The Map's tests join the suite, and the epoch trap covers its half

maps.flan and map-exhausted.flan as fixed-output cases, the six refusals
by name, and map-stale-region.flan beside stale-region.flan.

The last one is not a line in the Vec's program because the two reach
the check by different routes. A Vec's operations check on the way in
and stop there. A map's get goes on to call a hash and an equality
function through pointers into the block, so a missing check there is
not a wrong number — it is a probe loop walking released memory. It
traps naming the site and exits 134, as the Vec's does.

{K V} resolves now, so the test that asserted it was milestone 6 is
replaced by the one that still holds: the arity, refused for the reason
Vec's arity is refused, because a near-miss would otherwise resolve to a
type variable and come back as generics.

test/programs/map-stale-region.flan

@@ -0,0 +1,25 @@
+;;;; spec-memory.md, "Dev builds detect a released region" — the Map's half.
+;;;;
+;;;; A Map records the epoch of the allocator it was made with, exactly as a
+;;;; Vec does, and free-all bumps that counter. Any operation on a container
+;;;; whose recorded epoch has moved traps, naming the site.
+;;;;
+;;;; This is worth its own program rather than a line in stale-region.flan
+;;;; because the two containers reach the check by different routes: a Vec's
+;;;; every operation takes the Vec's address and checks on the way in, while a
+;;;; map's get goes on to call a hash and an equality function through pointers
+;;;; into a block that is no longer there. If the check were missing here, the
+;;;; failure would not be a wrong number — it would be a probe loop walking
+;;;; released memory.
+(defn main [] i32
+  (let [a (arena-new 65536)]
+    (let [m (map-new i32 i32 a)]
+      (put m 1 10)
+      (put m 2 20)
+      (match (get m 2) (Some v) (println v) None (println "missing"))
+      ;; The region goes. m is still in scope and still looks fine — nothing is
+      ;; released at scope exit and nothing marked m — which is exactly the
+      ;; case a static rule cannot see.
+      (free-all a)
+      (match (get m 2) (Some v) (println v) None (println "missing"))))
+  0)

test/test_acceptance.ml

@@ -581,6 +581,25 @@ let () =
     end;
     (try Sys.remove exe with Sys_error _ -> ());
 
