multi: add issue dedupe command and workflow

- add /dedupe command definition for Claude Code
- add workflow to run dedupe on issue opened
- add comment helper script for posting duplicates

.claude/commands/dedupe.md

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+---
+allowed-tools: Bash(gh issue view:*), Bash(gh search:*), Bash(gh issue list:*), Bash(./scripts/comment-on-duplicates.sh:*)
+description: Find duplicate GitHub issues
+---
+
+Find up to 3 likely duplicate issues for a given GitHub issue.
+
+To do this, follow these steps precisely:
+
+1. Use an agent to check if the Github issue (a) is closed, (b) does not need to be deduped (eg. because it is broad product feedback without a specific solution, or positive feedback), or (c) already has a duplicates comment that you made earlier. If so, do not proceed.
+2. Use an agent to view a Github issue, and ask the agent to return a summary of the issue
+3. Then, launch 5 parallel agents to search Github for duplicates of this issue, using diverse keywords and search approaches, using the summary from #2
+4. Next, feed the results from #2 and #3 into another agent, so that it can filter out false positives, that are likely not actually duplicates of the original issue. If there are no duplicates remaining, do not proceed.
+5. Finally, use the comment script to post duplicates:
+   ```
+   ./scripts/comment-on-duplicates.sh --base-issue <issue-number> --potential-duplicates <dup1> <dup2> <dup3>
+   ```
+
+Notes (be sure to tell this to your agents, too):
+
+- Use `gh` to interact with Github, rather than web fetch
+- Do not use other tools, beyond `gh` and the comment script (eg. don't use other MCP servers, file edit, etc.)
+- Make a todo list first

.github/workflows/claude-dedupe-issues.yml

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+name: Claude Issue Dedupe
+description: Automatically dedupe GitHub issues using Claude Code
+on:
+  issues:
+    types: [opened]
+  workflow_dispatch:
+    inputs:
+      issue_number:
+        description: 'Issue number to process for duplicate detection'
+        required: true
+        type: string
+
+jobs:
+  claude-dedupe-issues:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    permissions:
+      contents: read
+      issues: write
+      id-token: write
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Run Claude Code slash command
+        uses: anthropics/claude-code-action@v1
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          allowed_non_write_users: "*"
+          prompt: "/dedupe ${{ github.repository }}/issues/${{ github.event.issue.number || inputs.issue_number }}"
+          claude_code_oauth_token: ${{ secrets.CLAUDE_CODE_OAUTH_TOKEN }}

scripts/comment-on-duplicates.sh

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+#!/usr/bin/env bash
+#
+# Comments on a GitHub issue with a list of potential duplicates.
+# Usage: ./comment-on-duplicates.sh --base-issue 123 --potential-duplicates 456 789 101
+#
+
+set -euo pipefail
+
+REPO="${GITHUB_REPOSITORY:-lightningnetwork/lnd}"
+BASE_ISSUE=""
+DUPLICATES=()
+
+# Parse arguments
+while [[ $# -gt 0 ]]; do
+  case $1 in
+    --base-issue)
+      BASE_ISSUE="$2"
+      shift 2
+      ;;
+    --potential-duplicates)
+      shift
+      while [[ $# -gt 0 && ! "$1" =~ ^-- ]]; do
+        DUPLICATES+=("$1")
+        shift
+      done
+      ;;
+    *)
+      echo "Unknown option: $1" >&2
+      exit 1
+      ;;
+  esac
+done
+
+# Validate base issue
+if [[ -z "$BASE_ISSUE" ]]; then
+  echo "Error: --base-issue is required" >&2
+  exit 1
+fi
+
+if ! [[ "$BASE_ISSUE" =~ ^[0-9]+$ ]]; then
+  echo "Error: --base-issue must be a number, got: $BASE_ISSUE" >&2
+  exit 1
+fi
+
+# Validate duplicates
+if [[ ${#DUPLICATES[@]} -eq 0 ]]; then
+  echo "Error: --potential-duplicates requires at least one issue number" >&2
+  exit 1
+fi
+
+if [[ ${#DUPLICATES[@]} -gt 3 ]]; then
+  echo "Error: --potential-duplicates accepts at most 3 issues" >&2
+  exit 1
+fi
+
+for dup in "${DUPLICATES[@]}"; do
+  if ! [[ "$dup" =~ ^[0-9]+$ ]]; then
+    echo "Error: duplicate issue must be a number, got: $dup" >&2
+    exit 1
+  fi
+done
+
+# Validate that base issue exists
+if ! gh issue view "$BASE_ISSUE" --repo "$REPO" &>/dev/null; then
+  echo "Error: issue #$BASE_ISSUE does not exist in $REPO" >&2
+  exit 1
+fi
+
+# Validate that all duplicate issues exist
+for dup in "${DUPLICATES[@]}"; do
+  if ! gh issue view "$dup" --repo "$REPO" &>/dev/null; then
+    echo "Error: issue #$dup does not exist in $REPO" >&2
+    exit 1
+  fi
+done
+
+# Build comment body
+COUNT=${#DUPLICATES[@]}
+if [[ $COUNT -eq 1 ]]; then
+  HEADER="Found 1 possible duplicate issue:"
+else
+  HEADER="Found $COUNT possible duplicate issues:"
+fi
+
+BODY="$HEADER"$'\n\n'
+INDEX=1
+for dup in "${DUPLICATES[@]}"; do
+  BODY+="$INDEX. https://github.com/$REPO/issues/$dup"$'\n'
+  ((INDEX++))
+done
+
+BODY+=$'\n'"If this issue is a duplicate, please close it and 👍 the existing issue instead."$'\n\n'
+BODY+="🤖 Generated with [Claude Code](https://claude.ai/code)"
+
+# Post the comment
+gh issue comment "$BASE_ISSUE" --repo "$REPO" --body "$BODY"
+
+echo "Posted duplicate comment on issue #$BASE_ISSUE"