diff --git a/.ciagent/release/deploy.sh b/.ciagent/release/deploy.sh
index 6a5bde1..2d29b67 100755
--- a/.ciagent/release/deploy.sh
+++ b/.ciagent/release/deploy.sh
@@ -1,9 +1,10 @@
 #!/usr/bin/env bash
 # ResearchX release deploy (ciagent release system)
 #
-# Builds the frontend at a given version tag on the Docker host and
-# runs it as a container. Idempotent: re-deploying a version replaces
-# the running container, keeping the previous one as rollback.
+# Builds the frontend and the backend at a given version tag on the
+# Docker host and runs them as two containers. Idempotent: re-deploying
+# a version replaces the running containers, keeping the previous ones
+# as rollback.
 #
 # Usage: bash .ciagent/release/deploy.sh <version>   e.g. v0.1.4
 #
@@ -21,8 +22,14 @@ IMAGE_NAME="researchx"
 CONTAINER_NAME="researchx"
 CONTAINER_PREV="researchx-prev"
 HOST_PORT="3000"
+IMAGE_BACKEND="researchx-backend"
+CONTAINER_BACKEND="researchx-backend"
+CONTAINER_BACKEND_PREV="researchx-backend-prev"
+HOST_PORT_BACKEND="8000"
+BACKEND_DATA_DIR="/var/lib/researchx"
 REMOTE_BASE="/opt/researchx"
 HEALTH_PATH="/ask"
+BACKEND_HEALTH_PATH="/healthz"
 HEALTH_RETRIES=15
 HEALTH_INTERVAL=2
 # -----------------------------------------------------------------------
@@ -38,6 +45,7 @@ VERSION="$1"
 
 # ---- dependency checks --------------------------------------------------
 command -v ssh >/dev/null || die "ssh not found" 2
+command -v uv >/dev/null || die "uv not found (backend gates need it: pip install uv)" 2
 
 # ---- secrets (env file ONLY) -------------------------------------------
 [ -f "$SECRETS_FILE" ] || die "secrets file missing: $SECRETS_FILE" 2
@@ -156,37 +164,72 @@ if [ "$(git -C "$REPO_ROOT" rev-parse HEAD)" != "$TAG_COMMIT" ]; then
   WORKTREE=$(mktemp -d)
   git -C "$REPO_ROOT" worktree add --detach "$WORKTREE" "$TAG_COMMIT" >/dev/null
   trap 'git -C "$REPO_ROOT" worktree remove --force "$WORKTREE" 2>/dev/null || true' EXIT
-  BUILD_DIR="$WORKTREE/frontend"
+  BUILD_ROOT="$WORKTREE"
 else
-  BUILD_DIR="$REPO_ROOT/frontend"
+  BUILD_ROOT="$REPO_ROOT"
 fi
+BUILD_DIR="$BUILD_ROOT/frontend"
+BACKEND_DIR="$BUILD_ROOT/backend"
 
 (cd "$BUILD_DIR" && pnpm install --frozen-lockfile >/dev/null 2>&1)
 (cd "$BUILD_DIR" && pnpm typecheck >/dev/null) || die "typecheck failed at $VERSION" 3
 (cd "$BUILD_DIR" && pnpm lint >/dev/null) || die "lint failed at $VERSION" 3
 (cd "$BUILD_DIR" && pnpm test >/dev/null 2>&1) || die "tests failed at $VERSION" 3
 (cd "$BUILD_DIR" && pnpm build >/dev/null 2>&1) || die "build failed at $VERSION" 3
-log "gates passed: typecheck, lint, test, build"
+log "frontend gates passed: typecheck, lint, test, build"
 cd "$REPO_ROOT"
 
