Fix hook namespace swallowing packages with a matching name prefix

[jensens]

Problem

Section ownership in Configuration is decided by an unanchored string prefix match in config.py:

def is_ns_member(name) -> bool:
    for hook in hooks:
        if name.startswith(hook.namespace):   # the bug
            return True
    return False

With the uv hook declaring namespace = "uv", any section whose name merely starts with uv — e.g. uvst.addon, uvxs.addon — is classified as a hook section and dropped from config.packages. The package is never checked out, never written to requirements, and there is no error or warning. It just silently vanishes.

This is the issue reported in #87.

Fix

Anchor the match. A section belongs to a hook only when its name is exactly the namespace or is prefixed with "<namespace>:":

if name == hook.namespace or name.startswith(f"{hook.namespace}:"):

A colon can never appear in a PyPI/package name, so it is an unambiguous separator between hook sections and package sections. uvst.addon is now correctly a package; [uv] and [uv:sources] remain hook sections.

Relationship to #87

#87 fixes the same report by renaming the hook namespace from uv to __uv__. That treats the symptom: it makes a real-world collision unlikely but leaves the broken startswith matching in place, leaks an __uv__ sentinel into user-facing INI, and leaves every other (current and future) hook exposed to the same trap. This PR fixes the matching logic itself, so the uv hook can keep its clean namespace and all hooks are protected. I'd suggest this supersedes #87.

Migration

Hook config sections previously named [namespace-section] must be renamed to [namespace:section]. The only known hook (uv) owns no mx.ini sections, so practical impact is nil. EXTENDING.md is updated to document the : convention. Namespaced settings keys in [settings] (namespace-key) are unchanged.

Tests (TDD)

• test_package_name_starting_with_hook_namespace_is_not_swallowed — the regression; fails on main (package dropped), passes with the fix.
• test_hook_section_with_namespace_delimiter_belongs_to_hook — guards that [namespace] / [namespace:sub] are still routed to hooks.

Full suite: 212 passed, 4 skipped. Lint clean (ruff, isort, mypy).

[Copilot]

Pull request overview

Fixes a silent bug in Configuration where hook section ownership used an unanchored str.startswith match, causing any package section whose name began with a hook namespace (e.g. uvst.addon with the built-in uv hook) to be misclassified as a hook section and dropped from config.packages. The fix anchors the match: a section belongs to a hook only when its name equals the namespace exactly or is prefixed with "<namespace>:". This presents an alternative to PR #87 (which avoided the collision by renaming the namespace to __uv__).

Changes:

• Tighten is_ns_member in src/mxdev/config.py to require an exact namespace match or a "<namespace>:" prefix.
• Update EXTENDING.md (and add a CHANGES.md entry) to document the new [namespace:subsection] convention, including the required migration from [namespace-section].
• Add two regression tests in tests/test_config.py covering the swallowed-package case and the still-routed [namespace] / [namespace:sub] cases.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/mxdev/config.py	Anchors hook namespace matching to exact name or namespace: prefix; adds explanatory comment.
tests/test_config.py	Adds regression test for non-swallowing and a positive test for [namespace] / [namespace:sub] routing.
EXTENDING.md	Documents new : delimiter convention and updates the example hook code accordingly.
CHANGES.md	Adds changelog entry describing the fix and the section-rename migration.

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[jensens]

@erral does this solve the problem from #87 ?