/plan-a-feature

name: "plan-a-feature"
description: >
  Builds a feature specification from scratch through a relentless, evidence-based interview that walks the design tree
  decision-by-decision, resolving dependencies as it goes. Use when the user wants to plan, design, scope, specify, or
  flesh out a new feature, capability, or system behavior before implementation. Produces a feature specification
  focused on system behaviors, not implementation detail. Does not plan a restructure of code that already exists — use
  plan-a-change. Does not refine or stress-test an existing plan — use iterative-plan-review. Does not document already-built features — use project-documentation. Does not design the
  contract for an interface — use design-an-api. Does not research open-ended options before there is a feature to
  specify — use research. Does not map the bounded contexts of existing code — use ddd-analysis.
arguments: size
argument-hint: "[size: small | medium | large | dynamic] [feature description, optional: output folder path]"
allowed-tools:
  Read, Write, Edit, Glob, Grep, Agent, Bash(find *), Bash(mkdir *), Bash(cp *),
  Bash(bash "${CLAUDE_PLUGIN_ROOT}/scripts/han-config-dir.sh")

Project Context

• CLAUDE.md: !`find . -maxdepth 1 -name "CLAUDE.md" -type f`
• project-discovery.md: !`find . -maxdepth 3 -name "project-discovery.md" -type f`
• personal config directory: !`bash "${CLAUDE_PLUGIN_ROOT}/scripts/han-config-dir.sh" 2>/dev/null || echo "$HOME/.claude"`
• project .han/config.md: !`cat .han/config.md 2>/dev/null || echo ""`

As your first action, use the Read tool on `.han/config.md` inside the `personal config directory` path above. A read that returns no file is no personal configuration: continue silently. When that file or the `project .han/config.md` probe supplies content, apply it per [config-rule.md](../../references/config-rule.md), which governs precedence between the two files, relative-path resolution, and what to do with a file that reads but cannot be used.

Operating Principles

• **Interview relentlessly, but explore first.** If a question can be answered by reading the codebase, project docs,

coding standards, ADRs, or existing feature specs — or by querying a read-only tool already available to this session that authoritatively answers it (for example a connected schema or data-source tool) — explore instead of asking. Only surface questions that genuinely require the user's judgment. The connected-tool path is gated on availability, not on a fresh judgment: use it only when such a read-only tool is actually permitted to this skill; if none is available, ask the user as today (see Step 4).

• **Walk the design tree.** Decisions have dependencies. Resolve foundational decisions first (what the feature does,

who uses it, what outcome it produces). Then descend into dependent decisions (flow, states, edge cases, coordination points). Never ask a dependent question before its parent is settled.

• **Recommend, then ask.** For every question surfaced to the user, provide a recommended answer with rationale grounded

in evidence (code, docs, conventions, or stated goals). The user can accept, redirect, or provide a nuanced response.

• **Behavior, not implementation, in the spec.** The specification captures WHAT the feature does, for WHOM, and WHY —

at a level a reader who has never opened the codebase can understand. Language primitives, file/line references, function or class names, library mechanics, implementation patterns, and internal env/flag names DO NOT appear in `feature-specification.md`. Product-level subsystem names ("events processing system", "backend service"), user-facing UI vocabulary (popover, modal, toast), URL paths, behavioral verbs, and user-observable states DO. Technology brand names generalize one level up (NATS → "events processing system"; PostgreSQL → "database"; Redis → "cache"). This rule is language-agnostic — it applies equally to Go, Rails, Node, Python, Swift, Kotlin, and frontend JavaScript code. Any examples given in references or templates are illustrative, not an exhaustive deny-list.

• **Load-bearing mechanics go in `feature-technical-notes.md`, not the spec.** When a mechanic is load-bearing for a

behavior — meaning the behavioral commitment in the spec is only correct because of that mechanic (ordering, durability, consistency, visibility timing) — the behavioral consequence goes in the spec sentence, and the mechanic goes in a `T#` note linked inline from that sentence. The tech-notes file is LAZILY created — it exists only when at least one load-bearing mechanic qualified. Mechanics that are discoverable from the code repo (an existing pattern, an in-use library, a documented convention) do NOT belong in the tech-notes file either — `plan-implementation` will find them from the code. Mechanics that do not affect observable behavior are pure implementation and belong in the implementation plan, not here.

• **YAGNI is a first-class operating principle.** Apply the evidence-based YAGNI rule in

[yagni-rule.md](../../references/yagni-rule.md) to every commitment the spec carries. An item with no accepted evidence is demoted to `## Deferred (YAGNI)` with its reopening trigger, never silently dropped and never silently kept. An item with evidence gets the simpler-version test.

• **Evidence quality is the companion principle.** Apply [evidence-rule.md](../../references/evidence-rule.md) alongside

YAGNI. YAGNI gates inclusion; this one characterizes the quality of what each commitment rests on, through trust classes, the corroboration gate on web claims, and a distinct label for no evidence at any tier.

• **The run stays inside the boundary it descends from.** The skill records the work item's stated scope and exclusions

before the interview, per [planning-boundary-rule.md](../../references/planning-boundary-rule.md). Every commitment is checked against it, and anything the b