Document evidence context source unit excerpts

docs/consumers/subprocess.md

@@ -55,10 +55,10 @@ contract. The JSON bundle contract links to the available lane contracts.
 If `index.json` has an `evidence_context` descriptor, treat it as a
 pipeline-wide artifact rather than a lane entry. Verify its six descriptor
 fields before decoding the linked file according to the [Published Evidence
-Context contract](../integrations/evidence-context.md). Use each
-`evidence_refs` entry as the citation to source material. Its surrounding
-context range and included units explain the citation, but do not widen or
-replace the cited source reference.
+Context contract](../integrations/evidence-context.md). Decode its top-level
+source-unit array as a reading excerpt. Obtain authoritative citations and lane
+provenance from the normalized lane artifacts; the excerpt has neither and its
+nearby units do not widen a lane artifact's cited source reference.
 
 A zero exit status may still report rejected outputs, warnings, or absent
 lanes. The caller decides which lane IDs are required for its own work and
@@ -73,5 +73,5 @@ them. Treat the input, output bundle, cache, debug bundle, and captured process
 logs as potentially sensitive data. Apply the caller's access controls and
 retention policy, and avoid copying secrets into arguments, logs, or
 provenance records. An evidence-context artifact contains source-unit text and
-metadata, and selected lanes can cover most of an input; preserve and share it
-only when that source content is authorized for the recipient.
+metadata and can cover most of an input; preserve and share it only when that
+source content is authorized for the recipient.