rename crates/ to engrams/, bindings/ to receptors/

- crates/ → engrams/ (Rust engrams live here)
- bindings/ → receptors/ (cross-language access points into the graph)
- Cargo.toml workspace paths updated

receptors/go/engram.h

@@ -0,0 +1,70 @@
+/**
+ * engram.h — C header for the engram FFI.
+ *
+ * Generated from crates/engram-ffi/src/lib.rs.
+ * To regenerate: cargo install cbindgen && cbindgen --crate engram-ffi -o bindings/go/engram.h
+ *
+ * Build the shared library:
+ *   cargo build --package engram-ffi --release
+ *   # macOS: target/release/libengram_ffi.dylib
+ *   # Linux: target/release/libengram_ffi.so
+ */
+#pragma once
+
+#include <stdint.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** Opaque handle to an open EngramDb. Obtained via engram_open. */
+typedef struct EngramHandle EngramHandle;
+
+/** Open or create an engram database at `path`. Returns null on error. */
+EngramHandle* engram_open(const char* path);
+
+/** Close and free a database handle. The pointer must not be used afterwards. */
+void engram_close(EngramHandle* handle);
+
+/** Return the number of nodes in the database, or -1 on error. */
+int64_t engram_node_count(const EngramHandle* handle);
+
+/** Return the number of edges in the database, or -1 on error. */
+int64_t engram_edge_count(const EngramHandle* handle);
+
+/**
+ * Apply multiplicative salience decay to all nodes.
+ * `factor` should be in (0.0, 1.0). Returns nodes updated, or -1 on error.
+ */
+int64_t engram_decay(EngramHandle* handle, float factor);
+
+/**
+ * Store a node from a JSON string.
+ * JSON: { "content": "...", "node_type": "Memory", "tier": "Episodic",
+ *         "importance": 0.8, "embedding": [f32, ...] }
+ * Returns a heap-allocated UUID string on success, null on error.
+ * Free with engram_free_string.
+ */
+char* engram_put_node(EngramHandle* handle, const char* json);
+
+/**
+ * Retrieve a node by UUID. Returns a heap-allocated JSON string, or null.
+ * Free with engram_free_string.
+ */
+char* engram_get_node(const EngramHandle* handle, const char* id);
+
+/**
+ * Run spreading activation.
+ * `req_json`: { "seeds": ["uuid", ...], "query_embedding": [f32, ...],
+ *               "max_depth": 3, "limit": 10 }
+ * Returns a heap-allocated JSON array, or null on error.
+ * Free with engram_free_string.
+ */
+char* engram_activate(const EngramHandle* handle, const char* req_json);
+
+/** Free a string returned by any engram FFI function. */
+void engram_free_string(char* s);
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif