fix: crashes caused by invalid saved layout JSON and show toasts for recovery

[tonypzy]

Description

This PR adds defensive JSON parsing (safeJsonParse) to handle malformed JSON and prevent frontend runtime exceptions.

Motivation and Context

The following malformed JSON cases are now safely handled by safeJsonParse:

localStorage.setItem('envIDs', '["main", "demo"'); # Truncated JSON
localStorage.setItem('layout_main_pane_1', 'undefined'); # Non-JSON text
localStorage.setItem('layout_main_pane_1', '{x: 0, y: 0}'); # Invalid object syntax
localStorage.setItem('envIDs', ''); # Empty persisted value

How Has This Been Tested?

Check code manually

Screenshots (if appropriate):

N/A

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Code refactor or cleanup (changes to existing code for improved readability or performance)

Checklist:

• I adapted the version number under py/visdom/VERSION according to Semantic Versioning
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

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[tonypzy]

@vedansh-5 @rajnisht7 @Manik-Khajuria-5 @Jayantparashar10 please review

[Debajeet-1411]

@tonypzy Nice improvement. Consider adding a Cypress test for malformed localStorage JSON to verify the recovery path and guard against future regressions.

[Debajeet-1411]

One potential edge case came to mind—I've left an inline comment with the details.

[tonypzy]

@tonypzy Nice improvement. Consider adding a Cypress test for malformed localStorage JSON to verify the recovery path and guard against future regressions.

cytest is not meant for handling such trivial cases. it is primarily designed to verify higher-level functionality, such as plotting features and screenshot pixel comparisons.

[tonypzy]

@tonypzy Nice improvement. Consider adding a Cypress test for malformed localStorage JSON to verify the recovery path and guard against future regressions.

Or we can add to pytest #1543

[Debajeet-1411]

@tonypzy Thanks for the clarification. That makes sense-this is better suited as a unit test than an end-to-end Cypress test.

[rajnisht7]

@tonypzy it works good in ui but what about adding info for the same

[Manik-Khajuria-5]

@tonypzy I agree with @rajnisht7 idea of adding in the ui section also

[tonypzy]

@tonypzy it works good in ui but what about adding info for the same

This is the toast effect.

[Saksham-Sirohi]

Copilot flagged the following:

• No blocking issues.