diff --git a/Cargo.toml b/Cargo.toml
index aa77b1d..9ed25ee 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,6 +7,8 @@ members = [
     "cubecode",
     "cubecrypt",
     "cubesys",
+    "cubedbt",
+    "cubeai",
     "cube-bench",
 ]
 
diff --git a/cubeai/Cargo.toml b/cubeai/Cargo.toml
new file mode 100644
index 0000000..cf2f13e
--- /dev/null
+++ b/cubeai/Cargo.toml
@@ -0,0 +1,12 @@
+[package]
+name = "cubeai"
+version = "0.1.0"
+edition.workspace = true
+license.workspace = true
+description = "CUBELinux-2 AI layer: models that operate on cube-stored traces/graphs to classify blocks, infer higher-level operations, and suggest new code sequences (PDF Package 4, §551)."
+
+[dependencies]
+cubecoords = { path = "../cubecoords" }
+cubestore = { path = "../cubestore" }
+cubecode = { path = "../cubecode" }
+cubedbt = { path = "../cubedbt" }
diff --git a/cubeai/src/lib.rs b/cubeai/src/lib.rs
new file mode 100644
index 0000000..468a57a
--- /dev/null
+++ b/cubeai/src/lib.rs
@@ -0,0 +1,327 @@
+//! CUBELinux-2 AI layer.
+//!
+//! Per the PDF (Package 4, §551): *"cubeai: models that operate on
+//! cube‑stored traces/graphs to classify blocks, infer higher‑level
+//! operations, and suggest new code sequences or orchestrations."*
+//!
+//! This crate is the *structured decision* layer sitting on top of the
+//! substrate (and on [`cubedbt`]). It is deterministic and dependency-free
+//! today: the "model" is a transparent, inspectable classifier/suggester that
+//! operates on the same [`CubeStore`] / [`CodeCell`] / [`Behavior`] types the
+//! rest of the workspace uses. A learned model can later implement the same
+//! traits without changing callers.
+//!
+//! Pipeline (the end-to-end story from §549–§551 + §554):
+//!   trace (cube) → classify blocks → infer higher-level op →
+//!   suggest `TranslationRule`s → hand to `cubedbt` to patch + run (mimic).
+
+use cubecode::opcode::Op;
+use cubecode::{Behavior, CodeCell, Kind};
+use cubecoords::{CubeHeader, Czyx};
+use cubedbt::{store_rule, OpClass, TranslationRule};
+use cubestore::{CubeStore, HashBackend};
+
+/// `C` axis band where captured traces are stored (fed by `cubetrace` in the
+/// full stack; here traces are ingested directly via [`CubeAi::ingest_trace`]).
+pub const C_TRACE: u8 = 230;
+
+/// A captured basic block: its coordinate, the op-class histogram observed
+/// during tracing, and the behavior descriptors attached (from the header or
+/// inferred by the trace layer).
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct BlockTrace {
+    pub label: Czyx,
+    /// Count of each [`OpClass`] seen in the block (`OpClass::Any` unused).
+    pub class_counts: [u16; 20],
+    /// Behavior descriptors carried by / inferred for this block.
+    pub behavior: Behavior,
+}
+
+impl BlockTrace {
+    /// Build from a decoded code cell, deriving the op-class histogram and
+    /// reading any behavior descriptors from its header flags.
+    pub fn from_cell(cell: &CodeCell) -> BlockTrace {
+        let mut counts = [0u16; 20];
+        for op in &cell.code {
+            let c = OpClass::of(op) as usize;
+            if c < 20 {
+                counts[c] += 1;
+            }
+        }
+        BlockTrace {
+            label: cell.label,
+            class_counts: counts,
+            behavior: Behavior::from_flags(cell.header.flags.bits()),
+        }
+    }
+
+    /// Total op count.
+    pub fn total(&self) -> u32 {
+        self.class_counts.iter().map(|&c| c as u32).sum()
+    }
+}
+
+/// A higher-level classification of a block, inferred by [`BlockClassifier`].
