diff --git a/.claude/rules/services.md b/.claude/rules/services.md
new file mode 100644
index 0000000..650d2ee
--- /dev/null
+++ b/.claude/rules/services.md
@@ -0,0 +1,13 @@
+---
+paths:
+  - "lib/services/**/*.rb"
+---
+
+# Service Conventions
+
+- All HTTP calls use Ruby's native `Net::HTTP` — do not add external HTTP client gems
+- Services are plain Ruby classes initialized with tokens/config, no framework coupling
+- Constructor pattern: `initialize(token, debug: false, logger: nil)`
+- API clients define a private `api_request` method that handles GET/POST, auth headers, and JSON parsing
+- Error handling: check response status/`ok` field, log via `debug_log`, return empty/false on failure rather than raising
+- SlackService auto-joins channels on `not_in_channel` errors — preserve this retry pattern
diff --git a/.claude/rules/slack-modals.md b/.claude/rules/slack-modals.md
new file mode 100644
index 0000000..82c8bb8
--- /dev/null
+++ b/.claude/rules/slack-modals.md
@@ -0,0 +1,12 @@
+---
+paths:
+  - "lib/helpers/**/*.rb"
+---
+
+# Slack Modal Conventions
+
+- Modals use Slack Block Kit format — return Ruby hashes that serialize to JSON
+- Two modal types: `global_shortcut_modal` (needs both thread URL and issue URL inputs) and `message_shortcut_modal` (only needs issue URL, thread context passed via `private_metadata`)
+- `private_metadata` carries `channel_id` and `thread_ts` as JSON between shortcut trigger and submission
+- Callback IDs follow the pattern `gh_comment_modal_<type>` — these are matched in `app.rb` to route submissions
+- Use `plain_text_input` elements with `block_id`/`action_id` pairs for form fields
diff --git a/.claude/rules/testing.md b/.claude/rules/testing.md
new file mode 100644
index 0000000..b7f5915
--- /dev/null
+++ b/.claude/rules/testing.md
@@ -0,0 +1,15 @@
+---
+paths:
+  - "test/**/*.rb"
+---
+
+# Testing Rules
+
+- Use `Minitest::Spec` style (`describe`/`it` blocks)
+- All external HTTP calls must be stubbed with WebMock — `WebMock.disable_net_connect!` is enforced globally
+- Use the shared fixtures and stub helpers from `test/test_helper.rb`:
+  - Fixtures: `slack_message`, `slack_thread_response`, `slack_user_response`, `github_comment_response`, `slack_modal_payload`
+  - Stubs: `stub_slack_conversations_replies`, `stub_slack_users_info`, `stub_slack_chat_post_message`, `stub_github_create_comment`
+- Integration tests use `Rack::Test` — call endpoints via `get`, `post` etc. and the `app` method returns `Sinatra::Application`
+- `setup` calls `WebMock.reset!` automatically — no need to repeat it
+- Test env vars (`SLACK_BOT_TOKEN`, `GITHUB_TOKEN`) are set in `test_helper.rb`
diff --git a/.claude/skills/ci/SKILL.md b/.claude/skills/ci/SKILL.md
new file mode 100644
index 0000000..49825fd
--- /dev/null
+++ b/.claude/skills/ci/SKILL.md
@@ -0,0 +1,13 @@
+---
+name: ci
+description: Run the full CI suite (syntax + rubocop + tests) and report results
+allowed-tools: Bash(bundle exec *)
+---
+
+Run the full CI check suite:
+
+```bash
+bundle exec rake ci
+```
+
+Report the results clearly. If any step fails, identify which step failed and show the relevant error output.
diff --git a/.claude/skills/release/SKILL.md b/.claude/skills/release/SKILL.md
new file mode 100644
index 0000000..a04dc43
--- /dev/null
+++ b/.claude/skills/release/SKILL.md
@@ -0,0 +1,19 @@
+---
+name: release
+description: Walk through the release process - preview changelog, bump version, create PR
+disable-model-invocation: true
+argument-hint: "[major|minor|patch]"
+---
+
+Create a release for this project. The bump type is: $ARGUMENTS (default to what `rake release:preview` suggests if not specified).
