init: Engram v0.1 — native memory substrate for accumulating intelligence

Memory is not stored and retrieved — it is activated and propagated.
Implements the spreading activation model with salience decay, typed edges,
four memory tiers, and flat cosine vector search over a sled embedded store.

engram/crates/engram-core/src/lib.rs

@@ -0,0 +1,46 @@
+/// Engram — a local-first memory substrate for accumulating intelligence.
+///
+/// An engram is the physical trace of a memory in the brain — the actual encoded
+/// substrate. This crate provides the storage and retrieval primitives that model
+/// how biological memory works: not as query-and-retrieve, but as
+/// activation-and-propagation.
+///
+/// # Quick Start
+///
+/// ```rust,no_run
+/// use engram_core::{EngramDb, Node, Edge, NodeType, MemoryTier, RelationType};
+/// use std::path::Path;
+///
+/// let db = EngramDb::open(Path::new("/tmp/my-engram")).unwrap();
+///
+/// let node = Node::new(
+///     NodeType::Memory,
+///     vec![0.9, 0.1, 0.3, 0.7],
+///     b"The spreading activation model of memory".to_vec(),
+///     MemoryTier::Semantic,
+///     0.9,
+/// );
+/// let id = db.put_node(node).unwrap();
+///
+/// // Retrieve by spreading activation from a seed
+/// let results = db.activate(&[id], &[0.8, 0.2, 0.3, 0.6], 3, 10).unwrap();
+/// for r in results {
+///     println!("{:.4} hops={} {:?}", r.activation_strength, r.hops,
+///              String::from_utf8_lossy(&r.node.content));
+/// }
+/// ```
+pub mod activation;
+pub mod db;
+pub mod error;
+pub mod graph;
+pub mod salience;
+pub mod storage;
+pub mod types;
+pub mod vector;
+
+// Re-export the public surface
+pub use db::EngramDb;
+pub use error::{EngramError, EngramResult};
+pub use types::{
+    ActivatedNode, Edge, MemoryTier, Node, NodeType, RelationType, ScoredNode, now_ms,
+};