fix: clear() wipes the full native/derived footprint, not a subset

clear() removed entities, indexes, system and _cas but left three top-level
trees on disk: _blobs (raw HNSW/LSM segment bytes and the native dkann index),
_id_mapper (the native shared mmap id-mapper), and _column_index (column-store
manifests). A cleared brain therefore re-read stale native state.

Worse, the column store splits its state across two of those trees — manifests
under _column_index/ and their segment bytes under _blobs/_column_index/ — so
removing one without the other stranded a manifest listing segments that no
longer exist, which the hardened segment-load path now (correctly) refuses with
ColumnSegmentLoadError. The three trees now fall together as a set, exactly as
_cas already does. locks/ is deliberately preserved: it is live coordination
state, not data.

tests/unit/storage/clear-native-footprint.test.ts

@@ -0,0 +1,74 @@
+/**
+ * @module tests/unit/storage/clear-native-footprint
+ * @description clear() must remove the COMPLETE derived/native on-disk footprint
+ * (finding 7). Before the fix it wiped only entities/indexes/system/_cas and left
+ * three top-level trees behind:
+ *   - `_blobs`        raw binary blobs (HNSW/LSM segments, the native dkann index,
+ *                     and column-store segment bytes under `_blobs/_column_index/`)
+ *   - `_id_mapper`    the native shared mmap id-mapper
+ *   - `_column_index` the column-store MANIFEST.json files
+ * A cleared brain therefore re-read stale native state, and — worst — an orphaned
+ * column manifest whose segment bytes had been removed with `_blobs`, which the
+ * hardened load path now refuses with ColumnSegmentLoadError. The three must fall
+ * together as a set.
+ */
+import { describe, it, expect, beforeEach, afterEach } from 'vitest'
+import * as fs from 'node:fs'
+import * as os from 'node:os'
+import * as path from 'node:path'
+import { FileSystemStorage } from '../../../src/storage/adapters/fileSystemStorage.js'
+
+const exists = (p: string): boolean => fs.existsSync(p)
+
+describe('FileSystemStorage.clear() wipes the full native/derived footprint (finding 7)', () => {
+  let dir: string
+  let storage: any
+
+  beforeEach(async () => {
+    dir = fs.mkdtempSync(path.join(os.tmpdir(), 'brainy-clear-footprint-'))
+    storage = new FileSystemStorage(dir)
+    await storage.init()
+  })
+
+  afterEach(() => {
+    fs.rmSync(dir, { recursive: true, force: true })
+  })
+
+  it('removes _blobs, _id_mapper and _column_index (previously left stranded)', async () => {
+    // A raw blob (this is how HNSW/LSM/column segments persist) → creates _blobs.
+    await storage.saveBinaryBlob('graph-lsm/source/sstable-1', Buffer.from([1, 2, 3, 4]))
+    // A column segment blob lives UNDER _blobs/_column_index/...
+    await storage.saveBinaryBlob('_column_index/createdAt/L0-000000', Buffer.from([5, 6, 7, 8]))
+
+    // Simulate the native id-mapper mmap dir and the column manifest object-tree.
+    const idMapperDir = path.join(dir, '_id_mapper')
+    fs.mkdirSync(idMapperDir, { recursive: true })
+    fs.writeFileSync(path.join(idMapperDir, 'main.slotmap'), Buffer.from([0, 1]))
+    const colDir = path.join(dir, '_column_index', 'createdAt')
+    fs.mkdirSync(colDir, { recursive: true })
+    fs.writeFileSync(
+      path.join(colDir, 'MANIFEST.json'),
+      JSON.stringify({ segments: [{ id: 0, level: 0, count: 1 }] })
+    )
+
+    // Sanity: everything is present before the clear.
+    expect(exists(path.join(dir, '_blobs'))).toBe(true)
+    expect(exists(idMapperDir)).toBe(true)
+    expect(exists(path.join(dir, '_column_index'))).toBe(true)
+
+    await storage.clear()
+
+    // The complete derived footprint is gone — no stale native state, and no
+    // orphaned column manifest pointing at removed segment bytes.
+    expect(exists(path.join(dir, '_blobs'))).toBe(false)
+    expect(exists(idMapperDir)).toBe(false)
+    expect(exists(path.join(dir, '_column_index'))).toBe(false)
+  })
+
+  it('clear() is a no-op-safe when the native dirs never existed', async () => {
+    // Fresh store, no blobs written — clear must not throw on absent dirs.
+    await expect(storage.clear()).resolves.toBeUndefined()
+    expect(exists(path.join(dir, '_blobs'))).toBe(false)
+    expect(exists(path.join(dir, '_column_index'))).toBe(false)
+  })
+})