/**
 * v2.6 Phase 1 — OpenCodeServerBackend.
 *
 * Warm, multi-turn backend for the `opencode` agent. One `opencode serve` HTTP
 * server per BooCoder process; one opencode session per BooCode session (resumed
 * on switch-back); one SSE read loop PER session, each scoped to that session's
 * worktree directory so sessions in different directories stream concurrently
 * (P1.5-a — replaced the Phase-1 single-stream-last-directory model).
 *
 * Implements the Phase 0 `AgentBackend` interface. Emits transport-agnostic
 * `AgentEvent`s — the dispatcher (Phase 1.7, NOT wired in this batch) maps them
 * to WS frames. No dispatcher/route references this file yet.
 *
 * Spec: openspec/changes/v2-6-persistent-agent-sessions/design.md §2 / §2a.
 * SDK shapes verified by direct read of @opencode-ai/sdk@1.15.12 dist .d.ts:
 *   - client methods take FLATTENED params (sessionID/directory/body all inline),
 *     not {path,query,body}. create→{directory}, promptAsync→{sessionID,directory,
 *     parts,model}, abort→{sessionID,directory}. model is {providerID,modelID}.
 *   - client.event() resolves to { stream: AsyncGenerator<GlobalEvent> }; the
 *     real event is chunk.payload (discriminate on chunk.payload.type).
 *   - promptAsync is fire-and-forget (204); the turn completes via a
 *     'session.idle' event for that opencode session id.
 */
import { spawn, type ChildProcess } from 'node:child_process';
import { createHash } from 'node:crypto';
import { createServer } from 'node:net';
import type { FastifyBaseLogger } from 'fastify';
import {
  createOpencodeClient,
  type OpencodeClient,
  type Event,
  type Part,
  type ToolPart,
  type ToolState,
  type AssistantMessage,
} from '@opencode-ai/sdk/v2/client';
import type { ToolCallStatus } from '@agentclientprotocol/sdk';
import type { Sql } from '../../db.js';
import type { AcpToolSnapshot } from '../acp-tool-snapshot.js';
import type {
  AgentBackend,
  AgentEvent,
  AgentSessionHandle,
  EnsureSessionOpts,
  PromptCtx,
  TurnResult,
} from '../agent-backend.js';

const READY_TIMEOUT_MS = 30_000;
const SSE_RECONNECT_DELAY_MS = 1_000;
/**
 * No-activity backstop for an in-flight turn. opencode streams reasoning/text/tool
 * deltas continuously while working, so "zero events for this long" means the turn
 * is wedged or its terminal event (session.idle) was lost (see the reconnect race
 * below). Generous so a legitimately slow turn never trips it.
 */
const TURN_INACTIVITY_MS = 180_000;

/** One in-flight turn's emitter + completion settler. */
interface TurnState {
  onEvent: (e: AgentEvent) => void;
  settle: (r: TurnResult) => void;
}

/** Per-(opencode session) demux state. dedup sets scoped here, cleared per turn. */
interface SessionState {
  boocodeSessionId: string;
  agentSessionId: string;
  /** Worktree directory for SDK `directory` routing; refreshed each turn from ctx. */
  worktreePath: string;
  /** dedup gate: `${type}:${id}` added on delta, deleted-and-tested on updated. Cleared at turn end. */
  streamedPartKeys: Set<string>;
  /** partID → 'text' | 'reasoning', so a delta with a non-'reasoning' field is still classed right. Cleared at turn end. */
  partTypeById: Map<string, string>;
  activeTurn: TurnState | null;
  /** Inactivity backstop timer for the active turn; null when no turn in flight. */
  watchdog: ReturnType<typeof setTimeout> | null;
  /** Per-session SSE subscription handle. Non-null while the loop is running;
   *  aborting it tears down the underlying fetch and exits the loop. */
  sseAbort: AbortController | null;
}

export interface OpenCodeServerBackendDeps {
  sql: Sql;
  log: FastifyBaseLogger;
  /** Absolute path to the opencode binary (resolved from available_agents at wiring time, Phase 1.7). */
  opencodeBinary: string;
}

export class OpenCodeServerBackend implements AgentBackend {
  readonly backend = 'opencode_server' as const;

  private readonly sql: Sql;
  private readonly log: FastifyBaseLogger;
  private readonly opencodeBinary: string;

  private child: ChildProcess | null = null;
  private client: OpencodeClient | null = null;
  private port: number | null = null;
  private up = false;
  private serverStarting: Promise<void> | null = null;

