Bug 1: detect copilot.cmd/.bat on Windows and invoke the sibling .ps1 directly via powershell -File, bypassing cmd.exe %* re-tokenisation that mangled the multi-line -p prompt. Shared rewriteCmdToPS1() now serves cursor, pi, and copilot.
Bug 2: filterCustomArgs (shared by all agent backends) strips one outer layer of shell quotes via unshellQuoteArg() before processing, so shell-style custom args like --deny-tool='write' no longer reach the CLI with literal quotes.
