unknowns:impl — preview, approve, then implement with a deviation log

No matter how much planning was done, unknown unknowns lurk in implementation. This phase shows the user WHAT is about to be built (cheap to change), gets approval, then implements the plan AND captures what the plan missed, so the next attempt starts smarter.

Step 1 — Locate state

• Argument given (/unknowns:impl docs/unknowns-resolver/<slug>/) → use it.
• No argument: if exactly one directory exists under docs/unknowns-resolver/, use it; otherwise list them and ask which (one question).
• Directory or 06-plan.md missing → STOP and print: "No plan found. Run /unknowns:pre <task> first." (Do not improvise a plan.)

Step 2 — Load context

Read, in order: ledger.md, 06-plan.md, 04-prototype/reactions.md (if present), 05-reference.md (if present). Restate in ≤6 bullets: what's being built, the key decisions (by ledger #), and where the improvise points are.

Step 3 — Implementation preview (APPROVAL GATE — no code before approval)

Before touching any code, show the user what the implementation will look like:

1. Write 07-preview.md and generate 07-preview.html per ${CLAUDE_PLUGIN_ROOT}/skills/pre/references/design-system.md (§ 07-preview.html). Contents, all derived from 06-plan.md + a read of the ACTUAL target code:
   • Architecture diagram — components touched and how they connect after the change (new pieces highlighted).
   • File-change map — table: file → create/modify → purpose → plan section #.
   • Pseudocode — per major component, short and language-neutral, linked to the plan section it implements.
   • Data flow — the main path end-to-end (request → … → response, or input → output), with improvise points marked amber where they sit.
2. Open 07-preview.html for the user (open <path>), then invite critique IN CHAT: "React to the preview — wrong shape, missing case, better split? I revise until you approve."
3. On each critique: revise 07-preview.md, regenerate the HTML, summarize what changed in one line. Repeat.
4. Gate: proceed to Step 4 only on explicit approval (e.g. "approved", "go", "implement it"). Record at the top of 07-preview.md: Approved: <short user wording> (revision <n>). If a critique changes a decision (not just shape), update the ledger row and 06-plan.md section it touches before re-rendering.

# Implementation preview: <task>

Approved: — (pending)   ·   Revision: 1

## Architecture
<diagram description mirrored from the HTML, in text>

## File-change map
| File | Action | Purpose | Plan § |

## Pseudocode
### <component>   (plan § <n>)
...

## Data flow
1. ...

Step 4 — Implement

Work the plan top to bottom (data model → interfaces → user-facing → mechanical). Follow the target project's own conventions and verification commands (its CLAUDE.md rules win on style/test matters). The approved preview is the shape contract — deviate from it only via the deviation rule below.

Deviation rule — when an edge case forces a departure from the plan or the approved preview (or an improvise point fires):

1. Pick the CONSERVATIVE option (least surface area, most reversible).
2. Log it in 08-notes.md under ## Deviations — then KEEP GOING. Do not stop to ask.

# Implementation notes: <task>

## Deviations
### D1: <what forced it>   (plan section <n>, ledger #<id> if improvise point)
- Chose: <conservative option> — Rejected: <alternative> — Why: <1 line>

## New unknowns discovered
- <question> → added to ledger as #<id>

3. Brand-new unknowns (not deviations, genuinely new questions) → append to ledger: Quadrant UU, Found in 08-notes, Status open.

Step 5 — Verify

Run the plan's ## Verification commands. Report results honestly — failures are failures.

Step 6 — Exit handoff (MANDATORY)

Update ledger (Route status → impl complete), regenerate index.html (per ${CLAUDE_PLUGIN_ROOT}/skills/pre/references/design-system.md — deviations panel now populated, next-action banner → post). Print:

Implementation complete: {sections done}/{total} plan sections, {d} deviations logged, {u} new unknowns. Preview: 07-preview.html (approved rev {n}) · Notes: 08-notes.md · Dashboard: index.html

Next phase: /unknowns:post docs/unknowns-resolver/<slug>/ — builds the buy-in pitch, then quizzes you. Merge only after a perfect quiz.