diff --git a/errors/caching-artifacts/ca-154.yml b/errors/caching-artifacts/ca-154.yml
new file mode 100644
index 0000000..193dde4
--- /dev/null
+++ b/errors/caching-artifacts/ca-154.yml
@@ -0,0 +1,119 @@
+id: ca-154
+title: 'CodeQL TRAP caching fills GitHub Actions cache quota — other workflow caches evicted'
+category: caching-artifacts
+severity: warning
+tags:
+  - codeql
+  - trap-caching
+  - cache-limit
+  - cache-eviction
+  - code-scanning
+  - monorepo
+  - performance
+patterns:
+  - regex: 'Caching TRAP files for|TRAP cache.*saved|Restoring TRAP cache'
+    flags: 'i'
+  - regex: 'cache.*storage.*quota|Cache capacity reached.*Evicting'
+    flags: 'i'
+  - regex: 'Unable to restore.*TRAP.*cache|TRAP.*cache.*miss'
+    flags: 'i'
+error_messages:
+  - 'Caching TRAP files for org/repo (Language: javascript-typescript)'
+  - 'Restoring TRAP cache from org/repo...'
+  - 'Cache capacity reached. Evicting old cache entries.'
+root_cause: |
+  The `github/codeql-action` (init and analyze steps) uses `actions/cache`
+  internally to persist TRAP (Text Representation of Analyzed Programs) files
+  between runs. TRAP files are the compiled intermediate representation of source
+  code that CodeQL analyzes.
+
+  In high-frequency repositories (active monorepos with dozens of merges per
+  day), each CI run generates a new TRAP cache entry keyed to the exact code
+  state. Because the key changes on every commit, cache restoration is rare
+  and a new entry is written each time. GitHub Actions enforces a 10 GB
+  per-repository cache limit. When hundreds of TRAP cache entries accumulate,
+  they exhaust this quota within one to a few days.
+
+  Once the 10 GB limit is reached, GitHub begins evicting the
+  least-recently-used entries. This evicts OTHER workflow caches — npm
+  dependencies, Go modules, Docker layer caches, pip wheels — that were
+  actively providing value, causing build times to increase across all
+  workflows in the repository.
+
+  The TRAP caching feature was designed to accelerate incremental CodeQL
+  re-analysis. For repos where most source lines change between runs, the
+  cache hit rate is near zero, making TRAP caching net-negative: it consumes
+  cache space without improving CodeQL speed.
+
+  Source: github/codeql-action#2030 (May 2025, confirmed by GitHub staff).
+fix: |
+  Disable TRAP caching in the CodeQL init action by setting `trap-caching: false`.
+  This prevents TRAP files from being written to the GitHub Actions cache and
+  frees the full 10 GB budget for other workflow caches.
+
+  Use `trap-caching: false` when any of the following apply:
+    - Repository has high commit velocity (10+ merges per day)
+    - The Actions Cache tab shows many entries with "TRAP" in the key name
+    - Non-CodeQL workflows are experiencing more frequent cache misses
+    - Total repository cache usage is near the 10 GB limit
+
+  Alternatively, reduce CodeQL scan frequency (e.g., scan only on push to the
+  default branch rather than every PR) to reduce the number of unique TRAP
+  cache entries created per day.
+fix_code:
+  - language: yaml
+    label: 'Disable TRAP caching — prevents cache churn in high-frequency repos'
+    code: |
+      jobs:
+        analyze:
+          name: Analyze code
+          runs-on: ubuntu-latest
+          permissions:
+            actions: read
+            contents: read
+            security-events: write
+          steps:
+            - uses: actions/checkout@v4
+
+            - name: Initialize CodeQL
+              uses: github/codeql-action/init@v3
+              with:
+                languages: javascript-typescript
+                trap-caching: false   # prevents TRAP files from filling 10 GB cache quota
+
+            - name: Perform CodeQL Analysis
+              uses: github/codeql-action/analyze@v3
+  - language: yaml
+    label: 'Limit CodeQL scans to default branch to reduce TRAP cache entry growth'
+    code: |
+      on:
+        push:
+          branches: [main]     # analyze on merge to main only — not every PR
+        schedule:
+          - cron: '0 6 * * 1'  # weekly full-codebase scan
+
+      jobs:
+        analyze:
+          runs-on: ubuntu-latest
+          permissions:
+            actions: read
+            contents: read
+            security-events: write
+          steps:
+            - uses: actions/checkout@v4
+            - uses: github/codeql-action/init@v3
+              with:
+                languages: javascript-typescript
+            - uses: github/codeql-action/analyze@v3
+prevention:
+  - 'Set `trap-caching: false` in the CodeQL init step for repos with more than ~10 merges per day.'
