Wire the guarded conversational RAG answer layer end-to-end

docs/adr/0004-chunking-strategy.md

@@ -93,9 +93,15 @@ in a chunk shown to a doctor or pharmacist.
    — per CLAUDE.md's provenance rule): `chunk_id`
    (`{drug_id}__{section_key}__{part_index}`), `drug_id`, `drug_name`,
    `section_key`, `section_display_name`, `atc_codes` (inherited from the
-   monograph — enables ATC-class-filtered retrieval), `source_page_range`
-   (monograph-level, see Consequences), `part_index`/`part_count` (`0`/`1`
-   for un-split sections, keeps the schema uniform across all chunks).
+   monograph — enables ATC-class-filtered retrieval), exact per-chunk
+   `source_page_range` and `printed_page_range`, `part_index`/`part_count`
+   (`0`/`1` for un-split sections, keeps the schema uniform across all chunks).
+6. **Schema v4 separates source from retrieval context.** `source_text` is the
+   exact contiguous source span and is the basis for lossless reassembly and
+   page provenance. `text` may prefix repeated route/population labels so a
+   continuation chunk is independently safe to retrieve. Those retrieval-only
+   prefixes are recorded in `context_labels` and may not alter `source_text`.
+   Token counts use `cl100k_base`, not the earlier chars/4 estimate.
 
 ## Consequences
 
@@ -116,15 +122,10 @@ in a chunk shown to a doctor or pharmacist.
   by sub-compound — a chunk from this section is tagged with the class
   name only, not the specific analogue a query might target. Deferred to
   golden-dataset-driven eval rather than guessed at now.
-- **Known gap — sub-chunk page precision**: `source_page_range` is
-  monograph-level, not sub-chunk-exact. A sub-chunk from late in a
-  multi-page section inherits the whole monograph's page range rather than
-  its own precise page, because per-line page tracking doesn't currently
-  exist in `SectionSpan`/`Heading`. The monograph + section-heading page is
-  still real, checkable provenance, but this is a known precision gap, not
-  full sub-chunk traceability. Flagged as a future improvement.
-- **Not yet built**: the Vietnamese sentence-boundary splitter itself
-  (abbreviation handling, decimal-comma handling, ATC-code-period handling)
-  is specified here as a rule, not implemented or unit-tested. Building and
-  testing it is a separate, later task (`ingestion/ingestion/chunk/`, which
-  does not exist yet).
+- **Resolved — sub-chunk page precision**: schema v4 derives exact physical
+  support from the contiguous `source_text` span and maps it to verified
+  printed folios. Missing or ambiguous support fails readiness rather than
+  falling back to monograph-level provenance.
+- **Implemented**: the sentence/label-aware splitter is in
+  `ingestion/ingestion/chunk/` with regression tests for dose continuations,
+  compound label boundaries, parent route context and lossless reassembly.