Add fetchMapCells to api.js for TESSERA map endpoint

src/api.js

@@ -1,8 +1,10 @@
-// Thin client for the OTIVM save API
+// Thin client for the OTIVM save and map APIs
 // Backend: GET /api/save/:token  — load state
 //          POST /api/save/:token — write state
+//          GET /api/map/:h5/:epoch — H7 land/sea cells for one waypoint at one epoch
 
-const BASE = '/api/save'
+const BASE_SAVE = '/api/save'
+const BASE_MAP  = '/api/map'
 
 // Generate a random 8-character hex token
 export function generateToken() {
@@ -14,7 +16,7 @@ export function generateToken() {
 // Load state from server — returns parsed state object or null
 export async function loadState(token) {
   try {
-    const res = await fetch(`${BASE}/${token}`)
+    const res = await fetch(`${BASE_SAVE}/${token}`)
     if (!res.ok) return null
     return await res.json()
   } catch {
@@ -25,7 +27,7 @@ export async function loadState(token) {
 // Save state to server — returns true on success
 export async function saveState(token, state) {
   try {
-    const res = await fetch(`${BASE}/${token}`, {
+    const res = await fetch(`${BASE_SAVE}/${token}`, {
       method: 'POST',
       headers: { 'Content-Type': 'application/json' },
       body: JSON.stringify(state),
@@ -35,3 +37,18 @@ export async function saveState(token, state) {
     return false
   }
 }
+
+// Fetch H7 land/sea classification for one H5 waypoint at one named epoch.
+// h5: H3 res-5 hex string (e.g. '851e805bfffffff')
+// epochKey: named epoch from paleo_epochs (e.g. 'roman_14bce')
+// Returns: { epoch_key, sl_offset_cm, h5, cells: [{ h7, h7_land, h9_total, is_land }] }
+// Returns null on any error.
+export async function fetchMapCells(h5, epochKey) {
+  try {
+    const res = await fetch(`${BASE_MAP}/${h5}/${epochKey}`)
+    if (!res.ok) return null
+    return await res.json()
+  } catch {
+    return null
+  }
+}