docs(solutions): extend root-owned bind-mount doc to docker run / build-assets

The install-plugins fix (209b804) only covered docker exec. build-assets
runs `docker run node:20-alpine` without --user, so it still writes
root-owned node_modules + esbuild bundles into user/themes/ — which is what
blocked `git worktree remove` at teardown. Broaden the doc and prevention
rule to cover docker run, with the --user fix.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Mpdu3Dt1iVoozHwAMyjrbn

docs/solutions/integration-issues/docker-exec-root-owned-bind-mount-files.md

@@ -1,6 +1,7 @@
 ---
-title: docker exec defaults to root, writing root-owned files into the host bind mount
+title: docker exec/run defaults to root, writing root-owned files into the host bind mount
 date: 2026-07-08
+last_updated: 2026-07-08
 problem_type: integration_issue
 category: integration-issues
 module: docker-dev-environment
@@ -11,6 +12,7 @@ symptoms:
   - "make worktree-rm fails: cannot rm root-owned plugin files without sudo"
   - "files stay root-owned even though UID/GID env vars were set to the host user"
   - "install-plugins writes the entire plugin tree as root via php bin/gpm install"
+  - "build-assets (docker run node:20-alpine, no --user) writes root-owned node_modules + esbuild bundles into user/themes/intotheeast/, blocking git worktree remove and git merge"
 root_cause: config_error
 resolution_type: config_change
 related_components:
@@ -20,12 +22,15 @@ related_components:
 tags:
   - docker
   - docker-exec
+  - docker-run
   - bind-mount
   - file-permissions
   - uid-gid
   - makefile
   - grav
   - gpm
+  - build-assets
+  - esbuild
 ---
 
 ## Problem
@@ -56,9 +61,12 @@ Several plausible fixes were tried or considered and rejected:
 
 ## Root Cause
 
-`docker exec` defaults to running as root (uid 0). Because the grav container must boot as root, and `docker exec` inherits that default unless `-u` is passed explicitly, every make target that did `docker exec <container> <cmd>` without `-u` wrote root-owned files into the `./user` bind mount.
+Both `docker exec` **and** `docker run` default to running as root (uid 0). Because the grav container must boot as root, and neither inherits a non-root default unless `-u` / `--user` is passed explicitly, every make target that shelled into (or spun up) a container without dropping privileges wrote root-owned files into whatever host path it bind-mounted.
 
-The worst offender was `install-plugins`, which runs `php bin/gpm install` and writes the entire plugin tree into `./user/plugins`.
+There are **two** offenders, on two different bind mounts:
+
+- **`install-plugins`** — `docker exec … php bin/gpm install`, writing the entire plugin tree into `./user/plugins` as root. The worst by file count (11,624).
+- **`build-assets`** — `docker run --rm node:20-alpine … "npm install && npm run build"`, bind-mounting `./user/themes/intotheeast` → `/app`, writing root-owned `node_modules/` and esbuild bundle outputs (`js/…`, `css-compiled/`) into the tracked theme tree. This one uses **`docker run`**, not `docker exec`, and has **no `--user`** — so the `install-plugins` fix below does *not* cover it.
 
 ## Solution
 
@@ -94,6 +102,30 @@ install-plugins:
 	$(MAKE) apply-plugin-patches
 ```
 
+### The `build-assets` vector (same principle, `docker run`) — still open
+
+The 2026-07-08 fix (`209b804`) hardened `install-plugins` only. `build-assets` remains a root-writing target and surfaced later: `git worktree remove` aborted with `Permission denied` on root-owned esbuild bundles under `user/themes/intotheeast/js/post/`, and earlier a `build-assets` run had produced a root-owned `css-compiled/` dir that blocked a `git merge` on the main checkout. (session history)
+
+Apply the same drop-privileges principle — with `--user` on `docker run`:
+
+```makefile
+# Before — writes root-owned node_modules + bundles into the tracked theme tree
+build-assets:
+	docker run --rm \
+	  -v $(PWD)/user/themes/intotheeast:/app \
+	  -w /app node:20-alpine \
+	  sh -c "npm install && npm run build"
+
+# After — outputs owned by the host user (uid 1000)
+build-assets:
+	docker run --rm --user $(HOST_UID):$(HOST_GID) \
+	  -v $(PWD)/user/themes/intotheeast:/app \
+	  -w /app node:20-alpine \
+	  sh -c "npm install && npm run build"
+```
+
+Caveat: run as a non-root uid, npm needs a writable `$HOME`/cache. If the build errors on a read-only home dir, add `-e HOME=/tmp` (or `-e npm_config_cache=/tmp/.npm`). Recovery for the existing root-owned output is the same as anywhere else — `chown -R $(HOST_UID):$(HOST_GID)` from a container that already has root, then `rm`.
+
 ## Why This Works
 
 The container still *boots* as root — which it needs, to bind `:80` and set up cron. But the individual `docker exec` that writes into the bind mount now runs as the host uid/gid via `-u $(HOST_UID):$(HOST_GID)`. Files that exec creates on the host are therefore owned by the developer, not root. No post-hoc chown, no cleanup debt.
@@ -106,7 +138,7 @@ The preliminary chown of `cache/` and `tmp/` is container-internal: those paths
 
 The reusable principle, worth internalizing beyond this one repo:
 
-- **Any make/CI target that writes files into a host bind mount via `docker exec` must pass `-u $(HOST_UID):$(HOST_GID)`.** A container booting as root does *not* mean your exec commands must run as root. Drop privileges per-exec.
+- **Any make/CI target that writes files into a host bind mount must drop privileges — whether it uses `docker exec` (`-u $(HOST_UID):$(HOST_GID)`) or `docker run` (`--user $(HOST_UID):$(HOST_GID)`).** A container booting as root does *not* mean the commands you run in it must write as root. `build-assets` (a `docker run`) is the easy one to miss, because the original fix only patched the `docker exec` targets — so audit `docker run` invocations too, not just `docker exec`.
 - **Derive host identity once in the Makefile and reuse it:** `HOST_UID := $(shell id -u)` / `HOST_GID := $(shell id -g)`.
 - **Don't rely on `APACHE_RUN_USER` or compose-level `UID`/`GID` env vars to fix exec ownership** — they don't apply to `docker exec`. `APACHE_RUN_USER` only affects Apache workers; compose `user:`/env vars only affect services wired to consume them.
 - **You can't just add `user:` to a service whose entrypoint needs root** (to bind privileged ports, set up cron, etc.). Drop privileges per-exec instead of per-container.