feat: P4 qdrant collection lifecycle (self-heal + guarded rebuild)

- shared TS collection manager: self-heal creates missing collection (1024/cosine)
  and missing keyword payload indexes; never mutates incompatible contracts
  (semantic_index_incompatible); async index visibility polled with bounded deadline
- session admission (qdrantEnsure) uses the manager in self-heal mode; operator path
  keeps require_existing semantics
- runtime lease exposes semanticQdrantUrl to the operator
- operator commands vector-inspect/vector-rebuild with exact confirmation guards
- thothctl workspace vector inspect|rebuild (Go) with --collection/--confirm/--destroy
- p4 acceptance runner: real Qdrant (v1.18.2) lifecycle checks, 11/11 PASS
- docs: CLI contract, manual walkthrough P4 (PENDING), PROJECT_STATE

backend/src/workspaces/preprocessing-service.ts

@@ -125,6 +125,38 @@ function noEvidenceWarning(workspace: WorkspaceDescriptor): string[] {
 export class WorkspacePreprocessingService {
   constructor(private readonly deps: WorkspacePreprocessingServiceDeps) {}
 
+
+  async vectorInspect(options: { workspaceId: string }): Promise<WorkspaceOperationResult> {
+    const runtime = await this.deps.acquireActiveRuntime(options.workspaceId);
+    const collection = runtime.workspace.semantic_index.vector_store.collection;
+    const res = await fetch(`${runtime.configLease.semanticQdrantUrl}/collections/${encodeURIComponent(collection)}`, { method: "GET" });
+    if (!res.ok) return baseResult(runtime, "vector inspect", "failed", "semantic_index_incompatible", { warnings: ["collection unavailable"] });
+    const body = await res.json() as any;
+    const info = body?.result;
+    const vectors = info?.config?.params?.vectors;
+    return baseResult(runtime, "vector inspect", "succeeded", "ok", {
+      counts: { dimensions: vectors?.size ?? 0 },
+      warnings: [`collection=${collection} distance=${vectors?.distance ?? "unknown"}`],
+    });
+  }
+
+  async vectorRebuild(options: { workspaceId: string; collection?: string; confirm?: string; destroy?: boolean }): Promise<WorkspaceOperationResult> {
+    const runtime = await this.deps.acquireActiveRuntime(options.workspaceId);
+    const collection = runtime.workspace.semantic_index.vector_store.collection;
+    if (options.collection !== collection || options.confirm !== collection || options.destroy !== true) {
+      return baseResult(runtime, "vector rebuild", "failed", "semantic_index_incompatible", { warnings: ["rebuild requires exact confirmation and --destroy"] });
+    }
+    const q = `${runtime.configLease.semanticQdrantUrl}/collections/${encodeURIComponent(collection)}`;
+    const del = await fetch(q, { method: "DELETE" });
+    if (!del.ok && del.status !== 404) return baseResult(runtime, "vector rebuild", "failed", "semantic_index_incompatible", { warnings: ["collection delete failed"] });
+    const put = await fetch(q, {
+      method: "PUT",
+      headers: { "content-type": "application/json" },
+      body: JSON.stringify({ vectors: { size: runtime.workspace.semantic_index.vector_store.dimensions, distance: runtime.workspace.semantic_index.vector_store.distance } }),
+    });
+    if (!put.ok) return baseResult(runtime, "vector rebuild", "failed", "semantic_index_incompatible", { warnings: ["collection recreate failed"] });
+    return baseResult(runtime, "vector rebuild", "succeeded", "ok", { warnings: [`recreated collection=${collection}`] });
+  }
   async inspect(options: { workspaceId: string }): Promise<WorkspaceOperationResult> {
     try {
       const runtime = await this.deps.acquireActiveRuntime(options.workspaceId);