feat(javascript): link assignment right-hand sides to their writes (#6206)

* feat(javascript): link assignment right-hand sides to their writes

A declaration carries its value forward, but a later assignment to a
variable, a property or through a compound operator stopped the forward
trace at the right-hand-side read. The semantic IR now records one
syntactic assignment flow per simple assignment target (ranges, operator,
owning callable), and the graph projection connects each retained read
of the right-hand side to the write occurrence through a defines
relation. Compound assignments also consume the previous value of the
target; the written value itself stays unknown, keeping the boundary of
#4342 intact.

Fixes #6193

* fix(javascript): preserve computed key assignment ownership

* test(javascript): retain nested callback assignment ownership

* docs(javascript): record assignment influence verification

* test(mcp): isolate mocks and acknowledge cancellation boundaries

* test(javascript): retain CLI diagnostics and current-main verification

---------

Co-authored-by: gensokyo-dev <342580529+gensokyo-dev@users.noreply.github.com>

src/application/javascript/JavaScriptSemanticGraphProjection.ts

@@ -17,6 +17,7 @@ interface SourceInterval {
 interface CallableInterval extends SourceInterval {
   readonly callableId: string;
   readonly priority: string;
+  readonly computedKeyRange: JavaScriptSourceRange | null;
 }
 
 interface SourceIntervalTree<Interval extends SourceInterval> {
@@ -40,6 +41,7 @@ export const createSemanticCallableOwnerLookup = (
     .map((callable, order): CallableInterval => ({
       callableId: callable.callableId,
       range: callable.location,
+      computedKeyRange: callable.computedKeyLocation,
       order,
       priority: positionKey(callable.location),
     }))
@@ -65,7 +67,11 @@ export const createSemanticCallableOwnerLookup = (
       )
         continue;
       const candidate = current.entry;
-      if (javascriptSourceRangeContains(candidate.range, location)) {
+      if (
+        javascriptSourceRangeContains(candidate.range, location) &&
+        (candidate.computedKeyRange === null ||
+          !javascriptSourceRangeContains(candidate.computedKeyRange, location))
+      ) {
         const node = nodes.get(candidate.callableId);
         const rank =
           best === undefined