test: Horizon history gap-injection chaos (#706)

[jaymoneymanxl]

Overview

This PR adds deterministic Horizon transaction-history gap-injection chaos proving the ingest layer detects paging-token gaps, emits a fatal ingest.cursor.paused audit, and halts cursor advancement rather than silently skipping records. Recovery via resumeFromCursor() is covered when gaps close.

Related Issue

Closes #706

Changes

🌀 Horizon history gap chaos

• [MODIFY] src/services/horizonTransactionHistoryFetcher.ts
  • Gap halt emits ingest.cursor.paused with severity: fatal and alarm: horizon_history_gap.
  • Adds createHorizonHttpFetchPage() to wire the fetcher to a real Horizon HTTP endpoint from trusted config.
• [MODIFY] src/__tests__/chaos/horizonGapChaos.test.ts — asserts fatal pause metadata + HTTP fetchPage wiring; multi-seed deterministic sweep.
• [MODIFY] run-chaos-tests.sh — gap scenario for issue Stellar Horizon chaos: transaction-history gap injection and detection #706.
• [MODIFY] docs/horizon-history-gap-chaos.md — security model, acceptance criteria, wiring guide.

Verification Results

npx jest src/__tests__/chaos/horizonGapChaos.test.ts --runInBand --forceExit
✅ 60/60 passed

./run-chaos-tests.sh gap

Acceptance Criteria	Status
Chaos harness deterministic per seed	✅ seededRandom / buildDeterministicGaps
Gap detection emits ingest.cursor.paused	✅ fatal alert; cursor unchanged
No silent skip of records	✅ empty records on halt
Recovery when gaps close	✅ resumeFromCursor()
Multiple simultaneous gaps do not confuse cursor	✅ first gap only; cursor stays clean

Timeline

• Hardened fatal pause audit + Horizon HTTP wiring + docs/tests for Stellar Horizon chaos: transaction-history gap injection and detection #706.

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[jaymoneymanxl]

@thlpkee20-wq done closes #706