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

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

docs/javascript-application-workflows.md

@@ -197,6 +197,14 @@ registrations/removals and dispatch, Node timers and cancellation handles, async
 `node:child_process` creation and ownership, configuration sources and direct
 defaults, request construction and response consumers, parse/coercion/
 validation boundaries, and built-in resource acquisition/release.
+Reassignments connect retained right-hand reads to the binding or property
+write. Compound assignments also retain the previous-value input; logical
+assignments keep conditional inputs as candidates. These edges describe
+influence without evaluating arithmetic or establishing execution order or the
+resulting value. Deferred callback bodies do not become inputs to the enclosing
+assignment. Computed method keys belong to the enclosing callable; parameter
+defaults and method bodies belong to the method. Uncertain later property reads
+remain opt-in through `include_ambiguous_dynamic_edges`.
 Global timer, `fetch`, `WebSocket`, `JSON.parse`, and coercion calls receive
 these built-in effects only when the file has no visible possible write to that
 global, including a computed write through a global object. The check does not