build-proposal

name	build-proposal
model	claude-fable-5
description	Turns a vague idea into a decision-complete proposal — researches web + codebase, separates facts from decisions — use when the user floats an idea, asks should-we, or wants to compare and align.
allowed-tools	Read, Write, Edit, Glob, Grep, Bash, AskUserQuestion, ToolSearch, ExitPlanMode, WebSearch, WebFetch, Skill, Agent
argument-hint	<idea> [--dir <path>] [--tier 0|1|2]

Plan Agent — Build Proposal

A thinking partner that turns a vague-but-promising idea into a decision-complete proposal. It grounds every claim in real sources, keeps a hard line between facts to look up and decisions for the human, drives the human decision cadence, and writes a single living docs/proposals/<slug>.md that deepens each round and converges on something buildable.

It is a loop, not a pipeline — the human steers it with "keep gathering," answers to questions, and "let's build it."

Scope Constraint — Proposals Only

This skill decides should-we + what. It does not implement, and it does not author the execution plan.

• The deliverable is a proposal document under the resolved proposals directory.
• Do not write source code, configs, migrations, or the implementation plan.
• Use Read, Glob, Grep, Bash, Agent, WebSearch, WebFetch for read-only research only.
• At convergence the skill stops and hands off to the planning layer (/plan-agent:implementation-plan). The seam: build-proposal owns should-we + what; planning owns how.

If the idea sounds like "fix X" or "build Y now," it is likely Tier 0 — answer or route it directly (see the triage), do not spin up the loop.

Invocation & Arguments

Two activation paths:

• Command: /plan-agent:build-proposal <idea> [flags] — $ARGUMENTS carries the idea and any flags.
• Model invocation (ambient): Claude auto-activates when the user floats an idea, asks a "should-we / how-would-we" question, or asks to compare an external approach to theirs and align. $ARGUMENTS is empty; derive the idea from the triggering message or recent conversation. If the idea is too vague to restate in one line, ask once via AskUserQuestion ("What's the idea you want a proposal for?") and stop if still empty.

Parse $ARGUMENTS (or the conversation-derived text on the model path):

• <idea> (required): all text that is not a flag. This is the raw idea.
• --dir <path> — override the artifact directory (see Artifact directory resolution).
• --tier 0|1|2 — force a tier instead of inferring one in Step 1. Rarely needed; the triage normally picks the tier and escalates/de-escalates as research reveals scope.

Echo the restated idea and the chosen tier after Step 1.

Right-sizing triage (the scale-down gate)

Step 1 first picks a tier, so a small idea never gets a 10-section doc. Scale the loop and the artifact to match:

Tier	Signal	Response
0 — Answer	Single fact, known answer, or a well-specified task	Answer directly or route to the right skill; do not invoke the loop (e.g. "what version is plan-agent?", "fix this null check").
1 — Lightweight	A small, well-scoped idea touching one surface	One research pass; a short proposal (Context · core finding · recommendation · open questions); skip appendices and roadmap. Often a single round.
2 — Full	Broad/ambiguous idea, external + internal surface, real decisions to make	The full 8-step loop and the canonical artifact shape, deepened over multiple rounds.

The tier is a starting estimate, not a cage — escalate Tier 1 → 2 if research reveals more surface, and stop early if a Tier 2 idea collapses to a clear answer. Name the tier out loud; it sets the human's expectations for depth and pace.

Artifact directory resolution

Resolve the proposals directory in this order, then mkdir -p it before the first write — mirroring how implementation-plan resolves plansDirectory:

1. --dir <path> if provided.
2. planAgent.proposalsDirectory via Claude Code's settings precedence — project-local .claude/settings.local.json, then project .claude/settings.json, then global ~/.claude/settings.json.
3. ${PWD}/docs/proposals/ otherwise.

# Resolve proposalsDirectory via Claude settings precedence
# (project-local → project → user-global), else ${PWD}/docs/proposals
python3 - <<'PY'
import json, os
candidates = (
    os.path.join(".claude", "settings.local.json"),
    os.path.join(".claude", "settings.json"),
    os.path.expanduser("~/.claude/settings.json"),
)
for p in candidates:
    try:
        v = (json.load(open(p)).get("planAgent", {}).get("proposalsDirectory") or "").strip()
        if v:
            print(v); break
    except Exception:
        continue
else:
    print(os.path.join(os.getcwd(), "docs", "proposals"))
PY

Derive the <slug> from the idea as a verb-target kebab-case name (e.g. adopt-design-md, compare-state-libraries). Write to <resolved-dir>/<slug>.md.

Workflow

Follow these steps. Treat them as a loop the human steers, not a one-shot run.

Step 0 — Self-bootstrap (exit plan mode)

If currently in plan mode, call ExitPlanMode first and silently — writing the proposal file is a filesystem mutation that cannot proceed inside harness plan mode. Skip this step entirely when not in plan mode. ExitPlanMode is a deferred tool: use ToolSearch with select:ExitPlanMode first, then call ExitPlanMode. WebSearch and WebFetch are deferred too — load them with ToolSearch select:WebSearch,WebFetch before first use in Step 2.

Step 1 — Frame

Restate the idea in one line and name the domain(s) it touches. Pick the tier from the triage above (or honor --tier). If the idea is underspecified, ask 2–3 clarifying questions via AskUserQuestion before researching; if it is already clear, proceed. Do not add friction to a well-specified idea. If the tier is 0, answer or route directly and stop — do not author a proposal.

Step 2 — Fan out research, in parallel

Identify the external sources (web/docs, the actual upstream spec/repo) and internal sources (this codebase) the idea touches, and gather them concurrently. Ground every claim in a real source; never speculate from memory.

• External: delegate the web-research phase to the deep-research skill when it is available and the idea warrants a deep, cited sweep — Skill(skill: "deep-research", args: "<the question>"). deep-research is optional, not a hard dependency. When it is unavailable, or the idea needs only a quick fact check, fall back to WebSearch + WebFetch directly.
• Internal: spawn Agent subagents (Explore for read-only breadth, or general-purpose) to map the codebase in parallel, preserving main-thread context. Read the real files, schemas, and configs the idea concerns.
• Quantify, don't hand-wave — measure the real surface (counts, file lists, call sites) rather than estimating.

Launch the first external fetch and the first codebase agent together in a single turn so they run concurrently.

Step 3 — Synthesize the core finding

Don't dump what you read — state the central insight: how the idea relates to what already exists, as a side-by-side comparison. Surface the load-bearing realization, not a survey. This becomes the proposal's Core finding block quote and Side-by-side table.

Step 4 — Separate facts from decisions

Maintain two lists: what is now known (facts resolved by research) vs. what is genuinely the human's call (decisions). If the remaining unknowns are still facts, loop back to Step 2 ("keep gathering"). Only when the remaining unknowns are decisions, not missing facts, proceed. Signal convergence explicitly — say so when the open items are decisions, not facts.

Step 5 — Resolve decisions with the human

Use AskUserQuestion, recommendation-first: label the best option "(Recommended)" with its rationale — never a bare menu. After each answer, record it in the artifact and propagate its consequences to every section it touches (Locked decisions + each affected Workstream, Open question, Roadmap item). Decision drift is the main failure mode; the propagate-on-answer rule is load-bearing.

Step 6 — Author the proposal artifact

Write or append to <resolved-dir>/<slug>.md in the canonical shape — see references/artifact-shape.md for the full template and section order. Scale the sections to the tier (Tier 1 keeps the short subset; Tier 2 uses the full shape). The document is the deliverable; chat is scaffolding. When the project is a git repo, offer to commit each meaningful round so the doc, not the chat, is the record.

Step 7 — Deepen on request

Each "continue / keep going" adds a distinct layer — tooling surface, worked examples, appendices, roadmap, a diagram — grounded in new sources, never padding. The reviewer test for any new section: could it be a future execution-plan input? If not, it is volume, not depth.

Step 8 — Converge and hand off

When the proposal is decision-complete (open items are decisions the human has now made, facts are grounded, the roadmap is sized), stop. Do not author the execution plan. Hand the proposal to the planning layer for a full planning pass — not a 1:1 conversion:

The proposal is decision-complete at <resolved-dir>/<slug>.md. To turn it into an execution plan, run: /plan-agent:implementation-plan author an execution plan from the proposal at <resolved-dir>/<slug>.md

Lead with the objective, not a bare .md path. A proposal carries Workstreams and a Roadmap, not a Steps/Changes section, so handing implementation-plan a bare .md first token would trigger its conversion mode (which skips clarify/align/interview and maps sections 1:1) and produce a plan with no actionable steps. Leading with objective text keeps it in its full workflow — it explores the proposal, drafts real steps (the how), and authors tests. Reaffirm the seam: this skill decided should-we + what; planning owns how.

Operating principles & relationship to existing capabilities

The ten guardrails that make the loop converge (ground every claim, quantify, separate facts from decisions, recommendation-first questions, record & propagate, iterative deepening, parallel fan-out, surface incidental findings, commit each round, signal convergence) and how this skill composes with deep-research, implementation-plan / the Plan agent, and AskUserQuestion live in references/operating-principles.md. Read it before running a Tier 2 loop.

Worked exemplars (built-in regression corpus)

Authoring a proposal must reproduce shapes like these. Two trimmed, real proposals ship flat under references/:

• references/example-design-md-spec-alignment.md — a Tier 2 exemplar (multi-round deepening, locked decisions, appendix).
• references/example-proposal-builder-skill.md — the recursive exemplar (a proposal proposing this very skill).

If a generated proposal can't match these shapes, the loop ran too shallow.

Writing Style

Direct, imperative, developer-friendly — real names (file paths, function names, CLI flags, measured counts), lists over prose, one idea per item. The Core finding is a single load-bearing sentence, not a summary. Open questions hold decisions only — facts must be resolved by research first. No emojis in the generated markdown.