Add README + CHANGELOG for v0.0.1.alpha1

README (~140 LOC):
  - Why this gem exists (4 production needs opencode-ruby alone doesn't cover)
  - Install + quickstart (showing GenerateResponseJob wiring Session + Turn)
  - 12-constant API table with one-line role descriptions
  - Instrumentation + error-reporting adapter setup snippets
  - Position against opencode-ruby and Eric Guo's opencode_client

CHANGELOG documents what shipped, runtime deps, and known limitations
(apply_patch artifact drop, gem-side behavioral tests TBD, no Rails
generator yet). LICENSE was auto-generated by Gitea (MIT, 2026
ajaynomics) and is unchanged.

CHANGELOG.md

@@ -0,0 +1,34 @@
+# Changelog
+
+## 0.0.1.alpha1 — 2026-05-20
+
+Initial public alpha. Extracted from a production multi-product Rails app (`ajent-rails`) where these objects shipped under `lib/opencode/rails/` before being carved out into a standalone gem.
+
+**Includes:**
+
+- `Opencode::Session` — AR-coupled, row-level-locked session lifecycle (`ensure!`, `recreate!`, `abort!`)
+- `Opencode::Turn` — orchestrator covering send → stream → recover → finalize, with CAS-safe message terminal-state transitions
+- `Opencode::Exchange` — domain object over a turn's message array; emits `opencode.apply_patch.artifacts_dropped` when post-write file content is unavailable
+- `Opencode::Artifact` — value-object (filename + content + content_type + trust metadata), idempotent attach
+- `Opencode::MessageArtifacts` — ActiveStorage-aware artifact attachment pipeline with transform support
+- `Opencode::Sandbox` — disk-backed sandbox reader, returns `Artifact` list
+- `Opencode::SandboxFile` — single-file value object (pathname → bytes/content-type)
+- `Opencode::Transform` — base class for content-rewriting transforms
+- `Opencode::Impostor` — ActiveStorage download/upload round-trip helper
+- `Opencode::UploadedFilesPrompt` — user-prompt prefix builder listing uploaded files, sandbox-path inverted (injection-based, no `Opencode::Permissions` reference)
+- `Opencode::ToolDisplay` — view-model for tool-call hashes (Turbo Stream-friendly)
+- `Opencode::ErrorReporter` — pluggable adapter mirroring the `Opencode::Instrumentation` pattern
+
+**Runtime dependencies:**
+
+- `opencode-ruby ~> 0.0.1.alpha1` (wire client + Reply state machine)
+- `activerecord >= 7.1, < 9.0`
+- `activestorage >= 7.1, < 9.0`
+- `activesupport >= 7.1, < 9.0`
+
+**Known limitations (alpha):**
+
+- Apply-patch tool's post-write file content is not extracted (wire-format limitation in OpenCode v1.15+); affected files surface via the `opencode.apply_patch.artifacts_dropped` instrumentation event. Future work: optional sandbox-read fallback path.
+- Smoke tests only inside the gem (14 tests). Behavioral coverage lives in the host app that originally produced this code (`ajent-rails`'s `test/lib/opencode/rails/`). Standalone gem-side test suite using Combustion is open work.
+- No generator (`rails g opencode:install`) yet.
+- No Rails Engine integration — `require "opencode-rails"` is sufficient.

