Answer where asked, wait on a merge, and let the driver title PRs

From the new loop's first live run (sandbox #255, PR #256):
- A question asked on the PR is answered on the PR (an inline one quoted
  with its file and line, since the API can't reply in its thread), with
  a pointer in the item's Matrix thread; one asked in Matrix stays there.
- wait_for_review: when a review needs no change, or only the operator's
  merge is left, the item waits on the merge instead of on an answer.
- finish_milestone takes the PR's title from the driver.
The e2e test's merge waits out Gitea's brief 'try again later' after a
push.

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

tests/integration/test_end_to_end_loop.py

@@ -23,7 +23,7 @@ from e2e_support import base_branch, operator_gitea, task
 
 from nisse_dev.config import AgentConfig
 from nisse_dev.execution import SSHHost
-from nisse_dev.gitea import GiteaError
+from nisse_dev.gitea import GiteaClient, GiteaError
 from nisse_dev.loop.build import RunningLoop, build_loop_agent
 from nisse_dev.loop.items import ANSWER, GO_AHEAD, MERGE, WAITING, loop_of
 from nisse_dev.transport import InMemoryTransport
@@ -93,6 +93,22 @@ def is_artifact(path: str) -> bool:
     )
 
 
+def merge(gitea: GiteaClient, repo: str, pr: int, wait_s: float = 60) -> None:
+    """Merge, waiting out Gitea's "Please try again later": it answers that
+    while it is still checking a freshly pushed PR can merge."""
+    deadline = time.monotonic() + wait_s
+    while True:
+        try:
+            gitea._request(
+                "POST", f"/repos/{repo}/pulls/{pr}/merge", json={"Do": "merge"}
+            )
+            return
+        except GiteaError as exc:
+            if "try again later" not in str(exc) or time.monotonic() > deadline:
+                raise
+            time.sleep(3)
+
+
 class Operator:
     def __init__(self, agent: RunningLoop, transport: InMemoryTransport) -> None:
         self.agent = agent
@@ -191,9 +207,7 @@ def test_the_slice_end_to_end(
                 f"/repos/{repo}/pulls/{pr}/reviews",
                 json={"event": "APPROVED", "body": "looks good"},
             )
-        as_operator._request(
-            "POST", f"/repos/{repo}/pulls/{pr}/merge", json={"Do": "merge"}
-        )
+        merge(as_operator, repo, pr)
         operator.tick()
         deadline = time.monotonic() + DEADLINE_S
         nudges = 0