Include resolver: interpolation mismatch, no cycle detection, redirects ignored #103

Found while reviewing #102. All of the following reproduce on main (e797060, 5.4.1) in src/mxdev/including.py (resolve_dependencies).

1. Include paths are parsed with a different interpolation than the final config

resolve_dependencies reads each file with a plain ConfigParser() (BasicInterpolation), while read_with_included parses the final config with ExtendedInterpolation.

• ${...} is not resolved in include paths. With d = sub and include = ${settings:d}/c.ini, the resolver opens the literal path ${settings:d}/c.ini and raises FileNotFoundError, although the final config would show include = sub/c.ini.
• A % in an include path or URL (50%.ini, URL-encoded %20) raises configparser.InterpolationSyntaxError: '%' must be followed by '%' or '('. An escaped %% is read as % by the resolver but stays %% in the final config.

Possible fix: use ExtendedInterpolation in the resolver too (include values are resolved the same way as in the final config), or at least interpolation=None.

2. No cycle detection

mx.ini with include = b.ini, and b.ini with include = mx.ini, gives RecursionError: maximum recursion depth exceeded. A set of already visited (resolved) paths/URLs with a clear error message would help. This becomes more likely with include-optional (#102), where a custom file naturally refers back to the main file.

3. Relative includes ignore redirects

http_parent is built from the requested URL, not from the final URL after redirects (fio.geturl()). If https://example.com/latest/mx.ini redirects to https://cdn.example.com/v5/config/mx.ini, a relative include = other.ini in it is fetched from https://example.com/latest/other.ini instead of the sibling of the redirect target.

Assisted-by: Claude Opus 5.5