docs: clarify cascade/restrict wording — unaffected, not removed

Ancestors remain in the diagram but receive no restrictions and are
unaffected by delete/preview. Previous wording ("excluded") was
imprecise — they're not removed from the graph, just not operated on.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: dimitri-yatsenko

src/reference/specs/diagram.md

@@ -130,7 +130,7 @@ Diagrams can propagate restrictions through the dependency graph and execute dat
 diag.cascade(table_expr, part_integrity="enforce")
 ```
 
-Apply a cascade restriction and propagate it downstream through the dependency graph. Only the seed table and its descendants are affected — ancestors of the seed table are excluded. Uses **OR** semantics at convergence — a child row is affected if *any* restricted ancestor reaches it. Designed for delete operations.
+Apply a cascade restriction and propagate it downstream through the dependency graph. Only the seed table and its descendants receive restrictions — ancestors of the seed table are unaffected by subsequent `delete()` or `preview()` calls. Uses **OR** semantics at convergence — a child row is affected if *any* restricted ancestor reaches it. Designed for delete operations.
 
 | Parameter | Type | Default | Description |
 |-----------|------|---------|-------------|
@@ -165,7 +165,7 @@ restricted = diag.cascade(Session & {'subject_id': 'M001'})
 diag.restrict(table_expr)
 ```
 
-Apply a restrict condition and propagate it downstream. Only the seed table and its descendants are affected — ancestors of the seed table are excluded. Uses **AND** semantics at convergence — a child row is included only if it satisfies *all* restricted ancestors. Designed for data subsetting and export operations.
+Apply a restrict condition and propagate it downstream. Only the seed table and its descendants receive restrictions — ancestors of the seed table are unaffected by subsequent operations. Uses **AND** semantics at convergence — a child row is included only if it satisfies *all* restricted ancestors. Designed for data subsetting and export operations.
 
 | Parameter | Type | Default | Description |
 |-----------|------|---------|-------------|