feat(core): resource cache phase 2 — cache.key (#123)

* chore: add changeset for resource cache key

* feat(core): resource cache phase 2 - cache.key

Adds ResourceKey type and cache.key option for resource cache keying.

- cache.key derives a resource entry key from the current load context
- One ResourceNode holds multiple internal entries, one per key
- Each entry independently tracks value, error, status, stale flag,
  staleTime timer, and in-flight promise
- ResourceRef proxies the active key entry
- cache.staleTime timers are per key
- cache.deduplicate deduplicates per active key
- Resources without cache.key behave exactly as before

Reverts .changeset/pre.json to exclude the new changeset from the
prerelease consumed list (entries in pre.json changesets are treated
as already consumed; the source of truth is the .md file itself).

* docs: replace placeholder PR number with actual PR #123 in proposal doc

* fix: replace JSON.stringify with type-tagged key serializer, fix docs API mismatch

- Replace JSON.stringify normalizeKey with encodeResourceKey (type-tagged)
- Tagged approach preserves null vs undefined vs 'null' vs 'undefined',
  NaN, Infinity, -Infinity, -0, and nested array distinctions
- Fix docs/Resources.md: key() -> cache.key() nested API
- Fix proposal doc examples to match nested API
- Add 8 new tests for key serialization edge cases
- Update PR body to remove .changeset/pre.json references

Author: mahyarmlk

.changeset/tricky-terms-doubt.md

@@ -0,0 +1,15 @@
+---
+"@intent-framework/core": patch
+---
+
+feat(core): resource cache phase 2 - cache.key
+
+Adds `ResourceKey` type and `cache.key` option for resource cache keying.
+
+- `cache.key` derives a resource entry key from the current load context
+- One ResourceNode holds multiple internal entries, one per key
+- Each entry independently tracks value, error, status, stale flag, staleTime timer, and in-flight promise
+- ResourceRef proxies the active key entry
+- cache.staleTime timers are per key
+- cache.deduplicate deduplicates per active key
+- Resources without cache.key behave exactly as before

docs/Resources.md

@@ -251,20 +251,74 @@ On failure, `error` contains the error message and `status` is `"failed"`.
 
 See the [Inspect Screen and Diagnostics Guide](Inspect-Screen.md) for more detail.
 
-## Cache options (Phase 1)
+## Cache options (Phase 1 + Phase 2)
 
 Resources support optional `cache` configuration:
 
 ```ts
 const team = $.resource("team", {
-  load: async () => loadTeam(),
+  load: async ({ route }) => loadTeam(route.params.teamId),
   cache: {
-    staleTime: 5_000,    // ms (optional, default: Infinity — no time-based stale)
-    deduplicate: true,   // boolean (optional, default: true when cache is set)
+    key: ({ route }) => route.params.teamId,  // optional, derive cache key from context
+    staleTime: 5_000,                          // ms (optional, default: Infinity)
+    deduplicate: true,                         // boolean (optional, default: true when cache is set)
   },
 })
 ```
 
+### cache.key (Phase 2)
+
+`cache.key` is an optional function that derives a cache key from the resource's load context. When set, the resource holds multiple internal entries — one per unique key — each with its own:
+
+- value
+- error
+- status (idle/pending/ready/failed)
+- stale flag
+- staleTime timer
+- in-flight promise (for deduplication)
+
+The `ResourceRef` always reflects the **active key** entry — the key from the most recent `load()` or `reload()` call.
+
+```ts
+const team = $.resource("team", {
+  cache: {
+    key: ({ route }) => route.params.teamId,
+  },
+  load: async ({ route }) => loadTeam(route.params.teamId),
+})
+
+// Navigating to /teams/abc loads with key "abc"
+await team.load({ route: { params: { teamId: "abc" } } })
+team.value // team data for "abc"
+
+// Navigating to /teams/xyz loads with key "xyz"
+await team.load({ route: { params: { teamId: "xyz" } } })
+team.value // team data for "xyz"
+
+// Back to /teams/abc — the cached entry is reused
+await team.load({ route: { params: { teamId: "abc" } } })
+team.value // team data for "abc" (reloaded)
+```
+
+Key semantics:
+
+- `ResourceKey` type: `string | number | boolean | null | undefined | ResourceKey[]`
+- Keys are normalized via a type-tagged serializer for stable map lookups — preserving distinctions between `null`, `undefined`, `"null"`, `"undefined"`, `0`, `-0`, `NaN`, `Infinity`, `-Infinity`, and nested arrays.
+- Equivalent array content (e.g. `["a", "b"]`) maps to the same entry.
+- `no-arg reload()` uses the last context, therefore reloads the last active key.
+- `invalidate()` marks only the active entry stale.
+- `cache.deduplicate` deduplicates per active key.
+- `cache.staleTime` timers are per key.
+- Resources without `cache.key` behave exactly as before (single-entry behavior).
+
+Scope limitations (Phase 2):
+
+- **Single-runtime only.** Keyed entries live in one `ResourceNode` within one `ScreenRuntime`.
+- **No `cacheTime`.** Entries persist for the node's lifetime. No time-based eviction.
+- **No SWR.** Stale data must be explicitly reloaded.
+- **No cross-navigation cache.** Disposing the runtime clears all entries.
+- **No dependency-tracked keys.** Key is derived from context at load time; automatically reacting to context changes is future work.
+
 ### staleTime
 
