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-review/tests/review_fakes.py

@@ -1,8 +1,7 @@
 """A Gitea and a model to review against, in memory."""
 
-import io
-import tarfile
 from dataclasses import dataclass, field, replace
+from pathlib import Path
 from typing import Any
 
 from nisse_core.gitea import (
@@ -32,15 +31,39 @@ DIFF = """diff --git a/count.py b/count.py
 """
 
 
-def archive(files: dict[str, str], *, top: str = "demo") -> bytes:
-    out = io.BytesIO()
-    with tarfile.open(fileobj=out, mode="w:gz") as tar:
-        for path, text in files.items():
-            raw = text.encode()
-            info = tarfile.TarInfo(f"{top}/{path}")
-            info.size = len(raw)
-            tar.addfile(info, io.BytesIO(raw))
-    return out.getvalue()
+class FakeSources:
+    """The repository's code as plain folders: ``gitea.files`` at head,
+    and at base unless ``base`` is given."""
+
+    def __init__(self, gitea: "FakeGitea", root: Path) -> None:
+        self._gitea = gitea
+        self._root = root
+        self.base: dict[str, str] | None = None
+        self.opened: list[tuple[str, int, str, str]] = []
+
+    def open(self, repo: str, number: int, head: str, base: str) -> "FakeTrees":
+        self.opened.append((repo, number, head, base))
+        return FakeTrees(self, len(self.opened))
+
+
+class FakeTrees:
+    def __init__(self, sources: FakeSources, n: int) -> None:
+        self._sources = sources
+        self._n = n
+        self.made: list[str] = []
+
+    def tree(self, ref: str) -> Path:
+        root = self._sources._root / f"run{self._n}" / ref
+        if not root.exists():
+            self.made.append(ref)
+            files = self._sources._gitea.files
+            if ref == "base" and self._sources.base is not None:
+                files = self._sources.base
+            for path, text in files.items():
+                (root / path).parent.mkdir(parents=True, exist_ok=True)
+                (root / path).write_text(text)
+            root.mkdir(parents=True, exist_ok=True)
+        return root
 
 
 def pr(number: int = 7, **more: Any) -> PullRequest:
@@ -172,9 +195,6 @@ class FakeGitea:
     def checks(self, repo: str, sha: str) -> str:
         return self.ci.get(sha, "success")
 
-    def archive(self, repo: str, ref: str) -> bytes:
-        return archive(self.files)
-
     def issue(self, repo: str, index: int) -> Issue:
         return Issue(index, "Counting is wrong", f"in {repo}", "don", ())