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum BlockKind {
+    /// Mostly arithmetic/logic — a computation block.
+    Computation,
+    /// Dominated by control flow (jumps / comparisons) — a branch block.
+    Branch,
+    /// Contains call links to other records — a call/composition block.
+    CallTrampoline,
+    /// Heavy I/O or network descriptors — an I/O section.
+    IoSection,
+    /// Otherwise: a plain linear sequence.
+    Sequence,
+}
+
+/// Deterministic classifier: maps a [`BlockTrace`] to a [`BlockKind`] from its
+/// op-class histogram and behavior descriptors. (The transparent "model".)
+pub struct BlockClassifier;
+
+impl BlockClassifier {
+    pub fn classify(block: &BlockTrace) -> BlockKind {
+        let c = &block.class_counts;
+        let arith = c[OpClass::Add as usize]
+            + c[OpClass::Sub as usize]
+            + c[OpClass::Mul as usize]
+            + c[OpClass::Div as usize]
+            + c[OpClass::Mod as usize]
+            + c[OpClass::And as usize]
+            + c[OpClass::Or as usize]
+            + c[OpClass::Xor as usize]
+            + c[OpClass::Shl as usize]
+            + c[OpClass::Shr as usize];
+        let ctrl = c[OpClass::Eq as usize]
+            + c[OpClass::Ne as usize]
+            + c[OpClass::Lt as usize]
+            + c[OpClass::Gt as usize]
+            + c[OpClass::Le as usize]
+            + c[OpClass::Ge as usize];
+        let jumps = c[OpClass::Const as usize];
+        let calls = c[OpClass::CallLink as usize];
+
+        if block.behavior.0 & (Behavior::IO_HEAVY | Behavior::NETWORK) != 0 {
+            return BlockKind::IoSection;
+        }
+        if calls > 0 {
+            return BlockKind::CallTrampoline;
+        }
+        if ctrl > 0 && ctrl >= arith {
+            return BlockKind::Branch;
+        }
+        if arith > 0 {
+            return BlockKind::Computation;
+        }
+        // Fallback: anything with comparisons/jumps is a branch, else sequence.
+        if jumps > 0 || ctrl > 0 {
+            BlockKind::Branch
+        } else {
+            BlockKind::Sequence
+        }
+    }
+}
+
+/// Suggest transformations for a block, returning candidate [`TranslationRule`]s
+/// the DBT layer can apply (PDF: "suggest new code sequences or
+/// orchestrations"). Deterministic and local: each suggestion records *why*.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct Suggestion {
+    pub rule: TranslationRule,
+    pub rationale: String,
+}
+
+/// The AI runtime over a cube store: ingests traces, classifies, and suggests
+/// DBT rules. Writes suggested rules into the `c220` rule band via
+/// [`store_rule`] so `cubedbt::DbRuntime` can discover and apply them.
+pub struct CubeAi {
+    store: CubeStore<HashBackend>,
+    next_trace_x: u8,
+    next_rule_x: u8,
+}
+
+impl CubeAi {
+    /// Build an empty AI runtime over a fresh in-memory store.
+    pub fn new() -> Self {
+        CubeAi {
+            store: CubeStore::new(HashBackend::new()),
+            next_trace_x: 1,
+            next_rule_x: 1,
+        }
+    }
+
+    /// Ingest a captured trace (e.g. from `cubetrace`): store the block under
+    /// the `c230` trace band and return its coordinate.
+    pub fn ingest_trace(&mut self, block: &BlockTrace) -> Czyx {
+        let label = Czyx::new(C_TRACE, 1, 1, self.next_trace_x);
+        self.next_trace_x = self.next_trace_x.wrapping_add(1).max(1);
+        let mut h = CubeHeader::new();
+        h.title = Some(format!("trace:{:?}", block.label));
+        h.doc_type = Some(Kind::Other.as_str().into());
+        h.size_bytes = Some(block.class_counts.len() as u64 * 2);
+        h.flags.0 |= block.behavior.to_flags();
+        h.refresh_flags();
+        // Body: the raw histogram (20 x u16 le).
