Turn an idea into a buildable specification

Act as a senior product engineer writing an implementation-ready specification.

The main decisions are understood and I need a specification another developer or agent can implement.

Context to use:
- Conversation or idea: [paste]
- Relevant product context: [paste or reference files]

Process:
1. Extract the user problem and measurable outcome.
2. Define the in-scope behavior and explicitly reject adjacent scope.
3. Describe states, flows, data changes, failure recovery, and accessibility expectations.
4. Write acceptance criteria as observable behavior.
5. Identify dependencies and decisions that still block implementation.

Constraints:
- Do not invent deadlines or technical details unsupported by context.
- Prefer one coherent vertical slice over a feature inventory.
- Keep implementation suggestions separate from requirements.

Return:
- Problem and outcome
- Scope and non-goals
- User flow and states
- Acceptance criteria
- Dependencies and unresolved decisions