diff --git a/algebra/backend.py b/algebra/backend.py
new file mode 100644
index 00000000..ef9c22c9
--- /dev/null
+++ b/algebra/backend.py
@@ -0,0 +1,75 @@
+"""
+Backend dispatch: use Rust extension (core_rs) when available,
+fall back to pure Python (algebra/cl41.py etc.) transparently.
+
+This module is the single switch. All algebra modules import from here
+for performance-critical ops. Pure Python is always the fallback —
+the system is never broken by a missing Rust build.
+
+Usage:
+    from algebra.backend import geometric_product, versor_apply, cga_inner, vault_recall
+"""
+
+import numpy as np
+
+try:
+    import core_rs as _rs
+    _RUST = True
+except ImportError:
+    _RUST = False
+
+
+def geometric_product(A: np.ndarray, B: np.ndarray) -> np.ndarray:
+    if _RUST:
+        return np.asarray(_rs.geometric_product(A, B), dtype=np.float32)
+    from algebra.cl41 import geometric_product as _gp
+    return _gp(A, B)
+
+
+def versor_apply(V: np.ndarray, F: np.ndarray) -> np.ndarray:
+    if _RUST:
+        return np.asarray(_rs.versor_apply(V, F), dtype=np.float32)
+    from algebra.versor import versor_apply as _va
+    return _va(V, F)
+
+
+def versor_condition(F: np.ndarray) -> float:
+    if _RUST:
+        return float(_rs.versor_condition(F))
+    from algebra.versor import versor_condition as _vc
+    return _vc(F)
+
+
+def normalize_to_versor(F: np.ndarray) -> np.ndarray:
+    if _RUST:
+        return np.asarray(_rs.normalize_to_versor(F), dtype=np.float32)
+    from algebra.versor import normalize_to_versor as _nv
+    return _nv(F)
+
+
+def cga_inner(X: np.ndarray, Y: np.ndarray) -> float:
+    if _RUST:
+        return float(_rs.cga_inner(X, Y))
+    from algebra.cga import cga_inner as _ci
+    return _ci(X, Y)
+
+
+def vault_recall(versors: list, query: np.ndarray, top_k: int = 5) -> list:
+    """
+    Top-k CGA inner product recall.
+    Rust path: parallel Rayon scan (releases GIL, true multithreaded).
+    Python path: sequential list comprehension.
+    """
+    if _RUST:
+        results = _rs.vault_recall(versors, query, top_k)
+        # results: list of (index, score)
+        return results
+    from algebra.cga import cga_inner as _ci
+    scores = [(i, _ci(query, v)) for i, v in enumerate(versors)]
+    scores.sort(key=lambda x: -x[1])
+    return scores[:top_k]
+
+
+def using_rust() -> bool:
+    """Returns True if the Rust extension is loaded."""
+    return _RUST
diff --git a/core-rs/build.rs b/core-rs/build.rs
new file mode 100644
index 00000000..0c1c7b7b
--- /dev/null
+++ b/core-rs/build.rs
@@ -0,0 +1,7 @@
+// build.rs: nothing special needed for PyO3 — maturin handles the rest.
+// This file exists as an extension point for future build-time codegen
+// (e.g. generating the full Cl(4,1) multiplication table as a static array
+// rather than computing it at OnceLock init time).
+fn main() {
+    println!("cargo:rerun-if-changed=src/");
+}
diff --git a/core-rs/pyproject.toml b/core-rs/pyproject.toml
new file mode 100644
index 00000000..48ed8161
--- /dev/null
+++ b/core-rs/pyproject.toml
@@ -0,0 +1,8 @@
+[build-system]
+requires = ["maturin>=1.5,<2.0"]
+build-backend = "maturin"
+
+[tool.maturin]
+features = ["extension-module"]
+module-name = "core_rs"
+python-source = "python"
diff --git a/core-rs/src/holonomy.rs b/core-rs/src/holonomy.rs
new file mode 100644
index 00000000..dafda0c5
--- /dev/null
+++ b/core-rs/src/holonomy.rs
@@ -0,0 +1,81 @@
+//! Holonomy encoder in Rust — the forward+reverse versor walk.
+//!
+//! This is in Rust because:
+//!   - Long prompts (100+ tokens) do 200+ geometric products in sequence
+//!   - Each geometric product is O(32^2) = 1024 multiply-adds
+//!   - Python overhead per call makes this 10-50x slower than necessary
+//!   - Rust collapses the entire walk into a single allocation-free loop
+
+use crate::cl41::{geometric_product_raw, reverse_raw};
+use crate::versor::normalize_to_versor_raw;
+use thiserror::Error;
+
+#[derive(Debug, Error)]
+pub enum HolonomyError {
+    #[error("Empty word list")]
+    Empty,
+    #[error("Versor error: {0}")]
+    Versor(String),
+}
+
+/// Compute holonomy of a word versor sequence.
