feat(engine): EngineShardAdapter — engine as a canonical-mode shard (WP-0014 T5)

engine/adapter.py: EngineShardAdapter implements adapters.ShardAdapter (read/write
run extension transform hooks; profile derived from active extensions, E-5;
current_rev for apply-under-drift) + build_engine_shard() helper (explicit ids or
activation provider). runtime.available() added. Engine shard passes assert_conformant
and attaches to an InformationSpace — resolve + edit (overlay->apply->write-through)
work, and the declared profile reflects the active extensions. 5 tests green, pyflakes clean.

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

tests/test_engine_adapter.py

@@ -0,0 +1,80 @@
+"""Tests for EngineShardAdapter (SHARD-WP-0014 T5): engine as a canonical-mode shard."""
+
+from shard_wiki import InformationSpace
+from shard_wiki.adapters import assert_conformant
+from shard_wiki.engine import (
+    Extension,
+    ExtensionRuntime,
+    Hook,
+    ProfileContribution,
+    StaticProvider,
+    build_engine_shard,
+)
+from shard_wiki.engine.activation import ActivationContext
+from shard_wiki.model import Verb
+
+
+class StructProfileExt(Extension):
+    """Profile-only extension (no body transform → write stays content-preserving)."""
+
+    id = "ext.struct"
+
+    def hooks(self):
+        return {
+            Hook.ON_PROFILE: lambda p, c: ProfileContribution(
+                verbs_add=frozenset({Verb.STRUCTURED_PAYLOAD})
+            )
+        }
+
+
+def _runtime():
+    rt = ExtensionRuntime()
+    rt.register(StructProfileExt())
+    return rt
+
+
+def test_kernel_only_engine_shard_is_conformant():
+    shard = build_engine_shard("eng", ExtensionRuntime(), activate=set())
+    shard.write("Home", "hi")
+    report = assert_conformant(shard)            # read + positive write probe
+    assert report.ok
+    assert shard.profile().supports(Verb.WRITE)
+    assert not shard.profile().supports(Verb.STRUCTURED_PAYLOAD)
+
+
+def test_profile_reflects_activated_extensions():
+    off = build_engine_shard("a", _runtime(), activate=set())
+    on = build_engine_shard("b", _runtime(), activate={"ext.struct"})
+    assert not off.profile().supports(Verb.STRUCTURED_PAYLOAD)
+    assert on.profile().supports(Verb.STRUCTURED_PAYLOAD)   # E-5
+    assert_conformant(on)
+
+
+def test_activation_via_provider():
+    provider = StaticProvider(flags={"ext.struct": True})
+    shard = build_engine_shard("c", _runtime(), provider=provider, context=ActivationContext("c"))
+    assert shard.profile().supports(Verb.STRUCTURED_PAYLOAD)
+
+
+def test_attach_resolve_edit_through_engine_shard(tmp_path):
+    space = InformationSpace("team")
+    space.attach(build_engine_shard("wikiE", ExtensionRuntime(), activate=set()))
+    # seed a page directly via the shard, then read + edit through the orchestrator
+    space.union.shard("wikiE").write("Home", "v1")
+    assert space.read("Home").body == "v1"
+    result = space.edit("Home", "v2")            # overlay -> apply-under-drift -> write-through
+    assert result.status.value == "applied"
+    assert space.read("Home").body == "v2"
+
+
+def test_on_write_transform_runs():
+    class Upper(Extension):
+        id = "ext.upper"
+        def hooks(self):
+            return {Hook.ON_WRITE: lambda body, ctx: body.upper()}
+
+    rt = ExtensionRuntime()
+    rt.register(Upper())
+    shard = build_engine_shard("u", rt, activate={"ext.upper"})
+    shard.write("P", "quiet")
+    assert shard.read("P").body == "QUIET"       # extension transformed the write