From 02dd1f0a4563c65223546300ed19799665ad2ced Mon Sep 17 00:00:00 2001
From: Christopher Sellers <1@christophersellers.com>
Date: Sun, 25 Oct 2026 22:41:08 -0700
Subject: [PATCH 1/2] ci(vercel): diff ignore step against main merge-base;
 skip guard for non-frontend PRs

The ignore step diffed against VERCEL_GIT_PREVIOUS_SHA (the previous push), so a push that merged main or touched only non-frontend files cancelled the preview on frontend PRs (#3586, #3578, #3553, #3583: 'Canceled by Ignored Build Step'). The guard also failed backend-only PRs (#3599) whose preview is skipped by design.
---
 .github/workflows/vercel-preview-guard.yml | 25 +++++++++++++++++++++-
 frontend/scripts/vercel-ignore-build.sh    | 20 ++++++-----------
 2 files changed, 30 insertions(+), 15 deletions(-)

diff --git a/.github/workflows/vercel-preview-guard.yml b/.github/workflows/vercel-preview-guard.yml
index 21c95ebc0..c80d54b5a 100644
--- a/.github/workflows/vercel-preview-guard.yml
+++ b/.github/workflows/vercel-preview-guard.yml
@@ -15,15 +15,34 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 26
     permissions:
+      contents: read
       deployments: read
       statuses: read
       checks: read
     outputs:
       preview_url: ${{ steps.wait.outputs.preview_url }}
     steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v6
+        with:
+          fetch-depth: 0
+
+      - name: Check frontend scope
+        id: scope
+        env:
+          BASE_SHA: ${{ github.event.pull_request.base.sha }}
+          HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+        run: |
+          MERGE_BASE=$(git merge-base "$BASE_SHA" "$HEAD_SHA")
+          DIFF=$(git diff --name-only "$MERGE_BASE" "$HEAD_SHA" -- frontend/)
+          if [ -n "$DIFF" ]; then
+            echo "frontend=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "frontend=false" >> "$GITHUB_OUTPUT"
+          fi
+
       - name: Wait for the regengine preview
         id: wait
-        if: ${{ !startsWith(github.head_ref, 'dependabot/') }}
+        if: ${{ !startsWith(github.head_ref, 'dependabot/') && steps.scope.outputs.frontend == 'true' }}
         uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9
         env:
           HEAD_SHA: ${{ github.event.pull_request.head.sha }}
@@ -183,6 +202,10 @@ jobs:
             }
             throw new Error(`No ready regengine Vercel preview for ${sha} after 25 minutes`);
 
+      - name: Preview skipped
+        if: ${{ steps.scope.outputs.frontend == 'false' }}
+        run: echo "No frontend changes; Vercel preview intentionally skipped by ignore step."
+
   access-link:
     name: Preview Access Link
     needs: preview
diff --git a/frontend/scripts/vercel-ignore-build.sh b/frontend/scripts/vercel-ignore-build.sh
index 7ce3c5bef..9acb6a95d 100644
--- a/frontend/scripts/vercel-ignore-build.sh
+++ b/frontend/scripts/vercel-ignore-build.sh
@@ -9,21 +9,13 @@ fi
 
 BASE=""
 
-if [ -n "${VERCEL_GIT_PREVIOUS_SHA:-}" ]; then
-  if git cat-file -e "${VERCEL_GIT_PREVIOUS_SHA}^{commit}" 2>/dev/null; then
-    BASE="$VERCEL_GIT_PREVIOUS_SHA"
-  fi
-fi
-
+git fetch --quiet --depth=200 origin main 2>/dev/null || true
+BASE="$(git merge-base HEAD FETCH_HEAD 2>/dev/null || true)"
 if [ -z "$BASE" ]; then
-  git fetch --quiet --depth=100 origin main 2>/dev/null || true
-  BASE="$(git merge-base HEAD FETCH_HEAD 2>/dev/null || true)"
-  if [ -z "$BASE" ]; then
-    if git cat-file -e origin/main^{commit} 2>/dev/null; then
-      BASE="origin/main"
-    elif git rev-parse --verify origin/main >/dev/null 2>&1; then
-      BASE="origin/main"
-    fi
+  if git cat-file -e origin/main^{commit} 2>/dev/null; then
+    BASE="origin/main"
+  elif git rev-parse --verify origin/main >/dev/null 2>&1; then
+    BASE="origin/main"
   fi
 fi
 

From 21d0e81c5797201206b92e409f31ca3ce4fe1c5b Mon Sep 17 00:00:00 2001
From: Christopher Sellers <1@christophersellers.com>
Date: Sun, 25 Oct 2026 22:57:16 -0700
Subject: [PATCH 2/2] ci(vercel): skip Preview Access Link when no frontend
 preview URL

---
 .github/workflows/vercel-preview-guard.yml | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/.github/workflows/vercel-preview-guard.yml b/.github/workflows/vercel-preview-guard.yml
index c80d54b5a..c028222bd 100644
--- a/.github/workflows/vercel-preview-guard.yml
+++ b/.github/workflows/vercel-preview-guard.yml
@@ -21,6 +21,7 @@ jobs:
       checks: read
     outputs:
       preview_url: ${{ steps.wait.outputs.preview_url }}
+      frontend: ${{ steps.scope.outputs.frontend }}
     steps:
       - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v6
         with:
@@ -209,6 +210,7 @@ jobs:
   access-link:
     name: Preview Access Link
     needs: preview
+    if: needs.preview.outputs.frontend == 'true' && needs.preview.outputs.preview_url != ''
     runs-on: ubuntu-latest
     timeout-minutes: 5
     permissions: