diff --git a/tools/sync-web-artifacts.mjs b/tools/sync-web-artifacts.mjs
index 5cd871e..912e686 100644
--- a/tools/sync-web-artifacts.mjs
+++ b/tools/sync-web-artifacts.mjs
@@ -3,11 +3,21 @@ import { dirname, resolve } from "node:path";
 import { fileURLToPath, pathToFileURL } from "node:url";
 
 const repositoryRoot = resolve(dirname(fileURLToPath(import.meta.url)), "..");
-const bankRequirements = {
-  functions: ["contractVersion", "paused", "asset", "owner", "totalLiabilities", "balanceOf"],
-  events: ["Deposited", "Withdrawn", "Paused", "Unpaused", "OwnershipTransferred", "Upgraded"],
-};
-const tokenRequirements = { functions: ["balanceOf"], events: [] };
+const bankRequirements = [
+  functionSignature("contractVersion", [], ["uint256"], "pure"),
+  functionSignature("paused", [], ["bool"], "view"),
+  functionSignature("asset", [], ["address"], "view"),
+  functionSignature("owner", [], ["address"], "view"),
+  functionSignature("totalLiabilities", [], ["uint256"], "view"),
+  functionSignature("balanceOf", [parameter("account", "address")], ["uint256"], "view"),
+  eventSignature("Deposited", [parameter("account", "address", true), parameter("amount", "uint256", false)]),
+  eventSignature("Withdrawn", [parameter("account", "address", true), parameter("amount", "uint256", false)]),
+  eventSignature("Paused", [parameter("account", "address", false)]),
+  eventSignature("Unpaused", [parameter("account", "address", false)]),
+  eventSignature("OwnershipTransferred", [parameter("previousOwner", "address", true), parameter("newOwner", "address", true)]),
+  eventSignature("Upgraded", [parameter("implementation", "address", true)]),
+];
+const tokenRequirements = [functionSignature("balanceOf", [parameter("account", "address")], ["uint256"], "view")];
 
 export function extractAbi(artifact, contractName) {
   if (!artifact || typeof artifact !== "object" || !Array.isArray(artifact.abi)) {
@@ -15,16 +25,34 @@ export function extractAbi(artifact, contractName) {
   }
   const requirements = contractName === "BankV1" ? bankRequirements : contractName === "MockUSDC" ? tokenRequirements : null;
   if (!requirements) throw new Error(`unsupported contract artifact ${contractName}`);
-  for (const [type, names] of Object.entries(requirements)) {
-    for (const name of names) {
-      if (!artifact.abi.some((entry) => entry && entry.type === type.slice(0, -1) && entry.name === name)) {
-        throw new Error(`${contractName} ABI is missing required ${type.slice(0, -1)} ${name}`);
-      }
+  for (const requirement of requirements) {
+    const entries = artifact.abi.filter((entry) => entry && entry.type === requirement.type && entry.name === requirement.name);
+    if (entries.length === 0) throw new Error(`${contractName} ABI is missing required ${requirement.type} ${requirement.name}`);
+    if (!entries.some((entry) => matchesSignature(entry, requirement))) {
+      throw new Error(`${contractName} ABI has an invalid signature for ${requirement.name}`);
     }
   }
   return artifact.abi;
 }
 
+function parameter(name, type, indexed) { return { name, type, ...(indexed === undefined ? {} : { indexed }) }; }
+function functionSignature(name, inputs, outputs, stateMutability) {
+  return { type: "function", name, inputs, outputs: outputs.map((type) => parameter("", type)), stateMutability };
+}
+function eventSignature(name, inputs) { return { type: "event", name, inputs, anonymous: false }; }
+function matchesSignature(entry, requirement) {
+  return entry.stateMutability === requirement.stateMutability
+    && entry.anonymous === requirement.anonymous
+    && matchesParameters(entry.inputs, requirement.inputs)
+    && (requirement.outputs === undefined || matchesParameters(entry.outputs, requirement.outputs));
+}
+function matchesParameters(actual, expected) {
+  return Array.isArray(actual) && actual.length === expected.length && actual.every((parameter, index) => {
+    const required = expected[index];
+    return parameter && parameter.name === required.name && parameter.type === required.type && parameter.indexed === required.indexed;
+  });
+}
+
 export function renderContractsModule(bankV1Abi, mockUsdcAbi) {
   return `/* This file is generated by tools/sync-web-artifacts.mjs. Do not edit. */\n\nexport const bankV1Abi = ${JSON.stringify(bankV1Abi, null, 2)} as const;\n\nexport const mockUsdcAbi = ${JSON.stringify(mockUsdcAbi, null, 2)} as const;\n`;
 }
diff --git a/tools/test-sync-web-artifacts.mjs b/tools/test-sync-web-artifacts.mjs
index 16ee7dd..a5fdc4a 100644
--- a/tools/test-sync-web-artifacts.mjs
+++ b/tools/test-sync-web-artifacts.mjs
@@ -8,10 +8,20 @@ import { publishManifest } from "./publish-web-manifest.mjs";
 const address = "0x5FbDB2315678afecb367f032d93F642f64180aa3";
 const owner = "0xf39Fd6e51aad88F6F4ce6aB8827279cffFb92266";
 const bankAbi = [
-  ...["contractVersion", "paused", "asset", "owner", "totalLiabilities", "balanceOf"].map((name) => ({ type: "function", name, inputs: [], outputs: [], stateMutability: "view" })),
-  ...["Deposited", "Withdrawn", "Paused", "Unpaused", "OwnershipTransferred", "Upgraded"].map((name) => ({ type: "event", name, inputs: [], anonymous: false })),
+  { type: "function", name: "contractVersion", inputs: [], outputs: [{ name: "", type: "uint256" }], stateMutability: "pure" },
+  { type: "function", name: "paused", inputs: [], outputs: [{ name: "", type: "bool" }], stateMutability: "view" },
+  { type: "function", name: "asset", inputs: [], outputs: [{ name: "", type: "address" }], stateMutability: "view" },
+  { type: "function", name: "owner", inputs: [], outputs: [{ name: "", type: "address" }], stateMutability: "view" },
+  { type: "function", name: "totalLiabilities", inputs: [], outputs: [{ name: "", type: "uint256" }], stateMutability: "view" },
+  { type: "function", name: "balanceOf", inputs: [{ name: "account", type: "address" }], outputs: [{ name: "", type: "uint256" }], stateMutability: "view" },
+  { type: "event", name: "Deposited", inputs: [{ name: "account", type: "address", indexed: true }, { name: "amount", type: "uint256", indexed: false }], anonymous: false },
+  { type: "event", name: "Withdrawn", inputs: [{ name: "account", type: "address", indexed: true }, { name: "amount", type: "uint256", indexed: false }], anonymous: false },
+  { type: "event", name: "Paused", inputs: [{ name: "account", type: "address", indexed: false }], anonymous: false },
+  { type: "event", name: "Unpaused", inputs: [{ name: "account", type: "address", indexed: false }], anonymous: false },
+  { type: "event", name: "OwnershipTransferred", inputs: [{ name: "previousOwner", type: "address", indexed: true }, { name: "newOwner", type: "address", indexed: true }], anonymous: false },
+  { type: "event", name: "Upgraded", inputs: [{ name: "implementation", type: "address", indexed: true }], anonymous: false },
 ];
-const tokenAbi = [{ type: "function", name: "balanceOf", inputs: [{ name: "account", type: "address" }], outputs: [{ type: "uint256" }], stateMutability: "view" }];
+const tokenAbi = [{ type: "function", name: "balanceOf", inputs: [{ name: "account", type: "address" }], outputs: [{ name: "", type: "uint256" }], stateMutability: "view" }];
 const manifest = {
   schemaVersion: 1, network: "anvil", chainId: 31337, deploymentBlock: 3,
   rpcUrl: "http://127.0.0.1:8545", token: address, proxy: address,
@@ -41,6 +51,13 @@ await withFixture(async (root) => {
 
   // Catches a bridge that exports an ABI missing a V1 contract function or event.
   assert.throws(() => extractAbi({ abi: bankAbi.filter((entry) => entry.name !== "Withdrawn") }, "BankV1"), /Withdrawn/);
+  // Catches generated calls/log decoders accepting ABI entries with the right name but wrong wire signature.
+  const wrongFunction = structuredClone(bankAbi);
+  wrongFunction.find((entry) => entry.name === "balanceOf").outputs = [];
+  assert.throws(() => extractAbi({ abi: wrongFunction }, "BankV1"), /signature.*balanceOf/i);
+  const wrongEvent = structuredClone(bankAbi);
+  wrongEvent.find((entry) => entry.name === "Deposited").inputs[0].indexed = false;
+  assert.throws(() => extractAbi({ abi: wrongEvent }, "BankV1"), /signature.*Deposited/i);
   const rendered = renderContractsModule(extractAbi({ abi: bankAbi }, "BankV1"), extractAbi({ abi: tokenAbi }, "MockUSDC"));
   assert.match(rendered, /export const bankV1Abi = .* as const;/s);
   assert.match(rendered, /export const mockUsdcAbi = .* as const;/s);
diff --git a/web/src/data/bankClient.test.ts b/web/src/data/bankClient.test.ts
index 101805e..ed664bb 100644
--- a/web/src/data/bankClient.test.ts
+++ b/web/src/data/bankClient.test.ts
@@ -135,6 +135,17 @@ describe("loadDashboardSnapshot", () => {
     expect(snapshot.diagnostics).toEqual([expect.objectContaining({ blockNumber: 4n, logIndex: 2, message: expect.any(String) })]);
   });
 
