nisse-review: read code from a git clone kept between runs

Archives were downloaded and unpacked afresh for every run, which doesn't
scale to very large repositories. Each repository is now cloned once, with
its whole history, under scratch/repos/<owner>/<name>/ (head/ the clone,
base/ a worktree when read). A run fetches every branch and the PR's
refs/pull/N/head, checks out the head exactly, and fails if that head is
gone. Only the latest repository is kept for now.

Git runs walled off: none of the host's git configuration, links checked
out as plain files, no hooks, submodules or LFS, only the Gitea URL's
protocol, and the token as an http.extraHeader for that URL in git's
environment only. A stop ends a git command; a cut-short first clone is
removed. The reader never shows .git. GiteaClient.archive is gone.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01J5Utyfzw7gF7UhjRDEtjTk

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

@@ -2111,6 +2111,7 @@ class LoopAgent:
         result = delegation.run(
             self._store.transcript(item.id, "helper"), brief=brief, branch=branch
         )
+        lost: GitError | None = None
         try:
             # The milestone takes the helper's work (or, on failure, only
             # its own back) as uncommitted changes: harness branches never
@@ -2122,6 +2123,8 @@ class LoopAgent:
                 git._git("branch", "-q", "-D", branch)
         except GitError as exc:
             self._fact(item, f"after helper {number}: {exc}")
+            if isinstance(exc.__cause__, HostUnavailable):
+                lost = exc  # the VM went: the driver's run ends too (#137)
         for intent in self._store.pending_intents():
             # Cut off rather than finished: discarded all the same, never
             # resumed blindly (L8, L9).
@@ -2130,6 +2133,8 @@ class LoopAgent:
                 and intent.payload.get("branch") == branch
             ):
                 self._store.abort_intent(intent.id, cause=f"delegation {result.status}")
+        if lost is not None:
+            raise VMUnreachable(str(lost)) from lost
         if result.usable and result.handback is not None:
             self._fact(item, f"helper {number} finished: {result.handback.render()}")
             return f"the helper finished:\n{result.handback.render()}", True

nisse-dev/tests/test_loop_vm.py

@@ -338,3 +338,42 @@ def test_a_vm_lost_just_before_the_step_blocks_before_any_model_call(
     agent, _ = agent_for(world, project, model, clock=Clock())
     agent.intake()
     assert list(blocks(world).values()) == ["unreachable"]
+
+
+def test_a_vm_lost_as_a_helper_hands_back_ends_the_drivers_run(
+    world: dict[str, Any], project: str, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    # Found by the property walk (seed 468): taking the helper's work back
+    # onto the milestone's branch failed for the lost VM, was noted as a git
+    # error, and the driver's model was called with the VM gone.
+    from test_loop_help import Spy, hand_back, helpers
+
+    faults = Faults(monkeypatch, world["host"])
+
+    class Leaving(Spy):
+        def complete(self, events, tools, model, system=None) -> list[Any]:
+            out = super().complete(events, tools, model, system)
+            if not self.turns:  # gone as its work is taken back
+                faults.drop_on = "checkout -q -f -B"
+            return out
+
+    helper = Leaving(
+        [call("write_file", path="helped.py", content="H = 1\n")], [hand_back()]
+    )
+    model = ScriptedModel(
+        ready(),
+        RESTATE,
+        [
+            call("start_milestone", name="m"),
+            call("delegate", task="write helped.py"),
+        ],
+        [call("run_command", command="echo never")],  # never asked for
+    )
+    agent, transport = agent_for(
+        world, project, model, clock=Clock(), helpers=helpers(helper)
+    )
+    agent.intake()
+    say(transport, world, "go")
+    assert list(blocks(world).values()) == ["unreachable"]
+    assert the_item(world).position == READY
+    assert len(model.turns) == 1  # the driver's model wasn't called again