Give the build verb the command's other two shapes, so a changed base or a source that moved can be rebuilt through the console

The verb took only a repository; build --on <module> and build --behind were reachable only through the generic command verb. Each shape is one per call, and a second beside it is refused as passed over.

internal/catalogue/verbs.go

@@ -396,13 +396,22 @@ var ControllerVerbs = []Verb{
 			"machine": "one machine (optional)",
 			"retired": "\"true\": only what is retired",
 		}, nil, "retired")},
-	{Name: "build", Description: "Have the build machine build a repository. Answers at once with the build's id: " +
-		"`builds` with that id follows it line by line, and the module is registered when the outcome comes.",
+	// Three shapes, as the command has them: one repository, every module standing on a base (on), or
+	// every module behind its source (behind). One per call; a second is refused as passed over.
+	{Name: "build", Description: "Have the build machine build a repository — or, instead, every module that " +
+		"stands on a base (on), or every module behind its source (behind). Answers at once with each build's id: " +
+		"`builds` with an id follows it line by line, and a module is registered when its outcome comes.",
 		Input: schema(map[string]string{
-			"repository": "the repository's URL, or its path on the forge holding the git seat (owner/name)",
-			"path":       "the module's directory inside it (optional)",
-			"ref":        "the branch, tag or commit to build (optional)",
-		}, []string{"repository"})},
+			"repository": "the repository's URL, or its path on the forge holding the git seat (owner/name); " +
+				"needed unless on or behind is given",
+			"path": "with repository: the module's directory inside it (optional)",
+			"ref":  "with repository: the branch, tag or commit to build (optional)",
+			"on": "instead of a repository: a module's name. Every module the mesh holds that was built against " +
+				"its artifacts is built again from its own source, bases among them asked first — the rebuild a " +
+				"changed base needs, which behind does not see because their sources did not move",
+			"behind": "\"true\", instead of a repository: build every module the mesh holds whose source has moved " +
+				"past the commit it was built from, bases asked first",
+		}, nil, "behind")},
 }
 
 // schema is a JSON schema for an object of string properties, which is every argument the verbs