feat: folding-strategy migration utility (kv-stable ⇄ kv-unified)

changelog.d/folding-migration.added.md

@@ -0,0 +1 @@
+New `context-manager-migrate` CLI (and `src/migration/` library exports) for switching a store between folding strategies. `validate` dry-runs the strict kv-unified CanonicalSummaryForest against the store under each treeification policy and recommends one; `to-unified` synthesizes the initial presentation-receipt chain from the carried `autobio:resolutions` frontier (so the first kv-unified solve has a continuity baseline instead of a one-shot presentation jump), refusing to overwrite an existing chain without `--overwrite`; `to-stable` clears the receipt slot so a later flip back cannot resurrect a stale continuity anchor. Everything is dry-run unless `--apply` is passed, and the synthesized receipt's `acceptedAt` is an explicit required input so migrations are reproducible. Also: buildPicker's `[picker-config-drift]` alarm no longer fires for previewContext overrides — a mid-preview foldingStrategy swap is the caller's requested what-if, not drift.

package.json

@@ -16,6 +16,9 @@
     "dist",
     "src"
   ],
+  "bin": {
+    "context-manager-migrate": "./dist/src/migration/migrate-cli.js"
+  },
   "scripts": {
     "build": "tsc",
     "dev": "tsc --watch",

src/index.ts

@@ -30,6 +30,26 @@ export { KnowledgeStrategy } from './strategies/knowledge.js';
 export { splitMixedToolMessages, stripUnpairedToolBlocks } from './normalize-tool-messages.js';
 export { resolveEffectiveConfig } from './config-provenance.js';
 export type { ConfigLayer, ConfigResolutionSemantics, EffectiveConfigReport } from './config-provenance.js';
+export {
+  discoverAutobioNamespaces,
+  readFlavor,
+  validateStoreForKvUnified,
+  synthesizePresentation,
+  buildSyntheticChain,
+  migrateToUnified,
+  migrateToStable,
+  slotIds as migrationSlotIds,
+} from './migration/folding-migration.js';
+export type {
+  StoreFlavor,
+  TreeificationPolicy,
+  PolicyOutcome,
+  ValidateResult,
+  MigrationLeafWarning,
+  SynthesizedPresentation,
+  ToUnifiedResult,
+  ToStableResult,
+} from './migration/folding-migration.js';
 
 // Errors — cross-package behavioral surface. agent-framework gates its
 // OverBudget drain breaker on these errors (AF PR #58, framework.ts