diff --git a/.github/workflows/diff-pr.yml b/.github/workflows/diff-pr.yml
index 17b0abf..d8fbabb 100644
--- a/.github/workflows/diff-pr.yml
+++ b/.github/workflows/diff-pr.yml
@@ -17,10 +17,18 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
+          ref: ${{ github.event.pull_request.head.sha }}
           fetch-depth: 0
 
+      - name: merge base branch
+        run: |
+          git config user.email "ci@localhost"
+          git config user.name "CI"
+          git fetch origin ${{ github.event.pull_request.base.ref }}
+          git merge --no-edit origin/${{ github.event.pull_request.base.ref }}
+
       - name: worktree base for diff
-        run: git worktree add "$RUNNER_TEMP/base" "${{ github.event.pull_request.base.sha }}"
+        run: git worktree add "$RUNNER_TEMP/base" "origin/${{ github.event.pull_request.base.ref }}"
 
       - name: build closures and render diff
         run: |
diff --git a/.github/workflows/flake-update.yml b/.github/workflows/flake-update.yml
index 27ec96d..2baadce 100644
--- a/.github/workflows/flake-update.yml
+++ b/.github/workflows/flake-update.yml
@@ -5,21 +5,19 @@ on:
     - cron: "17 4 * * *"
   workflow_dispatch:
 
-permissions:
-  contents: write
-  pull-requests: write
-
 jobs:
   update:
     runs-on: nix
     steps:
       - uses: actions/checkout@v4
+        with:
+          persist-credentials: false
 
       - run: nix flake update -L
 
       - name: open/update PR
         env:
-          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          GH_TOKEN: ${{ secrets.BOT_TOKEN }}
           API: ${{ github.api_url }}
           REPO: ${{ github.repository }}
         run: |
diff --git a/ci.py b/ci.py
index 61076ea..a3d8db0 100644
--- a/ci.py
+++ b/ci.py
@@ -8,6 +8,7 @@ import re
 import subprocess
 import subprocess_tee
 import sys
+import urllib.error
 import urllib.request
 from collections import Counter
 from pathlib import Path
@@ -26,6 +27,10 @@ def git(*args, check=True):
     return run("git", *args, check=check, capture_output=True)
 
 
+class GiteaError(Exception):
+    pass
+
+
 def gitea(method, path, body=None):
     url = f'{os.environ["API"]}/repos/{os.environ["REPO"]}{path}'
     data = json.dumps(body).encode() if body is not None else None
@@ -37,7 +42,11 @@ def gitea(method, path, body=None):
         with urllib.request.urlopen(req) as resp:
             raw = resp.read()
     except urllib.error.HTTPError as e:
-        sys.exit(f"gitea {method} {path}: {e.code} {e.reason}\n{e.read().decode()}")
+        try:
+            detail = json.loads(e.read()).get("message", e.reason)
+        except (json.JSONDecodeError, UnicodeDecodeError):
+            detail = e.reason
+        raise GiteaError(f"{method} {path}: {e.code} {detail}") from None
     return json.loads(raw) if raw else None
 
 
@@ -466,16 +475,24 @@ def open_pr(args):
 
     host = os.environ["API"].removesuffix("/api/v1")
     auth = base64.b64encode(f'token:{os.environ["GH_TOKEN"]}'.encode()).decode()
-    git("-c", f"http.extraHeader=Authorization: Basic {auth}",
-        "push", "-f", f'{host}/{os.environ["REPO"]}.git', f"HEAD:{args.branch}")
+    push = git("-c", f"http.extraHeader=Authorization: Basic {auth}",
+               "push", "-f", f'{host}/{os.environ["REPO"]}.git', f"HEAD:{args.branch}",
+               check=False)
+    if push.returncode != 0:
+        raise RuntimeError(f"git push failed:\n{push.stderr}")
 
-    owner = os.environ["REPO"].split("/")[0]
-    if gitea("GET", f"/pulls?state=open&head={owner}:{args.branch}"):
+    pulls = gitea("GET", f"/pulls?state=open&base_branch={args.base}")
+    existing = next((pr for pr in pulls if pr["head"]["ref"] == args.branch), None)
+    if existing:
+        print(f"PR #{existing['number']} already open, pushed update")
         return
     labels = [label_id(args.label)] if args.label else []
-    gitea("POST", "/pulls",
-          {"title": args.title, "head": args.branch, "base": args.base,
-           "body": Path(args.body_file).read_text(), "labels": labels})
+    pr = gitea("POST", "/pulls",
+               {"title": args.title, "head": args.branch, "base": args.base,
+                "body": Path(args.body_file).read_text(), "labels": labels})
+    if not pr or "number" not in pr:
+        raise GiteaError(f"POST /pulls: unexpected response: {json.dumps(pr)}")
+    print(f"opened PR #{pr['number']}")
 
 
 def main():
diff --git a/configuration.nix b/configuration.nix
index 7461aba..da77608 100644
--- a/configuration.nix
+++ b/configuration.nix
@@ -5,6 +5,7 @@
   hostInfo,
   customPkgs,
   flakeRev,
+  deployLabel,
   ...
 }:
 let
@@ -62,14 +63,7 @@ in
 
   time.timeZone = "UTC";
   system.stateVersion = "26.05";
-  system.nixos.label =
-    let
-      labelFile = ./.nixos-label;
-    in
-    if builtins.pathExists labelFile then
-      lib.removeSuffix "\n" (builtins.readFile labelFile)
-    else
-      flakeRev;
+  system.nixos.label = if deployLabel != null then deployLabel else flakeRev;
 
