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Reposition Nexus as verification middleware, not standalone protocol
The 2026 landscape settled: A2A is the de-facto transport (Linux Foundation, 150+ orgs, 5 production SDKs, Signed Agent Cards). IATP covers identity and reputation. PayCrow / ERC-8004 / Nava cover escrow. None of them verify whether the agent's answer is factually correct — that is Nexus's unique lane. Changes: - README: new tagline + "Why Not Just A2A?" comparison table - README: architecture split into differentiating (Verification, Defense, Trust) and substrate (replaceable by A2A) layers - ROADMAP: Phase 2 reoriented around A2A bridge (Agent Card consumer, JSON-RPC adapter, verdict callback, reference example) - ROADMAP: identity / reputation / escrow explicitly delegated to A2A / IATP / PayCrow / Nava — out of scope as primary products No code changes. Existing 224 tests + verification engine stand as-is — they were always the differentiator, the rest was substrate. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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README.md

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# Nexus
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**The AI-to-AI Protocol Layer that catches unreliable agent outputs before they cost you money.**
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**The verification layer for AI agent networks. A2A and IATP prove agents are who they say they are. Nexus checks if they're telling the truth.**
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[![CI](https://github.com/timmeck/nexus/actions/workflows/ci.yml/badge.svg)](https://github.com/timmeck/nexus/actions/workflows/ci.yml)
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[![Python 3.11+](https://img.shields.io/badge/python-3.11%2B-blue.svg)](https://www.python.org/downloads/)
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## The Problem
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When Agent A asks Agent B for work, there's no guarantee the result is correct. Agent B can return garbage with 95% confidence, and Agent A pays anyway. No verification, no recourse, no accountability.
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Today's agent protocols verify the *sender* and the *delivery*. None of them verify the *answer*.
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**Nexus adds enforcement.** Agent outputs are verified. Payments are held in escrow. Bad actors get slashed. Every step is audited.
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- **A2A Signed Agent Cards** prove the agent is who it claims to be.
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- **IATP** scores reputation based on past behavior.
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- **PayCrow / ERC-8004** release escrow when bytes arrive matching a JSON schema.
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- **Nava** verifies intent against the user's request.
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But Agent B can return a cryptographically-signed, schema-valid, on-time response that is **factually wrong** — and every layer above passes it through. Partial cheaters, style mimics, semantic swaps, coordinated collusion: all defeat identity-based trust because they aren't lying about who they are. They're lying about *what they know*.
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**Nexus is the missing verdict.** Claim-level semantic verification that runs over A2A, IATP, or standalone. Verified outputs settle escrow. Failed verifications slash trust. Every step is audited.
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## Why Not Just A2A?
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A2A is the right transport. Nexus is the verdict on top.
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| Layer | A2A / IATP | PayCrow / ERC-8004 / Nava | **Nexus** |
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|---|---|---|---|
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| Sender authenticity | ✅ Signed Agent Cards || (delegated to A2A) |
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| Identity reputation | ✅ Trust score 0-1000 || (delegated to IATP) |
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| Delivery / schema match || ✅ Smart-contract escrow | (delegated) |
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| **Content correctness** |||**Claim-level verification** |
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| Adversarial test coverage | Identity attacks | Replay / non-delivery | **12/12 caught: partial cheat, style mimic, omission, collusion, meaning swap, negation, context shift** |
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Use A2A for *who* and *whether*. Use Nexus for *what*.
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## 60-Second Demo
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## Architecture
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9 layers, each in the enforced request path:
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Nexus has 9 layers. The differentiated value lives in **Verification + Defense + Trust** — these are what no other agent network does today. The rest exist so Nexus can also run standalone, but are best understood as substrate that A2A can replace.
