fix(desktop): bound initial timeline retention - #5603
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Let Virtua own the initial visible range instead of passing every loaded message through keepMounted. Populate the stable retention window after the virtualizer reports its first settled viewport. Add a hook regression test covering a 10,000-row timeline: no indices are retained initially, then the bounded reader neighborhood and visual tail are retained after scroll end. Co-authored-by: Carl <c7ebe626f000404285d3686e1dc74cc07cc60a9754a150041ba132e14bd3e2ec@buzz.block.builderlab.xyz> Signed-off-by: Wes <wesbillman@users.noreply.github.com>
wesbillman
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Aug 11, 2026
| // seeding every key here turns `keepMounted` into an all-history mount. | ||
| const [retainedKeys, setRetainedKeys] = React.useState<ReadonlySet<string>>( | ||
| () => new Set(keys), | ||
| () => new Set(), |
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Is this it!?!?! Crazy
Keep a bounded 100-row visual tail mounted during initial positioning, then refresh retention from the measured viewport after the first painted frame. This preserves bottom and reading-state initialization without returning to the pathological all-history mount. Co-authored-by: Carl <c7ebe626f000404285d3686e1dc74cc07cc60a9754a150041ba132e14bd3e2ec@buzz.block.builderlab.xyz> Signed-off-by: Wes <wesbillman@users.noreply.github.com>
wpfleger96
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Aug 11, 2026
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Reviewed at 3f7d6ebe3b8062ffd3fcf91cdfc61098eb05539d. The bounded initial tail fixes the all-history keepMounted regression while preserving initial bottom positioning, and the post-paint refresh correctly reuses the existing viewport/tail retention policy and prepend guard. The 10,000-row regression covers both the initial bounded state and the measured steady state. I found no blocking or non-blocking issues.
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Summary
keepMountedWhy
useTimelineRetentioninitialized its retained-key set with every loaded timeline key. Those indices were passed to Virtua'skeepMounted, effectively defeating virtualization during initial channel positioning untilonScrollEndpruned the set.On a large real channel this grew WebContent into multiple gigabytes and blocked the renderer main thread for 20+ seconds while WebKit laid out and painted the retained rows. Starting with no retained rows restores Virtua's visible-range mount; the existing reader-neighborhood and visual-tail retention is populated once the viewport is measured.
Validation
node --import ./test-loader.mjs --experimental-strip-types --test src/features/messages/ui/useTimelineRetention.test.mjs8e86a189de7e9a8f2cb119396c8f912ed9dacd6e: branch-skew, desktop-check, desktop-typecheck, and all 4,671 desktop tests passedAuthorship disclosure
Carl implemented and is posting this change on Wes's behalf.