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session.resume fails with 'Session file is corrupted' when attachments field is null

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@jmoseley is already working on this.

Since Mar 16, 2026.

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Description

batch runtime

Bug Report

Summary

Resuming a session via session.resume fails with a JSON-RPC error when the saved session file has attachments: null. The SDK now expects attachments to be an array, but previously saved sessions store null.

Error
JSON-RPC Error -32603: Request session.resume failed with message:
Session file is corrupted (line 24: data.attachments: Expected array, received null)
Steps to Reproduce
  1. Create a session (with SDK version that stores attachments: null in the session file)
  2. Save the session ID
  3. On a new run, call session.resume with the saved session ID
  4. Observe the error above
Expected Behavior

Either:

  • The SDK accepts null as a valid (empty) value for attachments during resume (backwards-compatible), or
  • A more graceful error that allows the caller to detect the corruption and fall back to starting a new session
Actual Behavior

Resume throws a hard JSON-RPC -32603 error that cannot be easily distinguished from other fatal errors, forcing the caller to start a fresh session without a clean signal.

Environment
  • github-copilot-sdk version: 0.1.32
  • Python: 3.12.3
  • OS: Linux (Ubuntu 24.04)
Suggested Fix

Treat null as equivalent to [] for the attachments field during session deserialization, to maintain backwards compatibility with older session files.

Dominant language
Java
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