feat(ai-skills): teach parent_id rule + trim PREFER list "Different from"

Two diet/teaching changes to elements.md, both motivated by today's
ab-v4 smoke results:

(a) parent_id teaching — minimax-m2.7 invented "members-section" /
    "canvas" as parent_id values on its multi-tool composite output,
    then every one of its 14 tags failed apply with "parent_id X not
    found in document". Same pattern as yesterday. Adds an explicit
    rule near the top of elements.md (right under the multi-tool
    banner) — `parent_id` is REAL or OMITTED, never invented. The
    `<page>` / `<panel>` / `<sidebar>` placeholders in the cookbook
    recipes are documentation conventions; in actual output, OMIT
    the field. Names the failure mode by reproducing the error
    message format so models learn to avoid it.

(b) Phase 3 token diet — strip ". Different from <tool> (...)"
    disambiguation suffixes from the PREFER list (22 entries had
    them, ~80-200 chars each = ~2.5kb / ~625 tokens saved). The
    primary keyword + tool-name + capability description survives
    intact; the cross-references pointing at sibling tools get
    dropped. Risk: slight increase in wrong-tool routing on
    ambiguous prompts. Worth it for the size reduction; the
    decision tree alone still shows the tool family in context.

Verified by mechanical diff — perl in-place edit, then visual
review confirms no other content was touched. 3785 vitest pass,
format clean, tsc silent.

Net effect on T-prompt size (chars / 4 estimate):
  T + composite + mobile: was 17,930 → now 17,475 (-455 chars)
  T + composite + dashboard: was 18,437 → now 17,983 (-454 chars)
  T + obvious + dashboard: ~14,009 → ~13,556 (-453 chars)

Per-arm savings are smaller than the raw 2.5kb trim because (a)
adds ~700 chars of parent_id teaching. Net win: ~450 chars / ~110
tokens per call. Modest but compounds across 520+ ab-v4 runs.

packages/pen-ai-skills/skills/phases/generation/elements.md

@@ -33,6 +33,8 @@ These narrow MCP tools emit well-known structures that batch_design frequently g
 
 Multi-tool example — a "Notifications" settings section with a header + 4 toggle rows is **5 tool calls** (1× `add_section_header_v0` + 4× `add_setting_row_v0`), NOT 1 batch_design.
 
+**`parent_id` is REAL or OMITTED — never invented.** Every `add_*_v0` tool's `parent_id` arg must either (1) be omitted entirely so the new node lands at the page root (the safe default for full-page composite briefs), or (2) name a real existing node id you already received from a prior tool call. The cookbook recipes below use placeholders like `<page>` / `<panel>` / `<sidebar>` as DOCUMENTATION shorthand only — when YOU emit the call in your output, OMIT the parent_id field entirely. Inventing strings (`"page"`, `"canvas"`, `"members-section"`, `"<page>"`) makes the tool reject the call with `parent_id "X" not found in document`.
+
 ## Decision tree (per component — pick first match)
 