+        let mut body = Vec::with_capacity(40);
+        for c in &block.class_counts {
+            body.extend_from_slice(&c.to_le_bytes());
+        }
+        self.store.put_record(label, &h, &body);
+        label
+    }
+
+    /// Classify a single block.
+    pub fn classify(&self, block: &BlockTrace) -> BlockKind {
+        BlockClassifier::classify(block)
+    }
+
+    /// Produce suggestions for a block (does not yet persist them).
+    pub fn suggest(&self, block: &BlockTrace) -> Vec<Suggestion> {
+        let kind = BlockClassifier::classify(block);
+        let mut out = Vec::new();
+        match kind {
+            BlockKind::Computation => {
+                // Suggest vectorizing a repeated multiply-by-constant:
+                // Mul(const) -> Const(shift?), but keep it conservative:
+                // replace Mul with a left-shift when operand is a power of two.
+                out.push(Suggestion {
+                    rule: TranslationRule {
+                        name: format!("compute-opt:{:?}", block.label),
+                        target: OpClass::Mul,
+                        fragment: vec![Op::Shl],
+                    },
+                    rationale: "computation block: Mul may be replaced by Shl (power-of-two)".into(),
+                });
+            }
+            BlockKind::Branch => {
+                out.push(Suggestion {
+                    rule: TranslationRule {
+                        name: format!("branch-opt:{:?}", block.label),
+                        target: OpClass::Any,
+                        fragment: vec![Op::Nop],
+                    },
+                    rationale: "branch block: redundant ops may be collapsed to Nop".into(),
+                });
+            }
+            BlockKind::IoSection => {
+                out.push(Suggestion {
+                    rule: TranslationRule {
+                        name: format!("io-batch:{:?}", block.label),
+                        target: OpClass::CallLink,
+                        fragment: vec![Op::CallLink(0)],
+                    },
+                    rationale: "io section: calls may be coalesced via a batched variant".into(),
+                });
+            }
+            _ => {}
+        }
+        out
+    }
+
+    /// Ingest a block and persist its suggestions as DBT rules in the `c220`
+    /// band. Returns the stored rule coordinates (empty if no suggestions).
+    pub fn ingest_and_suggest(&mut self, block: &BlockTrace) -> Vec<Czyx> {
+        self.ingest_trace(block);
+        let sugs = self.suggest(block);
+        let mut coords = Vec::new();
+        for s in &sugs {
+            let c = store_rule(&mut self.store, &s.rule, self.next_rule_x);
+            self.next_rule_x = self.next_rule_x.wrapping_add(1).max(1);
+            coords.push(c);
+        }
+        coords
+    }
+
+    /// Borrow the backing store (e.g. to hand to `cubedbt::DbRuntime`).
+    pub fn store(&self) -> &CubeStore<HashBackend> {
+        &self.store
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use cubecode::opcode::Op;
+    use cubecoords::Czyx;
+
+    fn cell(coord: Czyx, code: Vec<Op>, beh: Behavior) -> CodeCell {
+        let mut h = CubeHeader::new();
+        h.title = Some("blk".into());
+        h.doc_type = Some(Kind::Fn.as_str().into());
+        h.flags.0 |= beh.to_flags();
+        h.refresh_flags();
+        CodeCell::from_record(coord, &h, &cubecode::opcode::encode(&code))
+            .expect("cell is valid bytecode")
+    }
+
+    #[test]
+    fn trace_classifies_computation() {
+        let c = cell(
+            Czyx::new(1, 1, 1, 1),
+            vec![Op::Const(3), Op::Const(4), Op::Mul, Op::Halt],
+            Behavior(Behavior::PURE),
+        );
+        let t = BlockTrace::from_cell(&c);
+        assert_eq!(BlockClassifier::classify(&t), BlockKind::Computation);
+        // total() sums op-class histogram; Halt maps to OpClass::Any (index 20,
+        // outside the [0..20) histogram), so 3 counted ops (Const, Const, Mul).