  /** opencode session id → demux state. Maintained by ensureSession; read by the SSE loop. */
  private readonly byOpencodeId = new Map<string, SessionState>();

  constructor(deps: OpenCodeServerBackendDeps) {
    this.sql = deps.sql;
    this.log = deps.log;
    this.opencodeBinary = deps.opencodeBinary;
  }

  /** §2: liveness for the health endpoint + dispatcher fallback decision. */
  health(): 'up' | 'down' {
    return this.up ? 'up' : 'down';
  }

  // ─── Server lifecycle (1.2: spawn once + client + ready) ─────────────────────

  /** Lazy: start the single server on first use. Idempotent — one server per backend. */
  private ensureServer(): Promise<void> {
    if (!this.serverStarting) this.serverStarting = this.startServer();
    return this.serverStarting;
  }

  private async startServer(): Promise<void> {
    const port = await freePort();

    // Phase 1: run unsecured on loopback (opencode's documented default — serve.ts
    // only WARNS when OPENCODE_SERVER_PASSWORD is unset). The real boundary is the
    // 127.0.0.1 bind. Defense-in-depth basic-auth is deferred: the hey-api client's
    // auth wiring + opencode's exact scheme must be confirmed against a live server
    // first, else every request 401s. Recon explicitly said "do NOT block on it".
    const child = spawn(this.opencodeBinary, ['serve', '--hostname', '127.0.0.1', '--port', String(port)], {
      stdio: ['ignore', 'pipe', 'pipe'],
      env: { ...process.env },
    });
    this.child = child;
    this.port = port;

    // Child lifetime is the backend's (the pool's), NOT a request's. We never tie
    // it to a per-turn abort signal. On unexpected exit we mark down + log; crash
    // recovery is Phase 3.
    child.on('exit', (code, signal) => {
      this.up = false;
      this.log.warn({ code, signal, port }, 'opencode-server: child exited (recovery is Phase 3)');
    });

    await waitForReady(child, READY_TIMEOUT_MS);

    this.client = createOpencodeClient({ baseUrl: `http://127.0.0.1:${port}` });
    this.up = true;
    this.log.info({ port }, 'opencode-server: ready');
  }

  // ─── SSE read loop + demux + translate (1.3) + dedup (1.4) ───────────────────

  /** Per-session SSE subscription, scoped to the session's worktree directory.
   *  opencode scopes events by the `directory` query param (defaults to the
   *  server's cwd if omitted), so two sessions in different worktrees each get
   *  their own dir-scoped stream and never drop each other's events. Idempotent:
   *  a no-op if this session's loop is already running. Started from ensureSession
   *  (and defensively from prompt) once worktreePath is known. */
  private startSessionEventLoop(state: SessionState): void {
    if (state.sseAbort) return; // already running
    const abort = new AbortController();
    state.sseAbort = abort;
    void this.runSessionEventLoop(state, abort).finally(() => {
      // Only clear if this controller is still the live one (a later restart may
      // have already installed a new one).
      if (state.sseAbort === abort) state.sseAbort = null;
    });
  }

  private async runSessionEventLoop(state: SessionState, abort: AbortController): Promise<void> {
    const signal = abort.signal;
    while (this.up && this.client && !signal.aborted) {
      try {
        // Re-read worktreePath each (re)subscribe so a directory refresh is picked
        // up on reconnect. Passing `signal` lets close/dispose tear down a stream
        // that's parked in `for await` between events.
        const sub = await this.client.event.subscribe(
          { directory: state.worktreePath },
          { signal },
        );
        for await (const ev of sub.stream) {
          if (signal.aborted) break;
          // Dir-scoped streams should only carry this session's events, but two
          // sessions sharing a worktree (possible post-P1.5-b) each receive BOTH
          // sessions' events — so drop anything that isn't ours, else the other
          // session's deltas get processed twice (once per loop).
          const sid = eventSessionId(ev);
          if (sid != null && sid !== state.agentSessionId) continue;
          this.dispatchEvent(ev);
        }
        if (this.up && !signal.aborted) {
          await this.reconcile(state); // recover an idle/error lost during the gap
          await sleep(SSE_RECONNECT_DELAY_MS);
        }
      } catch (err) {
        if (!this.up || signal.aborted) break;
        this.log.warn(
          { err: errMsg(err), agentSessionId: state.agentSessionId },
          'opencode-server: session event loop error; reconnecting',
        );
        await this.reconcile(state);
        await sleep(SSE_RECONNECT_DELAY_MS);
      }
    }
  }

