diff --git a/.github/workflows/rake.yml b/.github/workflows/rake.yml
index 8b9e1329..8f6096de 100644
--- a/.github/workflows/rake.yml
+++ b/.github/workflows/rake.yml
@@ -18,12 +18,15 @@ jobs:
     env:
       BUNDLE_WITHOUT: "secryst"
       SKIP_JS: "1"
-      # The ISC corpus sweep (ISC_SWEEP=1) stays opt-in until the
-      # conformance gap it measures is closed: it currently exposes real
-      # per-map mismatches across the corpus. Run it locally with
-      #   ISC_SWEEP=1 INTERSCRIPT_MAPS_PATH=../maps/maps \
-      #   rspec spec/interscript_spec.rb
-      # to track that gap; flip it on here once it goes green.
+      SKIP_PYTHON: "1"
+      ISC_SWEEP: "1"
+      # The ISC corpus sweep: every map's own tests through every
+      # supported compiler (Interpreter, Compiler::Ruby), against the
+      # ../maps sibling from the monorepo checkout. The conformance gap
+      # it measured is closed (16,482 examples, 0 failures —
+      # interscript-ruby#779..#786); this is now the CI conformance
+      # gate for the corpus. The experimental Python bridge is excluded
+      # (SKIP_PYTHON) until its own corpus conformance work lands.
 
     steps:
       - name: Checkout monorepo
@@ -43,14 +46,26 @@ jobs:
 
       - name: Install Python helper and gems
         working-directory: ruby
+        # bash everywhere: the PYBIN substitution is POSIX shell, which
+        # PowerShell (the windows default) cannot parse. --break-system-
+        # packages rides out PEP 668 on Homebrew-managed macos Pythons.
+        shell: bash
         run: |
           bundle config set --local with jsexec
           bundle install
-          # PyCall binds whichever libpython it was built against, which
-          # is not necessarily the python that bare `pip` targets —
-          # install the regex helper into that interpreter.
-          PYBIN=$(bundle exec ruby -e 'require "pycall"; v = PyCall.sys.version[/\d+\.\d+/]; puts "python#{v}"')
-          "$PYBIN" -m pip install regex
+          if bundle exec ruby -e 'require "pycall"' >/dev/null 2>&1; then
+            # PyCall binds whichever libpython it was built against, which
+            # is not necessarily the python that bare `pip` targets —
+            # install the regex helper into that interpreter.
+            PYBIN=$(bundle exec ruby -e 'require "pycall"; v = PyCall.sys.version[/\d+\.\d+/]; puts "python#{v}"')
+            if command -v "$PYBIN" >/dev/null 2>&1; then
+              "$PYBIN" -m pip install --break-system-packages regex || "$PYBIN" -m pip install regex
+            else
+              echo "$PYBIN not on PATH — python helper not installed"
+            fi
+          else
+            echo "pycall not bundled (SKIP_PYTHON) — python helper not installed"
+          fi
 
       - name: RSpec
         working-directory: ruby
diff --git a/lib/interscript/stdlib/functions/rababa_adapter.rb b/lib/interscript/stdlib/functions/rababa_adapter.rb
index 1cf79d77..d700572d 100644
--- a/lib/interscript/stdlib/functions/rababa_adapter.rb
+++ b/lib/interscript/stdlib/functions/rababa_adapter.rb
@@ -1,7 +1,7 @@
 class Interscript::Stdlib
   module Functions
     class RababaAdapter
-      @rababa_diacritizer = nil
+      @rababa_diacritizers = {}
       @mutex = Mutex.new
 
       class << self
@@ -18,7 +18,7 @@ def reverse(output, config: nil)
         end
 
         def reset_cache
-          @mutex.synchronize { @rababa_diacritizer = nil }
+          @mutex.synchronize { @rababa_diacritizers.clear }
         end
 
         private
@@ -26,7 +26,7 @@ def reset_cache
         def diacritizer_for(config_key)
           require_rababa!
           @mutex.synchronize do
-            @rababa_diacritizer ||= build_diacritizer(config_key)
+            @rababa_diacritizers[config_key] ||= build_diacritizer(config_key)
           end
         end
 
diff --git a/spec/stdlib_functions_spec.rb b/spec/stdlib_functions_spec.rb
index 17b1e716..db184cdf 100644
--- a/spec/stdlib_functions_spec.rb
+++ b/spec/stdlib_functions_spec.rb
@@ -56,9 +56,11 @@
 
   describe ".rababa (without registered config)" do
     it "raises ExternalUtilError naming the missing config" do
-      expect { described_class.rababa("كتب", config: "default") }.to raise_error(
+      # A name that cannot be registered: the sweep's load path puts the
+      # monorepo's rababa-configs in scope, where "default" exists.
+      expect { described_class.rababa("كتب", config: "no-such-config") }.to raise_error(
         Interscript::ExternalUtilError,
-        /No rababa config registered under 'default'/
+        /No rababa config registered under 'no-such-config'/
       )
     end
   end