diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..116519f
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,43 @@
+name: CI
+
+on:
+  push:
+    branches: [main, dev, "fix/**"]
+  pull_request:
+    branches: [main, dev]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  check-and-test:
+    name: Build & Test
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Install Rust toolchain
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          components: rustfmt, clippy
+
+      - name: Cache cargo registry & build
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            target
+          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-
+
+      - name: Check compilation
+        run: cargo check --workspace --exclude program_methods
+
+      - name: Run tests
+        run: cargo test --workspace --exclude program_methods
+
+      - name: Check formatting
+        run: cargo fmt --all -- --check
\ No newline at end of file
diff --git a/e_identity_sdk/src/ffi.rs b/e_identity_sdk/src/ffi.rs
index 3592177..a5edd13 100644
--- a/e_identity_sdk/src/ffi.rs
+++ b/e_identity_sdk/src/ffi.rs
@@ -262,7 +262,10 @@ pub unsafe extern "C" fn ffi_username_registry_lookup_by_username(
         Err(_) => return error_json("invalid UTF-8"),
     };
     match (*handle).inner.lookup_by_username(name) {
-        Some(commitment) => ok_json(&format!("{{\"commitment\":\"{}\"}}", hex::encode(commitment))),
+        Some(commitment) => ok_json(&format!(
+            "{{\"commitment\":\"{}\"}}",
+            hex::encode(commitment)
+        )),
         None => ok_json("{\"commitment\":null}"),
     }
 }
diff --git a/program_methods/guest/src/bin/membership_registry.rs b/program_methods/guest/src/bin/membership_registry.rs
index a2a08df..aaff3f3 100644
--- a/program_methods/guest/src/bin/membership_registry.rs
+++ b/program_methods/guest/src/bin/membership_registry.rs
@@ -1,9 +1,8 @@
 #![no_main]
 
-use membership_registry::{ 
-    state::ForumInstance,
-    initialize, join_room, record_strike, register, 
-    register_room, slash, verify_post,
+use membership_registry::{
+    initialize, join_room, record_strike, register, register_room, slash, state::ForumInstance,
+    verify_post,
 };
 use nssa_core::account::AccountWithMetadata;
 use spel_framework::prelude::*;
@@ -136,7 +135,10 @@ mod forum_registry {
                 message: "Data too large".into(),
             })?;
 
-        Ok(SpelOutput::execute(vec![state.account, member.account], vec![]))
+        Ok(SpelOutput::execute(
+            vec![state.account, member.account],
+            vec![],
+        ))
     }
 
     #[instruction]
diff --git a/programs/membership_registry/src/join_room.rs b/programs/membership_registry/src/join_room.rs
index 4f4fcef..ce6cd2b 100644
--- a/programs/membership_registry/src/join_room.rs
+++ b/programs/membership_registry/src/join_room.rs
@@ -1,6 +1,6 @@
 use crate::state::{ForumInstance, OnChainMembership};
 
-/// Process a room join instruction. 
+/// Process a room join instruction.
 /// Validates that:
 /// 1. The room exists on-chain
 /// 2. The member commitment is registered and not revoked
diff --git a/programs/membership_registry/src/register.rs b/programs/membership_registry/src/register.rs
index 839daa2..4572ee9 100644
--- a/programs/membership_registry/src/register.rs
+++ b/programs/membership_registry/src/register.rs
@@ -13,9 +13,58 @@ pub fn process_register(
         return Err("Registration failed: This commitment is already registered.");
     }
 
+    // Reject commitments that were previously revoked via slashing.
+    // This prevents re-use of a compromised identity whose NSK was exposed.
+    if forum.revoked_commitments.contains(&commitment_bytes) {
+        return Err("Registration failed: This commitment has been revoked.");
+    }
+
     forum.registered_commitments.push(commitment_bytes);
     forum.member_stakes.push((commitment_bytes, stake_amount));
     forum.total_staked += stake_amount;
 
     Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::initialize::process_initialize;
+
+    #[test]
+    fn test_register_success() {
+        let mut forum = process_initialize(3, 2, 3).unwrap();
+        let commitment = [1u8; 32];
+        assert!(process_register(&mut forum, commitment, 1000).is_ok());
+        assert_eq!(forum.registered_commitments.len(), 1);
+        assert_eq!(forum.total_staked, 1000);
+    }
+
+    #[test]
+    fn test_register_insufficient_stake() {
+        let mut forum = process_initialize(3, 2, 3).unwrap();
+        let commitment = [1u8; 32];
+        assert!(process_register(&mut forum, commitment, 999).is_err());
+    }
+
+    #[test]
+    fn test_register_duplicate_commitment() {
+        let mut forum = process_initialize(3, 2, 3).unwrap();
+        let commitment = [1u8; 32];
+        assert!(process_register(&mut forum, commitment, 1000).is_ok());
+        assert!(process_register(&mut forum, commitment, 1000).is_err());
+    }
+
+    #[test]
+    fn test_register_revoked_commitment_rejected() {
+        let mut forum = process_initialize(3, 2, 3).unwrap();
+        let commitment = [2u8; 32];
+        forum.revoked_commitments.push(commitment);
+        let res = process_register(&mut forum, commitment, 1000);
+        assert!(res.is_err());
+        assert_eq!(
+            res.unwrap_err(),
+            "Registration failed: This commitment has been revoked."
+        );
+    }
+}