CI: pin XDG_CACHE_HOME=/runner/root/.cache on self-hosted runners

The self-hosted Linux runner's work dir lives on /runner, which is a
separate filesystem from /root. uv's default cache lives under
$HOME/.cache/uv (or $XDG_CACHE_HOME/uv if set) and uv hard-links from
the cache into the venv — hard-links can't cross filesystem
boundaries, so uv silently falls back to copying every dep, adding
tens of seconds to every ``uv sync`` / ``uv venv``.

Pin XDG_CACHE_HOME to a path on /runner (same fs as the work dir) so
uv keeps its cache there and hard-linking succeeds. Wrapped in
``if: runner.environment == 'self-hosted'`` so GitHub-hosted runs
(which don't have /runner and run as unprivileged ``runner`` user)
aren't affected.

Added to every job that runs uv: precheck, discover-standard-tests,
build, discover-live-tests, live-integration, deploy-pages build,
release-state.

Author: claude

.github/workflows/deploy-pages.yml

@@ -23,6 +23,10 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v6
 
+      - name: Pin XDG_CACHE_HOME for self-hosted
+        if: runner.environment == 'self-hosted'
+        run: echo "XDG_CACHE_HOME=/runner/root/.cache" >> "$GITHUB_ENV"
+
       - name: Install uv
         uses: astral-sh/setup-uv@v5
 

.github/workflows/release.yml

@@ -28,6 +28,10 @@ jobs:
           fetch-depth: 0
           ref: ${{ github.ref_name }}
 
+      - name: Pin XDG_CACHE_HOME for self-hosted
+        if: runner.environment == 'self-hosted'
+        run: echo "XDG_CACHE_HOME=/runner/root/.cache" >> "$GITHUB_ENV"
+
       - uses: actions/setup-python@v6
         with:
           python-version: "3.12"

.github/workflows/tests.yml

@@ -12,6 +12,12 @@ permissions:
 
 env:
   FORCE_JAVASCRIPT_ACTIONS_TO_NODE24: 'true'
+  # On self-hosted runners, the runner work dir lives on /runner which
+  # is a separate filesystem from /root — keep uv's cache on the same
+  # fs as the work dir so hard-linking into venvs succeeds (uv falls
+  # back to copying across fs boundaries, which is much slower). The
+  # "if" guards below no-op this on GitHub-hosted runners where the
+  # path doesn't exist.
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
@@ -26,6 +32,10 @@ jobs:
     steps:
     - uses: actions/checkout@v6
 
+    - name: Pin XDG_CACHE_HOME for self-hosted
+      if: runner.environment == 'self-hosted'
+      run: echo "XDG_CACHE_HOME=/runner/root/.cache" >> "$GITHUB_ENV"
+
     - name: Setup Python
       uses: actions/setup-python@v6
       with:
@@ -64,6 +74,10 @@ jobs:
     steps:
     - uses: actions/checkout@v6
 
+    - name: Pin XDG_CACHE_HOME for self-hosted
+      if: runner.environment == 'self-hosted'
+      run: echo "XDG_CACHE_HOME=/runner/root/.cache" >> "$GITHUB_ENV"
+
     - name: Discover standard test files
       id: set-matrix
       run: |
@@ -111,11 +125,15 @@ jobs:
     steps:
     - uses: actions/checkout@v6
 
+    - name: Pin XDG_CACHE_HOME for self-hosted
+      if: runner.environment == 'self-hosted'
+      run: echo "XDG_CACHE_HOME=/runner/root/.cache" >> "$GITHUB_ENV"
+
     - name: Setup Python
       uses: actions/setup-python@v6
       with:
         python-version: ${{ matrix.target.python_version }}
-   
+
     - name: Install uv
       uses: astral-sh/setup-uv@v8.0.0
       with:
@@ -240,6 +258,10 @@ jobs:
     steps:
     - uses: actions/checkout@v6
 
+    - name: Pin XDG_CACHE_HOME for self-hosted
+      if: runner.environment == 'self-hosted'
+      run: echo "XDG_CACHE_HOME=/runner/root/.cache" >> "$GITHUB_ENV"
+
     - name: Discover live integration test files
       id: set-matrix
       run: |
@@ -290,6 +312,10 @@ jobs:
     steps:
     - uses: actions/checkout@v6
 
+    - name: Pin XDG_CACHE_HOME for self-hosted
+      if: runner.environment == 'self-hosted'
+      run: echo "XDG_CACHE_HOME=/runner/root/.cache" >> "$GITHUB_ENV"
+
     - name: Setup Python
       uses: actions/setup-python@v6
       with: