askrene: deprecate `auto.no_mpp_support` layer in favor of `maxparts=1`.

diff --git a/contrib/msggen/msggen/schema.json b/contrib/msggen/msggen/schema.json
index f424c408..acd1792c 100644
--- a/contrib/msggen/msggen/schema.json
+++ b/contrib/msggen/msggen/schema.json
@@ -16577,7 +16577,7 @@
         "",
         "Layers are generally maintained by plugins, either to contain persistent information about capacities which have been discovered, or to contain transient information for this particular payment (such as blinded paths or routehints).",
         "",
-        "There are four automatic layers: *auto.localchans* contains information on local channels from this node (including non-public ones), and their exact current spendable capacities. *auto.sourcefree* overrides all channels (including those from previous layers) leading out of the *source* to be zero fee and zero delay.  These are both useful in the case where the source is the current node.  *auto.no_mpp_support* forces getroutes to return a single path solution which is useful for payments for which MPP is not supported. And *auto.include_fees* that fixes the send amount and deducts fee from there, ie. the receiver pays for fees instead of the sender."
+        "There are some automatic layers: *auto.localchans* contains information on local channels from this node (including non-public ones), and their exact current spendable capacities. *auto.sourcefree* overrides all channels (including those from previous layers) leading out of the *source* to be zero fee and zero delay.  These are both useful in the case where the source is the current node.  *auto.include_fees* that fixes the send amount and deducts fee from there, ie. the receiver pays for fees instead of the sender.  *auto.no_mpp_support* is deprecated in v26.06: use `maxparts=1` instead."
       ],
       "categories": [
         "readonly"
diff --git a/doc/developers-guide/deprecated-features.md b/doc/developers-guide/deprecated-features.md
index acbb3184..f66f8dfb 100644
--- a/doc/developers-guide/deprecated-features.md
+++ b/doc/developers-guide/deprecated-features.md
@@ -23,6 +23,8 @@ privacy:
 | channel_state_changed.null_message                 | Notification Field | v25.12           | v26.12         | In channel_state_changed notification, `message` will be missing instead of `null`                                        |
 | hsmtool.getcodexsecret                             | Command            | v25.12.1         | v26.12         | Doesn't work on nodes using mnemonic secrets (v25.12 or later).  Use `getsecret` instead.                                 |
 | experimental_splicing                              | Config             | v26.04           | v27.04         | Splicing is now enabled by default                                                                                       |
+| getroutes.layers.auto.no_mpp_support               | Parameter          | v26.06           | v27.03         | Use `maxparts=1` instead (since v25.09)                                                                                   |
+
 Inevitably there are features which need to change: either to be generalized, or removed when they can no longer be supported.
 
 Types of deprecation:
diff --git a/doc/schemas/getroutes.json b/doc/schemas/getroutes.json
index 7860aeb0..8ba2a7fa 100644
--- a/doc/schemas/getroutes.json
+++ b/doc/schemas/getroutes.json
@@ -11,7 +11,7 @@
     "",
     "Layers are generally maintained by plugins, either to contain persistent information about capacities which have been discovered, or to contain transient information for this particular payment (such as blinded paths or routehints).",
     "",
-    "There are four automatic layers: *auto.localchans* contains information on local channels from this node (including non-public ones), and their exact current spendable capacities. *auto.sourcefree* overrides all channels (including those from previous layers) leading out of the *source* to be zero fee and zero delay.  These are both useful in the case where the source is the current node.  *auto.no_mpp_support* forces getroutes to return a single path solution which is useful for payments for which MPP is not supported. And *auto.include_fees* that fixes the send amount and deducts fee from there, ie. the receiver pays for fees instead of the sender."
+    "There are some automatic layers: *auto.localchans* contains information on local channels from this node (including non-public ones), and their exact current spendable capacities. *auto.sourcefree* overrides all channels (including those from previous layers) leading out of the *source* to be zero fee and zero delay.  These are both useful in the case where the source is the current node.  *auto.include_fees* that fixes the send amount and deducts fee from there, ie. the receiver pays for fees instead of the sender.  *auto.no_mpp_support* is deprecated in v26.06: use `maxparts=1` instead."
   ],
   "categories": [
     "readonly"
diff --git a/plugins/askrene/askrene.c b/plugins/askrene/askrene.c
index f31043fb..b51ecb79 100644
--- a/plugins/askrene/askrene.c
+++ b/plugins/askrene/askrene.c
@@ -114,10 +114,15 @@ static struct command_result *param_layer_names(struct command *cmd,
 