+
+Steps:
+
+1. Run `bundle exec rake release:preview` to show the current version, suggested bump type, and changelog preview
+2. Confirm the bump type with the user before proceeding
+3. Ensure the working directory is clean (`git status`)
+4. Run `bundle exec rake ci` to verify all checks pass
+5. Run `bundle exec rake release:$ARGUMENTS` to create the release (this bumps version, updates CHANGELOG.md, and creates a git tag)
+6. Show the user the final commands to push: `git push origin main && git push origin <tag>`
+
+Do NOT push automatically — let the user decide when to push.
diff --git a/.claude/skills/review-pr/SKILL.md b/.claude/skills/review-pr/SKILL.md
new file mode 100644
index 0000000..8b6e5d2
--- /dev/null
+++ b/.claude/skills/review-pr/SKILL.md
@@ -0,0 +1,33 @@
+---
+name: review-pr
+description: Review a pull request for code style, architecture, and correctness
+disable-model-invocation: true
+context: fork
+agent: Explore
+argument-hint: "[PR number or URL]"
+allowed-tools: Bash(gh *)
+---
+
+Review pull request $ARGUMENTS against this project's conventions.
+
+## Gather context
+
+- PR diff: !`gh pr view $ARGUMENTS --json additions,deletions,changedFiles`
+- PR details: !`gh pr view $ARGUMENTS`
+- Full diff: !`gh pr diff $ARGUMENTS`
+
+## Review checklist
+
+1. **Code style**: RuboCop compliance (120-char lines, 20-line methods, single quotes)
+2. **Architecture**: Services stay in `lib/services/`, helpers in `lib/helpers/`. Services use Net::HTTP, not external HTTP gems
+3. **Testing**: New functionality has corresponding tests. All HTTP calls are stubbed with WebMock. Tests use shared fixtures from `test_helper.rb`
+4. **Commit messages**: Follow conventional commits format (`feat:`, `fix:`, `docs:`, etc.)
+5. **Error handling**: API errors handled gracefully, debug logging via `debug_log`
+
+## Output
+
+Provide a structured review with:
+- Summary of changes
+- Issues found (if any), with file and line references
+- Suggestions for improvement
+- Overall assessment (approve / request changes)
diff --git a/.github/copilot-instructions.md b/.github/copilot-instructions.md
new file mode 120000
index 0000000..949a29f
--- /dev/null
+++ b/.github/copilot-instructions.md
@@ -0,0 +1 @@
+../CLAUDE.md
\ No newline at end of file
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6c6642c..e44e864 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -14,7 +14,7 @@ jobs:
 
     strategy:
       matrix:
-        ruby-version: ['3.1', '3.2', '3.3']
+        ruby-version: ['3.2', '3.3', '3.4', '4.0']
 
     steps:
     - uses: actions/checkout@v4
diff --git a/.rubocop.yml b/.rubocop.yml
index edf398c..7d62055 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -8,7 +8,7 @@ plugins:
   - rubocop-rake
 
 AllCops:
-  TargetRubyVersion: 3.1
+  TargetRubyVersion: 3.2
   NewCops: enable
   Exclude:
     - "vendor/**/*"
diff --git a/CLAUDE.md b/CLAUDE.md
new file mode 100644
index 0000000..f78e4ce
--- /dev/null
+++ b/CLAUDE.md
@@ -0,0 +1,64 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+Slack-github-threads is a Ruby Sinatra app that exports Slack thread conversations as comments on GitHub issues. Users trigger it via a `/ghcomment` slash command or Slack shortcuts (global and message).
+
+## Common Commands
+
+```bash
+bundle install                  # Install dependencies
+bundle exec rake test           # Run all tests
+bundle exec rake test_services  # Run service unit tests only
+bundle exec rake test_app       # Run integration tests only
+bundle exec rake ci             # Full CI: syntax + rubocop + tests
+bundle exec rake rubocop        # Lint only
+bundle exec rake lint           # Syntax check + rubocop
+bundle exec rake server         # Start dev server
+DEBUG=true bundle exec ruby app.rb  # Run with debug logging
+```
+
+To run a single test file: `bundle exec ruby test/services/test_text_processor.rb`
+
+## Architecture
+
+```
+Slack (slash command / shortcut)
+  → app.rb (Sinatra routing, 3 endpoints: GET /up, POST /ghcomment, POST /shortcut)
+    → CommentService (orchestration)
+      ├→ SlackService (fetch thread via conversations.replies, resolve user mentions)
+      ├→ TextProcessor (format messages: HTML entity decoding, @mention replacement)
+      └→ GitHubService (POST comment to issue via REST API)
+```
+
+- **app.rb** — Entry point. Routes requests, validates params, delegates to CommentService.
+- **lib/services/comment_service.rb** — Orchestrates the flow: fetch thread → format → post to GitHub → reply in Slack.
+- **lib/services/slack_service.rb** — Slack API client (Net::HTTP). Auto-joins channels if bot isn't a member.
