maven: embedder config validation + docs (task 1)

- Tests: all-three-set → ok; one-missing → error; nil → ok
- Log message on HashEmbedder fallback in voice.go
- Document floor mode in START.md

Co-Authored-By: opencode <opencode@anthropic.com>

START.md

@@ -58,6 +58,8 @@ Config path: `~/.config/maven/mavend.json`. Full example with all options:
 }
 ```
 
+Omit the `embedder` block entirely to use the deterministic HashEmbedder floor (no ML, no ONNX runtime dependency). Useful for testing or low-resource setups.
+
 ## mavsttd — STT worker (optional, remote whisper.cpp)
 
 Requires `LD_LIBRARY_PATH` to include deps/lib (for libwhisper.so, libggml-vulkan.so).

cmd/mavend/voice.go

@@ -156,6 +156,7 @@ func wireVoice(cfg *config.Config, coreAPI ipc.CoreAPI, phr phraser.Phraser) (*v
 		log.Printf("voice: onnx embedder loaded (%d dim)", onnx.Dim())
 		emb = onnx
 	} else {
+		log.Printf("voice: embedder not configured, using HashEmbedder floor")
 		emb = router.NewHashEmbedder(1024)
 	}
 	w.embedder = emb

internal/config/config_test.go

@@ -82,6 +82,49 @@ func TestVoiceEnabledWithBindOK(t *testing.T) {
 	}
 }
 
+func TestEmbedderAllPathsSetOK(t *testing.T) {
+	p := writeConfig(t, `{
+		"voice": {
+			"enabled": true, "bind": "127.0.0.1:9100",
+			"embedder": {
+				"model_path": "m.onnx",
+				"tokenizer_path": "t.json",
+				"lib_path": "l.so"
+			}
+		}
+	}`)
+	if _, err := Load(p); err != nil {
+		t.Fatalf("Load: %v", err)
+	}
+}
+
+func TestEmbedderPartialConfigRejected(t *testing.T) {
+	tests := []struct {
+		name string
+		json string
+	}{
+		{"missing model_path", `{"voice":{"enabled":true,"bind":"127.0.0.1:9100","embedder":{"tokenizer_path":"t.json","lib_path":"l.so"}}}`},
+		{"missing tokenizer_path", `{"voice":{"enabled":true,"bind":"127.0.0.1:9100","embedder":{"model_path":"m.onnx","lib_path":"l.so"}}}`},
+		{"missing lib_path", `{"voice":{"enabled":true,"bind":"127.0.0.1:9100","embedder":{"model_path":"m.onnx","tokenizer_path":"t.json"}}}`},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			p := writeConfig(t, tt.json)
+			if _, err := Load(p); err == nil {
+				t.Fatal("Load succeeded for partial embedder; want error")
+			}
+		})
+	}
+}
+
+func TestEmbedderNilOK(t *testing.T) {
+	// voice block without embedder → ok (HashEmbedder floor)
+	p := writeConfig(t, `{"voice":{"enabled":true,"bind":"127.0.0.1:9100"}}`)
+	if _, err := Load(p); err != nil {
+		t.Fatalf("Load: %v", err)
+	}
+}
+
 func TestVoicePresentDisabledOK(t *testing.T) {
 	// voice block present but not enabled — acceptable (the listener stays
 	// down; the routing table's ChannelVoice selections drop).