fix(checkout): remove fabricated batch transaction results

[nasalehj]

Summary

Addresses part of #813

This slice removes fabricated batch checkout success and failure behavior from the frontend. Checkout now uses the connected wallet address, validates cart and slippage inputs before submission, and exposes an explicit executor boundary whose success result requires an observed successful receipt. The repository currently has no deployed batch-purchase or multicall ABI, address, function signature, or payment semantics, so the concrete chain adapter is intentionally not fabricated.

Why

The previous checkout waited for a timer, used Math.random() to select a failure branch, and returned a generated transaction hash without contacting a wallet or blockchain. That made the UI report purchases that never occurred and made failures nondeterministic. The new service fails closed when no configured executor exists and only returns success after an executor reports a successful receipt.

What was built

File	What it contains
src/lib/batchTransaction.ts	Deterministic cart, wallet, amount, and slippage validation; per-item quote/minimum amount calculation; executor interface; receipt-gated success; decoded provider/user errors; honest unconfigured-network failure.
src/components/CartSidebar.tsx	Uses the existing wallet store address and removes the hardcoded checkout wallet.
src/lib/__tests__/batchTransaction.test.ts	Nine focused tests covering validation, disconnected wallets, missing configuration, successful receipt handling, reverted receipts, decoded provider errors, user rejection, and slippage calculations.

The service tests inject an executor so receipt and error behavior can be verified without inventing a contract ABI or making network calls.

Integration changes outside src/lib/

• src/components/CartSidebar.tsx — uses the canonical wallet store address and no longer supplies a placeholder account.

Acceptance criteria coverage

• executeBatchPurchase submits a real transaction for the connected account and resolves success: true only after on-chain confirmation (receipt observed); no code path returns a fabricated hash. — Fabricated hashes and submission behavior are removed; the real chain adapter remains blocked by the missing deployed contract ABI/address and call semantics.
• The 20% Math.random() failure branch and the setTimeout simulation are gone. (src/lib/batchTransaction.ts and static inspection — no timer/random simulation remains)
• The per-item slippage math is either validated against the on-chain min-out or documented as an estimate with the real values computed from the quote. (src/lib/batchTransaction.ts, calculateMinimumAmount, and batchTransaction.test.ts — quote-derived estimates are passed to the executor seam)
• src/lib/tests/batchTransaction.test.ts is rewritten to mock wagmi/viem and assert: success returns the real hash; user rejection returns success: false with a decoded reason; disconnected wallet is rejected before any submission. (src/lib/__tests__/batchTransaction.test.ts — deterministic executor tests cover real executor hash, user rejection, decoded revert data, and no-call disconnected validation)
• npm run typecheck, npm test, and npm run lint pass. — Existing unrelated syntax errors, test-environment mock failures, and a missing eslint-plugin-jsdoc dependency prevent these repository-wide gates from passing.

Deliberately deferred

• Concrete wagmi/viem batch transaction adapter — the repository does not contain a deployed batch/multicall contract address, ABI, function signature, or payment/token semantics from which a safe call can be implemented.
• On-chain validation of minimum amounts — depends on the deferred contract call and quote format.
• Dynamic volatility-based slippage and EIP-712 typed-data slippage intent — explicitly out of scope in the issue.

Test plan

• npx prettier --check src/lib/batchTransaction.ts src/lib/__tests__/batchTransaction.test.ts src/components/CartSidebar.tsx — all matched files pass.
• npm test -- --runInBand src/lib/__tests__/batchTransaction.test.ts — 9/9 passing (9 rewritten tests).
• npm run validate:env — passes in development.
• npm run typecheck — blocked by pre-existing syntax errors in unrelated files including src/app/compare/page.tsx, src/components/ComparisonBar.tsx, src/components/PropertyCard.tsx, src/components/TransactionConfirmation.tsx, src/lib/toast.ts, and src/stories/ResponsiveContainerExample.stories.ts.
• npm test -- --runInBand — 63/140 suites passing; 986/1145 tests passing. Failures include existing viem mock incompatibility, Vitest/CommonJS incompatibilities, missing modules, and unrelated component/test failures.
• npx eslint src/lib/batchTransaction.ts src/lib/__tests__/batchTransaction.test.ts src/components/CartSidebar.tsx --max-warnings=0 — blocked before linting because eslint-plugin-jsdoc is not installed.
• npm run build — stops at the same pre-existing typecheck failures.

Env vars / Notes

No new environment variables.

No deployment or migration changes are included. The executor interface is the integration seam for the deployed contract details; until those details are added, valid checkout attempts return an explicit configuration error rather than claiming an on-chain purchase.

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If this PR is for one of the issues assigned to you as part of a Wave, please link it to ensure your contribution is tracked properly. You can do this by adding a keyword to the PR description (e.g., Closes #123), or by clicking a button below:

Issue	Title
#814	middleware.ts falls back to a hardcoded JWT secret: forged auth-token cookies verify when AUTH_SECRET is unset	Link to this issue
#813	Cart checkout fabricates transaction results: executeBatchPurchase never submits to the chain	Link to this issue
#816	Delete orphaned Pages Router file src/pages/security/TransactionSecurity.tsx	Link to this issue
#815	useAuth reports authentication from cookie presence and fabricates userAddress: client auth state is a mock	Link to this issue

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[nanaf6203-bit]

LGTM

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