feat: cursor/snapshot pagination for stream history

[euniceamoni]

Problem

History pages produced duplicate rows and gaps when new stream events arrived between page fetches, and had no bounds on result size.

Solution

• streamHistory.js: snapshot pagination engine

  • On first-page fetch the full filtered+sorted event list is frozen into a Map<snapshotId, events[]>. The cursor carries {snapshotId, offset, filters} so subsequent pages always read from the same frozen slice — concurrent inserts cannot shift page windows.
  • Stable sort: (timestamp DESC, id ASC) breaks ties deterministically.
  • Filters (status, token, direction) are baked into the snapshot; changing a filter creates a new snapshot, preventing stale pages.
  • Page size capped at MAX_PAGE_SIZE=50; default 20.
  • LRU eviction keeps at most 20 snapshots in memory.

• api.js: withLatency accepts an optional AbortSignal

  • Rejects immediately with AbortError on pre-aborted signals.
  • Clears the setTimeout and rejects on mid-flight aborts.

• streams.js: emits StreamEvents on create / withdraw / cancel

  • Seed data also emits events for existing streams.

• useStreamHistory.js hook

  • Cursor stack enables prev-page navigation without re-snapshotting.
  • New AbortController per fetch; previous request aborted before next fires, eliminating pagination race conditions.
  • Filter changes reset the cursor stack and trigger a fresh snapshot.

• StreamHistoryTable component + CSS

  • Filter dropdowns for status, token, direction.
  • Prev/Next pagination with disabled states.
  • ARIA live regions (polite on body, pagination info).
  • Styled with existing design tokens.

Tests (39 total, 23 new)

• stableSort: ordering, tie-break, determinism on 200 events, no mutation
• applyFilters: each filter dimension, conjunctive, empty passthrough
• snapshot pagination: concurrent inserts blocked, no duplicates/gaps
• filter contract: cursor carries filters, new filters = new snapshot
• page size cap: >MAX clamped, 0→1 minimum, exact MAX allowed
• cancellation: pre-aborted and mid-flight both reject with AbortError
• large fixture: 200 events with timestamp collisions, filtered totals
• regression: 12 events + 3 concurrent inserts, zero duplicates/gaps closes perf(frontend): add stable pagination and filtering for stream history #134