fn-2.3 Update impl-review skill for codex backend

fn-2.3 Update impl-review skill for codex backend

Description

Update /flow-next:impl-review skill to support codex backend alongside rp.

Changes needed

1. workflow.md - Add backend detection and branching:

   • Check FLOW_REVIEW_BACKEND env var
   • Check flowctl config get review.backend
   • If interactive, prompt user (show available options)
   • Branch to rp or codex workflow

2. Backend dispatch:

   If backend == "rp":
       [existing RP workflow - setup-review, select-add, chat-send]
   
   If backend == "codex":
       eval "$(flowctl codex impl-review $TASK_ID --base $BASE_BRANCH)"
       # VERDICT now set
   
   If backend == "none":
       Skip review
   

Files to modify

• plugins/flow-next/skills/flow-next-impl-review/workflow.md
• plugins/flow-next/skills/flow-next-impl-review/SKILL.md (if needed)

Acceptance

• Skill detects backend from env var or config
• Interactive mode shows available backends (based on which codex/rp-cli)
• Codex path calls flowctl codex impl-review
• RP path unchanged (no regression)
• none skips review
• Verdict returned correctly from both backends

Done summary

• Updated SKILL.md with backend selection logic
• Updated workflow.md with codex backend workflow (Phase 0 + codex section)
• Labeled RP phases for clarity
• Updated anti-patterns for both backends

Why:

• Enable codex as alternative to RepoPrompt for cross-platform support
• No regression on RP workflow

Verification:

• smoke_test.sh passes

Evidence

• Commits: 828c815859bad499bb92052a21b074f346587703
• Tests: smoke_test.sh
• PRs: