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diff --git a/ocaml/lib/effects.ml b/ocaml/lib/effects.ml
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+(* Effects - Output from Arvo event processing
+ *
+ * When Arvo processes an event (poke), it returns:
+ * - Updated kernel state
+ * - List of effects to perform
+ *
+ * Effects are messages to I/O drivers (vanes):
+ * - Behn: timers
+ * - Ames: network packets
+ * - Eyre: HTTP responses
+ * - Clay: filesystem operations
+ * - Dill: terminal output
+ * etc.
+ *)
+
+(* Effect type - what to do after processing an event *)
+type t =
+  (* Timer effect: set a timer *)
+  | SetTimer of {
+      id: int64;           (* Timer ID *)
+      time: float;         (* Unix timestamp when to fire *)
+    }
+
+  (* Timer effect: cancel a timer *)
+  | CancelTimer of {
+      id: int64;           (* Timer ID to cancel *)
+    }
+
+  (* Log effect: print to console *)
+  | Log of string
+
+  (* Network effect: send UDP packet (Ames) *)
+  | SendPacket of {
+      dest: string;        (* IP:port *)
+      data: bytes;         (* Packet data *)
+    }
+
+  (* HTTP effect: send HTTP response (Eyre) *)
+  | HttpResponse of {
+      id: int;             (* Request ID *)
+      status: int;         (* HTTP status code *)
+      headers: (string * string) list;
+      body: bytes;
+    }
+
+  (* File effect: write file (Clay) *)
+  | WriteFile of {
+      path: string;
+      data: bytes;
+    }
+
+  (* Generic placeholder for other effects *)
+  | Other of {
+      vane: string;        (* Which vane (behn, ames, eyre, etc) *)
+      data: Noun.noun;     (* Effect data as noun *)
+    }
+
+(* Effect result - what happened when we tried to execute an effect *)
+type effect_result =
+  | Success
+  | Failed of string
+
+(* Ovum - an input event to Arvo
+ *
+ * Format: [wire card]
+ *   wire: path for response routing
+ *   card: [driver-name data]
+ *)
+type ovum = {
+  wire: Noun.noun;         (* Response routing path *)
+  card: Noun.noun;         (* [vane-tag event-data] *)
+}
+
+(* Create a simple ovum *)
+let make_ovum ~wire ~card = { wire; card }
+
+(* Create a timer ovum (from behn) *)
+let timer_ovum ~id ~fire_time =
+  {
+    wire = Noun.Atom (Z.of_int64 id);
+    card = Noun.cell
+      (Noun.atom 0)  (* behn tag - simplified *)
+      (Noun.Atom (Z.of_float (fire_time *. 1000000.0)));  (* microseconds *)
+  }
+
+(* Create a log ovum *)
+let log_ovum ~msg:_ =
+  {
+    wire = Noun.atom 0;
+    card = Noun.cell
+      (Noun.atom 1)  (* log tag *)
+      (Noun.atom 0); (* simplified - would be text *)
+  }
+
+(* Parse effects from Arvo output
+ *
+ * In a real implementation, this would parse the noun structure
+ * that Arvo returns and convert it to our effect types.
+ *
+ * For now: simplified - just return empty list
+ *)
+let parse_effects (_arvo_output : Noun.noun) : t list =
+  (* TODO: Parse real Arvo effect format *)
+  []
+
+(* Effect queue - for async effect processing *)
+type queue = {
+  q: t Queue.t;
+  lock: Mutex.t;
+  cond: Condition.t;
+}
+
+(* Create effect queue *)
+let create_queue () = {
+  q = Queue.create ();
+  lock = Mutex.create ();
+  cond = Condition.create ();
+}
+
+(* Add effect to queue *)
+let enqueue queue eff =
+  Mutex.lock queue.lock;
+  Queue.add eff queue.q;
+  Condition.signal queue.cond;
+  Mutex.unlock queue.lock
+
+(* Get next effect from queue (blocking) *)
+let dequeue queue =
+  Mutex.lock queue.lock;
+  while Queue.is_empty queue.q do
+    Condition.wait queue.cond queue.lock
+  done;
+  let eff = Queue.take queue.q in
+  Mutex.unlock queue.lock;
+  eff
+
+(* Try to get effect without blocking *)
+let try_dequeue queue =
+  Mutex.lock queue.lock;
+  let result =
+    if Queue.is_empty queue.q then
+      None
+    else
+      Some (Queue.take queue.q)
+  in
+  Mutex.unlock queue.lock;
+  result
+
+(* Get queue length *)
+let queue_length queue =
+  Mutex.lock queue.lock;
+  let len = Queue.length queue.q in
+  Mutex.unlock queue.lock;
+  len