fix: backward-compatible renderMessage option for tool messages

[ranxianglei]

Problem

renderMessage() tags ALL messages including tool-call arguments in CoreMessage.text. In proxy adapters (e.g. acp-proxy) that store wire-format JSON in .text (OpenAI function.arguments), this corrupted the JSON → SchemaError(Missing key at ["command"]).

Approach (redesigned per review)

Unconditionally skip tool messages. ← rejected: breaking change for existing callers.

New approach: opt-in via RenderOptions + RenderConfig, zero behavior change for existing callers.

API changes

// New: optional parameter (backward compat — default = tag everything)
export function renderMessage(
  message, map, countTokens,
  options?: { skipToolMessages?: boolean },  // ← NEW
): CoreMessage

export function renderVisibleRefs(
  messages, state, countTokens?,
  options?: { skipToolMessages?: boolean },  // ← NEW
): CoreMessage[]

// New: config option
interface RenderConfig { skipToolMessageTags?: boolean }
interface Config { ...; render?: RenderConfig }

// New: helper for pipeline node
export function optionsFromConfig(config?): RenderOptions | undefined

Who opts in?

Caller	Behavior	Change needed?
Plugin (opencode-acp)	Tags all messages (original)	None
Pipeline default	Tags all messages (original)	None (render undefined)
Proxy (acp-proxy)	Skips tool messages	config.render = { skipToolMessageTags: true }

Tests (211/211 pass)

• renderVisibleRefs tags tool messages by default (backward compat) — existing behavior preserved
• renderVisibleRefs skips tool messages when options.skipToolMessages is set — opt-in works
• renderRefsNode respects config.render.skipToolMessageTags — pipeline integration

Why this is safe

• renderMessage() default path: identical to before
• renderVisibleRefs() default path: identical to before
• renderRefsNode with no config.render: identical to before
• renderMessage() now exported: adapters can reuse without reimplementing
• Refs still allocated for tool messages (assignRefs runs before render-refs)
• Tool pairs still tracked (adjustBoundariesForToolPairs auto-expands ranges)