Milestones and review in the new loop (M2.1, PR C)

A work item starts from a fresh workspace: fetch, set aside (never
discard) leftover changes, branches and unpushed commits, a clean default
branch, and a branch of its own (D3, #62). start_milestone cuts the
milestone's branch; finish_milestone commits only the work, pushes and
opens a PR that closes the issue, under an intent, adopting an open PR and
treating a closed one as the operator's answer (D4). Between runs the
loop watches each item's PR: operator comments and inline review notes
(#69) reach the item, a merge or close hands back to the driver. A review
fix is checked after it's pushed and goes out as a new PR if the PR merged
first (D5). At boot an interrupted publish is settled against Gitea (L8).

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

nisse-dev/src/nisse_dev/loop/driver.py

@@ -7,6 +7,7 @@ go to the build VM (L13); control tools are answered here, and a waiting one
 ends the run, so the scheduler can put it to the operator.
 """
 
+from collections.abc import Callable, Mapping
 from dataclasses import dataclass
 from typing import Any, Literal
 
@@ -55,7 +56,12 @@ class Driver:
         system: str,
         tools: list[dict[str, Any]],
         workspace: Workspace | None,
+        handlers: Mapping[str, Callable[[dict[str, Any]], tuple[str, bool]]]
+        | None = None,
     ) -> RunOutcome:
+        """``handlers`` answer control tools that don't end the run (e.g.
+        start_milestone): each returns a result and whether it succeeded."""
+        handlers = handlers or {}
         offered = names(tools)
         nudged = False
         for turn in range(self._max_turns):
@@ -95,7 +101,9 @@ class Driver:
                         transcript, calls[index + 1 :], "not run: the turn had ended"
                     )
                     return RunOutcome("wait", call.tool, dict(call.arguments))
-                if call.tool not in offered or workspace is None:
+                if call.tool in handlers and call.tool in offered:
+                    result, ok = handlers[call.tool](dict(call.arguments))
+                elif call.tool not in offered or workspace is None:
                     result, ok = (
                         f"no such tool: {call.tool}; the tools are "
                         + ", ".join(sorted(offered)),