fix(ci): run the container as the invoking user, not root

Docker on the dev boxes is rootful, so without `--user` every byte the build
writes into the bind-mounted repo is owned by root and the user needs `sudo` to
delete their own artifacts. This is not hypothetical: `export/` in a working
tree held 227 root-owned paths (149 MB) from earlier runs, and the `sylpheed.db`
regen in the workspace CLAUDE.md writes straight into /work, so it lands
root-owned every time.

The catch is that the daemon creates a named volume root-owned, so a `--user`
container cannot write /cargo or /target at all. So take ownership of both
volumes first -- once, and only when it is actually wrong, since a recursive
chown across a ~36 GB target volume is not something to repeat per invocation.
Both are sampled, not just one, because an older run can leave them drifted.

Volume names become overridable (SYLPH_CI_CARGO_VOL / SYLPH_CI_TARGET_VOL),
which is what let the chown path be tested without touching the real caches.

Placed above the corpus-mount block so it does not collide with #53.

Measured, not assumed:
  * fresh root-owned volumes  -> chowns once, then writes as uid 1000
  * second run                -> no chown, correctly cached
  * `cargo check -p sylpheed-ppc` through the runner -> passes, exit 0
  * a file touched in /work   -> owned fabi:fabi, removable without sudo

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docker/ci/run

@@ -21,18 +21,51 @@ IMAGE="${SYLPH_CI_IMAGE:-sylph-ci:local}"
 CPUS="${SYLPH_CI_CPUS:-6}"
 MEM_GB="${SYLPH_CI_MEM_GB:-7}"
 
+CARGO_VOL="${SYLPH_CI_CARGO_VOL:-sylph-ci-cargo}"
+TARGET_VOL="${SYLPH_CI_TARGET_VOL:-sylph-ci-target}"
+
+# 🔴 Docker on the dev boxes is ROOTFUL, so without `--user` every byte the build
+# writes into the bind-mounted repo is owned by root — and the user then needs
+# `sudo` to delete their own artifacts. The regen command in the workspace
+# `CLAUDE.md` writes `sylpheed.db` straight into /work, so it lands root-owned,
+# and a stray root-owned file is exactly what survived the last cleanup and had
+# to be sudo'd away.
+#
+# The catch is that the daemon creates a named volume root-owned, so a `--user`
+# container cannot write /cargo or /target at all. Take ownership once — and
+# only when it is actually wrong, because a recursive chown across a ~36 GB
+# target volume is not something to repeat on every invocation.
+RUN_UID="$(id -u)"
+RUN_GID="$(id -g)"
+
+docker volume create "$CARGO_VOL"  >/dev/null
+docker volume create "$TARGET_VOL" >/dev/null
+
+# Both volumes, not just one: they are chowned together but can drift apart if an
+# older root-owned run created only one of them.
+vol_owner="$(docker run --rm -v "$CARGO_VOL:/cargo" -v "$TARGET_VOL:/target" "$IMAGE" \
+             stat -c %u /cargo /target 2>/dev/null | sort -u | tr '\n' ' ' || echo unknown)"
+if [ "$vol_owner" != "$RUN_UID " ]; then
+  echo "docker/ci/run: chowning the cargo/target volumes to $RUN_UID:$RUN_GID (one-off)" >&2
+  docker run --rm \
+    -v "$CARGO_VOL:/cargo" -v "$TARGET_VOL:/target" \
+    "$IMAGE" chown -R "$RUN_UID:$RUN_GID" /cargo /target
+fi
+
 args=(
   --rm
   --cpus "$CPUS"
   --memory "${MEM_GB}g"
   --memory-swap "${MEM_GB}g"
   --pids-limit 2048
+  # Run as the invoking user so build output in /work is owned by them, not root.
+  --user "$RUN_UID:$RUN_GID"
   -v "$REPO:/work"
   # Named volumes, not bind mounts: the host tree keeps a 32 GB `target/` from
   # earlier host-side builds, and mixing the two produces rebuilds that look
   # like cache misses and are actually two toolchains fighting over one directory.
-  -v sylph-ci-cargo:/cargo   -e CARGO_HOME=/cargo
-  -v sylph-ci-target:/target -e CARGO_TARGET_DIR=/target
+  -v "$CARGO_VOL:/cargo"   -e CARGO_HOME=/cargo
+  -v "$TARGET_VOL:/target" -e CARGO_TARGET_DIR=/target
   -w /work
 )