diff --git a/.claude-plugin/marketplace.json b/.claude-plugin/marketplace.json
index 6edb337..2cffd56 100644
--- a/.claude-plugin/marketplace.json
+++ b/.claude-plugin/marketplace.json
@@ -12,7 +12,7 @@
     {
       "name": "ace",
       "source": "./",
-      "version": "0.13.278",
+      "version": "0.13.279",
       "description": "AI Connect Engine — orchestrates the CRISPR-Connect lifecycle from idea through app building, Connect setup, LLO management, and closeout"
     }
   ]
diff --git a/.claude-plugin/plugin.json b/.claude-plugin/plugin.json
index 47b1b7a..68565c1 100644
--- a/.claude-plugin/plugin.json
+++ b/.claude-plugin/plugin.json
@@ -1,6 +1,6 @@
 {
   "name": "ace",
-  "version": "0.13.278",
+  "version": "0.13.279",
   "description": "AI Connect Engine — orchestrates the CRISPR-Connect lifecycle from idea through app building, Connect setup, LLO management, and closeout",
   "author": {
     "name": "Jonathan Jackson",
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 49c8b83..db3c897 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,23 @@ All notable changes to the ACE plugin will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and the plugin follows [semantic versioning](https://semver.org/spec/v2.0.0.html).
 
+## 0.13.279 — 2026-05-19
+
+**New `ocs_get_chatbot_pipeline_id` atom — closes last orphan-storage class on OCS sweep.**
+
+Before this PR, `/ace:sweep ocs` could delete an orphan chatbot but had no way to discover its paired Pipeline row's id. The existing `PlaywrightBackend.pipelineIdFor` method (used internally by `cloneChatbot` + the pipeline-patch atoms) already scrapes the pipeline-builder HTML — but it wasn't exposed as an MCP atom, so sweep skills couldn't call it. Result: every chatbot delete left a zombie Pipeline row (`is_archived=False`, no parent chatbot in the live listing). Surfaced live in the 2026-05-18 OCS sweep that cleaned up 9 orphan chatbots + 12 collections but had to skip all 10 paired pipelines.
+
+Fix: thin one-line wrapper exposing the existing internal method.
+
+- `mcp/ocs/client.ts` — new `getChatbotPipelineId({ experiment_id }) → { pipeline_id }` capability.
+- `mcp/ocs/backends/composite.ts` — delegates to `playwright.pipelineIdFor(experiment_id)`.
+- `mcp/ocs/capability-map.ts` — new `get_chatbot_pipeline_id` entry routed to Playwright with `restTarget` noted as "pipeline_id field not yet exposed in REST schema" (lock-step swap if OCS adds it upstream).
+- `mcp/ocs-server.ts` — registers the new `ocs_get_chatbot_pipeline_id` tool. Description explains the use case (sweep wiring) and the OCS-side gap (REST schema omits pipeline_id).
+- `skills/sweep-ocs/SKILL.md § Process` — step 3 now calls `ocs_get_chatbot_pipeline_id` per chatbot; step 9 explicitly warns against skipping the pipeline delete.
+- `test/mcp/ocs/composite.test.ts` — new case asserts the composite routes `getChatbotPipelineId` to `pipelineIdFor` and wraps the integer in `{ pipeline_id }`. 9/9 tests pass.
+
+The 10 zombie pipelines from the 2026-05-18 sweep (chatbots 11839, 11994, 11996, 12000, 12003, 12018, 12042, 12050, 12101 + historical 12027 versions v2-v11) can be cleaned up in a follow-up sweep with the new atom in place.
+
 ## 0.13.277 — 2026-05-18
 
 **Mirror Vellum's slug/name separation in the Nova architect brief (follow-up to 0.13.274).**
diff --git a/VERSION b/VERSION
index cbeec60..2054863 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-0.13.278
+0.13.279
diff --git a/mcp/ocs-server.ts b/mcp/ocs-server.ts
index 8084515..befb72f 100644
--- a/mcp/ocs-server.ts
+++ b/mcp/ocs-server.ts
@@ -359,6 +359,13 @@ server.tool(
   async (args) => result(await composite.deleteChatbot(args)),
 );
 
