modified: readme

BEHAVE-TEXT/README.md

@@ -197,6 +197,49 @@ choose to weight these at zero until field-validated against labeled data.
 
 ---
 
+## Engine implementation notes
+
+### Cross-alphabet fingerprint comparisons are undefined
+
+Several primitives produce hash-based fingerprints by hashing over character or
+syntactic sequences:
+
+- `stylometric.character_ngram_simhash`
+- `stylometric.pos_ngram_signature`
+- `stylometric.function_word_distribution_top50` / `top200`
+- `stylometric.distinctive_vocabulary_signature`
+- `lexical.optional_grammar_signature`
+
+These fingerprints are only **meaningful within a single writing-system boundary**.
+A Latin-script actor (Spanish, English, French, Portuguese) and a Cyrillic-script
+actor (Russian, Bulgarian, Serbian) share zero character n-grams by definition.
+Comparing their `character_ngram_simhash` values produces a Hamming distance that
+is numerically valid but semantically undefined — it does not measure dissimilarity,
+it measures incomparability.
+
+The same applies to any other script boundary: Arabic vs Latin, Hangul vs Hiragana,
+Devanagari vs Cyrillic, and so on.
+
+**Engine rule:** before compositing or comparing any hash-based fingerprint between
+two actors, gate on script/language compatibility. Use `lexical.dialect_region` or
+`lexical.code_switching_matrix_language` to determine whether two actors share a
+writing system. If they do not, treat the fingerprint distance as `undefined` rather
+than as evidence of dissimilarity — do not include it in the similarity composite.
+
+Primitives that are **not** subject to this constraint (safe to compare across
+writing systems without gating):
+
+- All `meta.*` primitives — corpus-footprint metrics are script-agnostic.
+- All `interaction.*` primitives — timing and graph-structure signals are
+  script-agnostic.
+- `stylometric.emoji_usage`, `stylometric.emoji_placement` — Unicode emoji are
+  shared across scripts.
+- `stylometric.capitalization_habit` — only meaningful within scripts that have
+  case; emit `unknown` for caseless scripts (Arabic, CJK, etc.).
+- `network.*`, `temporal_evolution.*` — structural signals, script-agnostic.
+
+---
+
 ## Schema
 
 Machine-readable JSON Schema: