diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 752cac7..708978e 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -6,7 +6,34 @@ on:
       - "v*"
 
 jobs:
+  verify:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        ruby: ["3.2", "3.3", "3.4", "4.0"]
+    steps:
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+
+      - name: Set up Ruby ${{ matrix.ruby }}
+        uses: ruby/setup-ruby@003a5c4d8d6321bd302e38f6f0ec593f77f06600 # v1.319.0
+        with:
+          ruby-version: ${{ matrix.ruby }}
+          bundler-cache: true
+
+      - name: Run tests
+        run: bundle exec rake test
+
+      - name: Build gem
+        run: gem build opencode-ruby.gemspec
+
+      - name: Verify gem loads after install
+        run: |
+          gem install opencode-ruby-*.gem --no-document
+          ruby -ropencode-ruby -e 'puts Opencode::VERSION'
+
   push:
+    needs: verify
     if: ${{ github.server_url == 'https://github.com' }}
     runs-on: ubuntu-latest
     permissions:
diff --git a/README.md b/README.md
index 99bfc01..92a03ea 100644
--- a/README.md
+++ b/README.md
@@ -202,7 +202,8 @@ Want every OpenCode endpoint auto-generated from the OpenAPI spec? Use [`opencod
 ## Compatibility
 
 - Ruby ≥ 3.2
-- Runtime dependency: `activesupport (>= 6.1)` — *not* Rails. ActiveSupport is a standalone helpers gem (`blank?`, `present?`, `presence`, `truncate`, etc.).
+- Runtime dependency: `activesupport (>= 6.1, < 9.0)` — *not* Rails. ActiveSupport is a standalone helpers gem (`blank?`, `present?`, `presence`, `truncate`, etc.).
+- Runtime dependency: `marcel (~> 1.0)` for artifact MIME type detection.
 
 OpenCode server compatibility is evidence-based, not an open-ended SemVer
 promise. OpenCode's HTTP, SSE, and runtime behavior can change independently
diff --git a/test/readme_contract_test.rb b/test/readme_contract_test.rb
index f112525..59474ac 100644
--- a/test/readme_contract_test.rb
+++ b/test/readme_contract_test.rb
@@ -16,4 +16,9 @@ class ReadmeContractTest < Minitest::Test
     assert_includes README, "not configured as of `0.0.1.alpha7`"
     assert_includes README, "does not currently guarantee publication"
   end
+
+  def test_compatibility_documents_every_runtime_dependency
+    assert_includes README, "`activesupport (>= 6.1, < 9.0)`"
+    assert_includes README, "`marcel (~> 1.0)`"
+  end
 end
diff --git a/test/release_workflow_test.rb b/test/release_workflow_test.rb
index 723c13b..b34fb90 100644
--- a/test/release_workflow_test.rb
+++ b/test/release_workflow_test.rb
@@ -17,6 +17,10 @@ class ReleaseWorkflowTest < Minitest::Test
     workflow.fetch("jobs").fetch("push")
   end
 
+  def verify_job
+    workflow.fetch("jobs").fetch("verify")
+  end
+
   def test_release_job_is_inert_on_non_github_runners
     assert_equal "${{ github.server_url == 'https://github.com' }}", push_job.fetch("if")
   end
@@ -61,4 +65,15 @@ class ReleaseWorkflowTest < Minitest::Test
     assert_operator test_index, :<, publish_index
     assert_equal "bundle exec rake test", steps.fetch(test_index).fetch("run")
   end
+
+  def test_release_verifies_the_supported_matrix_and_installed_gem_before_publish
+    assert_equal %w[3.2 3.3 3.4 4.0], verify_job.dig("strategy", "matrix", "ruby")
+    assert_equal "verify", push_job.fetch("needs")
+
+    commands = verify_job.fetch("steps").filter_map { |step| step["run"] }.join("\n")
+    assert_includes commands, "bundle exec rake test"
+    assert_includes commands, "gem build opencode-ruby.gemspec"
+    assert_includes commands, "gem install opencode-ruby-*.gem --no-document"
+    assert_includes commands, "ruby -ropencode-ruby"
+  end
 end
diff --git a/test/workflow_contract_test.rb b/test/workflow_contract_test.rb
index 428d3ce..11a6cea 100644
--- a/test/workflow_contract_test.rb
+++ b/test/workflow_contract_test.rb
@@ -27,7 +27,7 @@ class WorkflowContractTest < Minitest::Test
       workflow_uses(workflow)
     end
 
-    assert_equal 5, action_uses.length
+    assert_equal 7, action_uses.length
     action_uses.each do |action_use|
       action, separator, revision = action_use.rpartition("@")