feat(adapters): GitShardAdapter read path + git-IS-store profile (WP-0012 T1)

A second substrate validating the contract beyond plain folders: a git-IS-store
shard reading Markdown from a git repo. Keys are tracked *.md paths; read returns
a Page whose source_rev is the per-path last-commit sha (so an edit to one page
never drifts another); profile is git-IS-store / substrate=git / history=git-native
/ addressing=path, validated against the §6.5 implication rules. Passes the
conformance read path with honest absence of unclaimed verbs. Zero new deps
(git CLI via subprocess). No core changes.

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

tests/test_git_adapter.py

@@ -0,0 +1,131 @@
+"""Tests for the GitShardAdapter read path + profile (SHARD-WP-0012 T1)."""
+
+import subprocess
+
+import pytest
+
+from shard_wiki.adapters import GitShardAdapter, run_conformance
+from shard_wiki.model import (
+    AttachmentMode,
+    History,
+    NotSupported,
+    ProfileError,
+    Substrate,
+    Verb,
+)
+
+
+def _git(repo, *args):
+    subprocess.run(
+        ["git", "-C", str(repo), *args],
+        check=True,
+        capture_output=True,
+        env={"GIT_AUTHOR_NAME": "t", "GIT_AUTHOR_EMAIL": "t@t",
+             "GIT_COMMITTER_NAME": "t", "GIT_COMMITTER_EMAIL": "t@t",
+             "PATH": __import__("os").environ.get("PATH", "")},
+    )
+
+
+def _repo(tmp_path, files, name="repo"):
+    repo = tmp_path / name
+    repo.mkdir()
+    _git(repo, "init", "--quiet")
+    for rel, text in files.items():
+        p = repo / rel
+        p.parent.mkdir(parents=True, exist_ok=True)
+        p.write_text(text, encoding="utf-8")
+        _git(repo, "add", rel)
+    _git(repo, "commit", "-m", "seed")
+    return repo
+
+
+def test_keys_are_tracked_md_paths(tmp_path):
+    repo = _repo(tmp_path, {"Home.md": "h", "docs/Guide.md": "g", "ignore.txt": "x"})
+    adapter = GitShardAdapter("git", repo)
+    assert set(adapter.keys()) == {"Home", "docs/Guide"}  # only tracked *.md
+
+
+def test_read_returns_page_with_commit_sha_rev(tmp_path):
+    repo = _repo(tmp_path, {"Home.md": "welcome"})
+    adapter = GitShardAdapter("git", repo)
+    page = adapter.read("Home")
+    assert page.identity.shard == "git"
+    assert page.body == "welcome"
+    head = subprocess.run(
+        ["git", "-C", str(repo), "rev-parse", "HEAD"], capture_output=True, text=True, check=True
+    ).stdout.strip()
+    assert page.envelope.source_rev == head  # source_rev is the commit sha
+    assert page.envelope.lineage == "git-native"
+
+
+def test_read_missing_key_raises(tmp_path):
+    adapter = GitShardAdapter("git", _repo(tmp_path, {"Home.md": "h"}))
+    with pytest.raises(KeyError):
+        adapter.read("Nope")
+
+
+def test_profile_validates_implication_rules(tmp_path):
+    profile = GitShardAdapter("git", _repo(tmp_path, {"Home.md": "h"})).profile()
+    assert profile.substrate is Substrate.GIT
+    assert profile.attachment_mode is AttachmentMode.GIT_IS_STORE
+    assert profile.history is History.GIT_NATIVE  # git-is-store ⟹ git-native
+    profile.validate()  # raises if the implication rule were violated
+
+
+def test_profile_is_read_only_in_t1(tmp_path):
+    profile = GitShardAdapter("git", _repo(tmp_path, {"Home.md": "h"})).profile()
+    assert profile.supports(Verb.READ)
+    assert not profile.supports(Verb.WRITE)
+
+
+def test_conformance_read_path_passes(tmp_path):
+    adapter = GitShardAdapter("git", _repo(tmp_path, {"Home.md": "h", "Other.md": "o"}))
+    report = run_conformance(adapter)
+    assert report.ok, report.diff()
+
+
+def test_unclaimed_write_raises_not_supported(tmp_path):
+    adapter = GitShardAdapter("git", _repo(tmp_path, {"Home.md": "h"}))
+    with pytest.raises(NotSupported):
+        adapter.write("Home", "new")  # read-only: honest absence
+
+
+def test_empty_repo_has_no_keys(tmp_path):
+    repo = tmp_path / "empty"
+    repo.mkdir()
+    _git(repo, "init", "--quiet")
+    adapter = GitShardAdapter("git", repo)
+    assert list(adapter.keys()) == []
+
+
+def test_bad_profile_combo_is_rejected():
+    # Sanity: the implication rule that backs the git profile actually bites when violated.
+    from shard_wiki.model import (
+        AccessGrant,
+        Addressing,
+        CapabilityProfile,
+        ContentOpacity,
+        MergeModel,
+        NativeQuery,
+        OperationalEnvelope,
+        Translation,
+        WriteGranularity,
+    )
+    from shard_wiki.provenance import Liveness
+
+    with pytest.raises(ProfileError):
+        CapabilityProfile(
+            substrate=Substrate.FILES,  # not git, but claims git-is-store
+            attachment_mode=AttachmentMode.GIT_IS_STORE,
+            write_granularity=WriteGranularity.NONE,
+            content_opacity=ContentOpacity.TRANSPARENT,
+            operational_envelope=OperationalEnvelope.LOCAL_UNBOUNDED,
+            access_grant=AccessGrant.OPEN,
+            liveness=Liveness.STATIC,
+            history=History.NONE,
+            merge_model=MergeModel.NONE,
+            addressing=Addressing.PATH,
+            native_query=NativeQuery.NONE,
+            translation=Translation.NATIVE,
+            supported_verbs=frozenset({Verb.READ}),
+        ).validate()