+server.tool(
+  'ocs_get_chatbot_pipeline_id',
+  'Resolve an experiment_id (integer chatbot id) to its working-version pipeline_id (integer). The OCS REST `/api/experiments/<id>/` response omits pipeline_id by design; this atom scrapes it from the pipeline-builder HTML (`SiteJS.pipeline.renderPipeline("#pipelineBuilder", "<team>", <pipeline_id>)`) via Playwright and caches the result per experiment_id. Used by /ace:sweep ocs to pair each orphan chatbot with its per-opp Pipeline row before deletion — without this, deleting an orphan chatbot leaves its Pipeline as a zombie row on the team (is_archived=False, no parent chatbot in the live listing). Returns `{ pipeline_id: number }`.',
+  { experiment_id: z.number().int() },
+  async (args) => result(await composite.getChatbotPipelineId(args)),
+);
+
 server.tool(
   'ocs_delete_pipeline',
   'Delete a pipeline (sets is_archived=True server-side). SAFE PER-OPP: when ACE clones a chatbot, Pipeline.create_new_version(is_copy=True) deep-clones the Pipeline row + its nodes — each clone has its own pipeline. Deleting the pipeline does NOT cascade-delete its referenced Collections — those need separate ocs_delete_collection calls. Routes through Playwright to /a/<team>/pipelines/<pk>/delete/ (HTTP DELETE method on Django View.delete(); returns 200 empty body).',
diff --git a/mcp/ocs/backends/composite.ts b/mcp/ocs/backends/composite.ts
index fbfd34d..597c59f 100644
--- a/mcp/ocs/backends/composite.ts
+++ b/mcp/ocs/backends/composite.ts
@@ -33,6 +33,9 @@ export class CompositeBackend implements OcsClient {
   publishChatbotVersion = (a: Parameters<OcsClient['publishChatbotVersion']>[0]) => this.opts.playwright.publishChatbotVersion(a);
   getChatbotEmbedInfo = (a: Parameters<OcsClient['getChatbotEmbedInfo']>[0]) => this.opts.playwright.getChatbotEmbedInfo(a);
   deleteChatbot = (a: Parameters<OcsClient['deleteChatbot']>[0]) => this.opts.playwright.deleteChatbot(a);
+  getChatbotPipelineId = async (a: Parameters<OcsClient['getChatbotPipelineId']>[0]) => ({
+    pipeline_id: await this.opts.playwright.pipelineIdFor(a.experiment_id),
+  });
   deletePipeline = (a: Parameters<OcsClient['deletePipeline']>[0]) => this.opts.playwright.deletePipeline(a);
   deleteCollection = (a: Parameters<OcsClient['deleteCollection']>[0]) => this.opts.playwright.deleteCollection(a);
 
diff --git a/mcp/ocs/capability-map.ts b/mcp/ocs/capability-map.ts
index c485175..d373493 100644
--- a/mcp/ocs/capability-map.ts
+++ b/mcp/ocs/capability-map.ts
@@ -19,6 +19,7 @@ export type Capability =
   | 'publish_chatbot_version'
   | 'get_chatbot_embed_info'
   | 'delete_chatbot'
+  | 'get_chatbot_pipeline_id'
   | 'delete_pipeline'
   | 'delete_collection'
   // Observation (12)
@@ -49,6 +50,7 @@ export const CAPABILITY_MAP: Record<Capability, CapabilityRoute> = {
   publish_chatbot_version:      { backend: 'PLAYWRIGHT', restTarget: 'POST /api/experiments/{id}/versions/' },
   get_chatbot_embed_info:       { backend: 'HYBRID',     restTarget: 'GET /api/experiments/{id}/embed/' },
   delete_chatbot:               { backend: 'PLAYWRIGHT', restTarget: 'DELETE /api/experiments/{id}/ (not yet shipped)' },
+  get_chatbot_pipeline_id:      { backend: 'PLAYWRIGHT', restTarget: 'GET /api/experiments/{id}/ (pipeline_id field not yet exposed in REST schema)' },
   delete_pipeline:              { backend: 'PLAYWRIGHT', restTarget: 'DELETE /api/pipelines/{id}/ (not yet shipped)' },
   delete_collection:            { backend: 'PLAYWRIGHT', restTarget: 'DELETE /api/collections/{id}/ (not yet shipped)' },
 
diff --git a/mcp/ocs/client.ts b/mcp/ocs/client.ts
index 31ca536..7c0067c 100644
--- a/mcp/ocs/client.ts
+++ b/mcp/ocs/client.ts
@@ -116,6 +116,21 @@ export interface OcsClient {
    */
   deleteChatbot(args: { experiment_id: number }): Promise<{ deleted: number }>;
 
