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/JavaScriptSemanticGraphBuilder.ts

@@ -34,6 +34,7 @@ import {
   projectSemanticRequests,
 } from "./JavaScriptSemanticGraphDataProjection.js";
 import { projectSemanticResources } from "./JavaScriptSemanticGraphResourceProjection.js";
+import { projectSemanticAssignments } from "./JavaScriptSemanticGraphAssignmentProjection.js";
 import { projectSemanticObjects } from "./JavaScriptSemanticGraphObjectProjection.js";
 import { projectSemanticValues } from "./JavaScriptSemanticGraphValueProjection.js";
 import {
@@ -712,6 +713,8 @@ function* projectFileSteps(
     returnSiteNodes,
     argumentNodes: new Map(),
     referenceNodes: [],
+    readNodes: [],
+    writeNodes: [],
     callResolutions: new Map(
       ir.callSites.map((call) => [
         call.callSiteId,
@@ -858,7 +861,11 @@ function* projectDefinitionsAndReferences(
       reference.bindingId === null
         ? undefined
         : context.bindingNodes.get(reference.bindingId);
-    if (expression !== null) context.referenceNodes.push(expression);
+    if (expression !== null) {
+      context.referenceNodes.push(expression);
+      if (reference.role === "read") context.readNodes.push(expression);
+      if (reference.role === "write") context.writeNodes.push(expression);
+    }
     if (binding === undefined || expression === null) continue;
     if (reference.role === "read")
       addRelation(context.state, {
@@ -977,6 +984,7 @@ const FILE_PROJECTION_PASSES: readonly ((
 ) => Iterator<void, void> | void)[] = [
   projectSemanticValues,
   projectSemanticObjects,
+  projectSemanticAssignments,
   projectCalls,
   projectSemanticPromises,
   projectSemanticEvents,