Challenge 2: Identify run vs uses — Possible Solution
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(a) actions/checkout@v4
    -> uses:

    This is a reference to a specific, versioned, reusable ACTION from
    the marketplace (per this chapter's own table listing
    actions/checkout as the action that "pulls the repo's code onto
    the runner") — it's not a shell command being executed directly,
    it's invoking prebuilt, community-maintained functionality by name
    and version.

(b) npm run build
    -> run:

    This is a direct SHELL COMMAND — exactly matching the chapter's
    definition of run: steps as executing "a shell command directly."
    npm run build isn't a marketplace action reference at all; it's
    literally the command a developer would type in their own terminal,
    just running on the CI runner instead.

(c) actions/setup-python@v5
    -> uses:

    Like (a), this is a reference to a specific, versioned marketplace
    action — the chapter's own table lists setup-python alongside
    setup-node and setup-go as actions that "install a specific
    language runtime version." The @v5 version pin is itself a strong
    signal this is a uses: reference, since run: shell commands don't
    have this kind of action-version syntax at all.

WHY THIS WORKS AS AN ANALYSIS
--------------------------------
The reliable test across all three: does this look like "org/action-
name@version" (a reference to prebuilt, reusable, versioned
functionality)? If so, it's uses:. Does it look like a command someone
would type directly into a terminal? If so, it's run:. (a) and (c) both
clearly match the org/action-name@version shape; (b) is unmistakably a
plain shell command with no such reference syntax at all.