[DevTools] Always include the root in the timeline and select it by default #34654
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Stacked on #34654. The root is special since it represents "Initial Paint" (or a "Transition" when an Activity is selected). This gives it a different color in the timeline as well as gives it an outline that's clickable. Hovering the timeline now shows "Initial Paint" or "Suspense". Also made the cursor a pointer to invite you to try to click things and some rounded corners. <img width="1219" height="420" alt="Screenshot 2025-10-02 at 1 26 38 PM" src="https://github.com/user-attachments/assets/12451f93-8917-4f3b-8f01-930129e5fc13" /> <img width="1217" height="419" alt="Screenshot 2025-10-02 at 1 26 54 PM" src="https://github.com/user-attachments/assets/02b5e94c-3fbe-488d-b0f2-225b73578608" /> <img width="1215" height="419" alt="Screenshot 2025-10-02 at 1 27 24 PM" src="https://github.com/user-attachments/assets/c24e8861-e74a-4ccc-8643-ee9d04bef43c" /> <img width="1216" height="419" alt="Screenshot 2025-10-02 at 1 27 10 PM" src="https://github.com/user-attachments/assets/d5cc2b62-fa64-41bf-b485-116b1cd67467" />
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Stacked on facebook#34654. The root is special since it represents "Initial Paint" (or a "Transition" when an Activity is selected). This gives it a different color in the timeline as well as gives it an outline that's clickable. Hovering the timeline now shows "Initial Paint" or "Suspense". Also made the cursor a pointer to invite you to try to click things and some rounded corners. <img width="1219" height="420" alt="Screenshot 2025-10-02 at 1 26 38 PM" src="https://github.com/user-attachments/assets/12451f93-8917-4f3b-8f01-930129e5fc13" /> <img width="1217" height="419" alt="Screenshot 2025-10-02 at 1 26 54 PM" src="https://github.com/user-attachments/assets/02b5e94c-3fbe-488d-b0f2-225b73578608" /> <img width="1215" height="419" alt="Screenshot 2025-10-02 at 1 27 24 PM" src="https://github.com/user-attachments/assets/c24e8861-e74a-4ccc-8643-ee9d04bef43c" /> <img width="1216" height="419" alt="Screenshot 2025-10-02 at 1 27 10 PM" src="https://github.com/user-attachments/assets/d5cc2b62-fa64-41bf-b485-116b1cd67467" /> DiffTrain build for [2e68dc7](facebook@2e68dc7)
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Stacked on facebook#34654. The root is special since it represents "Initial Paint" (or a "Transition" when an Activity is selected). This gives it a different color in the timeline as well as gives it an outline that's clickable. Hovering the timeline now shows "Initial Paint" or "Suspense". Also made the cursor a pointer to invite you to try to click things and some rounded corners. <img width="1219" height="420" alt="Screenshot 2025-10-02 at 1 26 38 PM" src="https://github.com/user-attachments/assets/12451f93-8917-4f3b-8f01-930129e5fc13" /> <img width="1217" height="419" alt="Screenshot 2025-10-02 at 1 26 54 PM" src="https://github.com/user-attachments/assets/02b5e94c-3fbe-488d-b0f2-225b73578608" /> <img width="1215" height="419" alt="Screenshot 2025-10-02 at 1 27 24 PM" src="https://github.com/user-attachments/assets/c24e8861-e74a-4ccc-8643-ee9d04bef43c" /> <img width="1216" height="419" alt="Screenshot 2025-10-02 at 1 27 10 PM" src="https://github.com/user-attachments/assets/d5cc2b62-fa64-41bf-b485-116b1cd67467" /> DiffTrain build for [2e68dc7](facebook@2e68dc7)
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Rebased on #34454.
Always include the root in the timeline even if it has no unique suspenders, since even if it won't suspend, we have to be able to see that and step to one step before the next boundary to see the first boundary that does suspend in its fallback state.
Also, if there's no current selection on initial mount, select the last entry in the timeline. We usually do this with
selectedSuspenseIDbut that doesn't happen on initial load. So this does it on initial load if nothing else is selected by then. That way when you reload you get the initial root selected.There's a problem here because we should really use one source of truth and
selectedSuspenseIDdoesn't really do anything now. Either it should be its separate source of truth and you can't show components in the side-panel or it should be derived from the other state.If it's derived, once there's a selection, e.g. in the root, then even if new timelines load it will never change but that's probably a good thing.