Harness spec 2.0.0: background work is a job — commands and subagents alike, seen and steered

One registry per process, every job owned by a session: bash's background commands (and a command
still running at its timeout, which now goes to the background instead of being killed) and
subagents started with task background: true. job_list, job_output, job_stop (the former
bash_list, bash_output, bash_kill) and the new job_send and report; a finished job wakes the owning
session in every front end with its marked note. The TUI counts jobs, lists them (/jobs), opens a
command's output, enters a subagent and messages it, moves a command to the background (ctrl+b)
and asks before quitting with jobs running. The link gains the jobs capability. Subagents get a
session row of their own, the spec's preamble and agent texts, and their errors reach the report.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

harness/tools/job_send.json

@@ -0,0 +1,29 @@
+{
+  "name": "job_send",
+  "scope": "shared",
+  "risk": "interact",
+  "exclusive": false,
+  "block": "tool",
+  "purpose": false,
+  "aliases": {
+    "cli": [],
+    "llembas": []
+  },
+  "description": "Send a message to a subagent running as a background job — an answer to something it reported, a correction, more to do. It is given to it at its next step. To a subagent that has finished, the message starts it again with its context intact, under the same job id; its new report comes to you when it ends.",
+  "parameters": {
+    "type": "object",
+    "properties": {
+      "id": {
+        "type": "string"
+      },
+      "text": {
+        "type": "string",
+        "minLength": 1
+      }
+    },
+    "required": [
+      "id",
+      "text"
+    ]
+  }
+}