fix(nsis-web): appPackageUrl regression: stop appending arch paths to explicit URLs

[Copilot]

When a user explicitly sets appPackageUrl in nsisWeb, arch-specific filenames were still being appended to it (e.g. https://example.com/download/latest/MyApp-1.0.0-x64.nsis.7z), making version-independent download URLs impossible.

Root cause: APP_PACKAGE_URL_IS_INCOMPLETE was unconditionally set in WebInstallerTarget.configureDefines, causing the NSIS template to always append /${APP_64_NAME} (etc.) regardless of whether the URL was user-supplied or auto-computed.

Changes

• WebInstallerTarget.ts: Move defines.APP_PACKAGE_URL_IS_INCOMPLETE = null inside the if (appPackageUrl == null) branch — the flag is now only set when the URL is auto-computed from publish configs (a base URL that genuinely needs arch filename appended at runtime). An explicit appPackageUrl is used as-is.

• webInstallerTest.ts: Add regression test asserting that APP_PACKAGE_URL_IS_INCOMPLETE is absent from defines when appPackageUrl is explicitly provided.

// Before: https://example.com/download/latest → https://example.com/download/latest/MyApp-1.0.0-x64.nsis.7z ❌
// After:  https://example.com/download/latest → https://example.com/download/latest ✅
nsisWeb: {
  appPackageUrl: "https://example.com/download/latest",
}

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Regression in nsis-web target for appPackageUrl option</issue_title>
<issue_description>

• Electron-Builder Version: 25.0.5
• Node Version: n/a
• Electron Version: n/a
• Electron Type (current, beta, nightly): n/a
• Target: nsis-web, Windows x64

Since #6964 the appPackageUrl doesn't work as intended because extra paths are appended to the URL, which means it's not possible to download the latest at a single URL (see #7732 for an example).

My understanding is that APP_PACKAGE_URL_IS_INCOMPLETE intentionally tried to skip setting the package name based on architecture, instead using the name specified with appPackageUrl, but #6964 will use the regular naming.</issue_description>

Comments on the Issue (you are @copilot in this section)

@mmaietta Would you mind sharing a minimum reproducible repo/gist for this issue? I'd like to create a unit test for this

Re: the PR, I'm wondering if it's just safer to revert, but I'd still like to do the unit test to prevent future regressions.</comment_new>
<comment_new>@mmaietta
Community PR contribution is welcome 🙃 </comment_new>

• Fixes Regression in nsis-web target for appPackageUrl option #8581

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