[Feature Request] Add support for forking conversations into separate threads

Bug Description
the btw fork feature doesn't seem to work although in principal it would be a HUGE benefit to be able to chase certain btws in their own thread off of a main chat.

Environment Info

• Platform: darwin
• Terminal: Apple_Terminal
• Version: 2.1.168
• Feedback ID: 0698f77e-a790-4b8c-bb60-a958c863de43

Errors

[{"error":"Error\n    at generate (/$bunfs/root/src/entrypoints/cli.js:11:65772)\n    at makeRequest (/$bunfs/root/src/entrypoints/cli.js:51:7694)\n    at processTicksAndRejections (unknown:7:39)","timestamp":"2026-06-22T13:15:43.408Z"},{"error":"Error: 401 {\"type\":\"error\",\"error\":{\"type\":\"authentication_error\",\"message\":\"Invalid authentication credentials\"},\"request_id\":\"req_011CcJMvpW5mHK5wz5zaWDRn\"}\n    at generate (/$bunfs/root/src/entrypoints/cli.js:11:65772)\n    at makeRequest (/$bunfs/root/src/entrypoints/cli.js:51:7694)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-06-22T13:16:37.258Z"},{"error":"Error: 500 {\"type\":\"error\",\"error\":{\"type\":\"api_error\",\"message\":\"Internal server error\"},\"request_id\":\"req_011CcLLxwqobFBTUY7zbH144\"}\n    at generate (/$bunfs/root/src/entrypoints/cli.js:11:65993)\n    at makeRequest (/$bunfs/root/src/entrypoints/cli.js:51:7694)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-06-23T14:25:17.833Z"},{"error":"Error: 500 {\"type\":\"error\",\"error\":{\"type\":\"api_error\",\"message\":\"Internal server error\"},\"request_id\":\"req_011CcLM7wbfhZfNvd8N2iys4\"}\n    at generate (/$bunfs/root/src/entrypoints/cli.js:11:65993)\n    at makeRequest (/$bunfs/root/src/entrypoints/cli.js:51:7694)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-06-23T14:27:20.787Z"},{"error":"Error: 500 {\"type\":\"error\",\"error\":{\"type\":\"api_error\",\"message\":\"Internal server error\"},\"request_id\":\"req_011CcLMUUKB9CNh17tzsvjPm\"}\n    at generate (/$bunfs/root/src/entrypoints/cli.js:11:65993)\n    at makeRequest (/$bunfs/root/src/entrypoints/cli.js:51:7694)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-06-23T14:32:58.862Z"},{"error":"Error: 500 {\"type\":\"error\",\"error\":{\"type\":\"api_error\",\"message\":\"Internal server error\"},\"request_id\":\"req_011CcLMnGrrfYzJHtxMySbLv\"}\n    at generate (/$bunfs/root/src/entrypoints/cli.js:11:65993)\n    at makeRequest (/$bunfs/root/src/entrypoints/cli.js:51:7694)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-06-23T14:36:02.023Z"}]