+///
+/// Forward walk:  F = w0 * w1 * ... * wn
+/// Reverse walk:  R = (1-alpha) * rev(wn) * ... * rev(w0)
+/// Holonomy:      H = normalize(F * R)
+///
+/// weights: per-word scalars (inverse frequency). If empty, uniform 1.0.
+/// alpha:   blend factor [0,1]. 0.5 recommended.
+pub fn holonomy_encode_raw(
+    words: &[[f32; 32]],
+    weights: &[f32],
+    alpha: f32,
+) -> Result<[f32; 32], HolonomyError> {
+    if words.is_empty() {
+        return Err(HolonomyError::Empty);
+    }
+
+    let n = words.len();
+    let use_weights = !weights.is_empty() && weights.len() == n;
+
+    // Forward accumulation
+    let mut scaled = words[0];
+    if use_weights {
+        let w = weights[0];
+        for x in scaled.iter_mut() { *x *= w; }
+    }
+    let mut f = normalize_to_versor_raw(&scaled)
+        .map_err(|e| HolonomyError::Versor(e.to_string()))?;
+
+    for k in 1..n {
+        let mut wk = words[k];
+        if use_weights {
+            let w = weights[k];
+            for x in wk.iter_mut() { *x *= w; }
+        }
+        let wk_norm = normalize_to_versor_raw(&wk)
+            .map_err(|e| HolonomyError::Versor(e.to_string()))?;
+        f = geometric_product_raw(&f, &wk_norm)
+            .map_err(|e| HolonomyError::Versor(e.to_string()))?;
+    }
+
+    // Reverse accumulation with (1-alpha) damping
+    let damp = 1.0 - alpha;
+    let mut last_rev = reverse_raw(&words[n - 1]);
+    for x in last_rev.iter_mut() { *x *= damp; }
+    let mut r = normalize_to_versor_raw(&last_rev)
+        .map_err(|e| HolonomyError::Versor(e.to_string()))?;
+
+    for k in (0..n - 1).rev() {
+        let rev_wk = reverse_raw(&words[k]);
+        let rev_norm = normalize_to_versor_raw(&rev_wk)
+            .map_err(|e| HolonomyError::Versor(e.to_string()))?;
+        r = geometric_product_raw(&rev_norm, &r)
+            .map_err(|e| HolonomyError::Versor(e.to_string()))?;
+    }
+
+    let h = geometric_product_raw(&f, &r)
+        .map_err(|e| HolonomyError::Versor(e.to_string()))?;
+    normalize_to_versor_raw(&h)
+        .map_err(|e| HolonomyError::Versor(e.to_string()))
+}
diff --git a/core-rs/src/propagate.rs b/core-rs/src/propagate.rs
new file mode 100644
index 00000000..b5ba75ee
--- /dev/null
+++ b/core-rs/src/propagate.rs
@@ -0,0 +1,48 @@
+//! Propagation loop in Rust — tight versor_apply chain.
+//!
+//! propagate_n steps runs N versor_apply calls in a single Rust stack frame,
+//! eliminating Python dispatch overhead for each step.
+//! Used by generate/stream.py when stepping more than one token at a time
+//! (e.g. prefill, speculative steps, or batch generation).
+
+use crate::versor::versor_apply_raw;
+use thiserror::Error;
+
+#[derive(Debug, Error)]
+pub enum PropagateError {
+    #[error("Versor error during propagation: {0}")]
+    Versor(String),
+}
+
+/// Run n versor_apply steps in sequence.
+/// rotors: slice of n [f32;32] versors to apply in order
+/// f0:     initial field state
+/// Returns final field state after n steps.
+pub fn propagate_n_raw(
+    rotors: &[[f32; 32]],
+    f0: &[f32; 32],
+) -> Result<[f32; 32], PropagateError> {
+    let mut f = *f0;
+    for v in rotors {
+        f = versor_apply_raw(v, &f)
+            .map_err(|e| PropagateError::Versor(e.to_string()))?;
+    }
+    Ok(f)
+}
+
+/// Parallel batch propagation: apply the same rotor V to a batch of field states.
+/// Used for beam search or multi-hypothesis generation.
+/// Returns new batch of field states.
