diff --git a/.github/workflows/rust-workspace.yml b/.github/workflows/rust-workspace.yml
new file mode 100644
index 0000000..dad46de
--- /dev/null
+++ b/.github/workflows/rust-workspace.yml
@@ -0,0 +1,38 @@
+name: Rust Workspace Validation
+
+on:
+  pull_request:
+    paths:
+      - 'src/**/*.rs'
+      - 'tests/**/*.rs'
+      - 'crates/**/*.rs'
+      - 'crates/**/Cargo.toml'
+      - 'Cargo.toml'
+      - 'Cargo.lock'
+      - '.github/workflows/rust-abi.yml'
+      - '.github/workflows/rust-workspace.yml'
+  push:
+    branches:
+      - main
+
+permissions:
+  contents: read
+
+jobs:
+  test-rust-workspace:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Rust Stable Toolchain
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Cache Cargo Dependencies
+        uses: Swatinem/rust-cache@v2
+
+      - name: Check workspace
+        run: cargo check --workspace
+
+      - name: Test workspace
+        run: cargo test --workspace --all-targets
diff --git a/Cargo.toml b/Cargo.toml
index a81a6fd..8832925 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -4,7 +4,7 @@ version = "0.1.0"
 edition = "2021"
 
 [workspace]
-members = ["crates/sentinel-core"]
+members = ["crates/sentinel-core", "crates/ghost-twin"]
 resolver = "2"
 
 [dependencies]
diff --git a/crates/ghost-twin/Cargo.toml b/crates/ghost-twin/Cargo.toml
new file mode 100644
index 0000000..de4f62e
--- /dev/null
+++ b/crates/ghost-twin/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "ghost-twin"
+version = "0.1.0"
+edition = "2021"
+description = "Deterministic Ghost/Twin execution boundary for SentinelAI"
+license = "Apache-2.0"
+
+[dependencies]
+sentinel-core = { path = "../sentinel-core" }
diff --git a/crates/ghost-twin/README.md b/crates/ghost-twin/README.md
new file mode 100644
index 0000000..420ff7d
--- /dev/null
+++ b/crates/ghost-twin/README.md
@@ -0,0 +1,12 @@
+# ghost-twin
+
+Isolated deterministic execution boundary for SentinelAI.
+
+```text
+Ghost -> TradeIntent -> Sentinel risk boundary -> Twin paper/shadow fill
+                                      \\-> ExecutionGate -> live only when allow_live=true
+```
+
+The crate contains no key management or signing and performs no external network operations. A future Jito adapter should accept already-signed transactions at an outer integration boundary.
+
+Live execution is disabled by default.
diff --git a/crates/ghost-twin/src/lib.rs b/crates/ghost-twin/src/lib.rs
new file mode 100644
index 0000000..763cd4e
--- /dev/null
+++ b/crates/ghost-twin/src/lib.rs
@@ -0,0 +1,140 @@
+#![forbid(unsafe_code)]
+
+use sentinel_core::{Decision, SentinelCore};
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct TradeIntent {
+    pub chain_id: u64,
+    pub max_slippage_bps: u16,
+    pub amount_units: u64,
+    pub live_requested: bool,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct PaperFill {
+    pub filled: bool,
+    pub amount_units: u64,
+    pub slippage_bps: u16,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum GateDecision {
+    Shadow,
+    Deny,
+    Live,
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct ExecutionGate {
+    pub allow_live: bool,
+}
+
+impl ExecutionGate {
+    pub const fn denied() -> Self {
+        Self { allow_live: false }
+    }
+
+    pub const fn live_enabled() -> Self {
+        Self { allow_live: true }
+    }
+
+    #[inline(always)]
+    pub const fn decide(&self, risk: Decision, live_requested: bool) -> GateDecision {
+        match risk {
+            Decision::Block => GateDecision::Deny,
+            Decision::Allow if live_requested && self.allow_live => GateDecision::Live,
+            Decision::Monitor => GateDecision::Shadow,
+            Decision::Allow => GateDecision::Shadow,
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub struct TwinEngine {
