docs(docs): add district topology diagram

D2 source + PNG render showing all zone connections, access tiers,
z-levels, maintenance corridor routing, and dual entry vectors.
Vertical layout with color-coded access tiers per D-093.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/diagrams/design/district-topology.d2

@@ -0,0 +1,235 @@
+# District Topology — Sova Transit District
+# D-093 spatial layout. D-094 hierarchy: 256×256 vt (4×4 blocks).
+# North = span gate entry. South-east = tram entry.
+
+direction: down
+
+vars: {
+  bg:    "#1a1e24"
+  txt:   "#c8d0e0"
+  acc:   "#c8d8f0"
+
+  pub:   "#1a3320"
+  spub:  "#2e2a10"
+  spriv: "#2e1a08"
+  priv:  "#2a0e0e"
+  comm:  "#0e1a2e"
+  neut:  "#1e2228"
+
+  s-pub:   "#3a8a50"
+  s-spub:  "#b8a020"
+  s-spriv: "#c86010"
+  s-priv:  "#c02020"
+  s-comm:  "#3060c0"
+  s-neut:  "#4a5060"
+}
+
+# ── LEGEND ──
+
+legend: Legend {
+  style.fill: ${bg}
+  style.stroke: ${acc}
+  style.font-color: ${txt}
+  style.font-size: 11
+  direction: right
+
+  l1: Public { style.fill: ${pub}; style.stroke: ${s-pub}; style.font-color: ${txt} }
+  l2: Semi-pub { style.fill: ${spub}; style.stroke: ${s-spub}; style.font-color: ${txt} }
+  l3: Semi-priv { style.fill: ${spriv}; style.stroke: ${s-spriv}; style.font-color: ${txt} }
+  l4: Private { style.fill: ${priv}; style.stroke: ${s-priv}; style.font-color: ${txt} }
+  l5: Commission { style.fill: ${comm}; style.stroke: ${s-comm}; style.font-color: ${txt} }
+}
+
+# ── NORTH ENTRY: SPAN GATE ──
+
+span_gate: The Ring\n(span gate aperture) {
+  shape: hexagon
+  style.fill: ${comm}
+  style.stroke: ${s-comm}
+  style.font-color: ${txt}
+}
+
+# ── GATE CLUSTER ──
+
+gate: Gate Cluster · 40×32 vt {
+  style.fill: ${bg}
+  style.stroke: ${s-comm}
+  style.font-color: ${txt}
+  style.border-radius: 4
+
+  aperture: Aperture\n8×4 {
+    style.fill: ${priv}; style.stroke: ${s-priv}; style.font-color: ${txt}
+  }
+  staging: Freight Staging\n24×8 {
+    style.fill: ${priv}; style.stroke: ${s-priv}; style.font-color: ${txt}
+  }
+  pab: Passenger Arrival\n12×8 {
+    style.fill: ${spub}; style.stroke: ${s-spub}; style.font-color: ${txt}
+  }
+  customs: Customs Lanes\n(freight 5×4vt + ped 3×2vt) {
+    style.fill: ${spriv}; style.stroke: ${s-spriv}; style.font-color: ${txt}
+  }
+  concourse: Concourse\n40×8 · PUBLIC {
+    style.fill: ${pub}; style.stroke: ${s-pub}; style.font-color: ${txt}
+  }
+  gallery: Gallery · z=2\n32×10 · COMMISSION {
+    style.fill: ${comm}; style.stroke: ${s-comm}; style.font-color: ${txt}
+  }
+
+  aperture -> staging: freight { style.stroke: ${s-priv} }
+  aperture -> pab: passenger { style.stroke: ${s-spub} }
+  staging -> customs { style.stroke: ${s-spriv} }
+  pab -> customs { style.stroke: ${s-spub} }
+  customs -> concourse { style.stroke: ${s-pub} }
+  concourse -> gallery: "staircase (Commission)" {
+    style.stroke: ${s-comm}; style.stroke-dash: 4
+  }
+  gallery -> customs: "LOS z=2 down" {
+    style.stroke: ${s-comm}; style.stroke-dash: 4
+  }
+}
+
+span_gate -> gate.aperture: "dual-use transit\n(90s flicker)" {
+  style.stroke: ${s-comm}
+}
+
+# ── TERMINAL ──
+
+terminal: Terminal · 44×28 vt {
+  style.fill: ${bg}
+  style.stroke: ${s-spriv}
+  style.font-color: ${txt}
+  style.border-radius: 4
+
+  forecourt: Forecourt\n44×4 {
+    style.fill: ${spub}; style.stroke: ${s-spub}; style.font-color: ${txt}
+  }
+  cargo: Cargo Floor + Main Corridor {
+    style.fill: ${spriv}; style.stroke: ${s-spriv}; style.font-color: ${txt}
+  }
+  storage: Restricted Storage\n(single coded door) {
+    style.fill: ${priv}; style.stroke: ${s-priv}; style.font-color: ${txt}
+  }
+  hatch_t: M-HATCH-T {
+    shape: diamond
+    style.fill: ${priv}; style.stroke: ${s-priv}; style.font-color: ${txt}
+  }
+
+  forecourt -> cargo { style.stroke: ${s-spriv} }
+  cargo -> storage: "coded door" { style.stroke: ${s-priv} }
+  storage -> hatch_t { style.stroke: ${s-priv} }
+}
+
+gate.concourse -> terminal.forecourt: "district spine (south)" {
+  style.stroke: ${s-pub}
+}
+
+# ── TRANSITION CORRIDOR ──
+
+corridor: Transition Corridor\n~40×6 vt {
+  style.fill: ${spub}
+  style.stroke: ${s-spub}
+  style.font-color: ${txt}
+  style.border-radius: 4
+}
+
+terminal.cargo -> corridor: "public route" {
+  style.stroke: ${s-spub}
+}
+
+# ── BAR ──
+
+bar: The Last Shift · 28×22 vt {
+  style.fill: ${bg}
+  style.stroke: ${s-pub}
+  style.font-color: ${txt}
+  style.border-radius: 4
+
+  approach: Bar Approach\n28×3 {
+    style.fill: ${spub}; style.stroke: ${s-spub}; style.font-color: ${txt}
+  }
+  floor: Main Floor\n(corner booth · card table) {
+    style.fill: ${pub}; style.stroke: ${s-pub}; style.font-color: ${txt}
+  }
+  bathroom: Bathroom Corridor\n(east ext.) {
+    style.fill: ${spriv}; style.stroke: ${s-spriv}; style.font-color: ${txt}
+  }
+  backroom: Back Room\n(Lera) {
+    style.fill: ${priv}; style.stroke: ${s-priv}; style.font-color: ${txt}
+  }
+  hatch_b: M-HATCH-B {
+    shape: diamond
+    style.fill: ${priv}; style.stroke: ${s-priv}; style.font-color: ${txt}
+  }
+
+  approach -> floor { style.stroke: ${s-pub} }
+  floor -> bathroom: "east door" { style.stroke: ${s-spriv} }
+  floor -> backroom: "staff only" { style.stroke: ${s-priv} }
+  bathroom -> hatch_b { style.stroke: ${s-priv} }
+}
+
+corridor -> bar.approach: "bar-side decompression" {
+  style.stroke: ${s-spub}
+}
+
+# ── MAINTENANCE CORRIDOR (z=0) ──
+
+maint: Maintenance Corridor\n(z=0 · Era 1 · 2vt wide)\nzero public traffic {
+  style.fill: ${priv}
+  style.stroke: ${s-priv}
+  style.font-color: ${txt}
+  style.border-radius: 4
+  style.stroke-dash: 5
+}
+
+junc: JUNC-1 {
+  shape: diamond
+  style.fill: ${priv}; style.stroke: ${s-priv}; style.font-color: ${txt}
+}
+
+terminal.hatch_t -> maint: "z=1 down z=0" {
+  style.stroke: ${s-priv}; style.stroke-dash: 5
+}
+maint -> junc { style.stroke: ${s-priv}; style.stroke-dash: 5 }
+junc -> bar.hatch_b: "z=0 up z=1" {
+  style.stroke: ${s-priv}; style.stroke-dash: 5
+}
+
+# ── SOUTH-EAST ENTRY: TRAM ──
+
+the_loop: The Loop\n(station tram · 6 districts) {
+  shape: hexagon
+  style.fill: ${neut}
+  style.stroke: ${s-neut}
+  style.font-color: ${txt}
+}
+
+platform: Transit Platform\n~12×8 vt · bar-side\n(encounter node) {
+  style.fill: ${pub}
+  style.stroke: ${s-pub}
+  style.font-color: ${txt}
+  style.border-radius: 4
+}
+
+the_loop -> platform: "workers arrive here (G-11)" {
+  style.stroke: ${s-neut}
+}
+platform -> bar.approach: "adjacent" {
+  style.stroke: ${s-pub}
+}
+
+# ── SECTOR 3 ──
+
+sector3: Sector 3 Residential\n~15×12 vt · Drin/Naia {
+  style.fill: ${spub}
+  style.stroke: ${s-spub}
+  style.font-color: ${txt}
+  style.border-radius: 4
+}
+
+sector3 -> terminal.forecourt: "near Terminal" {
+  style.stroke: ${s-spub}; style.stroke-dash: 3
+}
+sector3 -> maint: "adjacent to spine" {
+  style.stroke: ${s-neut}; style.stroke-dash: 3
+}