Loop combines Ultracode's parallel Codex worker orchestration with Fable-powered prompt review and Stop-hook course correction. Fable oversees the goal loop; Codex executes.

The Fable hook layer is opt-in per Codex thread. Start a prompt with [loop] or include [loop] in the prompt to activate Loop review for that thread. Prompts without [loop] are passed through unchanged, and the Stop hook stays inactive until a [loop] prompt marks the thread active.

The orchestration engine is copied from Ultracode so this plugin can be installed as a standalone public plugin. The CLI wrapper is:

node scripts/loop-cli.js "investigate this bug with parallel workers"

The underlying workflow surfaces remain compatible with Ultracode: task fan-out, steps[] DAGs, workers_spec[], imperative Workflow scripts, saved workflows, resume, status, budgets, and the run dashboard.

For open-ended research, start from examples/research-loop.workflow.js: it uses stateful loopUntilDry with dedupeFindings: true so each round sees the running finding/source memory and repeat-only rounds count as dry.

hooks/hooks.json defines:

• UserPromptSubmit: when the prompt contains [loop], asks Fable to improve the prompt and injects the result as additional context. The activating prompt is recorded as the loop's goal.
• Stop: after a [loop] prompt has activated the current thread, asks Fable whether the goal is genuinely met — Fable verifies with read-only tools (git status/diff, file reads, and web search/fetch when current external facts matter) rather than trusting Codex's final message. Fable also receives a turn digest: the hook reads the full transcript delta since Fable's last review and summarizes it with a cheap model (LOOP_DIGEST_MODEL, default haiku, one-shot claude -p with no tools) so Fable sees what Codex actually did — commands run, test results, errors — not just the final claim. Small deltas are included verbatim; digest failures fall back to a raw excerpt. It blocks with a course-correction instruction only for concrete unfinished work, failed verification, or a needed redirect. Consecutive forced continuations are capped by LOOP_MAX_CONTINUES (default 8); the counter resets on any new user prompt or an approved stop.

Loop does not install or trust hooks automatically.

Loop talks to Fable through the Claude Code CLI in headless mode (claude -p) by default:

• Subscription auth — uses your existing claude login; no ANTHROPIC_API_KEY needed.
• One persistent Fable session per Codex thread — the prompt review creates a Claude session and every later review (including Stop reviews) --resumes it, so Fable remembers the goal and everything it already verified. State lives under $CODEX_HOME/loop/sessions/.
• Structurally read-only — the child gets --tools Read,Glob,Grep,LS,WebSearch,WebFetch only (no Bash, no write/edit tools), --permission-mode dontAsk, --setting-sources user, --strict-mcp-config, and hooks disabled. Git state (branch, status, commits, diffstat — plus the working-tree diff for Stop reviews) is collected by the hook with a sanitized environment and injected into the prompt.
• Structured output via --json-schema — no tool-call retry protocol.
• No key leakage — ANTHROPIC_API_KEY/ANTHROPIC_AUTH_TOKEN and NODE_OPTIONS are stripped from the child environment; .env files are read with an allowlist (only LOOP_* keys and ANTHROPIC_API_KEY).

If the claude CLI is not installed and ANTHROPIC_API_KEY is set, Loop falls back to the legacy @just-every/ensemble API backend.

Optional environment variables (environment, project .env, plugin .env, or ~/.env):

LOOP_DISABLED=1              # turn the hooks off
LOOP_BACKEND=auto            # auto (default) | claude | ensemble
LOOP_CLAUDE_BIN=claude       # path to the Claude Code CLI
LOOP_MODEL=claude-fable-5    # model passed to the backend
LOOP_EFFORT=                 # optional --effort for the claude backend (low..max)
LOOP_TIMEOUT_MS=1200000      # per-review timeout (20 minutes)
LOOP_MAX_CONTEXT_CHARS=16000 # cap on conversation context sent with the prompt
LOOP_MAX_CONTINUES=8         # max consecutive Stop-hook continuations
LOOP_DIGEST_MODEL=haiku      # model that summarizes the turn transcript for stop reviews (off to disable)
LOOP_DIGEST_TIMEOUT_MS=60000 # digest call timeout
LOOP_DIGEST_MAX_CHARS=150000 # cap on transcript text fed to the digest model

ANTHROPIC_API_KEY is only required for the ensemble backend.

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