feat(lang): open registry - other modules' defs, in an order imports cannot change

A def from another module into a registry that is not open is refused,
and defs go through visibility (the registry exported, its module in the
definer's uses). Index order: the declaring module's entries, then the
other modules' by module name, each in reading order. A registry entry
is emitted as its own file's code, so what it names is seen from its
own module. Reseed.

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

examples/modules/open_registry.ludic

@@ -0,0 +1,17 @@
+# open_registry.ludic — L8 + L3: `export open registry Systems of System` takes defs from other
+# modules. The index order is the declaring module's entries, then every other module's by module
+# name - alpha before zeta, although zeta is imported first - so it never depends on import order.
+#
+# Running it prints:  clock animals weather / 2 2 3
+import "reg/core"
+import "reg/zeta"
+import "reg/alpha"
+program OpenRegistry {
+  entry {
+    var out = ""
+    for i in 0 .. SY_COUNT { out = out + Systems[i].key + " " }
+    let s = Systems[SY_ANIMALS]
+    let w = Systems[SY_WEATHER]
+    print(`{out}/ {s.run()} {SY_WEATHER} {w.run()}`)
+  }
+}

examples/modules/reg/alpha/index.ludic

@@ -0,0 +1,6 @@
+# alpha/index.ludic - another module's entry
+module alpha uses core
+def Systems animals { run: fn animals_run }
+function animals_run() -> int {
+  return 2
+}

examples/modules/reg/core/index.ludic

@@ -0,0 +1,11 @@
+# core/index.ludic - declares the registry other modules add to, and its own first entry
+module core
+export property System {
+  key: string = ""
+  run: fn() -> int = null
+}
+export open registry Systems of System as SY
+def Systems clock { run: fn clock_run }
+function clock_run() -> int {
+  return 1
+}

examples/modules/reg/zeta/index.ludic

@@ -0,0 +1,6 @@
+# zeta/index.ludic - adds an entry to core's open registry; its function stays private to zeta
+module zeta uses core
+def Systems weather { run: fn weather_run }
+function weather_run() -> int {
+  return 3
+}

examples/rejected/closed_kit/index.ludic

@@ -0,0 +1,7 @@
+# closed_kit/index.ludic - a registry that is not open
+module kit
+export property Tool {
+  name: string = ""
+}
+export registry Tools of Tool
+def Tools axe { name: "Axe" }

examples/rejected/hidden_kit/index.ludic

@@ -0,0 +1,10 @@
+# hidden_kit/index.ludic - open, but not exported: nothing outside kit can name it
+module kit
+export property Tool {
+  name: string = ""
+}
+open registry Tools of Tool
+def Tools axe { name: "Axe" }
+export function tool_count() -> int {
+  return TOOLS_COUNT
+}

examples/rejected/registry_closed.ludic

@@ -0,0 +1,8 @@
+# L8 + L3: only an `open registry` takes defs from another module
+import "closed_kit"
+program RegistryClosed {
+  def Tools saw { name: "Saw" }
+  entry {
+    print(TOOLS_COUNT)
+  }
+}

examples/rejected/registry_hidden.ludic

@@ -0,0 +1,8 @@
+# L8 + L3: a def goes through visibility like any reference - the registry must be exported
+import "hidden_kit"
+program RegistryHidden {
+  def Tools saw { name: "Saw" }
+  entry {
+    print(tool_count())
+  }
+}