feat(cli): -f/--file prompt-file support (llama.cpp-compatible)

[pekkah]

Summary

Adds -f/--file <path> to the run CLI (llama.cpp's arg name) to read the prompt from a file. Resolved once at the top of Execute into settings.Prompt, so every downstream prompt path (single-turn, chat, format/template) works unchanged. Overrides -p when both are given; reads the file as-is (no trailing-newline stripping); a missing file errors loudly (exit 1).

Motivation

A prompt longer than the OS command-line length limit (~32K chars on Windows) can't be passed via -p — it fails with "The filename or extension is too long." This surfaced while profiling long-context decode (#213): a ~16K-token prompt couldn't be fed via -p.

Verified (CLI)

• short file → prefilled (30 tok);
• ~16K-token file → prefilled 10460 tok, no arg-length error;
• missing file → Prompt file not found: … (exit 1).

Build clean under TreatWarningsAsErrors + AOT. ~15 lines; self-contained.

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request introduces a new -f|--file option to load prompts from a file, overriding the -p|--prompt option. The review feedback highlights two main issues: potential markup parsing errors in Spectre.Console when rendering the file path, and unhandled I/O exceptions when reading the file. It is recommended to escape the file path and wrap the file read operation in a try-catch block to ensure graceful error handling.

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[gemini-code-assist]

There are two issues in this block:

1. Spectre.Console Markup Parsing Error: If promptFile contains square brackets (e.g., [path]), AnsiConsole.MarkupLine will attempt to parse it as markup, leading to incorrect rendering or exceptions. Use Markup.Escape(promptFile) to prevent this.
2. Unhandled I/O Exceptions: File.ReadAllText can throw exceptions (e.g., UnauthorizedAccessException, IOException) if the file is locked or permissions are insufficient. Wrapping it in a try-catch block ensures the CLI exits gracefully with a clean error message instead of crashing with a stack trace.

        if (settings.PromptFile is { Length: > 0 } promptFile)
        {
            if (!File.Exists(promptFile))
            {
                AnsiConsole.MarkupLine($"[red]Prompt file not found:[/] {Markup.Escape(promptFile)}");
                return 1;
            }
            try
            {
                settings.Prompt = File.ReadAllText(promptFile);
            }
            catch (Exception ex)
            {
                AnsiConsole.MarkupLine($"[red]Error reading prompt file:[/] {Markup.Escape(ex.Message)}");
                return 1;
            }
        }

[pekkah]

Fixed: Markup.Escape on both the not-found and read-error messages, and File.ReadAllText is wrapped in try/catch (IOException/UnauthorizedAccessException/SecurityException/NotSupportedException) → clean message + exit 1. Verified a bracketed missing path renders correctly.