+  - 'Inspect the Actions Cache tab regularly — many entries with "TRAP" in the key name signal cache churn.'
+  - 'Limit CodeQL analysis to pushes on protected branches rather than every PR to reduce cache entry growth.'
+  - 'Review total cache usage periodically; if near 10 GB, CodeQL TRAP caches are a common culprit.'
+docs:
+  - url: 'https://github.com/github/codeql-action/issues/2030'
+    label: 'codeql-action#2030 — TRAP caching causes GitHub Actions Cache to churn (May 2025)'
+  - url: 'https://docs.github.com/en/code-security/code-scanning/creating-an-advanced-setup-for-code-scanning/codeql-code-scanning-for-compiled-languages#caching-trap-files'
+    label: 'GitHub Docs — CodeQL TRAP caching (advanced setup)'
+  - url: 'https://docs.github.com/en/actions/writing-workflows/choosing-what-your-workflow-does/caching-dependencies-to-speed-up-workflows#usage-limits-and-eviction-policy'
+    label: 'GitHub Docs — Cache usage limits and eviction policy (10 GB per repository)'
diff --git a/errors/runner-environment/re-503.yml b/errors/runner-environment/re-503.yml
new file mode 100644
index 0000000..d065b2d
--- /dev/null
+++ b/errors/runner-environment/re-503.yml
@@ -0,0 +1,103 @@
+id: re-503
+title: 'Ubuntu 26.04 public preview runner: DNS resolution failures for third-party package repositories'
+category: runner-environment
+severity: error
+tags:
+  - ubuntu-26.04
+  - runner-image
+  - dns
+  - network
+  - preview
+  - curl-error-6
+  - hostname-resolution
+  - third-party-repos
+patterns:
+  - regex: 'Curl error \(6\).*Could not resolve host|curl.*6.*resolve.*hostname'
+    flags: 'i'
+  - regex: 'Could not resolve host.*ubuntu-26|ubuntu-26.*Could not resolve host'
+    flags: 'i'
+  - regex: 'getaddrinfo.*Name or service not known.*26\.04|EAI_NONAME.*ubuntu-26'
+    flags: 'i'
+error_messages:
+  - 'Curl error (6): Could not resolve hostname for https://fedoraproject-updates-archive.fedoraproject.org'
+  - 'Could not resolve host: dl.fedoraproject.org'
+  - 'curl: (6) Could not resolve host: packages.example-repo.org'
+  - 'getaddrinfo: Name or service not known'
+root_cause: |
+  The Ubuntu 26.04 GitHub Actions runner (available as a public preview from
+  June 11, 2026, as `ubuntu-26.04` and `ubuntu-26.04-arm`) has intermittent
+  DNS resolution failures for some third-party package repository hostnames.
+
+  The Ubuntu 26.04 image switches from the traditional `resolv.conf` / `systemd-
+  resolved` DNS configuration used in Ubuntu 24.04 to a newer resolver stack.
+  Some third-party repository mirrors that rely on external DNS servers not
+  in the runner's configured resolver list may fail to resolve, producing
+  `Curl error (6): Could not resolve hostname`.
+
+  This issue is specific to the preview image. Ubuntu 24.04 runners using the
+  same workflows on the same network resolve the same hostnames successfully.
+  The failure is non-deterministic — the same hostname may resolve on some runs
+  but not others due to timing or caching differences in the new DNS stack.
+
+  Known affected scenarios include:
+    - Installing packages from Fedora/EPEL mirrors via `dnf`/`yum` within
+      container build steps
+    - `curl` or `wget` to third-party APT/YUM/pip repository hosts
+    - Custom Docker image builds that `apt-get` from third-party PPAs during
+      the build phase
+
+  Source: actions/runner-images#14230 (filed June 13, 2026, Ubuntu 26.04
+  public preview — network related issues).
+fix: |
+  **Short-term workaround while the preview image issue is investigated:**
+
+  1. **Pin to ubuntu-24.04** — Use an explicit runner version that does not
+     have the DNS issue. Ubuntu 24.04 runners are stable and resolve the
+     same hostnames correctly.
+
+  2. **Use `ubuntu-latest`** — `ubuntu-latest` currently aliases ubuntu-24.04
+     and is unaffected.
