docs: publish English public documentation

docs/contracts/workspace-preprocessing-cli.md

@@ -2,6 +2,18 @@
 
 `tht` is the only supported host entrypoint for workspace preprocessing.
 
+```mermaid
+flowchart LR
+    OP["Operator"] --> INVOKE["tht workspace preprocess"]
+    INVOKE --> VALIDATE["Validate descriptor\nand paths"]
+    VALIDATE --> SOURCE["Read source and\ncurated workspace"]
+    SOURCE --> NORMALIZE["Normalize and chunk"]
+    NORMALIZE --> INDEX["Update vector and\nBM25 indexes"]
+    INDEX --> VERIFY["Verify collection\nand generation"]
+    VERIFY --> READY["Generation ready"]
+    VALIDATE -->|"invalid"| STOP["Exit with diagnostic"]
+```
+
 ## Invocation
 
 ```text
@@ -58,6 +70,20 @@ tht --installation <absolute>/thothii-installation.yaml workspace vector rebuild
   performs the guarded rebuild; rebuild state is written before deletion and the
   collection is verified after recreation. No prefix matching or global Qdrant
   mutation is performed.
+
+## Additive BM25 for Evidence
+
+- Only `workspace preprocess evidence` (and the Evidence portion of `workspace preprocess run`)
+  may add the named sparse vector `bm25` with Qdrant modifier `idf`.
+- The upgrade uses Qdrant's additive named-vector operation. It preserves the existing unnamed
+  dense vector and never deletes, renames, or rebuilds the shared collection.
+- Session readiness remains read-only with respect to BM25. Schema, Memory, and solved-question
+  records therefore continue to use their existing dense-only points during and after an Evidence
+  upgrade.
+- A missing `bm25` is added and reread before Evidence preprocessing starts. An existing definition
+  other than `modifier: idf` fails as `semantic_index_incompatible` without any collection mutation.
+  If a later Evidence candidate fails, the compatible additive schema remains in place; it does not
+  make the dense-only records unavailable.
 ```
 
 ## Curated FK annotations (P5)
@@ -92,7 +118,13 @@ tht --installation <absolute>/thothii-installation.yaml workspace vector rebuild
   before any bytes are written and no partial root is published.
 - `preprocess evidence` and `preprocess run` operate directly on the materialized root; the
   temporary `evidence_materialization_required` stop is retired (the code remains only for
-  pre-P6 compatibility). HTTP/S3 Evidence is unchanged.
+  pre-P6 compatibility). For `evidence.schema_version: 2`, runtime acquisition receives exactly
+  `curated/**/*.md`; `source/` and support files remain in the materialized tree for traceability.
+  HTTP/S3 Evidence is unchanged.
+- The curator validates Evidence before merge. Preprocessing validates the pinned curated corpus
+  again before it constructs a candidate generation, so an invalid revision is never indexed.
+- The runtime writes only its immutable materialized snapshot and derived index state. It never
+  writes, stages, commits, or pushes the workspace authoring repository.
 - Materialized roots are retained with their commit-addressed snapshot directory and removed only
   when the revision becomes unreferenced.