diff --git a/.env.example b/.env.example
index 8bc956a..e2a6b8c 100644
--- a/.env.example
+++ b/.env.example
@@ -25,6 +25,7 @@ PIMLICO_SPONSORSHIP_POLICY_ID=
 #   dry-run    -> never broadcast, always simulate (good for dev)
 #   native     -> you-pay-gas even if a sponsorship policy is set
 #   sponsored  -> use the key's default policy (no explicit id)
+# Any other value stops startup instead of guessing (a typo of dry-run must not broadcast).
 # WDK_GAS_MODE=
 
 # ─── Local AI brain (QVAC) ───────────────────────────────────────────────────
diff --git a/src/cli.mjs b/src/cli.mjs
index 238bd1b..171143f 100644
--- a/src/cli.mjs
+++ b/src/cli.mjs
@@ -529,6 +529,13 @@ async function main() {
   // inherits fd 0 when it spawns; by then the input must already be ours.
   if (SCRIPTED) scriptLines = await readScriptLines();
 
+  // An unrecognised gas mode stops the agent before anything is shown or initialised: the
+  // operator asked for a mode, and none of the three is a safe guess at what they meant.
+  if (config.gasModeError) {
+    println(c.red(`   gas mode: ${config.gasModeError}`) + "\n");
+    process.exit(1);
+  }
+
   banner();
 
   // A malformed policy must stop the agent before any send, never be ignored.
diff --git a/src/config.mjs b/src/config.mjs
index b464dd0..7936175 100644
--- a/src/config.mjs
+++ b/src/config.mjs
@@ -58,7 +58,16 @@ if (process.env.RESERVOIR_API_URL) chain.reservoirUrl = process.env.RESERVOIR_AP
 
 const pimlicoKey = process.env.PIMLICO_API_KEY || "";
 const sponsorshipPolicyId = process.env.PIMLICO_SPONSORSHIP_POLICY_ID || "";
-const gasOverride = (process.env.WDK_GAS_MODE || "").toLowerCase();
+// WDK_GAS_MODE takes the three values .env.example documents. Anything else is refused at
+// startup instead of read as "sponsored": with a Pimlico key that fallthrough broadcast, so a
+// typo of dry-run was the thing that turned broadcasting on.
+const GAS_MODES = ["dry-run", "native", "sponsored"];
+const gasOverride = (process.env.WDK_GAS_MODE || "").trim().toLowerCase();
+const gasModeError =
+  gasOverride && !GAS_MODES.includes(gasOverride)
+    ? `WDK_GAS_MODE=${JSON.stringify(process.env.WDK_GAS_MODE)} is not a gas mode: ` +
+      `use dry-run, native or sponsored, or leave it empty to auto-detect`
+    : null;
 
 // NFT reads (get_nfts) go through Reservoir's indexed API, not raw eth_getLogs:
 // Monad prunes historical state, so Transfer-event scanning is unreliable. The host
@@ -72,7 +81,9 @@ const reservoirUrl = chain.reservoirUrl;
 //   sponsored -> gasless via Pimlico paymaster (agent pays 0)
 //   native    -> you-pay-gas in MON (still needs a bundler = Pimlico key)
 let gasMode;
-if (gasOverride === "dry-run" || !pimlicoKey) gasMode = "dry-run";
+// A refused value resolves to dry-run as well, so an entry point that never looks at
+// gasModeError still cannot broadcast on it.
+if (gasModeError || gasOverride === "dry-run" || !pimlicoKey) gasMode = "dry-run";
 else if (gasOverride === "native") gasMode = "native";
 else gasMode = "sponsored";
 
