SaveFilesAsArtifactsPlugin: Can't handle too big files (PDFs)

[Smponias]

Describe the bug
Using SaveFilesAsArtifactsPlugin works fine until the file gets too big.
Uploading a PDF with around 5MB - ✅
Uploading a PDF with around 50MB - ❌

Error: 400 INVALID_ARGUMENT. {'error': {'code': 400, 'message': 'Request contains an invalid argument.', 'status': 'INVALID_ARGUMENT'}}

To Reproduce
Run this code

root_agent = Agent(
    name="Super Cool Agent",
    model="gemini-2.5-flash",
    description="Analyzing the uploaded PDF",
    instruction="Analyze the uploaded PDF and give the user a short summary",
)

app = App(
    name='Super_Cool_Agent',
    root_agent=root_agent,
    plugins=[SaveFilesAsArtifactsPlugin()],
)

Expected behavior
I should be able to upload all files or get a proper error message.

Desktop (please complete the following information):

• OS: macOS
• Python version(python -V): 3.14
• ADK version(pip show google-adk): 1.19.0

Model Information:

• Are you using LiteLLM: No
• Which model is being used(e.g. gemini-2.5-pro): gemini-2.5-flash

[AakashSuresh2003]

Hi @GWeale,

Could you please review my PR and provide any suggestions?

[AakashSuresh2003]

Hi @GWeale,

As suggested, I’ve implemented an approach that uses file-size routing so the plugin now transparently supports files of all sizes without imposing a strict 20MB limit.

Summary of the Solution

I added automatic file-size detection and routing to ensure the correct upload path is used:

• ≤ 20MB → processed via inline_data (fast path, no upload required)
• 20MB–2GB → automatically uploaded via the Files API
• > 2GB → proactively rejected with a clear, user-friendly error message explaining the API limit

Additionally, the plugin now:

• Converts Files API URIs into file_data references automatically.
• Provides detailed feedback including filename, actual size, API limits, and next steps.
• Handles Files API failures gracefully with actionable messaging.
• Prevents the previous cryptic 400 INVALID_ARGUMENT error from reaching users.