Update documentation to clarify searchable repositories in CCA issue assignment dialog (#57765)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: labudis <2659733+labudis@users.noreply.github.com>
Co-authored-by: Tadas Labudis <labudis@github.com>
Co-authored-by: lukewar <7632110+lukewar@users.noreply.github.com>
Co-authored-by: Lukasz Warchol <lukewar@github.com>
Co-authored-by: Jules <19994093+jules-p@users.noreply.github.com>

Author: 4 people

content/copilot/how-tos/use-copilot-agents/coding-agent/create-a-pr.md

@@ -80,8 +80,11 @@ You can assign an issue to {% data variables.product.prodname_copilot_short %}:
 
 1. You can use the dropdown menus in the dialog to change the repository that {% data variables.product.prodname_copilot_short %} will work in and the branch that it will branch off from.
 
-   > [!NOTE]
-   > If you don't specify a repository, {% data variables.product.prodname_copilot_short %} will work in the same repository as the issue. If you don't specify a branch, {% data variables.product.prodname_copilot_short %} will work from the default branch of the selected repository.
+   All repositories where you have **at least** read access will be displayed in the repository dropdown menu. However, you can only select a repository if you have write access to it, **and** if {% data variables.copilot.copilot_coding_agent %} is enabled for that repository.
+
+   If you select a repository in a different organization than the issue's source organization, or if you select a public repository when the issue is in a private repository, a warning will be displayed.
+
+   If you don't specify a repository, {% data variables.product.prodname_copilot_short %} will work in the same repository as the issue. If you don't specify a branch, {% data variables.product.prodname_copilot_short %} will work from the default branch of the selected repository.
 
    > [!TIP]
    > When you assign an issue to {% data variables.product.prodname_copilot_short %}, it gets sent the issue title, description, any comments that currently exist, and any additional instructions you provide. After assigning the issue, {% data variables.product.prodname_copilot_short %} will not be aware of, and therefore won't react to, any further comments that are added to the issue. If you have more information, or changes to the original requirement, add this as a comment in the pull request that {% data variables.product.prodname_copilot_short %} raises.