+  it("diagnoses proxy logs with malformed topics or payload data", async () => {
+    // Catches payload-shape validation skipping malformed proxy logs before the diagnostic boundary.
+    const reader = new ReaderDouble();
+    const valid = depositedLog(4n, 1, owner, 7n);
+    reader.logs = [valid, { ...valid, logIndex: 2, topics: "not-topics" }, { ...valid, logIndex: 3, data: "not-hex" }, { ...valid, logIndex: 4, data: undefined }];
+    const snapshot = await loadDashboardSnapshot(reader, manifest);
+
+    expect(snapshot.activity).toHaveLength(1);
+    expect(snapshot.diagnostics.map((diagnostic) => diagnostic.logIndex)).toEqual([2, 3, 4]);
+  });
+
   it("preserves a rejected contract read instead of substituting zero", async () => {
     // Catches disconnected RPC reads being silently rendered as zero balances.
     const reader = new ReaderDouble(); reader.error = new Error("node read failed");
diff --git a/web/src/data/bankClient.ts b/web/src/data/bankClient.ts
index df07d4b..8b3673c 100644
--- a/web/src/data/bankClient.ts
+++ b/web/src/data/bankClient.ts
@@ -106,9 +106,10 @@ function decodeActivity(logs: readonly unknown[], proxy: Address): { activity: r
   const activity: Activity[] = [];
   const diagnostics: DecodeDiagnostic[] = [];
   for (const log of logs) {
-    if (!isLog(log) || !sameAddress(log.address, proxy)) continue;
+    if (!isLogIdentity(log) || !sameAddress(log.address, proxy)) continue;
     const identity = { blockNumber: log.blockNumber, logIndex: log.logIndex, transactionHash: log.transactionHash };
     try {
+      if (!isLogPayload(log)) throw new Error("proxy event payload is malformed");
       const decoded = decodeEventLog({ abi: bankV1Abi, data: log.data, topics: log.topics as [Hex, ...Hex[]] });
       const next = decodedActivity(decoded.eventName, decoded.args, identity);
       if (next) activity.push(next);
@@ -121,14 +122,18 @@ function decodeActivity(logs: readonly unknown[], proxy: Address): { activity: r
   return { activity, diagnostics };
 }
 
-function isLog(value: unknown): value is Readonly<{ address: Address; blockNumber: bigint; logIndex: number; transactionHash: Hex; data: Hex; topics: readonly Hex[] }> {
+function isLogIdentity(value: unknown): value is Readonly<{ address: Address; blockNumber: bigint; logIndex: number; transactionHash: Hex; data?: unknown; topics?: unknown }> {
   return typeof value === "object" && value !== null
     && typeof (value as { address?: unknown }).address === "string" && isAddress((value as { address: string }).address)
     && typeof (value as { blockNumber?: unknown }).blockNumber === "bigint"
     && typeof (value as { logIndex?: unknown }).logIndex === "number"
-    && typeof (value as { transactionHash?: unknown }).transactionHash === "string"
-    && typeof (value as { data?: unknown }).data === "string"
-    && Array.isArray((value as { topics?: unknown }).topics);
+    && typeof (value as { transactionHash?: unknown }).transactionHash === "string";
+}
+
+function isLogPayload(value: Readonly<{ data?: unknown; topics?: unknown }>): value is Readonly<{ data: Hex; topics: readonly Hex[] }> {
+  return typeof value.data === "string" && /^0x[0-9a-fA-F]*$/.test(value.data)
+    && Array.isArray(value.topics) && value.topics.length > 0
+    && value.topics.every((topic) => typeof topic === "string" && /^0x[0-9a-fA-F]*$/.test(topic));
 }
 
 function decodedActivity(eventName: string, args: unknown, identity: Readonly<{ blockNumber: bigint; logIndex: number; transactionHash: Hex }>): Activity | undefined {