fix: one predicate decides "are we on CI"

CHANGELOG.md

@@ -363,6 +363,17 @@ One removal 2.0 cannot warn about, written down instead: the legacy `LOADED_DRIV
   and omitted the README
 
 ### Fixed
+- **`CI: ""` means "not CI" for the HTML report too.** The report embedded every image
+  whenever the `CI` variable merely existed, so the documented opt-out (`CI: ""` in the
+  update-baselines job) still produced a report with inlined images while the record mode
+  read the same value as "not CI". One predicate, `SnapDiff::Config.ci?`, now serves every
+  reader: unset or empty is not CI
+- **The documented `ACCEPT_SCREENSHOTS` snippet no longer switches off the CI missing-baseline
+  check.** README and `docs/configuration.md` assigned
+  `record = ENV["ACCEPT_SCREENSHOTS"] ? :all : :once`, which sets an explicit `:once` on every
+  ordinary run. An explicit mode outranks the `:none`-under-CI default, so a CI that copied it
+  stopped failing on a screenshot with no committed baseline. Both now assign `:all` only when
+  the variable is non-empty and leave the default alone otherwise
 - **A screenshot with no committed baseline no longer passes silently** — it warns,
   names the file, and is counted as `new (not verified)` rather than as a pass
 - **An inherited `GIT_DIR` / `GIT_WORK_TREE` / `GIT_INDEX_FILE` no longer redirects

README.md

@@ -204,7 +204,9 @@ One failure at a time is fine for one screenshot. After a redesign that changed
 
 ```ruby
 # test_helper.rb
-SnapDiff.config.record = ENV["ACCEPT_SCREENSHOTS"] ? :all : :once
+# Set the mode only when asked: an explicit mode, even :once, outranks the
+# :none-under-CI default and would stop CI from failing on a missing baseline.
+SnapDiff.config.record = :all unless ENV["ACCEPT_SCREENSHOTS"].to_s.empty?
 ```
 
 ```bash

docs/configuration.md

@@ -72,8 +72,10 @@ than accepting them one failure at a time:
 
 ```ruby
 # test_helper.rb. There is no CLI flag — the gem has no runner to hang one on —
-# so gate it on an environment variable of your own if you want one:
-SnapDiff.config.record = ENV["ACCEPT_SCREENSHOTS"] ? :all : :once
+# so gate it on an environment variable of your own if you want one. Set the
+# mode only when asked: an explicit mode, even :once, outranks the
+# :none-under-CI default and would stop CI from failing on a missing baseline.
+SnapDiff.config.record = :all unless ENV["ACCEPT_SCREENSHOTS"].to_s.empty?
 ```
 
 ```bash

lib/snap_diff/config.rb

@@ -101,6 +101,12 @@ def self.validate_record_mode!(mode)
         "unknown record mode #{mode.inspect} -- one of #{RECORD_MODES.map(&:inspect).join(", ")} (or nil)"
     end
 
+    # Are we on CI? Read live, and an empty CI is not CI: `CI: ""` is how a
+    # job opts out (docs/ci-integration.md), so every reader must agree.
+    def self.ci?
+      !ENV["CI"].to_s.empty?
+    end
+
     # shift_distance_limit, driver and the three older new-screenshot
     # booleans are excluded from the generated writers and hand written
     # below (they announce their 2.1 removal, or validate); fail_if_new and
@@ -157,7 +163,7 @@ def root=(path)
     # ("normally, CLI flags take precedence over environment variables") and
     # the inverse of jest#12288.
     def fail_if_new
-      @fail_if_new.nil? ? !ENV["CI"].to_s.empty? : @fail_if_new
+      @fail_if_new.nil? ? Config.ci? : @fail_if_new
     end
 
     # Announces the 2.1 removal. The writer, not the reader: {#record} reads

lib/snap_diff/reporters/html.rb

@@ -220,5 +220,5 @@ def write_report
 # Framework adapters (Minitest, RSpec, Cucumber) call SnapDiff::Reporting.finalize! via native hooks.
 # For custom frameworks, call SnapDiff::Reporting.finalize! manually.
 unless SnapDiff::Reporting.reporters.any?(SnapDiff::Reporters::HTML)
-  SnapDiff::Reporting.register(SnapDiff::Reporters::HTML.new(embed_images: !!ENV["CI"]))
+  SnapDiff::Reporting.register(SnapDiff::Reporters::HTML.new(embed_images: SnapDiff::Config.ci?))
 end

lib/snap_diff/screenshot_matcher.rb

@@ -92,7 +92,7 @@ def resolve_record_mode(per_screenshot)
     # `record: :once` records them and still compares everything that has a
     # baseline (docs/ci-integration.md).
     def refuse_bulk_record_under_ci!
-      return if ENV["CI"].to_s.empty?
+      return unless SnapDiff::Config.ci?
 
       raise SnapDiff::ExpectationNotMet.new(<<~ERROR.chomp, caller)
         `record: :all` re-records every baseline WITHOUT comparing, so it refuses to run under CI (ENV["CI"] is set).

scripts/generate_sample_report.rb

@@ -20,7 +20,7 @@
   {name: "header-resized", base: "a", new: "a_cropped"} # dimensions change: 80x80 => 80x60
 ]
 
-embed = ARGV.include?("--embed") || !!ENV["CI"]
+embed = ARGV.include?("--embed") || SnapDiff::Config.ci?
 reporter = CapybaraScreenshotDiff::Reporters::HTML.new(output_path: output_path, embed_images: embed)
 fixtures = File.expand_path("../test/fixtures/images", __dir__)
 tmp_dir = File.expand_path("../tmp/sample_images", __dir__)

test/unit/snap_diff_config_test.rb

@@ -184,6 +184,15 @@ def with_env_ci(value)
     ENV["CI"] = original
   end
 
+  # One predicate for "are we on CI". The HTML reporter used `!!ENV["CI"]`,
+  # so the documented `CI: ""` recipe (docs/ci-integration.md) embedded every
+  # image into the report while the record mode read the same value as "not CI".
+  test "Config.ci? is false for an unset or empty CI, true otherwise" do
+    with_env_ci(nil) { assert_equal false, SnapDiff::Config.ci? }
+    with_env_ci("") { assert_equal false, SnapDiff::Config.ci?, "an empty CI is not CI" }
+    with_env_ci("true") { assert_equal true, SnapDiff::Config.ci? }
+  end
+
   test "an unset fail_if_new reads ENV['CI'] live, not once at require time" do
     config.fail_if_new = nil