docs(plan): §4.1 —— 宿主工具二进制没做,而它没做正是 14.1 那条边要单独声明的原因

Author: speak-agent

.agents/docs/2026-09-07-module-first-heterogeneous-surface.md

@@ -290,6 +290,21 @@ What this buys, in order of value:
 - The same path serves CUDA cubins and fatbins, textures, fonts, model weights
   and ICD JSON. The tool stops being shader-specific.
 
+> **Superseded, and the difference is load-bearing for 14.1.** The host-tool
+> binary was not built. What shipped is `mcpp::plugins::surface` -- a generator
+> in the collection's lib root that every rule calls FROM `build.mcpp`, writing
+> the interface, the implementation and the `.S` at plan time. The four values
+> listed above were all obtained anyway: both shader flavours produce identical
+> output, storage and surface are orthogonal options, `mcpp.rules.slang` joined
+> at no cost, and nothing in the generator is shader-specific.
+>
+> What the library form does NOT give is the property this section was reaching
+> for: a tool the GRAPH invokes has its inputs in the graph. A generator that
+> runs at plan time writes a `.S` naming a payload that does not exist yet, and
+> the edge between them has to be stated separately -- which is exactly the gap
+> 14.1 reports and `mcpp::recompile_if_changed` closes. The library form remains
+> the right shape; the missing edge was the cost of it, and it was payable.
+
 ### 4.2 One tool with options, not three
 
 `bin2c`, `bin2cppm` and `bin2obj` as three names would force a consumer to