docs: clarify code-only corpora skip semantic extraction (closes #836)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/how-it-works.md

@@ -7,6 +7,8 @@ graphify processes your files in three passes:
 **Pass 1 — Code structure (free, no API calls)**
 Tree-sitter parses your code files and extracts classes, functions, imports, call graphs, and inline comments. This runs locally with no LLM involved. 25 languages supported. SQL files get special treatment: tables, views, foreign keys, and JOIN relationships are extracted deterministically.
 
+Code files are not sent to the LLM semantic extractor in the normal pipeline. If a corpus contains only code files, Pass 3 is skipped entirely; semantic extraction is reserved for docs, papers, images, and transcripts.
+
 **Pass 2 — Video and audio (local, no API calls)**
 Video and audio files are transcribed with faster-whisper. To focus the transcript on your domain, the transcription prompt is seeded with your top god nodes (the most-connected concepts in your code graph so far). Transcripts are cached — re-runs skip already-processed files.
 

tests/test_install_strings.py

@@ -120,3 +120,11 @@ def test_report_is_still_referenced_as_fallback():
 def test_agents_section_does_not_skip_dirty_graph_output():
     assert "Dirty graphify-out/ files are expected" in _AGENTS_MD_SECTION
     assert "not a reason to skip graphify" in _AGENTS_MD_SECTION
+
+
+def test_how_it_works_clarifies_code_only_semantic_extraction():
+    from pathlib import Path
+    doc = (Path(__file__).parent.parent / "docs" / "how-it-works.md").read_text(encoding="utf-8")
+    assert "Code files are not sent to the LLM semantic extractor" in doc
+    assert "code files, Pass 3 is skipped entirely" in doc
+    assert "docs, papers, images, and transcripts" in doc