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>

src/shard_wiki/engine/adapter.py

@@ -0,0 +1,82 @@
+"""EngineShardAdapter — the engine exposed as a canonical-mode shard (WikiEngineCoreArchitecture
+§6, E-1/E-5).
+
+The engine is *one shard*: the orchestrator consumes it only through this `ShardAdapter`. The
+adapter is backed by the kernel (T1) + a composed extension set (T2/T3); its §A capability
+profile is **derived from the active extensions** (T4), so the orchestrator sees an honest,
+conformance-verifiable profile that reflects exactly what is activated. Read/write run the
+extensions' transform hooks; everything above this stays in the orchestrator (no union/projection
+import).
+"""
+
+from __future__ import annotations
+
+from collections.abc import Iterable
+
+from shard_wiki.adapters import ShardAdapter
+from shard_wiki.engine.activation import ActivationContext, ActivationProvider, ActivationResolver
+from shard_wiki.engine.extension import ActiveExtensions, ExtensionRuntime, Hook
+from shard_wiki.engine.kernel import EngineKernel
+from shard_wiki.engine.profile import derive_profile
+from shard_wiki.model import CapabilityProfile, NotSupported, Page, Verb
+
+__all__ = ["EngineShardAdapter", "build_engine_shard"]
+
+
+class EngineShardAdapter(ShardAdapter):
+    def __init__(
+        self,
+        kernel: EngineKernel,
+        active: ActiveExtensions,
+        base_profile: CapabilityProfile | None = None,
+    ) -> None:
+        self._kernel = kernel
+        self._active = active
+        self._profile = derive_profile(active, base_profile)  # validated (E-5)
+
+    @property
+    def shard_id(self) -> str:
+        return self._kernel.shard_id
+
+    def profile(self) -> CapabilityProfile:
+        return self._profile
+
+    def keys(self) -> Iterable[str]:
+        return self._kernel.keys()
+
+    def read(self, key: str) -> Page:
+        page = self._kernel.read(key)
+        return self._active.dispatch_transform(Hook.ON_READ, page, {"shard_id": self.shard_id})
+
+    def current_rev(self, key: str) -> str | None:
+        return self._kernel.current_rev(key)
+
+    def write(self, key: str, body: str) -> Page:
+        if not self._profile.supports(Verb.WRITE):
+            raise NotSupported(f"{type(self).__name__} ({self.shard_id}) is read-only")
+        body = self._active.dispatch_transform(
+            Hook.ON_WRITE, body, {"shard_id": self.shard_id, "key": key}
+        )
+        return self._kernel.write(key, body)
+
+
+def build_engine_shard(
+    shard_id: str,
+    runtime: ExtensionRuntime,
+    *,
+    activate: Iterable[str] | None = None,
+    provider: ActivationProvider | None = None,
+    context: ActivationContext | None = None,
+    base_profile: CapabilityProfile | None = None,
+) -> EngineShardAdapter:
+    """Stand up an engine shard: resolve which extensions are active (explicit ``activate`` ids,
+    or via an activation ``provider`` over the runtime's available set), compose them, and wrap a
+    fresh kernel as a `ShardAdapter`.
+    """
+    if provider is not None:
+        ctx = context or ActivationContext(shard_id)
+        ids = ActivationResolver(provider).active_extensions(runtime.available(), ctx)
+    else:
+        ids = set(activate or ())
+    active = runtime.activate(ids)
+    return EngineShardAdapter(EngineKernel(shard_id), active, base_profile)