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/src/nisse_review/scheduler.py

@@ -24,12 +24,10 @@ to ready, with nothing drafted posted and no failure counted.
 """
 
 import re
-import tempfile
 import threading
 import time
 from collections.abc import Callable
 from dataclasses import replace
-from pathlib import Path
 
 from nisse_core.gitea import GiteaClient, GiteaError, PullRequest
 from nisse_core.models.interruptible import Stopped
@@ -37,7 +35,7 @@ from nisse_core.oplog import OpLog
 from nisse_core.state.cancel import Cancel
 from nisse_core.state.store import WorkItem
 from nisse_review.access import check, reviewed
-from nisse_review.reader import Repository
+from nisse_review.reader import Repository, Sources
 from nisse_review.review import Draft, Posted, Reviewer, Said, answered, said_on
 from nisse_review.state import (
     CAPPED,
@@ -92,7 +90,7 @@ class Scheduler:
         reviewer: Reviewer,
         *,
         oplog: OpLog,
-        scratch: Path,
+        sources: Sources,
         poll_s: float = 60.0,
         attempts: int = 2,
         patterns: frozenset[str] | None = None,
@@ -107,7 +105,7 @@ class Scheduler:
         self._gitea = gitea
         self._reviewer = reviewer
         self._oplog = oplog
-        self._scratch = scratch
+        self._sources = sources  # the repositories' code, as clones
         self._poll_s = poll_s
         self._attempts = attempts
         # The repositories reviewed, as patterns; None: every one it was given.
@@ -388,19 +386,11 @@ class Scheduler:
             if kind == REPLIES and not known.fresh:
                 self._settle(item, known, pr, "done", Draft(), posted=None)
                 return
-            scratch = Path(tempfile.mkdtemp(dir=self._scratch, prefix="review-"))
-            repo = Repository(
-                self._gitea,
-                known.repo,
-                {"head": pr.head_sha, "base": pr.base},
-                scratch,
+            trees = self._sources.open(known.repo, pr.number, pr.head_sha, pr.base)
+            repo = Repository(self._gitea, known.repo, trees)
+            outcome, draft = self._reviewer.run(
+                item.id, pr, repo, kind=kind, known=known, said=said
             )
-            try:
-                outcome, draft = self._reviewer.run(
-                    item.id, pr, repo, kind=kind, known=known, said=said
-                )
-            finally:
-                repo.close()
             if outcome.kind == "capped" and draft.comments:
                 # Out of turns with points drafted: they're worth more posted
                 # than lost (#156), as a review that says it's partial.