+
+  3. **Retry logic** — For intermittent failures, add a retry mechanism around
+     the failing step using `--retry` flags in `curl` or a retry composite action.
+
+  4. **Check runner-images for updates** — The Ubuntu 26.04 preview image is
+     actively updated. Monitor runner-images#14230 for a fix or workaround from
+     GitHub's runner team.
+fix_code:
+  - language: yaml
+    label: 'Pin to ubuntu-24.04 until ubuntu-26.04 DNS issues are resolved'
+    code: |
+      jobs:
+        build:
+          # ubuntu-26.04 has intermittent DNS resolution failures (June 2026 preview)
+          # Use ubuntu-24.04 or ubuntu-latest (currently aliases ubuntu-24.04) as workaround
+          runs-on: ubuntu-24.04   # stable DNS, no hostname resolution issues
+          steps:
+            - uses: actions/checkout@v4
+            - name: Install packages from third-party repository
+              run: |
+                curl -fsSL https://packages.example-repo.org/install.sh | sh
+  - language: yaml
+    label: 'Add retry logic for curl calls on ubuntu-26.04 preview'
+    code: |
+      jobs:
+        build:
+          runs-on: ubuntu-26.04
+          steps:
+            - uses: actions/checkout@v4
+            - name: Download with retry (workaround for ubuntu-26.04 DNS issues)
+              run: |
+                # curl --retry retries on transient failures including DNS (Curl error 6)
+                curl --retry 3 --retry-delay 5 --retry-all-errors \
+                  -fsSL https://packages.example-repo.org/install.sh | sh
+prevention:
+  - 'Do not migrate CI workflows to ubuntu-26.04 during the public preview phase without testing for DNS resolution issues.'
+  - 'If using ubuntu-26.04 is required, add `--retry 3 --retry-all-errors` flags to curl/wget calls as a safety net.'
+  - 'Monitor actions/runner-images for a patch to the ubuntu-26.04 DNS configuration before adopting it in production workflows.'
+  - 'Use explicit runner version labels (ubuntu-24.04, ubuntu-26.04) rather than ubuntu-latest to control when new image versions take effect.'
+docs:
+  - url: 'https://github.com/actions/runner-images/issues/14230'
+    label: 'runner-images#14230 — [Ubuntu 26.04] network related issues (June 13, 2026)'
+  - url: 'https://github.com/actions/runner-images/issues/14226'
+    label: 'runner-images#14226 — Ubuntu 26.04 and Ubuntu 26.04 Arm public preview announcement (June 11, 2026)'
diff --git a/errors/runner-environment/re-504.yml b/errors/runner-environment/re-504.yml
new file mode 100644
index 0000000..0643780
--- /dev/null
+++ b/errors/runner-environment/re-504.yml
@@ -0,0 +1,129 @@
+id: re-504
+title: 'Ubuntu 26.04: setup-python only pre-caches Python 3.14 — older versions always trigger a live download'
+category: runner-environment
+severity: warning
+tags:
+  - ubuntu-26.04
+  - setup-python
+  - toolcache
+  - python
+  - slow-ci
+  - cache-miss
+  - runner-image
+  - migration
+patterns:
+  - regex: 'Downloading Python (3\.10|3\.11|3\.12|3\.13)\.[0-9]+ - ubuntu-26'
+    flags: 'i'
+  - regex: 'Python (3\.10|3\.11|3\.12|3\.13).*not.*toolcache.*ubuntu-26|ubuntu-26.*Python.*(3\.10|3\.11|3\.12|3\.13).*not.*cached'
+    flags: 'i'
+  - regex: 'No pre-built Python (3\.10|3\.11|3\.12|3\.13) found|Downloading cpython.*3\.(10|11|12|13)'
+    flags: 'i'
+error_messages:
+  - 'Downloading Python 3.12.x - ubuntu-26.04-x64'
+  - 'Python 3.11 not found in toolcache; downloading from python.org'
+  - 'No pre-cached Python 3.10 found for ubuntu-26.04; installing from source'
+root_cause: |
+  The Ubuntu 26.04 GitHub Actions runner image (public preview, June 11 2026)
+  ships with only Python 3.14 pre-installed in the toolcache. The following
+  Python versions are NOT pre-cached and trigger a live network download when
+  requested via `actions/setup-python`:
+    - Python 3.10.x
+    - Python 3.11.x
+    - Python 3.12.x
+    - Python 3.13.x
+
+  By contrast, the ubuntu-24.04 image pre-caches Python 3.10, 3.11, 3.12
+  (default), 3.13, and 3.14. Workflows that pin `python-version: '3.12'` or
+  any older version via `setup-python` on ubuntu-26.04 will trigger a
+  download from GitHub Toolcache servers on every job run.