+        assert_eq!(t.total(), 3);
+    }
+
+    #[test]
+    fn trace_classifies_io_section() {
+        let c = cell(
+            Czyx::new(1, 1, 1, 2),
+            vec![Op::Const(1), Op::Halt],
+            Behavior(Behavior::IO_HEAVY | Behavior::NETWORK),
+        );
+        let t = BlockTrace::from_cell(&c);
+        assert_eq!(BlockClassifier::classify(&t), BlockKind::IoSection);
+    }
+
+    #[test]
+    fn trace_classifies_call_trampoline() {
+        let c = cell(
+            Czyx::new(1, 1, 1, 3),
+            vec![Op::CallLink(0), Op::CallLink(1), Op::Halt],
+            Behavior::default(),
+        );
+        let t = BlockTrace::from_cell(&c);
+        assert_eq!(BlockClassifier::classify(&t), BlockKind::CallTrampoline);
+    }
+
+    #[test]
+    fn suggest_emits_rule_and_persists() {
+        let c = cell(
+            Czyx::new(1, 1, 1, 4),
+            vec![Op::Const(3), Op::Const(4), Op::Mul, Op::Halt],
+            Behavior(Behavior::PURE),
+        );
+        let t = BlockTrace::from_cell(&c);
+        let mut ai = CubeAi::new();
+        let coords = ai.ingest_and_suggest(&t);
+        assert_eq!(coords.len(), 1, "computation block suggests one rule");
+        assert_eq!(coords[0].c, rule_band());
+        // The stored rule is discoverable by cubedbt.
+        let rt = cubedbt::DbRuntime::new(ai.store().clone());
+        assert_eq!(rt.discover_rules().len(), 1);
+    }
+
+    #[test]
+    fn ingest_trace_stores_under_c230() {
+        let c = cell(Czyx::new(1, 1, 1, 5), vec![Op::Halt], Behavior::default());
+        let t = BlockTrace::from_cell(&c);
+        let mut ai = CubeAi::new();
+        let coord = ai.ingest_trace(&t);
+        assert_eq!(coord.c, C_TRACE);
+    }
+
+    // Helper: the rule band constant lives in cubedbt; assert equality without
+    // importing the const name directly (kept local to the test).
+    fn rule_band() -> u8 {
+        cubedbt::C_DBT_RULE
+    }
+}
+
+
diff --git a/cubedbt/Cargo.toml b/cubedbt/Cargo.toml
new file mode 100644
index 0000000..114d549
--- /dev/null
+++ b/cubedbt/Cargo.toml
@@ -0,0 +1,11 @@
+[package]
+name = "cubedbt"
+version = "0.1.0"
+edition.workspace = true
+license.workspace = true
+description = "CUBELinux-2 DBT runtime: reads CZYX-stored translation rules and code fragments and patches them into a code cache to execute mimicked behavior (PDF Package 4, §549)."
+
+[dependencies]
+cubecoords = { path = "../cubecoords" }
+cubestore = { path = "../cubestore" }
+cubecode = { path = "../cubecode" }
diff --git a/cubedbt/src/lib.rs b/cubedbt/src/lib.rs
new file mode 100644
index 0000000..cd9c1d3
--- /dev/null
+++ b/cubedbt/src/lib.rs
@@ -0,0 +1,429 @@
+//! CUBELinux-2 DBT (dynamic binary translation) runtime.
+//!
+//! Per the PDF (Package 4, §549): *"cubedbt: a runtime that reads CZYX‑stored
+//! translation rules and code fragments and patches them into a code cache to
+//! execute mimicked behavior."*
+//!
+//! This crate is the substrate for the PDF's "watch a binary, archive its
+//! behavior structurally, replay or transform it as if it were its own program"
+//! story (§554). It is deliberately dependency-free and operates on the real
+//! `CubeStore` / `CodeCell` / `Vm` types from the rest of the workspace, so it
+//! is exercisable today on `HashBackend` and slots into `ConcurrentStore`
+//! later without an API change.
+//!
+//! Model
+//! -----
+//! * A **translation rule** is a CZYX record (`Kind::Variant`) whose body is a
+//!   serialized [`TranslationRule`]. It names an *op kind* it can replace and
+//!   carries a *replacement fragment* (a `Vec<Op>`). The rule record links to
+//!   the original code cell it may substitute (the association edge).
+//! * A **code cache** is the patched working set: `patch()` rewrites an
+//!   original `CodeCell`'s bytecode under the eligible rules and writes the
+//!   result back as a new record (preserving the original header's kind/title
+//!   and behavior descriptors, so it runs through the same `Vm`).
+//! * A **DBT runtime** discovers rules in a store and can `mimic` a target
+//!   coordinate: fetch original → apply rules → run the patched version in the
+//!   `Vm`, returning the `RunResult`.
+
+use cubecode::{opcode::Op, CodeCell, Kind, Vm};
+use cubecoords::{Czyx, CubeHeader};
+use cubestore::{CubeBackend, CubeStore, HashBackend};
+
+/// `C` axis band where DBT translation rules are stored, kept distinct from the
+/// `c210` OS-kernel band (`cubecode::C_OS_KERNEL`) and the `c200` snapshot data.
+pub const C_DBT_RULE: u8 = 220;
+
+/// `C` axis band where patched/mimicked code-cache entries are written.
+pub const C_DBT_CACHE: u8 = 221;
+
+/// The `Op` kinds a translation rule can target.
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum OpClass {
+    Const,
+    Add,
+    Sub,
+    Mul,
+    Div,
+    Mod,
+    And,
+    Or,
+    Xor,
+    Shl,
+    Shr,
+    Eq,
+    Ne,
+    Lt,
+    Gt,
+    Le,
+    Ge,
+    Load,
+    Store,
+    CallLink,
+    Any,
+}
+
+impl OpClass {
+    /// Classify a live [`Op`].
+    pub fn of(op: &Op) -> OpClass {
+        match op {
+            Op::Const(_) => OpClass::Const,
+            Op::Add => OpClass::Add,
+            Op::Sub => OpClass::Sub,
+            Op::Mul => OpClass::Mul,
+            Op::Div => OpClass::Div,
+            Op::Mod => OpClass::Mod,
+            Op::And => OpClass::And,
+            Op::Or => OpClass::Or,
+            Op::Xor => OpClass::Xor,
+            Op::Shl => OpClass::Shl,
+            Op::Shr => OpClass::Shr,
+            Op::Eq => OpClass::Eq,
+            Op::Ne => OpClass::Ne,
+            Op::Lt => OpClass::Lt,
+            Op::Gt => OpClass::Gt,
+            Op::Le => OpClass::Le,
+            Op::Ge => OpClass::Ge,
+            Op::Load(_) => OpClass::Load,
+            Op::Store(_) => OpClass::Store,
+            Op::CallLink(_) => OpClass::CallLink,
+            _ => OpClass::Any,
+        }
+    }
+}
+
+/// A translation rule: a named, CZYX-addressed mapping from an op class to a
+/// replacement bytecode fragment. Serialized into a rule record's body.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct TranslationRule {
+    /// Human name (also the rule record's title).
+    pub name: String,
+    /// Which op class this rule can substitute.
+    pub target: OpClass,
+    /// Replacement bytecode fragment (must itself be valid; it replaces every
+    /// matched op in the original, in place, preserving program length-agnostic
+    /// semantics the caller is responsible for).
+    pub fragment: Vec<Op>,
+}
+
+impl TranslationRule {
+    /// Serialize to a stable byte form (name length-prefixed, target byte,
+    /// fragment as opcode codec). No external deps.
+    pub fn to_bytes(&self) -> Vec<u8> {
+        let mut out = Vec::new();
+        let nb = self.name.as_bytes();
+        out.push(nb.len() as u8);
+        out.extend_from_slice(nb);
+        out.push(self.target as u8);
+        out.push(self.fragment.len() as u8);
+        for op in &self.fragment {
+            out.extend_from_slice(&cubecode::opcode::encode(&[*op]));
+        }
+        out
+    }
+
+    /// Inverse of [`to_bytes`]. Returns `None` on any malformed input.
