feat(adapters): GitShardAdapter history adopt + cross-substrate integration (WP-0012 T3)

Adopt git-native history (TSD §A.5): a VERSION-gated history(key) surfaces the
commit list for a path (newest-first sha + subject) — declared by every git-IS-store
shard, read-only or not. Integration proves the union/overlay/edit machinery works
unchanged across folder + git substrates: resolve/chorus span both, edit through a
git shard fast-forwards as a commit, apply-under-drift refuses on an external commit
(sha drift) without clobbering, and a read-only git target keeps the overlay as a
draft. SCOPE updated; WP-0012 done. 196 tests green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_git_adapter_integration.py

@@ -0,0 +1,116 @@
+"""GitShardAdapter history adopt + cross-substrate integration (SHARD-WP-0012 T3)."""
+
+import os
+import subprocess
+
+import pytest
+
+from shard_wiki.adapters import FolderAdapter, GitShardAdapter
+from shard_wiki.coordination import ApplyStatus
+from shard_wiki.space import InformationSpace
+
+_ENV = {
+    "GIT_AUTHOR_NAME": "t", "GIT_AUTHOR_EMAIL": "t@t",
+    "GIT_COMMITTER_NAME": "t", "GIT_COMMITTER_EMAIL": "t@t",
+    "PATH": os.environ.get("PATH", ""),
+}
+
+
+def _git(repo, *args):
+    return subprocess.run(
+        ["git", "-C", str(repo), *args], check=True, capture_output=True, text=True, env=_ENV
+    ).stdout.strip()
+
+
+def _git_repo(tmp_path, files, name="git"):
+    repo = tmp_path / name
+    repo.mkdir()
+    _git(repo, "init", "--quiet")
+    for rel, text in files.items():
+        (repo / rel).parent.mkdir(parents=True, exist_ok=True)
+        (repo / rel).write_text(text, encoding="utf-8")
+        _git(repo, "add", rel)
+    _git(repo, "commit", "-m", "seed")
+    return repo
+
+
+def _folder(tmp_path, name, files, writable=False):
+    root = tmp_path / name
+    for rel, text in files.items():
+        p = root / rel
+        p.parent.mkdir(parents=True, exist_ok=True)
+        p.write_text(text, encoding="utf-8")
+    return FolderAdapter(name, root, writable=writable)
+
+
+# -- history adopt -------------------------------------------------------------
+
+
+def test_history_lists_commits_newest_first(tmp_path):
+    repo = _git_repo(tmp_path, {"Home.md": "v1"})
+    adapter = GitShardAdapter("git", repo, writable=True)
+    adapter.write("Home", "v2")
+    history = adapter.history("Home")
+    assert len(history) == 2
+    assert history[0].message == "write Home.md"  # newest first
+    assert history[-1].message == "seed"
+    assert all(rev.sha for rev in history)
+
+
+def test_history_unknown_key_raises(tmp_path):
+    adapter = GitShardAdapter("git", _git_repo(tmp_path, {"Home.md": "h"}))
+    with pytest.raises(KeyError):
+        adapter.history("Nope")
+
+
+# -- cross-substrate integration ----------------------------------------------
+
+
+def test_resolve_across_git_and_folder(tmp_path):
+    space = InformationSpace("space")
+    space.attach(GitShardAdapter("git", _git_repo(tmp_path, {"Home.md": "git home"})))
+    space.attach(_folder(tmp_path, "notes", {"Daily.md": "folder daily"}))
+    assert space.read("Home").body == "git home"  # resolved from the git shard
+    assert space.read("Daily").body == "folder daily"  # resolved from the folder shard
+
+
+def test_chorus_spans_substrates_with_divergence(tmp_path):
+    space = InformationSpace("space")
+    space.attach(GitShardAdapter("git", _git_repo(tmp_path, {"Shared.md": "from git"})))
+    space.attach(_folder(tmp_path, "notes", {"Shared.md": "from folder"}))
+    res = space.resolve("Shared")
+    assert {p.body for p in res.pages} == {"from git", "from folder"}  # chorus across substrates
+    git_page = next(p for p in res.pages if p.identity.shard == "git")
+    assert git_page.envelope.divergence  # divergence recorded, not erased
+
+
+def test_edit_through_git_shard_commits(tmp_path):
+    repo = _git_repo(tmp_path, {"Home.md": "original"})
+    space = InformationSpace("space")
+    space.attach(GitShardAdapter("git", repo, writable=True))
+    result = space.edit("Home", "edited via overlay")
+    assert result.status is ApplyStatus.APPLIED  # write-through fast-forward on a git shard
+    assert space.read("Home").body == "edited via overlay"
+    assert int(_git(repo, "rev-list", "--count", "HEAD")) == 2  # the edit became a commit
+
+
+def test_apply_under_drift_refuses_on_external_commit(tmp_path):
+    repo = _git_repo(tmp_path, {"Home.md": "original"})
+    space = InformationSpace("space")
+    space.attach(GitShardAdapter("git", repo, writable=True))
+    overlay = space.overlay("Home", "my draft")  # base_rev = current git sha
+    # Another writer commits to the same path → the sha moves underneath the draft.
+    (repo / "Home.md").write_text("someone else", encoding="utf-8")
+    _git(repo, "add", "Home.md")
+    _git(repo, "commit", "-m", "external")
+    result = space.apply_overlay(overlay.overlay_id)
+    assert result.status is ApplyStatus.REFUSED_DRIFT  # never clobber (sha drift detected)
+    # The shard itself is untouched — the external commit stands; the draft remains a draft.
+    assert space.union.shard("git").read("Home").body == "someone else"
+
+
+def test_overlay_on_read_only_git_shard_kept_as_draft(tmp_path):
+    space = InformationSpace("space")
+    space.attach(GitShardAdapter("git", _git_repo(tmp_path, {"Home.md": "ro"}), writable=False))
+    result = space.edit("Home", "wanted change")
+    assert result.status is ApplyStatus.KEPT_DRAFT  # read-only target → overlay retained