feat: migrate to OpenCode v2 plugin API

.github/workflows/ci.yml

@@ -46,3 +46,6 @@ jobs:
 
       - name: Test published package
         run: bun run test:package
+
+      - name: Test isolated OpenCode v2 host
+        run: npm exec --yes --package=@opencode/cli@2.0.3 -- bun run test:host

README.md

@@ -22,6 +22,10 @@ This plugin lets you write in your language while the model works in English —
 
 ## Install
 
+Version 2 of this plugin uses OpenCode's **v2 public plugin API**. The verified release is OpenCode **2.0.3**.
+For OpenCode v1, use `opencode-translate@1`.
+Start a fresh v2 session when upgrading: v1 activation metadata and historical bilingual trailers are not migrated.
+
 ```bash
 bun add -g opencode-translate
 ```
@@ -32,16 +36,23 @@ Add to `~/.config/opencode/opencode.jsonc`:
 
 ```jsonc
 {
-  "plugin": [
-    ["opencode-translate", {
-      "model": "openai/gpt-5.4-mini", // model to use for translation
-      "variant": "minimal",            // optional model variant / thinking effort
-      "lang": "Korean"                // language you speak
-    }]
+  "$schema": "https://opencode.ai/config.json",
+  "plugins": [
+    {
+      "package": "opencode-translate",
+      "options": {
+        "model": "openai/gpt-5.4-mini", // model to use for translation
+        "variant": "minimal",          // optional model variant / thinking effort
+        "lang": "Korean"               // language you speak
+      }
+    }
   ]
 }
 ```
 
+Quit and restart OpenCode after changing the plugin configuration. For a local build, run `bun install && bun run build`
+and set `package` to the absolute **directory** `/path/to/opencode-translate/dist`.
+
 ## Usage
 
 Prefix any message with `$en` to activate translation for that session.
@@ -52,6 +63,66 @@ $en 프로젝트 루트의 package.json을 읽고 요약해줘
 
 All subsequent messages in the same session are translated automatically — no need to repeat `$en`.
 
+- Your original message and its English translation remain visible in the transcript.
+- English assistant text streams normally; a translated Markdown section is appended when the text segment completes.
+- Both the **terminal and web UI** display the same persisted bilingual assistant text. No UI-specific plugin is needed.
+- Question forms are translated, with selected labels and custom answers converted back to English for the model.
+- Translation activates only in root sessions. Its state survives plugin/server restarts.
+
+Before model requests, the plugin removes its recorded display translations from context. It does not remove arbitrary
+Markdown based on its appearance. On inbound translation failure, the original prompt is sent unchanged; on outbound
+failure, the English response is retained with a translation-unavailable notice.
+
+## Authentication
+
+Connect the translation model's provider in **OpenCode itself**. Translation uses the public `ctx.generate.text()` API,
+so OpenCode owns provider selection, model variants, API keys, SQLite credentials, and OAuth refresh/persistence.
+The plugin does not read `auth.json`/`auth-v2.json`, query the credential database, or maintain separate tokens.
+Provider and OAuth support for the translation model is the support available in your OpenCode installation.
+
+## Inline reply support
+
+V2 has no `experimental.text.complete` hook or public display-only message append operation. Inline translations use
+`session.hook("http.response", ...)` with adapters for these **main-chat response protocols**:
+
+| Protocol | Recognized endpoint | Support |
+| --- | --- | --- |
+| OpenAI Responses, including Codex | `…/responses` | SSE text deltas and final snapshots |
+| OpenAI Chat Completions and compatible providers | `…/chat/completions` | SSE text choices |
+| Anthropic Messages | `…/messages` | SSE text blocks |
+| Gemini / Vertex Gemini | `…:streamGenerateContent` | SSE non-thinking text |
+
+Unknown endpoints, non-SSE responses, and binary protocols such as Bedrock Converse pass through unchanged with a server
+log message. They still support inbound/question translation when the translation model is available through OpenCode.
+Reasoning, tool calls, images, and other non-text outputs are not translated.
+
+**Transport:** OpenCode routes sessions through HTTP when HTTP hooks are registered. Loading this plugin therefore
+disables the session WebSocket fast path in its location, including sessions that have not activated `$en`.
+Translations add latency at text-completion boundaries and use additional model requests. Their usage is separate from
+the primary model's reported token counts.
+
+## Development and verification
+
+```sh
+bun install
+bun run check:ci
+bun run typecheck
+bun run knip
+bun test
+bun run build
+bun run test:package
+
+# Requires Node 24 and an OpenCode v2 binary; uses an isolated server and fake provider.
+OPENCODE_BINARY=/path/to/opencode bun run test:host
+```
+
+Tests include OpenCode's actual native protocol parsers. The real-host smoke test loads the built plugin, creates and
+rotates a test credential in an isolated SQLite database, checks bilingual persisted messages and English-only model
+requests, and restarts the server to verify recovery. It does not use your live server, credentials, or paid models.
+
+The old `opencode2 v0.0.0-dev-18322` binary does not pass this migration's host smoke test. Use the verified 2.0.3 release
+rather than assuming that any binary named `opencode2` exposes the current plugin API.
+
 ## Options
 
 | Option | Type | Default | Description |