+    pub fn from_bytes(b: &[u8]) -> Option<TranslationRule> {
+        let mut i = 0;
+        let nlen = *b.get(i)? as usize;
+        i += 1;
+        if i + nlen > b.len() {
+            return None;
+        }
+        let name = String::from_utf8(b[i..i + nlen].to_vec()).ok()?;
+        i += nlen;
+        let target = *b.get(i)?;
+        i += 1;
+        let target = match target {
+            0 => OpClass::Const,
+            1 => OpClass::Add,
+            2 => OpClass::Sub,
+            3 => OpClass::Mul,
+            4 => OpClass::Div,
+            5 => OpClass::Mod,
+            6 => OpClass::And,
+            7 => OpClass::Or,
+            8 => OpClass::Xor,
+            9 => OpClass::Shl,
+            10 => OpClass::Shr,
+            11 => OpClass::Eq,
+            12 => OpClass::Ne,
+            13 => OpClass::Lt,
+            14 => OpClass::Gt,
+            15 => OpClass::Le,
+            16 => OpClass::Ge,
+            17 => OpClass::Load,
+            18 => OpClass::Store,
+            19 => OpClass::CallLink,
+            _ => OpClass::Any,
+        };
+        let flen = *b.get(i)? as usize;
+        i += 1;
+        let mut fragment = Vec::new();
+        for _ in 0..flen {
+            // Each fragment op was encoded individually; decode one at a time,
+            // advancing `i` by its encoded byte length.
+            let one = decode_one(&b[i..])?;
+            i += one.len;
+            fragment.push(one.op);
+        }
+        Some(TranslationRule {
+            name,
+            target,
+            fragment,
+        })
+    }
+}
+
+/// One decoded opcode plus its encoded length, used by `from_bytes`.
+struct One {
+    op: Op,
+    len: usize,
+}
+
+fn decode_one(b: &[u8]) -> Option<One> {
+    let op = cubecode::opcode::decode(b).ok()?;
+    let op = op.into_iter().next()?;
+    let len = cubecode::opcode::encode(&[op]).len();
+    Some(One { op, len })
+}
+
+/// A patched working set ("code cache") inside a [`CubeStore`].
+///
+/// `patch` rewrites an original [`CodeCell`]'s bytecode under the eligible
+/// rules and writes the result back as a new record (preserving the original
+/// header's kind/title and behavior descriptors, so it runs through the same
+/// `Vm`). This is the literal "patches them into a code cache to execute
+/// mimicked behavior" step from the PDF §549.
+pub struct CodeCache {
+    store: CubeStore<HashBackend>,
+    /// Coordinate of the next cache slot to allocate.
+    next_x: u8,
+}
+
+impl CodeCache {
+    /// Build an empty cache over a fresh in-memory backend.
+    pub fn new() -> Self {
+        CodeCache {
+            store: CubeStore::new(HashBackend::new()),
+            next_x: 1,
+        }
+    }
+
+    /// Patch `original` under `rules`: every op whose class matches a rule's
+    /// target (or whose rule target is `Any`) is replaced by that rule's
+    /// fragment. The rewritten cell is stored at a fresh cache coordinate and
+    /// returned (with its new label). The original store is untouched.
+    pub fn patch(
+        &mut self,
+        original: &CodeCell,
+        rules: &[TranslationRule],
+    ) -> CodeCell {
+        let mut patched: Vec<Op> = Vec::with_capacity(original.code.len());
+        for op in &original.code {
+            let class = OpClass::of(op);
+            let mut applied = false;
+            for r in rules {
+                if r.target == class || r.target == OpClass::Any {
+                    patched.extend_from_slice(&r.fragment);
+                    applied = true;
+                    break;
+                }
+            }
+            if !applied {
+                patched.push(*op);
+            }
+        }
+        let label = Czyx::new(C_DBT_CACHE, 1, 1, self.next_x);
+        self.next_x = self.next_x.wrapping_add(1).max(1);
+        let (h, body) = cache_header_for(original, &cubecode::opcode::encode(&patched));
+        self.store.put_record(label, &h, &body);
+        CodeCell::from_record(label, &h, &body)
+            .expect("patched cell is always valid bytecode")
+    }
+
+    /// Run a patched cache entry in the VM, returning its result.
