# Feature Specification: [FEATURE NAME]

**Feature Branch**: `[###-feature-name]`  
**Created**: [DATE]  
**Status**: Draft  
**Input**: User description: "$ARGUMENTS"

## Constitution Alignment (REQUIRED)
This spec MUST comply with `constitution.md`. If not, document deviation + mitigation here.

### Mandatory Invariants
- [ ] Server computes price; client is display-only
- [ ] DB-level prevention of double booking
- [ ] Webhooks + rendering pipeline are idempotent
- [ ] Rendering occurs in queued job(s)

## Success Criteria (MUST)
Define measurable outcomes for "done".
- Performance:
  - [ ] Public page loads master image + metadata within ___ ms on ___ connection
- Correctness:
  - [ ] No double booking possible under concurrency
  - [ ] Paid orders render exactly once (idempotent)
- UX:
  - [ ] User can select cells, preview, and pay end-to-end
- Security:
  - [ ] Upload rules enforced (type/size/dimensions), safe link validation

## Acceptance Scenarios (MUST)
Write at least 3 end-to-end scenarios (Gherkin-style preferred).

### Scenario 1: Reserve → Pay → Render
Given …
When …
Then …

### Scenario 2: Concurrent selection conflict
Given …
When …
Then …

### Scenario 3: Webhook replay / retry
Given …
When …
Then …

## Scope (See <attachments> above for file contents. You may not need to search or read the file again.)

## User Scenarios & Testing *(mandatory)*

<!--
  IMPORTANT: User stories should be PRIORITIZED as user journeys ordered by importance.
  Each user story/journey must be INDEPENDENTLY TESTABLE - meaning if you implement just ONE of them,
  you should still have a viable MVP (Minimum Viable Product) that delivers value.
  
  Assign priorities (P1, P2, P3, etc.) to each story, where P1 is the most critical.
  Think of each story as a standalone slice of functionality that can be:
  - Developed independently
  - Tested independently
  - Deployed independently
  - Demonstrated to users independently
-->

### User Story 1 - [Brief Title] (Priority: P1)

[Describe this user journey in plain language]

**Why this priority**: [Explain the value and why it has this priority level]

**Independent Test**: [Describe how this can be tested independently - e.g., "Can be fully tested by [specific action] and delivers [specific value]"]

**Acceptance Scenarios**:

1. **Given** [initial state], **When** [action], **Then** [expected outcome]
2. **Given** [initial state], **When** [action], **Then** [expected outcome]

---

### User Story 2 - [Brief Title] (Priority: P2)

[Describe this user journey in plain language]

**Why this priority**: [Explain the value and why it has this priority level]

**Independent Test**: [Describe how this can be tested independently]

**Acceptance Scenarios**:

1. **Given** [initial state], **When** [action], **Then** [expected outcome]

---

### User Story 3 - [Brief Title] (Priority: P3)

[Describe this user journey in plain language]

**Why this priority**: [Explain the value and why it has this priority level]

**Independent Test**: [Describe how this can be tested independently]

**Acceptance Scenarios**:

1. **Given** [initial state], **When** [action], **Then** [expected outcome]

---

[Add more user stories as needed, each with an assigned priority]

### Edge Cases

<!--
  ACTION REQUIRED: The content in this section represents placeholders.
  Fill them out with the right edge cases.
-->

- What happens when [boundary condition]?
- How does system handle [error scenario]?

## Requirements *(mandatory)*

<!--
  ACTION REQUIRED: The content in this section represents placeholders.
  Fill them out with the right functional requirements.
-->

### Functional Requirements

- **FR-001**: System MUST [specific capability, e.g., "allow users to create accounts"]
- **FR-002**: System MUST [specific capability, e.g., "validate email addresses"]  
- **FR-003**: Users MUST be able to [key interaction, e.g., "reset their password"]
- **FR-004**: System MUST [data requirement, e.g., "persist user preferences"]
- **FR-005**: System MUST [behavior, e.g., "log all security events"]

*Example of marking unclear requirements:*

- **FR-006**: System MUST authenticate users via [NEEDS CLARIFICATION: auth method not specified - email/password, SSO, OAuth?]
- **FR-007**: System MUST retain user data for [NEEDS CLARIFICATION: retention period not specified]

### Key Entities *(include if feature involves data)*

- **[Entity 1]**: [What it represents, key attributes without implementation]
- **[Entity 2]**: [What it represents, relationships to other entities]

## Success Criteria *(mandatory)*

<!--
  ACTION REQUIRED: Define measurable success criteria.
  These must be technology-agnostic and measurable.
-->

### Measurable Outcomes

- **SC-001**: [Measurable metric, e.g., "Users can complete account creation in under 2 minutes"]
- **SC-002**: [Measurable metric, e.g., "System handles 1000 concurrent users without degradation"]
- **SC-003**: [User satisfaction metric, e.g., "90% of users successfully complete primary task on first attempt"]
- **SC-004**: [Business metric, e.g., "Reduce support tickets related to [X] by 50%"]