 `cache.staleTime` is an optional number in milliseconds. After a successful `load()` or `reload()`, a timer starts. When it fires, the resource transitions to stale automatically:
@@ -279,7 +333,8 @@ Behavior:
 - **Timer resets** on every successful `load()` or `reload()`.
 - **`invalidate()`** always marks stale immediately, regardless of `staleTime`.
 - **Failed loads** do not start a stale timer.
-- **`dispose()`** clears the stale timer and prevents late notifications.
+- **`dispose()`** clears all stale timers and prevents late notifications.
+- **With `cache.key`**, each key has an independent stale timer.
 
 ### deduplicate
 
@@ -293,23 +348,25 @@ When `false`, each call runs independently (preserving existing behavior).
 
 When `cache` is not set at all, deduplication is disabled to preserve backward compatibility. When `cache` is set, `deduplicate` defaults to `true`.
 
+**With `cache.key`:** Deduplication is per-key. Concurrent `load()` calls with the same key share one promise. Different keys each invoke the loader independently.
+
 ### Future cache options
 
 The following cache options remain as future work and are **not yet supported**:
 
-- **`cache.key`** — cache key function for parameterized resources
 - **`cacheTime`** — retention period for stale values before eviction
 - **`swr`** — stale-while-revalidate background refreshing
 - **Cross-navigation cache store** — persistent cache across screen navigations
+- **Dependency-tracked keys** — automatic key derivation and reload when context changes without explicit load/reload
 
 ## Current boundaries
 
 Resources are intentionally limited:
 
 - **No global cache.** Each runtime owns its resource nodes. There is no shared cache between runtimes.
-- **No cache keys.** Resource identity is by name within a screen. There is no key-based deduplication or caching.
-- **No `cacheTime`.** There is no time-based retention of stale values beyond `staleTime` transitions.
+- **No `cacheTime`.** There is no time-based retention of stale values beyond `staleTime` transitions. Keyed entries persist for the node's lifetime.
 - **No stale-while-revalidate (SWR).** Stale resources stay stale until explicitly reloaded.
 - **No Suspense integration.** Resources do not integrate with React Suspense or any other framework's loading boundaries.
 - **No server framework integration yet.** Resources live on screen definitions and runtimes. Server-side resource hydration is not implemented.
 - **No full concurrent multi-mount resource ref semantics.** A `ResourceRef` connects to one runtime at a time. The last runtime to start owns the ref.
+- **No dependency-tracked keys.** The `cache.key` function runs at load/reload time only. Automatically reacting to context changes is future work.

docs/proposals/Resource-Cache-And-Stale-Semantics.md

@@ -1,13 +1,13 @@
 # Resource Cache and Stale Semantics — Design Proposal
 
-**Status:** Phase 1 implemented (staleTime + deduplicate), Phase 2 designed (cache.key)  
+**Status:** Phase 1 implemented (staleTime + deduplicate), Phase 2 implemented (cache.key)  
 **Date:** 2026-06-27  
 **Author:** Big Pickle  
 **Affected package:** `@intent-framework/core`  
 **Related docs:** `docs/Resources.md`, `docs/Specification.md`
 
 > **Phase 1** (PR #119, `@intent-framework/core@0.1.0-alpha.8`): `cache.staleTime` and `cache.deduplicate`.  
-> **Phase 2 design** (this document): `cache.key` only, scoped to one runtime and one `ResourceNode`.  
+> **Phase 2** (PR #123, `@intent-framework/core@0.1.0-alpha.9`): `cache.key` only, scoped to one runtime and one `ResourceNode`.  
 > **Phase 3+**: `cacheTime`, SWR, cross-navigation cache store, dependency-tracked keys. These remain design-only until implementation begins.
 
 ---
@@ -119,7 +119,9 @@ the same cached entry. When they produce different keys, they are independent.
 
 ```ts
 const team = $.resource("team", {
-  key: ({ route }) => route.params.teamId,
+  cache: {
+    key: ({ route }) => route.params.teamId,
+  },
   load: async ({ route }) => loadTeam(route.params.teamId),
 })
 ```
@@ -432,7 +434,7 @@ type ResourceCacheOptions = {
 - No new exports from the package
 - PR #119
 
-### Phase 2 — `cache.key` (recommended next slice)
+### Phase 2 — `cache.key` (implemented)
 
 **Scope:** `cache.key` only, scoped to one runtime and one `ResourceNode`.
 
@@ -722,7 +724,7 @@ When no `key` option is provided:
 #### Migration
 
 - **No migration required** for existing resources — the `key` option is opt-in.
-- Users who want parameterized resources add `key: (ctx) => ctx.route.params.id` to their resource config.
+- Users who want parameterized resources add `cache: { key: (ctx) => ctx.route.params.id }` to their resource config.
 - Users who had workarounds (e.g., creating separate resources for each parameter) can consolidate into a single keyed resource.
 - `deduplicate` defaults to `true` when `cache` is set (already the case from Phase 1).
 
@@ -736,10 +738,10 @@ When no `key` option is provided:
 
 #### Open Questions (Deferred from Phase 2)
 
-- **Key equality function** — should we use `JSON.stringify` (fast, no deps) or a deep equality utility (more correct for complex keys like arrays/objects)? Recommendation: use `JSON.stringify` for Phase 2. Array keys are supported by the type but should be used sparingly.
+- **Key equality function** — should we use `JSON.stringify` (fast, no deps) or a deep equality utility (more correct for complex keys like arrays/objects)? Recommendation: use `JSON.stringify` with a type-tagged encoder for Phase 2 (see `encodeResourceKey`). This preserves distinctions between `null`, `undefined`, `NaN`, `Infinity`, `-0`, and nested arrays. Array keys are supported by the type but should be used sparingly.
 - **Active key change without explicit load** — should the key be reactive (automatically reload when route params change)? This is dependency-tracked keys (Phase 6+). Phase 2 requires an explicit `load()`/`reload()` call to change the active key.
 - **Entry eviction policy** — without `cacheTime`, entries accumulate in the map indefinitely. For Phase 2 this is acceptable (the node is disposed when the runtime is disposed). Future phases should add LRU or time-based eviction.
-- **`cache.key` as a top-level config property vs nested under `cache`** — the existing convention nests under `cache`. Phase 2 follows this convention for consistency. This can be revisited if the team prefers flat.
+- **`cache.key` as a top-level config property vs nested under `cache`** — the existing convention nests under `cache`. Phase 2 follows this convention for consistency. The nested API is the approved design.
 - **Key type validation** — `ResourceKey` allows `string | number | boolean | null | undefined | ResourceKey[]`. Should we restrict further (e.g., disallow arrays in Phase 2)? Recommendation: keep the union type but document that string keys are preferred.
 
 ---
@@ -861,7 +863,12 @@ No changeset is needed for this proposal — it is design-only.
 - `cache.deduplicate` — in-flight load deduplication
 - Resources without `cache` options behave exactly as before
 
-### Phase 2 (next implementation — `cache.key`)
+### Phase 2 (implemented in `@intent-framework/core@0.1.0-alpha.9`)
+
+- `cache.key` — per-key resource entries within a single ResourceNode
+- Per-key value, status, error, stale flag, staleTime timer, and in-flight promise
+- ResourceRef proxies the active key entry
+- Non-keyed resources preserve backward compatibility
 
 | Aspect | Decision |
 |--------|----------|