Display error when forming new ZHA network fails

[TheJulianJES]

Proposed change

This broadly catches all exceptions when ZHA network formation fails, displays a user-facing error message, and logs further detail. Before this PR, the UI spinner for the config flow progress task would spin endlessly, providing no feedback.

Example error message:

We want to broadly catch all exceptions for now, as there's an issue in HA Core where unexpected exceptions (in config flows progress tasks) are swallowed due to an underlying issue. Related PRs for that:

• Log config flow progress task errors instead of silently discarding them #157662
• Log exceptions raised in unawaited background tasks #157691

Background

We're seeing multiple people run into an issue where ZHA network formation fails for some unknown reason, causing them to end up with an endless spinner. Due to the Core issue, there's nothing in the logs about the error. Related issues:

• https://community.home-assistant.io/t/zbt-2-frustrations-forming-a-new-network/956361
• Issue with Zigbee Hom Automation Forming a new Zigbee network Hangs #157856

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Additional information

• This PR fixes or closes issue: fixes #
• This PR is related to issue:
• Link to documentation pull request:
• Link to developer documentation pull request:
• Link to frontend pull request:

Checklist

• I understand the code I am submitting and can explain how it works.
• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• I have followed the development checklist
• I have followed the perfect PR recommendations
• The code has been formatted using Ruff (ruff format homeassistant tests)
• Tests have been added to verify that the new code works.
• Any generated code has been carefully reviewed for correctness and compliance with project standards.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated for www.home-assistant.io

If the code communicates with devices, web services, or third-party tools:

• The manifest file has all fields filled out correctly.
  Updated and included derived files by running: python3 -m script.hassfest.
• New or updated dependencies have been added to requirements_all.txt.
  Updated by running python3 -m script.gen_requirements_all.
• For the updated dependencies - a link to the changelog, or at minimum a diff between library versions is added to the PR description.

To help with the load of incoming pull requests:

• I have reviewed two other open pull requests in this repository.

[home-assistant]

Hey there @dmulcahey, @Adminiuga, @puddly, mind taking a look at this pull request as it has been labeled with an integration (zha) you are listed as a code owner for? Thanks!

Code owner commands

Code owners of zha can trigger bot actions by commenting:

• @home-assistant close Closes the pull request.
• @home-assistant rename Awesome new title Renames the pull request.
• @home-assistant reopen Reopen the pull request.
• @home-assistant unassign zha Removes the current integration label and assignees on the pull request, add the integration domain after the command.
• @home-assistant add-label needs-more-information Add a label (needs-more-information, problem in dependency, problem in custom component) to the pull request.
• @home-assistant remove-label needs-more-information Remove a label (needs-more-information, problem in dependency, problem in custom component) on the pull request.

[Copilot]

Pull request overview

This PR adds error handling for ZHA network formation failures in the config flow. Previously, when network formation failed, the UI spinner would spin endlessly without providing any user feedback. Now, all exceptions during network formation are caught and displayed to the user with a clear error message.

Key Changes

• Added broad exception handling in async_step_form_new_network to catch all network formation failures
• User-facing error messages displayed via the abort flow mechanism with specific error details
• Comprehensive test coverage for the network formation failure scenario

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
homeassistant/components/zha/config_flow.py	Added try-except block to catch and handle network formation exceptions, setting progress error and returning progress_failed step
homeassistant/components/zha/strings.json	Added "cannot_form_network" abort reason with error placeholder for both config and options flows
tests/components/zha/test_config_flow.py	Added test case verifying proper error handling when network formation fails with an exception