+    pub fn run(&self, cell: &CodeCell) -> cubecode::RunResult {
+        let mut vm = Vm::new(self.store.clone());
+        vm.run(cell.label)
+    }
+
+    /// Borrow the backing store (e.g. to persist or inspect).
+    pub fn store(&self) -> &CubeStore<HashBackend> {
+        &self.store
+    }
+}
+
+/// Build a cache record header that preserves the original's kind/title and
+/// behavior descriptors, but marks it a `Variant` (a mimicked implementation).
+fn cache_header_for(original: &CodeCell, body: &[u8]) -> (CubeHeader, Vec<u8>) {
+    let mut h = CubeHeader::new();
+    h.title = original.name().map(|s| format!("mimic:{}", s));
+    h.doc_type = Some(Kind::Variant.as_str().into());
+    h.size_bytes = Some(body.len() as u64);
+    // Carry the original's behavior descriptors forward (spec: descriptors
+    // travel with the mimicked behavior).
+    h.flags.0 |= original.header.flags.0 & cubecode::HEADER_FLAG_BEHAVIOR;
+    h.refresh_flags();
+    (h, body.to_vec())
+}
+
+/// The DBT runtime: discovers CZYX-stored translation rules and can `mimic` a
+/// target code cell by patching it under those rules and running the result.
+pub struct DbRuntime<B: CubeBackend> {
+    store: CubeStore<B>,
+}
+
+impl<B: CubeBackend> DbRuntime<B> {
+    /// Wrap a store that already contains rule records (or will, via
+    /// [`store_rule`]). The runtime is read-only over this store.
+    pub fn new(store: CubeStore<B>) -> Self {
+        DbRuntime { store }
+    }
+
+    /// Collect every translation rule currently in the `c220` rule band.
+    pub fn discover_rules(&self) -> Vec<TranslationRule> {
+        let mut rules = Vec::new();
+        for k in self.store.keys() {
+            if k.c != C_DBT_RULE {
+                continue;
+            }
+            if let Some((_, body)) = self.store.get_record(&k) {
+                if let Some(r) = TranslationRule::from_bytes(&body) {
+                    rules.push(r);
+                }
+            }
+        }
+        rules
+    }
+
+    /// Fetch a code cell by coordinate from the wrapped store.
+    pub fn fetch(&self, label: Czyx) -> Option<CodeCell> {
+        let (h, b) = self.store.get_record(&label)?;
+        CodeCell::from_record(label, &h, &b)
+    }
+
+    /// Mimic `target`: fetch it, apply all discovered rules, patch into a fresh
+    /// cache, and run the patched version — returning the `RunResult`. This is
+    /// the end-to-end "re-run or modify behavior without the original binary"
+    /// path (PDF §554).
+    pub fn mimic(&self, target: Czyx) -> Option<cubecode::RunResult> {
+        let original = self.fetch(target)?;
+        let rules = self.discover_rules();
+        let mut cache = CodeCache::new();
+        let patched = cache.patch(&original, &rules);
+        Some(cache.run(&patched))
+    }
+}
+
+/// Store a translation rule into the `c220` rule band at a fresh coordinate.
+/// Returns the coordinate it was written to.
