V4.5 Complete - Enhanced trancription context, added option to restranscribe source under different models.

docs/ver4/schema_v4.md

@@ -71,6 +71,7 @@ UUID id PK
 UUID document_id FK
 VARCHAR status
 INTEGER retry_count
+VARCHAR purpose
 TEXT provider
 TEXT model
 TEXT prompt_name
@@ -93,6 +94,7 @@ TEXT file_path
 TEXT file_hash
 BIGINT file_size_bytes
 TEXT raw_transcription
+UUID preferred_execution_attempt_id FK
 TEXT revised_text
 TIMESTAMPTZ date_uploaded
 TIMESTAMPTZ date_revised
@@ -177,7 +179,9 @@ EXECUTION_ATTEMPT ||--o{ PROCESSING_ARTIFACT : produces
 - `EXECUTION_ATTEMPT(job_id, source_id, attempt_number)` is unique; retries increment the persisted attempt number.
 - Historical `JOB_SOURCE` rows without an `EXECUTION_ATTEMPT` remain SDK snapshots and are explicitly labeled as
   lacking transport evidence.
-- `SOURCE.raw_transcription` caches the latest successful machine output for that page.
+- `SOURCE.raw_transcription` caches the explicitly selected preferred machine output for that page.
+- `SOURCE.preferred_execution_attempt_id` records exact successful-attempt provenance. Legacy projections may remain
+  null until a new successful result is selected.
 
 ### Generic Processing Artifacts
 
@@ -185,6 +189,8 @@ EXECUTION_ATTEMPT ||--o{ PROCESSING_ARTIFACT : produces
 - Exactly one of `inline_payload` and `external_reference` is populated.
 - Externally stored artifacts use application-managed relative references and are verified by SHA-256 and byte size.
 - Coordinate metadata declares units, origin, dimensions, and transformations when geometry is present.
+- Orientation-normalized binary model inputs and JSON quality-warning results use distinct versioned artifact types
+  and are attached to the exact consuming `EXECUTION_ATTEMPT`.
 
 ### Image Storage and Integrity
 
@@ -195,7 +201,7 @@ EXECUTION_ATTEMPT ||--o{ PROCESSING_ARTIFACT : produces
 ### Page Ordering and Revisions
 
 - `SOURCE.page_number` dictates page ordering within a document.
-- `SOURCE.raw_transcription` remains immutable machine output.
+- `SOURCE.raw_transcription` changes only through first-success selection or explicit candidate promotion.
 - `SOURCE.revised_text` stores human edits and is the preferred display value when present.
 
 ### Semantic Registry Governance