plugin.js

/**
 * reasoning-pruner — opencode plugin
 * npm: @ghilteras/opencode-reasoning-pruner
 *
 * Structural hygiene of the context window: strips `reasoning` parts from the
 * message history BEFORE it is re-sent to the LLM on the next turn, while
 * KEEPING the reasoning parts of the last KEEP_TURNS user turn(s) (default 1).
 *
 * Reasoning is still shown in the TUI (native /thinking toggle) and consumed
 * by the model during generation; this plugin acts ONLY on the history, so
 * reasoning tokens do not accumulate in the context window.
 *
 * Approach: model-agnostic structural filtering, zero regex, zero event-stream
 * manipulation, zero system-prompt injection.
 *
 * History: home-grown since 2026-07-14 (homelab-config), replacing the earlier
 * thinking-suppressor.ts (regex + event-hook blanking that truncated DeepSeek
 * output). Published to npm 2026-08-07.
 */

// @ts-nocheck

const KEEP_TURNS = 1
const log = (m) => { try { console.log(`[reasoning-pruner] ${m}`) } catch {} }

export default async () => {
  log(`plugin caricato (model-agnostic, keepTurns=${KEEP_TURNS})`)
  return {
    "experimental.chat.messages.transform": async (_input, output) => {
      try {
        const messages = output?.messages
        if (!Array.isArray(messages)) return

        let lastUser = -1
        let userCount = 0
        for (let i = messages.length - 1; i >= 0; i--) {
          const role = messages[i]?.info?.role ?? messages[i]?.role
          if (role === "user") {
            userCount++
            if (userCount === KEEP_TURNS) { lastUser = i; break }
          }
        }
        if (lastUser < 0) return

        let removed = 0
        let kept = 0
        for (let i = 0; i < messages.length; i++) {
          const m = messages[i]
          if (!Array.isArray(m?.parts)) continue
          if (i >= lastUser) {
            kept += m.parts.filter(p => p?.type === "reasoning").length
            continue
          }
          const before = m.parts.length
          m.parts = m.parts.filter(p => p && p.type !== "reasoning")
          removed += before - m.parts.length
        }

        if (removed || kept)
          log(`pruned ${removed} historical reasoning parts, kept ${kept} in last ${KEEP_TURNS} user turn(s) (${messages.length} msgs)`)
      } catch (err) {
        log(`transform err: ${String(err)}`)
      }
    },
  }
}