CLI prompt argument's quotes/newlines get corrupted before being sent as the user message to the LLM provider #43923

Description

The CLI prompt argument (opencode run "...") is corrupted before being sent as the user message to the LLM provider, when it contains internal double-quotes and/or newlines. This appears to reliably break tool-calling for at least some local (Ollama, OpenAI-compatible) models, and may be a contributing factor in other reports of "model outputs tool calls as text instead of executing them" (e.g. #33959, #37543, #21181, #29757) — those reports show the same class of symptom, though I haven't verified they share this exact root cause.

Captured the real outgoing wire request via a transparent logging proxy in front of an OpenAI-compatible Ollama provider. The user message content opencode actually transmits is wrapped in a literal leading/trailing ", with every internal " backslash-escaped — but embedded newlines are left as raw literal newlines, not escaped as \n. This isn't valid JSON string content (real JSON.stringify would also escape \n); it looks like a hand-rolled "escape quotes for embedding" step that's missing newline handling. The system message (agent prompt config) in the same request was NOT corrupted — this is specific to how the CLI prompt argument becomes the user-turn message, not a general serialization bug.

Causal verification

Built matched payloads (real captured system prompt, same tool schema, temperature: 0.15, stream: false) and sent them directly to Ollama's native /api/chat, varying only the user message content:

Every real opencode run dispatch against this same prompt failed outright; the exact same prompt text sent uncorrupted via raw curl/direct API succeeds reliably. This also explains why "the model works fine when I test the API directly, but not through opencode" shows up in several other issues in this repo — testing the API directly naturally uses clean, uncorrupted prompt text.

Steps to reproduce

opencode run --agent <any> "text with \"internal quotes\" and
newlines"

Capture the outgoing request to the provider (e.g. via a logging reverse proxy in front of an OpenAI-compatible baseURL) and inspect the user message's content field — it will contain a stray wrapping ", escaped internal quotes, but raw unescaped newlines.

OpenCode version

1.18.18 (compiled Bun binary — could not locate readable source locally to pinpoint the exact code path; this may be in the CLI arg → message-part construction, or in provider message serialization)

Operating System

macOS