diff --git a/.github/scripts/close_duplicate_issues.py b/.github/scripts/close_duplicate_issues.py
new file mode 100755
index 00000000000..4e17e1d6d8b
--- /dev/null
+++ b/.github/scripts/close_duplicate_issues.py
@@ -0,0 +1,208 @@
+#!/usr/bin/env python3
+"""
+Detect and close duplicate GitHub issues using title similarity.
+
+Modes:
+  --scan           Compare all open issues against each other (batch)
+  --issue-number N Check a single issue against older open issues
+
+Requires the `gh` CLI to be authenticated.
+"""
+
+import argparse
+import difflib
+import json
+import re
+import subprocess
+import sys
+
+
+def normalize_title(title: str) -> str:
+    """Strip common prefixes, lowercase, and collapse whitespace."""
+    title = re.sub(
+        r"^\[?(bug|feature request|enhancement|question|docs)[:\]]?\s*",
+        "",
+        title,
+        flags=re.IGNORECASE,
+    )
+    return " ".join(title.lower().split())
+
+
+def gh(*args: str) -> str:
+    """Run a gh CLI command and return stdout."""
+    result = subprocess.run(
+        ["gh", *args],
+        capture_output=True,
+        text=True,
+        check=True,
+    )
+    return result.stdout
+
+
+def fetch_open_issues(repo: str | None) -> list[dict]:
+    """Fetch all open issues (excluding PRs) via gh api --paginate."""
+    if repo:
+        endpoint = f"repos/{repo}/issues?state=open&per_page=100&sort=created&direction=asc"
+    else:
+        endpoint = "repos/{owner}/{repo}/issues?state=open&per_page=100&sort=created&direction=asc"
+    cmd = ["api", "--paginate", endpoint]
+
+    raw = gh(*cmd)
+    # gh --paginate concatenates JSON arrays, so we may get multiple arrays
+    issues = []
+    for line in raw.strip().splitlines():
+        line = line.strip()
+        if not line:
+            continue
+        parsed = json.loads(line)
+        if isinstance(parsed, list):
+            issues.extend(parsed)
+        else:
+            issues.append(parsed)
+
+    # Filter out pull requests (they also appear in the issues endpoint)
+    return [i for i in issues if "pull_request" not in i]
+
+
+def close_as_duplicate(
+    issue_number: int, duplicate_of: int, repo: str | None, dry_run: bool
+) -> None:
+    """Close an issue as duplicate of another, adding a comment and label."""
+    repo_args = ["--repo", repo] if repo else []
+
+    if dry_run:
+        print(f"  [DRY RUN] Would close #{issue_number} as duplicate of #{duplicate_of}")
+        return
+
+    # Add comment
+    comment_body = (
+        f"Closing as duplicate of #{duplicate_of}.\n\n"
+        "If you believe this is not a duplicate, please reopen and add context "
+        "explaining how this differs."
+    )
+    gh("issue", "comment", str(issue_number), "--body", comment_body, *repo_args)
+
+    # Add label
+    gh("issue", "edit", str(issue_number), "--add-label", "duplicate", *repo_args)
+
+    # Close with not_planned reason
+    gh(
+        "api",
+        f"repos/{repo or '{owner}/{repo}'}/issues/{issue_number}",
+        "-X",
+        "PATCH",
+        "-f",
+        "state=closed",
+        "-f",
+        "state_reason=not_planned",
+    )
+
+    print(f"  Closed #{issue_number} as duplicate of #{duplicate_of}")
+
+
+def find_duplicate(
+    issue: dict, candidates: list[dict], threshold: float
+) -> dict | None:
+    """Return the first candidate whose normalized title is above threshold."""
+    norm = normalize_title(issue["title"])
+    for candidate in candidates:
+        if candidate["number"] == issue["number"]:
+            continue
+        cand_norm = normalize_title(candidate["title"])
+        ratio = difflib.SequenceMatcher(None, norm, cand_norm).ratio()
+        if ratio >= threshold:
+            return candidate
+    return None
+
+
+def scan_all(issues: list[dict], threshold: float, repo: str | None, dry_run: bool) -> int:
+    """Compare every issue against all older issues. Returns count of duplicates found."""
+    # Sort oldest first
+    issues.sort(key=lambda i: i["number"])
+    closed_count = 0
+
+    for idx, issue in enumerate(issues):
+        older = issues[:idx]
+        if not older:
+            continue
+        dup = find_duplicate(issue, older, threshold)
+        if dup:
+            ratio = difflib.SequenceMatcher(
+                None,
+                normalize_title(issue["title"]),
+                normalize_title(dup["title"]),
+            ).ratio()
+            print(
+                f"#{issue['number']}: \"{issue['title']}\"\n"
+                f"  -> duplicate of #{dup['number']}: \"{dup['title']}\" "
+                f"({ratio:.0%} similar)"
+            )
+            close_as_duplicate(issue["number"], dup["number"], repo, dry_run)
+            closed_count += 1
+
+    return closed_count
+
+
+def check_single(
+    issue_number: int, issues: list[dict], threshold: float, repo: str | None, dry_run: bool
+) -> bool:
+    """Check a single issue against all older open issues. Returns True if duplicate found."""
