Multi-milestone work and documents on the new loop (M2.4)

- Every milestone branch is cut from the latest default branch: the next
  milestone builds on the merged previous one, and a redo after a closed PR
  drops the rejected work. Uncommitted work comes along.
- While the item's PR is open, start_milestone is refused, with the PR's
  state read from Gitea at that moment, not the last watch round.
- finish_milestone(final): earlier PRs say "Part of #N", the last "Closes
  #N"; unsaid, it's final, as before.
- close_item with the item's PR still open waits for the merge (L2: a
  closed item leaves nothing open).
- The driver's instructions cover ARCHITECTURE.md and build plans under
  docs/plans/ (D2); the harness never parses a plan.
- Parking stashes uncommitted work and pushes it to <item>-parked, put back
  on resume, instead of committing it onto the item's branch. The walk
  found a half-done review fix parked onto a PR that had merged meanwhile,
  where it was lost. Architecture D4's parking line says so.

Tests: unit tests for fresh milestone branches, the merge wait (including
a merge not yet watched), redo after a closed PR, Part of/Closes, close
waiting on an open PR, and the parked-fix regression; the walk's new
milestones_start_fresh property (fork-from-current fails 9 seeds); an e2e
two-milestone feature.

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_queue.py

@@ -88,12 +88,14 @@ def test_switching_parks_the_work_and_resuming_finds_it(
     agent.watch()
     agent._schedule()
 
-    # Switching to 14 parked 15: its half-done work is committed and pushed.
+    # Switching to 14 parked 15: its half-done work is pushed as a stash to
+    # a side branch (new files in its third parent), never onto 15's branch.
     b_branch = loop_of(item(world, 15)).branch
-    pushed = git(
-        "--git-dir", str(world["bare"]), "show", f"refs/heads/{b_branch}:lines.py"
-    )
-    assert pushed == "L = 1"
+    bare = ["--git-dir", str(world["bare"])]
+    parked = f"refs/heads/{item(world, 15).id}-parked"
+    assert git(*bare, "show", f"{parked}^3:lines.py") == "L = 1"
+    # The branch has no commits of its own, so it wasn't pushed at all.
+    assert b_branch not in git(*bare, "branch", "--list")
     # 14's fix went to its own branch, without 15's work.
     assert loop_of(item(world, 14)).wait == MERGE
     files = git("--git-dir", str(world["bare"]), "ls-tree", "--name-only", a_branch)
@@ -105,6 +107,8 @@ def test_switching_parks_the_work_and_resuming_finds_it(
     say(transport, world, 15, "one per line")
     assert world["repo"].current_branch() == b_branch
     assert (world["repo"].root / "lines.py").read_text() == "L = 1\n"
+    # Put back, so the side branch is gone.
+    assert item(world, 15).id + "-parked" not in git(*bare, "branch", "--list")
     assert loop_of(item(world, 15)).wait == MERGE
     assert len(forge.prs) == 2
 
@@ -190,3 +194,52 @@ def test_status_shows_the_line(world: dict[str, Any]) -> None:
     assert "#15 Add count_lines: ready, 2 of 2 in line" in agent.status()
     agent.handle(InboundMessage(DON, "do #15 next"), None)
     assert "#15 Add count_lines: ready, 1 of 2 in line" in agent.status()
+
+
+def test_a_fix_half_done_when_its_pr_merges_survives_a_switch(
+    world: dict[str, Any],
+) -> None:
+    """Found by the walk: work on a review fix, parked after the PR merged,
+    was pushed onto the merged branch, where nobody would see it. Now it
+    comes back with the item and goes out in its next PR."""
+    forge: Forge = world["forge"]
+    two_issues(forge)
+    model = ScriptedModel(
+        [call("restate", text="count_words")],  # 14
+        [call("restate", text="count_lines")],  # 15
+        [  # 14: a PR
+            call("start_milestone", name="words"),
+            call("write_file", path="words.py", content="W = 1\n"),
+            call("finish_milestone", summary="words", final="yes"),
+        ],
+        [  # 14, a review comment: half a fix, then a question
+            call("write_file", path="fix.py", content="F = 1\n"),
+            call("ask_human", question="fix it in words.py too?"),
+        ],
+        [  # 15 runs meanwhile
+            call("start_milestone", name="lines"),
+            call("write_file", path="lines.py", content="L = 1\n"),
+            call("finish_milestone", summary="lines"),
+        ],
+        [call("finish_milestone", summary="the fix", final="yes")],  # 14 again
+    )
+    agent, transport = loop_agent(world, model)
+    agent.intake()
+    say(transport, world, 14, "go")
+    [pr] = forge.prs
+    forge.comments[pr] = [Comment(7, "don", "add fix.py", "t")]
+    agent.watch()
+    agent._schedule()
+    assert loop_of(item(world, 14)).wait == ANSWER
+    say(transport, world, 15, "go")  # parks 14's half-done fix
+    forge.merge(pr)
+    agent.watch()
+    agent._schedule()  # 14 resumes; its fix goes out as a new PR
+
+    bare = ["--git-dir", str(world["bare"])]
+    merged_head = forge.prs[pr]["head"]
+    assert "fix.py" not in git(*bare, "ls-tree", "--name-only", merged_head).split()
+    newest = max(
+        n for n, p in forge.prs.items() if p["head"].startswith(item(world, 14).id)
+    )
+    assert newest != pr and forge.files(newest) == ["fix.py"]