Threshold

A little less to carry. A household departure assistant that remembers different needs, shares the work, and changes the plan when real life changes.

The memorable moment: the elevator breaks. Threshold keeps Sam's step-free preference, switches to the garden ramp, and recomputes the time. Then it starts raining. A rain-cover task appears in the dependency graph before the household can be ready. Nobody has to repeat the whole morning to the next caregiver.

Built for the Alexa+ track of Build, Ship, Shape: Amazon Developer Hackathon during September 2026. This is a working web simulation backed by a real MCP server; it is not a live Alexa deployment. All people, building statuses, and device effects are synthetic.

Watch or download the 106-second demo and captions

Run in one minute

Requires Node.js 22 or newer. No API key, AWS account, hardware, or build step is required for the core demo.

npm ci
npm start

Open http://127.0.0.1:4318. Choose Plan our library morning, or open http://127.0.0.1:4318/?demo=1 to create the first plan automatically if none exists.

npm test
npm run check

The server binds to loopback only. Local state persists in data/household.json, which is ignored by Git. Reset rehearsal resets this synthetic data. Stop the process with Ctrl+C. PORT and THRESHOLD_DATA are optional environment overrides.

Related MCP server: alexa-plus

Try the complete story

1. Plan to be outside the building by 08:30. The rehearsal clock is fixed at 08:12; these are planning estimates, not a running clock or a library-arrival prediction.

2. Confirm Collect the library books and Fill the water bottle. Packing the shared bag becomes available only after both.

3. Say or click The elevator is out. The route changes to the garden ramp; the step-free requirement and completed work remain.

4. Say It's raining now. A rain-cover task becomes a prerequisite for meeting at the threshold.

5. Say Alex can take over Sam's tasks. The owner changes only for unfinished work, and the schedule accounts for the extra workload.

6. Say Turn on a quiet cue. The virtual hallway light glows; the action gets a receipt. Undo restores the earlier light state.

7. Open Receipts to inspect actual tool names, revisions, hash-linked receipts, and the negotiated MCP version. Reload the page: the context and plan survive.

Checking a task is a person's explicit confirmation. The assistant does not infer that someone packed a bag simply because it made a plan.

The UI supports text, keyboard, large check controls, reduced motion, and optional browser speech input when the browser exposes it. Browser speech may use the browser vendor's speech service. The demo is fully operable without a microphone. Alexa+ voice rendering is simulated, not impersonated.

Optional real language understanding

The no-key mode is visibly labeled Local demo parser. It recognizes the supported rehearsal phrases; it is not presented as model inference.

Physical completion requires a direct task-specific report. Both local and optional-model proposals pass a conservative English confirmation check: negations, questions, partial progress, and future intent produce a clarification. Other wording can use the task's explicit check control. This is a bounded rehearsal-language check, not a claim of general language accuracy.

To interpret more natural phrasing, provide an Anthropic API key through your environment or secret manager:

# Set ANTHROPIC_API_KEY in your shell or secret manager; never in source.
THRESHOLD_MODEL=claude-sonnet-5 npm start

On the author's workstation the scoped launcher is:

hsec exec --only ANTHROPIC_API_KEY -- npm start

src/interpret.js uses the Messages API's actual tool selection. The model receives the typed request and synthetic household state. It returns a tool proposal; the web client executes it through /mcp. The store validates arguments, revisions, dependencies, and reversals independently. Keys remain in the server process. Errors never print provider credentials.

On September 21, 2026, live claude-sonnet-5 calls selected the correct tools for an elevator outage expressed as “the lift has stopped working” and a quiet visual cue expressed as “make the hallway glow gently without a sound.” This is a two-case integration check, not a general accuracy benchmark.

Real MCP, small surface

Endpoint: http://127.0.0.1:4318/mcp. Transport: Streamable HTTP. Tested negotiated protocol: 2025-11-25. Implementation: official @modelcontextprotocol/sdk 1.30.0. A fresh server/transport handles each stateless request; household state is stored independently.

Every mutation takes expectedRevision and a unique requestId. Stale actions fail. Identical retries return the same receipt instead of executing twice. Reusing an ID with different arguments fails. The read-only threshold://household/current resource exposes the same household snapshot.

For a compatible host, configure a Streamable HTTP server URL at /mcp; the host must be able to reach this loopback endpoint. Host instructions describe the calling sequence. Direct Alexa+ onboarding, OAuth, and production hosting have not been completed or tested.

Architecture

flowchart LR
  U[Text / optional browser speech] --> I[Local parser or optional Claude tool selection]
  I --> C[Web MCP client]
  C --> H[Official SDK · Streamable HTTP]
  H --> V[Schema + revision + dependency checks]
  V --> S[Local household store]
  S --> P[Owner-aware task scheduler]
  S --> R[Hash-linked action receipts]
  P --> UI[Floorplan · tasks · timing · constraints]
  R --> UI

src/household.js owns the domain. It schedules prerequisites before dependents and serializes unfinished tasks belonging to the same person. When a changed constraint adds a prerequisite, an already completed terminal task is invalidated. A missing accessible route never silently becomes a stair route. The virtual device adapter only offers warm/off, making its effects small and reversible.

The receipt chain makes application changes inspectable and detects accidental edits against a retained chain. It is not a security-grade, externally anchored audit log: someone who can rewrite the whole file can also recompute its hashes. JSON is written to a temporary file and atomically renamed. This prototype supports one server process; it does not implement multi-process locking or a multi-household tenant boundary.

Evidence and honest limits

• Thirteen automated tests pass, including official MCP client interoperability, protocol negotiation, resources, Origin/Host rejection, blocked dependencies, inaccessible routes, changed prerequisites, persistence, safe undo, idempotency, owner scheduling, and completion-report rejection.

• The web UI was inspected in the Codex integrated browser. Elevator outage visibly selected the garden ramp; rain added a required rain-cover step and changed timing.

• Two live optional model calls passed as described above.

• No physical household device, Alexa account, weather service, location API, building sensor, or delivery service is connected. Sources explicitly identify fixtures and user reports.

• The only implemented trip template is a library departure. Durations are illustrative estimates. There is no medical, emergency, access-control, or building-safety certification.

• The server is a local single-user prototype. It checks Origin and Host and binds to loopback, but has no production OAuth. Do not expose it publicly unchanged.

Submission materials

Demo script · Project description · Product feedback · Host integration

All original application code and illustrated SVG artwork were created for this entry. The reusable hackathon planning framework informed prioritization; no prior project's implementation or private household data was copied. See LICENSE and THIRD_PARTY_NOTICES.md.

Primary references: Amazon hackathon rules, MCP 2025-11-25 Streamable HTTP, official TypeScript SDK, Claude models. Requirements and model ID were checked September 21, 2026.

Recorded validation

Thirteen local tests pass. The filmed demo also completed five real optional model requests and nine MCP tool calls, including dependency progress, outage, rain, handoff, virtual cue, and undo. This is a synthetic rehearsal, not deployed household use. Hosted CI has not been verified. See the recorded demo and captions.