Session becomes unusable after UnknownError: Failed to parse

[maddeye]

At irregular intervals, I encounter the error shown below. When this happens:

• opencode still runs, but the affected session becomes unusable.
• Any further prompts sent to this session just repeat the same error.
• Attempting to reopen the session after starting a new one also fails.

Error Log

failed to send message: POST
"http://127.0.0.1:55413/session/ses_73XXXX2aXffeDTHiXXTUpWNVvX/message": 400 Bad Request
{"name":"UnknownError","data":{"message":"SyntaxError: Failed to parse JSON"}}

Environment

• Using: GitHub Copilot with Claude Sonnet 4
• opencode version: v0.5.7
• OS: Windows with git Bash

Steps to Reproduce

The issue appears sporadically and I haven’t found a deterministic reproduction path, but:

1. Start a session.
2. Interact with opencode for some time.
3. At some point, the session fails with the above error.

Expected Behavior

The session should continue working without requiring a restart.

Actual Behavior

The session becomes permanently stuck, repeating the error until a new session is created. Old sessions cannot be reopened.

Additional Context

The error only occurs intermittently, but once triggered, it breaks the session workflow entirely.

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• TUI failed to send message #1743: TUI failed to send message with similar HTTP 400 Bad Request error pattern and session communication failures
• When opencode enters an interactive session, it will be in working... mode indefinitely #1561: Session becomes unusable and gets stuck indefinitely, requiring restart (same core symptom of session becoming permanently unusable)
• JSON Parse error: Expected '}' with the write tool after updating to v0.5.5 Description #2002: JSON Parse error with the write tool - reports similar "JSON parsing failed" errors that could be related to the "Failed to parse JSON" error you're experiencing
• Multiple message request to the same session get the same response #1895: Multiple message requests to same session causing response issues - demonstrates session-level message handling problems that could be related

Feel free to ignore if none of these address your specific case.

[rekram1-node]

Is there anything special with this session? is it super long or anything

[maddeye]

It's not consistent.
Sometimes it only takes one or two prompts, and sometimes it took 10+.

Deleting the cache have some effect on it. But nothing consistent to report.

[rekram1-node]

Are you still encountering this on latest @maddeye

[maddeye]

Cannot test ot right now. I will chrck on monday.

[maddeye]

The problem seems to be fixed. Thanks a lot!

[rekram1-node]

awesome!

[vanboom]

Curious if there is a way to fix this to resume the session? It is happening to us today multiple times leaving a corrupted session that can't continue.

[rekram1-node]

@vanboom whats the error, provider, etc? Can you share the session