@@ -151,6 +162,8 @@ export const config = {
   // Convenience flag for guardrails: mainnet moves real funds.
   isMainnet: network === "mainnet",
   gasMode,
+  // Set when WDK_GAS_MODE holds an unrecognised value; the CLI refuses to start on it.
+  gasModeError,
   slippagePercent,
   sponsorshipPolicyId,
   // ERC-4337 needs a bundler+paymaster. For a LOCAL CLI the Pimlico key stays on
diff --git a/test/gas-mode.test.mjs b/test/gas-mode.test.mjs
new file mode 100644
index 0000000..0b67af8
--- /dev/null
+++ b/test/gas-mode.test.mjs
@@ -0,0 +1,111 @@
+/**
+ * WDK_GAS_MODE accepts the three values .env.example documents and refuses anything else.
+ *
+ * config.mjs reads the environment at import, so each case loads it in a child process, as
+ * reservoir-network.test.mjs does. The CLI case runs the built dist/cli.mjs with the @qvac/sdk
+ * shim, as nfts-command.test.mjs does.
+ */
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { execFileSync, spawnSync } from "node:child_process";
+import { existsSync, mkdtempSync, writeFileSync, readFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { fileURLToPath, pathToFileURL } from "node:url";
+
+const CONFIG_URL = pathToFileURL(fileURLToPath(new URL("../src/config.mjs", import.meta.url))).href;
+
+/** gasMode and gasModeError for one environment, read in a fresh process. */
+function load(env) {
+  const script = `import(${JSON.stringify(CONFIG_URL)}).then(({ config }) =>
+    console.log(JSON.stringify({ gasMode: config.gasMode, gasModeError: config.gasModeError })))`;
+  const base = { ...process.env };
+  delete base.WDK_GAS_MODE;
+  delete base.PIMLICO_API_KEY;
+  const out = execFileSync(process.execPath, ["--input-type=module", "-e", script], {
+    env: { ...base, MONAD_NETWORK: "testnet", ...env },
+    encoding: "utf8",
+  });
+  return JSON.parse(out.trim().split("\n").pop());
+}
+
+test("a typo of a gas mode is refused, never read as sponsored", () => {
+  // On main each of these resolved to "sponsored" with a key set, which broadcasts.
+  for (const value of ["dryrun", "dry_run", "simulate", "dry run", "gasless"]) {
+    const r = load({ PIMLICO_API_KEY: "x", WDK_GAS_MODE: value });
+    assert.ok(r.gasModeError, `${JSON.stringify(value)} must be refused`);
+    assert.match(r.gasModeError, new RegExp(JSON.stringify(value).replace(/[.*+?^${}()|[\]\\]/g, "\\$&")));
+    assert.match(r.gasModeError, /dry-run, native or sponsored/);
+    assert.equal(r.gasMode, "dry-run", "a refused value must not be able to broadcast");
+  }
+});
+
+test("a refused value is refused without a key too", () => {
+  const r = load({ WDK_GAS_MODE: "dryrun" });
+  assert.ok(r.gasModeError);
+  assert.equal(r.gasMode, "dry-run");
+});
+
+test("the documented values resolve as documented, in any case and with padding", () => {
+  const cases = [
+    ["dry-run", "dry-run"], ["DRY-RUN", "dry-run"], [" dry-run ", "dry-run"],
+    ["native", "native"], ["Native", "native"],
+    ["sponsored", "sponsored"], ["SPONSORED ", "sponsored"],
+  ];
+  for (const [value, mode] of cases) {
+    const r = load({ PIMLICO_API_KEY: "x", WDK_GAS_MODE: value });
+    assert.ok(!r.gasModeError, `${JSON.stringify(value)} is documented`);
+    assert.equal(r.gasMode, mode, `${JSON.stringify(value)}`);
+  }
+});
+
+test("an empty value keeps the auto-detection, with and without a key", () => {
+  // Behaviour that must not change, so it holds on main as well.
+  const cases = [
+    [{ PIMLICO_API_KEY: "x" }, "sponsored"],
+    [{ PIMLICO_API_KEY: "x", WDK_GAS_MODE: "" }, "sponsored"],
+    [{}, "dry-run"],
+    // Without a key every documented value still simulates, as before.
+    [{ WDK_GAS_MODE: "sponsored" }, "dry-run"],
+  ];
+  for (const [env, mode] of cases) {
+    const r = load(env);
+    assert.ok(!r.gasModeError, JSON.stringify(env));
+    assert.equal(r.gasMode, mode, JSON.stringify(env));
+  }
+});
+
+test("the CLI stops before the banner or the wallet on every refused gas mode", () => {
+  const distCli = fileURLToPath(new URL("../dist/cli.mjs", import.meta.url));
+  assert.ok(existsSync(distCli), "dist/cli.mjs missing — run npm run build first (CI builds before testing)");
+  const shim = pathToFileURL(fileURLToPath(new URL("./helpers/shim-register.mjs", import.meta.url))).href;
+  const dir = mkdtempSync(join(tmpdir(), "nad-gas-"));
+  const policy = join(dir, "policy.json");
+  writeFileSync(policy, "{}");
+  const callLog = join(dir, "calls.log");
+  const env = {
+    ...process.env,
+    WDK_SEED: "abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon abandon about",
+    QVAC_MODEL_PATH: "shim-model.gguf",
+    MONAD_NETWORK: "testnet",
+    NAD_STATE_PATH: join(dir, "state.json"),
+    NAD_POLICY: policy,
+    NAD_MCP_CONFIG: join(dir, "no-mcp.json"),
+    NAD_SHIM_CALL_LOG: callLog,
+    NO_COLOR: "1",
+    PIMLICO_API_KEY: "x",
+  };
+  delete env.NAD_CLI_NO_RUN;
+  for (const value of ["dryrun", "dry_run", "simulate"]) {
+    const r = spawnSync(process.execPath, ["--import", shim, distCli], {
+      env: { ...env, WDK_GAS_MODE: value }, input: "/address\n", encoding: "utf8", timeout: 60_000,
+    });
+    const out = r.stdout + r.stderr;
+    assert.equal(r.status, 1, `${value}:\n${out}`);
+    assert.ok(out.includes(`gas mode: WDK_GAS_MODE="${value}" is not a gas mode`), `${value}:\n${out}`);
+    assert.doesNotMatch(out, /initializing wallet/, `${value}: the wallet must not be touched`);
+    assert.doesNotMatch(out, /gasless/, `${value}: the banner must not claim a mode`);
+  }
+  const calls = existsSync(callLog) ? readFileSync(callLog, "utf8").split("\n").filter(Boolean).length : 0;
+  assert.equal(calls, 0, "the model must not be called");
+});