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>

SCOPE.md

@@ -17,7 +17,7 @@ Learnings update both SCOPE and INTENT where necessary.
 
 | Layer | State |
 |-------|-------|
-| Code | Foundation slice implemented (SHARD-WP-0007): `provenance` + `policy` leaves, `model` (Identity/Placement/Span/Page/CapabilityProfile), `adapters` (contract + FolderAdapter + conformance suite), `coordination` (event-sourced DecisionLog), `union` (resolution + chorus, overlay-aware), `InformationSpace` orchestrator. Write path added (SHARD-WP-0008): writable adapter, overlay engine (draft→patch→apply-under-drift), edit() unifies write-through + overlay-before-mutation. Native engine implemented (SHARD-WP-0014): `engine` (kernel + typed-extension runtime + per-shard activation [ADR-0001] + capability-profile-from-extensions + EngineShardAdapter + the `ext.struct` built-in) — an engine shard attaches to an InformationSpace as a canonical-mode shard. Git-backed coordination log (SHARD-WP-0009): `DecisionLog` storage factored behind an `EventStore`; `GitEventStore` makes the log git-addressable (each space a ref, append = immutable CAS-guarded commit), a per-space `AppendAuthority` (lease) gives a single-writer total order with re-grantable HA hand-off, cross-process read-your-writes verified, and a verbatim one-time importer (`migrate_space`/JSONL) replays in-memory logs into git; `InformationSpace.git_backed(...)` wires it. Derived views (SHARD-WP-0010): `views` (wikilink + red-link model, BackLinks, RecentChanges, AllPages/SiteMap) — recomputable, provenance-carrying, presentation-free, exposed via `InformationSpace.backlinks/recent_changes/all_pages/site_map`. Incremental-first derived tier (SHARD-WP-0011): `incremental` (indexed equivalence via MinHash/LSH blocking + verify, change-driven delta maintenance with retraction/propagation, Merkle-style digest + self-healing I-2 consistency-checker, `UnionIndex` routed behind `InformationSpace.all_pages` with rebuild as explicit fallback). 173 tests green, ~97% coverage |
+| Code | Foundation slice implemented (SHARD-WP-0007): `provenance` + `policy` leaves, `model` (Identity/Placement/Span/Page/CapabilityProfile), `adapters` (contract + FolderAdapter + conformance suite), `coordination` (event-sourced DecisionLog), `union` (resolution + chorus, overlay-aware), `InformationSpace` orchestrator. Write path added (SHARD-WP-0008): writable adapter, overlay engine (draft→patch→apply-under-drift), edit() unifies write-through + overlay-before-mutation. Native engine implemented (SHARD-WP-0014): `engine` (kernel + typed-extension runtime + per-shard activation [ADR-0001] + capability-profile-from-extensions + EngineShardAdapter + the `ext.struct` built-in) — an engine shard attaches to an InformationSpace as a canonical-mode shard. Git-backed coordination log (SHARD-WP-0009): `DecisionLog` storage factored behind an `EventStore`; `GitEventStore` makes the log git-addressable (each space a ref, append = immutable CAS-guarded commit), a per-space `AppendAuthority` (lease) gives a single-writer total order with re-grantable HA hand-off, cross-process read-your-writes verified, and a verbatim one-time importer (`migrate_space`/JSONL) replays in-memory logs into git; `InformationSpace.git_backed(...)` wires it. Derived views (SHARD-WP-0010): `views` (wikilink + red-link model, BackLinks, RecentChanges, AllPages/SiteMap) — recomputable, provenance-carrying, presentation-free, exposed via `InformationSpace.backlinks/recent_changes/all_pages/site_map`. Incremental-first derived tier (SHARD-WP-0011): `incremental` (indexed equivalence via MinHash/LSH blocking + verify, change-driven delta maintenance with retraction/propagation, Merkle-style digest + self-healing I-2 consistency-checker, `UnionIndex` routed behind `InformationSpace.all_pages` with rebuild as explicit fallback). Second adapter (SHARD-WP-0012): `GitShardAdapter` — git-IS-store substrate (read=tracked *.md, write=commit, current_rev=per-path sha for drift, adopted git-native history), passes conformance, works across folder+git shards in union/overlay/edit with no core change (capability-as-data proven on a second substrate). 196 tests green, ~97% coverage |
 | Intent | `INTENT.md` established; authorization-in-core amendments drafted |
 | Research | yawex prior art; c2 origins; federation concepts; wikiengines overview (`research/260608-*/`); XWiki/TWiki/Foswiki deep dives (`research/260613-*/`); Xanadu + ZigZag + Roam + Obsidian + Notion + Joplin + Logseq + local-first workspaces (Anytype/AFFiNE/AppFlowy) + Trilium + Wiki.js + Federated Wiki + Wikibase + git-forge wikis + TiddlyWiki + ikiwiki + Quip + MojoMojo + Oddmuse + UseModWiki deep dives & shard-spectrum synthesis (`research/260614-*/`) |
 | Demand | NetKingdom integration asks captured, not yet negotiated |

src/shard_wiki/adapters/__init__.py

@@ -9,12 +9,13 @@ from shard_wiki.adapters.conformance import (
 )
 from shard_wiki.adapters.contract import CONTRACT_VERSION, ShardAdapter
 from shard_wiki.adapters.folder import FolderAdapter
-from shard_wiki.adapters.git import GitShardAdapter
+from shard_wiki.adapters.git import GitShardAdapter, PageRevision
 
 __all__ = [
     "ShardAdapter",
     "FolderAdapter",
     "GitShardAdapter",
+    "PageRevision",
     "CONTRACT_VERSION",
     "Check",
     "ConformanceReport",

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:

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

workplans/SHARD-WP-0012-git-shard-adapter.md

@@ -4,7 +4,7 @@ type: workplan
 title: "second adapter — git-IS-store shard (contract validation on a new substrate)"
 domain: whynot
 repo: shard-wiki
-status: active
+status: done
 owner: tegwick
 topic_slug: whynot
 created: "2026-06-15"
@@ -40,7 +40,7 @@ merge beyond fast-forward (apply-under-drift refuse is enough, as in SHARD-WP-00
 
 ```task
 id: SHARD-WP-0012-T1
-status: todo
+status: done
 priority: high
 state_hub_task_id: "8a1c7c80-a0cc-4e02-a611-1f1fd7dec57b"
 ```
@@ -54,7 +54,7 @@ implication rules. Tests: read tracked files; profile validates; conformance rea
 
 ```task
 id: SHARD-WP-0012-T2
-status: todo
+status: done
 priority: high
 state_hub_task_id: "b47dfb86-46c1-4e97-a62f-377719499ff2"
 ```
@@ -68,7 +68,7 @@ changes after an external commit.
 
 ```task
 id: SHARD-WP-0012-T3
-status: todo
+status: done
 priority: medium
 state_hub_task_id: "4c895f42-671d-4948-8bdf-941fd85644bb"
 ```