fix(cli): add idempotency-key protection to all write tools - #49

Summary

• Adds packages/cli/src/mcp/idempotency.ts: deterministicIdempotencyKey(operation, params, windowMinutes=5), deriving a stable SHA-256 key from the operation name, its params, and a 5-minute time bucket.
• Every CLI write tool now accepts an optional idempotencyKey input; when omitted, it falls back to the deterministic key. Compound tools (e.g. create_card, add_spending_category) suffix the key per internal step (:card, :fund) so each underlying write gets its own protected key.
• Fixed tools: transfer, batch_transfer, create_account (funding step), fund_card, add_spending_category (funding step), create_card, create_disposable_card, create_pse_order, create_bank_transfer_order, create_breb_order, topup_via_pse, cashout_to_bank, send_to_breb_key.

Why

Live testing surfaced a real double-submission bug: a single transfer call resulted in two independently-settled on-chain transactions (double the requested amount moved), traced to a transport-level retry after an MCP reconnect. No CLI write call ever passed an idempotency key to the SDK's HTTP client (packages/core/src/http-client.ts already supports one — it generates a fresh UUID per request() call, but that's only reused across that call's own internal retries, not across two genuinely independent calls). This time it was an inter-account transfer to the same user; in other flows (bank cashouts, BRE-B payouts) an unprotected retry could move real money to a third party twice.

Test plan

• bun run --filter @bloque/cli typecheck — clean
• bun test packages/cli — 51 pass, 0 fail (includes new idempotency.test.ts, 5 tests covering stability, param/operation/time-window sensitivity, and digest shape)
• End-to-end BRE-B send retest (send_to_breb_key to bbva@pablodorado.com) once this ships, to confirm no duplicate settlement under a forced retry

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