spec: vector primitives — bounds-checked ref/set!, vector-copy start/end slice

vector-ref and vector-set! now raise Eval_error on out-of-bounds index instead of
an OCaml array exception. vector-copy accepts optional start and end parameters for
slicing (R7RS §6.8). spec/primitives.sx doc updated to reflect slice params.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

hosts/ocaml/lib/sx_primitives.ml

@@ -1227,11 +1227,19 @@ let () =
     | _ -> raise (Eval_error "vector-length: expected vector"));
   register "vector-ref" (fun args ->
     match args with
-    | [Vector arr; Number n] -> arr.(int_of_float n)
+    | [Vector arr; Number n] ->
+      let i = int_of_float n in
+      if i < 0 || i >= Array.length arr then
+        raise (Eval_error (Printf.sprintf "vector-ref: index %d out of bounds (length %d)" i (Array.length arr)));
+      arr.(i)
     | _ -> raise (Eval_error "vector-ref: expected (vector index)"));
   register "vector-set!" (fun args ->
     match args with
-    | [Vector arr; Number n; v] -> arr.(int_of_float n) <- v; Nil
+    | [Vector arr; Number n; v] ->
+      let i = int_of_float n in
+      if i < 0 || i >= Array.length arr then
+        raise (Eval_error (Printf.sprintf "vector-set!: index %d out of bounds (length %d)" i (Array.length arr)));
+      arr.(i) <- v; Nil
     | _ -> raise (Eval_error "vector-set!: expected (vector index value)"));
   register "vector->list" (fun args ->
     match args with [Vector arr] -> List (Array.to_list arr)
@@ -1246,8 +1254,18 @@ let () =
     | [Vector arr; v] -> Array.fill arr 0 (Array.length arr) v; Nil
     | _ -> raise (Eval_error "vector-fill!: expected (vector value)"));
   register "vector-copy" (fun args ->
-    match args with [Vector arr] -> Vector (Array.copy arr)
+    match args with
-    | _ -> raise (Eval_error "vector-copy: expected vector"));
+    | [Vector arr] -> Vector (Array.copy arr)
+    | [Vector arr; Number s] ->
+      let start = int_of_float s in
+      let len = Array.length arr - start in
+      if len <= 0 then Vector [||] else Vector (Array.sub arr start len)
+    | [Vector arr; Number s; Number e] ->
+      let start = int_of_float s in
+      let stop = min (int_of_float e) (Array.length arr) in
+      let len = stop - start in
+      if len <= 0 then Vector [||] else Vector (Array.sub arr start len)
+    | _ -> raise (Eval_error "vector-copy: expected (vector) or (vector start) or (vector start end)"));
 
   (* Capability-based sandboxing — gate IO operations *)
   let cap_stack : string list ref = ref [] in

plans/agent-briefings/primitives-loop.md

@@ -50,8 +50,10 @@ Primitives to add:
 - `vector-copy` `v` `[start]` `[end]` → fresh copy of slice
 
 Steps:
-- [ ] OCaml: add `SxVector of value array` to `hosts/ocaml/sx_types.ml`; implement all
+- [x] OCaml: add `SxVector of value array` to `hosts/ocaml/sx_types.ml`; implement all
       primitives in `hosts/ocaml/sx_primitives.ml` (or equivalent); wire into evaluator.
+      Note: Vector type + most prims were already present; added bounds-checked vector-ref/set!
+      and optional start/end to vector-copy. 10/10 vector tests pass (r7rs suite).
 - [ ] Spec: add vector entries to `spec/primitives.sx` with type signatures and descriptions.
 - [ ] JS bootstrapper: implement vectors in `hosts/javascript/platform.js` (or equivalent);
       ensure `sx-browser.js` rebuild picks them up.
@@ -194,4 +196,5 @@ Brief each language's loop agent (or do inline) after rebasing their branch onto
 
 _Newest first._
 
+- 2026-04-25: Phase 1 OCaml step done — bounds-checked vector-ref/set!, vector-copy now accepts optional start/end, spec/primitives.sx doc updated. 10/10 r7rs vector tests pass, 4747 total (394 pre-existing hs-upstream fails unchanged).
 - 2026-04-25: Phase 0 complete — stopped CL/APL/Ruby/Tcl loops (all 4 idle at shell); confirmed E38 (tokenizer :end/:line) and E39 (WebWorker stub) both have implementation commits.

spec/primitives.sx

@@ -227,9 +227,11 @@
 
 (define-primitive
   "vector-copy"
-  :params ((v :as vector))
+  :params ((v :as vector)
+    (start :as number :optional true)
+    (end :as number :optional true))
   :returns "vector"
-  :doc "Independent shallow copy.")
+  :doc "Shallow copy of vector, optionally sliced from start (inclusive) to end (exclusive).")
 
 (define-primitive
   "min"