existential-birds/beagle/brainstorm-beagle

Brainstorm: Ideas Into Specs

Turn a fuzzy idea into a comprehensive, implementation-free project spec through collaborative dialogue.

The output is a standalone spec document — structured enough for any agentic system to consume, clear enough for a human to act on. It captures WHAT and WHY, never HOW.

<hard_gate> Do NOT write any code, create implementation plans, scaffold projects, or take any implementation action. This skill produces a SPEC DOCUMENT only. Every project goes through this process regardless of perceived simplicity — "simple" projects are where unexamined assumptions waste the most work. </hard_gate>

Workflow

Complete these steps in order:

1. Check for a concept brief — if .beagle/concepts/<slug>/brief.md exists for this idea, ingest it and skip most of steps 2-4 (see Concept brief ingestion below)
2. Explore context — read project files, docs, git history, existing specs (lighter pass if a brief is present)

• Prior art check (brownfield only): before specing a feature onto an existing codebase, run a neutral capability sweep to confirm the thing doesn't already exist (see Prior Art Check below). Runs regardless of whether a brief is present.

1. Assess scope — is this one spec or does it need decomposition?
2. Ask clarifying questions — one at a time, follow the thread (few to none if a brief is present)
3. Propose 2-3 directions — high-level product approaches with tradeoffs
4. Draft spec — write the structured spec document
5. Self-review — check for completeness, contradictions, implementation leakage (see references/spec-reviewer.md)
6. User review — present for approval, iterate if needed
7. Write to disk — save to .beagle/concepts/<slug>/spec.md

Brief present? ──→ Yes → Ingest brief (skip most discovery) ──┐
                ──→ No  → Explore context → Assess scope       │
                                            ├─ Too large? → Decompose → Brainstorm first sub-project
                                            └─ Right size? → Clarifying questions ─┘
                                                                                   │
Brownfield? ──→ Yes → Prior art check (neutral capability sweep) ─→ Already exists? ─→ surface, reshape/kill spec
            ──→ No  → skip ─────────────────────────────────────────────────────────────────────┐
                                                                                                  │
Both paths converge → Propose directions → Draft spec → Self-review (fix inline) → User review
                                                                                        ├─ Changes? → Revise
                                                                                        └─ Approved? → Write to concept folder

The terminal state is a written spec. This skill does not transition to implementation, planning, or any other skill. The user decides what to do with the spec.

Concept brief ingestion

If the user invokes brainstorm-beagle on a concept that already has .beagle/concepts/<slug>/brief.md (produced by prfaq-beagle on pass), ingest the brief at step 1 and skip most discovery:

1. Read the brief. Customer, problem, solution concept, stakes, forged decisions, and research pointers are already codified. Do not re-interview the user on these.
2. Skim the PRFAQ reference. Open .beagle/concepts/<slug>/prfaq.md for the Reasoning blocks — they explain what was challenged and why earlier decisions were made. This is context, not content to re-litigate.
3. Open questions become your starting point. The brief's Open Questions section lists what PRFAQ surfaced but did not close. These are what you ask the user about — not customer, problem, or motivation, which are already decided.
4. Proceed to Exploring Directions. Skip Clarifying Questions and Scope Assessment unless the brief is ambiguous about scope itself.

The brief is a context handoff, not a gate. Run your own Self-Review on the spec you produce — brainstorm-beagle remains responsible for implementation-leakage detection, requirement testability, and scope discipline regardless of how much discovery was pre-done upstream.

When there is no brief: proceed through steps 2-9 normally. Not every idea comes from PRFAQ.

The brief does not exempt you from the prior art check. A brief (or the issue behind it) frames the feature as something to build — that framing is exactly the bias the Prior Art Check exists to neutralize. Run the sweep even when ingesting a brief.

Prior Art Check

This step exists because of a specific, expensive failure: drafting a spec that reinvents a capability the codebase already has. It applies whenever the idea is a feature being added to an existing codebase (brownfield). For greenfield ideas with no existing code, skip it.

The failure mode it prevents: An issue or brief frames a feature as new ("we removed the old truncation, design fresh") or simply omits that prior work exists. You — or a subagent you delegate exploration to — inherit that framing, look only where the framing points, confirm the framing, and spec a feature that duplicates code already shipped and tested. The spec then teaches the downstream planner and executor to rebuild something that exists.

The discipline: search neutrally, independent of framing.

