diff --git a/.gitea/workflows/contributor-check.yml b/.gitea/workflows/contributor-check.yml
index c246b6de..8900c40c 100644
--- a/.gitea/workflows/contributor-check.yml
+++ b/.gitea/workflows/contributor-check.yml
@@ -22,6 +22,10 @@ jobs:
           set -euo pipefail
           BASE="${{ github.event.pull_request.base.sha }}"
           HEAD="${{ github.event.pull_request.head.sha }}"
+          # Ensure the base ref exists (Gitea checkout may not fetch it).
+          if ! git cat-file -e "$BASE" 2>/dev/null; then
+            git fetch --depth=100 origin main || true
+          fi
           changed="$(git diff --name-only "$BASE" "$HEAD")"
           printf '%s\n' "$changed"
           if printf '%s\n' "$changed" | grep -Eq '(^|/).*\.py$'; then
@@ -37,11 +41,26 @@ jobs:
       - name: Check for unmapped contributor emails
         if: steps.changes.outputs.run == 'true'
         run: |
-          # Get the merge base between this PR and main
-          MERGE_BASE=$(git merge-base origin/main HEAD)
+          set -euo pipefail
+          BASE="${{ github.event.pull_request.base.sha }}"
+          HEAD="${{ github.event.pull_request.head.sha }}"
+
+          # Ensure the base ref exists (Gitea checkout may not fetch it).
+          if ! git cat-file -e "$BASE" 2>/dev/null; then
+            git fetch --depth=100 origin main || true
+          fi
+
+          # If we still can't resolve the base, fall back to merge-base.
+          if ! git cat-file -e "$BASE" 2>/dev/null; then
+            BASE=$(git merge-base origin/main HEAD 2>/dev/null || echo "")
+            if [ -z "$BASE" ]; then
+              echo "❌ Cannot determine merge base — cannot verify attribution."
+              exit 1
+            fi
+          fi
 
           # Find any new author emails in this PR's commits
-          NEW_EMAILS=$(git log ${MERGE_BASE}..HEAD --format='%ae' --no-merges | sort -u)
+          NEW_EMAILS=$(git log "${BASE}..${HEAD}" --format='%ae' --no-merges | sort -u)
 
           if [ -z "$NEW_EMAILS" ]; then
             echo "No new commits to check."
diff --git a/.gitea/workflows/tests.yml b/.gitea/workflows/tests.yml
index c353b82c..39a322b3 100644
--- a/.gitea/workflows/tests.yml
+++ b/.gitea/workflows/tests.yml
@@ -44,8 +44,11 @@ jobs:
             git fetch --depth=100 origin main || true
           fi
           if ! git cat-file -e "$base" 2>/dev/null; then
-            echo "run=true" >> "$GITHUB_OUTPUT"
-            exit 0
+            base=$(git merge-base origin/main HEAD 2>/dev/null || echo "")
+            if [ -z "$base" ]; then
+              echo "run=true" >> "$GITHUB_OUTPUT"
+              exit 0
+            fi
           fi
           changed="$(git diff --name-only "$base" "$head")"
           printf '%s\n' "$changed"
@@ -134,8 +137,11 @@ jobs:
             git fetch --depth=100 origin main || true
           fi
           if ! git cat-file -e "$base" 2>/dev/null; then
-            echo "run=true" >> "$GITHUB_OUTPUT"
-            exit 0
+            base=$(git merge-base origin/main HEAD 2>/dev/null || echo "")
+            if [ -z "$base" ]; then
+              echo "run=true" >> "$GITHUB_OUTPUT"
+              exit 0
+            fi
           fi
           changed="$(git diff --name-only "$base" "$head")"
           printf '%s\n' "$changed"