Fix stackId null handling in frontend API calls

[Copilot]

Problem

The frontend was calling the changes_in_branch endpoint with stackId: "null" (string) instead of stackId: null (actual null value), causing API failures. The backend expects Option<StackId> but was receiving the string "null", which cannot be deserialized into the expected type.

Example of the failing API call:

{
  "projectId": "6b9eb2cd-016d-427d-872c-ec4e482b2387",
  "stackId": "null",
  "branch": "refs/heads/master"
}

Root Cause

URL parameters are always strings in web APIs. When a URL contains ?stackId=null, the URLSearchParams.get('stackId') method returns the string "null" instead of the actual null value. This string then gets passed through the application state and eventually to API calls where it should be null.

Solution

1. Fixed URL parameter processing

• Updated workspace page to convert string "null" to actual null when reading URL parameters
• Added comprehensive documentation explaining the web API behavior

2. Fixed API method calls

• Updated branchChanges, branchChange, and branchChangesByPaths methods in stackService.svelte.ts to sanitize stackId parameters
• Added conversion logic: stackId === 'null' ? null : stackId
• Updated TypeScript types to accept string | null for stackId parameters

3. Updated mock backend

• Modified validation functions to accept null values for stackId parameters
• Ensures test environment matches the fixed behavior

Result

The backend now correctly receives:

{
  "projectId": "6b9eb2cd-016d-427d-872c-ec4e482b2387",
  "stackId": null,
  "branch": "refs/heads/master"
}

This resolves the API failure while maintaining backward compatibility with existing valid stackId values. The fix is defensive and only converts the specific problematic case while preserving all other values unchanged.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• esm.ubuntu.com
  • Triggering command: /usr/lib/apt/methods/https (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

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1 Skipped Deployment

Project	Deployment	Preview	Comments	Updated (UTC)
gitbutler-web	Skipped			Sep 16, 2025 1:35pm

[Byron]

The issue occurs in single-branch mode, a 'null' string sneaks in and can't be decoded in the backend, and I'd hope this can be type-safe in the frontend as well.

Before

I am seeing:

API error: (changes_in_branch)
An asynchronous operation failed.
invalid args `stackId` for command `changes_in_branch`: UUID parsing failed: invalid character: expected an optional prefix of `urn:uuid:` followed by [0-9a-fA-F-], found `n` at 1

After

It works

Conclusion

I think this is worth a look @mtsgrd, the PR fixes the issue, even though I have a feeling that the solution isn't good or optimal. I'd the fix here can be salvaged though. Thanks.