[ucaeon]

Add an Expand task groups by default preference under Settings → Graph, following the user-settings approach suggested in the issue.

This uses browser-local settings rather than introducing the Dag and TaskGroup constructor parameters originally proposed.

Behavior

• The preference is disabled by default, preserving the current collapsed behavior.
• When enabled, all task groups, including nested groups, expand in Dags without a saved group selection.
• Existing per-Dag selections take precedence, including an explicitly saved collapse-all selection. Changing the preference does not overwrite these selections.
• The preference is stored in the browser and applies to both Graph and Grid, which share group selection state.

closes: #55305

Testing

• All 1,304 UI tests passed across 150 test files.
• TypeScript, ESLint, pre-commit checks, and manual checks passed, including the production UI build.
• Verified locally with example_task_group that the preference persists after reload, nested groups expand by default, and manual selections are preserved after reload.

Screenshots

Before — Settings

The Graph settings section has no option to choose whether task groups expand by default.

After — Settings with the new preference enabled

The new “Expand task groups by default” toggle lets users choose the default expansion behavior for Dags without a saved group selection.

Nested task groups expanded by default

With the preference enabled and no saved selection for this Dag, both top-level and nested task groups expand automatically.

Manual group selection preserved after reload

After manually collapsing section_2 and reloading, section_2 remains collapsed while section_1 stays expanded. The saved selection takes precedence over the enabled default.

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Was generative AI tooling used to co-author this PR?

• Yes — Codex (GPT-6)

Generated-by: Codex (GPT-6) following the guidelines