diff --git a/overleaf/README.md b/overleaf/README.md
index 17d3e6b..742083b 100644
--- a/overleaf/README.md
+++ b/overleaf/README.md
@@ -159,6 +159,15 @@ ln -s overleaf.env .env
 - **Mongo 8.0 needs AVX.** Mongo 5.0+ won't start on CPUs without it, and the
   failure is an immediate exit with nothing useful logged. Check first:
   `grep -o avx2 /proc/cpuinfo | head -1`
+- **`start_period` on Mongo's healthcheck is load-bearing.** Without it, slow
+  checks during startup count against `retries` straight away — five of them
+  (~50s) mark Mongo unhealthy, and the app's `condition: service_healthy`
+  refuses to start it. Mongo then recovers on its next check, so by morning
+  everything looks fine except the app, which is simply down. This bites on
+  backup scripts that stop and start containers: Mongo comes back while the
+  disks are still busy, `mongosh` is a Node process and answers slowly, and the
+  stack loses a race nobody knew it was running. Upstream's sample has no
+  `start_period` either.
 - **A healthy Mongo does not mean the replica set is up.** The healthcheck runs
   `db.stats().ok`, which passes without one — so `depends_on: service_healthy`
   is satisfied and the app starts anyway, then fails its own DB check.
@@ -189,27 +198,41 @@ TeX Live lives at `/usr/local/texlive/2026/`, **inside the image**. A
 `docker compose pull` does not. A document that compiled last month stops
 compiling and nothing tells you why.
 
-The fix is `TEXMFHOME`, which this stack bind-mounts to `${DATA_PATH}/texmf`.
-Install in user mode and packages land on the volume instead:
+The fix is user-mode installs plus a `TEXMFHOME` that both users agree on.
+That second half matters more than it looks: **tlmgr runs as root, but the
+compiles run as `www-data`**, and by default those two resolve `TEXMFHOME`
+differently:
+
+```
+root      /root/texmf        <- where a plain `tlmgr --usermode install` lands
+www-data  /var/www/texmf     <- where LaTeX actually looks
+```
+
+So the install succeeds, reports no error, and the package still isn't found —
+and `/root` isn't even readable by `www-data`, so no amount of mounting that
+path helps. This stack therefore sets:
+
+```yaml
+TEXMFHOME: /var/lib/overleaf/texmf
+```
+
+which is inside the persisted volume, so both users agree and the packages
+survive image updates. Then:
 
 ```bash
-# once, to create the tree
-docker exec overleaf tlmgr init-usertree
-
-# thereafter, for each package
+docker exec overleaf tlmgr --usermode init-usertree   # once
 docker exec overleaf tlmgr --usermode install booktabs
 ```
 
-Verify it took:
+Verify as the user that actually compiles, not as root:
 
 ```bash
-docker exec overleaf kpsewhich booktabs.sty
-#   /root/texmf/tex/latex/booktabs/booktabs.sty   <- persisted
-#   /usr/local/texlive/...                        <- inside the image, will be lost
+docker exec -u www-data overleaf kpsewhich booktabs.sty
+#  /var/lib/overleaf/texmf/...   correct, persisted
+#  /usr/local/texlive/...        inside the image, lost on update
+#  nothing                       installed somewhere the compiler can't see
 ```
 
-The path in the output tells you which mode you used.
-
 **Caveats.** User mode handles ordinary style packages cleanly. Packages that
 install fonts or need map-file updates may also want `updmap-user`, and a few
 that expect to modify the main tree won't work this way — install those with a
diff --git a/overleaf/compose.yaml b/overleaf/compose.yaml
index 3810bcb..821afcb 100644
--- a/overleaf/compose.yaml
+++ b/overleaf/compose.yaml
@@ -18,10 +18,6 @@ services:
 
     volumes:
       - ${DATA_PATH:-./data}/overleaf:/var/lib/overleaf
-      # TEXMFHOME. Packages installed with `tlmgr --usermode install` land here
-      # instead of inside the image, so they survive an image update. See the
-      # README -- without this, every upgrade silently drops them.
-      - ${DATA_PATH:-./data}/texmf:/root/texmf
 
     environment:
       OVERLEAF_APP_NAME: ${OVERLEAF_APP_NAME:-Overleaf}
@@ -40,6 +36,13 @@ services:
       # which is wrong the moment you use a port or a domain.
       OVERLEAF_SITE_URL: ${OVERLEAF_SITE_URL:-http://localhost:8020}
 
+      # Where `tlmgr --usermode install` puts packages. Overridden to a path on
+      # the persisted volume so they survive an image update -- and so that root
+      # (which runs tlmgr) and www-data (which runs the compiles) agree on one
+      # location. Left at the default they disagree, and packages install to a
+      # directory the compiler never searches. See the README.
+      TEXMFHOME: /var/lib/overleaf/texmf
+
       ENABLED_LINKED_FILE_TYPES: "project_file,project_output_file"
       ENABLE_CONVERSIONS: "true"
       EMAIL_CONFIRMATION_DISABLED: "true"
@@ -71,8 +74,16 @@ services:
     healthcheck:
       test: echo 'db.stats().ok' | mongosh localhost:27017/test --quiet
       interval: 10s
-      timeout: 10s
+      timeout: 20s
       retries: 5
+      # Without this, failures during startup count against `retries`
+      # immediately: five slow checks (~50s) mark Mongo unhealthy, and the app's
+      # `condition: service_healthy` then refuses to start. Mongo recovers a
+      # moment later, so by morning nothing looks wrong. `mongosh` is a Node
+      # process and is slow to answer on a loaded box -- e.g. right after a
+      # backup job. During start_period a failure is not counted, and a success
+      # promotes to healthy straight away.
+      start_period: 120s
 
   redis:
     image: redis:6.2