+    pub gate: ExecutionGate,
+}
+
+impl TwinEngine {
+    pub const fn new(gate: ExecutionGate) -> Self {
+        Self { gate }
+    }
+
+    #[inline(always)]
+    pub fn evaluate(
+        &self,
+        core: &mut SentinelCore,
+        intent: TradeIntent,
+        payload: &[u8],
+    ) -> (Decision, GateDecision, PaperFill) {
+        let risk = core.scan(payload);
+        let gate = self.gate.decide(risk, intent.live_requested);
+        let fill = match gate {
+            GateDecision::Deny => PaperFill {
+                filled: false,
+                amount_units: 0,
+                slippage_bps: 0,
+            },
+            GateDecision::Shadow | GateDecision::Live => PaperFill {
+                filled: true,
+                amount_units: intent.amount_units,
+                slippage_bps: intent.max_slippage_bps,
+            },
+        };
+        (risk, gate, fill)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn live_is_disabled_by_default() {
+        let engine = TwinEngine::new(ExecutionGate::denied());
+        let mut core = SentinelCore::new();
+        let intent = TradeIntent {
+            chain_id: 1,
+            max_slippage_bps: 50,
+            amount_units: 100,
+            live_requested: true,
+        };
+        let (_, gate, fill) = engine.evaluate(&mut core, intent, b"clean");
+        assert_eq!(gate, GateDecision::Shadow);
+        assert!(fill.filled);
+    }
+
+    #[test]
+    fn monitor_can_never_go_live() {
+        let engine = TwinEngine::new(ExecutionGate::live_enabled());
+        let mut core = SentinelCore::new();
+        core.observe(sentinel_core::Signal::Debugger, 0);
+        let intent = TradeIntent {
+            chain_id: 1,
+            max_slippage_bps: 50,
+            amount_units: 100,
+            live_requested: true,
+        };
+        let (risk, gate, fill) = engine.evaluate(&mut core, intent, b"clean");
+        assert_eq!(risk, Decision::Monitor);
+        assert_eq!(gate, GateDecision::Shadow);
+        assert!(fill.filled);
+    }
+
+    #[test]
+    fn breach_denies_even_when_live_enabled() {
+        let engine = TwinEngine::new(ExecutionGate::live_enabled());
+        let mut core = SentinelCore::new();
+        core.observe(sentinel_core::Signal::Tamper, 0);
+        core.observe(sentinel_core::Signal::Root, 0);
+        let intent = TradeIntent {
+            chain_id: 1,
+            max_slippage_bps: 50,
+            amount_units: 100,
+            live_requested: true,
+        };
+        let (risk, gate, fill) = engine.evaluate(&mut core, intent, b"clean");
+        assert_eq!(risk, Decision::Block);
+        assert_eq!(gate, GateDecision::Deny);
+        assert!(!fill.filled);
+    }
+}
diff --git a/crates/sentinel-core/src/lib.rs b/crates/sentinel-core/src/lib.rs
index 2af4349..2b4aa49 100644
--- a/crates/sentinel-core/src/lib.rs
+++ b/crates/sentinel-core/src/lib.rs
@@ -138,7 +138,7 @@ impl SentinelCore {
         self.decision()
     }
     #[inline(always)] fn scan_token(&mut self, data: &[u8], token: &[u8], signal: Signal) { if let Some(offset) = find_subslice(data, token) { self.observe(signal, offset); } }
-    #[inline(always)] pub const fn decision(&self) -> Decision { match State::from_raw(self.state.load(Ordering::Acquire)) { State::Monitor => Decision::Allow, State::Anomalous => Decision::Monitor, State::Breached => Decision::Block } }
+    #[inline(always)] pub fn decision(&self) -> Decision { match State::from_raw(self.state.load(Ordering::Acquire)) { State::Monitor => Decision::Allow, State::Anomalous => Decision::Monitor, State::Breached => Decision::Block } }
     #[inline(always)] pub const fn event_count(&self) -> usize { self.ring.len() }
     #[inline(always)] pub fn event(&self, index: usize) -> Option<Event> { self.ring.get(index) }
 }