feat(coordination): git backend wiring + verbatim log migration (WP-0009 T4)

InformationSpace.git_backed(space_id, repo_path) wires the git coordination log;
the default constructor stays in-memory for tests (new keyword-only store=). A
one-time importer (migrate_space / import_log / JSONL export+import) replays an
existing in-memory or JSON log into git verbatim — preserving seq, timestamp and
actor (union-without-erasure) and refusing out-of-order import. Same fold after
migration; no behavioural change to overlay/union. SCOPE updated; WP-0009 done.

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

src/shard_wiki/space.py

@@ -8,11 +8,15 @@ a network API is a later workplan.
 
 from __future__ import annotations
 
+from pathlib import Path
+
 from shard_wiki.adapters import ShardAdapter, assert_conformant
 from shard_wiki.coordination import (
     ApplyResult,
     DecisionLog,
+    EventStore,
     EventType,
+    GitEventStore,
     Overlay,
     OverlayEngine,
 )
@@ -24,12 +28,31 @@ __all__ = ["InformationSpace"]
 
 
 class InformationSpace:
-    def __init__(self, space_id: str, policy: Policy = DEFAULT_POLICY) -> None:
+    def __init__(
+        self,
+        space_id: str,
+        policy: Policy = DEFAULT_POLICY,
+        *,
+        store: EventStore | None = None,
+    ) -> None:
+        """Tie the slice together. ``store`` selects the coordination-log backend: the default
+        in-memory store (tests) or a git-addressable one. Use :meth:`git_backed` for the latter."""
         self.space_id = space_id
-        self.log = DecisionLog()
+        self.log = DecisionLog(store)
         self.union = UnionGraph(space_id, log=self.log, policy=policy)
         self.overlays = OverlayEngine(space_id, self.log)
 
+    @classmethod
+    def git_backed(
+        cls,
+        space_id: str,
+        repo_path: str | Path,
+        policy: Policy = DEFAULT_POLICY,
+    ) -> InformationSpace:
+        """An information space whose coordination log is git-addressable (history/patch/review/
+        backup — I-6). The decision log lives in the git repo at ``repo_path``."""
+        return cls(space_id, policy, store=GitEventStore(repo_path))
+
     def attach(self, adapter: ShardAdapter) -> None:
         """Attach a shard — only if it passes conformance (verified profile, I-3/§6.6)."""
         assert_conformant(adapter)