Fix: unregistered print.browser.useAlternate configuration error on startup

[Copilot]

Users who had passed through an intermediate version of the extension had print.browser.useAlternate and/or print.browser.alternateBrowserPath written to their settings.json. These keys were removed from package.json in a later refactoring, causing VS Code to error on every startup when encountering them.

Changes

• package.json: Register print.browser.useAlternate (boolean) and print.browser.alternateBrowserPath (string) as deprecated settings with deprecationMessage pointing to the current key names. This prevents VS Code from rejecting reads/writes to these keys on behalf of users still carrying them.

• src/settings-migration.ts:

  • Fix migration map: "alternateBrowser" now maps directly to "alternateBrowser.enable" (was "browser.useAlternate", an intermediate unregistered step); same for "browserPath" → "alternateBrowser.path".
  • Fix getSourceKeys(): previously excluded any key that was itself a migration target — this silently skipped browser.useAlternate and browser.alternateBrowserPath, leaving them stranded in settings. Now returns all non-self-referential keys so intermediate keys are also migrated and cleaned up.
  • Remove resolveMigrationChain(): no longer needed since all mappings are now direct.
  • Separate deletion into its own try/catch so a failed cleanup of an unregistered old key doesn't roll back a successful write to the new key.

• src/extension.ts: Fix typo in setAlternateBrowser() — "print.alternatBrowser" → "print.alternateBrowser" (missing e would write to an unregistered key).

Original prompt

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This section details on the original issue you should resolve

<issue_title>Bug: print.browser.useAlternate is not a registered configuration</issue_title>
<issue_description>Starting vs code with code . with pdconsec.vscode-print installed emits on extension host output the following error.

2025-09-17 14:22:16.724 [error] CodeExpectedError: Unable to write to User Settings because print.browser.useAlternate is not a registered configuration.
    at Y1t.z (vscode-file://vscode-app/usr/share/code/resources/app/out/vs/workbench/workbench.desktop.main.js:3677:6793)
    at Y1t.F (vscode-file://vscode-app/usr/share/code/resources/app/out/vs/workbench/workbench.desktop.main.js:3677:9281)
    at Y1t.o (vscode-file://vscode-app/usr/share/code/resources/app/out/vs/workbench/workbench.desktop.main.js:3677:3874)
    at Object.factory (vscode-file://vscode-app/usr/share/code/resources/app/out/vs/workbench/workbench.desktop.main.js:3677:3774)
    at _v.j (vscode-file://vscode-app/usr/share/code/resources/app/out/vs/workbench/workbench.desktop.main.js:30:75818)
    at vscode-file://vscode-app/usr/share/code/resources/app/out/vs/workbench/workbench.desktop.main.js:30:75730
    at new Promise (<anonymous>)
    at _v.queue (vscode-file://vscode-app/usr/share/code/resources/app/out/vs/workbench/workbench.desktop.main.js:30:75672)
    at Y1t.writeConfiguration (vscode-file://vscode-app/usr/share/code/resources/app/out/vs/workbench/workbench.desktop.main.js:3677:3743)
    at ofn.Hb (vscode-file://vscode-app/usr/share/code/resources/app/out/vs/workbench/workbench.desktop.main.js:3677:42740)

If uninstalling, this disappears. </issue_description>

<agent_instructions>Refactoring means some code is trying to use setting names that don't match the names in package.json contributions section. The problem is that you won't find these as a simple string match, you'll have to look for permutations of the same name that are conceptually equivalent then match the convention for other settings and finally align all the code.</agent_instructions>

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

@DavidRawling This looks like it's caused by a recent refactoring of the settings - it's cosmetic (or should be) - it's on the list for a fix (by which I mean we've already sorted it in the development branches), but releases of cosmetic fixes are going to be delayed a little by personal circumstances.

• Fixes Bug: print.browser.useAlternate is not a registered configuration #402

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