README.md

@@ -1,3 +1,123 @@
 # opencode-rails
 
-Production-grade Rails integration for OpenCode. ActiveRecord-aware session lifecycle, Turbo-friendly streaming, mid-stream snapshot pattern.
+Production-grade [OpenCode](https://opencode.ai) integration for Rails apps. Layers an ActiveRecord-aware session lifecycle, a turn orchestrator, an artifact pipeline, and a sandbox model on top of the wire-level client in [`opencode-ruby`](https://gitea.krishnan.ca/ajaynomics/opencode-ruby).
+
+> **Alpha software.** API will change before 1.0. Pin to a specific version.
+
+## Why this gem exists
+
+`opencode-ruby` gives you a clean Net::HTTP + SSE client. To turn it into something a Rails app can ship, you need:
+
+1. **Session lifecycle** — idempotent create-or-resolve with row-level locking so concurrent jobs don't double-mint sessions; recreation for stale-session recovery; best-effort upstream abort on teardown.
+2. **Turn orchestration** — drive `send_message_async`, stream events into `Opencode::Reply`, recover from `SessionNotFoundError` / `StaleSessionError` by recreating + retrying, fetch the final exchange for cost/artifact extraction, finalize the persisted message via CAS against `:pending`.
+3. **Mid-stream snapshot** — `update_columns` writes to bypass AR callbacks so app-level Turbo broadcasts fire on rate-limited intervals, not every SSE event.
+4. **Artifact pipeline** — extract files written by the agent (via the `write` tool's metadata, or by reading from a sandbox path), attach them to the assistant message via ActiveStorage, transform host-rendered artifacts (flight results HTML, etc.) before persisting.
+
+`opencode-rails` ships these as named, single-responsibility objects so you wire them up instead of re-implementing them.
+
+## Install
+
+```ruby
+# Gemfile
+gem "opencode-ruby"   # wire client + Reply state machine
+gem "opencode-rails"  # AR-coupled session/turn/artifact stack
+```
+
+```bash
+bundle install
+```
+
+Runtime deps: `activerecord`, `activestorage`, `activesupport` (>= 7.1). Depends on `opencode-ruby` for the underlying HTTP/SSE primitives.
+
+## Quickstart
+
+```ruby
+# config/initializers/opencode.rb
+Opencode::Instrumentation.adapter = ->(name, payload, &blk) {
+  ActiveSupport::Notifications.instrument(name, payload, &blk)
+}
+Opencode::ErrorReporter.adapter = ->(error, **opts) {
+  Rails.error.report(error, **opts) if Rails.respond_to?(:error)
+}
+```
+
+```ruby
+# app/jobs/generate_response_job.rb
+class GenerateResponseJob < ApplicationJob
+  def perform(assistant_message)
+    conversation = assistant_message.conversation
+    user_message = conversation.messages.where(role: :user).last
+    client       = Opencode::Client.new(base_url: ENV["OPENCODE_URL"])
+
+    session = Opencode::Session.new(
+      conversation,
+      permissions_for: ->(record) { permission_rules_for(record) },
+      on_error:        ->(e, **opts) { Opencode::ErrorReporter.report(e, **opts) }
+    )
+
+    Opencode::Turn.new(
+      message:        assistant_message,
+      subject:        conversation,
+      query_text:     user_message.content,
+      client:         client,
+      session:        session,
+      on_turn_finished: ->(result) {
+        # result.status   #=> :completed | :error | :cancelled
+        # result.message  #=> the AR row (reloaded)
+        # result.duration_ms
+      }
+    ).call
+  end
+
+  private
+
+  def permission_rules_for(conversation)
+    [
+      { type: "edit", action: "allow", path: "data/sandbox/#{conversation.id}/" }
+    ]
+  end
+end
+```
+
+The host's record (here `conversation`) must respond to `#title`, `#opencode_session_id`, `#opencode_session_id=`, `#with_lock(&block)`, `#update!`, `#reload`, `#id`. The host's message record (here `assistant_message`) must respond to `#error!(content)`, `#update_columns(...)`, `#with_lock(&block)`, `#reload`, `#pending?`.
+
+## What you get
+
+| Constant | Role |
+|---|---|
+| `Opencode::Session` | Idempotent ensure!/recreate!/abort! with row-level locking |
+| `Opencode::Turn` | End-to-end orchestrator: ensure session → send → stream → recover → finalize |
+| `Opencode::Exchange` | Domain object over a turn's message array; owns artifact extraction |
+| `Opencode::Artifact` | Value object: filename + bytes + content_type + trust metadata |
+| `Opencode::MessageArtifacts` | Idempotent attachment pipeline (ActiveStorage-aware, transform-applying) |
+| `Opencode::Sandbox` | Reads written files from disk, returns Artifact list |
+| `Opencode::SandboxFile` | Single-file value: pathname → bytes/content-type/identity Artifact |
+| `Opencode::Transform` | Base class for content-rewriting transforms (e.g. host-rendered HTML) |
+| `Opencode::Impostor` | ActiveStorage download/upload helper that round-trips bytes |
+| `Opencode::UploadedFilesPrompt` | Builds the user-prompt prefix listing uploaded files |
+| `Opencode::ToolDisplay` | View-model converting tool-call hashes to Turbo-friendly props |
+| `Opencode::ErrorReporter` | Pluggable adapter for routing swallowed errors |
+
+Plus everything from `opencode-ruby`: `Client`, `Reply`, `ReplyObserver`, `Tracer`, `Prompts`, `ResponseParser`, `ToolPart`, `PartSource`, `Todo`, `Instrumentation`, the error hierarchy.
+
+## Instrumentation + error reporting
+
+The gem emits events through `Opencode::Instrumentation.instrument(name, payload, &blk)` and reports swallowed errors through `Opencode::ErrorReporter.report(error, **opts)`. Both are no-ops by default. Wire your host's emitter / reporter in an initializer (see Quickstart above).
+
+Events emitted (non-exhaustive):
+
+- `opencode.turn.started`, `opencode.turn.finished`
+- `opencode.stream.completed`, `opencode.stream.interrupted`
+- `opencode.session.created`, `opencode.session.recreated`
+- `opencode.apply_patch.artifacts_dropped`
+- `opencode.response.upstream_error`
+
+Subscribe via `ActiveSupport::Notifications.subscribe("opencode.*")` once you've wired the adapter.
+
+## Position
+
+`opencode-rails` is for Rails apps that want production-grade OpenCode streaming without reimplementing the orchestration boilerplate. If you want only the wire client, use `opencode-ruby` directly. If you want every endpoint with generated types, use [`opencode_client`](https://rubygems.org/gems/opencode_client) (Eric Guo's auto-generated gem).
+
+## License
+
+MIT. See [LICENSE](LICENSE).