+    target = None
+    for i in issues:
+        if i["number"] == issue_number:
+            target = i
+            break
+
+    if target is None:
+        print(f"Issue #{issue_number} not found among open issues.")
+        return False
+
+    older = [i for i in issues if i["number"] < issue_number]
+    dup = find_duplicate(target, older, threshold)
+    if dup:
+        ratio = difflib.SequenceMatcher(
+            None,
+            normalize_title(target["title"]),
+            normalize_title(dup["title"]),
+        ).ratio()
+        print(
+            f"#{target['number']}: \"{target['title']}\"\n"
+            f"  -> duplicate of #{dup['number']}: \"{dup['title']}\" "
+            f"({ratio:.0%} similar)"
+        )
+        close_as_duplicate(issue_number, dup["number"], repo, dry_run)
+        return True
+
+    print(f"#{issue_number}: no duplicate found above threshold {threshold}")
+    return False
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(description="Detect and close duplicate GitHub issues")
+    mode = parser.add_mutually_exclusive_group(required=True)
+    mode.add_argument("--scan", action="store_true", help="Scan all open issues")
+    mode.add_argument("--issue-number", type=int, help="Check a single issue number")
+    parser.add_argument("--threshold", type=float, default=0.85, help="Similarity threshold (0-1)")
+    parser.add_argument("--close", action="store_true", help="Actually close duplicates (default is dry-run)")
+    parser.add_argument("--repo", type=str, help="Repository (owner/repo). Auto-detected if omitted.")
+    args = parser.parse_args()
+
+    dry_run = not args.close
+
+    if dry_run:
+        print("=== DRY RUN MODE (pass --close to actually close issues) ===\n")
+
+    print("Fetching open issues...")
+    issues = fetch_open_issues(args.repo)
+    print(f"Found {len(issues)} open issues.\n")
+
+    if args.scan:
+        count = scan_all(issues, args.threshold, args.repo, dry_run)
+        print(f"\nTotal duplicates {'found' if dry_run else 'closed'}: {count}")
+    else:
+        found = check_single(args.issue_number, issues, args.threshold, args.repo, dry_run)
+        sys.exit(0 if found else 0)  # Always exit 0; finding no dup is not an error
+
+
+if __name__ == "__main__":
+    main()
diff --git a/.github/workflows/check_duplicate_issues.yml b/.github/workflows/check_duplicate_issues.yml
index 9477dd2f8e2..6d11ce573eb 100644
--- a/.github/workflows/check_duplicate_issues.yml
+++ b/.github/workflows/check_duplicate_issues.yml
@@ -27,3 +27,26 @@ jobs:
             {{/issues}}
 
             Please review the linked issue(s) to see if they address your concern. If this is not a duplicate, please provide additional context to help us understand the difference.
+
+      - name: Checkout close script
+        if: github.event.action == 'opened'
+        uses: actions/checkout@v4
+        with:
+          sparse-checkout: .github/scripts
+
+      - name: Set up Python
+        if: github.event.action == 'opened'
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+
+      - name: Auto-close if high-confidence duplicate
+        if: github.event.action == 'opened'
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          python3 .github/scripts/close_duplicate_issues.py \
+            --issue-number ${{ github.event.issue.number }} \
+            --repo ${{ github.repository }} \
+            --threshold 0.85 \
+            --close
diff --git a/.github/workflows/scan_duplicate_issues.yml b/.github/workflows/scan_duplicate_issues.yml
new file mode 100644
index 00000000000..eb001db33e1
--- /dev/null
+++ b/.github/workflows/scan_duplicate_issues.yml
@@ -0,0 +1,49 @@
+name: Scan Duplicate Issues (One-Time)
+
+on:
+  workflow_dispatch:
+    inputs:
+      threshold:
+        description: "Similarity threshold (0-1)"
+        required: false
+        default: "0.85"
+      close:
+        description: "Actually close duplicates (false = dry run)"
+        required: false
+        type: boolean
+        default: false
+
+jobs:
+  scan:
+    runs-on: ubuntu-latest
+    permissions:
+      issues: write
+      contents: read
+    steps:
+      - name: Checkout scripts
+        uses: actions/checkout@v4
+        with:
+          sparse-checkout: .github/scripts
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+
+      - name: Scan for duplicate issues
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          INPUT_THRESHOLD: ${{ inputs.threshold }}
+          INPUT_CLOSE: ${{ inputs.close }}
+        run: |
+          CLOSE_FLAG=""
+          if [ "$INPUT_CLOSE" = "true" ]; then
+            CLOSE_FLAG="--close"
+          fi
+          python3 .github/scripts/close_duplicate_issues.py \
+            --scan \
+            --repo ${{ github.repository }} \
+            --threshold "$INPUT_THRESHOLD" \
+            $CLOSE_FLAG