[Bug] REPL silently exits to PowerShell prompt mid-turn on dense subprocess chains

Bug Description
Summary: REPL silently exits to bare PowerShell prompt mid-turn on 2.1.128, continuation of regression #55424 / #55562 past v2.1.126. Environment: Claude Code 2.1.128 (native, win32-x64, commit d6caed183d5f) Install path: C:\Users\<user>\.local\bin\claude.exe Windows 11 Host shell: PowerShell 7.6.1 CLAUDE_CODE_USE_POWERSHELL_TOOL=1 set and confirmed Symptom: REPL process disappears silently. Parent PowerShell tab survives, dropping to bare PS C:\...> prompt. No error, no traceback, no recovery banner. Recovery via claude --continue works but loses the in-progress turn, requiring a manual "continue" prompt to resume the agent. Trigger pattern: Dense subprocess chains in a single turn, specifically Edit/Update operations interleaved with PowerShell tool calls. Crash typically lands mid-Update during model "Transmuting" phase. Frequency: Variable. Ran stable ~1 hour, then crashed mid-Update. Was crashing on nearly every turn before setting CLAUDE_CODE_USE_POWERSHELL_TOOL=1, so that env var partially mitigates but does not fix. References: #55424 (original report, v2.1.121, expected to be addressed by v2.1.126 PowerShell host rework) #55562 (confirms regression persists 2.1.114 through 2.1.126) This report extends the band: still reproducing on 2.1.128 with PowerShell tool primary. Workarounds attempted: Set CLAUDE_CODE_USE_POWERSHELL_TOOL=1 → reduced frequency, did not eliminate Channel: on latest (2.1.128); stable (2.1.119) is inside the regression band so not a downgrade option

Environment Info

• Platform: win32
• Terminal: windows-terminal
• Version: 2.1.128
• Feedback ID: d4d3a660-32ad-4618-9bdc-2eb48cca17c3

Errors

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