fix: Add file-based output mode to avoid exceeding GitHub Actions output limits

[michalszelagsonos]

Summary

• Fixes Add file-based output mode to avoid exceeding GitHub Actions output limits with debug enabled #479
• Add output_to_file boolean input that redirects all output to files and returns file paths as step outputs instead of content
• Works independently of gemini_debug — when enabled, output always goes to files regardless of debug mode
• New outputs: output_mode (content/file) and artifacts_dir (path to gemini-artifacts/)

Motivation

When gemini_debug is enabled, recent gemini-cli versions (post-0.25.x) significantly increased the volume of diagnostic output behind --debug (auth info, API request/error counts, retry events, loop detection). This causes GITHUB_OUTPUT to exceed the ~1MB platform limit, resulting in truncated or failed step outputs.

The gemini-artifacts/ directory already exists and is populated on every run — this change leverages it by returning file paths instead of dumping content into step outputs.

Changes

New input (output_to_file, default false):

• When true, redirects stdout/stderr to files (no tee/console streaming)
• Returns file paths (gemini-artifacts/stdout.log, gemini-artifacts/stderr.log) as summary and error outputs instead of content
• Produces a compact job summary showing file sizes instead of full content
• Works with or without gemini_debug — the debug flag only controls whether --debug is passed to the CLI

New outputs:

• output_mode: "content" (default) or "file" — lets callers detect the mode programmatically
• artifacts_dir: absolute path to gemini-artifacts/ directory

Refactored execution block:

• Extracted GEMINI_ARGS to avoid duplicating the gemini CLI invocation across branches
• output_to_file is checked first, independently of gemini_debug
• The existing tee-based streaming only applies when output_to_file is false and gemini_debug is true

Backwards compatibility: When output_to_file is not set or false, behavior is identical to today.

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