[Security Solution] Case creation opens in full window mode instead of flyout when a saved timeline is attached to a new case

[vgomez-el]

Describe the bug:

When creating a new case from a timeline flyout and selecting the option to attach the timeline to a new case, the case creation page incorrectly opens in full window mode instead of maintaining the expected flyout behavior.

Kibana/Elasticsearch Stack version:

8.18 BC4

Server OS version:

Browser and Browser OS versions:

Google Chrome

Elastic Endpoint version:

Original install method (e.g. download page, yum, from source, etc.):

Cloud deployment

Functional Area (e.g. Endpoint management, timelines, resolver, etc.):

Timelines

Steps to reproduce:

1. Navigate to security timelines
2. Open a saved timeline in a flyout
3. Select the option to attach the timeline to a new case

Current behavior:

Observe that the case creation form opens in full window mode

Expected behavior:

Case creation should be opened in a flyout

Screenshots (if relevant):

REC-20250226185447.mp4

Errors in browser console (if relevant):

Provide logs and/or server output (if relevant):

Any additional context (logs, chat logs, magical formulas, etc.):

[elasticmachine]

Pinging @elastic/security-threat-hunting (Team:Threat Hunting)

[elasticmachine]

Pinging @elastic/security-solution (Team: SecuritySolution)

[elasticmachine]

Pinging @elastic/security-threat-hunting-investigations (Team:Threat Hunting:Investigations)