+    (* The same trap on the Map's side, and it is not the same code path: a
+       Vec's operations check on the way in and stop there, while a map's get
+       goes on to call a hash and an equality function through pointers into
+       the block. A missing check here is not a wrong number, it is a probe
+       loop walking released memory. *)
+    let exe = compile "programs/map-stale-region.flan" in
+    let code, text = run exe None in
+    if code <> 134 || not (contains text "programs/map-stale-region.flan:")
+       || not (contains text "allocator was released")
+       || not (contains text "20")
+    then begin
+      incr failures;
+      Printf.printf
+        "FAIL  a map used after its region was released\n\
+        \        got: %S (exit %d)\n     wanted: exit 134, naming the site\n"
+        text code
+    end;
+    (try Sys.remove exe with Sys_error _ -> ());
+
     (* §2's other half, which cannot be an [outputs] case because it does not
        exit 0: a handler runs, returns normally, and has still not answered the
        error, so the program stops and names the condition. *)
@@ -1531,6 +1550,60 @@ ERR@7 unexpected token: not the kind the caller was reading
     refuses_src "defer in a let inside a branch"
       "(defn g [] 0)\n(defn f [] (if true (let [x 1] (defer (g))) 0))"
       "not allowed inside a branch";
+
+    (* ── (Map K V), spec-memory.md step 4 ──────────────────────────
+
+       Odin's map: open-addressed Robin Hood hashing at a 75% load factor with
+       cache-line cell packing. maps.flan is seven claims, each one a plausible
+       wrong version gets wrong, and the numbers differ per failure.
+
+       The two worth naming, because nothing else in the suite would catch
+       them. A struct key is hashed *field by field*, never bytewise, because a
+       struct's padding bytes are indeterminate — hashing them makes two equal
+       keys hash differently and the entry unfindable, which shows up here as a
+       wrong count rather than a crash. And a grow rehashes against a fresh
+       seed, because the seed is derived from the block address; carrying the
+       old hashes across a grow puts every entry in a slot nothing will probe.
+       2000 entries is eight grows and then every one of them read back. *)
+    let maps_out =
+      "2000\n0\n1600\n709\ntrue\nfalse\n3\n20\nfalse\n2\n3\nfalse\n\
+       100\n999\n2\n1\n3\n500\n998\n"
+    in
+    outputs "maps" "programs/maps.flan" maps_out;
+    outputs ~opt:"-O0" "maps, -O0" "programs/maps.flan" maps_out;
+
+    (* The allocation-failure rule is one rule over every allocating operation,
+       so it has to hold for map-new, put, reserve and clone as it does for the
+       Vec's four. A map is the harder case: its growth allocates a new block,
+       rehashes into it and only then releases the old one, so a failure
+       partway must leave the map exactly as it was or the retry re-attempts
+       against a half-moved map. *)
+    let map_exhausted_out = "300\n0\ntrue\ntrue\ntrue\n0\n2\n2\ntrue\n" in
+    outputs "map StorageExhausted and retry" "programs/map-exhausted.flan"
+      map_exhausted_out;
+
+    (* The refusals, each by name. A float key is not a milestone question —
+       NaN is not equal to itself and 0.0 and -0.0 are equal while differing
+       bytewise, so there is no equality for a map to hash. A move-only value
+       is the refusal (Vec (Vec T)) already carries, for the identical reason.
+       Unit as a value is refused rather than dividing a cache line by zero,
+       and it is named because it is the natural spelling of a set. *)
+    refuses_src "a float is not a map key"
+      "(defn f [m (Map f32 i32)] 0)" "is not a map key";
+    refuses_src "a Ptr is not a map key"
+      "(defn f [m (Map (Ptr i32) i32)] 0)" "hash an address";
+    refuses_src "a map value may not own storage"
+      "(defn f [m (Map i32 (Vec i32))] 0)" "holds a move-only value";
+    refuses_src "a map value may not be Unit"
+      "(defn f [m (Map i32 Unit)] 0)" "cannot be Unit";
+    refuses_src "map-new with nothing to say what it maps"
+      "(defn main [] i32 (let [m (map-new)] (free m)) 0)"
+      "nothing here says what (map-new) maps";
+    (* A map is move-only like a Vec, and the refusal names the type that was
+       moved rather than saying "a Vec" whatever it was. *)
+    refuses_src "a map used after it was moved"
+      "(defn main [] i32 (let [m (map-new i32 i32)] (free m) (put m 1 2)) 0)"
+      "cannot be used again";
     let signed_out = "-4\n-1\nbig is not small\nbig is large\n1\n" in
     outputs "signedness" "programs/signedness.flan" signed_out;
     outputs ~opt:"-O0" "signedness, -O0" "programs/signedness.flan" signed_out;

test/test_flan.ml

@@ -685,8 +685,13 @@ let () =
      back as generics. *)
   rejects_check "Vec takes one type"    "(defn f [x (Vec i32 i32)])"
     ~needle:"exactly one type";
-  rejects_check "Map is milestone 6"    "(defn f [x {string i32}])"
+  (* {K V} resolves now — it is the Map type spelling, and the only one, since
-    ~needle:"milestone 6";
+     a bare map form in expression position is a struct literal's field list.
+     What is still refused is the arity, for the same reason Vec's is: a
+     near-miss would otherwise resolve to a type variable and come back as
+     generics. *)
+  rejects_check "Map takes two types"   "(defn f [x (Map i32)])"
+    ~needle:"exactly two types";
   rejects_check "Result is milestone 6" "(defn f [] (Result i32 i32) None)"
     ~needle:"milestone 6";
   rejects_check "try is milestone 6"    "(defn f [] i32 (try 1))"