diff --git a/.github/workflows/current.yml b/.github/workflows/current.yml
index a4acbf0a9..c8ff39279 100644
--- a/.github/workflows/current.yml
+++ b/.github/workflows/current.yml
@@ -546,11 +546,19 @@ jobs:
       BUNDLE_GEMFILE: ${{ github.workspace }}/gems/ast-merge-git/Appraisal.root.gemfile
       K_JEM_TEMPLATING: true
       STRUCTUREDMERGE_DEV: ${{ github.workspace }}/gems
+      STRUCTUREDMERGE_CORE_DEV: ${{ github.workspace }}/kernel
     steps:
       - name: Checkout
         uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           fetch-depth: 0
+      - name: Checkout kernel for the local core override
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          repository: structuredmerge/structuredmerge
+          ref: main
+          path: kernel
+          persist-credentials: false
       - name: Clone benchmark corpus
         shell: bash
         run: |
@@ -570,6 +578,7 @@ jobs:
           BUNDLE_GEMFILE: ${{ github.workspace }}/gems/ast-merge-git/Appraisal.root.gemfile
           K_JEM_TEMPLATING: true
           STRUCTUREDMERGE_DEV: ${{ github.workspace }}/gems
+          STRUCTUREDMERGE_CORE_DEV: ${{ github.workspace }}/kernel
         with:
           ruby-version: ruby
           bundler: latest
@@ -578,12 +587,28 @@ jobs:
           working-directory: gems/ast-merge-git
           appraisal-name: benchmark-dev
           appraisal-root-gemfile: Appraisal.root.gemfile
+          pre-bundle-gems: |
+            nomono --source https://gem.coop --source https://rubygems.org
+      - name: Compile the kernel Ruby binding
+        working-directory: kernel/packages/ruby
+        shell: bash
+        env:
+          BUNDLE_GEMFILE: ${{ github.workspace }}/kernel/packages/ruby/Gemfile
+        run: |
+          set -euo pipefail
+          ulimit -c 0
+          export CARGO_BUILD_JOBS="1" CARGO_INCREMENTAL="0"
+          export CARGO_TARGET_DIR="${GITHUB_WORKSPACE}/kernel/tmp/benchmark-core-target"
+          mkdir -p ../../tmp
+          bundle install --jobs 4 --retry 8
+          bundle exec rake compile
       - name: Run affected-capability benchmark
         working-directory: gems/ast-merge-git
         env:
           BASE_SHA: ${{ github.event.pull_request.base.sha || github.event.before }}
           K_JEM_TEMPLATING: true
           STRUCTUREDMERGE_DEV: ${{ github.workspace }}/gems
+          STRUCTUREDMERGE_CORE_DEV: ${{ github.workspace }}/kernel
         run: |
           set -euo pipefail
 