   nix = {
     settings = {
diff --git a/flake.lock b/flake.lock
index 0c21124..6a89746 100644
--- a/flake.lock
+++ b/flake.lock
@@ -1,5 +1,17 @@
 {
   "nodes": {
+    "deploy-label": {
+      "flake": false,
+      "locked": {
+        "path": "./misc/deploy-label",
+        "type": "path"
+      },
+      "original": {
+        "path": "./misc/deploy-label",
+        "type": "path"
+      },
+      "parent": []
+    },
     "flake-utils": {
       "inputs": {
         "systems": "systems"
@@ -47,11 +59,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1782711974,
-        "narHash": "sha256-ju0/qU6ZGqRxc5yDhuljrprG0BSPgguc8Kz3txktSjI=",
+        "lastModified": 1790093442,
+        "narHash": "sha256-n0t8bN5x0NU9Ugwa/Vr0bcnA4YKA3YmyVg+Vp7t70HU=",
         "owner": "Floweynt",
         "repo": "monumenta-charm-eval",
-        "rev": "1aa8b532975679787f7c5bed180fd7fc0da6b905",
+        "rev": "0aaac697ff4d65e7af2fc9bebaf4f479d7c763b6",
         "type": "github"
       },
       "original": {
@@ -63,11 +75,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1789546076,
-        "narHash": "sha256-zVxLZiSnmaaPLwnhj7pwmqe3axBg/C6nG5JZsJMh2g4=",
+        "lastModified": 1790046670,
+        "narHash": "sha256-MYiI+CzL0tuWgRPjGsKCDHqYs2T3OzMlMQWOYWG0qso=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "b1b875982b17dabde9b4a37f3e229e74913e6db3",
+        "rev": "6774f7bc253789b113a4f39285dc0fa100abeacc",
         "type": "github"
       },
       "original": {
@@ -79,6 +91,7 @@
     },
     "root": {
       "inputs": {
+        "deploy-label": "deploy-label",
         "microvm": "microvm",
         "mtce": "mtce",
         "nixpkgs": "nixpkgs"
diff --git a/flake.nix b/flake.nix
index 541b7fc..95b7e43 100644
--- a/flake.nix
+++ b/flake.nix
@@ -7,6 +7,8 @@
     mtce.inputs.nixpkgs.follows = "nixpkgs";
     microvm.url = "github:microvm-nix/microvm.nix";
     microvm.inputs.nixpkgs.follows = "nixpkgs";
+    deploy-label.url = "path:./misc/deploy-label";
+    deploy-label.flake = false;
   };
 
   outputs =
@@ -15,6 +17,7 @@
       nixpkgs,
       mtce,
       microvm,
+      deploy-label,
       ...
     }:
     let
@@ -23,6 +26,12 @@
       pkgs = import nixpkgs { inherit system; };
 
       flakeRev = self.shortRev or self.dirtyShortRev or "unknown";
+      deployLabel =
+        let
+          labelFile = "${deploy-label}/label";
+          raw = lib.removeSuffix "\n" (builtins.readFile labelFile);
+        in
+        if raw != "" then raw else null;
 
       customPkgs = {
         hopper-rs = pkgs.callPackage ./packages/hopper-rs.nix { };
@@ -56,7 +65,7 @@
 
       specialArgsFor = hostName: {
         hostInfo = hostInfoFor hostName;
-        inherit inputs customPkgs flakeRev;
+        inherit inputs customPkgs flakeRev deployLabel;
       };
 
       hostDefFor =
diff --git a/misc/deploy-label/label b/misc/deploy-label/label
new file mode 100644
index 0000000..e69de29
diff --git a/modules/autodeploy.nix b/modules/autodeploy.nix
index 2d8c7d3..f49c766 100644
--- a/modules/autodeploy.nix
+++ b/modules/autodeploy.nix
@@ -38,7 +38,7 @@ in
       type = lib.types.listOf lib.types.str;
       default = [ ];
     };
-    
+
     repoOwner = lib.mkOption {
       type = lib.types.str;
       description = "User that owns the configuration checkout";
diff --git a/scripts/server-autodeploy.sh b/scripts/server-autodeploy.sh
index f2559f2..54a236c 100644
--- a/scripts/server-autodeploy.sh
+++ b/scripts/server-autodeploy.sh
@@ -48,13 +48,17 @@ runas git tag -v "$latest" || {
 sha=$(runas git rev-list -1 "$latest")
 report_status "pending" "deploying $latest" "$sha"
 
+label_dir=$(mktemp -d)
+echo "$latest" > "$label_dir/label"
 flake_url="git+${GITEA_URL}/${GITEA_REPO}?ref=refs/tags/${latest}&rev=${sha}#$HOSTNAME"
 
-if nixos-rebuild switch --flake "$flake_url"; then
+if nixos-rebuild switch --flake "$flake_url" --override-input deploy-label "path:$label_dir"; then
+  rm -rf "$label_dir"
   echo "$latest" > "$STATE_DIR/tag"
   report_status "success" "deployed $latest" "$sha"
   echo "deployed $latest"
 else
+  rm -rf "$label_dir"
   report_status "failure" "nixos-rebuild failed" "$sha"
   exit 1
 fi