1. Run a capability-keyword sweep across the WHOLE workspace — every crate/package/module, not just the directory the issue points at. Search for the capability by its likely names, synonyms, and abbreviations, not the issue's vocabulary. For a truncation feature: grep -riE 'truncat|spill|cap|max_bytes|head_bytes|limit|trim|elide' across all source roots. Cast wide; one matching file kills the assumption.
2. Do not trust "this doesn't exist" claims. Issues and briefs go stale relative to the code — someone may have built the thing after the issue was filed. The issue's "we removed X / X doesn't exist yet" is a hypothesis to disprove with grep, not a fact to inherit.
3. If you delegate exploration to a subagent, give it the neutral sweep, not the narrative scope. Brief it as "grep the entire workspace for these capability keywords and report every hit," not "look in module/foo for where X is written." A scoped brief reproduces the framing bias inside the subagent. Pass the keyword list; do not pass the issue's theory of where the code lives.
4. Surface what you find. If the capability (or a large part of it) already exists:

• Say so plainly, citing the file(s) — "agent/src/spill.rs already implements head-tail capping with a sidecar, and it's tested."
• Reframe the spec around the gap, not the whole feature: extend/fix/wire-up what exists rather than rebuild it. Often this shrinks the spec dramatically or dissolves the need for one.
• Record the discovery as a Key Decision ("Build on existing spill.rs rather than a fresh truncation module") so the downstream planner doesn't re-litigate.

1. Composition check. For each existing mechanism the sweep surfaced, ask: does it sit upstream or downstream in the same data pipeline as the feature, and does it transform (truncate, filter, buffer, reorder, dedupe) the data this feature depends on? If yes, "the mechanism exists" is not the end of the inquiry — its composition with the new feature is the load-bearing question. Record the interaction as a Key Decision ("bash already caps output to 50 KiB upstream; the spill must capture before that cap or it cannot deliver full output") AND tag that decision needs-spike-before-planning, adding to its Rationale: **Spike required:** before plan-lock, verify the upstream/downstream data shape (what it truncates/filters/buffers/reorders/dedupes and whether this feature captures before or after) against this repo and revise this decision if the result diverges from the assumption. A new mechanism that composes wrongly with an existing one in the same pipeline ships broken even though neither piece was reinvented.

This is distinct from Explore context (step 2), which reads to understand the project. The prior art check is adversarial: its job is to disprove the assumption that the feature is new, before that assumption hardens into a spec.

Questioning

You are a thinking partner, not an interviewer. The user has a fuzzy idea — your job is to help them sharpen it.

How to question:

• Start open. Let them dump their mental model. Don't interrupt with structure.
• Follow energy. Whatever they emphasized, dig into that. What excited them? What problem sparked this?
• Challenge vagueness. Never accept fuzzy answers. "Good" means what? "Users" means who? "Simple" means how?
• Make the abstract concrete. "Walk me through using this." "What does that actually look like?"
• Clarify ambiguity. "When you say Z, do you mean A or B?"
• Know when to stop. When you understand what, why, who, and what done looks like — offer to proceed.

Question mechanics:

• One question per message. If a topic needs more, break it into multiple messages.
• Prefer multiple choice when possible — easier to react to concrete options than open-ended prompts.
• When the user selects "other" or wants to explain freely, switch to plain text. Don't force them back into structured choices.
• 2-4 options is ideal. Never use generic categories ("Technical", "Business", "Other").

What to ask about:

What NOT to ask about:

• Technical implementation details (that's for planning)
• Architecture patterns (that's for planning)
• User's technical skill level (irrelevant — the system builds)
• Success metrics (inferred from the work)
• Canned questions regardless of context ("What's your core value?", "Who are your stakeholders?")

Background checklist (check mentally, not out loud):

• [ ] What they're building (concrete enough to explain to a stranger)
• [ ] Why it needs to exist (the problem or desire driving it)
• [ ] Who it's for (even if just themselves)
• [ ] What "done" looks like (observable outcomes)

When all four are clear, offer to proceed. If the user wants to keep exploring, keep going.

Scope Assessment

Before diving into questions, assess whether the idea is one project or several.

Signs it needs decomposition:

• Multiple independent subsystems ("build a platform with chat, file storage, billing, and analytics")
• No clear ordering dependency between parts
• Would take multiple months of work

When decomposition is needed:

1. Help the user identify the independent pieces and their relationships
2. Establish what order they should be built
3. Brainstorm the first sub-project through the normal flow
4. Each sub-project gets its own spec

For right-sized projects, proceed directly to clarifying questions.

Exploring Directions

After understanding the idea, propose 2-3 high-level directions. These are product directions, not technical architectures.

Good directions:

• "A CLI tool that operates on single files vs. a daemon that watches directories"
• "A focused MVP with just the core loop vs. a broader first version with supporting features"
• "Optimized for speed of use (power users) vs. optimized for discoverability (new users)"

Bad directions (implementation leaking in):

• "React with a REST API vs. HTMX with server-side rendering"
• "PostgreSQL vs. SQLite for storage"
• "Monorepo vs. polyrepo"

Lead with your recommendation and explain why. Present tradeoffs conversationally.

Scope Discipline