  /** Demux one event to the owning session's active turn. Unknown/between-turns → drop. */
  private dispatchEvent(ev: Event): void {
    switch (ev.type) {
      // ─── session.next.* — live streaming events (the primary path) ─────────
      case 'session.next.text.delta': {
        const p = ev.properties;
        const st = this.byOpencodeId.get(p.sessionID);
        if (!st?.activeTurn) return;
        this.bumpActivity(st);
        const cleaned = stripDcpTags(p.delta);
        if (cleaned) st.activeTurn.onEvent({ type: 'text', text: cleaned });
        return;
      }
      case 'session.next.reasoning.delta': {
        const p = ev.properties;
        const st = this.byOpencodeId.get(p.sessionID);
        if (!st?.activeTurn) return;
        this.bumpActivity(st);
        st.activeTurn.onEvent({ type: 'reasoning', text: p.delta });
        return;
      }
      case 'session.next.tool.called': {
        const p = ev.properties;
        const st = this.byOpencodeId.get(p.sessionID);
        if (!st?.activeTurn) return;
        this.bumpActivity(st);
        const snap: AcpToolSnapshot = {
          toolCallId: p.callID,
          title: p.tool,
          kind: null,
          status: 'in_progress',
          rawInput: p.input,
          rawOutput: undefined,
        };
        st.activeTurn.onEvent({ type: 'tool_call', toolCall: snap });
        return;
      }
      case 'session.next.tool.success': {
        const p = ev.properties;
        const st = this.byOpencodeId.get(p.sessionID);
        if (!st?.activeTurn) return;
        this.bumpActivity(st);
        const output = p.content?.map((c) => ('text' in c ? (c as { text: string }).text : '')).join('') ?? '';
        const snap: AcpToolSnapshot = {
          toolCallId: p.callID,
          title: p.callID,
          kind: null,
          status: 'completed',
          rawInput: undefined,
          rawOutput: output,
        };
        st.activeTurn.onEvent({ type: 'tool_update', toolCall: snap });
        return;
      }
      case 'session.next.tool.failed': {
        const p = ev.properties;
        const st = this.byOpencodeId.get(p.sessionID);
        if (!st?.activeTurn) return;
        this.bumpActivity(st);
        const snap: AcpToolSnapshot = {
          toolCallId: p.callID,
          title: p.callID,
          kind: null,
          status: 'failed',
          rawInput: undefined,
          rawOutput: errToString(p.error),
        };
        st.activeTurn.onEvent({ type: 'tool_update', toolCall: snap });
        return;
      }
      // ─── message.part.* — terminal/post-hoc events (dedup gate) ────────────
      case 'message.part.delta': {
        const p = ev.properties;
        const st = this.byOpencodeId.get(p.sessionID);
        if (!st?.activeTurn) return;
        this.bumpActivity(st);
        const isReasoning = p.field === 'reasoning' || st.partTypeById.get(p.partID) === 'reasoning';
        if (isReasoning) {
          st.streamedPartKeys.add(`reasoning:${p.partID}`);
          st.activeTurn.onEvent({ type: 'reasoning', text: p.delta });
        } else if (p.field === 'text') {
          st.streamedPartKeys.add(`text:${p.partID}`);
          const cleaned = stripDcpTags(p.delta);
          if (cleaned) st.activeTurn.onEvent({ type: 'text', text: cleaned });
        }
        return;
      }
      case 'message.part.updated': {
        const part = ev.properties.part;
        const st = this.byOpencodeId.get(part.sessionID);
        if (!st?.activeTurn) return;
        this.bumpActivity(st);
        this.handleUpdatedPart(part, st);
        return;
      }
      // ─── lifecycle ─────────────────────────────────────────────────────────
      case 'session.idle': {
        this.byOpencodeId.get(ev.properties.sessionID)?.activeTurn?.settle({ ok: true });
        return;
      }
      case 'session.error': {
        const sid = ev.properties.sessionID;
        if (!sid) return;
        this.byOpencodeId.get(sid)?.activeTurn?.settle({ ok: false, error: errToString(ev.properties.error) });
        return;
      }
      default:
        return;
    }
  }

