[BUG] Session-start repo/branch picker ignores the GitHub repository's configured default branch

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When starting a new Claude Code on the web session against a GitHub repository, the repo/branch selector dropdown shown at session start does not respect the "Default branch" configured for that repository in GitHub Settings → General.

Steps to reproduce:

In GitHub, change a repository's default branch from main to develop (Settings → General → Default branch).
Start a new Claude Code on the web session and select that repository.
Observe the branch shown/pre-selected in the dropdown.
Expected: The dropdown pre-selects develop (the repository's actual configured default branch on GitHub).

Actual: The dropdown still shows/pre-selects main, even though main is no longer the default branch on GitHub.

Impact: New sessions/branches can silently get created off the stale main reference instead of the real default branch, unless the user manually reselects the correct branch every time.

Context: Default branch was changed on 2026-07-11 specifically so that new Claude Code web sessions would start from the intended branch automatically.

What Should Happen?

The new-session repository/branch picker in Claude Code on the web does not reflect an updated GitHub default branch. I changed the default branch of my repository from main to develop in GitHub Settings → General → Default branch. New sessions started afterward still show/pre-select main in the picker instead of develop.

When starting a new session against a GitHub repository, the picker should pre-select whatever branch is currently configured as that repository's default branch on GitHub. After changing the default branch from main to develop, new sessions should default to develop.

N/A — this is not a crash or exception, it's the picker defaulting to a stale branch value instead of the repository's current GitHub-configured default.

Possibly related to #57265 ("[BUG] Desktop app 'Code' section shows GitHub default branch instead of active working branch"), though that issue is about the Desktop app preferring the active branch over the default branch for a persistent status display — a different failure mode from this one, which is the web session-start picker not picking up a changed default branch at all.

Error Messages/Logs

Steps to Reproduce

1. In GitHub, open a repository's Settings → General → Default branch, and change it from main to another branch (e.g. develop).
2. Go to Claude Code on the web (claude.ai/code) and start a new session, selecting that repository as the source.
3. Observe the branch shown/pre-selected in the repository/branch picker at session start.

Expected: the picker pre-selects develop (the repository's current default branch on GitHub).
Actual: the picker still shows/pre-selects main, even though main is no longer the configured default branch.

Note: This was verified with EBUSSCHILE/remotjobapp, where the default branch was switched from main to develop on 2026-07-11.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Sonnet 5 Extra

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_