docs: the toolchain builders listed are the ones the module has

The page named `compose`, which does not exist, and left out `newest_under`,
`managed` and `with_family`. Every name on that line and in the tool section was
then checked against the sources.

Author: speak-agent

docs/plugin-development.md

@@ -101,9 +101,9 @@ build reports.
 **Stating the build toolchain.** `mcpp.plugins.toolchain` (feature
 `plugins-toolchain`) builds the statement a root build program makes in its
 toolchain phase, for a project whose `[toolchain]` says
-`configure = "build.mcpp"`: `layout`, `prefixed`, `compose`,
-`from_env_script`, `with_launcher`, `with_sysroot`, `with_tool`, `managed`,
-`env`, and `configure(fn)` / `use(d)`.
+`configure = "build.mcpp"`: `layout`, `prefixed`, `managed`, `from_env_script`,
+`newest_under`, `env`, the `with_launcher` / `with_sysroot` / `with_family` /
+`with_tool` refinements, and `configure(fn)` / `use(d)`.
 
 **Testing a plugin.** `mcpp.plugins.testing` runs a plugin function in a child
 process against a stated build context (`row::windows_visual_studio()`,

src/toolchain.cppm

@@ -29,7 +29,8 @@
 // and the engine reads both in one place, so a toolchain stated here and one
 // named in the manifest behave alike. What this module adds are the builders
 // a manifest cannot express: a value read from the environment, a tree found
-// by looking, a vendor SDK's environment script, a toolchain composed of parts.
+// by looking, a vendor SDK's environment script, and a tree refined part by part
+// (a launcher, a sysroot, a tool named by role).
 
 export module mcpp.plugins.toolchain;