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.py

@@ -49,6 +49,7 @@ class FakeGitea:
         self.comments: list[tuple[int, str]] = []
         self.closed: list[int] = []
         self.deps: dict[int, list[int]] = {}
+        self.reassigned: dict[int, str] = {}  # issue -> when assigned again
 
     def create_issue(self, repo: str, title: str, body: str) -> int:
         n = max([i.number for i in self.issues] + [0]) + 1
@@ -67,6 +68,9 @@ class FakeGitea:
     def assigned_by(self, repo: str, index: int, assignee: str) -> str:
         return self.assigner
 
+    def assigned_at(self, repo: str, index: int, assignee: str) -> str | None:
+        return self.reassigned.get(index)
+
     def post_comment(self, repo: str, index: int, body: str) -> None:
         self.comments.append((index, body))