Kimi built-in assistant consumes credits but gives "HTTP 422: Unprocessable Entity"

[kahloutg]

Summary:
When BrowserOS forwards agent/graph-mode MCP payloads containing BrowserOS-only fields (for example: response_format with json_schema+strict, parallel_tool_calls, tools/tool_calls) to Moonshot (model: kimi-k2.5), the provider rejects or errors on those fields. Minimal chat payloads (model + messages) succeed.

Observed behavior:

• Minimal request (model + messages) → 200 OK.
• response_format with empty/missing json_schema.name → 400 (e.g., 'missing required parameter: response_format.json_schema.name').
• parallel_tool_calls can time out or cause connection resets; behavior inconsistent (sometimes 200, sometimes 502/timeout).
• Using a local proxy that strips BrowserOS-only fields often makes the request succeed, though the provider returned intermittent 429/502 under test load.

Environment:

• BrowserOS: 0.44.0.1
• Chromium: 146.0.7821.31
• Local BrowserOS MCP endpoint: /mcp (localhost)
• Provider: Moonshot / Kimi (https://api.moonshot.ai/v1, model: kimi-k2.5)

Reproduction (representative payloads):

1. Baseline payload that should succeed: { model: 'kimi-k2.5', messages: [...] }
2. response_format payload (provider returned 4xx): { model: 'kimi-k2.5', messages: [...], response_format: { type: 'json_schema', strict: true, json_schema: {} } }
3. parallel_tool_calls payload (provider may timeout or return connection errors): { model: 'kimi-k2.5', messages: [...], parallel_tool_calls: { calls: [ { tool: 'open_url', args: { url: 'https://example.com' } } ] } }

Findings & suggested fixes:

1. Payload sanitization: add a compatibility mode to strip BrowserOS-agent-only fields before forwarding to third-party providers.
2. Provider capability profiles: per-provider feature flags (e.g., supports_parallel_tool_calls, supports_json_schema_response_format).
3. Optional validation/preflight to detect unsupported fields and return actionable errors to users.
4. Better error mapping: interpret provider 4xx messages and surface guidance to end users.
5. Documentation: list which payload features are safe to forward to third-party providers; include example proxy used for diagnostics.

Attachments: none (reporter requested no captures attached). Redaction guidance: do not include Authorization/API keys, user emails, or internal hostnames/IPs.

If it helps, the reporter can provide anonymized capture files (Authorization headers redacted) on request.

-- Reported by BrowserOS user

[shadowfax92]

Hey kahloutg — thanks for the detailed report! This looks like a payload compatibility issue — BrowserOS is forwarding fields like response_format and parallel_tool_calls that Moonshot rejects. Logged as a bug. We'll look into stripping unsupported fields before forwarding to third-party providers.

[papatistos]

Having the same issue. Any way to work around this in the meantime?