  /** Terminal part: dedup gate for text/reasoning; tool parts → tool_call/tool_update. */
  private handleUpdatedPart(part: Part, st: SessionState): void {
    const turn = st.activeTurn;
    if (!turn) return;

    if (part.type === 'text' || part.type === 'reasoning') {
      st.partTypeById.set(part.id, part.type);
      const key = resolvePartDedupeKey(part, part.type);
      if (key && st.streamedPartKeys.delete(key)) return; // already streamed via delta
      const raw = part.text ?? '';
      const text = part.type === 'text' ? stripDcpTags(raw) : raw;
      if (text && part.time?.end != null) {
        turn.onEvent({ type: part.type, text });
      }
      return;
    }

    if (part.type === 'tool') {
      const snap = toolPartToSnapshot(part);
      const status = part.state?.status;
      // tool_call on start (pending/running), tool_update on terminal (completed/error).
      // The current ACP path merges both into one frame; the contract keeps them
      // distinct because opencode's SSE distinguishes start from result.
      const event: AgentEvent =
        status === 'completed' || status === 'error'
          ? { type: 'tool_update', toolCall: snap }
          : { type: 'tool_call', toolCall: snap };
      turn.onEvent(event);
      return;
    }
    // NOTE: opencode's SSE payload union carries no available-commands event, so the
    // AgentEvent 'commands' arm is intentionally never emitted here (1.3).
  }

  // ─── turn-completion resilience (watchdog + reconnect reconcile) ─────────────

  /** Reset the inactivity backstop on any event routed to a session's active turn. */
  private bumpActivity(st: SessionState): void {
    if (!st.activeTurn) return;
    if (st.watchdog) clearTimeout(st.watchdog);
    st.watchdog = setTimeout(() => {
      void this.onTurnStall(st);
    }, TURN_INACTIVITY_MS);
    st.watchdog.unref?.();
  }

  /** Watchdog fired: reconcile once; if the server says still-running we can't tell, so fail closed.
   *  Also mark the agent_sessions row crashed so a stale session isn't resumed next turn. */
  private async onTurnStall(st: SessionState): Promise<void> {
    const settled = await this.reconcile(st);
    if (!settled) {
      this.log.warn({ agentSessionId: st.agentSessionId }, 'opencode-server: turn stalled (no activity), failing + marking crashed');
      await this.sql`
        UPDATE agent_sessions SET status = 'crashed'
        WHERE agent_session_id = ${st.agentSessionId}
      `.catch(() => {});
      st.activeTurn?.settle({ ok: false, error: 'turn timed out (no activity)' });
    }
  }

  /**
   * Ask the server whether this session's turn already finished — recovers a
   * session.idle/error lost during an SSE gap. Returns true if it settled the turn.
   * Inconclusive (still running / call failed) → false; the watchdog covers that.
   */
  private async reconcile(st: SessionState): Promise<boolean> {
    const turn = st.activeTurn;
    if (!turn || !this.client) return false;
    try {
      const res = await this.client.session.messages({
        sessionID: st.agentSessionId,
        directory: st.worktreePath,
      });
      if (res.error || !res.data) return false;
      let lastAssistant: AssistantMessage | undefined;
      for (let i = res.data.length - 1; i >= 0; i--) {
        const info = res.data[i]!.info;
        if (info.role === 'assistant') {
          lastAssistant = info;
          break;
        }
      }
      if (!lastAssistant) return false;
      if (lastAssistant.error != null) {
        turn.settle({ ok: false, error: errToString(lastAssistant.error) });
        return true;
      }
      if (lastAssistant.time.completed != null) {
        turn.settle({ ok: true });
        return true;
      }
      return false; // still running — the live stream will deliver session.idle
    } catch {
      return false; // inconclusive — watchdog backstop covers it
    }
  }

