diff --git a/docs/deployment.md b/docs/deployment.md
index 90bd5904..1b2c7c60 100644
--- a/docs/deployment.md
+++ b/docs/deployment.md
@@ -41,9 +41,19 @@ cd pediatric-ai-scribe-v3
 cp .env.example .env
 # edit .env — required: APP_URL, JWT_SECRET, DATA_ENCRYPTION_KEY, DB_PASSWORD, an AI provider
 ./scripts/build-image.sh
+sed -i "s|^PED_AI_IMAGE=.*|PED_AI_IMAGE=ped-ai-local:$(git rev-parse HEAD)|" .env
 docker compose up -d --no-build
+curl -fsS http://127.0.0.1:3552/api/build     # must equal `git rev-parse HEAD`
 ```
 
+**Building does not change what `up` starts.** `docker compose` takes the image
+from `PED_AI_IMAGE` in `.env`, and `build-image.sh` deliberately does not move
+that pin — naming a revision is also how a rollback is done. A pin left from an
+earlier deploy therefore starts the older image, and nothing short of
+`/api/build` shows it: the build succeeds, `up` reports the container started,
+and `/api/health` returns `{ok:true}` from the wrong revision. `build-image.sh`
+warns when the pin does not match what it just built.
+
 The build uses Node 24 LTS and `npm ci --omit=dev` from the root lockfile.
 `./scripts/build-image.sh` resolves the full checkout Git commit (including
 worktrees/packed refs) and passes `GIT_REVISION` through Compose. It only builds;
diff --git a/docs/developer-guide.md b/docs/developer-guide.md
index 0045493e..6677618f 100644
--- a/docs/developer-guide.md
+++ b/docs/developer-guide.md
@@ -451,14 +451,31 @@ If a dynamic value enters an HTML string, escape it at the point of insertion. I
 
 ## Deployment checks
 
-After deployment:
+After deployment, check *which revision* is running, not only that something is:
 
 ```bash
+curl -fsS http://127.0.0.1:3552/api/build     # must equal `git rev-parse HEAD`
 curl -fsS http://127.0.0.1:3552/api/health
 docker compose ps pediatric-scribe
 ```
 
-If the browser still shows old frontend behavior, force-refresh or check the injected `BUILD_ID` asset query string.
+`/api/health` passing proves a container is up, not that it is the one you
+built. `docker compose up` starts whatever `PED_AI_IMAGE` in `.env` names, and
+that pin does not move when you build — so a pin left from an earlier deploy
+silently starts the older image, and every signal short of `/api/build` looks
+fine. `scripts/build-image.sh` warns when the pin does not match the revision it
+just built; the fix is to update the pin:
+
+```bash
+sed -i "s|^PED_AI_IMAGE=.*|PED_AI_IMAGE=ped-ai-local:$(git rev-parse HEAD)|" .env
+docker compose up -d --no-build
+```
+
+The pin is not updated for you, because naming a revision is also how a
+deliberate rollback is done.
+
+If the browser still shows old frontend behavior after the revision checks out,
+force-refresh or check the injected `BUILD_ID` asset query string.
 
 ## Documentation expectations
 
diff --git a/scripts/build-image.sh b/scripts/build-image.sh
index 29cee869..1239ba50 100755
--- a/scripts/build-image.sh
+++ b/scripts/build-image.sh
@@ -37,3 +37,33 @@ if [ "$GIT_REVISION" != unknown ]; then
 else
   echo 'Built ped-ai-local:latest with no recorded revision' >&2
 fi
+
+# A deploy runs `docker compose up`, which reads PED_AI_IMAGE from .env — not
+# the tag just built. A pin left behind from an earlier deploy therefore starts
+# that older image, and `up` reports success either way: the build looks done,
+# the health check passes, and the running app is silently an older revision.
+# That has already cost a session — it rolled the app back far enough to remove
+# a feature, and the missing feature was read as a new bug.
+#
+# Not corrected automatically: the pin is how a deploy names a revision on
+# purpose, including a deliberate rollback. Said loudly instead.
+if [ "$GIT_REVISION" != unknown ] && [ -f .env ]; then
+  PINNED=$(sed -n 's/^PED_AI_IMAGE=//p' .env | tail -1)
+  case "$PINNED" in
+    '') ;;
+    *"$GIT_REVISION") ;;
+    *)
+      echo >&2
+      echo "WARNING: .env pins PED_AI_IMAGE=$PINNED" >&2
+      echo "         which is NOT the image just built." >&2
+      echo "         'docker compose up -d --no-build' will start the pinned image," >&2
+      echo "         not this build. To deploy what was just built:" >&2
+      echo >&2
+      echo "           sed -i 's|^PED_AI_IMAGE=.*|PED_AI_IMAGE=ped-ai-local:$GIT_REVISION|' .env" >&2
+      echo >&2
+      echo "         Then confirm after starting it:" >&2
+      echo "           curl -fsS http://127.0.0.1:3552/api/build" >&2
+      echo >&2
+      ;;
+  esac
+fi