ci: split nix into two workflows

nix.yml: PR-only build check.
nix-update-hash.yml: push-to-main hash update via paseo-ai App token.

.github/workflows/nix-update-hash.yml

@@ -0,0 +1,60 @@
+name: Nix Update Hash
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - "nix/**"
+      - "flake.nix"
+      - "flake.lock"
+      - "package.json"
+      - "package-lock.json"
+      - "packages/highlight/**"
+      - "packages/server/**"
+      - "packages/relay/**"
+      - "packages/cli/**"
+      - "scripts/update-nix.sh"
+      - "scripts/fix-lockfile.mjs"
+      - ".github/workflows/nix-update-hash.yml"
+
+permissions:
+  contents: read
+
+jobs:
+  update-hash:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/create-github-app-token@v1
+        id: app-token
+        with:
+          app-id: ${{ secrets.PASEO_BOT_APP_ID }}
+          private-key: ${{ secrets.PASEO_BOT_APP_PRIVATE_KEY }}
+
+      - uses: actions/checkout@v4
+        with:
+          ref: ${{ github.ref }}
+          token: ${{ steps.app-token.outputs.token }}
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: "22"
+          cache: "npm"
+
+      - uses: cachix/install-nix-action@v31
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+
+      - name: Update lockfile + Nix hash if stale
+        run: ./scripts/update-nix.sh
+
+      - name: Build Nix package
+        run: nix build .#default -o result
+
+      - name: Commit hash/lockfile updates
+        run: |
+          git diff --quiet package-lock.json nix/npm-deps.hash && exit 0
+          git config user.name "paseo-ai[bot]"
+          git config user.email "266920839+paseo-ai[bot]@users.noreply.github.com"
+          git add package-lock.json nix/npm-deps.hash
+          git commit -m "fix: update lockfile signatures and Nix hash [skip ci]"
+          git push

.github/workflows/nix.yml

@@ -1,21 +1,6 @@
 name: Nix
 
 on:
-  push:
-    branches: [main]
-    paths:
-      - "nix/**"
-      - "flake.nix"
-      - "flake.lock"
-      - "package.json"
-      - "package-lock.json"
-      - "packages/highlight/**"
-      - "packages/server/**"
-      - "packages/relay/**"
-      - "packages/cli/**"
-      - "scripts/update-nix.sh"
-      - "scripts/fix-lockfile.mjs"
-      - ".github/workflows/nix.yml"
   pull_request:
     branches: [main]
     paths:
@@ -41,7 +26,7 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          ref: ${{ github.event.pull_request.head.sha || github.ref }}
+          ref: ${{ github.event.pull_request.head.sha }}
 
       - uses: actions/setup-node@v4
         with:
@@ -57,42 +42,3 @@ jobs:
 
       - name: Build Nix package
         run: nix build .#default -o result
-
-  update-hash:
-    if: github.event_name == 'push' && github.ref == 'refs/heads/main'
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/create-github-app-token@v1
-        id: app-token
-        with:
-          app-id: ${{ secrets.PASEO_BOT_APP_ID }}
-          private-key: ${{ secrets.PASEO_BOT_APP_PRIVATE_KEY }}
-
-      - uses: actions/checkout@v4
-        with:
-          ref: ${{ github.ref }}
-          token: ${{ steps.app-token.outputs.token }}
-
-      - uses: actions/setup-node@v4
-        with:
-          node-version: "22"
-          cache: "npm"
-
-      - uses: cachix/install-nix-action@v31
-        with:
-          nix_path: nixpkgs=channel:nixos-unstable
-
-      - name: Update lockfile + Nix hash if stale
-        run: ./scripts/update-nix.sh
-
-      - name: Build Nix package
-        run: nix build .#default -o result
-
-      - name: Commit hash/lockfile updates
-        run: |
-          git diff --quiet package-lock.json nix/npm-deps.hash && exit 0
-          git config user.name "paseo-ai[bot]"
-          git config user.email "266920839+paseo-ai[bot]@users.noreply.github.com"
-          git add package-lock.json nix/npm-deps.hash
-          git commit -m "fix: update lockfile signatures and Nix hash [skip ci]"
-          git push