 		/* Must be a known layer name */
 		if (streq((*arr)[i], "auto.localchans")
-		    || streq((*arr)[i], "auto.no_mpp_support")
 		    || streq((*arr)[i], "auto.sourcefree")
 		    || streq((*arr)[i], "auto.include_fees"))
 			continue;
+
+		if (streq((*arr)[i], "auto.no_mpp_support")
+		    && command_deprecated_in_ok(cmd, "layers.auto.no_mpp_support",
+						"v26.06", "v27.03"))
+			continue;
+
 		if (!find_layer(get_askrene(cmd->plugin), (*arr)[i])) {
 			return command_fail_badparam(cmd, name, buffer, t,
 						     "unknown layer");
@@ -264,7 +269,8 @@ static struct layer *remove_small_channel_layer(const tal_t *ctx,
 						struct amount_msat min_amount,
 						struct gossmap_localmods *localmods)
 {
-	struct layer *layer = new_temp_layer(ctx, askrene, "auto.no_mpp_support");
+	/* We use the prefix auto. to avoid clashing */
+	struct layer *layer = new_temp_layer(ctx, askrene, "auto.remove_small_channels");
 	struct gossmap *gossmap = askrene->gossmap;
 	struct gossmap_chan *c;
 
@@ -389,8 +395,7 @@ static const struct layer **apply_layers(const tal_t *ctx,
 				cmd_log(tmpctx, cmd, LOG_DBG, "Adding auto.localchans");
 				l = local_layer;
 			} else if (streq(layernames[i], "auto.no_mpp_support")) {
-				cmd_log(tmpctx, cmd, LOG_DBG, "Adding auto.no_mpp_support, sorry");
-				/* We will add a layer later, in the caller. */
+				/* deprecated */
 				continue;
 			} else if (streq(layernames[i], "auto.include_fees")) {
 				cmd_log(tmpctx, cmd, LOG_DBG, "Adding auto.include_fees");
@@ -405,6 +410,7 @@ static const struct layer **apply_layers(const tal_t *ctx,
 		}
 		add_layer(&layers, l, askrene->gossmap, localmods, capacities);
 	}
+
 	return layers;
 }
 
@@ -584,6 +590,12 @@ static struct command_result *do_getroutes(struct command *cmd,
 		}
 	}
 
+	/* auto.no_mpp_support layer forces maxparts == 1. */
+	if (have_layer(info->layers, "auto.no_mpp_support")) {
+		cmd_log(tmpctx, cmd, LOG_DBG, "Adding auto.no_mpp_support, sorry");
+		info->maxparts = 1;
+	}
+
 	/* apply selected layers to the localmods */
 	layers = apply_layers(cmd, askrene, cmd,
 			      &info->source, localmods,
@@ -591,7 +603,7 @@ static struct command_result *do_getroutes(struct command *cmd,
 
 
 	/* no parallel payments means we can drop any smaller channels */
-	if (have_layer(info->layers, "auto.no_mpp_support") || info->maxparts == 1) {
+	if (info->maxparts == 1) {
 		add_layer(&layers,
 			  remove_small_channel_layer(layers, askrene, info->amount, localmods),
 			  askrene->gossmap,
@@ -634,14 +646,6 @@ static struct command_result *do_getroutes(struct command *cmd,
 		goto fail;
 	}
 
-	/* auto.no_mpp_support layer overrides any choice of algorithm. */
-	if (have_layer(info->layers, "auto.no_mpp_support") &&
-	    info->dev_algo != ALGO_SINGLE_PATH) {
-		info->dev_algo = ALGO_SINGLE_PATH;
-		cmd_log(tmpctx, cmd, LOG_DBG,
-		       "Layer no_mpp_support is active we switch to a "
-		       "single path algorithm.");
-	}
 	if (info->maxparts == 1 &&
 	    info->dev_algo != ALGO_SINGLE_PATH) {
 		info->dev_algo = ALGO_SINGLE_PATH;