await mkdtemp(join(tmpdir(), "opencode-rift-rpc-"))
@@ -69,7 +69,7 @@ test("failed RPCs include a bounded stderr tail", async () => {
   )
   await chmod(executable, 0o755)
   try {
-    await expect(rpc(executable, {}, AbortSignal.timeout(1500))).rejects.toThrow(
+    await expect(rpc(executable, {}, AbortSignal.timeout(3000))).rejects.toThrow(
       `Rift exited with status 1: ${"x".repeat(8 * 1024 - "hook failed\n".length)}hook failed`,
     )
   } finally {
@@ -96,7 +96,7 @@ process.stdout.write(${JSON.stringify(JSON.stringify({ status: "error", error: f
   )
   await chmod(executable, 0o755)
   try {
-    const error = await rpc(executable, {}, AbortSignal.timeout(1500)).catch((error: unknown) => error)
+    const error = await rpc(executable, {}, AbortSignal.timeout(3000)).catch((error: unknown) => error)
     expect(error).toBeInstanceOf(RpcError)
     expect({ ...(error as RpcError), message: (error as RpcError).message }).toEqual({
       name: "RiftRpcError",
@@ -154,3 +154,19 @@ test("signal deaths name the signal", async () => {
     await rm(temp, { recursive: true, force: true })
   }
 })
+
+test("stderr tails do not start inside a multi-byte character", async () => {
+  const temp = await mkdtemp(join(tmpdir(), "opencode-rift-rpc-"))
+  const executable = join(temp, "rift")
+  await writeFile(
+    executable,
+    '#!/usr/bin/env node\nprocess.stderr.write("é".repeat(5000) + "\\n", () => process.exit(1))\n',
+  )
+  await chmod(executable, 0o755)
+  try {
+    const error = await rpc(executable, {}, AbortSignal.timeout(3000)).catch((error: Error) => error)
+    expect((error as Error).message).toBe(`Rift exited with status 1: ${"é".repeat(4095)}`)
+  } finally {
+    await rm(temp, { recursive: true, force: true })
+  }
+})