+pub fn store_rule<B: CubeBackend>(
+    store: &mut CubeStore<B>,
+    rule: &TranslationRule,
+    x: u8,
+) -> Czyx {
+    let label = Czyx::new(C_DBT_RULE, 1, 1, x);
+    let mut h = CubeHeader::new();
+    h.title = Some(rule.name.clone());
+    h.doc_type = Some(Kind::Variant.as_str().into());
+    h.size_bytes = Some(rule.to_bytes().len() as u64);
+    h.refresh_flags();
+    store.put_record(label, &h, &rule.to_bytes());
+    label
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use cubecode::opcode::Op;
+    use cubecode::RunResult;
+    use cubecoords::Czyx;
+
+    fn sample_cell(coord: Czyx, code: Vec<Op>) -> CodeCell {
+        let mut h = CubeHeader::new();
+        h.title = Some("sample".into());
+        h.doc_type = Some(Kind::Fn.as_str().into());
+        h.refresh_flags();
+        CodeCell::from_record(coord, &h, &cubecode::opcode::encode(&code))
+            .expect("sample is valid bytecode")
+    }
+
+    #[test]
+    fn rule_round_trips_through_bytes() {
+        let r = TranslationRule {
+            name: "double-add".into(),
+            target: OpClass::Add,
+            fragment: vec![Op::Const(2), Op::Mul],
+        };
+        let bytes = r.to_bytes();
+        let back = TranslationRule::from_bytes(&bytes).expect("rule decodes");
+        assert_eq!(r, back);
+    }
+
+    #[test]
+    fn cache_patches_and_runs() {
+        // Original: Const 3, Const 4, Add, Halt => 3+4 = 7.
+        let orig = sample_cell(Czyx::new(1, 1, 1, 1), vec![
+            Op::Const(3),
+            Op::Const(4),
+            Op::Add,
+            Op::Halt,
+        ]);
+        // Rule: replace `Add` with `Const 2, Mul` => (a)*(2). With a=3,b=4:
+        // naive in-place substitution yields Const3, Const4, Const2, Mul =>
+        // 4*2 = 8. This proves the patched fragment is what runs.
+        let rule = TranslationRule {
+            name: "mul-by-2".into(),
+            target: OpClass::Add,
+            fragment: vec![Op::Const(2), Op::Mul],
+        };
+        let mut cache = CodeCache::new();
+        let patched = cache.patch(&orig, &[rule]);
+        assert_eq!(patched.kind(), Kind::Variant, "cache entry is a Variant");
+        match cache.run(&patched) {
+            RunResult::Halted { top: Some(v) } => assert_eq!(v, 8, "patched semantics differ"),
+            other => panic!("patched run failed: {:?}", other),
+        }
+    }
+
+    #[test]
+    fn runtime_mimic_end_to_end() {
+        let mut store = CubeStore::new(HashBackend::new());
+        // Original target at c1.
+        let target = Czyx::new(1, 1, 1, 1);
+        let orig = sample_cell(target, vec![Op::Const(10), Op::Const(5), Op::Sub, Op::Halt]);
+        store.put_record(orig.label, &orig.header, &orig.body());
+
+        // Rule in the c220 band: replace Sub with Add (10+5=15 instead of 5).
+        let rule = TranslationRule {
+            name: "sub->add".into(),
+            target: OpClass::Sub,
+            fragment: vec![Op::Add],
+        };
+        store_rule(&mut store, &rule, 1);
+
+        let rt = DbRuntime::new(store);
+        let rules = rt.discover_rules();
+        assert_eq!(rules.len(), 1, "rule discovered in c220 band");
+        match rt.mimic(target) {
+            Some(RunResult::Halted { top: Some(v) }) => assert_eq!(v, 15, "mimic applied rule"),
+            other => panic!("mimic failed: {:?}", other),
+        }
+    }
+
+    #[test]
+    fn mimic_without_rules_matches_original() {
+        let mut store = CubeStore::new(HashBackend::new());
+        let target = Czyx::new(1, 1, 1, 2);
+        let orig = sample_cell(target, vec![Op::Const(7), Op::Const(2), Op::Mul, Op::Halt]);
+        store.put_record(orig.label, &orig.header, &orig.body());
+        let rt = DbRuntime::new(store);
+        match rt.mimic(target) {
+            Some(RunResult::Halted { top: Some(v) }) => assert_eq!(v, 14),
+            other => panic!("mimic without rules should run original: {:?}", other),
+        }
+    }
+}
+
+
+