helium/ui: Add visual tab switcher

[beeltec]

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Tested on (check one or more):

• Windows
• macOS
• Linux

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This adds a Ctrl+Tab overlay with thumbnail and list layouts.

Closes #238.

Unfortunately #1376 seems to be abandoned by the original author. That's why I rethought the implementation approach to not only support the usual thumbnail view but also a list view (which during my tests I found much more useful when having a lot of tabs).

Full disclosure: I did use an LLM for autocomplete and code review.

Screenshots

thumbnail strip:

list layout:

appearance settings:

[greptile-apps]

[Medium impact] The PR appears safe to merge, with no new actionable correctness or security issue established.

_{Reviews (4) · Last reviewed commit: "fix(helium/core/session-restore): handle..." · Reviewed by Greptile}

[immadolf]

A useful open-source reference for the interaction model here is Phi Browser, which has already implemented an Arc-style Ctrl+Tab switcher on macOS:

https://github.com/phibrowser/phibrowser-mac/blob/main/Sources/States/TabSwitchManager.swift

The interesting part is not just the thumbnail UI, but the switching session behavior:

• Tabs are ordered by MRU (most recently used).
• The first Ctrl+Tab selects the previous MRU tab but does not immediately show the overlay.
• A ~250 ms reveal timer is started.
• If Ctrl is released before the timer fires, it simply switches to the selected tab without ever showing the UI.
• If Ctrl is still held after the threshold, the visual switcher appears.
• If Tab is pressed again before the timer expires, the overlay appears immediately, since that indicates the user is browsing through multiple tabs.
• Further Tab / Shift+Tab presses only move the highlighted selection.
• Releasing Ctrl commits the currently highlighted tab.

This creates the Arc-style feel where a quick Ctrl+Tab works as an instant previous-tab toggle with no UI flash, while holding Ctrl or pressing Tab repeatedly turns it into a visual MRU browser.

From the current implementation in this PR, the release-Ctrl-to-confirm behavior already appears to be present. The main interaction improvement worth borrowing from Phi seems to be the delayed overlay/session behavior.

Phi also limits the switcher to a small recent working set (maxRecentTabs = 5). That may be worth considering as well: Ctrl+Tab works especially well as a quick switcher between recent tabs, while Tab Search can handle browsing a large number of open tabs.

The thumbnail implementation in this PR already looks more appropriate for Chromium than Phi's Swift/Chromium bridge approach, so the most useful part to borrow is probably the interaction/session model rather than the rendering implementation.

[beeltec]

A useful open-source reference for the interaction model here is Phi Browser, which has already implemented an Arc-style Ctrl+Tab switcher on macOS:

https://github.com/phibrowser/phibrowser-mac/blob/main/Sources/States/TabSwitchManager.swift

The interesting part is not just the thumbnail UI, but the switching session behavior:

• Tabs are ordered by MRU (most recently used).
• The first Ctrl+Tab selects the previous MRU tab but does not immediately show the overlay.
• A ~250 ms reveal timer is started.
• If Ctrl is released before the timer fires, it simply switches to the selected tab without ever showing the UI.
• If Ctrl is still held after the threshold, the visual switcher appears.
• If Tab is pressed again before the timer expires, the overlay appears immediately, since that indicates the user is browsing through multiple tabs.
• Further Tab / Shift+Tab presses only move the highlighted selection.
• Releasing Ctrl commits the currently highlighted tab.

This creates the Arc-style feel where a quick Ctrl+Tab works as an instant previous-tab toggle with no UI flash, while holding Ctrl or pressing Tab repeatedly turns it into a visual MRU browser.

From the current implementation in this PR, the release-Ctrl-to-confirm behavior already appears to be present. The main interaction improvement worth borrowing from Phi seems to be the delayed overlay/session behavior.

Phi also limits the switcher to a small recent working set (maxRecentTabs = 5). That may be worth considering as well: Ctrl+Tab works especially well as a quick switcher between recent tabs, while Tab Search can handle browsing a large number of open tabs.

The thumbnail implementation in this PR already looks more appropriate for Chromium than Phi's Swift/Chromium bridge approach, so the most useful part to borrow is probably the interaction/session model rather than the rendering implementation.

Thanks for the input! I already added an option to switch trough the tabs in MRU order. The idea with the small delay until the overview is displayed is really good. I will implement that.

Regarding the max recent tabs I see where you are coming from. I do use it with more tabs. I think I will implement it but with an experimental option to enable unlimited tabs in the normal switcher view (list view will retain it's behaviour).

[beeltec]

@immadolf Your proposed solution regarding the small 250ms delay and capping the maximum number of tabs shown in the thumbnail strip view is now implemented. Thanks again for the suggestions!

[beeltec]

@greptileai please review

[beeltec]

Empty session restores can now complete correctly. @greptileai please review

[beeltec]

Merged with latest main and fixed conflicts. @greptileai please review

[marlonjames71]

@beeltec This looks awesome. The only other thing I'd want if it isn't already implemented is the ability to move the selection backwards with CTRL + ` (backtick or tilde key). This is how Arc and Dia's tab switcher works as well as all the other ones I've seen that are well implemented. I guess CTRL + Shift + Tab works as well, but that's more keys to press. CTRL + ` is simpler and aligns with the macOS app switcher as well.

My only other suggestion just looking at the provided images is to round the corners a bit more to make it look more modern. The corner radius currently looks very very small and it could look a bit dated. For example, here's what Dia's looks like which is super clean:

Maybe, instead of the blue selection color you can reuse the focused tab color. Might look a bit cleaner.

Nice job with this. Having the layout option is very cool too and I'm looking forward to trying it.