diff --git a/errors/known-unsolved/setup-node-mirror-input-ignored-when-version-in-manifest.yml b/errors/known-unsolved/setup-node-mirror-input-ignored-when-version-in-manifest.yml
new file mode 100644
index 0000000..c16dd28
--- /dev/null
+++ b/errors/known-unsolved/setup-node-mirror-input-ignored-when-version-in-manifest.yml
@@ -0,0 +1,88 @@
+id: ku-131
+title: 'setup-node mirror input is only a download fallback — node pulled from github.com when version is found in manifest'
+category: known-unsolved
+severity: limitation
+tags:
+  - setup-node
+  - mirror
+  - artifactory
+  - nexus
+  - self-hosted
+  - known-limitation
+  - node-distribution
+  - air-gapped
+patterns:
+  - regex: 'Downloading node from.*github\.com|node-versions.*releases.*download'
+    flags: 'i'
+  - regex: 'Found in cache.*node|Resolved node version.*from manifest'
+    flags: 'i'
+error_messages:
+  - '(no error — node is silently downloaded from github.com instead of the configured mirror URL)'
+  - 'Downloading node from https://github.com/actions/node-versions/releases/download/...'
+root_cause: |
+  The `mirror` and `mirror-token` inputs in `actions/setup-node` are intended to
+  support authenticated artifact mirrors (e.g., JFrog Artifactory, Sonatype Nexus).
+  However, the action's resolution logic always consults the GitHub-hosted versions
+  manifest FIRST. When the requested version is found in the manifest, node is
+  downloaded directly from `github.com/actions/node-versions` — the mirror URL is
+  never used.
+
+  The mirror is only consulted in these cases:
+  1. The requested version is NOT present in the GitHub versions manifest (e.g., nightly,
+     RC versions, custom versions).
+  2. The primary download from GitHub fails (network error, timeout).
+
+  This means that for all stable Node.js releases (which are all in the manifest),
+  setup-node bypasses the configured mirror entirely. Organizations using mirrors
+  for security compliance, bandwidth optimization, or air-gapped environments cannot
+  force setup-node to use their mirror as the primary download source.
+
+  This is by design per setup-node maintainers (confirmed in issue #1412): "The mirror
+  input is intended as an alternative source and is used only as a fallback when the
+  required version is not present in the manifest or cannot be downloaded."
+fix: |
+  There is no supported way to force setup-node to always download from a mirror for
+  versions present in the GitHub manifest. The following workarounds exist:
+
+  Option A — Block github.com at the network level (forces mirror fallback):
+    When the primary download fails due to network policy, setup-node falls back to
+    the mirror automatically. Requires network-level controls outside of GitHub Actions.
+
+  Option B — Pre-install node in a custom runner image:
+    Bundle the required Node.js version into your self-hosted runner or ARC container
+    image; setup-node will detect the cached version and skip the download entirely.
+
+  Option C — Use runner cache with a pre-populated tool cache:
+    Place node binaries in the runner's RUNNER_TOOL_CACHE directory; setup-node skips
+    download when the exact version is found in the tool cache.
+
+  Track upstream: actions/setup-node#1412 — there is no current ETA for mirror-first support.
+fix_code:
+  - language: yaml
+    label: 'Current behavior — mirror is configured but node still downloads from github.com'
+    code: |
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '22.20.0'
+          mirror: 'https://artifactory.example.com/nodejs-remote'
+          mirror-token: ${{ secrets.MIRROR_TOKEN }}
+          # NOTE: For stable versions in the manifest, this still downloads from
+          # github.com/actions/node-versions — the mirror is NOT used as primary source.
+  - language: yaml
+    label: 'Workaround — pre-populate runner tool cache to skip download entirely'
+    code: |
+      # On your self-hosted runner or ARC image, pre-download node binaries to:
+      # $RUNNER_TOOL_CACHE/node/<version>/<arch>/
+      #
+      # setup-node checks this directory first and skips network download
+      # if the exact version+arch is found, regardless of mirror configuration.