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**Differentiating layers (the product):**
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| Layer | Purpose |
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|---|---|
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| Discovery | Agent registry, capability search, heartbeat monitoring |
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| Trust | Reputation scoring, interaction tracking |
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| Protocol | NexusRequest/NexusResponse lifecycle |
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| Routing | Best, cheapest, fastest, or most trusted agent matching |
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| Federation | Cross-instance agent registry sync |
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| Payments | Credit wallets, pay-per-request |
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| Schemas | Formal capability definitions |
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| **Verification** | Claim-level extraction, normalization, semantic-tension detection, SUSPICIOUS verdict |
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| **Defense** | Slashing, escrow disputes, challenges, sybil detection — driven by verification verdicts |
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| **Trust** | Append-only reputation ledger fed by verification outcomes |
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**Substrate layers (replaceable by A2A or similar):**
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| Layer | Purpose | Can be replaced by |
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|---|---|---|
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| Discovery | Agent registry, capability search, heartbeat monitoring | A2A Agent Cards |
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| Protocol | NexusRequest/NexusResponse lifecycle | A2A JSON-RPC 2.0 |
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| Routing | Best, cheapest, fastest, or most trusted agent matching | A2A discovery + routing |
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| Federation | Cross-instance agent registry sync | A2A federation |
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| Payments | Credit wallets, pay-per-request | x402 / PayCrow / on-chain escrow |
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| Schemas | Formal capability definitions | A2A Agent Cards |
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| Defense | Slashing, escrow, challenges, sybil detection |
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| Policy | Data locality, compliance claims, routing policies |
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| Policy | Data locality, compliance claims, routing policies | — (keep, used by both modes) |
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**Roadmap:** an A2A bridge is the top Phase 2 item — Nexus consumes A2A Agent Cards as discovery, accepts A2A JSON-RPC requests, and emits Nexus verdicts back into A2A's response flow. See `ROADMAP.md`.
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## Known Detection Boundaries
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ROADMAP.md

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# Roadmap
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Nexus's Phase 1 (enforcement, verification, defense) is complete: 224 tests, 12/12 adversarial patterns caught, 4/4 meta-agent attacks caught, 9 enforced layers in the request path.
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Nexus's Phase 1 (enforcement, verification, defense) is complete: 224 tests, 12/12 adversarial patterns caught, 4/4 meta-agent attacks caught.
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This document tracks what is **not yet built** so external readers can see what is fact vs. plan.
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The agent-protocol landscape in 2026 changed how Nexus is positioned. **Google A2A is the de-facto transport** (Linux Foundation, 150+ orgs, 5 production SDKs, Signed Agent Cards). Microsoft IATP is the de-facto identity-and-reputation layer. PayCrow / ERC-8004 / Nava cover escrow. None of them verify **whether the agent's answer is factually correct**. That is Nexus's lane.
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Phase 2 reorients Nexus from "standalone protocol" to **verification middleware** — a verdict service that runs over A2A, IATP, or standalone.
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## Status Legend
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- **Done** — shipped on `master`, tested, in the request path
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- **Planned** — committed direction, no code yet
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- **Considered** — credible idea, not committed
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## Phase 1 — Core Protocol (Done)
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## Phase 1 — Verification Engine (Done)
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- 9 enforced layers: Discovery, Trust, Protocol, Routing, Federation, Payments, Schemas, Defense, Policy
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- Claim-level verification with SUSPICIOUS verdict for semantic tension
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- Claim-level extraction with SUSPICIOUS verdict for semantic tension
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- 12/12 adversarial patterns caught (partial cheater, style mimic, omission, collusion, meaning swap, negation, context shift, others)
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- 4/4 meta-agent attacks caught (adversaries that know the verifier)
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- 0/4 false positives on stylistically diverse honest agents
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- HMAC + timestamp + signature-cache replay protection (3 layers)
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- Compare-and-swap pattern enforced via CI guards
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- Reconciliation job for stuck requests and orphaned escrows
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- 198 → 224 tests (chaos, crash injection, cross-object consistency, claim extraction)
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- 8 reference agents on the standalone SDK
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- 224 tests
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- See `README.md` and `docs/invariants.md` for the full surface
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## Phase 2 — Distribution & Trust Completeness (Planned)
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## Phase 2 — A2A Integration + Verification Reach (Planned)
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The unblocking question is: how does an existing A2A network start using Nexus verdicts?
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These are the items that, if closed, move Nexus from "impressive demo" to "thing the industry can adopt."
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### A2A bridge (top priority)
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### Trust completeness
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- **A2A Agent Card consumer** — Nexus's Discovery layer accepts A2A Agent Cards as input. Agents already registered in A2A become available to Nexus verifiers without re-registration.
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- **A2A JSON-RPC adapter** — Nexus exposes `/api/protocol/verify` as a JSON-RPC 2.0 endpoint that an A2A client can call directly. Returns Nexus verdict (PASS / FAIL / SUSPICIOUS) plus claim-level diff.
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- **A2A verdict callback** — Nexus emits verdicts back into A2A's response flow so they can be consumed by A2A-native escrow (PayCrow, ERC-8004, Nava). Verdict drives release-or-dispute decision.
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- **Reference: A2A + Nexus example** — one end-to-end working flow: agent registered on A2A, query routed via A2A, response verified by Nexus, escrow released or slashed based on the verdict.