 Rows (horizontal, in-card or scrolling):
@@ -377,29 +379,29 @@ PREFER an element tool when the spec says any of:
 - "pricing card", "plan card", "SaaS tier", "subscription plan", "pricing tier", "billing card", "价格卡", "套餐卡", "定价卡片" → `add_pricing_card_v0` (set one tile's `emphasis: "featured"` to visually recommend it — auto-gets "Most popular" badge unless `badge` overrides). For a 3-tier pricing section, call this 3× under the same parent section.
 - "slider", "range input", "volume control", "opacity slider", "brightness slider", "filter slider", "滑块", "滑动条", "音量条" → `add_range_slider_v0` (single-handle; set `show_value=true` + `value_suffix="%"` to render the readout). For a dual-handle range (min+max), still fall through to batch_design.
 - "phone input", "phone field", "international phone", "country code input", "+1 (555) ...", "电话号码", "手机号输入", "国际电话" → `add_phone_input_v0` (renders country dial code button + digits input in a 44px row; pass `country_flag` for emoji prefix). For a plain single-line text input without the country prefix, use `add_form_field_v0`.
-- "newsletter signup", "subscribe form", "subscribe to newsletter", "promo code input", "apply discount", "send message input", "chat composer", "search with submit", "订阅", "应用优惠码", "发送消息" → `add_input_with_action_v0` (action_kind="text" for "Subscribe" pill button, action_kind="icon" for chat send arrow). Different from `add_form_field_v0` (no inline button) and `add_search_bar_v0` (no trailing action button).
+- "newsletter signup", "subscribe form", "subscribe to newsletter", "promo code input", "apply discount", "send message input", "chat composer", "search with submit", "订阅", "应用优惠码", "发送消息" → `add_input_with_action_v0` (action_kind="text" for "Subscribe" pill button, action_kind="icon" for chat send arrow).
 - "cookie banner", "cookie consent", "GDPR banner", "CCPA banner", "privacy notice", "cookie disclosure", "cookie 提示", "隐私同意条" → `add_cookie_banner_v0` (set `show_settings_link: true` for fine-grained GDPR consent UX). Caller positions sticky-bottom; the tool emits the banner card itself.
-- "sidebar", "side nav", "sidebar nav", "left rail", "dashboard nav rail", "admin sidebar", "settings sidebar", "docs sidebar", "vertical nav", "侧边栏", "侧边导航", "左侧导航" → `add_sidebar_nav_v0` (desktop persistent rail; pass `title` for a brand row above the items, mark current page with `active: true` on the item). Different from `add_bottom_nav_v0` (mobile bottom tabs) and `add_top_nav_bar_v0` (mobile top header).
-- "stacked avatars", "avatar group", "avatar stack", "team avatars", "5 contributors", "online users", "+N more", "viewers row", "presence indicator", "成员头像", "团队头像", "在线用户", "头像组" → `add_avatar_group_v0` (renders up to `max_visible` ringed avatar circles + a "+N" overflow tile; pen-core flex doesn't allow negative gap so the white ring + 4px gap is the affordance, not literal overlap). Different from `add_avatar_v0` (single tile) and `add_member_row_v0` (full list row with name + role per member, not a stacked indicator).
-- "data table row", "table row", "table header row", "customer row", "order row", "report row", "transaction row", "users table", "数据表行", "表格行", "表头行" → `add_data_table_row_v0` (desktop pattern; pass `header: true` for the column-header row, `selected: true` to tint a hover/selected body row). For row separators stack `add_divider_v0` between rows. Different from `add_list_row_v0` which is the iOS / mobile leading-icon list cell.
-- "filter chip", "filter tag", "applied filter", "selected criterion", "category pill", "removable tag", "Status: Active ×", "可移除标签", "筛选标签" → `add_tag_v0` (single chip with optional × close icon, default removable=true; pass `tone` for accent / success / warning / error palettes). Different from `add_badge_v0` (read-only static, smaller, no × affordance) and `add_chip_input_v0` (multi-tag INPUT FIELD with caret).
-- "user card", "contact card", "people picker row", "user mini card", "用户卡片", "联系人卡片" → `add_user_card_v0` (compact fit_content tile, no trailing slot — used in lobbies / chip-style lists). Different from `add_member_row_v0` (full-width row WITH trailing slot for role / menu / status), `add_comment_v0` (carries body + timestamp), and `add_avatar_v0` (just the disk).
-- "members list", "team page row", "people row", "sharing dialog row", "user list with role", "team member row", "团队成员", "成员列表行" → `add_member_row_v0` (avatar + name + optional subtitle + trailing role badge / kebab menu / status dot). Different from `add_user_card_v0` (compact tile, fit_content, no trailing) and `add_list_row_v0` (no avatar slot — uses leading icon).
