Phase 8 Sprint 1: FFI Export for Slash Protocol

- Zig L1: Implemented qvl_issue_slash_signal (constructs SlashSignal)
- Rust L2: Added FFI binding and safe wrapper issue_slash_signal
- Config: Wired l1_slash_mod into qvl_ffi build
- Verified: Unit test for signal creation passing

The active defense loop is closed. L2 can now pull the trigger.

build.zig

@@ -303,6 +303,7 @@ pub fn build(b: *std.Build) void {
         .optimize = optimize,
     });
     l1_qvl_ffi_mod.addImport("qvl", l1_qvl_mod);
+    l1_qvl_ffi_mod.addImport("slash", l1_slash_mod);
     l1_qvl_ffi_mod.addImport("time", time_mod);
 
     // QVL FFI static library (for Rust L2 Membrane Agent)

l1-identity/qvl_ffi.zig

@@ -13,6 +13,7 @@ const qvl = @import("qvl.zig");
 const pop_mod = @import("proof_of_path.zig");
 const trust_graph = @import("trust_graph.zig");
 const time = @import("time");
+const slash = @import("slash");
 
 const RiskGraph = qvl.types.RiskGraph;
 const RiskEdge = qvl.types.RiskEdge;
@@ -260,6 +261,38 @@ export fn qvl_revoke_trust_edge(
     return -2; // Not found
 }
 
+/// Issue a SlashSignal for a detected betrayal
+/// Returns 0 on success, < 0 on error
+/// If 'out_signal' is non-null, writes serialized signal (82 bytes)
+export fn qvl_issue_slash_signal(
+    ctx: ?*QvlContext,
+    target_did: [*c]const u8,
+    reason: u8,
+    out_signal: [*c]u8,
+) callconv(.c) c_int {
+    _ = ctx; // Context not strictly needed for constructing signal, but good for future validation
+    if (target_did == null) return -2;
+
+    var did: [32]u8 = undefined;
+    @memcpy(&did, target_did[0..32]);
+
+    const signal = slash.SlashSignal{
+        .target_did = did,
+        .reason = @enumFromInt(reason),
+        .punishment = .Quarantine, // Default to Quarantine
+        .evidence_hash = [_]u8{0} ** 32, // TODO: Hash actual evidence
+        .timestamp = std.time.timestamp(),
+        .nonce = 0,
+    };
+
+    if (out_signal != null) {
+        const bytes = signal.serializeForSigning();
+        @memcpy(out_signal[0..82], &bytes);
+    }
+
+    return 0;
+}
+
 // ============================================================================
 // TESTS (C ABI validation)
 // ============================================================================

membrane-agent/src/qvl_ffi.rs

@@ -83,6 +83,13 @@ extern "C" {
         from: u32,
         to: u32,
     ) -> c_int;
+
+    fn qvl_issue_slash_signal(
+        ctx: *mut QvlContext,
+        target_did: *const u8,
+        reason: u8,
+        out_signal: *mut u8,
+    ) -> c_int;
 }
 
 // ============================================================================
@@ -261,6 +268,29 @@ impl QvlClient {
             Err(QvlError::MutationFailed)
         }
     }
+
+    /// Issue a SlashSignal (returns 82-byte serialized signal for signing/broadcast)
+    pub fn issue_slash_signal(&self, target_did: &[u8; 32], reason: u8) -> Result<[u8; 82], QvlError> {
+        if self.ctx.is_null() {
+            return Err(QvlError::NullContext);
+        }
+
+        let mut out = [0u8; 82];
+        let result = unsafe {
+            qvl_issue_slash_signal(
+                self.ctx,
+                target_did.as_ptr(),
+                reason,
+                out.as_mut_ptr(),
+            )
+        };
+
+        if result == 0 {
+            Ok(out)
+        } else {
+            Err(QvlError::MutationFailed)
+        }
+    }
 }
 
 impl Drop for QvlClient {
@@ -321,4 +351,19 @@ mod tests {
         assert_eq!(anomaly.score, 0.0);
         assert_eq!(anomaly.reason, AnomalyReason::None);
     }
+
+    #[test]
+    fn test_issue_slash_signal() {
+        let client = QvlClient::new().unwrap();
+        let target = [1u8; 32];
+        let reason = 1; // BetrayalNegativeCycle
+
+        let signal = client.issue_slash_signal(&target, reason).unwrap();
+        // Verify first byte (target DID[0] = 1)
+        assert_eq!(signal[0], 1);
+        // Verify reason (offset 32 = 1)
+        assert_eq!(signal[32], 1);
+        // Verify punishment (offset 33 = 1 Quarantine)
+        assert_eq!(signal[33], 1);
+    }
 }