fix: sidebar title disappears when switching between two sidebars

[nzjrs]

I have buttons in the header which are used to switch between two sidebars (or rather, switch out the contents of the one cl.ElementSidebar to make it look like two sidebars). I observer visual artefacts and inconsistency when doing this, specifically I replace the contents of it and its title regularly, yet sometimes only half of the replacement sticks, often the title replacement is ignored.

To reproduce:

Open sidebar A with ElementSidebar.set_title("A") followed by set_elements([a]), then open sidebar B with set_title("B") followed by set_elements([b], key="b"). Click back and forth between the two. Steady state: #side-view-title contains only the back-arrow button, no title text node after it. During each switch the title flashes for a render frame then vanishes. Body content renders fine; only the header title is lost.

The set_title handler writes the sideView atom, then the set_elements handler reads prev in its updater and falls back to title: prev?.title || '' when prev is undefined. Instrumenting the updater with a console.log shows prev observed as undefined on every set_elements call even though the preceding set_title handler just wrote to the atom synchronously in the same tick. Something in React 18 + Recoil 0.7.7's nextTree/Batcher interaction drops the staged write across socket.io event callbacks; I did not isolate the Recoil-internals bug.

It's hard to finesse the Recoil to coordinate state across two events so I Add ElementSidebar.set(title, elements, key=None) that emits a single set_sidebar frame carrying all three fields, and a frontend handler that writes the atom from the payload alone and never reading prev for state it did not produce. The existing set_title and set_elements APIs and handlers are untouched for back-compat; callers that migrate to .set() stop seeing the title loss.

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Summary by cubic

Fixes the disappearing sidebar title when switching between sidebars by sending a single atomic update. Adds a new backend API and client handler to set title, elements, and key together without relying on prior state.

• Bug Fixes
  • Added ElementSidebar.set(title, elements, key=None) to emit one set_sidebar payload; empty elements closes the sidebar.
  • Client listens to set_sidebar and sets sideView directly, avoiding the React 18 + Recoil batching race that dropped the title.
  • Keeps set_title and set_elements for back-compat; callers can migrate to .set() to prevent the flicker.
  • Skips redundant updates when key and title match; element URL hydration is preserved.

^{Written for commit a58f84d. Summary will update on new commits.}

[cubic-dev-ai]

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[github-actions]

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