Add AI-powered duplicate issue detection system

.github/prompts/dedupe.prompt.yml

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+messages:
+  - role: system
+    content: You are a duplicate issue detector. You have access to GitHub MCP tools to read and search issues.
+  - role: user
+    content: |
+      Find up to 3 likely duplicate issues for issue #{{issue_number}} in the acacode/swagger-typescript-api repository.
+
+      To do this, follow these steps precisely:
+
+      1. Read issue #{{issue_number}} including its comments. Check if the issue (a) is closed, (b) does not need to be deduped (e.g. because it is broad product feedback without a specific solution, or positive feedback), or (c) already has a duplicates comment containing `<!-- ai-duplicate-check -->`. If so, do not proceed — return an empty duplicates array.
+      2. Summarize the issue: what is the core problem, symptoms, and affected features.
+      3. Search for duplicates of this issue using diverse keywords and search approaches based on the summary. Try at least 5 different search queries to maximize coverage.
+      4. Filter out false positives that are likely not actually duplicates of the original issue. If there are no duplicates remaining, return an empty duplicates array.
+      5. Return the remaining duplicate issue numbers (up to 3), ranked by confidence (highest first).
+model: openai/gpt-4o
+responseFormat: json_schema
+jsonSchema: |-
+  {
+    "name": "duplicate_detection_result",
+    "strict": true,
+    "schema": {
+      "type": "object",
+      "properties": {
+        "duplicates": {
+          "type": "array",
+          "items": {
+            "type": "integer"
+          },
+          "description": "Issue numbers of potential duplicates, ranked by confidence (highest first). Empty array if no duplicates found or issue should be skipped."
+        }
+      },
+      "additionalProperties": false,
+      "required": ["duplicates"]
+    }
+  }

.github/workflows/auto-close-duplicates.yml

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+name: Auto-Close Duplicate Issues
+
+on:
+  schedule:
+    - cron: 0 9 * * *
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  issues: write
+
+jobs:
+  auto-close:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+
+    steps:
+      - name: Checkout tree
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - name: Set-up Mise
+        uses: jdx/mise-action@6d1e696aa24c1aa1bcc1adea0212707c71ab78a8 # v3.6.1
+        with:
+          cache: false
+      - name: Run auto-close script
+        run: bun run scripts/auto-close-duplicates.ts
+        env:
+          GITHUB_TOKEN: ${{ github.token }}
+          GITHUB_REPOSITORY_OWNER: ${{ github.repository_owner }}
+          GITHUB_REPOSITORY_NAME: ${{ github.event.repository.name }}

.github/workflows/backfill-duplicate-detection.yml

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+name: Backfill Duplicate Detection
+
+on:
+  workflow_dispatch:
+    inputs:
+      days_back:
+        description: Number of days to look back for issues
+        required: false
+        default: "90"
+      dry_run:
+        description: Run in dry-run mode (only log, do not trigger workflows)
+        required: false
+        default: "true"
+        type: choice
+        options:
+          - "true"
+          - "false"
+
+permissions:
+  contents: read
+  issues: read
+  actions: write
+
+jobs:
+  backfill:
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+
+    steps:
+      - name: Checkout tree
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - name: Set-up Mise
+        uses: jdx/mise-action@6d1e696aa24c1aa1bcc1adea0212707c71ab78a8 # v3.6.1
+        with:
+          cache: false
+      - name: Run backfill script
+        run: ./scripts/backfill-duplicate-detection.ts
+        env:
+          GITHUB_TOKEN: ${{ github.token }}
+          GITHUB_REPOSITORY_OWNER: ${{ github.repository_owner }}
+          GITHUB_REPOSITORY_NAME: ${{ github.event.repository.name }}
+          DAYS_BACK: ${{ github.event.inputs.days_back }}
+          DRY_RUN: ${{ github.event.inputs.dry_run }}

.github/workflows/dedupe-issues.yml

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+name: Issue Dedupe
+
+on:
+  issues:
+    types:
+      - opened
+  workflow_dispatch:
+    inputs:
+      issue_number:
+        description: Issue number to check for duplicates
+        required: true
+        type: number
+
+permissions:
+  contents: read
+  issues: write
+  models: read
+
+jobs:
+  dedupe:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+
+    steps:
+      - name: Checkout tree
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+
+      - name: AI duplicate detection
+        uses: actions/ai-inference@a380166897b5408b8fb7dddd148142794cb5624a # v2.0.6
+        id: ai
+        with:
+          prompt-file: .github/prompts/dedupe.prompt.yml
+          input: |
+            issue_number: ${{ github.event.issue.number || inputs.issue_number }}
+          enable-github-mcp: true
+
+      - name: Post comment if duplicates found
+        run: |
+          DUPLICATES=$(echo "$AI_RESPONSE" | jq -r '.duplicates | map(tostring) | join(" ")')
+
+          if [ -z "$DUPLICATES" ] || [ "$DUPLICATES" = "null" ]; then
+            echo "No duplicates found"
+            exit 0
+          fi
+
+          echo "Duplicates found: $DUPLICATES"
+          ./scripts/comment-on-duplicates.sh --base-issue "$ISSUE_NUMBER" --potential-duplicates $DUPLICATES
+        env:
+          AI_RESPONSE: ${{ steps.ai.outputs.response }}
+          GH_TOKEN: ${{ github.token }}
+          ISSUE_NUMBER: ${{ github.event.issue.number || inputs.issue_number }}

