bug: readJson() lacks error handling for malformed JSON #18351

Bug Description

In packages/opencode/src/util/filesystem.ts:37-38, the readJson function doesn't have error handling:

export async function readJson<T = any>(p: string): Promise<T> {
  return JSON.parse(await readFile(p, "utf-8"))
}

If the file contains malformed JSON, this will throw an unhandled error that may crash the caller.

Impact

• Malformed JSON files cause unhandled exceptions
• No opportunity to provide a default value or recovery mechanism
• Makes debugging harder in production

Files Affected

• packages/opencode/src/util/filesystem.ts lines 37-38

Suggested Fix

Wrap JSON.parse in try/catch and provide a meaningful error:

export async function readJson<T = any>(p: string): Promise<T> {
  try {
    return JSON.parse(await readFile(p, "utf-8"))
  } catch (e) {
    throw new Error(`Failed to parse JSON from ${p}`, { cause: e })
  }
}

Acceptance Criteria

• Malformed JSON throws a meaningful error with file path
• Error chain preserves original exception