fix(streams): VT-strip dedup-known set so cmdlet ANSI output stops leaking into HOST.UI

The dedup pass that drops HostWrite lines already present in another
section was comparing VT-stripped \$hostRaw against a HashSet built
from the raw section sources — pipelineText etc. still carried the
SGR codes from cmdlet renderers like AnsiColors.Inserted /
AnsiColors.Deleted. The trim-then-Contains check then mismatched on
the ANSI runs: a HostWrite line of \`: Line 3\` never matched the
known entry \`: \e[31mLine 3\e[0m\`, so every coloured line a
cmdlet emitted leaked into the HOST.UI section as a plain-text
duplicate.

Strip VT codes from each section source before populating \$known.
\$hostRaw is already VT-stripped earlier in the method, so after
this fix both sides of the comparison are normalised the same way
and the duplicate suppression actually fires.

Verified end-to-end against the deployed module: a body that runs
Update-LinesInFile + a WhatIf-bearing Remove-Item now surfaces only
the WhatIf message in HOST.UI; the cmdlet's coloured context /
deleted / inserted / context block stays in pipelineText where it
belongs and no longer echoes into the HOST.UI section.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: yotsuda

PowerShell.MCP/Resources/MCPPollingEngine.ps1

@@ -576,11 +576,23 @@ if (-not (Test-Path Variable:global:McpTimer)) {
                         # exactly matches one of these is treated as a
                         # render-time duplicate and dropped from
                         # HostWrite.
+                        # VT-strip both sides before comparison.
+                        # pipelineText (and the other section sources)
+                        # carries the cmdlet's own SGR codes from
+                        # AnsiColors.* renders — Update-LinesInFile in
+                        # particular emits coloured context / inserted
+                        # / deleted lines. $hostRaw was already
+                        # VT-stripped earlier in this method. Without
+                        # also stripping the comparison set, the dedup
+                        # mismatched on the ANSI runs and let the
+                        # whole cmdlet output leak into the HOST.UI
+                        # section as plain text duplicates.
                         $known = [System.Collections.Generic.HashSet[string]]::new(
                             [System.StringComparer]::Ordinal)
                         foreach ($src in @($pipelineText, $exceptionText, $infoText, $consoleOutText, $consoleErrText)) {
                             if (-not [string]::IsNullOrEmpty($src)) {
-                                foreach ($line in $src -split "`r?`n") {
+                                $srcStripped = $src -replace $vtPattern, ""
+                                foreach ($line in $srcStripped -split "`r?`n") {
                                     $trimmed = $line.Trim()
                                     if ($trimmed) { [void]$known.Add($trimmed) }
                                 }