KateRTX OS · multi-tab SPV seats · SDF bus · designer headers
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Product path · not demo · ESSIE hotswap · JSON + long details

WHAT
  Tabbed "OS" surface: each open SPV is a live seat (not remount-on-focus).
  Seats speak SDF frames on BGS/BGF with mode insecure | secure | broadcast.
  SPV designer <header> faces become desktop icons + Start launchers.

STACK (linear pins)
  BGS  ground   · field_one(v)=v|1
  BGF  measure  · (a-b)|1 · SPV free rides
  BGL  secure   · surface|1 · field hygiene
  SDF  place    · shell · raised · store · message envelope
  SPV  free     · |1 · never folds into SDF/BGS

FILES
  js/bus.js              · BGRTX_BUS / BGRTX_SDF
  js/desktop.js          · multi-seat tabs · launchers · bus UI
  css/shell.css          · seat panes · bus-bar · designer faces
  spvs/headers.json      · designer header catalog (generated)
  spvs/manifest.json     · plugs + os block
  bin/pack-os-desktop    · rebuild out/desktop_os.html
  bin/pack_os_desktop.py · packer + header parse
  out/desktop_os.html    · offline pack

BUS MODES (easily selectable)
  insecure   · open lab channel · all seats may hear
  secure     · token ring · secure peers / explicit `to`
  broadcast  · force * delivery · every listener

  UI: tabbar SDF [INSEC|SEC|BC] | [BGF|BGS]
  Chat: /bus secure · /lane BGF · /say hello · /peers · /spit
  Context menu: Bus · insecure/secure/broadcast · Lane · BGF/BGS
  API: BGRTX_BUS.setMode('secure'); BGRTX_BUS.setLane('BGS');
       BGRTX_SPV.speak('ping', { text: 'hi' }, { to: 'seat:term' });

SDF FRAME (JSON · long details welcome)
  {
    "v": 1,
    "kind": "sdf",
    "protocol": "SDF",
    "lane": "BGF" | "BGS",
    "mode": "insecure" | "secure" | "broadcast",
    "from": "seat:term" | "os",
    "to": "seat:mail" | "*" | "secure-ring",
    "topic": "speak" | "seat.open" | "chat" | "sample" | ...,
    "payload": { ... },
    "details": { "long": "...", ... },
    "ts": "ISO-8601",
    "seq": 1,
    "field": <BGF|BGS measure>,
    "free": 1,
    "place": "SDF",
    "ride": "BGF",
    "ground": "BGS"
  }

MULTI-SEAT TABS
  open/launch  → create seat pane · inject DOM+JS · mount once
  focus        → hide other panes · show this seat (state kept)
  close        → unmount + remove peer from bus
  Ctrl+Tab     · cycle seats · Ctrl+W close · Ctrl+1..9

DESIGNER HEADERS = ICONS + LAUNCHERS
  Pack parses each plug's first <header> for:
    title (.spv-title / h1 / h2 / .mail-app-title)
    subtitle (.meta / .mail-app-sub)
    glyph (icon span or manifest icon)
  Catalog: spvs/headers.json · window.__BGRTX_HEADERS__
  Desk icons + Start menu use header face + long title tooltip.
  Tab strip shows header glyph + title.

PACK
  ./bin/pack-os-desktop
  → out/desktop_os.html
  → spvs/headers.json
  open pack in engine sheet path or file:// / local viewer
  preferred: krtx-engine sheet when native; pack is full OS HTML lane

CHAT COMMANDS
  /list · /in <id> · /bus insecure|secure|broadcast
  /lane BGF|BGS · /say <text> · /peers · /spit
  /close · /js · /fox · /online · /offline · /help
  bare <id> launches that SPV seat

API SURFACE
  window.BGRTX_SPV.listApps()   · designer launchers
  window.BGRTX_SPV.headers()    · header catalog faces
  window.BGRTX_SPV.seats()      · live concurrent seats
  window.BGRTX_SPV.spit()       · full JSON dump + bus spit
  window.BGRTX_SPV.speak(...)   · SDF from active seat / os
  window.BGRTX_BUS.spit()       · bus law + history tail

LAW
  remain IN · never ML · ESSIE ≠ EZZIE · GRIN free=1 · <3