+pub fn propagate_batch_raw(
+    v: &[f32; 32],
+    fields: &[[f32; 32]],
+) -> Result<Vec<[f32; 32]>, PropagateError> {
+    use rayon::prelude::*;
+    fields
+        .par_iter()
+        .map(|f| {
+            versor_apply_raw(v, f)
+                .map_err(|e| PropagateError::Versor(e.to_string()))
+        })
+        .collect()
+}
diff --git a/core-rs/tests/test_cga.rs b/core-rs/tests/test_cga.rs
new file mode 100644
index 00000000..0555e3cc
--- /dev/null
+++ b/core-rs/tests/test_cga.rs
@@ -0,0 +1,48 @@
+#[cfg(test)]
+mod tests {
+    use crate::cga::{cga_inner_raw, embed_point_raw, is_null_raw, null_project_raw};
+
+    #[test]
+    fn test_embedded_point_is_null() {
+        let p = [1.0f32, 2.0, 3.0];
+        let x = embed_point_raw(&p);
+        assert!(is_null_raw(&x, 1e-5).unwrap(), "Embedded point should be null");
+    }
+
+    #[test]
+    fn test_origin_is_null() {
+        let x = embed_point_raw(&[0.0, 0.0, 0.0]);
+        assert!(is_null_raw(&x, 1e-5).unwrap());
+    }
+
+    #[test]
+    fn test_cga_inner_symmetry() {
+        let x = embed_point_raw(&[1.0, 0.0, 0.0]);
+        let y = embed_point_raw(&[0.0, 1.0, 0.0]);
+        let xy = cga_inner_raw(&x, &y).unwrap();
+        let yx = cga_inner_raw(&y, &x).unwrap();
+        assert!((xy - yx).abs() < 1e-6, "cga_inner not symmetric");
+    }
+
+    #[test]
+    fn test_cga_distance_identity() {
+        // Points at distance 1: cga_inner = -d^2/2 = -0.5
+        let x = embed_point_raw(&[0.0, 0.0, 0.0]);
+        let y = embed_point_raw(&[1.0, 0.0, 0.0]);
+        let inner = cga_inner_raw(&x, &y).unwrap();
+        assert!((inner - (-0.5)).abs() < 1e-5,
+            "Expected -0.5 for unit-distance points, got {}", inner);
+    }
+
+    #[test]
+    fn test_null_project_restores_null() {
+        let p = [1.0f32, 2.0, 3.0];
+        let mut x = embed_point_raw(&p);
+        // Introduce drift
+        x[0] += 0.05;
+        x[7] -= 0.03;
+        let fixed = null_project_raw(&x);
+        assert!(is_null_raw(&fixed, 1e-5).unwrap(),
+            "null_project failed to restore null cone");
+    }
+}
diff --git a/core-rs/tests/test_cl41.rs b/core-rs/tests/test_cl41.rs
new file mode 100644
index 00000000..abaa6007
--- /dev/null
+++ b/core-rs/tests/test_cl41.rs
@@ -0,0 +1,69 @@
+#[cfg(test)]
+mod tests {
+    use crate::cl41::{geometric_product_raw, reverse_raw, BLADE_MASKS, MASK_TO_IDX};
+
+    fn basis(i: usize) -> [f32; 32] {
+        let mut v = [0f32; 32];
+        v[1 + i] = 1.0; // grade-1 component
+        v
+    }
+
+    fn scalar(s: f32) -> [f32; 32] {
+        let mut v = [0f32; 32];
+        v[0] = s;
+        v
+    }
+
+    #[test]
+    fn test_e1_squared_is_plus1() {
+        let e1 = basis(0);
+        let r = geometric_product_raw(&e1, &e1).unwrap();
+        // e1^2 = +1 (signature index 0 = +1)
+        assert!((r[0] - 1.0).abs() < 1e-6, "e1^2 should be +1, got {}", r[0]);
+    }
+
+    #[test]
+    fn test_e5_squared_is_minus1() {
+        let e5 = basis(4);
+        let r = geometric_product_raw(&e5, &e5).unwrap();
+        // e5^2 = -1 (signature index 4 = -1)
+        assert!((r[0] + 1.0).abs() < 1e-6, "e5^2 should be -1, got {}", r[0]);
+    }
+
+    #[test]
+    fn test_e1_e2_anticommute() {
+        let e1 = basis(0);
+        let e2 = basis(1);
+        let e1e2 = geometric_product_raw(&e1, &e2).unwrap();
+        let e2e1 = geometric_product_raw(&e2, &e1).unwrap();
+        // e1*e2 = -e2*e1
+        for i in 0..32 {
+            assert!((e1e2[i] + e2e1[i]).abs() < 1e-6,
+                "e1*e2 + e2*e1 != 0 at index {}", i);
+        }
+    }
+
+    #[test]
+    fn test_scalar_identity() {
+        let e1 = basis(0);
+        let one = scalar(1.0);
+        let r = geometric_product_raw(&one, &e1).unwrap();
+        assert!((r[1] - 1.0).abs() < 1e-6, "1*e1 should be e1");
+    }
+
+    #[test]