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- **External truth anchoring** — closes the only architectural gap left after the red team. Consensus-based verification is structurally blind to shared hallucination (all agents wrong in the same way). Adding an oracle/citation pass for high-stakes requests would close this. Today this is documented in `README.md` under "Known Detection Boundaries" — Phase 2 makes it concrete.
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- **Verifier diversity** — current verifiers are claim-extraction variants. Add a structural/logical verifier and an LLM-judge verifier so disagreement among verifier classes becomes a signal.
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- **Trust score decay + recovery curve** — reputation should age, and slashed agents need a rehabilitation path. Without one, the network only ever loses participants.
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### Verification reach
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- **External truth anchoring** — closes the only architectural gap left from the red team. Consensus-based verification is structurally blind to shared hallucination (all agents wrong identically). Adding an oracle / citation pass for high-stakes requests would close this.
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- **Verifier diversity** — current verifiers are claim-extraction variants. Add a structural / logical verifier and an LLM-judge verifier so disagreement *among verifier classes* becomes a signal.
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- **Trust score decay + recovery curve** — reputation should age, and slashed agents need a rehabilitation path. Otherwise the network only loses participants.
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### Distribution
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- **JS / TS SDK** — Python-only adapter locks out the largest agent ecosystem (LangChain, CrewAI, Vercel AI SDK). Highest single-step adoption lever.
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- **Public testnet** — a hosted Nexus instance anyone can register against with one curl command. Without it, "federated" is a claim, not a demo.
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- **Formal protocol spec (versioned)** — RFC-style document plus conformance test suite, so third parties can build compatible servers and clients.
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- **Reference third-party agent** — at least one agent on the network shipped by someone other than the maintainer.
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- **JS / TS SDK** — Python-only adapter locks out LangChain, CrewAI, Vercel AI SDK. The A2A bridge reduces the urgency (A2A already has 5 SDKs), but a thin JS verdict-client is still useful for native Nexus mode.
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- **Verdict-as-a-service reference deployment** — a public Nexus that exposes the verifier as a callable service. Anyone with an A2A agent can submit a verification request without running Nexus themselves.
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## Phase 3 — Production Operations (Considered, Not Yet Committed)
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These are listed so the gap is honest, not because they are queued. Production-grade hardening before there are real users is premature optimization.
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Listed for honesty, not queued. Production hardening before there are real users is premature.
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- PostgreSQL migration path (SQLite is fine for single-node)
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- OpenTelemetry traces, Prometheus metrics, SLO dashboards
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- OAuth / mTLS / key rotation beyond HMAC
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- OAuth / mTLS / key rotation beyond HMAC (less urgent with A2A's Signed Agent Cards in front)
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- Rate limiting and quotas at the registry edge
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- Docker + Helm chart, documented backup/restore
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- Real money rails (Stripe / Lightning) instead of credit-only wallets
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- gRPC or GraphQL transport alongside REST + WebSocket
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- Provider → Nexus → Sub-provider delegation chains
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- SLA enforcement with automatic slashing for breaches
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- Compliance claim verification (today policy accepts claims as strings)
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- gRPC transport alongside REST + WebSocket
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- Agent versioning (capability hashes, semver)
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## Out of Scope
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The following are intentionally **not** on the roadmap:
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- A blockchain. Nexus uses an append-only audit trail and credit ledger because that is what the invariants require — adding consensus layers would be cargo culting.
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- A hosted SaaS managed by us. The point is self-hostable + federated.
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- A general-purpose agent framework. Nexus is the protocol between agents, not a replacement for LangChain / CrewAI / AutoGen.
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- **Competing with A2A on transport.** A2A won. Nexus runs over it.
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- **A blockchain.** Nexus uses an append-only ledger because that's what the invariants require — adding consensus layers would be cargo culting.
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- **A hosted SaaS managed by us.** The point is self-hostable, open-source, no vendor lock-in.
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- **A general-purpose agent framework.** Nexus is a verdict, not a framework.
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- **Identity / reputation / escrow** as primary products. Those are solved by A2A / IATP / PayCrow / Nava. Nexus delegates to them.
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## How to Influence the Roadmap
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- Open an issue describing the gap you hit and the use case behind it
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- For trust / verification gaps specifically: open a PR with a failing adversarial test case under `tests/test_red_team.py` — that is the fastest path to a fix
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- For SDK contributions, see `CONTRIBUTING.md` for the open vs. core boundary
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- Open an issue describing where you'd plug Nexus into an existing A2A or agent network — concrete integration friction is the most useful input
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- Adversarial test cases — if you can craft an agent pattern that escapes verification, that is the most valuable contribution. PR with a failing test under `tests/test_red_team.py`
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- A2A bridge work — pick any of the four sub-items in Phase 2 and open a PR

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