dsh-jev-interceptor

dsh-jev-interceptor

⚡ Millisecond judgement for every tool call — for about two millionths of a dollar.

Your agent's most expensive habit is asking a poetry-writing LLM yes/no questions. This plugin wires Jev — the non-generative "System One" model that broke everyone's feed — straight into the two decision points of DeepSeek Harness where an LLM is overkill and rules are blind.

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What it does, in one breath: before a tool call runs, Jev classifies its risk, irreversibility, task-fit, and injection-suspicion in one ~$0.00002 request — confident high-risk calls get denied, medium ones escalate to a human, and clearly-granted reversible ones stop wasting your clicks on approval dialogs. Every doubt, every timeout, every missing key degrades to stock dsh behavior. Nothing to configure away, nothing that can widen a permission.

Why this exists

dsh ships zero per-call risk classification — the pre-execute waterfall's default is a bare allow. Its only built-in precedent, experimental/auto-review, does the classification with a generative LLM: one full model request per tool call, temperature 0, hand-rolled JSON text protocol, self-described as slow, expensive, and experimental. That's a System-2 scribe doing a System-1 reflex's job:

	auto-review (generative LLM)	dsh-jev-interceptor (Jev)
Decision shape	emits JSON token-by-token, then parses it and prays	typed choice/noul answers — type errors are structurally impossible
Cost per call	one full LLM request	~$0.00002 (measured: 501 input tokens)
Latency	seconds	~100ms provider-side (TypeSafe-reported p50); ~1s end-to-end from outside US-West
Uncertainty	buried in prose	per-question probability distributions + calibrated confidence
Failure path	parse fallback → deny	low confidence → next() — it never guesses

Jev's maker TypeSafe reports up to 200× faster / 400× cheaper than LLMs on classification workflows — and this plugin is that number, landed in a real agent harness, with receipts in /jev-stats.

We believe this is the first System-1 decision plugin in the dsh ecosystem. The full map of where decision models fit in dsh — this plugin's two hooks plus eleven more verified hooks (semantic model routing, context-retention scoring, image-offload pre-planning, worker-report verification...) — is in docs/jev-usage-points.md.

The 60-second tour

dsh plugin --profile  add dsh-jev-interceptor

# in your profile's cordis.patch.yml
- id: jev-interceptor
  name: dsh-jev-interceptor
  config:
    enabled: true
    mode: shadow            # watch mode first: records every decision, enforces nothing
    provider: typesafe      # or 'openrouter' (works today, no waitlist) | 'custom'

Use your agent normally. In shadow mode every decision lands in telemetry with its full probability distribution; /jev-stats summarizes:

[guard] calls: 41  degraded: 0  cached: 9
  actions: delegate=33 ask=6 deny=2
  input tokens: 18234  est. cost: $0.000766
  latency: p50 247ms  p95 512ms  max 611ms

Happy with the numbers? Flip mode: enforce. That's the whole rollout plan — shadow first, then trust, never guess.

Safety model (the part you should actually read)

• Never allow. "No objection" is expressed as next(), so downstream listeners (external hooks, auto-review) keep their veto.
• Fail-closed everywhere. No key / provider cooldown / timeout / parse mismatch / internal error → delegate to stock behavior. The approval service's never policy is enforced upstream of every listener, so this plugin structurally cannot relax it.
• Evidence-gated auto-approval. allowed-once requires captured argument evidence: only a call the guard escalated (fresh pending entry, matching session and tool) can be auto-approved. Hook asks and sandbox escalations carry no arguments and always go to the human.
• Injection-aware. Tool arguments enter the Jev state data field only; instructions are fixed strings; a suspected-injection answer escalates rather than suppresses. (Jev's maker acknowledges adversarial inputs can sway classifiers — so denial here is an accelerator, never the last line of defense.)
• Bounded input. Head+tail argument previews and trailing-message digests — Jev's own guidance is to filter in code and send only what a question needs.
• Resilient by construction. Wall-clock timeout per attempt, single retry on 429/529, cooldown after consecutive failures (timeouts count), concurrency cap, LRU decision cache, queue-bound semaphore. A dead provider costs you zero behavior, not your harness.
• Observable. Every decision lands in /plugins/dsh-jev-interceptor/telemetry.jsonl (honoring $DSH_HOME); /jev-stats aggregates it per hook.

All of this is enforced by 52 tests, including adversarial-review regression cases (a concurrency leak that could hang the tool pipeline, cross-session callId collisions, evidence-free auto-approval).

Configure

Everything is a config field — timeouts, cooldown, concurrency, cache, per-hook thresholds, tool lists — see the Config schema in src/config.ts. Notable defaults:

• read-only tools (read, read_image, grep, glob, todo_write) short-circuit with zero cost;
• the Auto permission preset is left entirely to auto-review (no double review, no double billing);
• the pre-approval allowlist starts empty — until you name tools in preapproveToolAllowlist, nothing is ever auto-approved.

OpenRouter works today with no waitlist (decisions models live on a dedicated endpoint there):

    provider: openrouter
    apiKeyEnv: OPENROUTER_API_KEY

The client speaks the plain state + questions wire shape shared by TypeSafe direct, OpenRouter, and the Apache-2.0 local alternative Laya — providers stay swappable, and a closed provider never becomes a lock-in.

Development

npm install --legacy-peer-deps   # devDeps pin a current dsh API generation
npm run typecheck                # src + tests, against real @deepseek-ai types
npm test                         # vitest, 52 tests, no network
npm run build                    # tsc -> lib/
node scripts/smoke.mjs           # one real decision against a live provider

Roadmap: the other eleven hooks

v0.1 holds the approval loop. The verified next frontiers — where selection, not just safety, meets System-1 (full catalog):

• Semantic context retention — score every message when an @session snapshot is injected, so the error traceback survives the byte budget instead of the oldest small talk
• Image-offload pre-planning — dsh's own README admits "nothing plans an offload before dispatch"; Jev plans it
• Content-aware model routing — routine steps on the cheap route, deep work on the strong one
• Worker-report verification — when a subagent says "done", something checks

License

MIT