chore: v2.8.12 — clone queue and progress, session defaults, chat agents, drops as @ mentions

Whole tree from parallel sessions, plus the version bump:
- Clone: a queue with live progress (Add workspace and extra folders),
  clones run under nice/ionice so the machine stays responsive.
- Settings → AI tools → Session defaults: a new session's default
  permission mode / bypass per account.
- Chat lists the background subagents that have not reported back yet.
- A file pasted or dropped into a claude pane goes in as an @ mention.
- Changes panel: say why amend/undo is refused on a pushed commit.
- openapi.yaml regenerated (Artifacts, Host, resumeById).

server/openapi-extra/files.js

@@ -253,12 +253,40 @@ const paths = {
               remember: { type: "boolean" },
             },
           },
+          partial: {
+            type: "boolean",
+            description:
+              "Blobless clone (`--filter=blob:none`): file contents fetched on checkout.",
+          },
+          progressToken: {
+            type: "string",
+            pattern: "^[A-Za-z0-9_-]{16,64}$",
+            description:
+              "The caller's name for this clone, to poll `/api/lanes/clone/progress/{token}`.",
+          },
         },
         ["url", "parent"]
       ),
       responses: { 201: { description: "{lane, created: true, path}" } },
     },
   },
+  "/api/lanes/clone/progress/{token}": {
+    get: {
+      tags: ["Git identity"],
+      summary: "A clone's place in the queue, then git's progress",
+      description:
+        "Clones run a few at a time machine-wide (`AGENTHUB_CLONE_CONCURRENCY`). Only the user who started the clone sees it; kept 60 s after it ends.",
+      operationId: "cloneProgress",
+      parameters: [{ name: "token", in: "path", required: true, schema: { type: "string" } }],
+      responses: {
+        200: {
+          description:
+            "{state: queued|running|done|failed, position, running, waiting, limit, phase: remote|receiving|resolving|checkout|other|null, label, percent, detail}",
+        },
+        404: { description: "ENOTFOUND" },
+      },
+    },
+  },
   "/api/me/git": {
     get: {
       tags: ["Git identity"],