examples: pin mcpp:plugins 0.5.2

0.5.2 fixes a defect the cross-platform run of the generator's fixture found:
`namespace_of` trimmed a base directory off a file's directory as a string, and
on Windows a root stated with forward slashes against a directory iterator
appending with the preferred separator left `\image` rather than `image` -- so
the root directory became a namespace segment and an entry point landed in
`app::kernels::_::image`.

The shader lane shares that function and had the defect latent: its Windows
fixture keeps every payload in one directory, so a segment was never derived
there. `examples/09-heterogeneous/vulkan` and `examples/10-graphics/offscreen`
therefore take this pin for a reason of their own.

Verified against the published package: `boundary` resolves
`mcpp-x-plugins/0.5.2` from the index and prints `6 12 18 24`.

Author: speak-agent

.agents/docs/2026-09-08-island-boundary-names.md

@@ -413,6 +413,8 @@ negation.
 | a flatter fallback tree is accepted | fixture: `cuda/image/blur.cu` with `cpu/ops.cpp`; the namespace is `image` |
 | a backend-only entry point still has a place | fixture: a name only the second root declares; its namespace is that root's path |
 | the disagreement check still fires | the existing `island-interface` negative fixture, unchanged in behaviour |
+| overlapping roots are refused | negative fixture: `src` named beside `src/kernels`; the message names both roots |
+| the derivation runs on every host | the fixture builds and its namespaces are asserted on macOS and Windows, not only Linux |
 | the output is a function of the tree, not of the walk | the same tree scanned twice produces byte-identical files, and a no-op rebuild touches neither |
 | an empty root set is an error | a fixture whose roots hold sources but no marker; the build fails naming the root |
 | two files in ONE root, one name | refused, and the message says the two belong in two roots |
@@ -421,17 +423,33 @@ negation.
 ## 12. What shipped
 
 `mcpp:plugins` **0.5.0** (2026-09-08) carries §2 through §8 and §6.1. **0.5.1**
-carries the refusal of overlapping roots that §6 states and 0.5.0 omitted --
-the shape of defect §10 of the plan warns about, where a requirement folded
-into a larger change disappears when that change ships. It also stops a
+carries the refusal of overlapping roots that §6 states and 0.5.0 omitted. That
+is the shape of defect where a requirement folded into a larger change
+disappears when that change ships: §6 stated it in prose and §11 gave it no
+criterion of its own, so nothing was red when it was absent. It has one now. It also stops a
 single-file root from registering a re-run glob over the directory that file
 happens to sit in.
 
-Both are indexed, and `mcpp` pins 0.5.1 across the example tree. The published
-0.5.1 was verified in an xlings sandbox against the index rather than a working
-tree: a project written inside the sandbox resolved
-`registry/data/xpkgs/mcpp-x-plugins/0.5.1`, printed `6 12 18 24`, and its
-generated module carried `export namespace sandbox::kernels` and
+**0.5.2** carries a defect the cross-platform run found. `mcpp.tools.island`
+compiled on all three hosts and had been exercised on one; the first Windows
+run of the fixture failed to compile with `no member named 'image' in namespace
+'island_interface::kernels'`. `namespace_of` trimmed the base directory off a
+file's directory as a STRING, and a root stated with forward slashes against a
+directory iterator appending with the preferred separator left `\image` rather
+than `image` -- so the root directory became a segment, sanitised to `_`. It
+compares components now.
+
+The shader lane shares that function and had the defect latent: its Windows
+fixture keeps every payload in one directory, so a segment was never derived
+there. The leg that surfaced it is not the lane it lives on, and a step now
+asserts the derivation exists once so the island fixture's cross-platform run
+keeps protecting both.
+
+All three are indexed, and `mcpp` pins 0.5.2 across the example tree. The
+published package was verified in an xlings sandbox against the index rather
+than a working tree: a project written inside the sandbox resolved
+`registry/data/xpkgs/mcpp-x-plugins`, printed `6 12 18 24`, and its generated
+module carried `export namespace sandbox::kernels` and
 `export namespace sandbox::kernels::vec`.
 
 ## 13. Decided in review

docs/42-heterogeneous-builds.md

@@ -287,6 +287,8 @@ exported whatever a file contained would make the boundary an accident of that
 file's contents.
 
 ```cpp
+const std::string root = std::string(mcpp::manifest_dir());
+
 mcpp::tools::island::options opt;
 opt.module_name  = "app.kernels";
 opt.out_dir      = std::string(mcpp::out_dir()) + "/island";
@@ -322,6 +324,12 @@ point implemented several times, and the declarations must then agree verbatim.
 The second is the check nothing else in the toolchain can perform; the first is
 what makes the namespace honest.
 
+Two configuration errors are refused beside them: roots that overlap, because a
+file reachable from both has two namespace paths and which one it got would
+depend on the order of the list; and roots that hold no marked entry point at
+all, because an empty module fails later and less clearly than a misspelled
+path does here.
+
 **`strip_prefix` is a spelling, not a second entity.** An island's symbol is
 global to the whole program, so an entry point carries a package prefix whether
 or not it sits in a namespace, and the namespace then repeats it. The option

docs/zh/42-heterogeneous-builds.md

@@ -237,6 +237,8 @@ int app_saxpy(float a, const float* x, const float* y, float* out, unsigned n)
 变成那个文件恰好包含了什么的意外结果。
 
