PTY Resize Hardening Against Native Crashes

What Changed

Core terminal handling now verifies process existence before PTY resize operations to prevent native crashes. Improved error handling for undefined error messages and expanded EBADF detection to cover both message-based and code-based checks. Added null-safe assignment and early return on process verification failures.

Operator Implication

Eliminates crashes during terminal resize operations, particularly in Termux and multi-process environments. Reduces support burden from terminal instability reports.

Receipt

• Commit title: 'fix(core): harden PTY resize against native crashes (#27496)' with changes to packages/cli/index.ts and packages/core/src/services/shellExecution