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Matt Pocock
45 lines
2.7 KiB
Markdown
45 lines
2.7 KiB
Markdown
# Interface Design
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When the user wants to explore alternative interfaces for a chosen deepening candidate, use this parallel sub-agent pattern. Based on "Design It Twice" (Ousterhout) — your first idea is unlikely to be the best.
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Uses the vocabulary in [LANGUAGE.md](LANGUAGE.md) — **module**, **interface**, **seam**, **adapter**, **leverage**.
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## Process
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### 1. Frame the problem space
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Before spawning sub-agents, write a user-facing explanation of the problem space for the chosen candidate:
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- The constraints any new interface would need to satisfy
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- The dependencies it would rely on, and which category they fall into (see [DEEPENING.md](DEEPENING.md))
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- A rough illustrative code sketch to ground the constraints — not a proposal, just a way to make the constraints concrete
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Show this to the user, then immediately proceed to Step 2. The user reads and thinks while the sub-agents work in parallel.
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### 2. Spawn sub-agents
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Spawn 3+ sub-agents in parallel using the Agent tool. Each must produce a **radically different** interface for the deepened module.
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Prompt each sub-agent with a separate technical brief (file paths, coupling details, dependency category from [DEEPENING.md](DEEPENING.md), what sits behind the seam). The brief is independent of the user-facing problem-space explanation in Step 1. Give each agent a different design constraint:
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- Agent 1: "Minimize the interface — aim for 1–3 entry points max. Maximise leverage per entry point."
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- Agent 2: "Maximise flexibility — support many use cases and extension."
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- Agent 3: "Optimise for the most common caller — make the default case trivial."
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- Agent 4 (if applicable): "Design around ports & adapters for cross-seam dependencies."
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Include both [LANGUAGE.md](LANGUAGE.md) vocabulary and CONTEXT.md vocabulary in the brief so each sub-agent names things consistently with the architecture language and the project's domain language.
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Each sub-agent outputs:
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1. Interface (types, methods, params — plus invariants, ordering, error modes)
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2. Usage example showing how callers use it
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3. What the implementation hides behind the seam
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4. Dependency strategy and adapters (see [DEEPENING.md](DEEPENING.md))
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5. Trade-offs — where leverage is high, where it's thin
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### 3. Present and compare
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Present designs sequentially so the user can absorb each one, then compare them in prose. Contrast by **depth** (leverage at the interface), **locality** (where change concentrates), and **seam placement**.
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After comparing, give your own recommendation: which design you think is strongest and why. If elements from different designs would combine well, propose a hybrid. Be opinionated — the user wants a strong read, not a menu.
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