## 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
## Summary
Generated memory rows and their stage-one/stage-two job state currently
live in `state_5.sqlite` alongside thread metadata. That makes memory
cleanup and regeneration share the main state schema even though those
rows are memory-pipeline data and can be rebuilt independently from the
durable thread records.
This PR moves the memory-owned tables into a dedicated
`memories_1.sqlite` runtime database while keeping thread metadata in
`state_5.sqlite`.
## Changes
- Adds a separate memories DB runtime, migrator, path helpers, telemetry
kind, and Bazel compile data for `state/memory_migrations`.
- Introduces `MemoryStore` behind `StateRuntime::memories()` and moves
memory table/job operations onto that store.
- Drops the old memory tables from the state DB and recreates their
schema in `state/memory_migrations/0001_memories.sql`.
- Updates memory startup, citation usage tracking, rollout pollution
handling, `debug clear-memories`, and app-server `memory/reset` to
operate through the memories DB.
- Preserves cross-DB behavior by hydrating thread metadata from the
state DB when selecting visible memory outputs and checking stage-one
staleness.
## Verification
- Added/updated `codex-state` tests for deleted-thread memory visibility
and already-polluted phase-two enqueue behavior.
- Updated `debug clear-memories`, app-server `memory/reset`, and
memories startup tests to seed and assert memory rows through
`memories_1.sqlite`.
