transcription/docs/ver1/ver1-step4-results.md

Ver1 Step 4 Results: Data Model and Migration Safety

Summary

Step 4 implementation status: complete (baseline scope).

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

Implemented in this step:

1. Added explicit migration framework module with revision history tracking.
2. Added schema compatibility validation and startup guardrails.
3. Added migration runner CLI for list/apply/check operations.
4. Added migration tests and Step 4 validation evidence.
5. Added Step 4 migration/rollback runbook.

---

Implemented Changes

1) Schema audit and invariant lock

Implemented read-only compatibility checks in src/transcription/db.py:

• validate_schema_compatibility(...) verifies required V1 tables:
  • document
  • job
  • transcript
  • transcriptrevision
• verifies required job.retry_count column
• returns explicit issue identifiers (non-mutating check)

2) Migration policy/tooling lock

Added explicit migration revision model in src/transcription/migrations.py:

• MigrationRevision dataclass
• ordered MIGRATIONS registry
• migration history table: schema_migration_history
• explicit pending-list and apply operations

3) Forward migration implementation

Implemented two baseline forward migrations:

1. 0001_add_retry_count_to_job
2. 0002_create_transcriptrevision_table

Each migration is idempotent and recorded in migration history.

4) Rollback and mitigation runbook

Created docs/ver1/ver1-step4-migration-runbook.md with:

• preconditions
• list/apply/check command sequence
• backup-first procedure
• verification checklist
• rollback/mitigation decision tree
• error classification guidance aligned to docs/error_handling.md

5) Backfill implementation or explicit no-backfill decision

No backfill required for this baseline Step 4 scope.

Rationale:

• additive migration operations only
• default values and new-table creation do not require historical row rewrites for current V1 invariants
• residual advanced backfill scenarios deferred unless future schema evolution introduces incompatible transforms

---

Test and Verification Evidence

Added/Updated Tests

1. tests/test_migrations.py
   • pending migration discovery
   • migration apply + history recording
   • idempotent re-apply behavior
2. tests/test_db.py
   • compatibility-check behavior on fresh schema
   • table expectation updates for transcriptrevision
3. tests/test_config.py
   • migration safety setting defaults
4. tests/test_app.py
   • lifespan test compatibility with migration/validation startup hooks

Validation Runs

Run and record outcomes:

• uv run pytest --collect-only -q -> passed
• uv run pytest -m unit -q -> passed
• uv run pytest -m "not external" -q -> passed
• uv run pytest -q -> passed

Migration Rehearsal Evidence

Migration rehearsal details (test-based):

• baseline data set used: in-memory SQLite legacy-shaped schema fixture (job table missing Step 4 additions)
• forward migration result: pending revisions applied successfully (0001, 0002)
• post-migration verification result: schema checks pass and migration history recorded
• rollback/mitigation rehearsal result: runbook defined backup-restore primary rollback class for personal-scale SQLite deployment

---

Requirement Traceability (Step 4)

Step 4 Area	REQ Coverage	Status	Evidence
Schema lifecycle and state persistence safety	REQ-3, REQ-4, REQ-11	met	src/transcription/migrations.py, tests/test_migrations.py, tests/test_db.py
Lifespan/runtime ownership continuity	REQ-7	met	src/transcription/app.py startup checks + existing lifespan ownership model
Explicit non-mutating production startup policy	REQ-10	met	migration_auto_apply_on_startup=False default + explicit runner workflow + startup validation gate
Prompt/data continuity constraints	REQ-12	met (continued)	no prompt-contract mutation in Step 4 changes

---

Operational Artifacts Produced

• docs/ver1/ver1-step4.md
• docs/ver1/ver1-step4-migration-runbook.md
• src/transcription/migrations.py
• src/transcription/migration_runner.py
• README migration workflow updates

---

Risks, Exceptions, and Follow-Ups

1. This lightweight migration system is appropriate for current personal-scale scope but may require a dedicated framework as schema complexity grows.
2. Rollback remains backup-restore primary; reversible down-migration coverage is intentionally limited in this baseline.
3. Startup compatibility checks currently fail fast with generic runtime error text and can be further normalized under API/operator error envelopes in later hardening.

Open follow-ups to carry forward:

• Evaluate migration framework escalation criteria in Step 9/10 readiness updates.
• Add optional richer structured migration logging fields if observability scope expands.

---

Step 4 Exit Assessment

• Schema validation against finalized V1 domain: met
• Forward migration path safety and repeatability: met (baseline scope)
• Rollback/mitigation readiness: met (backup-restore primary path)
• Backfill risk closure: met (no backfill required for current deltas)
• Test and regression safety: met

Step 4 completion status: complete (baseline scope)

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