feat: support opencode v2 plugin API alongside v1

[jvacek]

Summary

One package supporting both opencode v1 (@opencode-ai/plugin, plugin key)
and v2 (@opencode/plugin, plugins key). V1 minimum >= 1.18.29 (object
entrypoints), v2 ^2.0.0. See docs/v2.md for the full mapping.

V2 replaces the single mutable config object with replayable, synchronous,
per-domain transforms, so each override key maps to the domain that owns it
(mcp/agent/model/provider); everything else warns instead of merging.

What's in the stack (13 commits)

Base v2 support (6):

• refactor: extract shared sync plugin core — executeSyncCommand,
  command loading, tool args into src/shared.ts
• feat: injectable AI provider and node shell shim — createV1AiProvider
  in src/sync/ai.ts, createNodeShell in src/shell-node.ts
• feat: support opencode v2 plugin API — setupV2 in src/v2.ts
• test: v2 dual export and domain transforms, docs, CI assertion

Review hardening (7, from senior review of docs/v2.md):

• feat: shared blankEnvPlaceholders helper — single {env:…} pattern in
  src/sync/config.ts, reused by v2 for secret-free disabled MCP configs
• feat: SyncService.dispose — stops the Turso sync loop/idle-flush timers;
  wired into v2 setup cleanup (fixes hot-reload leak)
• docs: node shell shim differences — POSIX//bin/sh, inherited env,
  32 MiB buffer, exec error shape
• refactor: harden v2 transforms — single-read override load (no TOCTOU),
  shared deepMerge, pure replay callbacks (unknown-ID warnings moved
  outside via best-effort list()), removed dead no-op fallback call,
  Set-based command lookup, hardened bare-repo parsing, prefixed logging
• fix: explicit dual entrypoint — {id, setup, server}, no spread
• test: replay purity, arg parsing, idempotent cleanup
• docs: rewrite docs/v2.md to match the implementation

Known parity gaps (documented in docs/v2.md)

• Non-MCP runtime keys are warn-only in v2; no fake global merge.
• No toasts in v2 (console); Turso idle-gating skipped (empty status = idle,
  syncs immediately).
• Slash commands parse a bare owner/repo token only; full options need the
  opencode_sync tool.
• Overrides require host restart; no watcher/reload() calls.
• V2 CommandDefinition has no template/agent/model — md templates execute
  directly with a session.synthetic reply.

Test plan

• bun run check clean
• bun test / vitest run — 205 pass (incl. 9 new v2 tests)
• bun run build clean; dist exposes {id, setup, server}
• Manual packed-tarball smoke on opencode v1 (plugin) and v2 (plugins)
• CI matrix smoke (v1 + v2 installs vs packed plugin)

Fixes: n/a (new feature). Breaking: no — v1 server() behavior unchanged.

[jvacek]

Hey @iHildy! Hope all's well, just wanted to tag you here so it shows up on your radar in case you're not watching the PRs here.

Thanks in advance!