Brainstorm: a brainstorm phase for the-loop

The root artifact for issue-17 — dogfooding the very feature it specifies. Locked; the chosen direction carries forward into requirements.md.

Problem / opportunity

the-loop begins a work item at requirements.md. But not every work item is ready for EARS acceptance criteria on day one — some start as a fuzzy idea that needs a scratchpad to think in. And there's a deeper observation in issue #17: the loop's real engine is feedback + iteration on each artifact, advancing only when one is locked. Requirements is just the first place that engine runs today; it should be visible as a general rule with an explicit root artifact at the top.

Context & constraints

• Existing chain: requirements → design → tasks → implementation, each human-reviewed per phase (requireHumanReviewPerPhase).
• Phase state machine is tracked via ticket labels and mirrored in the execution log.
• Everything the-loop manages is enumerated in .the-loop/manifest.yaml and driven by config.schema.json / config.yaml.
• Must stay backwards compatible: existing specs have no brainstorm.

Ideas & options

• Option A — a separate optional brainstorm.md root artifact + /brainstorm command, converted to requirements by new-requirement. Clean separation; rejected options stay in the scratchpad; conversion reuses an existing command. ✅ chosen.
• Option B — a "scratch" section inside requirements.md. Mixes throwaway exploration with the locked contract; muddies the single source of truth. ✗
• Option C — mandatory brainstorm for every work item. Too much ceremony for well-scoped work. ✗ (make it optional instead.)

Open questions (resolved)

• Mandatory or optional? → Optional. Well-defined work starts at requirements.
• New convert command or extend new-requirement? → Extend new-requirement to read a sibling brainstorm; conversion is just "requirements from prior context".
• Where in the state machine? → after not-started, before requirements-definition.

Leaning / working hypothesis

Add brainstorming as an optional Phase 0 with brainstorm.md as the root artifact, and state the "iterate-until-locked, then advance" rule as a first-class principle applied at every link of the artifact chain.

Hand-off → requirements

Carries forward: the new artifact + template, the /brainstorm command, the conversion path, the state-machine insertion, and the generalized iteration principle. Everything in Options B/C stays here as the record of what was considered and rejected.