[app-bug] Regression test: dashboard CallGraph silently renders empty when extractCallGraph shape changes

[Gbangbolaoluwagbemiga]

Problem

On 2026-05-20 the dashboard was silently rendering an empty call graph for valid reports. Root cause: the destructuring in frontend/app/dashboard/page.tsx expected { callGraphNodes, callGraphEdges } but extractCallGraph() returns { nodes, edges }. The bug only surfaced when a stricter ReturnType<> annotation was added; nothing in CI would have caught the silent-empty case.

Acceptance Criteria

• Add a unit test under frontend/app/dashboard/ that calls the memo's logic with a known report and asserts non-empty nodes and edges
• Add a Playwright spec that loads a known JSON report and asserts at least one SVG node renders in the call-graph viewer
• Bonus: a TypeScript-level guard so the destructuring shape is statically enforced (e.g. extract the memo body into a named function with a return type alias)

Pointers

• frontend/app/dashboard/page.tsx
• frontend/app/lib/transform.ts:341 (extractCallGraph)
• frontend/app/components/CallGraph.tsx

Difficulty

Easy. Two short tests.