diff --git a/.github/workflows/llms-txt-sync.yml b/.github/workflows/llms-txt-sync.yml
index 518195c0..55e175cb 100644
--- a/.github/workflows/llms-txt-sync.yml
+++ b/.github/workflows/llms-txt-sync.yml
@@ -1,30 +1,94 @@
-# Weekly freshness check for the custom nested llms.txt.
-# If docs.json drifted from the committed llms.txt, the run FAILS with the fix command and
-# GitHub emails you. Then run `python3 scripts/generate_llms_txt.py` locally and open a PR.
+# Daily sync of the custom nested llms.txt to docs.json.
 #
-# Read-only by design: this org blocks GitHub Actions from creating PRs (verified), so we
-# don't attempt one — the run just alerts you when llms.txt needs regenerating.
-name: Check llms.txt freshness
+# The custom llms.txt overrides Mintlify's auto one, so it does NOT self-update when pages
+# change. This job regenerates it daily and lands the result on main via an auto-merging PR.
+#
+# Flow: regenerate -> validation guards -> (if drift) open/refresh a PR -> enable auto-merge.
+# GitHub merges the PR automatically once the required "Mintlify Deployment" check passes.
+#
+# Permissions: this org allows GITHUB_TOKEN to push branches AND create PRs (granted via
+# HD-270). It does NOT allow Actions to push straight to main (the org ruleset on main
+# requires the Mintlify check), so we go through a PR. Auto-merge needs the repo setting
+# "Allow auto-merge" (Settings -> General) ON; until it is, the PR is simply left open for a
+# one-click manual merge (the workflow does not fail).
+name: Sync llms.txt
 
 on:
   schedule:
-    - cron: "17 6 * * 1"      # Mondays 06:17 UTC
+    - cron: "55 6 * * *"     # 06:55 UTC = 14:55 SGT, daily
   workflow_dispatch: {}
 
 permissions:
-  contents: read
+  contents: write
+  pull-requests: write
+
+concurrency:
+  group: llms-txt-sync
+  cancel-in-progress: false
 
 jobs:
-  check:
+  sync:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
         with:
           python-version: "3.x"
-      - name: Verify llms.txt matches docs.json
+
+      - name: Regenerate llms.txt and run validation guards
         run: |
-          python3 scripts/generate_llms_txt.py --check || {
-            echo "::error::llms.txt drifted from docs.json — run 'python3 scripts/generate_llms_txt.py', commit, and open a PR."
-            exit 1
-          }
+          set -euo pipefail
+          out=$(python3 scripts/generate_llms_txt.py)
+          echo "$out"
+
+          # Guard 1: root llms.txt must stay small (AFDocs llms-txt-size pass threshold).
+          root=$(wc -c < llms.txt)
+          [ "$root" -lt 50000 ] || { echo "::error::root llms.txt ${root}B >= 50K — aborting"; exit 1; }
+
+          # Guard 2: every sub-index is well-formed (non-empty, heading + Pages section) and < 50K.
+          fail=0
+          while IFS= read -r f; do
+            [ "$f" = "./llms.txt" ] && continue
+            if [ ! -s "$f" ] || ! head -1 "$f" | grep -q '^# ' || ! grep -q '^## Pages' "$f"; then
+              echo "::error::malformed sub-index: $f"; fail=1
+            fi
+            sz=$(wc -c < "$f")
+            [ "$sz" -lt 50000 ] || { echo "::error::sub-index $f ${sz}B >= 50K"; fail=1; }
+          done < <(find . -name llms.txt -not -path './node_modules/*')
+          [ "$fail" -eq 0 ] || exit 1
+
+          # Guard 3: page count must not have cratered (a corrupt/truncated docs.json).
+          pages=$(printf '%s\n' "$out" | grep -oE 'pages: [0-9]+' | grep -oE '[0-9]+' | head -1)
+          [ "${pages:-0}" -ge 1500 ] || { echo "::error::page count cratered (${pages:-0} < 1500) — aborting"; exit 1; }
+
+          echo "guards OK — root=${root}B pages=${pages}"
+
+      - name: Open/refresh PR and enable auto-merge
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          set -euo pipefail
+          if git diff --quiet; then
+            echo "No llms.txt drift — nothing to do."
+            exit 0
+          fi
+
+          BR="auto/llms-txt-sync"
+          git config user.name "github-actions[bot]"
+          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
+          git checkout -B "$BR"
+          git add -A
+          git commit -m "chore: sync nested llms.txt to docs.json"
+          git push -f origin "$BR"
+
+          # Create the PR if none is open; otherwise the force-push already updated it.
+          if ! gh pr view "$BR" --json state --jq .state 2>/dev/null | grep -q OPEN; then
+            gh pr create --base main --head "$BR" \
+              --title "chore: sync llms.txt" \
+              --body "Automated regeneration of the nested llms.txt from docs.json (\`scripts/generate_llms_txt.py\`). Passed size/parse/page-count guards. Auto-merges once the Mintlify Deployment check passes."
+          fi
+
+          # Enable auto-merge. If the repo setting "Allow auto-merge" is off, this is a no-op
+          # warning and the PR stays open for a manual one-click merge — the workflow still succeeds.
+          gh pr merge "$BR" --squash --auto \
+            || echo "::warning::Could not enable auto-merge (is 'Allow auto-merge' enabled in repo settings?). PR left open for manual merge."