Add PowerShell-specific error-handling idioms

[MariusStorhaug]

Context

The baseline Error-Handling standard says fail fast, never swallow, and write helpful messages; Functions.md covers throw vs Write-Error; index.md sets $ErrorActionPreference = 'Stop'.

Gap

The PowerShell-specific error idioms are missing:

• Call cmdlets with -ErrorAction Stop when you intend to trap them, so they raise terminating, catchable errors.
• Around native (non-cmdlet) commands, set $ErrorActionPreference = 'Stop' and restore it afterward.
• Put the whole transaction inside the try block rather than setting success flags to gate later code.
• Do not rely on $? — it reports only whether the last command considered itself successful, with no detail.
• Avoid treating a $null result as an error condition where a proper terminating error is available.
• In a catch, copy $_ / $Error[0] into your own variable immediately, before later commands overwrite it.

Proposed change

Add a "PowerShell error handling" section to the PowerShell standard (Functions.md, or a dedicated page) that builds on the baseline Error-Handling page.

Source

PoshCode — Best Practices "Error Handling" (ERR-01…ERR-06).

Acceptance

The PowerShell standard captures the -ErrorAction Stop, transaction-in-try, avoid-$?, and copy-$_-in-catch rules.