feat: SPO stack hardening — bitmap widening, sparse fingerprints, integrity verification

Core fixes from PR #167/#168 review, rewritten from spec:

- sparse.rs: Widen bitmap [u64;2] → [u64;BITMAP_WORDS=4] to cover all 256 positions
- builder.rs: Fix invalid hex literal (0xCHA1_D15C → 0xC4A1_D15C), rewrite label_fp()
  to produce ~11% density sparse fingerprints via xorshift64 PRNG
- store.rs: Add TruthGate epistemic filter (OPEN/STRONG/CERTAIN), fix scent/Hamming
  scale mismatch with separate scent_radius parameter, add gated query methods
- geometry.rs: Add ContainerGeometry::Spo = 6 variant
- mod.rs: Wire pub mod spo (was missing — ~2000 lines of dead code)
- bind_space.rs: Add clam_merkle field to BindNode, stamp ClamPath + MerkleRoot
  on write_dn_node()/write_dn_path(), add verify_lineage() + Epoch snapshot

All 61 tests pass (24 SPO + 32 ClamPath + 5 bind_space integrity).

https://claude.ai/code/session_013JU8MRtxRRTtuc5217r6s5

Author: claude

crates/ladybug-contract/src/geometry.rs

@@ -34,6 +34,12 @@ pub enum ContainerGeometry {
     /// Adjacency is implicit in position. Spine = XOR of children.
     /// Total record: (N+1) × 1 KB.
     Tree = 5,
+
+    /// 1 content container: three sparse axes (Subject × Predicate × Object)
+    /// packed into a single Container. Forward, reverse, and relation queries
+    /// are native axis scans — no join, no edge table.
+    /// Total record: 2 × 2 KB = 4 KB (meta + content).
+    Spo = 6,
 }
 
 impl ContainerGeometry {
@@ -46,6 +52,7 @@ impl ContainerGeometry {
             ContainerGeometry::Extended => 2,
             ContainerGeometry::Chunked => 1, // just summary; chunks added later
             ContainerGeometry::Tree => 1,    // root; children added later
+            ContainerGeometry::Spo => 1,     // three sparse axes in one container
         }
     }
 
@@ -58,6 +65,7 @@ impl ContainerGeometry {
             3 => Some(ContainerGeometry::Extended),
             4 => Some(ContainerGeometry::Chunked),
             5 => Some(ContainerGeometry::Tree),
+            6 => Some(ContainerGeometry::Spo),
             _ => None,
         }
     }

src/graph/mod.rs

@@ -13,6 +13,8 @@ pub use edge::{Edge, EdgeType};
 pub use traversal::Traversal;
 
 pub mod avx_engine;
+
+pub mod spo;
 pub use avx_engine::{
     FingerprintGraph, QueryMatch, avx512_available, batched_query, hamming_distance, simd_info,
 };

src/graph/spo/builder.rs

@@ -4,7 +4,7 @@
 //! Edges:  X = BIND(src, permute(verb,1)), Y = verb, Z = BIND(tgt, permute(verb,2))
 //! Meta:   X = BUNDLE(chain X axes), Y = CHAIN_DISCOVERED, Z = BUNDLE(chain Z axes)
 
-use ladybug_contract::container::Container;
+use ladybug_contract::container::{Container, CONTAINER_WORDS};
 use ladybug_contract::nars::TruthValue;
 use ladybug_contract::record::CogRecord;
 
@@ -118,8 +118,8 @@ impl SpoBuilder {
         let z_refs: Vec<&Container> = z_denses.iter().collect();
 
         let x_dense = Container::bundle(&x_refs);
-        // Y axis: deterministic "chain discovered" marker
-        let y_dense = Container::random(0xCHA1_D15C); // CHAIN_DISCOVERED seed
+        // Y axis: sparse deterministic "chain discovered" marker
+        let y_dense = label_fp("CHAIN_DISCOVERED");
         let z_dense = Container::bundle(&z_refs);
 
         let x = SparseContainer::from_dense(&x_dense);
@@ -187,15 +187,40 @@ impl SpoBuilder {
 // CONVENIENCE FUNCTIONS
 // ============================================================================
 
-/// Create a deterministic fingerprint from a string label (for testing/seeding).
+/// Target density for label fingerprints (~11%).
+/// At 256 words, 28 non-zero words ≈ 11% density.
+/// Three such axes (28+28+28 + 12 bitmap = 96) fit comfortably in 256 words.
+const LABEL_FP_TARGET_WORDS: usize = 28;
+
+/// Create a deterministic sparse fingerprint from a string label.
+///
+/// Produces ~11% density so three axes pack into one Container.
+/// Deterministic: same label always produces the same fingerprint.
 pub fn label_fp(label: &str) -> Container {
-    // Simple hash: sum bytes with mixing
+    // Hash the label to a seed
     let mut seed = 0u64;
     for (i, b) in label.bytes().enumerate() {
         seed ^= (b as u64).wrapping_mul(0x9e3779b97f4a7c15);
         seed = seed.rotate_left((i as u32) % 64);
     }
-    Container::random(seed)
+
+    // Use the seed to deterministically select which words are non-zero
+    // and what values they contain.
+    let mut container = Container::zero();
+    let mut rng = seed;
+    for _ in 0..LABEL_FP_TARGET_WORDS {
+        // Simple xorshift64 for deterministic PRNG
+        rng ^= rng << 13;
+        rng ^= rng >> 7;
+        rng ^= rng << 17;
+        let pos = (rng as usize) % CONTAINER_WORDS;
+        // Generate a non-zero value
+        rng ^= rng << 13;
+        rng ^= rng >> 7;
+        rng ^= rng << 17;
+        container.words[pos] = rng | 1; // ensure non-zero
+    }
+    container
 }
 
 /// Create a deterministic DN hash from a string (for testing).
@@ -254,9 +279,9 @@ mod tests {
 
     #[test]
     fn test_build_edge_three_axes() {
-        let src = Container::random(1); // Jan
-        let verb = Container::random(2); // KNOWS
-        let tgt = Container::random(3); // Ada
+        let src = label_fp("Jan");
+        let verb = label_fp("KNOWS");
+        let tgt = label_fp("Ada");
 
         let record = SpoBuilder::build_edge(
             dn_hash("jan_knows_ada"),
@@ -283,11 +308,11 @@ mod tests {
 
     #[test]
     fn test_build_meta_awareness() {
-        let src = Container::random(10);
-        let verb1 = Container::random(20);
-        let tgt1 = Container::random(30);
-        let verb2 = Container::random(40);
-        let tgt2 = Container::random(50);
+        let src = label_fp("Alice");
+        let verb1 = label_fp("KNOWS");
+        let tgt1 = label_fp("Rust");
+        let verb2 = label_fp("ENABLES");
+        let tgt2 = label_fp("CAM");
 
         let edge1 = SpoBuilder::build_edge(
             dn_hash("e1"), &src, &verb1, &tgt1,

src/graph/spo/mod.rs

@@ -17,7 +17,7 @@ pub mod store;
 pub mod builder;
 
 // Re-exports
-pub use sparse::{SparseContainer, SpoError, AxisDescriptors, pack_axes, unpack_axes};
+pub use sparse::{SparseContainer, SpoError, AxisDescriptors, pack_axes, unpack_axes, BITMAP_WORDS};
 pub use scent::NibbleScent;
-pub use store::{SpoStore, QueryHit, QueryAxis};
+pub use store::{SpoStore, QueryHit, QueryAxis, TruthGate};
 pub use builder::{SpoBuilder, label_fp, dn_hash};