docs(rl-next): note URL path sub-delims no longer percent-encoded

Author: lovesegfault

doc/manual/rl-next/url-path-subdelims.md

@@ -0,0 +1,14 @@
+---
+synopsis: URL paths no longer percent-encode `+` and other sub-delims
+prs: []
+---
+
+URL path segments containing characters from the RFC 3986 sub-delims set
+(`!$&'()*+,;=`) now render unencoded. Previously `file:///tmp/a+b` would
+round-trip through `ParsedURL::to_string()` as `file:///tmp/a%2Bb`; it now
+round-trips as itself. This fixes confusing `%2B` appearing in error messages,
+`nix store info` output, and flake lock files when filesystem paths contain `+`.
+
+Store URLs with `+` in their path will produce a different NarInfoDiskCache key
+on upgrade, causing a one-time cache miss (the cache repopulates on the next
+query).