When /bin is a symlink to /usr/bin (common on modern Linux distros), find_cached() canonicalizes /bin → /usr/bin and only caches entries under /usr/bin. A subsequent try_from call with /bin/python3 fails the direct cache lookup and returns None, causing the environment to be reported as Unknown.

Fix: In try_from, after a cache miss, canonicalize the executable path and retry the lookup. When found via the canonical path, add the original path as a symlink and update both cache entries for consistency.

• Canonicalize executable once, use for both path guard and cache fallback
• Path guard accepts executables whose canonical path resolves to a known bin dir
• Cache fallback adds the original path as a symlink for complete metadata
• Both canonical and original cache entries updated to keep symlink lists consistent

Fixes #405