fix: honest index readiness — no silently-empty queries on a cold index

Closes the "dishonest readiness proxy" anti-pattern (Pattern A): size()>0 /
isInitialized were treated as "this index serves queries", but a cold native
index can load its COUNT before its SERVING structure, so a query returned a
silent [] indistinguishable from "no such data". A shared assessIndexReadiness()
now reads only the provider's honest isReady() signal (never size()), applied at
every site:

- Vector: a one-shot verifyVectorLive() guard on the semantic/proximity search
  path (a pure semantic find({query}) has no filter, so nothing guarded it). It
  prefers isReady(), else a known-vector self-match probe; self-heals via rebuild
  or throws the new VectorIndexNotReadyError instead of a silent [].
- Graph: getVerbsBySource/ByTarget skip the fast path when the provider reports
  not-ready (falling to the canonical shard scan), plus a one-shot probe that
  self-heals a no-isReady provider whose adjacency did not cold-load.
- getIndexStatus(): folds in per-index honest `ready` (making `populated`
  honest) + rebuildFailed/rebuildError/degradedIds, so a readiness probe never
  200s a brain that is still warming up or degraded.

Unblocked by the native providers now reporting serving-truth (graph via
SSTable-residency readiness, vector via durableBaseLoadFailed). New export:
VectorIndexNotReadyError. getIndexStatus gains additive fields. No breaking API.
13 new tests; existing readiness guards green.

tests/unit/graph/graph-fastpath-honest-readiness.test.ts

@@ -0,0 +1,95 @@
+/**
+ * @module tests/unit/graph/graph-fastpath-honest-readiness
+ * @description Pattern-A / Finding 2: getVerbsBySource/ByTarget gated the graph
+ * fast path on `graphIndex.isInitialized` (a proxy that reads true once the
+ * manifest/count loaded even if the source→target adjacency did NOT → the fast
+ * path then returned a silent []). The honest gate skips the fast path when the
+ * provider reports isReady()===false, falling to the correct canonical shard
+ * scan; and a one-shot probe self-heals a no-isReady provider whose adjacency
+ * did not cold-load.
+ */
+import { describe, it, expect, beforeEach } from 'vitest'
+import { Brainy, NounType, VerbType } from '../../../src/index.js'
+
+describe('graph fast-path honest readiness (Finding 2)', () => {
+  let brain: any
+  let storage: any
+  let a: string
+  let b: string
+  let c: string
+
+  beforeEach(async () => {
+    process.env.BRAINY_DETERMINISTIC_EMBEDDINGS = 'true'
+    brain = new Brainy({ requireSubtype: false, storage: { type: 'memory' }, dimensions: 384 })
+    await brain.init()
+    a = await brain.add({ data: 'a', type: NounType.Concept })
+    b = await brain.add({ data: 'b', type: NounType.Concept })
+    c = await brain.add({ data: 'c', type: NounType.Concept })
+    await brain.relate({ from: a, to: b, type: VerbType.Contains })
+    await brain.relate({ from: a, to: c, type: VerbType.Contains })
+    await brain.flush()
+    storage = brain.storage
+    // Warm + wire the storage graph index (lazy) so we can stub it.
+    await storage.getVerbsBySource(a)
+  })
+
+  it('not-ready provider → shard scan returns the REAL edges, not a silent []', async () => {
+    const gi = storage.graphIndex
+    // Simulate a cold native provider: count/manifest loaded (isInitialized) but
+    // the source→target adjacency is NOT (isReady false; fast-path lookup empty).
+    gi.isReady = () => false
+    const origBySource = gi.getVerbIdsBySource.bind(gi)
+    gi.getVerbIdsBySource = async () => [] // cold adjacency — old fast path trusted this
+    storage._graphFastPathProbed = true // isolate the GATE (probe skips isReady-capable anyway)
+    try {
+      const verbs = await storage.getVerbsBySource(a)
+      // Honest gate skipped the cold fast path → canonical shard scan → real edges.
+      expect(verbs.length).toBe(2)
+    } finally {
+      delete gi.isReady
+      gi.getVerbIdsBySource = origBySource
+    }
+  })
+
+  it('ready provider → fast path is used and an empty result is trusted', async () => {
+    const gi = storage.graphIndex
+    gi.isReady = () => true
+    let fastPathCalls = 0
+    const origBySource = gi.getVerbIdsBySource.bind(gi)
+    gi.getVerbIdsBySource = async (...args: any[]) => { fastPathCalls++; return origBySource(...args) }
+    storage._graphFastPathProbed = true
+    try {
+      // `c` has no OUTGOING edges — a genuinely empty result via the fast path.
+      const verbs = await storage.getVerbsBySource(c)
+      expect(verbs).toEqual([])
+      expect(fastPathCalls).toBeGreaterThan(0) // fast path was taken, not a shard scan
+    } finally {
+      delete gi.isReady
+      gi.getVerbIdsBySource = origBySource
+    }
+  })
+
+  it('no-isReady provider whose adjacency did not cold-load → probe rebuilds once', async () => {
+    const gi = storage.graphIndex
+    if ('isReady' in gi) delete gi.isReady // force the "unknown" (no honest signal) path
+    // Force the probe to see a cold adjacency: a known edge resolves to no ints.
+    const origBySource = gi.getVerbIdsBySource.bind(gi)
+    let cold = true
+    gi.getVerbIdsBySource = async (...args: any[]) => (cold ? [] : origBySource(...args))
+    let rebuilds = 0
+    const origRebuild = gi.rebuild.bind(gi)
+    gi.rebuild = async (...args: any[]) => { rebuilds++; cold = false; return origRebuild(...args) }
+    storage._graphFastPathProbed = false // re-arm the one-shot probe
+    try {
+      await storage.getVerbsBySource(a)
+      expect(rebuilds).toBe(1)                    // probe detected cold adjacency + rebuilt once
+      expect(storage._graphFastPathProbed).toBe(true) // latched — no second rebuild
+      rebuilds = 0
+      await storage.getVerbsByTarget(b)
+      expect(rebuilds).toBe(0)                    // probe does not re-run
+    } finally {
+      gi.getVerbIdsBySource = origBySource
+      gi.rebuild = origRebuild
+    }
+  })
+})