The queue: parking, the operator's order, blocked items (M2.2)

Several work items on the new loop (L1, D4):
- Switching parks the item on the workspace: its work is committed and its
  branch pushed; resuming checks the item's branch back out. Branches of
  open items are never set aside by a fresh workspace.
- Next item: the operator's "do #N next" first, otherwise the oldest.
- Issues with open Gitea dependencies are blocked until they close, checked
  at intake and on every round; status shows blocked items and the line.

Tests: queue unit tests, the property walk over several issues with
dependencies and a new parked_work_safe property (it catches parking
disabled), and an end-to-end test with two issues where B depends on A.

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/milestones.py

@@ -57,11 +57,14 @@ class Milestones:
 
     # -- a work item's workspace (D3) ------------------------------------------
 
-    def prepare(self, item_branch: str) -> list[str]:
+    def prepare(self, item_branch: str, *, keep: tuple[str, ...] = ()) -> list[str]:
         """A fresh workspace for a work item: fetch, set aside (never
         discard) whatever was left, check out a clean default branch, and put
-        the item on a branch of its own. Returns what was set aside."""
+        the item on a branch of its own. Branches starting with a ``keep``
+        prefix belong to open work items, which parking has pushed: they are
+        left alone. Returns what was set aside."""
         git = self._git
+        self.park(keep=keep)
         git.fetch(credential=self._credential)
         stamp = time.strftime("%Y%m%d-%H%M%S")
         notes: list[str] = []
@@ -73,6 +76,8 @@ class Milestones:
         for branch in git.local_branches():
             if branch == self._base or branch.startswith(f"{SET_ASIDE}/"):
                 continue
+            if keep and branch.startswith(keep):
+                continue
             git.rename_branch(branch, f"{SET_ASIDE}/{stamp}/{branch}")
             notes.append(f"branch {branch}, as {SET_ASIDE}/{stamp}/{branch}")
         if self._base in git.local_branches() and self._ahead_of_origin():
@@ -83,6 +88,42 @@ class Milestones:
         git.checkout_new_branch(item_branch)
         return notes
 
+    # -- parking and resuming (L1, D4) -----------------------------------------
+
+    def park(self, *, keep: tuple[str, ...]) -> str | None:
+        """Before another item uses the workspace: commit whatever the item
+        on it left, and push its branch, so nothing of a parked item lives
+        only on the build VM. Only a harness branch of an open item (one
+        starting with a ``keep`` prefix) is parked; returns its name."""
+        git = self._git
+        branch = git.current_branch()
+        if not keep or not branch.startswith(keep):
+            return None
+        git.commit_all("WIP: parked while another work item runs")
+        if git.remote_sha(self._remote, branch, credential=self._credential) != (
+            git.head_sha()
+        ):
+            git.push(self._remote, branch, credential=self._credential)
+        return branch
+
+    def resume(self, branch: str, *, keep: tuple[str, ...], mine: str = "") -> None:
+        """Back to a parked item: park whatever is on the workspace now, then
+        check out the item's branch. The local branch wins when it exists (it
+        can only be ahead: parking pushed it); otherwise it comes from origin.
+        A workspace already on one of the item's own branches (``mine``, a
+        prefix) is where it left off, and stays."""
+        git = self._git
+        current = git.current_branch()
+        if current == branch or (mine and current.startswith(mine)):
+            return
+        self.park(keep=keep)
+        if branch in git.local_branches():
+            git.checkout_existing_branch(branch)
+            git.reset_to(branch, branch)
+        else:
+            git.fetch(credential=self._credential)
+            git.reset_to(branch, f"origin/{branch}")
+
     def _ahead_of_origin(self) -> bool:
         current = self._git.current_branch()
         try: