# Phase 20: Aion-Aware Sidecar Startup - Context

**Gathered:** 2026-03-27
**Status:** Ready for planning
**Mode:** Auto-generated (infrastructure phase)

<domain>
## Phase Boundary

Sidecar startup for Aion symbols preserves pre-midnight bars and produces zero midnight-boundary Stathera gaps on restart. GitHub Issue #310.

</domain>

<decisions>
## Implementation Decisions

### Claude's Discretion

All implementation choices are at Claude's discretion. Key constraint: the A3 Stathera audit found 8 midnight-boundary gaps at 100dbps caused by fill_from_rest always anchoring at crossover_tid. The fix must seed from max(last_committed_bar_tid, crossover_tid - 1) for Aion symbols.

</decisions>

<code_context>

## Existing Code Insights

Codebase context will be gathered during plan-phase research.

</code_context>

<specifics>
## Specific Ideas

From A3 audit: 8 gaps across BTC/ETH/SOL at 100dbps on dates Mar 5, 22, 26. Root cause: \_create_engine() anchors at crossover_tid regardless of mode.

</specifics>

<deferred>
## Deferred Ideas

None.

</deferred>
