fix(weave): netrc entry handling in Weave JS SDK login method

[thanos-wandb]

Description

• Fixes WB-22046

This PR resolves an issue in the Weave JS SDK's login method where the .netrc file was being modified or created incorrectly if the apiKey arg was empty.

Changes:

• Added a validation check to ensure the apiKey is provided and non-empty
• Throws an error if the apiKey is missing
• Prevents overwriting existing .netrc entries unless both host and apiKey are valid and non-empty

Key fixes:

• Ensures that .netrc entries remain intact and prevent removal of the password line for existing entries
• Avoids introducing extra blank lines between machine blocks in the .netrc file

Testing

To reproduce the issue:

• Start with an existing .netrc file containing valid machine entries
• Execute the following JS script where login method is missing the apiKey arg

import * as weave from 'weave';
async function main() {
    await weave.login()
    await weave.init('examples');
    console.log('Hello there, Weave JS');
}
main().catch(console.error);

• The .netrc file gets modified incorrectly (password line of api.wandb.ai is removed and blank lines are introduced between machine blocks)

Fix testing:

• Verified that .netrc won't be created, if doesn't already exist, and no apiKey is provided
• Verified that previous valid entries in .netrc remain intact when weave.login() is invoked

[circle-job-mirror]

Preview this PR with FeatureBee: https://beta.wandb.ai/?betaVersion=4548123596a830d1ea214ba166d6e63ac6545fde

[andrewtruong]

This is specifically for apiKey === ''?

[thanos-wandb]

@andrewtruong yes if apiKey is either null or not provided at all as an arg

[andrewtruong]

I think apiKey is required

[thanos-wandb]

I think there was no validation in place to enforce this requirement at runtime before, but should raise an error now by adding that !apiKey check. I had tested with this script:

import * as weave from 'weave';
async function main() {
    await weave.login()
    await weave.init('examples');
    console.log('Hello there, Weave JS');
}
main().catch(console.error);