Fix duplicate issue detection not performing searches

The AI inference action's default max-tokens (200) was too low, causing
the model's response to be truncated before it could make search_issues
tool calls. Increase max-tokens to 100000 and upgrade the model from
gpt-4o to gpt-5-mini for better tool use and instruction following.

Also replace the HTML comment marker (<!-- ai-duplicate-check -->) and
github-actions[bot] user check with the visible text "This issue will be
automatically closed as a duplicate in 3 days." for filtering duplicate
comments, since the marker may be missing when posted from a personal
account.

Author: smorimoto

.github/prompts/dedupe.prompt.yml

@@ -7,12 +7,12 @@ messages:
 
       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.
+      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 `This issue will be automatically closed as a duplicate in 3 days.`. 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
+model: openai/gpt-5-mini
 responseFormat: json_schema
 jsonSchema: |-
   {

.github/workflows/dedupe-issues.yml

@@ -32,6 +32,7 @@ jobs:
           prompt-file: .github/prompts/dedupe.prompt.yml
           input: |
             issue_number: ${{ github.event.issue.number || inputs.issue_number }}
+          max-tokens: 100000
           enable-github-mcp: true
 
       - name: Post comment if duplicates found

scripts/auto-close-duplicates.ts

@@ -107,10 +107,10 @@ async function main(): Promise<void> {
 
     const comments = await getIssueComments(issue.number);
 
-    const botComment = comments.find(
-      (comment) =>
-        comment.user?.login === "github-actions[bot]" &&
-        comment.body.includes("<!-- ai-duplicate-check -->"),
+    const botComment = comments.find((comment) =>
+      comment.body.includes(
+        "This issue will be automatically closed as a duplicate in 3 days.",
+      ),
     );
 
     if (!botComment) {

scripts/backfill-duplicate-detection.ts

@@ -29,10 +29,10 @@ async function hasDuplicateDetectionComment(
 ): Promise<boolean> {
   const comments = await getIssueComments(issueNumber);
 
-  return comments.some(
-    (comment) =>
-      comment.user?.login === "github-actions[bot]" &&
-      comment.body.includes("<!-- ai-duplicate-check -->"),
+  return comments.some((comment) =>
+    comment.body.includes(
+      "This issue will be automatically closed as a duplicate in 3 days.",
+    ),
   );
 }