flow-next-impl-review

# Implementation Review Mode

**Workflow is backend-split. Read [workflow-common.md](workflow-common.md) for Phase 0 (backend detection + philosophy + trivial-diff triage), then read ONLY the file matching your active backend. The opt-in `--deep`/`--validate`/`--interactive` phase detail (including the phase-ordering matrix) lives in [optional-phases.md](optional-phases.md), loaded only when a flag fires:**

- `BACKEND=codex` → [workflow-codex.md](workflow-codex.md)
- `BACKEND=copilot` → [workflow-copilot.md](workflow-copilot.md)
- `BACKEND=cursor` → [workflow-cursor.md](workflow-cursor.md)
- `BACKEND=host` → [workflow-host.md](workflow-host.md)
- `BACKEND=rp` → [workflow-rp.md](workflow-rp.md)

Do not load the others — only the active backend's file is needed. Each backend file carries its own Critical Rules and anti-patterns.

Conduct a John Carmack-level review of implementation changes on the current branch.

**Role**: Code Review Coordinator (NOT the reviewer)
**Backends** (branch on the Phase 0 `RP_ELIGIBLE` probe):
- When `RP_ELIGIBLE=1`: RepoPrompt (rp), Codex CLI (codex), GitHub Copilot CLI (copilot), Cursor CLI (cursor), or host-native (`host`)
- When `RP_ELIGIBLE=0`: Codex CLI (codex), GitHub Copilot CLI (copilot), Cursor CLI (cursor), or host-native (`host`) — rp is macOS-only; never list it in guidance you surface (`--review=rp` stays accepted)

## Preamble — execute Phase 0 exactly once

**The executable Phase 0 lives in [workflow-common.md](workflow-common.md) §"Phase 0: Backend Detection" — Read it and execute it ONCE, before any other bash in this skill.** It defines `$FLOWCTL` (bundled — NOT installed globally; `which flowctl` fails, expected), probes `RP_ELIGIBLE`, resolves `$BACKEND` via the single `flowctl review-backend` call, and handles the ASK / `none` cases. Every later bash block here (triage, deep-pass selection) uses the `$FLOWCTL` it defines. Never invoke `flowctl review-backend` a second time in the same run.

Exception: a `--review=<backend>` argument (see Backend Selection below) wins — when present, set `BACKEND` from the flag and skip Phase 0's `review-backend` call + ASK handling (still run its `$FLOWCTL` / `RP_ELIGIBLE` setup lines).

When `RP_ELIGIBLE=0` (not macOS, no supported RepoPrompt CLI), never *steer* the user toward rp: every backend summary, recommendation, or override hint you surface presents only the runnable configured backends `codex`, `copilot`, `cursor`, `host` (plus `none`). `export` is not an impl-review mode at all — a manual export review lives in `/flow-next:plan-review --review=export`; never present it here. Suppression is not a ban: an explicit `--review=rp`, `FLOW_REVIEW_BACKEND=rp`, or `review.backend=rp` still resolves to rp and errors at runtime via `require_rp_cli()`.

## Backend Selection

**Priority** (first match wins):
1. `--review=rp|codex|copilot|cursor|host|none` argument
2. `FLOW_REVIEW_BACKEND` env var — bare backend (`rp`, `codex`, `copilot`, `cursor`, `host`, `none`) OR spec form (`codex:gpt-5.4:xhigh`, `copilot:claude-opus-4.5`, `cursor:gpt-5.5-high`); `host` is bare-only (`host:<model>` is rejected)
3. `.flow/config.json` → `review.backend` (same bare / spec forms)
4. **Error** - no auto-detection

### Parse from arguments first

Check $ARGUMENTS for:
- `--review=rp` or `--review rp` → use rp
- `--review=codex` or `--review codex` → use codex
- `--review=copilot` or `--review copilot` → use copilot
- `--review=cursor` or `--review cursor` → use cursor
- `--review=host` or `--review host` → use host
- `--review=export` or `--review export` → fail closed: report that `export` is not an impl-review backend and stop before any dispatch; the manual path is `/flow-next:plan-review --review=export`
- `--review=none` or `--review none` → skip review

If found, use that backend and skip all other detection.

### Otherwise: Phase 0 resolves it

No `--review` flag → `$BACKEND` comes from [workflow-common.md](workflow-common.md) Phase 0 (executed once per the Preamble): the single `flowctl review-backend "$REVIEW_ID"` call with ASK handling included. Do not re-resolve here.

### Backend detail (model / effort / spec grammar) — on demand

The per-backend "at a glance" descriptions, the `backend[:model[:effort]]` spec grammar, and the `FLOW_REVIEW_BACKEND` spec-form examples live in [references/backend-specs.md](references/backend-specs.md). Read it only when you must surface backend guidance to the user or resolve a model/effort spec — a normal review already has `$BACKEND` and needs nothing from it. When `RP_ELIGIBLE=0`, omit the **rp** line from any guidance you surface (explicit `--review=rp` still honored).

## Critical Rules

**Per-backend rules** for `rp`, `codex`, `copilot`, and `cursor` live at the top of each `workflow-<backend>.md` — read the active backend's file (routing table above) and follow its Critical Rules section.

**For host backend (fn-123 R5 / fn-126):**
`host` is bare-only. After selection, read [workflow-host.md](workflow-host.md).
The review must use a fresh, tool-enforced read-only reviewer from a different
model family and fail closed when no cross-family pin is available.

**For all backends:**
- If `REVIEW_RECEIPT_PATH` set: write receipt after review (any verdict)
- Any failure → output `<promise>RETRY</promise>` and stop

**Hard invariants:**
- **The coordinator never authors a verdict.** A SHIP with no backend response behind it has broken this.
- **One backend per review.** A transcript that dispatches a second backend after the first answered has broken this.
- **Review is never skipped without consent.** A `none` backend that ends the run without the user's consent has broken this.

## Input

Arguments: $ARGUMENTS
Format: `[task ID] [--base <commit>] [--validate] [--deep[=passes]] [--interactive] [focus areas]`

- `--base <commit>` - Compare against this commit instead of main/master (for task-scoped reviews)
- `--validate` - After NEEDS_WORK verdict, run a validator pass that drops f