+# Backend gates: the repo's own commands, same as the CI backend job
+# (.gitea/workflows/ci.yml), run from the committed lockfile.
+(cd "$BACKEND_DIR" && uv sync --frozen >/dev/null 2>&1) || die "backend dependency sync failed at $VERSION" 3
+(cd "$BACKEND_DIR" && uv run ruff check src tests >/dev/null) || die "backend ruff failed at $VERSION" 3
+(cd "$BACKEND_DIR" && uv run mypy src >/dev/null) || die "backend mypy failed at $VERSION" 3
+(cd "$BACKEND_DIR" && uv run pytest >/dev/null) || die "backend pytest failed at $VERSION" 3
+log "backend gates passed: ruff, mypy, pytest"
+
 # ---- remote host prep ----------------------------------------------------
 log "connecting to $DEPLOY_USER@${DEPLOY_HOST%%:*} and preparing $REMOTE_BASE"
 SSH "mkdir -p '$REMOTE_BASE/releases/$BASE_VERSION'" || die "cannot reach host or create remote dir" 4
 SSH "command -v docker >/dev/null" || die "docker not found on host" 4
 
 # ---- sync source ---------------------------------------------------------
-log "syncing source to host ($REMOTE_BASE/releases/$BASE_VERSION) via $SYNC_TRANSPORT"
-sync_source "$BUILD_DIR" "$REMOTE_BASE/releases/$BASE_VERSION" \
-  || die "source sync failed" 4
+RELEASE_DIR="$REMOTE_BASE/releases/$BASE_VERSION"
+log "syncing source to host ($RELEASE_DIR) via $SYNC_TRANSPORT"
+sync_source "$BUILD_DIR" "$RELEASE_DIR/frontend" || die "frontend source sync failed" 4
+sync_source "$BACKEND_DIR" "$RELEASE_DIR/backend" || die "backend source sync failed" 4
 
 # ---- remote build --------------------------------------------------------
-log "building docker image $IMAGE_NAME:$VERSION on host (this takes a few minutes)"
-SSH "cd '$REMOTE_BASE/releases/$BASE_VERSION' && \
+log "building docker images $IMAGE_BACKEND:$VERSION and $IMAGE_NAME:$VERSION on host (this takes a few minutes)"
+SSH "cd '$RELEASE_DIR/backend' && \
+  docker build -t '$IMAGE_BACKEND:$VERSION' -t '$IMAGE_BACKEND:latest' ." \
+  || die "backend docker build failed on host" 4
+SSH "cd '$RELEASE_DIR/frontend' && \
   docker build -t '$IMAGE_NAME:$VERSION' -t '$IMAGE_NAME:latest' ." \
-  || die "docker build failed on host" 4
+  || die "frontend docker build failed on host" 4
 
 # ---- swap container ------------------------------------------------------
-log "swapping container (previous kept as $CONTAINER_PREV for rollback)"
+log "swapping backend container (previous kept as $CONTAINER_BACKEND_PREV for rollback)"
+SSH "
+  docker rm -f '$CONTAINER_BACKEND_PREV' 2>/dev/null || true
+  if docker ps -a --format '{{.Names}}' | grep -qx '$CONTAINER_BACKEND'; then
+    docker rename '$CONTAINER_BACKEND' '$CONTAINER_BACKEND_PREV'
+    docker stop '$CONTAINER_BACKEND_PREV' >/dev/null 2>&1 || true
+  fi
+  mkdir -p '$BACKEND_DATA_DIR'
+  # The container runs as the image's non-root user and a bind mount
+  # SHADOWS the image's own (correctly owned) /var/lib/researchx, so a
+  # root-owned host dir makes every write to the data root (users.json,
+  # sessions.json, keys/) fail with EACCES while /healthz still answers
+  # 200. Take the owner from the image itself.
+  chown -R \$(docker run --rm --entrypoint stat '$IMAGE_BACKEND:$VERSION' -c '%u:%g' /var/lib/researchx) '$BACKEND_DATA_DIR'
+  docker run -d --name '$CONTAINER_BACKEND' --restart unless-stopped \
+    -p '$HOST_PORT_BACKEND:8000' \
+    -v '$BACKEND_DATA_DIR:$BACKEND_DATA_DIR' \
+    -e RESEARCHX_DATA_DIR='$BACKEND_DATA_DIR' \
+    '$IMAGE_BACKEND:$VERSION'
+" || die "backend docker run failed" 5
+
+log "swapping frontend container (previous kept as $CONTAINER_PREV for rollback)"
 SSH "
   docker rm -f '$CONTAINER_PREV' 2>/dev/null || true
   if docker ps -a --format '{{.Names}}' | grep -qx '$CONTAINER_NAME'; then
@@ -195,19 +238,39 @@ SSH "
   fi
   docker run -d --name '$CONTAINER_NAME' --restart unless-stopped \
     -p '$HOST_PORT:3000' '$IMAGE_NAME:$VERSION'
-" || die "docker run failed" 5
+" || die "frontend docker run failed" 5
 
 # ---- health check ---------------------------------------------------------
-log "health-checking http://$DEPLOY_HOST:$HOST_PORT$HEALTH_PATH (retries: $HEALTH_RETRIES)"
+log "health-checking backend http://$DEPLOY_HOST:$HOST_PORT_BACKEND$BACKEND_HEALTH_PATH (retries: $HEALTH_RETRIES)"
+i=0
+while [ "$i" -lt "$HEALTH_RETRIES" ]; do
+  if SSH "curl -sf -o /dev/null --max-time 5 'http://127.0.0.1:$HOST_PORT_BACKEND$BACKEND_HEALTH_PATH'"; then
+    log "backend healthy after $((i + 1)) check(s)"
+    break
+  fi
+  i=$((i + 1))
+  sleep "$HEALTH_INTERVAL"
+done
+[ "$i" -lt "$HEALTH_RETRIES" ] || die "backend container did not become healthy within $((HEALTH_RETRIES * HEALTH_INTERVAL))s" 5
+
+# The health check above is a GET: it proves the app answers, not that it
+# can persist. Probe the write path the auth/key stores use, so a
+# mis-owned data root fails the deploy instead of the first signup.
+log "checking the backend can write its data root"
+SSH "docker exec '$CONTAINER_BACKEND' sh -c 'touch \"\$RESEARCHX_DATA_DIR/.write-probe\" && rm -f \"\$RESEARCHX_DATA_DIR/.write-probe\"'" \
+  || die "backend data root is not writable by the container user" 5
+
+log "health-checking frontend http://$DEPLOY_HOST:$HOST_PORT$HEALTH_PATH (retries: $HEALTH_RETRIES)"
 i=0
 while [ "$i" -lt "$HEALTH_RETRIES" ]; do
   if SSH "curl -sf -o /dev/null --max-time 5 'http://127.0.0.1:$HOST_PORT$HEALTH_PATH'"; then
-    log "healthy after $((i + 1)) check(s)"
-    log "RELEASED: $VERSION — http://${DEPLOY_HOST%%:*}:$HOST_PORT (container $CONTAINER_NAME)"
-    log "rollback: ssh $DEPLOY_USER@${DEPLOY_HOST%%:*} 'docker stop $CONTAINER_NAME; docker rename $CONTAINER_PREV $CONTAINER_NAME; docker start $CONTAINER_NAME'"
+    log "frontend healthy after $((i + 1)) check(s)"
+    log "RELEASED: $VERSION — http://${DEPLOY_HOST%%:*}:$HOST_PORT (containers $CONTAINER_NAME, $CONTAINER_BACKEND)"
+    log "backend: http://${DEPLOY_HOST%%:*}:$HOST_PORT_BACKEND$BACKEND_HEALTH_PATH (container $CONTAINER_BACKEND)"
+    log "rollback: ssh $DEPLOY_USER@${DEPLOY_HOST%%:*} 'docker stop $CONTAINER_NAME $CONTAINER_BACKEND; docker rename $CONTAINER_PREV $CONTAINER_NAME; docker rename $CONTAINER_BACKEND_PREV $CONTAINER_BACKEND; docker start $CONTAINER_NAME $CONTAINER_BACKEND'"
     exit 0
   fi
   i=$((i + 1))
   sleep "$HEALTH_INTERVAL"
 done
-die "container did not become healthy within $((HEALTH_RETRIES * HEALTH_INTERVAL))s" 5
\ No newline at end of file
+die "frontend container did not become healthy within $((HEALTH_RETRIES * HEALTH_INTERVAL))s" 5
\ No newline at end of file