debounced swap interface search with request cancellation

[mikewheeleer]

Summary

The swap interface search fires a request per keystroke and can render a stale response over a newer one. Add debouncing and cancel/ignore superseded requests.

Why this matters

Per-keystroke, race-prone search wastes work and shows wrong results. Debounce + cancellation is the standard, testable fix.

Requirements

• Debounce swap interface search input before querying.
• Cancel or ignore responses from superseded requests (guard against stale results).
• Show loading, empty-result, and error states distinctly.
• Keyboard and screen-reader accessible.

Technical guidance

• Track the latest request token and drop out-of-order responses.
• Trim/normalize the query before sending.

Edge cases — each must have a test

• typing quickly -> one query after the pause
• fast then slow response -> newest result wins
• no matches -> empty state
• cleared input -> resets results
• error -> error state with retry

Acceptance criteria

• All requirements and every edge case above implemented and covered by tests
• New unit and integration tests; existing tests still pass and no regressions
• Structured, typed errors (no leaked internals; stable codes)
• npm run lint, npm test, and npm run build all pass locally
• Code follows the repo's existing conventions; no duplication or dead code
• Short docs/comments explaining the design and any non-obvious decisions
• PR description explains the approach and includes Closes #<issue>

Out of scope

• Search history/suggestions
• Server-side ranking

Rewards

Part of the GrantFox OSS / Official Campaign (FWC26) — this task may be rewarded. PR quality is assessed by AI: depth, correctness under edge cases, meaningful tests, and clean design are what earn the reward. Shallow changes (typos, formatting, trivial docs) do not qualify.