diff --git a/.github/workflows/sdk_generation.yaml b/.github/workflows/sdk_generation.yaml
index bacd793..92e9c17 100644
--- a/.github/workflows/sdk_generation.yaml
+++ b/.github/workflows/sdk_generation.yaml
@@ -150,15 +150,39 @@ jobs:
           GH_REPO: ${{ github.repository }}
           BRANCH: ${{ steps.branch.outputs.name }}
         run: |
-          # Failure policy: fail open to human review, never to merge. If the
-          # diff touches anything outside the generated paths the PR is left
-          # unapproved with the offending paths printed. Auto-merge completes
-          # only after the required status checks pass.
-          pr=$(GH_TOKEN="$APP_TOKEN" gh pr list --head "$BRANCH" --state open --json number --jq '.[0].number // empty')
-          if [ -z "$pr" ]; then
+          # Failure policy: fail open to human review, never to merge. Any
+          # gate miss below (wrong base, stale head, non-generated paths)
+          # leaves the PR unapproved for a human. Clearing a stale auto-merge
+          # is the one hard failure: if --disable-auto errors, this step goes
+          # red instead of leaving a rejected head silently mergeable.
+          set -euo pipefail
+
+          deny() {
+            # Auto-merge is cleared before commenting: under set -e a comment
+            # failure must not skip the disable, and a disable failure must
+            # fail the step, not be swallowed.
+            enabled=$(GH_TOKEN="$APP_TOKEN" gh pr view "$pr" --json autoMergeRequest --jq '.autoMergeRequest != null')
+            if [ "$enabled" = "true" ]; then
+              GH_TOKEN="$MERGE_TOKEN" gh pr merge "$pr" --disable-auto
+            fi
+            printf '%s\n' "$1" | GH_TOKEN="$APP_TOKEN" gh pr comment "$pr" --body-file - || true
+            exit 0
+          }
+
+          pr_json=$(GH_TOKEN="$APP_TOKEN" gh pr list --head "$BRANCH" --state open \
+            --json number,baseRefName,headRefOid --jq '.[0] // empty')
+          if [ -z "$pr_json" ]; then
             echo "No open PR for $BRANCH; nothing to approve."
             exit 0
           fi
+          pr=$(echo "$pr_json" | jq -r .number)
+          base=$(echo "$pr_json" | jq -r .baseRefName)
+          head_sha=$(echo "$pr_json" | jq -r .headRefOid)
+
+          if [ "$base" != "main" ]; then
+            echo "Not approving PR #$pr: base is $base, not main."
+            deny "SDK reviewer app: not auto-approving; the PR base is \`$base\`, not \`main\`. Left for human review (policy: fail open to human review, never to merge)."
+          fi
 
           # Only regen PRs authored by the bot app qualify for auto-review.
           # REST is used because it returns the stable "convoy-sdk-bot[bot]"
@@ -166,15 +190,33 @@ jobs:
           author=$(GH_TOKEN="$APP_TOKEN" gh api "repos/$GH_REPO/pulls/$pr" --jq '.user.login')
           if [ "$author" != "convoy-sdk-bot[bot]" ]; then
             echo "Not approving PR #$pr: author is $author, not convoy-sdk-bot[bot]."
-            GH_TOKEN="$APP_TOKEN" gh pr comment "$pr" --body "SDK reviewer app: not auto-approving; PR author is not convoy-sdk-bot[bot]. Left for human review (policy: fail open to human review, never to merge)."
-            exit 0
+            deny "SDK reviewer app: not auto-approving; PR author is not convoy-sdk-bot[bot]. Left for human review (policy: fail open to human review, never to merge)."
+          fi
+
+          # Bind the approval to the commit this run pushed; a concurrent
+          # push to the regen branch means the diff is no longer this run's
+          # generated output.
+          pushed_sha=$(git rev-parse HEAD)
+          if [ "$head_sha" != "$pushed_sha" ]; then
+            echo "Not approving PR #$pr: head $head_sha is not the commit this run pushed."
+            deny "SDK reviewer app: not auto-approving; the PR head is not the commit this generation run pushed. Left for human review (policy: fail open to human review, never to merge)."
+          fi
+
+          # This run committed a real diff, so an empty changed-files listing
+          # is an API anomaly, not a clean PR; it must not count as an
+          # allowlist pass.
+          files=$(GH_TOKEN="$APP_TOKEN" gh api "repos/$GH_REPO/pulls/$pr/files" --paginate \
+            --jq '.[] | .filename, (.previous_filename // empty)')
+          if [ -z "$files" ]; then
+            echo "Not approving PR #$pr: changed-files listing came back empty."
+            deny "SDK reviewer app: not auto-approving; the changed-files listing came back empty for a non-empty regen commit. Left for human review (policy: fail open to human review, never to merge)."
           fi
 