  // ─── ensureSession: create-or-resume against agent_sessions (1.5) ────────────

  async ensureSession(sessionId: string, opts: EnsureSessionOpts): Promise<AgentSessionHandle> {
    await this.ensureServer();
    if (!this.client) throw new Error('opencode-server: client not ready after ensureServer');

    const configHash = sessionConfigHash(opts.model);
    // P1.5-b: agent_sessions is keyed (chat_id, agent) — the tab/chat is the
    // context unit (two tabs in one session = two contexts sharing one worktree).
    // session_id + worktree_id are retained as informational (SET NULL) columns.
    const [row] = await this.sql<{ agent_session_id: string | null; status: string; config_hash: string | null }[]>`
      SELECT agent_session_id, status, config_hash FROM agent_sessions
      WHERE chat_id = ${opts.chatId} AND agent = ${opts.agent}
    `;
    let agentSessionId = row?.agent_session_id ?? null;

    // Don't resume crashed sessions or sessions whose config drifted (model change).
    const shouldResume = agentSessionId
      && row!.status !== 'crashed'
      && (row!.config_hash == null || row!.config_hash === configHash);

    if (!shouldResume) {
      if (agentSessionId) {
        this.log.info({ sessionId, oldStatus: row!.status, hashMatch: row!.config_hash === configHash },
          'opencode-server: not resuming stale session, creating fresh');
        this.byOpencodeId.delete(agentSessionId);
      }
      const created = await this.client.session.create({ directory: opts.worktreePath });
      if (created.error || !created.data) {
        throw new Error(`opencode-server: session.create failed: ${errToString(created.error)}`);
      }
      agentSessionId = created.data.id;
      await this.sql`
        INSERT INTO agent_sessions
          (chat_id, session_id, worktree_id, agent, backend, agent_session_id, server_port, status, last_active_at, config_hash)
        VALUES
          (${opts.chatId}, ${sessionId}, ${opts.worktreeId}, ${opts.agent}, 'opencode_server', ${agentSessionId}, ${this.port}, 'active', clock_timestamp(), ${configHash})
        ON CONFLICT (chat_id, agent) DO UPDATE SET
          session_id = EXCLUDED.session_id,
          worktree_id = EXCLUDED.worktree_id,
          backend = 'opencode_server',
          agent_session_id = EXCLUDED.agent_session_id,
          server_port = EXCLUDED.server_port,
          status = 'active',
          last_active_at = clock_timestamp(),
          config_hash = EXCLUDED.config_hash
      `;
    } else {
      await this.sql`
        UPDATE agent_sessions
        SET status = 'active', last_active_at = clock_timestamp(), server_port = ${this.port}, config_hash = ${configHash}
        WHERE chat_id = ${opts.chatId} AND agent = ${opts.agent}
      `;
    }

    // Both branches above guarantee agentSessionId is non-null.
    const ocSessionId = agentSessionId!;

    // Register / refresh the demux entry the SSE loop keys on. Preserve an existing
    // entry (and any in-flight turn) — just refresh the routing fields.
    let state = this.byOpencodeId.get(ocSessionId);
    if (state) {
      state.boocodeSessionId = sessionId;
      state.worktreePath = opts.worktreePath;
    } else {
      state = {
        boocodeSessionId: sessionId,
        agentSessionId: ocSessionId,
        worktreePath: opts.worktreePath,
        streamedPartKeys: new Set(),
        partTypeById: new Map(),
        activeTurn: null,
        watchdog: null,
        sseAbort: null,
      };
      this.byOpencodeId.set(ocSessionId, state);
    }

    // Start this session's own SSE loop, scoped to its worktree directory. Both
    // fresh-create and resume reach here; idempotent, so a re-ensure (e.g. a
    // second turn) won't spawn a duplicate loop.
    this.startSessionEventLoop(state);

    return {
      sessionId,
      agent: opts.agent,
      backend: 'opencode_server',
      chatId: opts.chatId,
      worktreeId: opts.worktreeId,
      agentSessionId: ocSessionId,
      serverPort: this.port,
    };
  }

  // ─── prompt: send one turn (1.6) ─────────────────────────────────────────────

  async prompt(handle: AgentSessionHandle, input: string, ctx: PromptCtx): Promise<TurnResult> {
    if (!this.client) throw new Error('opencode-server: client not ready');
    const oc = handle.agentSessionId;
    if (!oc) throw new Error('opencode-server: handle has no agentSessionId');

    let state = this.byOpencodeId.get(oc);
    if (!state) {
      state = {
        boocodeSessionId: handle.sessionId,
        agentSessionId: oc,
        worktreePath: ctx.worktreePath,
        streamedPartKeys: new Set(),
        partTypeById: new Map(),
        activeTurn: null,
        watchdog: null,
        sseAbort: null,
      };
      this.byOpencodeId.set(oc, state);
    }
    const session = state;
    // Authoritative per-turn directory for SDK routing + reconcile.
    session.worktreePath = ctx.worktreePath;
    // Defensive: ensureSession normally starts the loop, but if prompt is reached
    // with a freshly-created state (no loop yet), start it so the turn streams.
    // Idempotent when ensureSession already started one.
    this.startSessionEventLoop(session);
    const client = this.client;

    return await new Promise<TurnResult>((resolve) => {
      let settled = false;
      const cleanup = () => {
        session.activeTurn = null;
        if (session.watchdog) {
          clearTimeout(session.watchdog);
          session.watchdog = null;
        }
        session.streamedPartKeys.clear();
        session.partTypeById.clear();
        ctx.signal.removeEventListener('abort', onAbort);
      };
      const settle = (r: TurnResult) => {
        if (settled) return;
        settled = true;
        cleanup();
        resolve(r);
      };
      const onAbort = () => {
        // Abort the turn only — never the server.
        client.session.abort({ sessionID: oc, directory: ctx.worktreePath }).catch(() => {});
        settle({ ok: false, error: 'aborted' });
      };

      session.activeTurn = { onEvent: ctx.onEvent, settle };
      this.bumpActivity(session); // arm the inactivity backstop

      if (ctx.signal.aborted) {
        onAbort();
        return;
      }
      ctx.signal.addEventListener('abort', onAbort, { once: true });

      const model = parseModel(ctx.model);
      client.session
        .promptAsync({
          sessionID: oc,
          directory: ctx.worktreePath,
          parts: [{ type: 'text', text: input }],
          ...(model ? { model } : {}),
        })
        .then((res) => {
          // promptAsync is fire-and-forget (204); the turn completes via session.idle.
          // Only a submission error settles here.
          if (res.error) settle({ ok: false, error: errToString(res.error) });
        })
        .catch((err) => settle({ ok: false, error: errMsg(err) }));
    });
  }

  // ─── teardown ────────────────────────────────────────────────────────────────

  async closeSession(handle: AgentSessionHandle): Promise<void> {
    if (handle.agentSessionId) {
      // Stop this session's SSE loop before dropping its demux entry.
      this.byOpencodeId.get(handle.agentSessionId)?.sseAbort?.abort();
      this.byOpencodeId.delete(handle.agentSessionId);
    }
    await this.sql`
      UPDATE agent_sessions SET status = 'closed'
      WHERE chat_id = ${handle.chatId} AND agent = ${handle.agent}
    `.catch(() => {});
  }

  async dispose(): Promise<void> {
    this.up = false;
    // Abort every per-session SSE loop so none survive the teardown.
    for (const st of this.byOpencodeId.values()) st.sseAbort?.abort();
    const child = this.child;
    this.child = null;
    this.client = null;
    this.byOpencodeId.clear();
    if (child && !child.killed) {
      child.kill('SIGTERM');
      const t = setTimeout(() => {
        if (!child.killed) child.kill('SIGKILL');
      }, 5_000);
      t.unref();
    }
  }
}

// ─── helpers ──────────────────────────────────────────────────────────────────

/** Extract the opencode sessionID an event belongs to, across event shapes.
 *  Most carry `properties.sessionID`; `message.part.updated` nests it under
 *  `properties.part.sessionID`. Returns null when the event has no session
 *  (the per-session loop then leaves it to dispatchEvent, which drops it). */
function eventSessionId(ev: Event): string | null {
  const props = (ev as { properties?: unknown }).properties;
  if (!props || typeof props !== 'object') return null;
  if (ev.type === 'message.part.updated') {
    const part = (props as { part?: { sessionID?: string } }).part;
    return part?.sessionID ?? null;
  }
  return (props as { sessionID?: string }).sessionID ?? null;
}

/** BooCoder model string "provider/model" → opencode's structured {providerID, modelID}. */
function parseModel(model: string | undefined): { providerID: string; modelID: string } | undefined {
  if (!model || !model.trim()) return undefined;
  const trimmed = model.trim();
  const idx = trimmed.indexOf('/');
  if (idx > 0 && idx < trimmed.length - 1) {
    return { providerID: trimmed.slice(0, idx), modelID: trimmed.slice(idx + 1) };
  }
  // No slash but non-empty → infer llama-swap (the only configured provider).
  // Guard against bare '/' or trailing/leading slash.
  if (idx < 0 && trimmed.length > 0) {
    return { providerID: 'llama-swap', modelID: trimmed };
  }
  return undefined;
}

