lightningd: expose funding PSBT (if we have it) in JSON API.

Changelog-Added: JSON-RPC: `psbt` field in `funding` in listpeerchannels, and `funding_psbt` in listclosedchannels.
Signed-off-by: Rusty Russell <[email protected]>

Author: rustyrussell

contrib/msggen/msggen/schema.json

@@ -18584,6 +18584,13 @@
                     "The 0-based output number of the funding transaction which opens the channel."
                   ]
                 },
+                "funding_psbt": {
+                  "type": "string",
+                  "added": "v25.12",
+                  "description": [
+                    "The PSBT (may be non-final or unsigned) we should use to open the channel, if any"
+                  ]
+                },
                 "leased": {
                   "type": "boolean",
                   "description": [
@@ -24327,6 +24334,13 @@
                       "description": [
                         "Amount we were paid by peer at open."
                       ]
+                    },
+                    "psbt": {
+                      "type": "string",
+                      "added": "v25.12",
+                      "description": [
+                        "The PSBT (may be non-final or unsigned) we should use to open the channel, if any.  This is initially from `fundchannel_complete`, but will be updated with if `sendpsbt` is called with an updated PSBT."
+                      ]
                     }
                   }
                 },

doc/schemas/listclosedchannels.json

@@ -188,6 +188,13 @@
                 "The 0-based output number of the funding transaction which opens the channel."
               ]
             },
+            "funding_psbt": {
+              "type": "string",
+              "added": "v25.12",
+              "description": [
+                "The PSBT (may be non-final or unsigned) we should use to open the channel, if any"
+              ]
+            },
             "leased": {
               "type": "boolean",
               "description": [

doc/schemas/listpeerchannels.json

@@ -502,6 +502,13 @@
                   "description": [
                     "Amount we were paid by peer at open."
                   ]
+                },
+                "psbt": {
+                  "type": "string",
+                  "added": "v25.12",
+                  "description": [
+                    "The PSBT (may be non-final or unsigned) we should use to open the channel, if any.  This is initially from `fundchannel_complete`, but will be updated with if `sendpsbt` is called with an updated PSBT."
+                  ]
                 }
               }
             },

lightningd/closed_channel.c

@@ -59,6 +59,8 @@ static void json_add_closed_channel(struct json_stream *response,
 	} else if (!amount_msat_is_zero(channel->push))
 		json_add_amount_msat(response, "funding_pushed_msat",
 				     channel->push);
+	if (channel->funding_psbt)
+		json_add_psbt(response, "funding_psbt", channel->funding_psbt);
 
 	json_add_amount_sat_msat(response, "total_msat", channel->funding_sats);
 	json_add_amount_msat(response, "final_to_us_msat", channel->our_msat);

lightningd/peer_control.c

@@ -1155,6 +1155,8 @@ static void NON_NULL_ARGS(1, 2, 4, 5) json_add_channel(struct command *cmd,
 				     channel->push);
 	}
 
+	if (channel->funding_psbt)
+		json_add_psbt(response, "psbt", channel->funding_psbt);
 	json_object_end(response);
 
 	if (!amount_sat_to_msat(&funding_msat, channel->funding_sats)) {

tests/test_plugin.py

@@ -3295,6 +3295,8 @@ def test_sql(node_factory, bitcoind):
                          'type': 'txid'},
                         {'name': 'funding_outnum',
                          'type': 'u32'},
+                        {'name': 'funding_psbt',
+                         'type': 'string'},
                         {'name': 'leased',
                          'type': 'boolean'},
                         {'name': 'funding_fee_paid_msat',
@@ -3606,6 +3608,8 @@ def test_sql(node_factory, bitcoind):
                          'type': 'msat'},
                         {'name': 'funding_fee_rcvd_msat',
                          'type': 'msat'},
+                        {'name': 'funding_psbt',
+                         'type': 'string'},
                         {'name': 'to_us_msat',
                          'type': 'msat'},
                         {'name': 'min_to_us_msat',