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>

tests/test_coordination_migration.py

@@ -0,0 +1,74 @@
+"""Migration + wiring of the git coordination backend (SHARD-WP-0009 T4)."""
+
+from shard_wiki.coordination import (
+    DecisionLog,
+    EventType,
+    GitEventStore,
+    InMemoryEventStore,
+    export_jsonl,
+    import_jsonl,
+    migrate_space,
+)
+from shard_wiki.space import InformationSpace
+
+
+def test_information_space_git_backed_uses_git_log(tmp_path):
+    space = InformationSpace.git_backed("space-1", tmp_path / "coord")
+    assert isinstance(space.log._store, GitEventStore)
+    space.alias("Home", "shardA:Index")
+    # Read-your-writes through the orchestrator's git-backed log.
+    assert space.log.fold("space-1").resolve_alias("Home") == "shardA:Index"
+
+
+def test_default_information_space_stays_in_memory():
+    space = InformationSpace("space-1")
+    assert isinstance(space.log._store, InMemoryEventStore)
+
+
+def test_migrate_space_preserves_order_and_provenance(tmp_path):
+    source = InMemoryEventStore()
+    e0 = source.append("s", EventType.ALIAS_SET, {"alias": "Home", "target": "x:1"}, actor="ana")
+    source.append("s", EventType.BINDING_MADE, {"members": ["a", "b"]}, actor="ben")
+
+    dest = GitEventStore(tmp_path / "coord")
+    n = migrate_space(source, "s", dest)
+    assert n == 2
+
+    migrated = dest.events("s")
+    assert [e.seq for e in migrated] == [0, 1]
+    # Provenance preserved verbatim — actor and timestamp survive the move (no restamping).
+    assert migrated[0].actor == "ana"
+    assert migrated[1].actor == "ben"
+    assert migrated[0].timestamp == e0.timestamp
+
+
+def test_migration_yields_identical_fold(tmp_path):
+    source = DecisionLog(InMemoryEventStore())
+    for typ, payload in [
+        (EventType.ALIAS_SET, {"alias": "Home", "target": "x:1"}),
+        (EventType.BINDING_MADE, {"members": ["a", "b"]}),
+        (EventType.BINDING_MADE, {"members": ["b", "c"]}),
+        (EventType.ALIAS_SET, {"alias": "Home", "target": "x:2"}),
+    ]:
+        source.append("s", typ, payload)
+
+    dest = GitEventStore(tmp_path / "coord")
+    migrate_space(source._store, "s", dest)
+    after = DecisionLog(dest)
+    assert after.fold("s").aliases == source.fold("s").aliases
+    assert after.fold("s").equivalence_groups == source.fold("s").equivalence_groups
+
+
+def test_jsonl_round_trip_into_git(tmp_path):
+    source = InMemoryEventStore()
+    source.append("s", EventType.ALIAS_SET, {"alias": "Home", "target": "x:1"})
+    source.append("s", EventType.PAGE_FORKED, {"source": "p", "fork": "q"})
+
+    path = tmp_path / "log.jsonl"
+    assert export_jsonl(source.events("s"), path) == 2
+
+    dest = GitEventStore(tmp_path / "coord")
+    assert import_jsonl(path, dest) == 2
+    state = DecisionLog(dest).fold("s")
+    assert state.resolve_alias("Home") == "x:1"
+    assert state.equivalent_to("p") == frozenset({"p", "q"})