Port plugin to the OpenCode V2 TUI plugin API

[LucasInstra]

Port plugin to the OpenCode V2 TUI plugin API

Migrates the plugin from the V1 TUI plugin API (@opencode-ai/plugin/tui) to the V2 CLI plugin API (@opencode/plugin/tui + @opencode/client). Fixes #24.

As requested, this PR now contains only the V2 port (feature parity with V1). The new features built on top of it live in #26 — please review this one first.

Tested against opencode 2.0.3 and verified up to 2.0.8.

V1 → V2 mapping

• Entrypoint: export default { id, tui(api, options, meta) } → Plugin.define({ id, setup(ctx) }); cleanup is returned from setup.
• Slots & keymap: the overlay still renders in the app slot (ctx.ui.slot). Keymap layers are registered inside the slot component because ctx.keymap.layer() requires a component owner. The V1 legacy api.command fallback was dropped.
• Routing: api.route.current → ctx.ui.router.current().
• Dialogs / toasts / theme: ctx.ui.dialog and ctx.ui.toast.show; ctx.theme is mapped to the token names the components already use (src/opencode.ts). The adapter reads every token defensively and supports both the <= 2.0.7 background.surface and the 2.0.8 background.raised shapes, so a theme change degrades gracefully instead of crashing the slot.
• Messages: V1 state.session.messages + state.part → client.session.context({ sessionID }) (V2 embeds content parts in the message and has no separate part store).
• Models / providers: V1 provider map → client.model.list() + client.provider.list(); the fallback default model comes from client.model.default().
• Sessions: session.create with location, model and V2 permission rules; the mini system prompt is attached with session.instructions.entry.put; session.prompt delivers the question; session.interrupt / session.remove on close.
• Streaming: V1 session.next.text.delta / message.part.updated → V2 events session.text.delta, session.reasoning.delta, session.tool.*, session.execution.*, session.idle via ctx.data.on().
• Permissions: the plugin-managed mini agent is enforced with V2 permission rules — deny *, then allow the configured tools (list is not a V2 permission action; the read tool lists directories).
• Auto-update: checks the npm registry and shows the warning in the overlay plus a toast pointing at opencode plugin update opencode-mini-session. Unlike V1 it does not delete its own package cache, because V2 ships a first-class plugin update command.
• Dependencies: @opencode-ai/plugin / @opencode-ai/sdk → @opencode/plugin / @opencode/client ^2.0.5 (@opencode/plugin is a runtime dependency, as the migration guide recommends, so the packaged entrypoint resolves it). OpenTUI ^0.4.3 → ^0.5.11 (@opentui/solid pins solid-js@1.9.12, so babel-preset-solid is pinned to 1.9.12 as well); engines.opencode → >=2.
• Version: bumped to 2.0.0 for the breaking V2 port — happy to drop that if you prefer to handle releases yourself.

Behavior notes (no exact V2 equivalent)

• Continue (shift+enter): V1's tui.appendPrompt has no V2 client API, so the transcript is queued into the main session with session.prompt({ delivery: "queue" }).
• Root sessions: SessionCreateInput has no parentID, so mini sessions are regular sessions. They are tagged with metadata.opencodeMiniSession and deleted on close.
• Legacy keymap fallback for older V1 hosts was dropped (V2 only).

Tooling

• CI: .github/workflows/ci.yml runs typecheck, unit tests, build, and the packaged output check. The package check now verifies the V2 entrypoint (id + setup), handles npm 11's npm pack --json output, and works on Windows.
• Git installs: a prepare script builds dist/, so opencode plugin add github:... works without a manual build step.

Tests

84 tests across 7 files (agent, context, model, session, update, counter, routing), ported from the V1 suite and adapted to the V2 API.

Verification

• Plugin loads cleanly on opencode 2.0.3 (stage=setup completed, no plugin failed banner).
• Overlay opens with alt+b; context counter, transcript, input, and footer render.
• Interactive round-trip against a live 2.0.3 server: typed question → streamed answer.
• API contract verified end-to-end: session created with the plugin payload (permissions + model + variant) → instructions entry attached → prompt delivered → assistant reply with the expected model.
• tsc --noEmit, vitest run, npm run build, and npm run test:package pass.

How to try it

• After the 2.x release on npm: opencode plugin add opencode-mini-session.

• Without waiting for a release, from this branch: clone, build, and load the checkout through the global plugin directory:

  git clone https://github.com/LucasInstra/opencode-mini-session.git -b v2
  cd opencode-mini-session
  npm install && npm run build
  mkdir -p ~/.config/opencode/plugins/mini-session
  ln -s "$PWD/dist" ~/.config/opencode/plugins/mini-session/dist
  ln -s "$PWD/node_modules" ~/.config/opencode/plugins/mini-session/node_modules
  printf 'export { default } from "./dist/index.js";\n' > ~/.config/opencode/plugins/mini-session/tui.ts

  On Windows use mklink /J for the two links. Restart OpenCode after rebuilding.

• opencode plugin add github:... works where Git packages are enabled. npm 12 disables them by default (allow-git=none), so enable it first (npm config set allow-git all) if the install is refused.

[LucasInstra]

Split as requested: this PR now contains only the V2 port (feature parity with V1). The branch was rebuilt so the port commits come first — it is content-identical to the previous head, no code was dropped. The new features moved to #26, which is stacked on this branch; please review/merge this one first. Once it is merged I will rebase #26 so that PR shows only the feature commits.

[LucasInstra]

Compatibility fix pushed: OpenCode 2.0.8 renamed the resolved theme background (background.surface -> background.raised), and reading the old field inside the app slot crashed the plugin with undefined is not an object (evaluating 'theme.background.surface.overlay').

The theme adapter now reads every token defensively with fallbacks for both shapes, and tests cover the 2.0.8 shape plus a partial theme. Verified by calling the built adapter with both theme shapes (2.0.8 -> raised.high/raised.base; older -> surface.overlay/surface.offset) and with an empty theme (falls back without throwing).