msggen: add source argument for currencyrate

Changelog-None

Author: daywalker90

.msggen.json

@@ -1323,7 +1323,8 @@
             "CurrencyConvert.msat": 1
         },
         "CurrencyrateRequest": {
-            "CurrencyRate.currency": 1
+            "CurrencyRate.currency": 1,
+            "CurrencyRate.source": 2
         },
         "CurrencyrateResponse": {
             "CurrencyRate.rate": 1
@@ -6085,6 +6086,10 @@
             "added": "v26.04",
             "deprecated": null
         },
+        "CurrencyRate.source": {
+            "added": "v26.06",
+            "deprecated": null
+        },
         "Datastore": {
             "added": "pre-v0.10.1",
             "deprecated": null

cln-grpc/proto/node.proto

@@ -7433,11 +7433,24 @@
       "$schema": "../rpc-schema-draft.json",
       "type": "object",
       "rpc": "currencyrate",
-      "title": "Command to determine a reasonable rate of conversion for a given currency",
+      "title": "Command to determine a reasonable BTC exchange rate for a given currency",
       "added": "v26.04",
       "description": [
-        "The **currencyrate** RPC command provides the conversion of one BTC into the given currency",
-        "It uses the median of the available exchange-rate sources for the requested currency."
+        "The **currencyrate** RPC command returns the exchange rate of one BTC in the given currency.",
+        "Rates are rounded to 3 decimal places as specified by ISO 4217.",
+        "",
+        "Without the optional *source* argument the command returns the median rate across all",
+        "configured exchange-rate sources.",
+        "",
+        "With *source* specified, the rate reported by that specific source is returned.",
+        "The list of active source names can be obtained via **listcurrencyrates**.",
+        "",
+        "To add or disable sources see the *currencyrate-add-source* and *currencyrate-disable-source*",
+        "options in **lightningd-config(5)**.",
+        "",
+        "EXAMPLE USAGE:",
+        "Get the median USD rate: `lightning-cli currencyrate USD`",
+        "Get the Binance USD rate: `lightning-cli currencyrate USD binance`"
       ],
       "request": {
         "required": [
@@ -7448,8 +7461,18 @@
           "currency": {
             "type": "string",
             "description": [
-              "The ISO-4217 currency code (e.g. USD) to convert to.",
-              "The plugin normalizes this value to uppercase before querying sources."
+              "The ISO 4217 currency code (e.g. USD) to convert to.",
+              "The plugin normalises this value to uppercase before querying sources."
+            ]
+          },
+          "source": {
+            "added": "v26.06",
+            "type": "string",
+            "description": [
+              "The name of a specific exchange-rate source to query.",
+              "If omitted, the median across all available sources is returned.",
+              "An error is returned if the source name is not recognised or has no",
+              "cached data for the requested currency."
             ]
           }
         }
@@ -7463,7 +7486,9 @@
           "rate": {
             "type": "number",
             "description": [
-              "The median value of one BTC, computed using the median result from the available sources."
+              "The number of currency units per 1 BTC, rounded to 3 decimal places (ISO 4217).",
+              "When *source* is omitted this is the median across all available sources.",
+              "When *source* is specified this is the rate reported by that source."
             ]
           }
         }
@@ -7472,10 +7497,45 @@
         "daywalker90 is mainly responsible."
       ],
       "see_also": [
-        "lightning-listcurrencyrates(7)"
+        "lightning-listcurrencyrates(7)",
+        "lightning-currencyconvert(7)",
+        "lightningd-config(5)"
       ],
       "resources": [
         "Main web site: [https://github.com/ElementsProject/lightning](https://github.com/ElementsProject/lightning)"
+      ],
+      "examples": [
+        {
+          "description": [
+            "Get the median BTC/USD rate across all configured sources:"
+          ],
+          "request": {
+            "id": "example:currencyrate#1",
+            "method": "currencyrate",
+            "params": {
+              "currency": "USD"
+            }
+          },
+          "response": {
+            "rate": 67889.825
+          }
+        },
+        {
+          "description": [
+            "Get the BTC/USD rate from the Binance source only:"
+          ],
+          "request": {
+            "id": "example:currencyrate#2",
+            "method": "currencyrate",
+            "params": {
+              "currency": "USD",
+              "source": "binance"
+            }
+          },
+          "response": {
+            "rate": 67931.9
+          }
+        }
       ]
     },
     "datastore.json": {