v1.18.39: Local sandbox exec output cap

Highlights

• Cap local sandbox Bash/exec captured output at 100,000 bytes.
• Terminate the sandbox process tree promptly when the output cap is exceeded.
• Surface outputLimited metadata from sandbox exec through SandboxBashTool.
• Document the bounded local sandbox command output behavior.

Validation

• composer validate --strict
• composer audit --format=plain
• composer run lint
• composer test
• GitHub Actions main and tag test runs passed.