@@ -703,15 +728,24 @@ jobs:
       BUNDLE_GEMFILE: ${{ github.workspace }}/gems/tree_haver/Appraisal.root.gemfile
       K_JEM_TEMPLATING: true
       STRUCTUREDMERGE_DEV: ${{ github.workspace }}/gems
+      STRUCTUREDMERGE_CORE_DEV: ${{ github.workspace }}/kernel
     steps:
       - name: Checkout
         uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - name: Checkout kernel for the local core override
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          repository: structuredmerge/structuredmerge
+          ref: main
+          path: kernel
+          persist-credentials: false
       - name: Setup Ruby
         uses: appraisal-rb/setup-ruby-flash@6f8ad36ba7488db591541483afb5464d01e8861b # v2.14
         env:
           BUNDLE_GEMFILE: ${{ github.workspace }}/gems/tree_haver/Appraisal.root.gemfile
           K_JEM_TEMPLATING: true
           STRUCTUREDMERGE_DEV: ${{ github.workspace }}/gems
+          STRUCTUREDMERGE_CORE_DEV: ${{ github.workspace }}/kernel
         with:
           ruby-version: ruby
           bundler: latest
@@ -720,12 +754,28 @@ jobs:
           working-directory: gems/tree_haver
           appraisal-name: tslp-cold-start
           appraisal-root-gemfile: Appraisal.root.gemfile
+          pre-bundle-gems: |
+            nomono --source https://gem.coop --source https://rubygems.org
+      - name: Compile the kernel Ruby binding
+        working-directory: kernel/packages/ruby
+        shell: bash
+        env:
+          BUNDLE_GEMFILE: ${{ github.workspace }}/kernel/packages/ruby/Gemfile
+        run: |
+          set -euo pipefail
+          ulimit -c 0
+          export CARGO_BUILD_JOBS="1" CARGO_INCREMENTAL="0"
+          export CARGO_TARGET_DIR="${GITHUB_WORKSPACE}/kernel/tmp/tslp-core-target"
+          mkdir -p ../../tmp
+          bundle install --jobs 4 --retry 8
+          bundle exec rake compile
       - name: Run cold-start TSLP checks
         working-directory: gems/tree_haver
         env:
           K_JEM_TEMPLATING: true
           K_SOUP_COV_DO: false
           STRUCTUREDMERGE_DEV: ${{ github.workspace }}/gems
+          STRUCTUREDMERGE_CORE_DEV: ${{ github.workspace }}/kernel
         run: |
           set -euo pipefail
           export TREE_SITTER_LANGUAGE_PACK_CACHE_DIR
diff --git a/.structuredmerge/fixtures.lock b/.structuredmerge/fixtures.lock
index 020469cdf..52004bd67 100644
--- a/.structuredmerge/fixtures.lock
+++ b/.structuredmerge/fixtures.lock
@@ -1,3 +1,3 @@
 repository: https://github.com/structuredmerge/structuredmerge-fixtures.git
 branch: main
-revision: ad5fd0b66b084e63576e6b006a1addf5bad8fcf5
+revision: 9c6e4bb0625f28207d1f40e5d103936eed56154a
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1ac0c501b..345b85b06 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -20,6 +20,8 @@ Please file a bug if you notice a violation of semantic versioning.
 
 ### Added
 
+- kettle-jem: the `current.yml` workflow template now removes the eMudhra-related roots that Apple still ships in `/etc/ssl/cert.pem` as its first step (before checkout) on macOS runners, when `macos` is a declared platform. The inlined script, `lib/kettle/jem/ci/harden_macos_ca_bundle.sh`, matches by certificate subject, logs each removed fingerprint and fails if any remains; it is not emitted for destinations without macOS lanes (galadran/we-have-a-problem.com#157)
+
 - ast-crispr-yaml-psych: `Selectors.mapping_entry` and `Selectors.sequence_item` can be used as `Insert` destinations (insert after the matched owner) (#105)
 
 ### Changed
diff --git a/gems/ast-merge-git/Appraisal.root.gemfile b/gems/ast-merge-git/Appraisal.root.gemfile
index f65feba32..807167db7 100644
--- a/gems/ast-merge-git/Appraisal.root.gemfile
+++ b/gems/ast-merge-git/Appraisal.root.gemfile
@@ -1,5 +1,11 @@
 # frozen_string_literal: true
 
+# kettle-jem:freeze
+# To retain chunks of comments & code during kettle-jem templating:
+# Wrap custom sections with freeze markers (e.g., as above and below this comment chunk).
+# kettle-jem will then preserve content between those markers across template runs.
+# kettle-jem:unfreeze
+
 source 'https://gem.coop'
 
 # Shared baseline for the Appraisal2 CI lanes in this gem.
@@ -25,3 +31,25 @@ if !structuredmerge_dev_root.empty? && !%w[false 0 no off].include?(structuredme
     end
   end
 end
+
+if respond_to?(:generator_only)
+  generator_only do
+    if ENV.fetch('K_JEM_TEMPLATING', 'false').casecmp('true').zero?
+      eval_gemfile 'gemfiles/modular/templating.gemfile'
+    end
+  end
+end
+# kettle-jem:freeze
+# The lockstep tree_haver depends on structuredmerge-core ~> 0.2, which no
+# registry carries before the kernel publishes. Appraisal's root resolution
+# runs under plain Bundler, where generator_only is unavailable, so wire core
+# from the local kernel checkout through the modular templating gemfile
+# whenever the family dev env is engaged. Without that env the modular file
+# retains registry mode, and published gems resolve normally.
+unless respond_to?(:generator_only)
+  if ENV.fetch('K_JEM_TEMPLATING', 'false').casecmp('true').zero? ||
+      !ENV.fetch('STRUCTUREDMERGE_DEV', '').strip.empty?
+    eval_gemfile 'gemfiles/modular/templating.gemfile'
+  end
+end
+# kettle-jem:unfreeze
diff --git a/gems/kettle-jem/lib/kettle/jem.rb b/gems/kettle-jem/lib/kettle/jem.rb
index ebac8fbde..56cf45e6c 100644
--- a/gems/kettle-jem/lib/kettle/jem.rb
+++ b/gems/kettle-jem/lib/kettle/jem.rb
@@ -7825,8 +7825,10 @@ def finalize_gemfile_template_source(recipe, content, destination_content, facts
           end
           removable = [package_name, *(runtime_dependencies - named_fragment_dependencies)]
           # A modular Gemfile may repeat a runtime gem only to select its local
-          # source. Keep explicit path overrides while pruning ordinary duplicates.
-          removable -= gemfile_path_source_override_names(template_content)
+          # source. Keep explicit path overrides while pruning ordinary
+          # duplicates. The package's own gem is never exempt: a self-reference
+          # is a prohibited declaration, not a local source override.
+          removable -= (gemfile_path_source_override_names(template_content) - [package_name])
           output = remove_gemfile_dependency_blocks(content, removable)
           output = remove_gemfile_percent_w_entries(output, removable)
         end
@@ -9483,7 +9485,9 @@ def merge_gemfile_template_policy(content, facts:, template_content: nil, preser
       # A Gemfile path declaration can override the source of a runtime gemspec
       # dependency. Keep those declarations so local development can resolve an
       # unpublished dependency without changing the runtime dependency graph.
-      removable_gems -= gemfile_path_source_override_names(template_content.to_s)
+      # The package's own gem is never exempt: a self-reference is a prohibited
+      # declaration, not a local source override.
+      removable_gems -= (gemfile_path_source_override_names(template_content.to_s) - [package_name])
       removable_gems << "version_gem" unless version_gem_enabled?(facts)
       pruned = remove_gemfile_dependency_blocks(content, removable_gems)
       pruned = remove_gemfile_percent_w_entries(pruned, [package_name]) unless preserve_self_word_entries
@@ -14985,6 +14989,7 @@ def template_tokens(facts, funding)
         "KJ|CI:EXEC_CMD" => facts.dig(:ci, :exec_cmd).to_s,
         "KJ|CI:OS_MATRIX_ENTRIES" => github_actions_current_os_matrix_entries(facts),
         "KJ|CI:OS_TEST_STEPS" => github_actions_current_os_test_steps(facts),
+        "KJ|CI:MACOS_HARDENING_STEP" => github_actions_macos_hardening_step(facts),
         "KJ|README:CURRENT_MRI_PLATFORMS" => readme_current_mri_platforms(facts),
         "KJ|RAKE:TOP_LEVEL_DOCS_TASK" => rake_top_level_docs_task_token(facts).rstrip,
         "KJ|GITHUB_ACTIONS:COVERAGE_UPLOAD_STEPS" => github_actions_coverage_steps(disabled_integrations: facts.dig(:integrations, :disabled))
@@ -20960,6 +20965,38 @@ def github_actions_current_os_matrix_entries(facts)
       end.join("\n")
     end
 
+    MACOS_CA_HARDENING_SCRIPT = File.expand_path("jem/ci/harden_macos_ca_bundle.sh", __dir__)
+    private_constant :MACOS_CA_HARDENING_SCRIPT
+
+    # The first step of current.yml's test job when macos is a declared platform:
+    # removes the eMudhra-related roots Apple still ships in /etc/ssl/cert.pem
+    # (https://github.com/galadran/we-have-a-problem.com/issues/157). The script is
+    # inlined, not fetched or run from the repo, because it has to run before the
+    # first download, and actions/checkout runs git. Like the Windows guard, the
+    # step exists only when its platform is declared, so no dead `if:` is emitted
+    # for linux-only or linux+windows destinations. Returns the step plus a blank
+    # line, or "" so the token vanishes without leaving a stray line behind. The
+    # script is a copy of structuredmerge/structuredmerge
+    # workspace-scripts/harden_macos_ca_bundle.sh (tested there against a bundle
+    # containing an eMudhra root).
+    def github_actions_macos_hardening_step(facts)
+      platforms = facts.dig(:ci, :platforms)
+      platforms = DEFAULT_PLATFORMS if platforms.nil? || platforms.empty?
+      return "" unless platforms.include?("macos")
+
+      header = [
+        "      - name: Remove eMudhra roots from the macOS CA bundle",
+        "        if: runner.os == 'macOS'",
+        "        shell: bash",
+        "        run: |"
+      ]
+      script = File.read(MACOS_CA_HARDENING_SCRIPT).rstrip.lines(chomp: true).map do |line|
+        line.empty? ? "" : "          #{line}"
+      end
+
+      "#{(header + script).join("\n")}\n\n"
+    end
+
     # The current.yml test steps, generated from the same platforms facts. The
     # Windows-only guard and step exist only when windows is declared, so no
     # tautological `if:` survives in a linux+macos destination (spec slice
diff --git a/gems/kettle-jem/lib/kettle/jem/ci/harden_macos_ca_bundle.sh b/gems/kettle-jem/lib/kettle/jem/ci/harden_macos_ca_bundle.sh
new file mode 100755
index 000000000..611970054
--- /dev/null
+++ b/gems/kettle-jem/lib/kettle/jem/ci/harden_macos_ca_bundle.sh
@@ -0,0 +1,75 @@
+#!/bin/sh
+# Remove the eMudhra-related roots from the macOS system CA bundle.
+#
+# Apple's /etc/ssl/cert.pem still carries roots from the eMudhra incident, and the
+# developer tools Apple ships (git, curl, python3) read that file, so a network
+# attacker could tamper with downloads made during a release build. GitHub's macOS
+# runners are ephemeral, so removing the roots at job start needs no re-application
+# after OS updates. Reference: https://github.com/galadran/we-have-a-problem.com/issues/157
+#
+# It must run BEFORE the first step that downloads anything (actions/checkout runs
+# git), so the workflows inline this exact file. A contract test keeps them identical.
+#
+# Matching is by certificate subject so no fingerprints need to be guessed; every
+# removed certificate is printed with its SHA-256 fingerprint for the audit log, and
+# the script fails if any matching certificate is still present afterwards.
+#
+# Environment (for tests): CA_BUNDLE (default /etc/ssl/cert.pem), SUDO (default sudo).
+set -eu
+
+bundle="${CA_BUNDLE:-/etc/ssl/cert.pem}"
+sudo_cmd="${SUDO-sudo}"
+work="$(mktemp -d)"
+trap 'rm -rf "$work"' EXIT
+
+matches() {
+  case "$1" in
+    *"AAA Certificate Services"* | *"emSign ECC Root CA - G3"* | *[eE][mM]udhra*) return 0 ;;
+    *) return 1 ;;
+  esac
+}
+
+total="$(grep -c -- '-----BEGIN CERTIFICATE-----' "$bundle")"
+[ "$total" -ge 100 ] || { echo "refusing to edit $bundle: only $total certificates" >&2; exit 1; }
+
+awk -v dir="$work" '
+  /-----BEGIN CERTIFICATE-----/ { if (out != "") close(out); n++; out = dir "/c" n ".pem" }
+  out != "" { print > out }
+' "$bundle"
+
+: > "$work/clean.pem"
+removed=0
+i=1
+while [ "$i" -le "$total" ]; do
+  file="$work/c$i.pem"
+  subject="$(openssl x509 -in "$file" -noout -subject 2>/dev/null || true)"
+  if [ -n "$subject" ] && matches "$subject"; then
+    fingerprint="$(openssl x509 -in "$file" -noout -fingerprint -sha256)"
+    echo "removing: $subject ($fingerprint)"
+    removed=$((removed + 1))
+  else
+    cat "$file" >> "$work/clean.pem"
+  fi
+  i=$((i + 1))
+done
+
+if [ "$removed" -gt 0 ]; then
+  $sudo_cmd tee "$bundle" < "$work/clean.pem" > /dev/null
+fi
+
+# Verify what is on disk now, not what we intended to write.
+after="$(grep -c -- '-----BEGIN CERTIFICATE-----' "$bundle")"
+[ "$after" -eq $((total - removed)) ] || { echo "certificate count mismatch: $after != $total - $removed" >&2; exit 1; }
+rm -f "$work"/c*.pem
+awk -v dir="$work" '
+  /-----BEGIN CERTIFICATE-----/ { if (out != "") close(out); n++; out = dir "/v" n ".pem" }
+  out != "" { print > out }
+' "$bundle"
+for file in "$work"/v*.pem; do
+  subject="$(openssl x509 -in "$file" -noout -subject 2>/dev/null || true)"
+  if [ -n "$subject" ] && matches "$subject"; then
+    echo "still trusted after cleanup: $subject" >&2
+    exit 1
+  fi
+done
+echo "CA bundle $bundle: $total certificates, removed $removed, $after remain."
diff --git a/gems/kettle-jem/lib/kettle/jem/templates/.github/workflows/current.yml.example b/gems/kettle-jem/lib/kettle/jem/templates/.github/workflows/current.yml.example
index 25cc40d17..7f4a6fce1 100644
--- a/gems/kettle-jem/lib/kettle/jem/templates/.github/workflows/current.yml.example
+++ b/gems/kettle-jem/lib/kettle/jem/templates/.github/workflows/current.yml.example
@@ -41,7 +41,7 @@ jobs:
 {KJ|CI:OS_MATRIX_ENTRIES}
 
     steps:
-      - name: Checkout
+{KJ|CI:MACOS_HARDENING_STEP}      - name: Checkout
         uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
diff --git a/gems/kettle-jem/spec/integration/appraisals_and_gemfile_template_spec.rb b/gems/kettle-jem/spec/integration/appraisals_and_gemfile_template_spec.rb
index 614ba98cc..2926a28df 100644
--- a/gems/kettle-jem/spec/integration/appraisals_and_gemfile_template_spec.rb
+++ b/gems/kettle-jem/spec/integration/appraisals_and_gemfile_template_spec.rb
@@ -1072,9 +1072,11 @@
       {
         "KJ|CI:EXEC_CMD" => "bundle exec kettle-test",
         "KJ|CI:OS_MATRIX_ENTRIES" => described_class.send(:github_actions_current_os_matrix_entries, {ci: {exec_cmd: "bundle exec kettle-test", platforms: %w[linux macos windows]}}),
-        "KJ|CI:OS_TEST_STEPS" => described_class.send(:github_actions_current_os_test_steps, {ci: {exec_cmd: "bundle exec kettle-test", platforms: %w[linux macos windows]}})
+        "KJ|CI:OS_TEST_STEPS" => described_class.send(:github_actions_current_os_test_steps, {ci: {exec_cmd: "bundle exec kettle-test", platforms: %w[linux macos windows]}}),
+        "KJ|CI:MACOS_HARDENING_STEP" => described_class.send(:github_actions_macos_hardening_step, {ci: {exec_cmd: "bundle exec kettle-test", platforms: %w[linux macos windows]}})
       }
     )
+    expect(resolved_current_workflow.index("Remove eMudhra roots from the macOS CA bundle")).to be < resolved_current_workflow.index("- name: Checkout")
     expect(resolved_current_workflow).to include("appraisal: \"current\"\n            os: ubuntu-latest")
     expect(resolved_current_workflow).to include("appraisal: \"current\"\n            os: macos-latest")
     expect(resolved_current_workflow).to include("appraisal: \"current\"\n            os: windows-latest")
diff --git a/gems/kettle-jem/spec/kettle/jem_platforms_config_spec.rb b/gems/kettle-jem/spec/kettle/jem_platforms_config_spec.rb
index 8affcb621..5ec8f7dea 100644
--- a/gems/kettle-jem/spec/kettle/jem_platforms_config_spec.rb
+++ b/gems/kettle-jem/spec/kettle/jem_platforms_config_spec.rb
@@ -195,6 +195,59 @@ def ci_facts(platforms, exec_cmd: "bundle exec kettle-test")
     end
   end
 
+  describe "github_actions_macos_hardening_step" do
+    let(:script) { File.read(File.expand_path("../../lib/kettle/jem/ci/harden_macos_ca_bundle.sh", __dir__)).rstrip }
+
+    def step_for(platforms)
+      described_class.send(:github_actions_macos_hardening_step, ci_facts(platforms))
+    end
+
+    it "is empty when macos is not declared, so no dead step is emitted" do
+      expect(step_for(%w[linux])).to eq("")
+      expect(step_for(%w[linux windows])).to eq("")
+    end
+
+    it "emits a macOS-only inline step when macos is declared, including by default" do
+      step = step_for(%w[linux macos])
+
+      expect(step).to start_with("      - name: Remove eMudhra roots from the macOS CA bundle\n")
+      expect(step).to include("        if: runner.os == 'macOS'\n")
+      expect(step).to end_with("\n\n")
+      expect(described_class.send(:github_actions_macos_hardening_step, {ci: {}})).to eq(step)
+    end
+
+    it "inlines the packaged script verbatim and parses as a workflow step" do
+      steps = YAML.safe_load(step_for(%w[linux macos windows]))
+
+      expect(steps.length).to eq(1)
+      expect(steps.first).to include("if" => "runner.os == 'macOS'", "shell" => "bash")
+      expect(steps.first.fetch("run").rstrip).to eq(script)
+      expect(steps.first).not_to have_key("uses")
+    end
+
+    it "is wired in before checkout in the current.yml template" do
+      template = File.read(File.expand_path("../../lib/kettle/jem/templates/.github/workflows/current.yml.example", __dir__))
+
+      expect(template).to match(/steps:\n\{KJ\|CI:MACOS_HARDENING_STEP\}      - name: Checkout\n/)
+    end
+
+    it "produces a current.yml whose first step hardens macOS before checkout" do
+      template = File.read(File.expand_path("../../lib/kettle/jem/templates/.github/workflows/current.yml.example", __dir__))
+      rendered = template.sub("{KJ|CI:MACOS_HARDENING_STEP}", step_for(%w[linux macos]))
+      rendered = rendered.sub("{KJ|CI:OS_MATRIX_ENTRIES}", "")
+      names = rendered.scan(/^      - name: (.+)$/).flatten
+
+      expect(names.first(2)).to eq(["Remove eMudhra roots from the macOS CA bundle", "Checkout"])
+    end
+
+    it "leaves the template unchanged for destinations without macos" do
+      template = File.read(File.expand_path("../../lib/kettle/jem/templates/.github/workflows/current.yml.example", __dir__))
+      rendered = template.sub("{KJ|CI:MACOS_HARDENING_STEP}", step_for(%w[linux]))
+
+      expect(rendered).to include("    steps:\n      - name: Checkout\n")
+    end
+  end
+
   describe "readme_current_mri_platforms" do
     def summary_facts(platforms:)
       {ci: {platforms: platforms}}
@@ -215,7 +268,7 @@ def summary_facts(platforms:)
   end
 
