fix(coprocessor): host-listener, dependency chain

coprocessor/fhevm-engine/Cargo.toml

@@ -72,6 +72,7 @@ sqlx = { version = "0.8.6", default-features = false, features = [
     "time",
     "postgres",
     "uuid",
+    "chrono"
 ] }
 testcontainers = "0.24.0"
 thiserror = "2.0.12"
@@ -93,6 +94,7 @@ tracing-subscriber = { version = "0.3.20", features = ["fmt", "json"] }
 humantime = "2.2.0"
 bytesize = "2.0.1"
 http = "1.3.1"
+chrono = { version = "0.4.41", features = ["serde"] }
 
 [profile.dev.package.tfhe]
 overflow-checks = false

coprocessor/fhevm-engine/db-migration/migrations/20251205154454_create_dependence_chain_table.sql

@@ -0,0 +1,27 @@
+CREATE TABLE dependence_chain (
+    dependence_chain_id  bytea PRIMARY KEY,
+
+    -- Scheduling / Coordination
+    status              TEXT NOT NULL CHECK (status IN (
+                                'updated', 'processing', 'processed'
+                            )),
+    error_message              TEXT,  -- optional error message if processing failed
+
+    -- Worker Ownership (updated by tfhe-workers)
+    worker_id           UUID,              
+    lock_acquired_at    TIMESTAMPTZ,
+    lock_expires_at     TIMESTAMPTZ,
+
+    -- Execution (updated by host-listener(s))
+    last_updated_at     TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX idx_pending_dependence_chain
+    ON dependence_chain USING BTREE (last_updated_at)
+    WHERE status = 'updated' AND worker_id IS NULL;
+
+CREATE INDEX idx_dependence_chain_worker_id
+    ON dependence_chain (worker_id);
+
+CREATE INDEX idx_dependence_chain_worker_id_and_dependence_chain_id
+    ON dependence_chain (dependence_chain_id, worker_id);