docs(indexing): §G.5 amendment — index_modality (not modality) for retrieval-modality discriminator (#1728)

Bryce T3.2 implementation (PR #1727 follow-up commit 5325788 on
chenyexuan/celery-wave3-cutover) flagged a name collision: D10.h
already locked SearchResultMetadata.modality as the content-modality
field (Literal["text", "image"]). v3 design pack §G.5 narrative
re-used `modality` for "which retrieval modality served this hit"
(Literal["vector", "fulltext", "graph", "summary", "vision"]),
which would shadow the D10.h field.

Architect ack of Bryce's chosen disambiguation: rename the new field
to `index_modality`. D10.h `modality` (content) preserved.
SearchResultMetadata gains three new fields total: parse_version /
index_modality / index_state_per_modality. The two are orthogonal —
a hit can be (index_modality="vector", modality="text") or
(index_modality="vision", modality="image").

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: earayu

docs/modularization/indexing-redesign-design-pack.md

@@ -1085,16 +1085,18 @@ Each `SearchResultItem.metadata` carries:
 class SearchResultMetadata(BaseModel):
     # ... existing fields (chunk_id / section_path / heading_anchor etc) ...
     parse_version: Optional[str] = None       # which parse_version served this hit
-    modality: Literal["vector","fulltext","graph","summary","vision"]
+    index_modality: Optional[Literal["vector","fulltext","graph","summary","vision"]] = None
     index_state_per_modality: Optional[Dict[str, Literal["ACTIVE","FAILED","NOT_ENABLED","INDEXING"]]] = None
 ```
 
+> **Naming amendment 2026-04-27 (Bryce T3.2 implementation, msg=1a02cbcb)**: the field for "which retrieval modality produced this hit" is **`index_modality`**, not `modality`. D10.h already locked `SearchResultMetadata.modality: Optional[Literal["text", "image"]]` for **content modality** (whether the hit's content is text or an image), and the two concepts are orthogonal — a hit can be `index_modality="vector"` + `modality="text"`, or `index_modality="vision"` + `modality="image"`. The `index_` prefix disambiguates and preserves the D10.h-locked field.
+
 Clients (and the agent layer) can:
 - Detect mixed-version results in one response (different modalities show different `parse_version`)
-- Skip a modality that's currently FAILED/INDEXING
+- Skip a retrieval modality that's currently FAILED/INDEXING
 - Decide whether to wait + retry vs proceed with partial coverage
 
-Schema-wise this is a small extension of the D10.h `SearchResultMetadata` allowlist (already locked at chunk_id / section_path / heading_anchor; v2 adds `parse_version` and `index_state_per_modality`).
+Schema-wise this is a small extension of the D10.h `SearchResultMetadata` allowlist (already locked at chunk_id / section_path / heading_anchor / source / title / collection_id / document_id / asset_id / mimetype / page_idx / url / modality; v3 adds `parse_version` / `index_modality` / `index_state_per_modality`).
 
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