+    fn test_reverse_grade2_sign() {
+        // A grade-2 blade should flip sign under reverse
+        let mut a = [0f32; 32];
+        a[6] = 1.0; // first grade-2 component
+        let r = reverse_raw(&a);
+        assert!((r[6] + 1.0).abs() < 1e-6, "reverse of grade-2 blade should negate");
+    }
+
+    #[test]
+    fn test_reverse_grade1_unchanged() {
+        let e1 = basis(0);
+        let r = reverse_raw(&e1);
+        assert!((r[1] - 1.0).abs() < 1e-6, "reverse of grade-1 blade should be unchanged");
+    }
+}
diff --git a/core-rs/tests/test_vault.rs b/core-rs/tests/test_vault.rs
new file mode 100644
index 00000000..77468611
--- /dev/null
+++ b/core-rs/tests/test_vault.rs
@@ -0,0 +1,50 @@
+#[cfg(test)]
+mod tests {
+    use crate::vault::vault_recall_raw;
+    use crate::versor::normalize_to_versor_raw;
+
+    fn random_versor(seed: u64) -> [f32; 32] {
+        let mut state = seed ^ 0xdeadbeef_cafebabe;
+        let mut raw = [0f32; 32];
+        for x in raw.iter_mut() {
+            state = state.wrapping_mul(6364136223846793005).wrapping_add(1442695040888963407);
+            *x = ((state >> 33) as f32) / (u32::MAX as f32) * 2.0 - 1.0;
+        }
+        normalize_to_versor_raw(&raw).expect("normalize failed")
+    }
+
+    #[test]
+    fn test_recall_self() {
+        let versors: Vec<[f32; 32]> = (0..20).map(|i| random_versor(i as u64)).collect();
+        for (i, query) in versors.iter().enumerate() {
+            let results = vault_recall_raw(&versors, query, 1).unwrap();
+            assert_eq!(results[0].0, i,
+                "Versor {} should recall itself as top-1, got {}", i, results[0].0);
+        }
+    }
+
+    #[test]
+    fn test_empty_vault() {
+        let query = random_versor(0);
+        let results = vault_recall_raw(&[], &query, 5).unwrap();
+        assert!(results.is_empty());
+    }
+
+    #[test]
+    fn test_top_k_count() {
+        let versors: Vec<[f32; 32]> = (0..10).map(|i| random_versor(i as u64)).collect();
+        let query = random_versor(99);
+        let results = vault_recall_raw(&versors, &query, 3).unwrap();
+        assert_eq!(results.len(), 3);
+    }
+
+    #[test]
+    fn test_scores_descending() {
+        let versors: Vec<[f32; 32]> = (0..10).map(|i| random_versor(i as u64)).collect();
+        let query = random_versor(99);
+        let results = vault_recall_raw(&versors, &query, 5).unwrap();
+        for w in results.windows(2) {
+            assert!(w[0].1 >= w[1].1, "Scores not descending");
+        }
+    }
+}
diff --git a/core-rs/tests/test_versor.rs b/core-rs/tests/test_versor.rs
new file mode 100644
index 00000000..db13261b
--- /dev/null
+++ b/core-rs/tests/test_versor.rs
@@ -0,0 +1,59 @@
+#[cfg(test)]
+mod tests {
+    use crate::versor::{versor_apply_raw, normalize_to_versor_raw, versor_condition_raw};
+
+    fn random_versor(seed: u64) -> [f32; 32] {
+        // Simple LCG for deterministic test data — no external deps
+        let mut state = seed ^ 0xdeadbeef_cafebabe;
+        let mut raw = [0f32; 32];
+        for x in raw.iter_mut() {
+            state = state.wrapping_mul(6364136223846793005).wrapping_add(1442695040888963407);
+            *x = ((state >> 33) as f32) / (u32::MAX as f32) * 2.0 - 1.0;
+        }
+        normalize_to_versor_raw(&raw).expect("normalize failed")
+    }
+
+    #[test]
+    fn test_normalize_produces_versor() {
+        for seed in 0..20u64 {
+            let v = random_versor(seed);
+            let cond = versor_condition_raw(&v).unwrap();
+            assert!(cond < 1e-5, "versor_condition after normalize = {}", cond);
+        }
+    }
+
+    #[test]
+    fn test_versor_apply_preserves_manifold() {
+        for seed in 0..20u64 {
+            let v = random_versor(seed);
+            let f = random_versor(seed + 1000);
+            let result = versor_apply_raw(&v, &f).unwrap();
