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>

src/shard_wiki/adapters/git.py

@@ -16,6 +16,7 @@ from __future__ import annotations
 import os
 import subprocess
 from collections.abc import Iterable
+from dataclasses import dataclass
 from pathlib import Path
 
 from shard_wiki.adapters.contract import ShardAdapter
@@ -40,7 +41,15 @@ from shard_wiki.model import (
 )
 from shard_wiki.provenance import Liveness, ProvenanceEnvelope, Staleness
 
-__all__ = ["GitShardAdapter"]
+__all__ = ["GitShardAdapter", "PageRevision"]
+
+
+@dataclass(frozen=True, slots=True)
+class PageRevision:
+    """One adopted git-native revision of a page: the commit sha and its subject line."""
+
+    sha: str
+    message: str
 
 _GIT_IDENTITY = {
     "GIT_AUTHOR_NAME": "shard-wiki",
@@ -66,11 +75,12 @@ class GitShardAdapter(ShardAdapter):
         return self._shard_id
 
     def profile(self) -> CapabilityProfile:
-        # Write is a commit; VERSION is git-native history (adopt, §A.5). Read-only drops both.
-        verbs = {Verb.READ}
+        # VERSION is always available — a git-IS-store has git-native history to adopt (§A.5),
+        # read-only or not. WRITE (= commit, PER_PAGE) is added only in writable mode.
+        verbs = {Verb.READ, Verb.VERSION}
         granularity = WriteGranularity.NONE
         if self._writable:
-            verbs |= {Verb.WRITE, Verb.VERSION}
+            verbs |= {Verb.WRITE}
             granularity = WriteGranularity.PER_PAGE
         return CapabilityProfile(
             substrate=Substrate.GIT,
@@ -133,6 +143,23 @@ class GitShardAdapter(ShardAdapter):
         sha = self._git("log", "-1", "--format=%H", "--", rel).decode().strip()
         return sha or None
 
+    def history(self, key: str) -> tuple[PageRevision, ...]:
+        """Adopt git-native history (§A.5): the commit list for ``key``'s path, newest-first.
+
+        VERSION-gated; raises ``KeyError`` for an unknown page. Each revision is a commit sha +
+        subject — the native log surfaced through the contract, not re-implemented.
+        """
+        if not self.profile().supports(Verb.VERSION):
+            raise NotSupported(f"{type(self).__name__} does not support version")
+        if not self._path_for(key).is_file():
+            raise KeyError(key)
+        out = self._git("log", "--format=%H%x00%s", "--", f"{key}.md").decode()
+        revisions = []
+        for line in out.splitlines():
+            sha, _, message = line.partition("\x00")
+            revisions.append(PageRevision(sha=sha, message=message))
+        return tuple(revisions)
+
     # -- git plumbing --------------------------------------------------------
 
     def _path_for(self, key: str) -> Path: