# Ver1 Step 4 Results: Data Model and Migration Safety

## Summary

Step 4 implementation status: **in progress**.

This document records completed migration-safety work, validation evidence, and remaining follow-ups for Ver1 Step 4.

Implemented in this step:

1. _TBD_
2. _TBD_
3. _TBD_

---

## Implemented Changes

### 1) Schema audit and invariant lock

_TBD_

### 2) Migration policy/tooling lock

_TBD_

### 3) Forward migration implementation

_TBD_

### 4) Rollback and mitigation runbook

_TBD_

### 5) Backfill implementation or explicit no-backfill decision

_TBD_

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## Test and Verification Evidence

### Added/Updated Tests

1. _TBD_
2. _TBD_
3. _TBD_

### Validation Runs

Run and record outcomes:

- `uv run pytest --collect-only -q` -> _TBD_
- `uv run pytest -m unit -q` -> _TBD_
- `uv run pytest -m "not external" -q` -> _TBD_
- `uv run pytest -q` -> _TBD_

### Migration Rehearsal Evidence

Record migration rehearsal details:

- baseline data set used: _TBD_
- forward migration result: _TBD_
- post-migration verification result: _TBD_
- rollback/mitigation rehearsal result: _TBD_

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## Requirement Traceability (Step 4)

| Step 4 Area | REQ Coverage | Status | Evidence |
| --- | --- | --- | --- |
| Schema lifecycle and state persistence safety | REQ-3, REQ-4, REQ-11 | _TBD_ | _TBD_ |
| Lifespan/runtime ownership continuity | REQ-7 | _TBD_ | _TBD_ |
| Explicit non-mutating production startup policy | REQ-10 | _TBD_ | _TBD_ |
| Prompt/data continuity constraints | REQ-12 | _TBD_ | _TBD_ |

---

## Operational Artifacts Produced

- `docs/ver1/ver1-step4.md`
- `docs/ver1/ver1-step4-migration-runbook.md` (_if created_)
- _TBD additional artifacts_

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## Risks, Exceptions, and Follow-Ups

1. _TBD_
2. _TBD_
3. _TBD_

Open follow-ups to carry forward:

- _TBD_

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## Step 4 Exit Assessment

- Schema validation against finalized V1 domain: **_TBD_**
- Forward migration path safety and repeatability: **_TBD_**
- Rollback/mitigation readiness: **_TBD_**
- Backfill risk closure: **_TBD_**
- Test and regression safety: **_TBD_**

Step 4 completion status: **_TBD_**

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## Handoff to Step 5

Once Step 4 is marked complete, Step 5 can proceed with:

- verified migration safety baseline
- explicit rollback and recovery procedures
- reduced data-integrity risk entering private-network safety hardening