i18n: a key used only in a listener counts as used - the key check walked prog but not the bodies kept beside it (@On listeners, the lifecycle hooks, tests, computed fields, scenes), so their keys were never checked against en.po and ludic schema listed them unused (the game's 15 itemuse.* keys, emitted through ItemPlace); they are walked now as privates.ludic walks them. examples/lang/i18n_listen and its schema case (added, not run); reseeded, bootstrap-cfree fixpoint holds

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

examples/lang/i18n_listen/i18n_listen.ludic

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+# i18n_listen.ludic - a key used only inside an @On listener is a used key: the check walks the
+# bodies kept beside the program's declarations (listeners, hooks, tests, scenes), so listen.put is
+# checked against en.po and `ludic schema` does not report it unused.
+#
+# Running it prints:  listen.put
+program I18nListen {
+  event Put { n: int = 0 }
+  function tr(key: Key) -> string {
+    let s = string(key)
+    return s[1..len(s)]
+  }
+  @On(Put) handler Said { print(tr(k"listen.put")) }
+  entry { emit Put(n: 1) }
+}

examples/lang/i18n_listen/lang/en.po

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+# The source language of the listener keys example.
+msgid ""
+msgstr ""
+"Content-Type: text/plain; charset=UTF-8\n"
+
+#. What is said when something is put down.
+msgid "listen.put"
+msgstr "Put down"

examples/lang/i18n_listen/package.ludic

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+# the listener keys example (i18n_listen.ludic): lang/en.po is the source every key is checked against
+lang "lang" en