+  /**
+   * Resolve an experiment_id (integer chatbot id) to its working-version
+   * pipeline_id (integer). Required by `/ace:sweep ocs` to pair each orphan
+   * chatbot with its per-opp Pipeline row before deletion — without this,
+   * deleting an orphan chatbot leaves its Pipeline as a zombie row on the
+   * team (`is_archived=False`, no parent chatbot in the live listing).
+   *
+   * OCS's REST `/api/experiments/<id>/` response intentionally omits
+   * `pipeline_id`; the value is rendered inline in the pipeline-builder
+   * HTML page as `SiteJS.pipeline.renderPipeline("#pipelineBuilder", ...,
+   * <pipeline_id>)`. This atom scrapes that page (Playwright-backed) and
+   * caches the result per experiment_id.
+   */
+  getChatbotPipelineId(args: { experiment_id: number }): Promise<{ pipeline_id: number }>;
+
   /**
    * Delete a pipeline by integer id. Sets `is_archived=True` on the Pipeline
    * row server-side. Each clone gets its own Pipeline (verified 2026-05-15:
diff --git a/package-lock.json b/package-lock.json
index e22116a..a2caa1f 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "ace",
-  "version": "0.13.276",
+  "version": "0.13.279",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "ace",
-      "version": "0.13.276",
+      "version": "0.13.279",
       "license": "ISC",
       "dependencies": {
         "@anthropic-ai/sdk": "^0.94.0",
diff --git a/package.json b/package.json
index f49bd23..2921a85 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "ace",
-  "version": "0.13.278",
+  "version": "0.13.279",
   "description": "AI Connect Engine - orchestrator for building Connect Opps using AI",
   "type": "module",
   "scripts": {
diff --git a/skills/sweep-ocs/SKILL.md b/skills/sweep-ocs/SKILL.md
index ffaae57..9e07954 100644
--- a/skills/sweep-ocs/SKILL.md
+++ b/skills/sweep-ocs/SKILL.md
@@ -52,7 +52,7 @@ No dedup at the file or vector layer means uploading the same PDD into 19 per-op
 3. **List OCS inventory** using existing atoms:
    - `ocs_list_chatbots` (paginate as needed)
    - `ocs_list_sessions` (filter to `OCS_TEAM_SLUG`; last 90 days by default).
-   - For each chatbot, derive its pipeline id and per-opp collection ids from the chatbot's published version description / pipeline definition. The chatbot's most-recent version description embeds the per-opp collection id explicitly (e.g. "shared Connect collection 350 + new per-run collection 418"). Parse it; cross-check by reading the pipeline's LLM node params for collection refs.
+   - For each chatbot, derive its pipeline_id via `ocs_get_chatbot_pipeline_id({ experiment_id })` (added 0.13.277 — scrapes the pipeline-builder HTML; cached). Per-opp collection ids come from the chatbot's most-recent published version description (e.g. "shared Connect collection 350 + new per-run collection 418"); cross-check against the pipeline's LLM node params via the pipeline-builder page if the description is thin.
 4. **Diff** each item's id against the live-set:
    - chatbots → `liveSet.identifiers.ocsChatbotIds` (now includes golden template).
    - sessions → `liveSet.identifiers.ocsSessionIds`.
@@ -67,7 +67,7 @@ No dedup at the file or vector layer means uploading the same PDD into 19 per-op
 8. **Surface to human** in chat. Prompt for approval per actionable chunk.
 9. **On approval (in order, per orphan chatbot):**
    - Call `ocs_delete_chatbot({ experiment_id })`.
-   - Call `ocs_delete_pipeline({ pipeline_id })` for the paired pipeline.
+   - Call `ocs_delete_pipeline({ pipeline_id })` for the paired pipeline (resolved via `ocs_get_chatbot_pipeline_id` in step 3 — never skip this; pipeline deletes are the only way to clear the per-opp Pipeline row).
    - For each per-opp collection_id derived in step 3, call `ocs_delete_collection({ collection_id })` — but ONLY if collection_id ≠ `OCS_SHARED_COLLECTION_ID`. The atom itself doesn't enforce this; the skill must filter.
    - For each approved orphan session, call `ocs_end_session`.
 
diff --git a/test/mcp/ocs/composite.test.ts b/test/mcp/ocs/composite.test.ts
index 2b0b6bd..00cf93c 100644
--- a/test/mcp/ocs/composite.test.ts
+++ b/test/mcp/ocs/composite.test.ts
@@ -25,4 +25,13 @@ describe('CompositeBackend routing', () => {
     await c.getChatbotEmbedInfo({ experiment_id: 1 });
     expect(pw.getChatbotEmbedInfo).toHaveBeenCalled();
   });
+
+  it('getChatbotPipelineId calls playwright.pipelineIdFor and wraps the result', async () => {
+    const rest = {};
+    const pw = { pipelineIdFor: vi.fn().mockResolvedValue(5942) };
+    const c = new CompositeBackend({ rest: rest as never, playwright: pw as never });
+    const out = await c.getChatbotPipelineId({ experiment_id: 12167 });
+    expect(pw.pipelineIdFor).toHaveBeenCalledWith(12167);
+    expect(out).toEqual({ pipeline_id: 5942 });
+  });
 });