WIP: Starting to improve failure/error handling (errors as values)

test/Readme.md

@@ -13,3 +13,27 @@ The first command generates base component tables, segmented C++, single-header
 It compiles and runs the C++17 and C11 single-header host smokes. The second command reuses the same mirror.
 
 The verification wrapper copies them into the disposable mirror; it does not embed C or C++ source text.
+
+## Parser bounds probe
+
+`test/parser_bounds/test.cpp` is a GEN_TIME program. It includes `base/gen.cpp`. It is not part of `verify_baseline.ps1`.
+
+From the project root:
+
+```powershell
+.\scripts\build.ps1 clang parser_bounds
+```
+
+The script builds and runs the probe. A pass prints `parser bounds passed` and `PASSED: parser_bounds`.
+The probe covers helper positions, formatting skip at the slice end, empty and whitespace `parse_variable`, and two direct end-of-slice reads.
+It does not prove in-slice syntax errors return.
+
+## Lexer failure probe
+
+```powershell
+.\scripts\build.ps1 clang lexer_failures
+```
+
+A pass prints `lexer failures passed` and `PASSED: lexer_failures`.
+The probe covers nine lexer failures, six successful sibling inputs, and a baseline variable after each failure.
+It does not prove in-slice parser errors return.