refactor(web): extract duplicated fetchJson / error handling into shared lib

[jerry609]

Problem

PR #291 introduced friendly upstream error handling in the Research components, but the implementation was copy-pasted identically into 3 files:

• web/src/components/research/ResearchDashboard.tsx
• web/src/components/research/ResearchDiscoveryPage.tsx
• web/src/components/research/ResearchPageNew.tsx

Duplicated code (3 copies each)

Item	Lines per copy	Total duplicated
type UpstreamErrorBody	4 lines	12 lines
function toFriendlyErrorMessage()	~25 lines	~75 lines
async function fetchJson<T>()	~12 lines	~36 lines

Additionally, `e instanceof Error ? e.message : String(e)` appears 47 times across the entire frontend codebase, scattered across:

• ResearchDashboard (12x), ResearchPageNew (7x), ResearchDiscoveryPage (2x)
• Settings page (5x), WorkspacePanel (11x), RunbookPanel (4x)
• ScholarSubscriptionsPanel (4x), and others

Proposed fix

1. Create web/src/lib/fetch.ts — shared module:

   export type UpstreamErrorBody = { detail?: string; error?: string }
   
   export function toFriendlyErrorMessage(status: number, rawText: string): string | null { ... }
   
   export async function fetchJson<T>(url: string, init?: RequestInit): Promise<T> { ... }
   
   export function getErrorMessage(e: unknown): string {
     return e instanceof Error ? e.message : String(e)
   }

2. Update 3 Research components to import from shared lib, delete inline copies

3. Optionally replace scattered inline error extraction with getErrorMessage(e) across all components (low priority, incremental)

Context

• web/src/lib/api.ts already has postJson<T>() but returns null on error (different contract)
• web/src/lib/dashboard-api.ts has fetchJsonOrNull<T>() — yet another variant
• Long-term consider unifying all three fetch wrappers

[Linjie-top]

Thanks for the review — I’ve refactored the implementation as suggested.

Changes:

• Added shared helper src/lib/fetch.ts:
  • UpstreamErrorBody
  • toFriendlyErrorMessage(status, rawText)
  • fetchJson<T>(url, init) with friendly upstream error mapping
  • getErrorMessage(e: unknown) for consistent error extraction
• Updated the 3 Research components to import from the shared helper and removed the inline copies:
  • ResearchPageNew (web/src/components/research/ResearchPageNew.tsx)
  • ResearchDiscoveryPage (web/src/components/research/ResearchDiscoveryPage.tsx)
  • ResearchDashboard (web/src/components/research/ResearchDashboard.tsx)
• Replaced e instanceof Error ? e.message : String(e) with getErrorMessage(e) in related Research subcomponents:
  • FeedTab, ApprovalQueuePanel, SavedTab, MemoryTab