[khalyaro]

Summary

Four front-end issues around upload throughput, query caching, and two shared a11y primitives.

#854 — Bound upload concurrency, throttle progress (DeliverableUpload)

• New runWithConcurrency(items, limit, task) helper (unit-tested) drives uploads through a pool of 3 in-flight requests, so selecting 20 files no longer opens 20 presign/PUT/confirm chains at once.
• Each file records its own uploadStatus/progress/error; a failed file no longer cancels its siblings, and there is no longer a single isPending/error that only reflects the last call.
• XHR progress events are buffered in a useRef and flushed on a 250 ms timer (~4 Hz) instead of mapping the whole array per event.
• The unstable useCallback deps are gone (the whole mutation object and the unused listingId are no longer dependencies).

#855 — Tune query caching

• Global staleTime raised from 30 s to 5 minutes.
• select projections added to the purchases, transactions and listings list queries so only rendered columns flow through (new response fields no longer churn row identity).
• Removed the manual window focus listener in WalletBalanceDisplay that duplicated its refetchOnWindowFocus: true.
• Test asserts the new defaults (5 * 60_000, refetchOnWindowFocus: false).

#856 — Focus management + labelling for Modal

• Focus moves into the dialog on open, Tab/Shift+Tab cycle within it, and focus returns to the trigger on close/unmount.
• The backdrop is now a real <button> instead of an interactive div.
• The dialog keeps its accessible name from the visible title (already aria-labelledby); new optional headingLevel prop (default h2) lets callers fit the page outline.
• Escape and body-scroll locking keep working. Tests added for focus-in, focus-restore, tab trapping and the button backdrop.

#857 — ARIA tabs on the artist profile

• The strip is a role="tablist"; each control is a role="tab" with aria-selected, aria-controls, id and roving tabIndex.
• Arrow Left/Right, Home and End move selection and focus.
• The panel is role="tabpanel", aria-labelledby the active tab and focusable.
• The injected <meta name="description"> is restored/removed on unmount, so navigating artist → artist no longer leaks the previous bio. Trustline keyboard-nav test added.

Notes

• Per the repo instructions I did not run install/CI/tests locally.
• eslint-plugin-jsx-a11y is unrelated to this branch.

Closes #854
Closes #855
Closes #856
Closes #857

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[ayshadogo]

GBEW