The image installs gems with `without development`, where
`bundle exec irb` cannot find the gem.

Assisted-by: GLM-5.3 via pi

diff --git a/Dockerfile b/Dockerfile
index e06773b..c70d612 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -22,6 +22,11 @@ ENV VERSION=${VERSION}
 ENV RACK_ENV=production
 # Set TZ at runtime — Date.today drives the birthday list's rollover.
 
+# git, for the dump `rake console` commits before its prompt
+# (tasks/console.rake): a mistake at the prompt is then a revert in
+# the dump's repository rather than a restore from backup.
+RUN apt-get update && apt-get install -y git && rm -rf /var/lib/apt/lists/*
+
 WORKDIR /app
 
 COPY --from=build /usr/local/bundle /usr/local/bundle
diff --git a/Gemfile b/Gemfile
index 66f5afb..b5a4010 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,6 +1,7 @@
 source "https://rubygems.org"
 
 gem "base64"
+gem "irb"
 gem "logger"
 gem "nokogiri"
 gem "phlex"
@@ -14,7 +15,6 @@ gem "sqlite3"
 
 group :development do
   gem "hegeltest"
-  gem "irb"
   gem "minitest"
   gem "rack-test"
   gem "ruby-lsp"