[Frauschi]

What

Two input mistakes that produced a misleading result now fail early.

• Unreadable --options-h: gen-sbom warned and wrote an SBOM with an empty build configuration and exit status 0. It now exits with the path and the OS error.
• TARGETS with LIB: the driver already rejects --lib with --srcs-file. The CMake helper now rejects TARGETS with LIB at configure time, and sbom.mk rejects SBOM_SRCS with SBOM_LIB before calling the driver. A LIB left as <VAR>-NOTFOUND by a failed find_library() now stops configure with "LIB was not found"; next to TARGETS it used to be dropped silently.
• The driver's message for a missing checksum source names all three options, and share/README.md says "pick one" instead of "at least one" (the leftover nit from sbom: record a traced library, zlib, and explicit dependency versions #37).

Tests

• test_missing_file_exits in test_gen_sbom.py, a configure-failure test in test_sbom_cmake_install.py (both set, and -NOTFOUND with and without TARGETS), and in test_sbom.py the missing-source message plus the sbom.mk check through make.
• Independent of the other two open follow-ups; all three merge cleanly in any order and pass together.

[Copilot]

🟢 Approval recommended

The focused validation changes match the driver contract and include regression coverage, with no blocking issues identified in static review; tests were not executed.

No open issues 🎉

What changed in this PR

This PR tightens SBOM input validation so unreadable configuration files and conflicting checksum sources fail explicitly rather than produce misleading output.

Changes:

• Fail with the path and OS error when --options-h cannot be read.
• Reject conflicting composition inputs in CMake and Make, and reject unresolved CMake library paths.
• Clarify checksum-source guidance and add regression coverage.

File	Description
tests/​test_sbom.py	Tests missing-source diagnostics and conflicting Make inputs.
tests/​test_sbom_cmake_install.py	Tests configure failures for conflicting inputs and unresolved libraries.
tests/​test_gen_sbom.py	Tests failure when the options header is missing.
share/​sbom-driver.py	Names all three checksum-source options in the diagnostic.
share/​README.md	Clarifies that composition inputs are mutually exclusive.
share/​gen-sbom	Exits with an error when the options header is unreadable.
share/​build/​sbom.mk	Rejects simultaneous source and library inputs.
share/​build/​sbom.cmake	Rejects conflicting inputs and unresolved library paths.

_{Review effort: Balanced}