chore: sort discovered deps for stable ordering across environments

[nallwhy]

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Problem

Different environments (machines, Elixir versions) running mix usage_rules.sync can produce different output for the same config. This causes unnecessary diffs and noisy commits when collaborators sync on their own machines.

The root cause is discover_deps/1 returning deps from Mix.Project.deps_paths() (a Map) without sorting. Since Erlang Map iteration order is not guaranteed, regex-matched deps in usage_rules config can appear in different orders.

Config style	Ordering
Explicit atoms (:ash)	Stable (config order)
Regex (~r/^ash_/)	Unstable (Map order dependent)
Sub-rules	Stable (Enum.sort already applied)

Solution

Add Enum.sort_by(&elem(&1, 0)) to the end of discover_deps/1 so that all_deps is always in alphabetical order. This makes regex matching produce deterministic results without affecting explicit atom ordering (which is handled in resolve_usage_rules).

Notes

The test verifies the intended sorted order but cannot reproduce the non-deterministic behavior in test mode, since Erlang small maps (<=32 keys) store keys in sorted order internally.

[Copilot]

Pull request overview

This PR addresses non-deterministic output from mix usage_rules.sync by ensuring discovered dependencies are always sorted alphabetically. Previously, regex-matched dependencies could appear in different orders across different environments due to Erlang's Map iteration order being non-deterministic for larger maps.

Changes:

• Added Enum.sort_by(&elem(&1, 0)) to discover_deps/1 to ensure alphabetical ordering of dependencies
• Added test to verify regex-matched dependencies appear in stable sorted order

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
lib/mix/tasks/usage_rules.sync.ex	Added sorting to discover_deps/1 to ensure deterministic alphabetical ordering of dependencies
test/mix/tasks/usage_rules.sync_test.exs	Added test verifying regex produces sections in stable sorted order

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[Copilot]

The test uses :binary.match/2 followed by elem(0) to extract positions. If any of these matches fail and return :nomatch, calling elem(0) on the atom :nomatch will crash with a BadArgumentError rather than providing a clear test failure message. Consider using pattern matching to provide better error messages, for example: {alpha_pos, _} = :binary.match(content, "## alpha usage") or adding explicit assertions that the content contains these strings before extracting positions.

Suggested change

	alpha_pos = :binary.match(content, "## alpha usage") |> elem(0)
	mango_pos = :binary.match(content, "## mango usage") |> elem(0)
	zeta_pos = :binary.match(content, "## zeta usage") |> elem(0)
	assert content =~ "## alpha usage"
	assert content =~ "## mango usage"
	assert content =~ "## zeta usage"
	{alpha_pos, _} = :binary.match(content, "## alpha usage")
	{mango_pos, _} = :binary.match(content, "## mango usage")
	{zeta_pos, _} = :binary.match(content, "## zeta usage")