Fix one bug found in a live run, close one review finding and add the live demo. Change nothing else.

1 src/chain.ts declares TurnsBought with uint8 league, but SwarmDerby.sol line 126 has uint8 indexed league. ethers cannot decode a real TurnsBought log with the current line (data out-of-bounds), so after a buy that succeeded on-chain derby_buy_pack returns isError ("did not emit TurnsBought") and an agent may buy again. Use the contract's event: event TurnsBought(address indexed player, uint8 indexed league, uint256 count, uint256 cost, uint256 burned).

2 Add test/turnsbought.test.ts. It decodes this real log (Robinhood Chain block 82726982, tx 0xbf148a71...) with the same ABI that src/chain.ts uses (export it) and asserts player 0xc3F59E5dD9e8D8a74631c0ea68E38fD49FF1b04b, league 1, count 5, cost 0.5 IMD, burned 0.2 IMD. Log: {"address": "0xba58bc6b5acf8043daea2bf1bf6c1c09cf84b03c", "topics": ["0x13daa21a239e5704156c30acf2e5703c9ffd93f09461b809fb3df4c6ce5bfa98", "0x000000000000000000000000c3f59e5dd9e8d8a74631c0ea68e38fd49ff1b04b", "0x0000000000000000000000000000000000000000000000000000000000000001"], "data": "0x000000000000000000000000000000000000000000000000000000000000000500000000000000000000000000000000000000000000000006f05b59d3b2000000000000000000000000000000000000000000000000000002c68af0bb140000"}

3 ethers v6 tx.wait() throws CALL_EXCEPTION, with a receipt of status 0, for a reverted transaction. send() in src/chain.ts reports that as "broadcast but not confirmed", so a reverted buy keeps its cap reservation. Treat CALL_EXCEPTION with a status-0 receipt as confirmedNoCharge, and add a fake-chain test that a confirmed revert releases the reservation.

4 Add scripts/demo.mjs (run with node scripts/demo.mjs after npm run build; package.json is protected, so add no npm script): like scripts/smoke.mjs, but it keeps DERBY_PRIVATE_KEY and calls derby_status, derby_buy_pack {packs:1}, derby_swing until it returns isError, derby_buy_pack {packs:1}, derby_board and derby_status, and prints each call with a UTC time and its result. Do not run it: it spends real IMD.

5 README.md: replace <owner>/swarm-derby-mcp with identity-md-launches/launch-937-build-swarm-derby-mcp-typescript-stdio, and link DEMO.md under the title.

6 Add DEMO.md with the text between the lines. Keep every number and hash. Make each hash a link to https://robinhoodchain.blockscout.com/tx/.

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Live demo

A recorded session on Robinhood Chain mainnet, 2026-10-07 19:41:16 to 19:41:36 UTC. An MCP SDK client over stdio made the calls of scripts/demo.mjs against dist/index.js of commit b6dee81, with fix 1 of the next commit applied (the TurnsBought ABI line). Wallet 0xc3F59E5dD9e8D8a74631c0ea68E38fD49FF1b04b (the Swarm Derby house bot), DERBY_MAX_IMD=0.5, a new ledger.

| # | Call | Result |

|---|---|---|

| 1 | derby_status | play mode, 4.5 IMD, 0 agent turns, today 1684 ft, rank 1, cap 0.5, spent 0 |

| 2 | derby_buy_pack {"packs":1} | cost 0.5 IMD (approve, then buy), 5 turns, spent 0.5, remaining 0 |

| 3 | derby_swing | swing 25: POP, 202 ft |

| 4 | derby_swing | swing 26: FOUL, 119 ft |

| 5 | derby_swing | swing 27: POP, 253 ft |

| 6 | derby_swing | swing 28: POP, 281 ft |

| 7 | derby_swing | swing 29: POP, 265 ft, 0 turns left |

| 8 | derby_swing | isError: No agent turns left. Call derby_buy_pack to buy a pack of 5 turns first. |

| 9 | derby_buy_pack {"packs":1} | isError: Refused: buying 1 pack(s) costs 0.5 IMD, which would take spending to 1.0 IMD, past the DERBY_MAX_IMD cap of 0.5 IMD (0.5 already spent). Nothing was signed. |

| 10 | derby_board | agent day 20733: #1 0xc3F5...b04b with 1684 ft, pot 0.45 IMD, not ready to settle |

| 11 | derby_status | 4.0 IMD, 0 turns, cap remaining 0 |

No swing in this run was a homer, so the score stayed at 1684 ft from the bot's earlier run. Gas for the 12 transactions was about 0.00002 ETH.

Transactions: approve 0xa94491a594d033abb4c7b6139086cd1a2d99ab2cc88eccdcc55af0eefc0c1527; buy 0xbf148a714fa18783b6db21157066190dfce471a4ed34c8e28fbf311b1310ccd3; swing 25 commit 0x7b86ecd9a1344bc6b02391f087fbb85976f153346e3d0ee0be7d921fc93ac09a, finalize 0x5c488e99edc709b04c4cf518ae4aaeb7ead774fbe4411ec63245509b279b3879; swing 26 commit 0xcdb883b7a2a5dd711dfbc67ca72533dff919139f005a8544cca31828dd056336, finalize 0x8842a6a7168eeb71f5e871ba28e1a2ad09f81ff56872383da4b45f31ed158972; swing 27 commit 0x34af48cc8166a68e8df4c19725bfc4e92bd5587911d30da5c76a9cbb044364c8, finalize 0x33ff174e9e979d2d9c5a7d4ea9e7f11b104e674fba690859338a9488a6a319e4; swing 28 commit 0xa2f385682c73950aafe7ce8343c3f61a3d43458dbf1918bb5664b9ceddbf2268, finalize 0x5d77bdc52d7f9400b29ff3d5e00a9d50a369b85440c66a4132999ef27642b025; swing 29 commit 0xa2157170edc4231f5cf79bf2e9dcb80f6811701dbd9ef94d9db17356ab36c5ea, finalize 0xd554c86a02ba4cac0564c27fbf2396ad66ce31e2f97bdd8f9b04532a2e2b8bd6.

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Then run npm run typecheck, npm test and npm run build, and update the README's test output.