feat(explorer): decode Cartesi sequencer batches natively

.changeset/sequencer-user-ops-decoder.md

@@ -0,0 +1,5 @@
+---
+"@deroll/decoder": minor
+---
+
+Add the `userOp` decode method and the `UserOp` record: the payload of one user operation inside a Cartesi sequencer batch, with the batch envelope and the recovered signer already decoded by the explorer.

apps/docs/pages/explorer/decoders.mdx

@@ -13,12 +13,13 @@ optional); each method receives the full API record:
 
 | method | record | bytes decoded |
 | --- | --- | --- |
-| `input` | `Input` | `input.decodedData.payload` — the advance payload sent by the user. Never called for portal deposits: the explorer decodes those itself |
+| `input` | `Input` | `input.decodedData.payload` — the advance payload sent by the user. Never called for portal deposits or sequencer batches: the explorer decodes those itself |
 | `deposit` | `Deposit` | the app-specific data attached to a portal deposit (`execLayerData`, and `baseLayerData` on the NFT portals; `"0x"` when absent). The deposit envelope — asset, amounts, sender — arrives already decoded |
 | `output` | `Output` | `output.decodedData.payload` — the payload of a Notice, Voucher or DelegateCallVoucher |
 | `report` | `Report` | `report.rawData` — the full report body (inspect responses, error messages, …) |
 | `withdrawalAccount` | `Withdrawal` | `withdrawal.account` — the account encoding produced by the app's `WithdrawalOutputBuilder` |
 | `withdrawalOutput` | `Withdrawal` | `withdrawal.output` — the raw output blob emitted for that account |
+| `userOp` | `UserOp` | `userOp.data` — the payload of one user operation inside a sequencer batch. The batch envelope — frames, nonces, fees, recovered signer — arrives already decoded |
 
 An exported method is also the capability signal: the explorer only calls what you
 export and falls back to its hex/UTF-8 view for everything else, so new payload sources
@@ -32,6 +33,22 @@ and the structured deposit natively — with or without a registered decoder. Yo
 `deposit` method only decodes the app-specific bytes riding inside, and its result is
 shown alongside the native deposit view.
 
+## Sequencer user operations
+
+With a Cartesi sequencer, users sign operations off-chain and a batch submitter posts them to the InputBox in batches. The batch envelope is protocol-defined, so once the application's **batch submitter** address is set on its **Overview** page, the explorer recognizes batches by sender, decodes them, recovers each operation's signer and unfolds the operations under their input — `input` is never called for a batch. Each operation's `data` is application-defined, and that is what your `userOp` method decodes:
+
+```ts
+import type { UserOpDecoder } from "@deroll/decoder";
+
+export const userOp: UserOpDecoder = (op, context) => {
+    // op.signer is the recovered signer (null when unrecoverable), and
+    // op.nonce, op.maxFee, op.frameIndex, … describe the operation.
+    return { summary: `${op.signer ?? "unknown signer"} · ${op.data}` };
+};
+```
+
+A decoded operation was **submitted**, not necessarily executed: the scheduler may skip a whole batch or drop an operation (unrecoverable signature, fee or application validation), and none of that is visible in the batch bytes alone. Don't word a summary as if the operation took effect.
+
 ## What the kit gives you
 
 The [`@deroll/decoder`](https://www.npmjs.com/package/@deroll/decoder) package is
@@ -117,8 +134,8 @@ export const deposit: DepositDecoder = (deposit, context) => {
 ```
 
 Each method has a named type — `InputDecoder`, `DepositDecoder`, `OutputDecoder`,
-`ReportDecoder`, `WithdrawalAccountDecoder`, `WithdrawalOutputDecoder` — and the
-`Decoder` interface types a whole module.
+`ReportDecoder`, `WithdrawalAccountDecoder`, `WithdrawalOutputDecoder`,
+`UserOpDecoder` — and the `Decoder` interface types a whole module.
 
 ## Loading from a GitHub source (no publish)
 

apps/explorer/package.json

@@ -7,7 +7,8 @@
         "dev": "vite",
         "build": "tsc -b && vite build",
         "preview": "vite preview",
-        "lint": "biome check"
+        "lint": "biome check",
+        "test": "vitest"
     },
     "dependencies": {
         "@cartesi/client": "2.0.0-alpha.38",
@@ -29,6 +30,7 @@
         "@vitejs/plugin-react": "^6.1.2",
         "tailwindcss": "^4.3.3",
         "typescript": "^7.0.2",
-        "vite": "^8.3.4"
+        "vite": "^8.3.4",
+        "vitest": "^5.0.4"
     }
 }

apps/explorer/scripts/fixturegen/.gitignore

@@ -0,0 +1 @@
+/target