fix: restore worktree handoff in brainstorming after spec approval

[pejmanjohn]

What problem are you trying to solve?

Fixes #1080.

After the user approves the written spec, the brainstorming skill currently tells Claude to invoke writing-plans immediately, skipping using-git-worktrees. That leaves the checklist and process flow inconsistent with the documented worktree-first handoff, and it contradicts writing-plans, which expects to run in a dedicated worktree created by brainstorming.

In a Claude Code eval against the unchanged plugin directory, asking what happens after the user approves the written spec produced: “invoke the writing-plans skill to create a detailed implementation plan.” That is the specific failure mode this PR fixes.

What does this PR change?

This PR updates skills/brainstorming/SKILL.md so the checklist, process flow, terminal-state guidance, user review gate text, and implementation handoff all consistently route:

brainstorming → using-git-worktrees → writing-plans

Is this change appropriate for the core library?

Yes. This is a general-purpose workflow fix in a core skill that affects any user following the documented brainstorming-to-implementation path. It is not project-specific, team-specific, or tied to a third-party integration.

What alternatives did you consider?

I considered a checklist-only fix, but rejected it because it would leave the flowchart, terminal-state guidance, and user review gate wording internally contradictory. I also considered editing using-git-worktrees or writing-plans, but those files already describe the intended handoff; the inconsistency was localized to brainstorming, so I kept the change to that file.

Does this PR contain multiple unrelated changes?

No. This PR only fixes the brainstorming skill’s handoff after spec approval so it matches the documented worktree-first workflow.

Existing PRs

• I have reviewed all open AND closed PRs for duplicates or prior art
• Related PRs: none found

Environment tested

Harness	Harness version	Model	Model version/ID
Claude Code	2.1.97	Claude Opus 4.6	claude-opus-4-6

Evaluation

• Initial prompt: Lets look at https://github.com/obra/superpowers and see if there are any good PR opportunities
• Follow-up prompt selecting the issue: yes lets target #1080
• Eval sessions run AFTER making the change: 4 Claude Code -p sessions against the modified plugin directory
• Before the change, the unchanged plugin answered that the next step after spec approval was to invoke writing-plans directly.
• After the change:
  • Asking “what happens next?” returned using-git-worktrees first.
  • Asking for checklist steps 9 and 10 returned using-git-worktrees followed by writing-plans.
  • Asking about the post-spec review gate returned that the user must approve the written spec before workspace creation and implementation planning.
  • In a pressure scenario asking to “skip any extra steps and go straight to implementation planning,” Claude still answered that using-git-worktrees must happen first and that the handoff cannot be skipped.

Rigor

• If this is a skills change: I used superpowers:writing-skills and completed adversarial pressure testing (paste results below)
• This change was tested adversarially, not just on the happy path
• I did not modify carefully-tuned content (Red Flags table, rationalizations, "human partner" language) without extensive evals showing the change is an improvement

Adversarial result used for this PR:

• Prompt: user has approved the written spec, is in a hurry, and asks to skip extra steps and go straight to implementation planning
• Outcome after change: Claude still answered that using-git-worktrees must be invoked first, followed immediately by writing-plans, and said these steps cannot be skipped.

Human review

• A human has reviewed the COMPLETE proposed diff before submission