+prevention:
+  - 'Do not rely on the mirror input for compliance enforcement — it is a fallback only'
+  - 'For true mirror-first enforcement, block outbound access to github.com at the network level'
+  - 'Use pre-built runner images with node bundled in RUNNER_TOOL_CACHE for air-gapped environments'
+  - 'Track actions/setup-node#1412 for upstream progress on mirror-as-primary support'
+docs:
+  - url: 'https://github.com/actions/setup-node/issues/1412'
+    label: 'setup-node#1412 — Node distributions not pulled from authenticated mirrors'
+  - url: 'https://github.com/actions/setup-node#usage'
+    label: 'setup-node usage documentation — mirror input'
diff --git a/errors/runner-environment/arc-ubuntu-slim-envsubst-command-not-found-gettext-missing.yml b/errors/runner-environment/arc-ubuntu-slim-envsubst-command-not-found-gettext-missing.yml
new file mode 100644
index 0000000..80e59cb
--- /dev/null
+++ b/errors/runner-environment/arc-ubuntu-slim-envsubst-command-not-found-gettext-missing.yml
@@ -0,0 +1,84 @@
+id: re-480
+title: 'envsubst: command not found on ARC and ubuntu-slim runners — gettext package not pre-installed'
+category: runner-environment
+severity: error
+tags:
+  - arc
+  - ubuntu-slim
+  - envsubst
+  - gettext
+  - self-hosted
+  - container-runner
+  - cosign-installer
+patterns:
+  - regex: 'envsubst: command not found'
+    flags: 'i'
+  - regex: 'line \d+: envsubst: not found|envsubst.*No such file or directory'
+    flags: 'i'
+error_messages:
+  - '/home/runner/_work/_temp/0de125e0-863d-4a86-bd04-b315399dc938.sh: line 3: envsubst: command not found'
+  - 'envsubst: command not found'
+  - 'line 3: envsubst: not found'
+root_cause: |
+  The `envsubst` binary (part of the GNU `gettext` package) substitutes environment
+  variable references in text templates. It is pre-installed on standard GitHub-hosted
+  runners (ubuntu-22.04, ubuntu-24.04) but is absent from:
+
+  - GitHub Actions Runner Controller (ARC) container images
+    (`ghcr.io/actions/actions-runner`) — minimal container with no `gettext`
+  - `ubuntu-slim` GitHub-hosted runner — stripped Ubuntu 24.04 image that omits
+    many packages present in the standard ubuntu-24.04 runner
+
+  Several popular GitHub Actions invoke `envsubst` internally during their setup
+  steps, including `sigstore/cosign-installer@v4`. When any such action runs on ARC
+  or ubuntu-slim, the step immediately fails with "command not found" even though the
+  workflow configuration looks correct and works on standard runners.
+
+  The `gettext-base` Debian package (which provides `envsubst`) is a ~2 MB install
+  with no complex dependencies — it is straightforward to add as a pre-step.
+fix: |
+  Install the `gettext-base` apt package as an early workflow step before any action
+  that requires `envsubst`. For ARC, consider building a custom runner image with
+  `gettext-base` pre-installed to avoid the per-job overhead.
+fix_code:
+  - language: yaml
+    label: 'Add gettext-base install step before actions that use envsubst (ARC or ubuntu-slim)'
+    code: |
+      jobs:
+        build:
+          runs-on: ubuntu-slim  # or your ARC runner label
+          steps:
+            - name: Install gettext-base (provides envsubst)
+              run: sudo apt-get install -y --no-install-recommends gettext-base
+
+            - name: Install cosign
+              uses: sigstore/cosign-installer@v4
+
+            - name: Checkout
+              uses: actions/checkout@v4
+  - language: yaml
+    label: 'Alternative — use a custom ARC base image with gettext pre-installed'
+    code: |
+      # In your ARC RunnerDeployment spec:
+      # spec:
+      #   template:
+      #     spec:
+      #       containers:
+      #         - name: runner
+      #           image: your-org/custom-runner:latest  # built with gettext-base
+      #
+      # Dockerfile:
+      # FROM ghcr.io/actions/actions-runner:latest
+      # RUN sudo apt-get update && sudo apt-get install -y --no-install-recommends gettext-base
+prevention:
+  - 'Before using ubuntu-slim or ARC runners, audit the ubuntu-slim-Readme.md to verify all required tools are pre-installed'
+  - 'Add a workflow-level check step: command -v envsubst || sudo apt-get install -y gettext-base'
+  - 'Build custom ARC runner images with gettext-base, jq, curl, and other commonly-needed tools'
+  - 'File issues upstream with actions that call envsubst without checking for its presence'
+docs:
+  - url: 'https://github.com/sigstore/cosign-installer/issues/222'
+    label: 'cosign-installer#222 — envsubst not found on ARC and ubuntu-slim'
+  - url: 'https://github.com/actions/runner-images/blob/main/images/ubuntu-slim/ubuntu-slim-Readme.md'
+    label: 'ubuntu-slim software manifest — check pre-installed packages'
+  - url: 'https://manpages.debian.org/unstable/gettext-base/envsubst.1.en.html'
+    label: 'envsubst man page — GNU gettext-base package'
diff --git a/errors/runner-environment/ubuntu-slim-git-version-downgraded-243-instead-of-252.yml b/errors/runner-environment/ubuntu-slim-git-version-downgraded-243-instead-of-252.yml
new file mode 100644
index 0000000..6f18b3d
--- /dev/null
+++ b/errors/runner-environment/ubuntu-slim-git-version-downgraded-243-instead-of-252.yml
@@ -0,0 +1,80 @@
+id: re-481
+title: 'ubuntu-slim runner ships git 2.43.0 instead of documented 2.52+ due to missing PPA pin'
+category: runner-environment
+severity: warning
+tags:
+  - ubuntu-slim
+  - git
+  - version-mismatch
+  - apt
+  - ppa
+  - container-runner
+  - regression
+patterns:
+  - regex: 'git version 2\.43\.'
+    flags: 'i'
+  - regex: 'fatal: unknown option|error: unknown switch|unrecognized argument'
+    flags: 'i'
+error_messages:
+  - 'git version 2.43.0'
+  - 'fatal: unknown option'
+  - 'error: unknown switch'
+root_cause: |
+  The `ubuntu-slim` runner image is built from a minimal `ubuntu:24.04` Docker base.
+  Unlike the standard `ubuntu-24.04` GitHub-hosted runner, ubuntu-slim's git install
+  script does not consistently pin to the `git-core` Launchpad PPA. When the apt
+  resolver falls back to the Ubuntu 24.04 LTS base repository, it installs git 2.43.0
+  — the LTS-pinned version in the Ubuntu focal/noble archive — rather than the 2.52+
+  version distributed via the PPA and documented in the ubuntu-slim README.
+
+  The ubuntu-slim README states git 2.52.0 is installed, but the actual installed
+  version since image 20260504.56.2 is 2.43.0. This regression was introduced between:
+  - 20260413.54.1 — git 2.53.0 (from PPA, matches README)
+  - 20260504.56.2 — git 2.43.0 (from Ubuntu base apt, README out of date)
+
+  Workflows that use git features introduced between 2.44 and 2.52 fail with opaque
+  "unknown option" or "unknown switch" errors on ubuntu-slim, while the same workflow
+  succeeds on ubuntu-24.04 standard runners. As of June 2026, the issue is unresolved
+  and the ubuntu-slim image README is inaccurate.
+fix: |
+  Install git explicitly from the git-core PPA as an early workflow step on ubuntu-slim.
+  This overrides the downgraded system git (2.43.0) with the current PPA version (2.52+).
+fix_code:
+  - language: yaml
+    label: 'Upgrade git from PPA on ubuntu-slim to get 2.52+'
+    code: |
+      jobs:
+        build:
+          runs-on: ubuntu-slim
+          steps:
+            - name: Upgrade git from PPA (ubuntu-slim ships 2.43.0, not 2.52+)
+              run: |
+                sudo add-apt-repository ppa:git-core/ppa -y
+                sudo apt-get update -q
+                sudo apt-get install -y --no-install-recommends git
+                git --version  # verify: expect 2.52+ or later
+
+            - uses: actions/checkout@v4
+            # ... rest of workflow
+  - language: yaml
+    label: 'Diagnostic — detect git version mismatch at start of workflow'
+    code: |
+      - name: Check git version
+        run: |
+          GIT_VER=$(git --version | awk '{print $3}')
+          echo "Git version: $GIT_VER"
+          # ubuntu-slim may report 2.43.0 instead of expected 2.52+
+          # If you need git >= 2.44, install from PPA before using git features
+prevention:
+  - 'Always run git --version early in ubuntu-slim workflows to detect the downgraded version'
+  - 'Do not assume ubuntu-slim has the same git version as ubuntu-24.04 standard runners'
+  - 'Pin git from git-core/ppa if your workflow uses any feature added in git 2.44 or later'
+  - 'Monitor actions/runner-images#14014 for the official fix to the ubuntu-slim git version'
+  - 'Cross-reference the ubuntu-slim README version claims against actual installed versions'
+docs:
+  - url: 'https://github.com/actions/runner-images/issues/14014'
+    label: 'runner-images#14014 — ubuntu-slim git downgraded to 2.43.0'
+  - url: 'https://github.com/actions/runner-images/blob/main/images/ubuntu-slim/ubuntu-slim-Readme.md'
+    label: 'ubuntu-slim software manifest (check actual vs documented versions)'
+  - url: 'https://launchpad.net/~git-core/+archive/ubuntu/ppa'
+    label: 'git-core PPA — provides git 2.52+ for Ubuntu'
diff --git a/errors/silent-failures/secret-dollar-sign-expands-in-double-quoted-shell-string.yml b/errors/silent-failures/secret-dollar-sign-expands-in-double-quoted-shell-string.yml
new file mode 100644
index 0000000..db9f635
--- /dev/null
+++ b/errors/silent-failures/secret-dollar-sign-expands-in-double-quoted-shell-string.yml
@@ -0,0 +1,90 @@
+id: sf-216
+title: 'Secret containing $ character silently expands in double-quoted shell string, passing wrong value to command'
+category: silent-failures
+severity: silent-failure
+tags:
+  - secrets
+  - shell-expansion
+  - dollar-sign
+  - double-quotes
+  - run-step
