Workspace build graph: members' dependencies announced, the module-name limit documented

Author: speak-agent

.agents/docs/2026-09-29-workspace-build-graph-design.md

@@ -517,6 +517,7 @@ left open, the answer is recorded here.
 | The lock | `<workspace>/mcpp.lock`. A plan of all members writes the whole record; a plan of some keeps the other entries, and `--locked` then reports no entry of another member as drift. A selected member's git dependencies are locked as a root's. | prepare/records.cpp |
 | Tests | `mcpp test` keeps one plan per member (`-p X` each), in the shared directory; the members' dev-dependencies are their own. | cmd_build.cppm |
 | Concurrency | Groups are planned in turn and built on threads with a static share of the jobs; the `.build_cache` write is one locked step. | cmd_build.cppm |
+| Module names across members | A graph has one module namespace (BMIs are found by name), so two members that each provide a module of one name are refused in one `--workspace` plan, as two `artifacts` programs are (#732, which tracks per-provider BMI names). Measured over the package index's 172 members: no module name is provided twice. | scanner |
 
 Readings with the implementation (Linux, llvm 22.1.8):
 

docs/07-workspace.md

@@ -438,6 +438,9 @@ member that several members use is compiled once.
   member order.
 - **No-op builds.** A command repeated with nothing changed is answered by one
   check per configuration, without planning.
+- **Module names.** Members built in one graph share one module namespace:
+  two members that each provide a module of the same name cannot be built in
+  one `--workspace` command; build each with `-p`.
 
 ## 6. Directory Layout
 

docs/zh/07-workspace.md

@@ -405,6 +405,8 @@ mcpp test --workspace --workspace-timeout 1800   # whole fan-out (default 0 = no
   命令被拒绝。
 - **Hooks。** 每个被选成员的 `[hooks]` 按成员顺序在构建前后运行。
 - **无事可做的构建。** 在没有任何改动时重复执行的命令，每个配置只做一次检查，不重新规划。
+- **模块名。** 在同一张图中构建的成员共享一个模块命名空间：两个成员各自提供同名模块时，不能在
+  同一条 `--workspace` 命令中构建；分别用 `-p` 构建。
 
 ## 6. 目录布局
 

src/build/execute.cppm

@@ -941,7 +941,22 @@ export int run_build_plan(BuildContext& ctx, bool verbose, bool no_cache,
         mcpp::ui::status("Compiling",
             std::format("{} v{} (.)",
                         ctx.manifest.package.name, ctx.manifest.package.version));
-    for (auto& [name, spec] : ctx.manifest.dependencies) {
+    // The packages announced: the root's dependencies, and in a workspace
+    // plan each member followed by the member's own dependencies (§15), as
+    // the member's own build announced them.
+    std::vector<std::pair<std::string, mcpp::manifest::DependencySpec>> announcedDeps;
+    for (auto const& [name, spec] : ctx.manifest.dependencies) {
+        announcedDeps.emplace_back(name, spec);
+        if (!spec.workspaceMember) continue;
+        for (auto const& m : ctx.workspaceMembers) {
+            std::error_code e1, e2;
+            if (std::filesystem::weakly_canonical(spec.path, e1)
+                != std::filesystem::weakly_canonical(m.root, e2))
+                continue;
+            for (auto const& [dn, ds] : m.manifest.dependencies) announcedDeps.emplace_back(dn, ds);
+        }
+    }
+    for (auto& [name, spec] : announcedDeps) {
         if (announced.contains(name)) continue;
         announced.insert(name);
         // Two keys that resolved to one identity (#634, A2) are one package