Libr Delegate (Cursor → LibrAgent Session API)

Spawn and steer LibrAgent sessions over HTTP from Cursor. LibrAgent must already be running (desktop or headless). This skill does not ship into LibrAgent bundled_skills.

vs in-app delegate

Base URL

PORT=$(cat ~/.libragent/http_port 2>/dev/null || echo 3030)
BASE="http://127.0.0.1:${PORT}"

Port file is written when LibrAgent’s HTTP server binds; fallback is 3030.

Workflow

1. Confirm LibrAgent is up — GET $BASE/api/health (or assistants list)
2. Resolve assistantId — GET $BASE/api/assistants
3. Write a self-contained handoff (LibrAgent child does not see Cursor chat, parent workspace instructions, or workspace-local skills unless you pass an absolute workspacePath)
4. Create — write JSON payload to a file, validate non-empty JSON, then POST $BASE/api/sessions (include request or create idle). See references/session-api.md (preferred file recipe + empty-body guard)
5. If idle — POST $BASE/api/sessions/:id/messages with {"content":"..."}
6. Poll — GET $BASE/api/sessions/:id until terminal (prefer scripts/poll-until-done.sh)
7. Read result — GET $BASE/api/sessions/:id/messages
8. On paused after crash — POST …/resume, then poll again
9. Optional lineage — set parentSessionId; list with GET …/children
10. Extract transcript before delete — dump GET …/messages?limit=500 to a file (see below)
11. Cleanup one-shot sessions — POST …/terminate then DELETE …/sessions/:id (delete cascades descendants)

Curl recipes: references/session-api.md. Handoff / isolation: references/handoff.md. Poll helper: scripts/poll-until-done.sh.

Extract transcript (API-side "trace") then delete

There is no HTTP /api/sessions/:id/trace and no ATIF/Markdown export endpoint on the Session API. UI session export (Markdown / ATIF) is separate. For Cursor/harness handoffs, the recoverable history is message JSON:

# After idle (or error) — save BEFORE delete
curl -sS "$BASE/api/sessions/$SID/messages?limit=500" \
  > ".libragent/work/libr-delegate-${SID}-messages.json"

• Default limit is 50 — use a high limit for full history
• Treat latest assistant text as the deliverable; keep the JSON dump when debugging tool calls / failures (role user | assistant | tool)
• Optional deeper analysis of a dumped file: Cursor skill trace-analyzer expects .trace.json shape — only use it if the dump matches that format; otherwise inspect the messages JSON directly
• Order matters: extract → terminate → DELETE. Delete removes DB history

One-shot / automation default: always extract (or confirm you only need the final assistant text) then terminate+delete so sessions do not accumulate.

Create payload essentials

{
  "assistantId": "<from GET /api/assistants>",
  "request": "<self-contained task + deliverable format>",
  "workspacePath": "/absolute/path/optional",
  "parentSessionId": "<optional exact parent session id>",
  "executionMode": "normal | yolo | unsafe",
  "name": "optional label"
}

• Blank/omit request → idle (no LLM turn until messages POST)
• Unattended automation: prefer yolo; use unsafe only when hard-approval tools must also auto-run
• Child inherits non-normal parent executionMode when omitted on create

Polling rules

Wire status is always lowercase (serde(rename_all = "lowercase")): idle | busy | paused | error | queued | provisioning.

Preferred poll (normalizes case; exits on terminal):

./.agents/skills/libr-delegate/scripts/poll-until-done.sh "$SID" "$BASE"

If writing a one-off loop, lowercase before match:

status=$(curl -sS "$BASE/api/sessions/$SID" \
  | python3 -c 'import sys,json; print(json.load(sys.stdin).get("status","").lower())')
case "$status" in idle|error|paused) break ;; esac

Follow-ups: another POST …/messages (queued if still busy).

Isolation (critical)

The LibrAgent session is not a clone of this Cursor chat:

• Default: LibrAgent session workspace, not the Cursor CWD unless workspacePath is set to that absolute path
• Put objective, scope, paths, and output format in request / message body
• Require deliverables in the session’s final assistant text
• Do not assume Cursor files, notes, or tools are visible inside LibrAgent

Anti-patterns

• Calling nonexistent MCP tools (spawnSession, session_api__*) from Cursor
• Echo-only stubs instead of real POST …/messages
• Rapid fixed-interval polls with no backoff
• Matching PascalCase statuses (Idle/Busy) — API returns idle/busy; a case Idle) branch never fires and the poll loops until timeout even after the session finished (postmortem: editObject smoke, 2026-04)
• Treating paused / empty history / error as success
• Deleting a session before saving …/messages when a transcript is needed
• Assuming ~/.libragent/traces/*.trace.json or /api/.../trace exists (they are not part of the Session API)
• Leaving one-shot delegate sessions undeleted after the handoff completes
• Putting this skill under src-tauri/bundled_skills (Cursor-only)
• Referencing shell vars as bare Python names inside <<'PY' (e.g. workspacePath: WORKSPACE) → NameError → empty payload file → create 400 EOF while parsing a value
• curl -d @file without checking the file is non-empty valid JSON first

Related repo docs

• HTTP API: docs/api/http_api.md
• In-app sub-agents (product): docs/user/guides/sub-agents.md