/** Ported verbatim from Paseo opencode-agent.ts: id → message-id fallback → null. */
function resolvePartDedupeKey(part: { id: string; messageID: string }, type: string): string | null {
  if (part.id.trim().length > 0) return `${type}:${part.id}`;
  if (part.messageID.trim().length > 0) return `${type}:message:${part.messageID}`;
  return null;
}

/** opencode ToolPart → ACP-shaped snapshot (reuses the existing persist/render path). */
function toolPartToSnapshot(part: ToolPart): AcpToolSnapshot {
  const state = part.state;
  let rawInput: unknown;
  let rawOutput: unknown;
  let title: string | undefined;
  if (state) {
    if ('input' in state) rawInput = (state as { input?: unknown }).input;
    if ('output' in state) rawOutput = (state as { output?: unknown }).output;
    else if ('error' in state) rawOutput = (state as { error?: unknown }).error;
    if ('title' in state) title = (state as { title?: string }).title;
  }
  return {
    toolCallId: part.callID,
    title: title ?? part.tool,
    kind: null,
    status: mapToolStatus(state?.status),
    rawInput,
    rawOutput,
  };
}

function mapToolStatus(s: ToolState['status'] | undefined): ToolCallStatus | null {
  switch (s) {
    case 'pending':
      return 'pending';
    case 'running':
      return 'in_progress';
    case 'completed':
      return 'completed';
    case 'error':
      return 'failed';
    default:
      return null;
  }
}

/** Bind-probe an ephemeral port on loopback. */
function freePort(): Promise<number> {
  return new Promise((resolve, reject) => {
    const srv = createServer();
    srv.unref();
    srv.on('error', reject);
    srv.listen(0, '127.0.0.1', () => {
      const addr = srv.address();
      if (addr && typeof addr === 'object') {
        const { port } = addr;
        srv.close(() => resolve(port));
      } else {
        srv.close(() => reject(new Error('opencode-server: could not determine a free port')));
      }
    });
  });
}

/** Resolve when the child prints the ready line; reject on timeout or early exit. */
function waitForReady(child: ChildProcess, timeoutMs: number): Promise<void> {
  return new Promise((resolve, reject) => {
    let done = false;
    let stderrBuf = '';

    const finish = (err?: Error) => {
      if (done) return;
      done = true;
      clearTimeout(timer);
      child.stdout?.off('data', onOut);
      child.stderr?.off('data', onErr);
      child.off('exit', onExit);
      if (err) reject(err);
      else resolve();
    };

    const onOut = (buf: Buffer) => {
      if (buf.toString().includes('opencode server listening on')) finish();
    };
    const onErr = (buf: Buffer) => {
      stderrBuf += buf.toString();
    };
    const onExit = (code: number | null) =>
      finish(new Error(`opencode serve exited before ready (code ${code}); stderr: ${stderrBuf.slice(-2000)}`));
    const timer = setTimeout(
      () => finish(new Error(`opencode serve not ready in ${timeoutMs}ms; stderr: ${stderrBuf.slice(-2000)}`)),
      timeoutMs,
    );

    child.stdout?.on('data', onOut);
    child.stderr?.on('data', onErr);
    child.on('exit', onExit);
  });
}

function sleep(ms: number): Promise<void> {
  return new Promise((r) => setTimeout(r, ms));
}

/** Strip opencode-dcp plugin tags that render as literal text in the UI. */
function stripDcpTags(s: string): string {
  return s.replace(/<dcp-message-id>[^<]*<\/dcp-message-id>/g, '');
}

function errMsg(e: unknown): string {
  return e instanceof Error ? e.message : String(e);
}

function errToString(e: unknown): string {
  if (e == null) return 'unknown error';
  if (typeof e === 'string') return e;
  if (e instanceof Error) return e.message;
  try {
    return JSON.stringify(e);
  } catch {
    return String(e);
  }
}

/** Hash of stable config — detects model changes across sessions without
 *  invalidating on ephemeral state like the random server port (which changes
 *  every BooCoder restart). */
function sessionConfigHash(model: string): string {
  return createHash('sha256').update(`opencode_server|${model}`).digest('hex').slice(0, 16);
}