| name | create-spec |
| description | Create a detailed execution plan/spec/PRD for implementing features or refactors in a codebase, designed around the program's entrypoints, the doors that carry domain intent, by leveraging existing research in the codebase. |
You are tasked with creating a spec for implementing a new feature or system change in the codebase by leveraging existing research in the $ARGUMENTS path. If no research path is specified, use the entire research/ directory. IMPORTANT: Research documents are located in the research/ directory — do NOT look in the specs/ directory for research. Follow the template below to produce a comprehensive specification as output in the specs/ folder using the findings from RELEVANT research documents found in research/. The spec file MUST be named using the format YYYY-MM-DD-topic.md (e.g., specs/2026-03-26-my-feature.md), where the date is the current date and the topic is a kebab-case summary. Tip: It's good practice to use the codebase-research-locator and codebase-research-analyzer agents to help you find and analyze the research documents in the research/ directory. It is also HIGHLY recommended to cite relevant research throughout the spec for additional context.
Design philosophy: a spec is a theory of its doors
The entrypoints of a program, read together, are the program's theory of its own purpose. Everything inside the boundary is mechanism — the how. Only at the boundary does the code speak in terms of meaning — the what and the why. So the single most important thing this spec defines is not the mechanism inside the system, but the set of doors the system keeps: the functions, routes, and RPC methods through which untrusted input arrives and irreversible effects happen.
Two acts hide inside that claim, and a good spec performs both. One is finding the doors — discovering where the domain is already jointed, using the research in research/ to learn what actually matters in the world the software serves. The other is crafting them — naming and shaping each door so it tells the truth about what lies behind it. Treat entrypoint design as the spine of the spec: a reviewer should be able to read the door set alone and reconstruct what the system is for before reading a single implementation detail.
Apply the five principles below to every entrypoint the spec introduces or changes, and run the rubric on each.
The five principles
-
Name a joint, not a tool. A domain has seams — places reality is already divided into meaningful units (authenticate a user, settle a payment, revoke access, publish a draft). These exist before your code does. Name each door after such a joint, never after the mechanism behind it (run the query, call the service, update the row). A door named for a tool lets a reader learn how it works without ever learning what it is for — an ontological mismatch no clean mechanism repairs. Listen to the domain (and to the research), not to the code.
-
Compress honestly, or not at all. A door's value is roughly the ratio of mechanism hidden to surface exposed — but only when the name promises exactly what the body delivers. No less (so it hides no danger or incompleteness), no more (so it implies no guarantee it does not keep). A save() that sometimes silently doesn't, a delete() that soft-deletes, a validate() that mutates, a getUser() that creates one — each is a lie at the boundary, and lies at the boundary compound across every caller who reasons from the name. Encode cost and risk in the vocabulary (cheap-borrow vs allocate vs consume; read vs read_exact; panic-risk in the name).
-
Intent lives in what the door refuses. A boundary communicates as much by what it forbids as by what it allows. The shape of the door set — what it makes easy, what it makes impossible — is a direct statement of what the designers held sacred. Prefer making the illegal unrepresentable (in types and structure) over merely checked at runtime: a door that checks a rule trusts the caller; a door that makes the rule structurally necessary need trust no one. Use newtypes (AccountId, OrderId) over primitives, sum types over independent booleans, and capability-carrying types (an AdminSession, an AuthorizedCharge) that can only be produced by the door that earns them.
-
Write for the stranger across time. You craft the door not for the machine but for a competent stranger who arrives years from now, never meets you, and must understand the system's purpose before they dare change it. The governing test: could they reconstruct the purpose of the system from the entrypoints alone, without reading a single body? If they would have to read implementations to learn what the system means, intent has leaked out of the doors into the mechanism.
The rubric you run on every entrypoint in the spec
For each non-trivial entrypoint the spec introduces or changes, walk these in order. Stop at the first one you cannot answer cleanly — that is a finding, and it belongs in the spec (often in §5 as a constraint, or in §9 as an open question). Run it forward to audit a door you've drafted, and backward — asking what door each obligation deserves — to find the doors the system is still missing.
- Joint, not tool. Is the name a unit of domain intent a non-engineer would recognize — not a description of the mechanism? If you can only name it in implementation terms, it's a step, not a door.
- The sentence holds. Can you state its guarantee in one declarative sentence with no and? If not, it's fused (split it) or undefined (the most dangerous case — stop and find out what it actually promises).
- The name is honest. Does it promise exactly what the body will deliver — hiding no danger, implying no guarantee it won't keep? List the ways the name could be read as a lie.
- Obligations are discharged. Read the pre / invariant / post / never off the sentence. Does each obligation map to a real step in the design, and each step to an obligation?
- Every exit keeps the promise. Walk the error return, the retry, the timeout, the partial write, the concurrent caller, the second entry. The guarantee must survive all of them, not just the happy path.
- The refusals are real. What does this door make impossible? Are the illegal states unrepresentable, or merely checked and trusted?
- The trust transition is explicit and singular. If untrusted becomes trusted or authority increases, does it happen here — and only here?
- Irreversible effects pass one chokepoint. Is this the single dominating door for the effect it guards? If the effect can be reached another way, that other way is the bug.
- The airlock is at the boundary. Validation, authorization, conversion, and the error boundary live at the door, leaving the inside free to trust its own invariants. Defensive code deep within means the boundary is misplaced.
- A stranger could reconstruct intent. Could someone read this door alone — name and signature, not the body — and know what it is for and what it owes?
The joint is the same at every boundary
settle_payment in process, POST /v1/payment_intents/{id}/capture over REST, and Billing.SettlePayment over gRPC are one door, three transports, one name. When the function, the route, and the RPC method disagree about what the joints are, at least one of them is naming a tool — flag it. On the wire, the HTTP verb is honesty the protocol gives you for free (GET is safe, PUT/DELETE are idempotent, POST is neither — which is exactly why money doors carry an Idempotency-Key), and the status code is the door's honest exit (201 created, 204 done, 202 accepted; 409/412 are real refusals). The cardinal lie is 200 OK wrapping {"error": ...}. Authentication is one gate at the edge so every handler behind it may trust it speaks to a known caller.
<EXTREMELY_IMPORTANT>
- Please use your ask_user_question tool to provide a rich interface to ask the user for their input on a question.
- Please DO NOT implement anything in this stage, just create the comprehensive spec as described below.
- When writing the spec, DO NOT include information about concrete dates/timelines (e.g. # minutes, hours, days, weeks, etc.) and favor explicit phases (e.g. Phase 1, Phase 2, etc.).
- The spec MUST treat its entrypoint set as a first-class artifact. Section 5 is built around the doors (typed signatures, named failures, refusals expressed in types) and must pass the rubric above. Do not let intent leak into mechanism: a reviewer should reconstruct the system's purpose from §4.4 and §5.1 alone.
- Once the spec is generated ask questions one at a time OR in logical groups:
- Refer to section "## 9. Open Questions / Unresolved Issues", go through each question one by one, and use contrastive clarification (presenting 2-3 specific options with concrete tradeoffs) rather than open-ended questions. This means presenting interpretations like "(A) Option X — tradeoff Y" and "(B) Option Z — tradeoff W" instead of asking "what do you think about X?". Update the spec with the user's answers as you walk through the questions.
- Interview the user relentlessly about every aspect of this plan/spec until you reach a shared understanding with them. Walk down each branch of the design tree, resolving dependencies between decisions one-by-one. For each question, provide your recommended answer (i.e., contrastive clarification). Pay special attention to the doors: every disagreement about what a joint is, what a door promises, what it refuses, or where a dangerous effect is funneled is a question worth resolving with the user.
- If a question can be answered by exploring the codebase, explore the codebase instead and confirm with the user that this is their inferred intent.
- Finally, once the spec is generated and after open questions are answered, provide an executive summary of the spec to the user including the path to the generated spec document in the
specs/ directory.
- In the summary, list the door set by name alone (the stranger-across-time view) and call out which doors guard irreversible effects.
- Encourage the user to review the spec for best results and provide feedback or ask any follow-up questions they may have.
</EXTREMELY_IMPORTANT>
[Project Name] Technical Design Document / RFC
| Document Metadata | Details |
|---|
| Author(s) | !git config user.name |
| Status | Draft (WIP) / In Review (RFC) / Approved / Implemented / Deprecated / Rejected |
| Team / Owner | |
| Created / Last Updated | |
1. Executive Summary
Instruction: A "TL;DR" of the document. Assume the reader is a VP or an engineer from another team who has 2 minutes. Summarize the Context (Problem), the Solution (Proposal), and the Impact (Value). Name the one or two doors at the heart of the change. Keep it under 200 words.
Example: This RFC proposes replacing our current nightly batch billing system with an event-driven architecture. Currently, billing delays cause a 5% increase in customer support tickets. The proposed solution introduces two money doors — authorize_charge (reversible hold) and settle_payment (irreversible capture) — as the single chokepoint for outbound money, reducing billing latency from 24 hours to <5 minutes while making double-charges structurally impossible.
2. Context and Motivation
Instruction: Why are we doing this? Why now? Link to the Product Requirement Document (PRD) and cite the relevant research/ documents.
2.1 Current State
Instruction: Describe the existing architecture. Use a "Context Diagram" if possible. Be honest about the flaws — including which existing doors leak (named for tools, dishonest compression, scattered danger).
- Architecture: Currently, Service A communicates with Service B via a shared SQL database.
- Limitations: This creates a tight coupling; when Service A locks the table, Service B times out.
- Leaking doors (today): e.g.
chargeCard(token, cents) is reachable from checkout, the retry job, and the admin panel — no one owns "charge exactly once." processPayment(...) -> bool collapses a declined card, a network failure, and a duplicate submission into the same false.
2.2 The Problem
Instruction: What is the specific pain point?
- User Impact: Customers cannot download receipts during the nightly batch window.
- Business Impact: We are losing $X/month in churn due to billing errors.
- Technical Debt: Danger is scattered; the boundary is misplaced, with defensive code deep inside the core instead of at the door.
3. Goals and Non-Goals
Instruction: This is the contract / Definition of Success. Be precise.
3.1 Functional Goals
3.2 Non-Goals (Out of Scope)
Instruction: Explicitly state what you are NOT doing. Remember: intent lives in what the door refuses — the doors you deliberately do not build are as much a statement of purpose as the ones you do. This prevents scope creep.
4. Proposed Solution (High-Level Design)
Instruction: The "Big Picture." Diagrams are mandatory here.
4.1 System Architecture Diagram
Instruction: Insert a C4 System Context or Container diagram. Show the "Black Boxes" and mark where the airlock sits (the single edge where untrusted network becomes a trusted request).
%%{init: {'theme':'base', 'themeVariables': { 'primaryColor':'#f8f9fa','primaryTextColor':'#2c3e50','primaryBorderColor':'#4a5568','lineColor':'#4a90e2','secondaryColor':'#ffffff','tertiaryColor':'#e9ecef','clusterBkg':'#ffffff','clusterBorder':'#cbd5e0'}}}%%
flowchart TB
classDef person fill:#5a67d8,stroke:#4c51bf,stroke-width:3px,color:#fff,font-weight:600
classDef core fill:#4a90e2,stroke:#357abd,stroke-width:2.5px,color:#fff,font-weight:600
classDef support fill:#667eea,stroke:#5a67d8,stroke-width:2.5px,color:#fff,font-weight:600
classDef db fill:#48bb78,stroke:#38a169,stroke-width:2.5px,color:#fff,font-weight:600
classDef external fill:#718096,stroke:#4a5568,stroke-width:2.5px,color:#fff,font-weight:600,stroke-dasharray:6 3
User(("◉<br><b>User</b>")):::person
subgraph Boundary["◆ System Boundary — Airlock at the edge"]
direction TB
Gateway{{"<b>API Gateway</b><br><i>auth · validate · authorize</i><br>the one trust transition"}}:::core
API["<b>Core Service</b><br><i>trusts its own invariants</i>"]:::core
Worker(["<b>Worker</b><br><i>async</i>"]):::support
DB[("●<br><b>Primary DB</b>")]:::db
end
Ext{{"<b>Payment Provider</b>"}}:::external
User -->|"1. HTTPS (untrusted)"| Gateway
Gateway -->|"2. trusted request"| API
API -->|"3. persist (txn)"| DB
API -.->|"4. enqueue"| Worker
Worker -.->|"5. settle (irreversible)"| Ext
style Boundary fill:#fff,stroke:#cbd5e0,stroke-width:2px,stroke-dasharray:8 4
4.2 Architectural Pattern
Instruction: Name the pattern (e.g., "Event Sourcing", "BFF — Backend for Frontend", "Publisher-Subscriber").
- We are adopting a Publisher-Subscriber pattern where the Order Service publishes
OrderCreated events, and the Billing Service consumes them asynchronously.
4.3 Key Components
| Component | Responsibility | Technology Stack | Justification |
|---|
| Ingestion Service | Validates incoming webhooks | Go, Gin Framework | High concurrency performance needed. |
| Event Bus | Decouples services | Kafka | Durable log, replay capability. |
| Projections DB | Read-optimized views | MongoDB | Flexible schema for diverse receipt formats. |
4.4 The Door Set at a Glance (Stranger-Across-Time View)
Instruction: List the entrypoint names alone — no signatures, no bodies. A competent stranger should reconstruct the system's purpose from this list. If they cannot, intent has leaked into the mechanism; return to §5 and rename until they can. Mark every door that guards an irreversible effect with ⚠.
Example: register_account, authenticate, authorize_charge, settle_payment ⚠, grant_access ⚠, revoke_access, publish_draft. Reading these alone tells you who the system lets in, that money moves in exactly two steps and only those two, who may hand out access, and what it means for work to go live.
5. Detailed Design
Instruction: The "Meat" of the document. Sufficient detail for an engineer to start coding. Lead with the doors — they are the load-bearing part of the spec — then describe the mechanism behind them.
5.1 The Doors (Entrypoint Contracts)
Instruction: For each non-trivial entrypoint, give a typed signature (typed pseudocode is fine — read the types, not the syntax), the one-sentence guarantee (no "and"), the named failure set, and the refusals it enforces in the type system. Then record the rubric result. Make illegal states unrepresentable, not merely checked. Cite the research/ doc that establishes each joint.
// — Money. Two doors, and there is no third way to move a cent. —
authorize_charge(
account: AccountId, // newtype: cannot be confused with any other id
amount: Money, // currency-typed: USD and JPY will not add
idempotency_key: IdempotencyKey,
): Result<AuthorizedCharge, ChargeError>
// Guarantee: places a reversible hold and returns proof an authorization exists.
// ChargeError = InsufficientFunds | CardDeclined | NetworkError | DuplicateKey
settle_payment(
authorized: AuthorizedCharge, // ← can ONLY be produced by authorize_charge
idempotency_key: IdempotencyKey,
): Result<Settlement, SettlementError>
// Guarantee: captures the held funds. IRREVERSIBLE. The single chokepoint for outbound money.
// You cannot settle a charge you did not authorize — not because a check forbids it,
// but because there is no way to CONSTRUCT an AuthorizedCharge except by calling
// authorize_charge. The illegal state is unrepresentable. The idempotency key makes
// the retry, the double-click, and the at-least-once queue converge on ONE settlement.
Per-door audit (run the rubric):
| Door | (1) Joint | (2) One sentence, no "and" | (3) Honest name | (5) Every exit | (6) Refusals real | (7) Trust transition | (8) One chokepoint |
|---|
authorize_charge | ✅ business verb | ✅ "places a reversible hold" | ✅ | retry → DuplicateKey; timeout → NetworkError | currency mismatch unrepresentable | n/a | reversible, not the chokepoint |
settle_payment ⚠ | ✅ business verb | ✅ "captures held funds" | ✅ irreversibility in doc + type | replay converges via key | cannot settle un-authorized charge (type) | n/a | ✅ the sole outbound-money door |
5.2 API Interfaces — The Same Doors on the Wire
Instruction: A web service's real boundary is its transport surface. The URL names the joint, the HTTP verb declares its safety class, the status code is the door's honest exit. Never 200 OK wrapping an error. The wire door MUST carry the same name as its in-process twin (§5.1).
# Identity — the one trust transition, at the edge
POST /v1/sessions 201 Created # = authenticate; 401 on bad credentials
DELETE /v1/sessions/current 204 No Content # = log out
# Money — two doors, one chokepoint, idempotent under retry
POST /v1/payment_intents 201 Idempotency-Key: <key> # = authorize_charge (reversible)
POST /v1/payment_intents/{id}/capture 200 Idempotency-Key: <key> # = settle_payment (IRREVERSIBLE)
# 409 Conflict if the key is replayed with a different body
# 422 Unprocessable if the intent was never authorized
# Access — authority demanded by the route, destructive door made idempotent
POST /v1/accounts/{id}/grants 201 (admin scope required) # = grant_access
DELETE /v1/grants/{id} 204 (204 even if already revoked) # = revoke_access
# Publishing — the domain's own verb, refusing to clobber a concurrent edit
POST /v1/drafts/{id}/publish 200 If-Match: <etag> # = publish_draft
# 412 Precondition Failed if the draft moved under you — the wire's --force-with-lease
If using gRPC, define the same joints in the .proto; the typed request message is the airlock by construction. Use honest status codes (INVALID_ARGUMENT, PERMISSION_DENIED, NOT_FOUND, ALREADY_EXISTS, FAILED_PRECONDITION, retryable ABORTED/UNAVAILABLE) — never a lone OK carrying an error field.
5.3 Data Model / Schema
Instruction: Provide ERDs or JSON schemas. Discuss normalization vs. denormalization. Prefer schemas that make illegal states unrepresentable (sum-type status columns over independent boolean flags).
Table: invoices (PostgreSQL)
| Column | Type | Constraints | Description |
|---|
id | UUID | PK | |
user_id | UUID | FK -> Users | Partition Key |
status | ENUM | 'DRAFT','LOCKED','PROCESSING','PAID' | A sum type, not three booleans |
5.4 Algorithms and State Management
Instruction: Describe complex logic, state machines, or consistency models. Tie each state transition to the door that performs it.
- State Machine: An invoice moves
DRAFT → LOCKED → PROCESSING → PAID; the PROCESSING → PAID transition happens only through settle_payment.
- Concurrency: Optimistic locking on the
version column; on the wire this surfaces as If-Match/412.
6. Alternatives Considered
Instruction: Prove you thought about trade-offs — including alternative door sets (e.g., one god endpoint vs. distinct joints). Why is your boundary better than the others?
| Option | Pros | Cons | Reason for Rejection |
|---|
Option A: Single POST /execute {action} | One route, flexible | God door; intent hidden in payload; danger un-funneled | Fails "joint, not tool" and "few dangerous doors." |
Option B: One-step chargeCard() | Fewest calls | No reversible hold; retries double-charge | Cannot make double-charge unrepresentable. |
Option C: authorize + settle (Selected) | Reversible hold; one chokepoint; idempotent | Two calls instead of one | Selected: the two real joints, with the irreversible effect funneled once. |
7. Cross-Cutting Concerns
7.1 Security and Privacy
Instruction: This is where "keep the dangerous doors few and honest" and "the airlock at the boundary" become concrete.
- The trust transition is singular: untrusted callers become trusted only at
POST /v1/sessions / the gateway. No other door promotes an anonymous caller. (Rubric #7.)
- Authority carried by type: destructive/privileged doors demand a capability (
AdminSession) that only authenticate can mint — the permission check cannot be forgotten at a call site because there is no call site where it is absent. (Rubric #6.)
- Irreversible effects pass one chokepoint: money via
settle_payment, deletion via the single guarded door; the catastrophic version must be asked for explicitly. (Rubric #8.)
- Data Protection: PII (names, emails) encrypted at rest (AES-256);
Password is a newtype that cannot be logged, printed, or compared by accident.
- Threat Model: Primary threat is a compromised API key; remediation is rapid rotation and rate limiting.
8. Test Plan
Instruction: Test the doors at their promises and their refusals — not just the happy path. Every exit in rubric #5 deserves a test. The interactive verification is what lets a human or another agent confirm the feature is correct without reading the bodies — the stranger-across-time test, made executable.
- Unit Tests: each door's named failure variants; the refusals (e.g., a type/construction test proving
settle_payment cannot accept anything but an AuthorizedCharge).
- End-to-End Tests: full domain flows named by joint (register → authenticate → authorize → settle), driven through the real wire doors of §5.2.
- Integration Tests: idempotency under replay (same key → one settlement); concurrent-edit
412; trust transition (no door promotes an anonymous caller except authenticate).
- Fuzz / Property Tests: throw malformed and adversarial input at the doors (the airlock); the boundary must reject everything the types forbid and never crash the core. Assert invariants over random inputs (e.g.,
settle_payment converges on one settlement under any interleaving of retries; no input sequence reaches a money move except through the chokepoint).
- Interactive Verification: a runnable checklist or script a human OR another agent can execute to confirm the feature was implemented correctly — each step names a door, supplies an input, and states the expected honest exit (status code / named error / resulting state), so correctness is observable from the boundary alone. Include the exact commands or requests to run and the pass/fail condition for each.
9. Open Questions / Unresolved Issues
Instruction: List known unknowns. These must be resolved before the doc is marked "Approved." Include any door whose rubric could not be answered cleanly — especially undefined guarantees (rubric #2, the most dangerous case) and any irreversible effect not yet funneled to a single chokepoint (rubric #8). Resolve these with the user via contrastive clarification.
