feat(memory): add graph runtime import store

docs/memory-graph-runtime.md

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+# Memory Graph Runtime
+
+`kontextual-engine` owns the operational side of the Markitect memory graph
+contracts. The engine imports Markitect-compatible graph/profile envelopes,
+maps source contract ids to stable runtime ids, and stores graph nodes, edges,
+and append-only events for later governed retrieval and lifecycle operations.
+
+This repository does not redefine the Markitect syntax vocabulary. The first
+runtime slice checks only schema compatibility, required ids, edge endpoint
+integrity, and append-only event identity. Node and edge kind validation remains
+with `markitect-tool`.
+
+## Implemented Slice
+
+- `MemoryGraphImportResult` maps `markitect.memory.graph.v1` contracts into
+  runtime records.
+- `MemoryProfileRecord` maps `markitect.memory.profile.v1` profiles without
+  enforcing runtime policy, latency, retention, or compaction declarations yet.
+- `MemoryGraphRepository` defines the storage port for profile, node, edge, and
+  event records.
+- `InMemoryMemoryGraphRepository` provides deterministic local storage for
+  tests and future service wiring.
+- `MemoryRuntimeService.import_markitect_graph()` persists an imported graph and
+  can attach an audit event when an `OperationContext` is supplied.
+
+## Boundary
+
+`markitect-tool` remains responsible for:
+
+- profile and graph syntax validation
+- graph selection compilation into context packages
+- deterministic package summaries and source-span preservation
+
+`kontextual-engine` is responsible for:
+
+- runtime ids and persistence
+- append-only event storage
+- permission-aware retrieval and context assembly
+- retention, refresh, compaction, review gates, and audit behavior
+
+`infospace-bench` should consume these records and Markitect fixtures to measure
+retrieval quality, latency, budget pressure, and regression behavior.