docs: capture fork-gather research and verification plan

CONTEXT.md

@@ -5,6 +5,21 @@ This context defines the core workflow runtime language used by `wf_core`,
 
 ## Language
 
+**Fork Control Claim**:
+The outstanding branch obligations carried by a fork/gather continuation in the
+proposed concurrency model; complete sibling obligations restore their parent
+claim.
+_Avoid_: Historical trace, state lineage
+
+**Referenced Fork Visit**:
+An unresolved fork occurrence on which at least one component of a control
+claim depends.
+_Avoid_: Assuming it encloses the entire claim
+
+**Enclosing Fork Visit**:
+An unresolved fork occurrence encompassing every component of a control claim.
+_Avoid_: Any fork mentioned in historical provenance
+
 **lda.chat**:
 An AI agent platform for authoring and executing workspace workflows.
 _Avoid_: Chatbot, MCP server