   describe "packaged current.yml template" do
-    it "resolves both tokens through the real pipeline into valid YAML" do
+    it "resolves its tokens through the real pipeline into valid YAML" do
       facts = ci_facts(%w[linux macos windows])
       resolved = described_class.send(
         :resolve_template_tokens,
@@ -223,12 +276,17 @@ def summary_facts(platforms:)
         {
           "KJ|CI:EXEC_CMD" => "bundle exec kettle-test",
           "KJ|CI:OS_MATRIX_ENTRIES" => described_class.send(:github_actions_current_os_matrix_entries, facts),
-          "KJ|CI:OS_TEST_STEPS" => described_class.send(:github_actions_current_os_test_steps, facts)
+          "KJ|CI:OS_TEST_STEPS" => described_class.send(:github_actions_current_os_test_steps, facts),
+          "KJ|CI:MACOS_HARDENING_STEP" => described_class.send(:github_actions_macos_hardening_step, facts)
         }
       )
 
       expect(resolved).not_to include("{KJ|")
-      expect(YAML.safe_load(resolved.gsub(/\{\{.*?}}/, "x"), aliases: true).dig("jobs", "test", "strategy", "matrix", "include").length).to eq(3)
+      workflow = YAML.safe_load(resolved.gsub(/\{\{.*?}}/, "x"), aliases: true)
+      expect(workflow.dig("jobs", "test", "strategy", "matrix", "include").length).to eq(3)
+      steps = workflow.dig("jobs", "test", "steps")
+      expect(steps.first(2).map { |step| step["name"] }).to eq(["Remove eMudhra roots from the macOS CA bundle", "Checkout"])
+      expect(steps.first["if"]).to eq("runner.os == 'macOS'")
     end
   end
 end
diff --git a/gems/tree_haver/Appraisal.root.gemfile b/gems/tree_haver/Appraisal.root.gemfile
index 75e03f7a1..33df9e3b5 100644
--- a/gems/tree_haver/Appraisal.root.gemfile
+++ b/gems/tree_haver/Appraisal.root.gemfile
@@ -1,8 +1,37 @@
 # frozen_string_literal: true
 
+# kettle-jem:freeze
+# To retain chunks of comments & code during kettle-jem templating:
+# Wrap custom sections with freeze markers (e.g., as above and below this comment chunk).
+# kettle-jem will then preserve content between those markers across template runs.
+# kettle-jem:unfreeze
+
 source 'https://gem.coop'
 
 # Shared baseline for the Appraisal2 CI lanes in this gem.
 gemspec
 
 gem 'nomono', '~> 1.1', '>= 1.1.18'
+
+if respond_to?(:generator_only)
+  generator_only do
+    if ENV.fetch('K_JEM_TEMPLATING', 'false').casecmp('true').zero?
+      eval_gemfile 'gemfiles/modular/templating.gemfile'
+    end
+  end
+end
+# kettle-jem:freeze
+# The gemspec's runtime dependency on structuredmerge-core ~> 0.2 cannot be
+# resolved from any registry before the kernel publishes. Appraisal's root
+# resolution runs under plain Bundler, where generator_only is unavailable, so
+# wire core (and any lockstep siblings) from local checkouts through the
+# modular templating gemfile whenever the family dev env is engaged. Without
+# that env the modular file retains registry mode, and published gems resolve
+# normally.
+unless respond_to?(:generator_only)
+  if ENV.fetch('K_JEM_TEMPLATING', 'false').casecmp('true').zero? ||
+      !ENV.fetch('STRUCTUREDMERGE_DEV', '').strip.empty?
+    eval_gemfile 'gemfiles/modular/templating.gemfile'
+  end
+end
+# kettle-jem:unfreeze