-- "profile header", "profile hero", "about me block", "account header", "user profile page", "个人主页头部" → `add_profile_header_v0` (large centered avatar + display name + optional handle / bio). Different from `add_user_card_v0` (compact horizontal row).
-- "drawer", "side panel", "slide-in panel", "edit drawer", "detail panel", "抽屉", "侧滑面板" → `add_drawer_shell_v0` (full-height drawer with title + close ×; body composed via subsequent calls under its id). Different from `add_modal_shell_v0` (centered card with scrim).
-- "combobox", "autocomplete", "open dropdown", "command palette", "open select", "search with results", "自动补全", "下拉补全" → `add_combobox_v0` (OPEN-state input + dropdown with N suggestion rows; one row optionally `highlighted: true`). Different from `add_select_v0` (closed state) and `add_search_bar_v0` (no suggestion list).
-- "toolbar", "editor toolbar", "formatting toolbar", "kanban actions", "icon button row", "工具栏" → `add_toolbar_v0` (horizontal 36×36 icon buttons + optional vertical dividers). Different from `add_top_nav_bar_v0` (mobile header) and `add_icon_button_v0` (single button).
-- "callout", "tip block", "doc note", "did you know", "info box", "提示框", "信息块" → `add_callout_v0` (tinted block with body + optional title + tone-driven leading icon: info / success / warning / danger / note). Different from `add_alert_v0` (banner with × dismiss) and `add_tooltip_v0` (small dark hover pill).
-- "inline action", "Undo button inline", "Saved • Retry", "comment deleted undo", "inline feedback", "inline action row" → `add_inline_action_v0` (left message + right blue action label, NO floating). Different from `add_toast_v0` (floating) and `add_alert_v0` (banner).
-- "share row", "share to social", "share buttons", "post share", "send via", "分享按钮组" → `add_share_row_v0` (horizontal circular icon buttons each labeled below). Different from `add_social_login_row_v0` (sign-in CTAs).
-- "chart legend", "legend item", "legend entry", "数据图例", "图例条目" → `add_legend_item_v0` (marker + label + optional value). Different from `add_status_badge_v0` (semantic dot + text).
-- "inbox row", "email row", "message list cell", "mail item", "email preview", "邮件条目", "收件箱条目" → `add_inbox_message_v0` (sender + subject + preview + timestamp + unread dot). Different from `add_notification_row_v0` (single title + body) and `add_list_row_v0` (no timestamp).
-- "settings row", "preference row", "menu item with toggle", "settings list item", "设置项", "偏好项", "开关行" → `add_setting_row_v0` (icon + title/subtitle + trailing chevron/value/switch/badge). Different from `add_list_row_v0` (trailing always icon, no switch/value/badge variants) and `add_form_field_v0` (label-above-input pattern for forms).
-- "facet panel", "filter sidebar", "category checklist", "brand filter", "applied filters group", "搜索筛选侧栏", "分面筛选", "类目筛选" → `add_filter_group_v0` (heading + vertical checkbox-style option list with optional counts). Different from `add_nav_chip_row_v0` (horizontal scrolling chips), `add_tag_v0` (single applied chip with × close), and `add_segmented_control_v0` (mutex pill tabs).
-- "pending invite", "invitation row", "team invite", "邀请列表行", "待接受邀请", "invitations table row" → `add_invite_row_v0` (initial avatar + email/role + status pill + trailing action). Different from `add_member_row_v0` (a JOINED member, no status pill or action slot) and `add_list_row_v0` (no avatar / status / action).
-- "audit log row", "activity feed entry", "recent activity item", "audit entry", "审计日志条目", "活动记录", "操作日志行" → `add_activity_log_v0` (single line: optional tinted icon dot + "<actor> <action>" + right-aligned timestamp). Different from `add_timeline_v0` (multi-event vertical with connecting line + per-event title + body) and `add_notification_row_v0` (title + body, no actor focus).
-- "event card", "agenda item", "meeting tile", "upcoming event", "calendar event row", "日程卡片", "会议条目", "活动卡片" → `add_event_card_v0` (date column with month band + day number, then title + time + location). Different from `add_calendar_grid_v0` (the full month grid) and `add_card_row_v0` (horizontally scrolling cards with title + subtitle + image, no date column).
-- "onboarding step", "how-it-works step", "tutorial step card", "setup checklist item", "操作步骤卡片", "教程步骤", "新手引导步骤" → `add_step_card_v0` (numbered circle / check + title + description, stacks vertically). Different from `add_stepper_v0` (horizontal progress nav with connectors) and `add_faq_item_v0` (collapsible Q&A header).
+- "sidebar", "side nav", "sidebar nav", "left rail", "dashboard nav rail", "admin sidebar", "settings sidebar", "docs sidebar", "vertical nav", "侧边栏", "侧边导航", "左侧导航" → `add_sidebar_nav_v0` (desktop persistent rail; pass `title` for a brand row above the items, mark current page with `active: true` on the item).
+- "stacked avatars", "avatar group", "avatar stack", "team avatars", "5 contributors", "online users", "+N more", "viewers row", "presence indicator", "成员头像", "团队头像", "在线用户", "头像组" → `add_avatar_group_v0` (renders up to `max_visible` ringed avatar circles + a "+N" overflow tile; pen-core flex doesn't allow negative gap so the white ring + 4px gap is the affordance, not literal overlap).
+- "data table row", "table row", "table header row", "customer row", "order row", "report row", "transaction row", "users table", "数据表行", "表格行", "表头行" → `add_data_table_row_v0` (desktop pattern; pass `header: true` for the column-header row, `selected: true` to tint a hover/selected body row). For row separators stack `add_divider_v0` between rows.
+- "filter chip", "filter tag", "applied filter", "selected criterion", "category pill", "removable tag", "Status: Active ×", "可移除标签", "筛选标签" → `add_tag_v0` (single chip with optional × close icon, default removable=true; pass `tone` for accent / success / warning / error palettes).
+- "user card", "contact card", "people picker row", "user mini card", "用户卡片", "联系人卡片" → `add_user_card_v0` (compact fit_content tile, no trailing slot — used in lobbies / chip-style lists).
+- "members list", "team page row", "people row", "sharing dialog row", "user list with role", "team member row", "团队成员", "成员列表行" → `add_member_row_v0` (avatar + name + optional subtitle + trailing role badge / kebab menu / status dot).
+- "profile header", "profile hero", "about me block", "account header", "user profile page", "个人主页头部" → `add_profile_header_v0` (large centered avatar + display name + optional handle / bio).
+- "drawer", "side panel", "slide-in panel", "edit drawer", "detail panel", "抽屉", "侧滑面板" → `add_drawer_shell_v0` (full-height drawer with title + close ×; body composed via subsequent calls under its id).
+- "combobox", "autocomplete", "open dropdown", "command palette", "open select", "search with results", "自动补全", "下拉补全" → `add_combobox_v0` (OPEN-state input + dropdown with N suggestion rows; one row optionally `highlighted: true`).
+- "toolbar", "editor toolbar", "formatting toolbar", "kanban actions", "icon button row", "工具栏" → `add_toolbar_v0` (horizontal 36×36 icon buttons + optional vertical dividers).
+- "callout", "tip block", "doc note", "did you know", "info box", "提示框", "信息块" → `add_callout_v0` (tinted block with body + optional title + tone-driven leading icon: info / success / warning / danger / note).
+- "inline action", "Undo button inline", "Saved • Retry", "comment deleted undo", "inline feedback", "inline action row" → `add_inline_action_v0` (left message + right blue action label, NO floating).
+- "share row", "share to social", "share buttons", "post share", "send via", "分享按钮组" → `add_share_row_v0` (horizontal circular icon buttons each labeled below).
+- "chart legend", "legend item", "legend entry", "数据图例", "图例条目" → `add_legend_item_v0` (marker + label + optional value).
+- "inbox row", "email row", "message list cell", "mail item", "email preview", "邮件条目", "收件箱条目" → `add_inbox_message_v0` (sender + subject + preview + timestamp + unread dot).
+- "settings row", "preference row", "menu item with toggle", "settings list item", "设置项", "偏好项", "开关行" → `add_setting_row_v0` (icon + title/subtitle + trailing chevron/value/switch/badge).
+- "facet panel", "filter sidebar", "category checklist", "brand filter", "applied filters group", "搜索筛选侧栏", "分面筛选", "类目筛选" → `add_filter_group_v0` (heading + vertical checkbox-style option list with optional counts).
+- "pending invite", "invitation row", "team invite", "邀请列表行", "待接受邀请", "invitations table row" → `add_invite_row_v0` (initial avatar + email/role + status pill + trailing action).
+- "audit log row", "activity feed entry", "recent activity item", "audit entry", "审计日志条目", "活动记录", "操作日志行" → `add_activity_log_v0` (single line: optional tinted icon dot + "<actor> <action>" + right-aligned timestamp).
+- "event card", "agenda item", "meeting tile", "upcoming event", "calendar event row", "日程卡片", "会议条目", "活动卡片" → `add_event_card_v0` (date column with month band + day number, then title + time + location).
+- "onboarding step", "how-it-works step", "tutorial step card", "setup checklist item", "操作步骤卡片", "教程步骤", "新手引导步骤" → `add_step_card_v0` (numbered circle / check + title + description, stacks vertically).
 
 STILL use batch_design when (emit a SINGLE batch_design for the whole response — do NOT mix with element-tool calls):