feat(benchmarks): standardize LLM/LoRA artifact preflight for benchmarks

[Copilot]

LLM/LoRA benchmarks were silently producing invalid results (or crashing) because MultiLoRAManager::loadLoRA() validates file existence but benchmarks passed hardcoded /loras/... paths that never exist. Missing-artifact failures also had no actionable guidance.

Changes

New: Unit tests for preflight utilities (tests/test_artifact_preflight.cpp, PF-01..PF-14)

Tests cover modelBaseDir() env-var priority/fallbacks, stubModelsEnabled() case-insensitive parsing, resolveModelPath()/resolveLoraPath() path resolution, and LLMArtifactPreflight::create() success/failure/LoRA-required modes. Verifies error messages contain setup guidance.

tests/CMakeLists.txt

Added ${CMAKE_SOURCE_DIR}/benchmarks to include_directories so tests can include benchmark_artifact_preflight.h.

benchmarks/bench_llm_inference_performance.cpp — 9 functions

benchmarks/bench_lora_auto_binding.cpp — 12 functions

benchmarks/bench_lora_inline.cpp — 5 functions

All three files now:

• #include "benchmark_artifact_preflight.h"
• Guard each LoRA-dependent function with THEMIS_BENCH_SKIP_IF_ARTIFACT_MISSING
• Replace every hardcoded /loras/....bin with resolveLoraPath()

// Before – silently benchmarks a failed load
mgr.loadLoRA("adapter-a", "/loras/adapter-a.bin", base_model, 1.0f);

// After – skips with actionable guidance if stub isn't present
THEMIS_BENCH_SKIP_IF_ARTIFACT_MISSING(state, themis::bench::resolveLoraPath(), "LoRA adapter");
const std::string lora_path = themis::bench::resolveLoraPath();
mgr.loadLoRA("adapter-a", lora_path, base_model, 1.0f);

On missing artifact the benchmark emits: "LLM artefact preflight FAILED: LoRA adapter not found. Run scripts/download_models.sh --stub-only or set THEMIS_MODEL_DIR. See docs/BENCHMARK_RUNBOOK.md §LLM/LoRA Model Setup."

Type of Change

• Bug fix (non-breaking)
• New feature (non-breaking)
• Refactoring (non-breaking)
• Documentation
• Breaking change (requires MAJOR version bump — see VERSIONING.md)
• Security fix
• Other:

Breaking Change Checklist

• MAJOR version bump planned in VERSION and CMakeLists.txt
• Migration guide added in docs/migration/
• Announcement prepared for GitHub Discussions (≥ 2 weeks before release)
• CHANGELOG ### Removed / ### Changed section updated

Testing

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed
• Benchmarks run (if performance-sensitive change)

📚 Research & Knowledge (wenn applicable)

• Diese PR basiert auf wissenschaftlichen Paper(s) oder Best Practices?
  • Falls JA: Research-Dateien in /docs/research/ angelegt?
  • Falls JA: Im Modul-README unter "Wissenschaftliche Grundlagen" verlinkt?
  • Falls JA: In /docs/research/implementation_influence/ eingetragen?

Relevante Quellen:

• Paper:
• Best Practice:
• Architecture Decision:

Checklist

• Code follows project style guidelines (clang-format / clang-tidy)
• Self-review completed
• Documentation updated (if needed)
• CHANGELOG.md updated under [Unreleased]
• No new warnings introduced
• Security-sensitive paths reviewed by security maintainer (if applicable)