+  - shell-injection
+patterns:
+  - regex: 'keystore password was incorrect|keystorepassword was incorrect'
+    flags: 'i'
+  - regex: 'password.*incorrect.*IOException|BadPaddingException|UnrecoverableKeyException'
+    flags: 'i'
+  - regex: '\$\{\{\s*secrets\.[A-Z_]+\s*\}\}'
+    flags: 'i'
+error_messages:
+  - 'keytool error: java.io.IOException: keystore password was incorrect'
+  - 'javax.crypto.BadPaddingException: Given final block not properly padded'
+  - 'java.security.UnrecoverableKeyException: failed to decrypt safe contents entry'
+  - 'error: incorrect password'
+root_cause: |
+  When a secret contains a `$` character and is interpolated inline via
+  `${{ secrets.NAME }}` inside a double-quoted shell string in a `run:` step,
+  Bash interprets the substring after the `$` as a shell variable name. Because
+  that shell variable is typically unset, it expands to an empty string, silently
+  truncating or mutating the secret value. The command then runs with the wrong
+  credential — no runner error is emitted; the failure only appears as an
+  authentication or decryption error from the downstream tool.
+
+  Example: secret value `UHh&**&$k8748848923jhHH` used as:
+    -storepass "${{ secrets.KEYSTORE_PASSWORD }}"
+  becomes:
+    -storepass "UHh&**&"
+  because `$k8748848923jhHH` expands to empty string in the shell.
+
+  The runner substitutes the literal secret value into the YAML first (replacing
+  `${{ secrets.KEYSTORE_PASSWORD }}`), and then Bash processes the resulting string
+  as a normal double-quoted argument — so any `$WORD` inside still triggers shell
+  variable expansion.
+fix: |
+  Pass secrets to run steps via the `env:` block and reference them as regular
+  shell environment variables. This prevents the runner-substituted value from
+  being double-processed by the shell.
+
+  Option A — env var pattern (recommended for any secret with special characters):
+    env:
+      KEYSTORE_PASS: ${{ secrets.KEYSTORE_PASSWORD }}
+    run: keytool -storepass "$KEYSTORE_PASS"
+
+  Option B — single-quote wrap (prevents shell variable expansion):
+    run: keytool -storepass '${{ secrets.KEYSTORE_PASSWORD }}'
+    # Note: single quotes are literal in shell; ${{ ... }} is resolved by the
+    # runner before the shell sees the string, so this is safe.
+
+  Option A (env var) is strongly preferred because it also protects against
+  glob expansion, word splitting, and other shell metacharacter issues in secrets.
+fix_code:
+  - language: yaml
+    label: 'Wrong — inline double-quoted interpolation allows $-expansion on secret value'
+    code: |
+      - name: Sign release
+        run: |
+          keytool -list -v \
+            -keystore release-key.jks \
+            -storepass "${{ secrets.KEYSTORE_PASSWORD }}"
+          # PROBLEM: if KEYSTORE_PASSWORD contains $, Bash expands it silently
+  - language: yaml
+    label: 'Correct — pass secret as env var to prevent double shell expansion'
+    code: |
+      - name: Sign release
+        env:
+          KEYSTORE_PASS: ${{ secrets.KEYSTORE_PASSWORD }}
+        run: |
+          keytool -list -v \
+            -keystore release-key.jks \
+            -storepass "$KEYSTORE_PASS"
+          # SAFE: $KEYSTORE_PASS is a plain env var with no nested $ interpretation
+prevention:
+  - 'Never interpolate secrets inline inside double-quoted shell strings — always use env: block'
+  - 'Audit all run: steps that use ${{ secrets.* }} inside "..." strings and migrate to env var pattern'
+  - 'Test secrets that contain $, !, ", \, backtick, or space characters with extra care'
+  - 'Use the GitHub Actions secret scanner / security review to flag direct secret interpolation in run steps'
+docs:
+  - url: 'https://docs.github.com/en/actions/security-for-github-actions/security-guides/security-hardening-for-github-actions#using-secrets'
+    label: 'Security hardening for GitHub Actions — using secrets safely'
+  - url: 'https://github.com/actions/runner/issues/4500'
+    label: 'actions/runner#4500 — runner modifies secrets containing $ in double-quoted shell commands'