Recursion guard and static klammer checking

A klammer that reaches itself, directly or through a cycle, expanded
until the C++ stack was exhausted: the process died from SIGSEGV with no
message and no location. The former limit guarded only the top-level
fixed-point iteration, never the descent through klammer application. A
depth guard now raises a recursion error naming the klammer and where it
was applied. The same loop's termination test moves from "the katom list
stopped growing" to "a pass applied no klammer", since a klammer whose
body expands to nothing is a reduction that adds no katoms; exceeding the
round limit is now an error rather than a message followed by rendering a
document with live klammers still in it.

ktext --check locates every klammer application written in a document or
in a klammer body and checks name existence, argument count, option
names, and target coverage without applying anything, reporting all
problems at once. This is possible because Klammertext has no catcodes:
katom structure is fixed when a file is read, so a klammer body has a
determinate shape before it is expanded. The check therefore reaches what
the engine cannot -- the branch of a @cond that is not selected, and
bodies a given render never enters.

@cond's set of truth values is an open language question, so its meaning
is unchanged here; an unrecognized predicate now warns, giving its value
and location.

tst/ gains recursion_test.sh (7 cases) and check_test.sh (19 cases), and
this snapshot's test Makefile is generated from the shipped suite list so
the two cannot drift apart.

(from dev c27e63802406)

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

mac/machine.h

@@ -79,7 +79,10 @@ public:
     void apply_klammer_registry(Klammer_registry& klammer_registry,
                katom_list& katoms, const std::string& target, katom_iter begin, katom_iter end);
 
-    void apply(Klammer_registry& klammer_registry, katom_list& katoms, const std::string& target);
+    // Returns the number of klammers applied in this pass.  The top-level
+    // fixed point loops while that count is nonzero: reduction is detected by
+    // a redex having been reduced, not by the katom list having grown.
+    int apply(Klammer_registry& klammer_registry, katom_list& katoms, const std::string& target);
 
     std::string run_phase_functions();
     std::string apply(const std::string& target_name, bool final_processing=true, bool escape_characters=true);