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.

tst/filename_test.sh

@@ -14,7 +14,7 @@
 #     regrouping is announced on stderr.
 #   - A leading "~/" expands to $HOME (shells do not expand a quoted tilde).
 #
-# Engine tier: uses -k none; no SKS.
+# Engine tier: uses --klammersets none; no SKS.
 #
 # Usage: ./filename_test.sh
 # Exit code: 0 if all tests pass, 1 otherwise.
@@ -98,36 +98,49 @@ echo "======================="
 
 check "1. quoted filename with a space is one file" \
       "ALPHA" "" \
-      "my file.kt" -d -k none
+      "my file.kt" -d --klammersets none
 
-check "2. unquoted spaces rescued into an existing file (announced)" \
+# The regrouping is a DERIVED value -- the command completed a name the input
+# left ambiguous -- so since 2026-08-15 it is reported at "-v 1" and the
+# default run is silent.  Silence is safe because a rescue only succeeds when
+# the joined name names an existing file: a mistyped name fails instead of
+# resolving to something else.
+check "2. unquoted spaces are rescued into an existing file" \
+      "ALPHA" "" \
+      my file.kt -d --klammersets none
+
+check "2a. ... silently at the default verbosity" \
+      "ALPHA" "" \
+      my file.kt -d --klammersets none
+
+check "2b. ... and reported at -v 1" \
       "ALPHA" "interpreting \"my file.kt\" as one filename" \
-      my file.kt -d -k none
+      my file.kt -d --klammersets none -v 1
 
 check "3. standalone / separates a filename list" \
       "ALPHA
 BETA" "" \
-      my file.kt / b.kt -d -k none
+      my file.kt / b.kt -d --klammersets none
 
 check "4. space in a directory component" \
       "GAMMA" "" \
-      "my dir/c.kt" -d -k none
+      "my dir/c.kt" -d --klammersets none
 
 check "5. quoted name that exists is never split (b.kt also exists)" \
       "ALPHA" "" \
-      "my file.kt" -d -k none
+      "my file.kt" -d --klammersets none
 
 HOME="$DIR" check "6. quoted ~/ expands to \$HOME inside ktext" \
       "BETA" "" \
-      "~/b.kt" -d -k none
+      "~/b.kt" -d --klammersets none
 
 check "7. @read argument keeps its internal space" \
       "ALPHA" "" \
-      -s '@read my file.kt @' -d -k none
+      -s '@read my file.kt @' -d --klammersets none
 
 check_error "8. unrescuable name is reported as written" \
       "no such.kt" \
-      "no such.kt" -d -k none
+      "no such.kt" -d --klammersets none
 
 echo
 echo "======================="