+
+  The download itself typically succeeds and produces the correct Python version,
+  but the impact is:
+    - 30–120 seconds of additional download time per job, depending on the
+      Python version and runner network conditions
+    - Increased sensitivity to GitHub Toolcache server availability
+    - Higher CI costs on paid runners proportional to download time
+
+  This is expected to be resolved as the ubuntu-26.04 image matures beyond
+  public preview and GitHub populates the toolcache with additional Python
+  versions.
+
+  Source: actions/runner-images#14226 (Ubuntu 26.04 public preview
+  announcement, June 11, 2026) — Python row shows "3.14.* (default)" only.
+fix: |
+  **Option 1 — Stay on ubuntu-24.04** (recommended for stable Python toolcache):
+  Ubuntu 24.04 pre-caches Python 3.10–3.14. Workflows requiring specific
+  Python versions incur no download overhead.
+
+  **Option 2 — Pin python-version: '3.14'** on ubuntu-26.04:
+  Python 3.14 is the only pre-cached version. If your workflow can target
+  Python 3.14, there is no download delay.
+
+  **Option 3 — Use pip caching to amortize download cost**:
+  If you must use an older Python version on ubuntu-26.04, add
+  `cache: 'pip'` to `setup-python` to cache installed packages and reduce
+  total CI time, even though the Python binary itself downloads each run.
+fix_code:
+  - language: yaml
+    label: 'Pin to ubuntu-24.04 for consistent Python toolcache (no download for 3.10–3.13)'
+    code: |
+      jobs:
+        test:
+          # ubuntu-26.04 only pre-caches Python 3.14 — use ubuntu-24.04 for 3.10/3.11/3.12/3.13
+          runs-on: ubuntu-24.04
+          steps:
+            - uses: actions/checkout@v4
+            - uses: actions/setup-python@v5
+              with:
+                python-version: '3.12'   # pre-cached on ubuntu-24.04, instant
+                cache: 'pip'
+            - run: pip install -r requirements.txt
+            - run: pytest
+  - language: yaml
+    label: 'Use Python 3.14 on ubuntu-26.04 to avoid toolcache download'
+    code: |
+      jobs:
+        test:
+          runs-on: ubuntu-26.04
+          steps:
+            - uses: actions/checkout@v4
+            - uses: actions/setup-python@v5
+              with:
+                python-version: '3.14'   # only pre-cached version on ubuntu-26.04 at preview launch
+                cache: 'pip'
+            - run: pip install -r requirements.txt
+            - run: pytest
+  - language: yaml
+    label: 'Matrix test across Python versions — pin runner per version for speed'
+    code: |
+      jobs:
+        test:
+          strategy:
+            matrix:
+              include:
+                - python-version: '3.12'
+                  runs-on: ubuntu-24.04    # pre-cached — no download
+                - python-version: '3.13'
+                  runs-on: ubuntu-24.04    # pre-cached — no download
+                - python-version: '3.14'
+                  runs-on: ubuntu-26.04    # pre-cached on ubuntu-26.04
+          runs-on: ${{ matrix.runs-on }}
+          steps:
+            - uses: actions/checkout@v4
+            - uses: actions/setup-python@v5
+              with:
+                python-version: ${{ matrix.python-version }}
+                cache: 'pip'
+            - run: pytest
+prevention:
+  - 'On ubuntu-26.04, only Python 3.14 is pre-cached in the toolcache at public preview launch (June 2026); use ubuntu-24.04 for older versions.'
+  - 'Add `cache: pip` to setup-python to reduce total job time even when the Python binary must be downloaded.'
+  - 'Monitor runner-images announcements for when ubuntu-26.04 toolcache is updated to include Python 3.10–3.13.'
+  - 'Use explicit ubuntu-24.04 or ubuntu-26.04 labels instead of ubuntu-latest to control which toolcache versions are available.'
+docs:
+  - url: 'https://github.com/actions/runner-images/issues/14226'
+    label: 'runner-images#14226 — Ubuntu 26.04 public preview announcement — Python toolcache row'
+  - url: 'https://github.com/actions/setup-python'
+    label: 'actions/setup-python — Python version management in GitHub Actions'
+  - url: 'https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-python#caching-dependencies'
+    label: 'GitHub Docs — Caching Python dependencies'