An output policy for the three commands, and @cond as a true special form

A snapshot of the development tree.  The substantial changes since the last one:

COMMAND OUTPUT POLICY.  The three commands display text in exactly three cases,
and each owns a stream: LOGGING under "-v" greater than 0 and an ERROR before
termination go to STDERR; OUTPUT THE USER ASKED FOR goes to STDOUT.  For ktext
that output is a document, so "ktext doc.kt -d | ..." is now safe -- logging
used to share the stream and land inside the document.  A bare command prints
its usage and succeeds rather than failing.  Colour is emitted only to a
terminal, per stream, and NO_COLOR is honoured.

"-v 1" reports every decision whose outcome you could not have read off your own
input: the klammerset that was loaded and from which file, a font's directory, a
":files" name's file, how "-o" was expanded.  Higher levels are the trace.

The commands no longer warn and continue: an anomaly is an error, described with
its location.  Two exceptions remain, each for a stated reason -- a condition
that is expected and temporary by design, and a judgment that is a heuristic
rather than exact.

@cond IS NOW A TRUE SPECIAL FORM, resolved at APPLICATION time rather than when
the file is read.  Two consequences for a writer:

  * a state variable reaches the predicate.  "@@@state Flag :value true @@@
    @cond *Flag* | T | F @" renders "T"; it used to see the literal "*Flag*" and
    silently take the false branch.  The document now behaves like a klammer
    body, whose arguments are bound before its conditionals are decided.
  * nothing in a discarded branch happens -- it is not read, not evaluated, not
    expanded.  An @eval in the branch not taken used to run anyway.

Its predicate relation is total and strict: true, True, 1; false, False, 0, and
empty; anything else is an error at the @cond rather than silently false.

@eval REACHING OUTSIDE.  ":shell" and ":haskell" now keep the command's standard
error out of the document (it appears under "-v 1") and treat a nonzero exit as
an error naming what the command reported.  A command that exits nonzero on
purpose -- "grep" finding no match -- says so with "|| true".

KLAMMER SETS.  Several combine: "--klammersets a b c" loads all three in the
order given, sharing one namespace, with the definition modes deciding
collisions.  "none" means none and may not be combined with other symbols.  A
klammerset with symbol X is declared in a file X/X.k, which is what lets two
sets require the same third set without loading it twice.

TESTS.  Four new suites: the kdiag command's interface, the @eval primitive's
contract with the outside world, and verbosity at both tiers.  Three suites
that could not run on macOS at all now do.

Assembled from dev commit 6c8ee6c22fca.

mac/klammer_registry.cpp

@@ -71,7 +71,14 @@ void Klammer_registry::add(
                 std::string msg = result.message;
                 msg = string_replace(msg, "NAME", q_(name_target));
                 msg = string_replace(msg, "AT", at_desc);
-                warning(msg, begin->m_loc);
+                // An override is not a warning: ":::" exists to override, and
+                // a klammer set a user did not write may be overridden by
+                // design (TODO #33).  A warning nobody can act on is not a
+                // warning.  It IS worth reporting at "-v 1", because the
+                // definition being replaced usually lives in another file, in
+                // another klammerset, which the user cannot see from what they
+                // wrote (Andy, 2026-08-15).
+                (void)K::log(1, msg + " at " + begin->m_loc.desc());
             }
             m_klammers[klammer_name].remove_target_definition(target_name);
         }
@@ -172,7 +179,8 @@ std::string Klammer_registry::instance_list(int margin) const
     return ss.str();
 }
 
-std::string Klammer_registry::describe(int margin, const std::string& search) const
+std::string Klammer_registry::describe(int margin, const std::string& search,
+                                       const strings_t& defined_outside) const
 {
     /*
     strings_t names {};
@@ -182,6 +190,9 @@ std::string Klammer_registry::describe(int margin, const std::string& search) co
     std::string result;
     std::string query = collapse_whitespace(search);
     for (const auto& [name, k] : m_klammers) {
+        if (!defined_outside.empty() && !k.defined_outside(defined_outside)) {
+            continue;
+        }
         if (!query.empty() &&
             !contains_fold(name, query) &&
             !contains_fold(collapse_whitespace(k.description_text()), query)) {