Use Opencode::Instrumentation.notify; bump dep + own version to alpha2

Paired-release commit that completes the .notify migration started in
opencode-ruby v0.0.1.alpha2.

Changes:
  - lib/opencode/exchange.rb: drops the empty '{ }' block from the
    apply_patch.artifacts_dropped emission, switching from
    .instrument(...) { } to .notify(...). Identical wire semantics,
    cleaner read at the call site.
  - opencode-rails.gemspec: pins opencode-ruby runtime dep to
    '= 0.0.1.alpha2' (was alpha1). Lockstep versions during alpha.
  - lib/opencode/rails_version.rb: 0.0.1.alpha1 -> 0.0.1.alpha2.
  - CHANGELOG: documents the Exchange call-site change and the
    opencode-ruby pin bump.

53 tests pass, 134 assertions, 0 failures.

CHANGELOG.md

@@ -1,5 +1,21 @@
 # Changelog
 
+## 0.0.1.alpha2 — 2026-05-20
+
+### Changed
+
+- `Opencode::Exchange` now emits `opencode.apply_patch.artifacts_dropped`
+  via the new `Opencode::Instrumentation.notify` fire-and-forget API
+  (introduced in opencode-ruby v0.0.1.alpha2) instead of
+  `.instrument(name, payload) { }` with an empty block. Cleaner read
+  at the call site; identical semantics on the wire (same event name,
+  same payload).
+
+### Bumped
+
+- Runtime dependency `opencode-ruby` pinned to `= 0.0.1.alpha2` (was
+  `= 0.0.1.alpha1`). Versions stay in lockstep during alpha.
+
 ## 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.

lib/opencode/exchange.rb

@@ -65,13 +65,13 @@ module Opencode
           eligible = file_entries.reject { |e| e[:type] == "delete" }
           next if eligible.empty?
 
-          Opencode::Instrumentation.instrument("opencode.apply_patch.artifacts_dropped",
+          Opencode::Instrumentation.notify("opencode.apply_patch.artifacts_dropped",
             file_count:     eligible.size,
             relative_paths: eligible.filter_map { |e| e[:relativePath] }.first(5),
             message_id:     part[:messageID],
             session_id:     part[:sessionID],
             reason:         "apply_patch v1.15+ metadata does not include post-write file content; " \
-                            "extraction requires sandbox-read which is not yet wired into ResponseParser") { }
+                            "extraction requires sandbox-read which is not yet wired into ResponseParser")
         end
       end
     end

lib/opencode/rails_version.rb

@@ -11,5 +11,5 @@
 # We can't reuse the same constant from a second gem, so we use a
 # distinct, non-namespaced constant.
 module Opencode
-  RAILS_VERSION = "0.0.1.alpha1"
+  RAILS_VERSION = "0.0.1.alpha2"
 end

opencode-rails.gemspec

@@ -37,7 +37,7 @@ Gem::Specification.new do |spec|
   # this gem builds on. During alpha both gems evolve in lockstep — we pin
   # exactly (= not ~>) so that consumers always pick the version this gem
   # was tested against. Bump to alpha2 when the paired release ships.
-  spec.add_runtime_dependency "opencode-ruby", "= 0.0.1.alpha1"
+  spec.add_runtime_dependency "opencode-ruby", "= 0.0.1.alpha2"
 
   # Rails sub-libraries used at runtime. Depending on these individually
   # (instead of the `rails` umbrella) avoids forcing host apps to load