feat(lang): friend module lab of fishing, data - a friend of the modules it names

A scoped friend sees those modules' private names and only the exports
of every other; a plain friend module still sees everything. Reseed.

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

LANGUAGE.md

@@ -103,7 +103,8 @@ visible.ludic:5: error: add is private to module bank; mark it 'export' where it
 A file in no module - the program's own file, the runtime - is public, and a package found
 through `ludic_modules` or the toolchain keeps its own module rather than its importer's. A
 program that says `friend module lab` sees every module's private names: that is for a test
-harness, which has to reach inside what it tests. `export` is a keyword before a declaration
+harness, which has to reach inside what it tests. `friend module lab of fishing, data` narrows
+that to the modules named: `lab` sees their private names, and every other module's exports only. `export` is a keyword before a declaration
 and is not the `@export` annotation, which names a C symbol.
 
 To move an existing codebase onto modules, build it once with `LUDIC_VIS_REPORT=1`: every
@@ -132,7 +133,8 @@ fishing/land.ludic:4: error: fishing uses items.inv_add (items/index.ludic:3): a
   switched on one module at a time. Two module lines for one module add their lists together.
 - A file in no module (the program's root, the runtime) is unaffected either way, and a package's
   module (found through `ludic_modules` or the toolchain, such as `ludic_ui`) is always usable.
-- A friend of a module (below) is not held to its `uses` for that module.
+- A friend of a module (`friend module lab`, or `friend module lab of fishing`) is not held to its
+  `uses` for that module.
 - The declared graph may not go round: `module a uses b` beside `module b uses a` is refused
   (`the modules' uses go round in a circle: a -> b -> a`) - one of them takes the other through a
   port instead.

changes/friend-of.md

@@ -0,0 +1,5 @@
+bump: minor
+type: feature
+**`friend module lab of fishing, data` - a friend of some modules, not all.** A scoped friend sees
+the private names of the modules it names and only the exports of every other; `friend module lab`
+alone still sees everything.

examples/modules/friend_of.ludic

@@ -0,0 +1,12 @@
+# friend_of.ludic — L3: `friend module lab of bank` sees bank's private names and no other module's;
+# a test harness reaches inside exactly what it tests. `friend module lab` alone still sees all.
+#
+# Running it prints:  7 7
+import "bank"
+program FriendOf {
+  friend module lab of bank
+  entry {
+    add(7)
+    print(`{balance} {total()}`)
+  }
+}

examples/rejected/friend_scope.ludic

@@ -0,0 +1,10 @@
+# L3: a friend of kit is not a friend of bank - bank's private `add` stays out of reach
+import "private_bank"
+import "private_kit"
+program FriendScope {
+  friend module lab of kit
+  entry {
+    add(5)
+    print(total())
+  }
+}

selfhost/frontend/modules.ludic

@@ -61,7 +61,11 @@ function mod_parse_friend() -> void {
   pi += 2
   let fm = eat_id()
   module_set(g_parse_file, fm)
-  let scope = ""
+  var scope = ""
+  if is_id("of") {
+    pi += 1
+    scope = mod_parse_names()
+  }
   push(g_mod_friends, fm)
   push(g_fr_scope, scope)
 }

tools/ludic-cli/test.ludic

@@ -738,6 +738,8 @@ function cmd_dev_test() -> int {
   feat_case("modules/uses", "", "8 3", "uses.ludic (L3: `module fishing uses base` - a module reaches only the modules it names)")
   reject_case("rejected/uses_missing", "fishing uses items.inv_add", "a module that says `uses` cannot reach a module it does not name, exported or not")
   reject_case("rejected/uses_cycle", "go round in a circle: a -> b -> a", "a cycle in the declared uses is refused")
+  feat_case("modules/friend_of", "", "7 7", "friend_of.ludic (L3: `friend module lab of bank` sees bank's private names)")
+  reject_case("rejected/friend_scope", "add is private to module bank", "a friend of one module is not a friend of another")
   vis_report_case("rejected/uses_missing", "uses: examples/rejected/uses_valley/items/index.ludic:3: items.inv_add used from", "LUDIC_VIS_REPORT=1 lists a uses violation and builds")
   feat_case("lang/checked", "", "7.5 3 12 hi 2 ok", "checked.ludic (L4: literals take their slot's kind, string(p), []string as []pointer, null, named args)")
   reject_case("rejected/wrong_arity", "this call to area leaves out h, which has no default", "a call with the wrong number of arguments is refused")