Fixes from the rest of the live session

- A near miss for abandon ("abort", "cancel", "drop it", ...) in an item's
  thread is asked about, and changes nothing.
- The driver is told only the operator stops or closes an item, so it
  doesn't claim to have done either.
- An issue assigned again after its item closed starts a new item that
  notes the one before (Gitea's timeline gives the assignment time);
  item_for_issue returns the latest item.
- Abandoning an issue Gitea won't close because of open dependencies says
  so, naming them.
- An agreed item isn't offered restate.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPQ14L3LikyefCMFBqEbKE

nisse-dev/tests/test_loop_milestones.py

@@ -61,6 +61,7 @@ class Forge:
         self.issues = [Issue(14, "Add count_words", "count words", "don", ())]
         self.deps: dict[int, list[int]] = {}  # issue -> the issues it depends on
         self.assigned: list[int] = []  # issues the agent assigned to itself
+        self.reassigned: dict[int, str] = {}  # issue -> when assigned again
 
     # intake
     def assigned_issues(self, repo: str, assignee: str) -> list[Issue]:
@@ -84,6 +85,9 @@ class Forge:
     def assigned_by(self, repo: str, index: int, assignee: str) -> str:
         return "don"
 
+    def assigned_at(self, repo: str, index: int, assignee: str) -> str | None:
+        return self.reassigned.get(index)
+
     # PRs
     def _pr(self, n: int) -> PullRequest:
         p = self.prs[n]