Document completion scope and gaps

docs/BUILD_PLAN.md

@@ -180,6 +180,14 @@ corpus-scale invariant that needs no human judgment.
 
 ---
 
+### Completion follow-up (not yet scheduled)
+
+Phase 5 completion is intentionally limited to keywords, compiler directives,
+and `#import`/`#load` module and file paths. It does not yet offer declarations,
+imported symbols, parameters, struct fields, or module-qualified members.
+Symbol-aware completion is a possible follow-up before or after Phase 6, but it
+is not currently a committed milestone.
+
 ## 5. Risks and how the plan handles them
 
 | Risk | Mitigation |