# IMP-18 — Phase Z SVG Coordinate Pre-compute Gap Report

**Status**: documented (reference-only, dormant)
**Scope**: doc-only. No runtime surface modified.
**Related issue**: https://gitea.hmac.kr/Kyeongmin/C.E.L_Slide_test2/issues/18
**Soft dependency**: IMP-04 (frame_partials registration) — IMP-18 activates only when a SVG-bearing partial lands under `templates/phase_z2/`.

---

## A1 — Phase R' source pattern (read-only reference)

Phase R' implements SVG coordinate pre-compute as a renderer hook. References (do **not** modify):

- `src/renderer.py:169-207` — `_preprocess_svg_data(block_type, block_data)` — mutates `block_data` with computed coordinates when `block_type` ∈ `SVG_BLOCKS`; warns and falls back on exception.
- `src/renderer.py:175` — `SVG_BLOCKS = {"venn-diagram", "relationship"}` — exhaustive type allow-list.
- `src/renderer.py:321` — call site inside `render_multi_page()` (`block_data = _preprocess_svg_data(block_type, block_data)`), right before `_resolve_template_path` lookup.
- `src/svg_calculator.py:15-156` — five helpers:
  - L15 `calc_circle_positions(n, center_x, center_y, radius)` — 12 o'clock clockwise N-element layout.
  - L47 `calc_item_radius(n, base_radius=75.0)` — auto-shrink small-circle radius for crowding.
  - L59 `calc_orbit_radius(n, base_orbit=120.0)` — auto-expand orbit for crowding.
  - L70 `calc_outer_radius(n, orbit_radius, item_radius)` — outer enclosing circle, 40 px margin.
  - L77 `prepare_venn_data(items, center_label, center_sub, description, viewbox_width=600.0, viewbox_height=550.0)` — top-level entry; mutates `items[*].cx/cy/r` and returns `outer_r`/`center_x`/`center_y`/`viewbox_width`/`viewbox_height`.

## A2 — Phase Z partial SVG inventory (gap)

Phase Z active partials surface:

- `templates/phase_z2/families/*.html` — **13** files.
- `templates/phase_z2/frames/*.html` — **2** files.
- Total surface = **15 partials**.

SVG usage scan (evidence): `rg "<svg|viewBox" templates/phase_z2/` → **0 matches** (exit 1).

Closest geometric candidate is `templates/phase_z2/families/construction_goals_three_circle_intersection.html` (frame_id `1171281189`, "cycle-3way-intersection" intent), but it renders three intersecting circles via HTML/CSS — `border-radius:50%` + `linear-gradient` + `::before` outer ring — **not** SVG. The Figma source's six accent kanji circles, six side labels, three decorative rects, and three arcs are explicitly **NOT PROMOTED** at the partial header (compact MDX-mapped focus). No partial currently demands the pre-computed `items[*].cx/cy/r` contract.

## A3 — IMP-04 activation gate (soft dependency)

IMP-18 has no Phase Z runtime consumer today. Re-activation triggers:

1. IMP-04 (frame_partials registration) lands an SVG-bearing partial under `templates/phase_z2/` (e.g., a venn-diagram or relationship frame promoted from Figma).
2. The partial declares slots that consume `items[*].cx/cy/r` + `outer_r` + `viewbox_*` (the `prepare_venn_data` return contract).

Until both conditions hold, IMP-18 stays dormant and this gap report is the sole deliverable.

## A4 — Phase R' guardrail (read-only lock)

Per `CLAUDE.md` Phase R' regression prevention rules and the Stage 1/2 exit reports:

- `src/renderer.py` — read-only. No edit to `_preprocess_svg_data` body, `SVG_BLOCKS` set, or `render_multi_page` call site.
- `src/svg_calculator.py` — read-only. No edit to the five helpers or their public signatures.
- `templates/phase_z2/families/*.html` (13) + `templates/phase_z2/frames/*.html` (2) — no `<svg>` / `viewBox` insertion in IMP-18 scope. SVG-bearing partial onboarding is owned by IMP-04.
- F12 `construction_goals_three_circle_intersection.html` HTML/CSS → SVG migration is **out of scope** (separate post-IMP-04 issue).
- No hardcoded SVG coordinates in Phase Z templates — when IMP-18 re-activates, coordinates must be derived from `svg_calculator` helpers (or equivalent forward-port into `phase_z2_renderer`), not hand-copied.

---

## Re-activation checklist (future)

When IMP-04 introduces the first SVG-bearing Phase Z partial:

- [ ] Identify partial(s) consuming `items[*].cx/cy/r` + `outer_r` + `viewbox_*`.
- [ ] Decide port target — extend `phase_z2_renderer` with a `_preprocess_svg_data` analog, or reuse `src/svg_calculator.py` directly.
- [ ] Keep Phase R' references untouched.
- [ ] Add anchor SHA bump only if runtime source surface changes.