feat(core): implement resource cache phase 1 - staleTime and deduplicate

[mahyarmlk]

Summary

Implement resource cache semantics phase 1: cache.staleTime and cache.deduplicate.

API

const team = $.resource("team", {
  cache: {
    staleTime: 5_000,
    deduplicate: true,
  },
  load: async () => loadTeam(),
})

Behavior

cache.staleTime: After a successful load/reload, a timer starts. When it fires, the resource becomes stale — stale condition fires, status stays "ready", value stays available. Resets on every successful load/reload. Failed loads do not start the timer. dispose() clears the timer.

cache.deduplicate: When true (default when cache is set), concurrent load()/reload() calls while a load is pending share a single in-flight promise. Only one loader invocation runs. When false, preserves current independent concurrent behavior. Resources without cache options are unaffected.

Changed files

• packages/core/src/resource.ts — new ResourceCacheOptions type, cache on ResourceConfig, dispose on ResourceNode, staleTime/deduplicate logic
• packages/core/src/screen.ts — builder accepts cache option
• packages/core/src/runtime.ts — passes cache to createResourceNode, calls node.dispose()
• packages/core/src/index.ts — export ResourceCacheOptions
• packages/core/src/core.test.ts — 13 new tests covering staleTime, deduplicate, error/dispose edge cases
• docs/Resources.md — cache options section with phase-1 docs and future-work callout
• docs/proposals/Resource-Cache-And-Stale-Semantics.md — implementation status notes
• .changeset/seven-cobras-tan.md — patch changeset for core

Validation

• pnpm --filter @intent-framework/core test ✅ (174 pass)
• pnpm test ✅ (384 pass across all packages)
• pnpm typecheck ✅
• pnpm build ✅
• pnpm lint ✅
• pnpm pack:check ✅
• pnpm changeset status ✅

Not implemented (still future)

• cache.key
• cacheTime
• swr
• Cross-navigation cache store
• Streaming, SSR, optimistic updates