+            let cond = versor_condition_raw(&result).unwrap();
+            assert!(cond < 1e-4,
+                "versor_apply broke manifold: condition={:.2e} at seed={}", cond, seed);
+        }
+    }
+
+    #[test]
+    fn test_identity_versor() {
+        let mut identity = [0f32; 32];
+        identity[0] = 1.0;
+        let f = random_versor(42);
+        let result = versor_apply_raw(&identity, &f).unwrap();
+        for i in 0..32 {
+            assert!((result[i] - f[i]).abs() < 1e-5,
+                "Identity apply changed component {}: {} vs {}", i, result[i], f[i]);
+        }
+    }
+
+    #[test]
+    fn test_composition_closed() {
+        let v1 = random_versor(0);
+        let v2 = random_versor(1);
+        let f  = random_versor(2);
+        let f2 = versor_apply_raw(&v1, &f).unwrap();
+        let f3 = versor_apply_raw(&v2, &f2).unwrap();
+        let cond = versor_condition_raw(&f3).unwrap();
+        assert!(cond < 1e-4, "Composition broke manifold: condition={:.2e}", cond);
+    }
+}
diff --git a/docs/RUST.md b/docs/RUST.md
new file mode 100644
index 00000000..b91b7b9e
--- /dev/null
+++ b/docs/RUST.md
@@ -0,0 +1,81 @@
+# Rust Extension (core-rs)
+
+## Why Rust
+
+Three operations dominate CORE-AI's runtime:
+
+1. geometric_product — O(32^2) = 1024 multiply-adds per call, called 2-3x per versor_apply
+2. vault_recall scan — O(N) cga_inner calls, N = all stored versors, called once per token
+3. holonomy_encode — 2 * prompt_length geometric products in sequence
+
+None of these release the Python GIL. Rayon gives vault_recall true multithreaded
+parallelism across CPU cores. The geometric product loop is cache-friendly and
+compiler-autovectorized when opt-level=3 + lto=true.
+
+## What is in Rust
+
+| Module | Rust file | Why |
+|---|---|---|
+| Cl(4,1) product | cl41.rs | Hot inner loop, 1024 MADs, autovectorizable |
+| Versor ops | versor.rs | 3x geometric_product per step, allocation-free |
+| CGA inner product | cga.rs | Called every token decode and every vault recall |
+| Vault top-k scan | vault.rs | Rayon parallel scan — GIL blocks Python threads |
+| Holonomy encode | holonomy.rs | 200+ products for long prompts |
+| Batch propagation | propagate.rs | Beam search / speculative decode |
+
+## What stays in Python
+
+| Layer | Why |
+|---|---|
+| VocabManifold | Word lookup, edge rotor construction — called once per token, not per step |
+| SessionContext | Orchestration, not arithmetic |
+| FieldState | Plain dataclass |
+| PersonaMotor | Motor construction is infrequent |
+
+## Zero-Copy Semantics
+
+All f32 arrays are passed as numpy arrays from Python.
+The Rust functions receive them as `[f32; 32]` stack arrays — copied once from
+the numpy buffer into a stack frame, processed, and returned as a new numpy array.
+No heap allocation inside any hot-path function.
+
+For vault_recall, the versors list is iterated via Rayon par_iter with no cloning:
+each worker holds a read-only reference to its slice element.
+
+## Build
+
+Requires maturin and a Rust toolchain (stable 1.75+).
+
+```bash
+cd core-rs
+pip install maturin
+maturin develop --release   # installs core_rs into current venv
+```
+
+Or build a wheel:
+```bash
+maturin build --release
+pip install target/wheels/*.whl
+```
+
+Verify Rust backend is active from Python:
+```python
+from algebra.backend import using_rust
+print(using_rust())  # True if core_rs is installed
+```
+
+## Running Rust Tests
+
+```bash
+cd core-rs
+cargo test
+```
+
+## Type Safety Contract
+
+All multivectors entering the Rust layer are validated as f32 arrays of length 32
+by extract_f32_slice() in lib.rs. Type errors surface immediately as Python
+ValueError with a descriptive message rather than silent memory corruption.
+
+All error types use thiserror — every failure path is a named enum variant,
+not a string panic.