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Latch

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Latch

Standing spend rules for the house.

Alexa+ filled a $250 cart and added things people excluded. A yes on checkout does not stop the next restock. Latch is the rule that stays after the chat dies.

Grant a cap. It restocks inside that cap. A price jump holds. You undo until 9pm. You revoke, and it stops.

Not a shopping chatbot. Not “confirm this one order.” Not a booking receipt.

Amazon Developer Hackathon · Alexa+ track · 23 Oct 2026. Product name is Latch.

Demo (about three minutes)

  1. Grant: Hill’s Science Diet 15lb, max $40, fire at 3 days left, hold if price jumps 15 percent, undo until 9pm. Card shows LCH-14.

  2. Time-skip to 3 days. It buys at $28. Card shows LED-8821 and mock order ORD-440.

  3. Kill the tab. “What did you buy?” Same IDs.

  4. Mutate the fixture to $33. Trigger. Hold. No charge.

  5. Undo the $28 buy. Ledger is undone.

  6. Revoke. Next trigger is denied.

Speech is illegal without entry_id and provider_ref. Empty ledger → it says it failed.

Local: npm run dev then open the printed URL. Buttons on the left are the tape.

Related MCP server: dingdawg-agent-wallet

Golden cases

#

Case

Pass

1

Grant then trigger → commit under cap

committed + LED- + ORD-

2

Excluded SKU (Sony under a Hill’s rule)

denied / excluded_sku

3

Price +18%

held / price_jump

4

Undo before 9pm

undone

5

Undo after deadline

rejected

6

Revoke then trigger

denied / rule_revoked

7

New session

same entry_id

8

Empty ledger

cannot say “bought”

9

Qty 2 when max 1

denied / qty_exceeded

10

Clock advance, no grant

no buy

npm test

Protocol

  • MCP 2025-11-25 Streamable HTTP at POST /mcp

  • Tools: grant_latch, get_latch, run_triggers, undo_entry, revoke_latch

  • Demo-gated: advance_clock, set_catalog_price

  • Cards: /apps/grant.html, /apps/hold.html, /apps/ledger.html (resourceUri on mutating results)

  • State: D1 rules + ledger. Catalog: KV fixture hills-15lb / sony-headphones

  • Household: X-Latch-Household. No MCP session id required.

  • Privacy / terms: /privacy, /terms

Friction Amazon asked for: FRICTION.md.

Setup

Needs Node and Wrangler. No Token Factory key. No model.

npm install
npx wrangler types
npx wrangler d1 migrations apply latch --local
npm test
npm run dev

Deploy only when you want a public URL:

npx wrangler d1 create latch
npx wrangler kv namespace create CATALOG
# put the real ids in wrangler.jsonc, then:
npx wrangler types
npx wrangler d1 migrations apply latch --remote
npx wrangler deploy

Custom hostname later: mcp.latch.<your-domain>.

What this is not

  • No runtime LLM

  • No real Amazon cart

  • No VoiceCart confirmed=true checkout

  • No restaurant booking

  • No Alexa or Amazon in the product name

Law: PRODUCT.md. Design: DESIGN.md.

This server cannot be deployed

One endpoint for every MCP toolRayrun runs every MCP server behind one URL and holds the credentials. Each call is decided per client, tool, and argument, then recorded.ray.runAd

Resources

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