Implements plan §13.7 atomic index aliases for blue-green reindexing.
## Implementation Summary
All components are fully implemented and tested:
**Database & Storage:**
- Aliases table with history tracking (001_initial.sql)
- TaskStore trait: create_alias, get_alias, flip_alias, delete_alias, list_aliases
- SQLite implementation with atomic flip transactions
- History retention bound (default: 10 entries)
**In-Memory Cache:**
- AliasRegistry with sync_from_store() for hot path resolution
- resolve() for single/multi-target lookup
- is_multi_target_alias() for write rejection
**Admin API Endpoints:**
- POST /_miroir/aliases/{name} - create single or multi-target
- GET /_miroir/aliases - list all
- GET /_miroir/aliases/{name} - get with flip history
- PUT /_miroir/aliases/{name} - atomic flip
- DELETE /_miroir/aliases/{name} - delete alias
**Routing Integration:**
- Search route resolves aliases before scatter
- Documents route rejects writes to multi-target aliases (409)
- Multi-target aliases fan out to all targets
**Config & Metrics:**
- aliases.enabled, aliases.history_retention, aliases.require_target_exists
- miroir_alias_resolutions_total{alias}
- miroir_alias_flips_total{alias}
## Acceptance Criteria (All Met)
✓ Create single-target alias → both writes + reads resolve
✓ Flip: new writes land on new target; in-flight requests complete against old target
✓ Create multi-target alias → read fans out; write returns 409
✓ Operator edit of ILM-managed multi-target alias → 409 (only ILM can modify)
✓ History: 11th flip evicts the oldest
All 17 acceptance tests pass.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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