 ```cpp
+const std::string root = std::string(mcpp::manifest_dir());
+
 mcpp::tools::island::options opt;
 opt.module_name  = "app.kernels";
 opt.out_dir      = std::string(mcpp::out_dir()) + "/island";
@@ -265,6 +267,10 @@ layout root 的目录才延长命名空间;其余的根只需要定义同样的
 声明必须逐字一致。后者是工具链里没有别的东西能做的检查;前者是让命名空间不说谎的
 那一条。
 
+此外还有两种配置错误被拒绝:互相重叠的根 —— 同时可以从两个根到达的文件有两条命名
+空间路径,而它拿到哪一条取决于这个列表的顺序;以及根里一个被标记的入口点都没有 ——
+一个什么都不导出的模块,比一个写错的路径在这里被指出来要晚得多、也难懂得多。
+
 **`strip_prefix` 是一种拼法,不是第二个实体。** 岛的符号对整个程序是全局的,所以
 入口点无论是否落在命名空间里都带着包前缀,而命名空间随后又把它重复一遍。这个选项在
 `using ::app_blur;` 旁边写出 `inline constexpr auto blur = app_blur;`。作者写下的

examples/09-heterogeneous/README.md

@@ -104,7 +104,7 @@ selects it and the accelerator it serves, so a project writes one edge and no
 
 ```toml
 [build-dependencies.mcpp]
-plugins = { version = "0.5.1", features = ["rules-cuda", "tools-island"], host-module = true }
+plugins = { version = "0.5.2", features = ["rules-cuda", "tools-island"], host-module = true }
 ```
 
 `multi-backend/` is the one example here that also pins a version, and it does

examples/09-heterogeneous/boundary/mcpp.toml

@@ -8,7 +8,7 @@ standard = "c++23"
 # `tools-island` is not a device rule: it claims no extension and names no rule
 # module, so the edge states `host-module = true` itself.
 [build-dependencies.mcpp]
-plugins = { version = "0.5.1", features = ["tools-island"], host-module = true }
+plugins = { version = "0.5.2", features = ["tools-island"], host-module = true }
 
 [build]
 sources = ["src/*.cpp", "src/kernels/**/*.c"]

examples/09-heterogeneous/cann/app/mcpp.toml

@@ -14,7 +14,7 @@ import_std = true
 # imports it as `mcpp.rules.ascendc`. `[build-dependencies]`, because a rule
 # package's library must never reach the target while its rule is wanted.
 [build-dependencies.mcpp]
-plugins = { version = "0.5.1", features = ["rules-ascendc"], host-module = true }
+plugins = { version = "0.5.2", features = ["rules-ascendc"], host-module = true }
 
 # NO [xlings.workspace]. `mcpp.rules.ascendc` declares `xim:cann-toolkit`
 # itself, gated on this accelerator and on the feature that selects the rule --

examples/09-heterogeneous/cuda/README.md

@@ -98,7 +98,7 @@ The rule names it. This project writes one edge and no payload list at all:
 
 ```toml
 [build-dependencies.mcpp]
-plugins = { version = "0.5.1", features = ["rules-cuda", "tools-island"], host-module = true }
+plugins = { version = "0.5.2", features = ["rules-cuda", "tools-island"], host-module = true }
 ```
 
 `mcpp.rules.cuda` declares nvcc, cudart, cuRAND's headers, CCCL and the driver

examples/09-heterogeneous/cuda/app/mcpp.toml

@@ -23,7 +23,7 @@ default = "llvm@22.1.8"
 # `extern "C"` boundary the island's compiler reads and the module the seam
 # imports, so neither signature is stated twice.
 [build-dependencies.mcpp]
-plugins = { version = "0.5.1", features = ["rules-cuda", "tools-island"], host-module = true }
+plugins = { version = "0.5.2", features = ["rules-cuda", "tools-island"], host-module = true }
 
 # The driver's userspace library, reached through an index package that owns
 # the one hop mcpp needs: a directory on the artifact's runtime search path.

examples/09-heterogeneous/hip/app/mcpp.toml

@@ -20,7 +20,7 @@ import_std = true
 default = "llvm@22.1.8"
 
 [build-dependencies.mcpp]
-plugins = { version = "0.5.1", features = ["rules-hip"], host-module = true }
+plugins = { version = "0.5.2", features = ["rules-hip"], host-module = true }
 
 # The driver's userspace library. HIP reaches the device through the CUDA
 # runtime here, so this is the same one hop the CUDA consumer needs: mcpp's

examples/09-heterogeneous/multi-backend/README.md

@@ -93,7 +93,7 @@ saying it after the vocabulary grows.
 
 ```toml
 [build-dependencies.mcpp]
-plugins = { version = "0.5.1", features = ["rules-cuda", "rules-spirv"], host-module = true }
+plugins = { version = "0.5.2", features = ["rules-cuda", "rules-spirv"], host-module = true }
 ```
 
 Two rules, in one build program, which is what an additive-backend package