[indexer/verifier] Define reorg-state model and fixture tests

[FlowmemoryAI]

Objective

Define the first reorg-state model for FlowPulse observations and add fixture-only tests for state transitions.

Allowed folders

• services/indexer/
• services/shared/
• services/verifier/ only for status cross-references
• docs/ only for behavior or assumption updates
• research/indexer-verifier/ only for reorg research notes

Forbidden folders

• contracts/
• hardware/
• apps/
• crypto implementation
• chain/L1 implementation
• tokenomics
• production RPC deployment
• production database deployment

Acceptance criteria

• Defines pending, mined, finalized, reorged, and superseded transition rules.
• Distinguishes exact duplicate, conflicting duplicate, pulse duplicate, and reorg replacement.
• Adds fixture-based transition tests without live RPC.
• Documents finality depth as a future chain-specific policy, not a hardcoded production setting.
• Does not add a database, queue, RPC client, or deployment config.

Risk level

Medium

Recommended agent

FlowMemory Indexer / Verifier Agent