[tazztone]

Problem

httpPost() attached its diagnostic metadata to the same object it later serialized:

lastPayload = payload;
lastPayload.__meta = { prompts };

Both transports then sent that object, so every request body carried a __meta property containing a second copy of the system and user prompts. OpenRouter's gateway does not reject unknown top-level fields, so this went unnoticed; strict OpenAI-compatible endpoints do. Groq returns:

{ "error": { "message": "property '__meta' is unsupported", "type": "invalid_request_error" } }

Fixes #17

Fix

• lastPayload is now a shallow copy, so "Show Last Payload" keeps the prompts while the request payload stays clean.
• lib/serialize.js adds toRequestBody(), which strips __meta before serialization. Both transports (fetch and curl) use it, so a future diagnostic field cannot leak back onto the wire.

Tests

npm test (node:test) covers:

• __meta is stripped and the remaining fields are preserved verbatim
• the caller payload is not mutated
• payloads without __meta serialize unchanged
• a tripwire fails if extension.js regains lastPayload.__meta = or JSON.stringify(payload), or loses either toRequestBody(payload) call site

Verification

• npm ci && npm test → 5/5 pass
• npx @vscode/vsce package → packages cleanly; lib/ included, test/ excluded
• Extracted the real httpPost from the built extension and drove both transports against a local echo server: wire body keys are exactly model, messages, temperature, response_format, with no __meta, while "Show Last Payload" still renders __meta.prompts

No version bump: the release workflow handles that on merge.

Docs

Adds a Troubleshooting entry for HTTP 413 provider token-budget failures, with the settings that shrink the prompt.