feat(depin-attest): T1 Solana DePIN attestation plugin with durable-nonce replay guard

[Emran-goat]

Summary

Adds depin-attest, a read-only T1 tool plugin that builds unsigned Solana versioned transactions committing a DePIN device attestation on-chain via a memo instruction with a durable-nonce advance as replay guard.

Track C (DePIN & the physical edge) — the bounty's stated favorite.

What it does

The agent calls depin_attest with a device identifier, a sensor reading (kind, value, timestamp, device signature), and a monotonic nonce counter. The plugin:

1. Validates config (rpc_url, device_id, nonce_account, nonce_authority)
2. Replay guard: rejects if nonce_counter <= last_committed_counter
3. Clock skew guard: rejects if |now - ts| > 300s
4. Fetches recent blockhash via Solana RPC
5. Builds a versioned transaction with [advance-nonce, memo] instructions
6. Returns base64 + a human-readable summary (~20 tokens)
7. Human or Squads multisig signs externally

Key design decisions

• Durable nonce solves Trap Self-contained WIT plugin registry + example plugins (wikipedia-summary, mastodon-post) #1 (blockhash expiry) — the bounty explicitly calls this out
• No solana-sdk — hand-encoded Solana message v0 format, base58 constants, zero wasm friction
• T1 custody — no signing, no secret keys, no private key in config. The plugin is a transaction builder, not a wallet
• Pure core / thin shim — core.rs has zero wasm deps, tests run with plain cargo test
• Nonce account is NOT a signer — only the nonce authority signs; nonce_account is readonly unsigned (verified in code review)

Test results

running 13 tests (lib) — all passed
running 16 tests (integration) — all passed
cargo build --target wasm32-wasip2 — clean (363 KB component)

Tests cover: happy path, nonce replay, counter regression, clock skew (old/future/zero), RPC failure, missing config, memo overflow, prompt injection (2 cases), base64 decodability, cold-start guard.

Custody tier: T1 (Build)

Returns unsigned transaction. No signing, no secret keys. The human always signs. T0 is too limited for real DePIN flows; T2 carries unacceptable prompt-injection risk for a reference implementation.

Threat model (8 threats, each with named error variant)

Threat	Defense
Prompt injection: change device_id	Summary shows device_id, human rejects
Nonce replay	AttestError::NonceReplay — strict advance required
Clock skew	AttestError::TsSkew — 5min max
Memo overflow	AttestError::MemoTooLarge — 1024 byte limit
RPC failure	AttestError::RpcError — never panics
Missing config	AttestError::MissingRpcUrl/NonceAccount
Device key compromise	Advisory at T1, human verifies
Nonce account drained	Operator controls nonce_authority

Prompt-injection transcript

See README.md — two scenarios: (a) counter advances → tx built, summary reveals attack, human rejects; (b) counter already maxed → NonceReplay rejected.

Permissions

["http_client", "config_read"] — minimal. Only outbound HTTPS to Solana RPC and read access to own config section.

What's next

• Verify ed25519 device signature in-plugin (when crypto capability ships)
• Read on-chain nonce account state directly (instead of config-tracked counter)
• Support sensor WIT capability for real GPIO/I2C/SPI reads

Build

rustup target add wasm32-wasip2
cargo build --target wasm32-wasip2 --release

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Superteam Earn submission: depin-attest (Track C, T1)
Building in public: updates on X during the bounty period