scripts/auto-close-duplicates.ts

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+#!/usr/bin/env bun
+
+import { consola } from "consola";
+import type {
+  GitHubComment,
+  GitHubIssue,
+  GitHubReaction,
+} from "./lib/github.js";
+import {
+  API_BASE,
+  fetchAllPages,
+  fetchGitHub,
+  GITHUB_REPOSITORY_NAME,
+  GITHUB_REPOSITORY_OWNER,
+  getIssueComments,
+} from "./lib/github.js";
+
+const THREE_DAYS_MS = 3 * 24 * 60 * 60 * 1000;
+
+async function getOpenIssuesOlderThan3Days(): Promise<GitHubIssue[]> {
+  const threeDaysAgo = new Date(Date.now() - THREE_DAYS_MS);
+  const url = `${API_BASE}/issues?state=open&per_page=100&sort=created&direction=asc`;
+
+  const issues = await fetchAllPages<GitHubIssue>(url);
+
+  return issues.filter((issue) => {
+    if (issue.pull_request) return false;
+    return new Date(issue.created_at) < threeDaysAgo;
+  });
+}
+
+async function getCommentReactions(
+  commentId: number,
+): Promise<GitHubReaction[]> {
+  const url = `${API_BASE}/issues/comments/${commentId}/reactions?per_page=100`;
+  return fetchAllPages<GitHubReaction>(url);
+}
+
+async function closeIssue(issueNumber: number, reason: string): Promise<void> {
+  await fetchGitHub(`${API_BASE}/issues/${issueNumber}/labels`, {
+    method: "POST",
+    body: JSON.stringify({ labels: ["duplicate"] }),
+  });
+
+  await fetchGitHub(`${API_BASE}/issues/${issueNumber}`, {
+    method: "PATCH",
+    body: JSON.stringify({
+      state: "closed",
+      state_reason: "not_planned",
+    }),
+  });
+
+  await fetchGitHub(`${API_BASE}/issues/${issueNumber}/comments`, {
+    method: "POST",
+    body: JSON.stringify({
+      body: reason,
+    }),
+  });
+}
+
+async function hasActivityAfterComment(
+  issue: GitHubIssue,
+  botCommentDate: Date,
+): Promise<boolean> {
+  const comments = await getIssueComments(issue.number);
+
+  const laterComments = comments.filter((comment) => {
+    if (comment.user?.login.endsWith("[bot]")) return false;
+    const commentDate = new Date(comment.created_at);
+    return commentDate > botCommentDate;
+  });
+
+  return laterComments.length > 0;
+}
+
+async function hasCreatorThumbsDown(
+  issue: GitHubIssue,
+  botComment: GitHubComment,
+): Promise<boolean> {
+  if (!issue.user) {
+    return false;
+  }
+
+  const reactions = await getCommentReactions(botComment.id);
+
+  return reactions.some(
+    (reaction) =>
+      reaction.content === "-1" && reaction.user?.login === issue.user?.login,
+  );
+}
+
+async function main(): Promise<void> {
+  consola.info("Starting auto-close duplicates script...");
+  consola.info(
+    `Repository: ${GITHUB_REPOSITORY_OWNER}/${GITHUB_REPOSITORY_NAME}`,
+  );
+
+  const issues = await getOpenIssuesOlderThan3Days();
+  consola.info(`Found ${issues.length} open issues older than 3 days`);
+
+  let processedCount = 0;
+  let closedCount = 0;
+
+  for (const issue of issues) {
+    processedCount++;
+    consola.info(`Processing issue #${issue.number}: ${issue.title}`);
+
+    const comments = await getIssueComments(issue.number);
+
+    const botComment = comments.find(
+      (comment) =>
+        comment.user?.login === "github-actions[bot]" &&
+        comment.body.includes("<!-- ai-duplicate-check -->"),
+    );
+
+    if (!botComment) {
+      consola.info(`  No duplicate bot comment found, skipping`);
+      await new Promise((resolve) => setTimeout(resolve, 1000));
+      continue;
+    }
+
+    const botCommentDate = new Date(botComment.created_at);
+    const now = new Date();
+    const timeSinceComment = now.getTime() - botCommentDate.getTime();
+
+    if (timeSinceComment < THREE_DAYS_MS) {
+      consola.info(`  Bot comment is less than 3 days old, skipping`);
+      await new Promise((resolve) => setTimeout(resolve, 1000));
+      continue;
+    }
+
+    const hasActivity = await hasActivityAfterComment(issue, botCommentDate);
+    if (hasActivity) {
+      consola.info(`  Has activity after bot comment, skipping`);
+      await new Promise((resolve) => setTimeout(resolve, 1000));
+      continue;
+    }
+
+    const hasThumbsDown = await hasCreatorThumbsDown(issue, botComment);
+    if (hasThumbsDown) {
+      consola.info(`  Creator reacted with thumbs down, skipping`);
+      await new Promise((resolve) => setTimeout(resolve, 1000));
+      continue;
+    }
+
+    consola.info(`  Closing issue #${issue.number} as duplicate`);
+    await closeIssue(
+      issue.number,
+      "This issue has been automatically closed as a duplicate. It was marked as a duplicate over 3 days ago with no further activity. If you believe this was closed in error, please comment and we'll re-evaluate.",
+    );
+
+    closedCount++;
+
+    await new Promise((resolve) => setTimeout(resolve, 1000));
+  }
+
+  consola.info("\n=== Summary ===");
+  consola.info(`Processed issues: ${processedCount}`);
+  consola.info(`Closed issues: ${closedCount}`);
+}
+
+try {
+  await main();
+} catch (error) {
+  consola.error("Error running auto-close script:", error);
+  process.exit(1);
+}