NFC/NFD, narrow no-break space (U+202F), and curly quotes render
identically in a terminal — a model retyping a visually-correct path
gets 'file not found' and can never discover the byte mismatch on its
own. On not-found, canonicalize the requested name and compare against
directory entries; exactly ONE equivalent spelling reads transparently
with an explanatory note. Zero or several matches (homoglyph twins)
fall through — never guess between collisions.
Also: difflib.SequenceMatcher >=0.8 fallback in _suggest_similar_files
catches near-miss typos (AGENT.md -> AGENTS.md) that substring scoring
misses entirely.
Measured (file-only arm, 3 reps, control=guard-only vs feature):
unicode task qwen3.8-max 31k->16k tok (-48%), turns 6.7->3.7;
opus-4.8 57k->33k tok (-42%), turns 8.3->5.0; accuracy held 1.00.
near-miss: opus mildly better, qwen flat, no regressions.
Teknium
fd452e26e3