feat(08-02): ARG2 codec — one version, one decode path (G-suite GREEN)

graph.ts versioned IN PLACE (no second codec): GRAPH_MAGIC 0x41524732,
GRAPH_VERSION 2, HEADER_SIZE 72 (72%8==0 keeps f64 views aligned);
header gains landmarkCount u32 @60 (the old pad), landmarkQuantumS f32
@64, reserved u32 @68; the landmark suffix (u16 toTable, u16 fromTable,
u32 landmarkNodes) extends layoutFor's total arithmetic — exact-size
law covers the variable suffix BEFORE any view allocation (T-08-01).
D-01 fail-honest: ARG1 bytes / version!=2 / landmarkCount=0 / hostile
quantum / size mismatch all decode null (committed mini-graph-arg1.bin
is the standing rejection vector). GraphInput.landmarks REQUIRED and
loud-validated (T-08-04). RoadGraph gains the five landmark fields
(Plan 08-03's ALT potentials consume them).

Fixture regenerated as ARG2 through the SAME encode authority: the
builder gains the tiny real landmark stage (L=2, anchors [0,18],
quantum 0.1s, coverage 1.0 — identical bytes every re-run).

Rule-3 call-site updates forced by the required-landmarks law (missed
by the plan's files list): astar.test A3 + snap.test S3 synthetics
carry inert hand landmark blocks. Fixture regen pulled forward from
task 3 so this commit's own battery is green (74 passed, 0 failed).

routing/test/snap.test.mjs

@@ -110,12 +110,20 @@ test("S3 nameId — a perimeter fix resolves 'Jalan Persiaran Mini'; an unnamed
   assert.equal(g.nameAt(atNode1.nameId), "Jalan Persiaran Mini");
 
   // Synthetic 2-node graph with ONE unnamed edge -> nameId null.
+  // ARG2 (plan 08-02): the landmark block is required by the one encode
+  // authority; values are inert steering data until ALT lands (08-03).
   const bare = encodeGraph({
     lat: [3.15, 3.1505],
     lng: [101.69, 101.6905],
     edges: [{ from: 0, to: 1, seconds: 4 }],
     names: [],
     maxSpeedKmh: 60,
+    landmarks: {
+      quantumS: 0.5,
+      nodes: [0],
+      to: Uint16Array.of(0, 30),
+      from: Uint16Array.of(0, 30),
+    },
   });
   const { decodeGraph, UNNAMED_NAME_ID } = await loadGraph();
   const bg = decodeGraph(bare);