+- **lib/services/github_service.rb** — GitHub API client (Net::HTTP). Parses issue URLs to extract org/repo/number.
+- **lib/services/text_processor.rb** — Converts Slack message formatting to GitHub-compatible markdown.
+- **lib/helpers/modal_builder.rb** — Constructs Slack Block Kit modals for shortcut flows.
+- **lib/version_helper.rb** — Semantic versioning and changelog generation from conventional commits.
+
+All API calls use Ruby's native `Net::HTTP` — no external HTTP client gems.
+
+## Testing
+
+- Framework: Minitest with `Minitest::Spec` style
+- HTTP mocking: WebMock (all external calls must be stubbed)
+- `test/test_helper.rb` provides shared fixtures (`slack_message`, `slack_thread_response`) and stub helpers (`stub_slack_conversations_replies`, `stub_github_create_comment`)
+- Integration tests use `Rack::Test` against the Sinatra app
+
+## Environment Variables
+
+Required: `SLACK_BOT_TOKEN` (xoxb_*), `GITHUB_TOKEN` (ghp_*)
+Optional: `DEBUG` (true/false), `RACK_ENV`, `PORT` (default 3000)
+
+## Code Style
+
+RuboCop enforced. Key rules: 120-char line limit, 20-line method limit, single quotes preferred. Uses rubocop-minitest and rubocop-rake plugins.
+
+## Commit Conventions
+
+Uses conventional commits: `feat:`, `fix:`, `docs:`, `chore:`, `refactor:`, `test:`, `perf:`, `style:`. Breaking changes use `feat!:` or `BREAKING CHANGE:` footer. These drive automatic version bumping (major/minor/patch).
diff --git a/Gemfile.lock b/Gemfile.lock
index 6500f63..eb52870 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -11,27 +11,30 @@ GEM
       rexml
     daemons (1.4.1)
     dotenv (3.1.8)
+    drb (2.2.3)
     eventmachine (1.2.7)
     hashdiff (1.2.0)
     json (2.13.2)
     language_server-protocol (3.17.0.5)
     lint_roller (1.1.0)
     logger (1.7.0)
-    minitest (5.25.5)
-    mustermann (3.0.3)
+    minitest (6.0.2)
+      drb (~> 2.0)
+      prism (~> 1.5)
+    mustermann (3.0.4)
       ruby2_keywords (~> 0.0.1)
     nio4r (2.7.4)
     parallel (1.27.0)
     parser (3.3.9.0)
       ast (~> 2.4.1)
       racc
-    prism (1.4.0)
+    prism (1.9.0)
     public_suffix (6.0.2)
     puma (7.0.1)
       nio4r (~> 2.0)
     racc (1.8.1)
-    rack (3.1.16)
-    rack-protection (4.1.1)
+    rack (3.2.5)
+    rack-protection (4.2.1)
       base64 (>= 0.1.0)
       logger (>= 1.6.0)
       rack (>= 3.0.0, < 4)
@@ -43,7 +46,7 @@ GEM
     rainbow (3.1.1)
     rake (13.3.0)
     regexp_parser (2.10.0)
-    rexml (3.4.1)
+    rexml (3.4.4)
     rubocop (1.79.1)
       json (~> 2.3)
       language_server-protocol (~> 3.17.0.2)
@@ -67,11 +70,11 @@ GEM
       rubocop (>= 1.72.1)
     ruby-progressbar (1.13.0)
     ruby2_keywords (0.0.5)
-    sinatra (4.1.1)
+    sinatra (4.2.1)
       logger (>= 1.6.0)
       mustermann (~> 3.0)
       rack (>= 3.0.0, < 4)
-      rack-protection (= 4.1.1)
+      rack-protection (= 4.2.1)
       rack-session (>= 2.0.0, < 3)
       tilt (~> 2.0)
     thin (2.0.1)
@@ -79,10 +82,10 @@ GEM
       eventmachine (~> 1.0, >= 1.0.4)
       logger
       rack (>= 1, < 4)
-    tilt (2.6.1)
+    tilt (2.7.0)
     unicode-display_width (3.1.4)
       unicode-emoji (~> 4.0, >= 4.0.4)
-    unicode-emoji (4.0.4)
+    unicode-emoji (4.2.0)
     webmock (3.25.1)
       addressable (>= 2.8.0)
       crack (>= 0.3.2)
@@ -106,4 +109,4 @@ DEPENDENCIES
   webmock
 
 BUNDLED WITH
-   2.6.8
+  4.0.3