feat(ecs): things_now / things_changed - a consumer keeps the tick it read up to and asks only for the Things written since (untouched 64-row blocks skipped)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.things/chunks.ludic

@@ -15,3 +15,20 @@ export function things_drop_chunk(things_st: mut ThingsState, chunk: int) -> int
   }
   return n
 }
+
+# change detection: the tick now, the table moving on to the next - a consumer keeps what this
+# returned and asks things_changed(since: it) for what was written after
+export function things_now(things_st: mut ThingsState) -> int {
+  let t = tb_tick(things_st.th.tab)
+  tb_advance(things_st.th.tab)
+  return t
+}
+
+# every Thing a verb wrote after `since`, into the caller's list (untouched 64-row blocks skipped)
+export function things_changed(things_st: ThingsState, since: int, rows: words, out: []Thing) -> int {
+  List.clear(out)
+  let tb = things_st.th.tab
+  let n = tb_changed_since(tb, since, rows)
+  for k in 0 .. n { push(out, tb.rec[rows[k]]) }
+  return n
+}

packages/ludic.things/tests/things_test.ludic

@@ -197,4 +197,22 @@ program ThingsTest {
     expect_eq(len(facts(things_st)), 3)
     expect_eq(things_verify(things_st), 0)
   }
+
+  test "change detection names what a verb wrote since the tick a consumer kept" (things_st: mut ThingsState) {
+    things_clear(things_st)
+    let a = put(things_st, TH_BRANCH, 1.0, 0.0)
+    let b = put(things_st, TH_BRANCH, 2.0, 0.0)
+    let seen = things_now(things_st)
+    let rows = words(0)
+    let out = new []Thing
+    expect_eq(things_changed(things_st, seen, rows, out), 0)
+    thing_hide(b)
+    expect_eq(things_changed(things_st, seen, rows, out), 1)
+    expect(out[0] == b)
+    let later = things_now(things_st)
+    thing_move(a, 9.0, 9.0, 0.0)
+    expect_eq(things_changed(things_st, later, rows, out), 1)
+    expect(out[0] == a)
+    expect_eq(things_changed(things_st, seen, rows, out), 2)
+  }
 }