## Why
Allow v2 memories to build in the background while the selected memory version continues supplying context, and let clients check whether v2 has enough consolidated data and a valid summary to use.
## What changed
- Add `memories.dual_write`, disabled by default, to run v1 and v2 extraction and consolidation concurrently with separate stores and directories.
- Add the experimental `memory/status` endpoint, returning `v2ConsolidatedThreads` and `v2Ready`. Readiness requires a valid v2 summary and a consolidation thread count meeting `minConsolidatedThreads` (default 20, supported range 1–4096).
- Persist the largest thread count from a successful consolidation across pruning and clear it on memory reset.
- Share v2 summary validation between consolidation and status reporting, and tag memory metrics with `memory_version`.
## Testing
Add tests for independent dual-write outputs, preserving existing notes without importing them into v2, and readiness behavior across consolidation ownership checks, missing summaries, configurable thresholds, thread deletion, and memory reset.
GitOrigin-RevId: 54417cc60bf419062401355c0da8c79119995f61
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