grep's glob filter is ignored for a named file (while the summary says it ran), and the pattern its description advertises selects nothing #2063

Measured 2026-10-10 (cyc20261010-220909) on master 2673769b, in this checkout.

grep's glob parameter answers two different questions under one name: it filters the
directory branch, and it is ignored by the file branch while the summary still says it
was applied — and the pattern its own description advertises selects nothing at all.

1. A named file is not filtered, and the reading says it was

$ # emrg/tools/read_tool.py holds one "def definition"
$ grep pattern="def definition" path=emrg/tools/read_tool.py                     
Found 1 matches ... (searched 1 files)
$ grep pattern="def definition" path=emrg/tools/read_tool.py glob="*.py"          
Found 1 matches ... (searched 1 files)
$ grep pattern="def definition" path=emrg/tools/read_tool.py glob="*.nomatch"     
Found 1 matches ... (searched 1 files)          <- identical to no filter at all

*.nomatch matches nothing in any tree, so the third call is a search of a file the
caller's own filter excludes. When the file happens to hold no match, the same call reads:

No matches for 'def main' in .../read_tool.py (searched 1 files) matching '*.nomatch'

matching '*.nomatch' is a claim about a filter that never ran. The description says
"Only search files matching this glob pattern", and the code (master):

if root.is_file():
    files = [root]                    # `file_glob` is not consulted
else:
    files = self._collect_files(root, file_glob)

The directory branch applies it, so the same parameter means two things depending on
whether path names a file.

2. The pattern the description advertises selects nothing

The glob parameter's description lists its examples as
Examples: '*.py', '*.{py,rs}', 'src/**/*.ts'. — and the walk is Path.rglob, whose
pattern language has no brace expansion. *.{py,rs} is not two patterns; it is one
literal string that matches no file whose name contains a brace. Over emrg/tools/:

glob='*.py'       ->  Found 9 matches for 'def definition' ... (searched 15 files)
glob='*.{py,rs}'  ->  No matches for 'def definition' ... (searched 0 files)

No matches is the sentence a real absence produces, so a model that follows the
description's own example is told "this pattern does not occur in the tree" about a
question the tool never asked. Nothing in the repo passes a brace pattern — the
description is its only user.

The same holds for glob's sibling: glob pattern='**/*.{py,md}' answers
No files matched pattern '**/*.{py,md}' on a tree that plainly holds both kinds of file.

Acceptance

• the glob filter is applied to a named file too (the same predicate the directory
  branch uses), so glob means one thing;
• a search that names one file and is excluded by the filter says which of the two
  readings it is (searched 0 files plus the reason), rather than printing a filter it
  did not apply;
• a brace pattern is refused with the reason by both grep and glob — never
  searched to an empty answer that reads like a true one — through one shared rule;
• the description's examples are true: a test reads the advertised list out of the schema
  and runs each one against a tree holding the file it names, so an unreadable form cannot
  re-enter it.