-          # The head branch is the regen branch this run pushed, so the
-          # branch condition holds by construction of the lookup above.
           # Allowlist mirrors scripts/generate.sh: only the api, client, and
-          # models packages are generated; webhook/ is hand-written.
-          bad=$(GH_TOKEN="$APP_TOKEN" gh api "repos/$GH_REPO/pulls/$pr/files" --paginate --jq '.[].filename' \
+          # models packages are generated; webhook/ is hand-written. Renames
+          # are checked on both sides so a file cannot be moved into the
+          # generated tree from outside it.
+          bad=$(printf '%s\n' "$files" \
             | while read -r f; do
                 case "$f" in
                   src/main/java/com/getconvoy/api/*) ;;
@@ -186,22 +228,40 @@ jobs:
           if [ -n "$bad" ]; then
             echo "Not approving PR #$pr: diff touches non-generated paths:"
             echo "$bad"
-            {
-              echo "SDK reviewer app: not auto-approving; the diff touches paths outside the generated allowlist:"
-              echo
-              echo '```'
-              echo "$bad"
-              echo '```'
-              echo
-              echo "Left for human review (policy: fail open to human review, never to merge)."
-            } | GH_TOKEN="$APP_TOKEN" gh pr comment "$pr" --body-file -
-            exit 0
+            deny "$(printf '%s\n' \
+              "SDK reviewer app: not auto-approving; the diff touches paths outside the generated allowlist:" \
+              "" '```' "$bad" '```' "" \
+              "Left for human review (policy: fail open to human review, never to merge).")"
           fi
 
-          GH_TOKEN="$APP_TOKEN" gh api -X POST "repos/$GH_REPO/pulls/$pr/reviews" \
+          review_id=$(GH_TOKEN="$APP_TOKEN" gh api -X POST "repos/$GH_REPO/pulls/$pr/reviews" \
             -f event=APPROVE \
-            -f body="SDK reviewer app: approving a generated-paths-only diff on the regen branch. Auto-merge completes only after required status checks pass."
+            -f commit_id="$head_sha" \
+            -f body="SDK reviewer app: approving a generated-paths-only diff on the regen branch. Auto-merge completes only after required status checks pass." \
+            --jq '.id')
+
+          # Close the validate-then-approve race: a push landing between the
+          # allowlist check and the approval is not covered by
+          # dismiss_stale_reviews (that only dismisses on pushes after the
+          # review), so re-read the head and dismiss our own approval if it
+          # moved off the validated commit.
+          now_sha=$(GH_TOKEN="$APP_TOKEN" gh pr view "$pr" --json headRefOid --jq '.headRefOid')
+          if [ "$now_sha" != "$head_sha" ]; then
+            echo "Head moved from $head_sha to $now_sha during approval; dismissing review."
+            # Best-effort: dismiss_stale_reviews normally dismissed this
+            # approval already when the head moved. The hard gate is deny
+            # below, which clears auto-merge or fails the step; a dismiss
+            # error must not skip it.
+            GH_TOKEN="$APP_TOKEN" gh api -X PUT "repos/$GH_REPO/pulls/$pr/reviews/$review_id/dismissals" \
+              -f message="Head moved during approval; the approved commit is no longer the PR head." \
+              -f event=DISMISS || true
+            deny "SDK reviewer app: approval dismissed; the PR head changed while the review was being submitted. Left for human review (policy: fail open to human review, never to merge)."
+          fi
 
+          # Post-validation head drift is closed by branch protection, not
+          # here: the approval is pinned to the validated commit_id and
+          # dismiss_stale_reviews dismisses it on any later push, so
+          # auto-merge fail-closes back to human review.
           enabled=$(GH_TOKEN="$APP_TOKEN" gh pr view "$pr" --json autoMergeRequest --jq '.autoMergeRequest != null')
           if [ "$enabled" = "true" ]; then
             echo "Auto-merge already enabled on PR #$pr."