Independent reproduction on 7.6.6 stable, with the exact zh-Hans numbers:

• PowerShell 7.6.6 (MSI x64), Windows 10 22H2, UI culture zh-CN
• Interactive ConPTY terminal, $Host.UI.SupportsVirtualTerminal = True
• Update cache contained update1_v7.6.7_2026-10-13 (7.08 days old at startup), so the notification path ran
• zh-Hans StableUpdateNotificationMessage: line 1 = 38 chars, line 3 = 58 chars
• 38 - 58 + 3 = -17 -> PadRight(-17) -> FailFast, matching the reported stack exactly
• The same terminal starts normally with POWERSHELL_UPDATECHECK=Off, confirming the notification is the only trigger

The line-2 expression is positive for zh-Hans, but the other locale reports show it can also go negative, so clamping both expressions in this PR is the right minimal fix. The template-length assumption is the real bug; console width is not involved.

wait4x (@wait4xx) Thanks for the fix! I prepared some additional test coverage for the update notification padding issue in my fork:

https://github.com/boylin0/PowerShell/tree/fix/update-notification-padding

BTW, besides adding the tests, the commit also moves the message formatting in ShowUpdateNotification into an internal FormatUpdateNotification method so it can be unit tested. The formatting logic itself is unchanged.

Feel free to take a look! If you find these tests useful, you can git cherry-pick 29fd033ce. Alternatively, If you'd rather keep this PR minimal, I can open a follow-up PR after this one is merged.

Thanks!

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Thanks BOYI (@boylin0)! Since your commit is based directly on the PR head, I fast-forwarded the branch to 29fd033ce and took it verbatim — authorship preserved as-is.

I also double-checked that the test assembly (powershell-tests) already gets internals visibility from Microsoft.PowerShell.ConsoleHost, and verified the neutral-template equal-width assertions against the shipped templates. PR description updated to cover the extraction and the new tests.

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Independent verification on the shipped 7.6.6 binaries, plus one gap I think this PR's description understates.

I disassembled Microsoft.PowerShell.ConsoleHost.dll from the 7.6.6 MSI (the IL of ShowUpdateNotification): the shipped code is exactly the unguarded pair of PadRight calls, so this is not a source-only issue. Reproduced on 7.6.6 / zh-CN / ConPTY: pwsh with no arguments exits with 0x80131623 and totalWidth ('-17'); both pwsh -NoLogo and POWERSHELL_UPDATECHECK=Off start normally, confirming the notification path is the only trigger.

I then extracted all three templates from the 13 satellite assemblies shipped with 7.6.6 and evaluated both widths with release tag 7.6.7:

10 of the 13 cultures are affected. The part worth highlighting: line 2 alone is negative in six cultures that none of the linked issues mention — cs, de, fr, it, ru and tr. In those templates the first line is longer than the third, so the "several templates have a longer URL line" explanation in the PR description does not describe them at all. The worst case is fr stable: line 1 = 74, line 2 = 98, so 74 - 98 + 5 = -19. ko is negative on both (-23 / -20).

That means clamping both expressions is required rather than merely defensive: clamping only line 3 would still crash for those six cultures.

Two things worth considering before merge:

1. The new TestLocalizedTemplate only asserts Contains($"tag=v{ReleaseTag}"). It passes for every culture as long as the clamp is present, but it does not pin the reported case. Adding the zh-Hans stable/preview numbers (38 - 58 + 3 = -17) and at least one line-2-only culture (e.g. fr stable, -19) would catch a regression with the real numbers.
2. After the clamp, the zh-Hans stable template formats to line widths 41 / 41 / 58 — the third line still overflows the highlighted block. That is the intended cosmetic trade-off, but it means the alignment is not actually restored for these cultures. If the goal is a correctly aligned banner rather than only a non-crashing one, the padding should be derived from the longest of the three lines instead of assuming line 1.

Happy to help with either if it is useful.

Thank you, wait4x (@wait4xx), BOYI (@boylin0), and other folks, for reporting and trying to fix the issue.
The PowerShell team has decided to remove the Update Notification feature as it provides limited additional value nowadays.
So, this PR is superseded by #28242. We will backport that PR to v7.6 in the next servicing release.