Fix: Require explicit assignee verification in auto-assign workflow

.github/workflows/daily-assign-issue-to-user.md

@@ -24,17 +24,26 @@ safe-outputs:
 # Auto-Assign Issue
 
 Find ONE open issue that:
-- **Has no assignees** - When you retrieve issues from GitHub, explicitly check the `assignees` field. Skip any issue where `issue.assignees` is not empty or has length > 0.
+- **Has no assignees** - This is CRITICAL. You MUST verify this in two places:
+  1. Use `no:assignee` in your search query
+  2. After retrieving the issue details, explicitly check that `issue.assignees` is an empty array or has length 0
+  3. **SKIP AND EXIT if `issue.assignees` is not empty** - DO NOT assign issues that already have assignees
 - Does not have label `ai-generated`
 - Does not have a `campaign:*` label (these are managed by campaign orchestrators)
 - Does not have labels: `no-bot`, `no-campaign`
 - Was not opened by `github-actions` or any bot
 
-Pick the oldest unassigned issue.
+**Verification Steps (REQUIRED):**
+1. Search for issues using `no:assignee` filter
+2. Pick the oldest unassigned issue from search results
+3. Retrieve full issue details using `issue_read`
+4. **VERIFY** that `issue.assignees` is empty (length === 0)
+5. **IF assignees is NOT empty, EXIT WITHOUT ASSIGNING** - the issue was assigned by someone else
+6. Only if `issue.assignees` is empty, proceed to list contributors and assign
 
 Then list the 5 most recent contributors from merged PRs. Pick one who seems relevant based on the issue type.
 
-If you find a match:
+If you find a match AND the issue has no assignees:
 1. Use `assign-to-user` to assign the issue
 2. Use `add-comment` with a short explanation (1-2 sentences)