Design: Surface the used custom variables for manual jobs and allow to retry the job with updated variables
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### Release notes
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## :point_up: Problem
When running a manual job from the manual job page, it's possible to [add custom variables for that job](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/24935).
Right now it's not possible to view or override the variables being used when retrying the job. Developers want to be able to tweak variables used by a manual job when working on a deployment, for example. Sometimes you need to go back and tweak the input.
### Intended users
* [Devon (DevOps Engineer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#devon-devops-engineer)
* [Sasha (Software Developer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#sasha-software-developer)
### Metrics
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- Click rate on the Variables tab
- Number of users retrying manual jobs with updated variables vs. retrying with the existing variables
### User experience goal
The user should be able to view the custom variables used by a manual job, update them if necessary, and retry the manual with with updated variables.
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## :bulb: MVC Proposal
- For manual jobs, add offer two "Retry" action types: "retry" and "update variables".
- The "retry" action remains unchanged, it retries the job with the same variables.
- The "update variables" action opens the manual job page with the variables form where the used variables can be viewed and updated.
:point_right: For the detailed description of the user flows [see the designs.](https://gitlab.com/gitlab-org/gitlab/-/issues/32712/designs/Manual_job.png)
:triangular_ruler: [**SPECS IN FIGMA**](https://www.figma.com/file/8WqthzcG69lRQtG5Lusfdb/%F0%9F%92%9C-CI%2FCD-Variables?node-id=2095%3A12228)
:frame_photo: [**DESIGNS**](https://gitlab.com/gitlab-org/gitlab/-/issues/32712/designs/Manual_job.png)
#### Permissions and Security
User can only view the variable and value in the manual job if they have the permissions to view those variables based on their role in the project.
### Documentation
This feature needs to be documented in the Variables and manual jobs documentation.
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### Availability & Testing
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* Unit test changes
* Integration test changes
* End-to-end test change
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### Available Tier
* Free
### Further iterations
* Surface all available variables for that job (not only custom variables)
* Add the variables form to all jobs (not only manual jobs)
* Improve the form input to [include filtered search to make it easy to select available variables](https://gitlab.com/gitlab-org/gitlab/-/issues/344826)
* Surface the project level variables that are being inherited by the job, and indicate when they're being overridden by the custom variables. Those can be view-only since they're set on project level, but it can be useful to see them for the context.
* There can be further improvements to the variables form, for example when a variables has "true" or "false" values we can automatically offer those options in the dropdown.
* Offer possible variable values to choose from a given variable
## Implementation Table
| Group | Issue Link |
| ------ | ------ |
| ~UX Design | **:point_left: You are here** |
| ~backend | https://gitlab.com/gitlab-org/gitlab/-/issues/361236 |
| ~frontend | https://gitlab.com/gitlab-org/gitlab/-/issues/361237 |
issue
GitLab AI Context
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