fix(runner): a package's program may sit at the payload root, and two already do

D4's LEG WAS RED AND THE PACKAGE WAS INSTALLED CORRECTLY. Measured on a
macos-15 runner with `xim:apple-simulator-tools` declared and present:

  error: runner 'simctl-run' for 'aarch64-ios-sim' was not found on any
         search path.
  Searched: .../xim-x-apple-simulator-tools/0.1.0/bin

The directory searched was right and the program was one level up. `bin/` is
the convention and stays FIRST; it is not universal -- `xim:7zip` puts `7zz`
straight into its install directory, and so did the first version of
`xim:apple-simulator-tools`. Two directories per declared package is cheaper
than a rule every recipe has to know, and a recipe that does use `bin/` is
unaffected because that entry is still tried first.

The recipe moves too (openxlings/xim-pkgindex#820, merged): a package whose
whole purpose is to provide a program puts it where consumers look, and its
`xvm` registration moves with it -- a recipe that wrote into `bin/` and
registered the root would install without complaint and produce a shim
resolving to nothing.

And the fixture uses `[xlings.workspace]`, which is what mcpp asks for:
"deps is superseded by [xlings.workspace] and will stop being read".

WHAT THE macOS RUN MEASURED FOR ALL THREE ROWS, `ios_deployment_target
= "18.0"`, Xcode 16.4, SDKs 18.5:

  aarch64-ios      arm64  LC_BUILD_VERSION platform 2 (IOS)          minos 18.0
  aarch64-ios-sim  arm64  LC_BUILD_VERSION platform 7 (IOSSIMULATOR) minos 18.0
  x86_64-ios-sim   x86_64 LC_BUILD_VERSION platform 7 (IOSSIMULATOR) minos 18.0

`platform 2` against `platform 7` is the pair worth having a reading for: a
successful build cannot tell them apart, and an artefact reporting
IOSSIMULATOR from the device row is one no later step refuses. The simulator
artefact ran under `simctl spawn` and printed `1-2-3`.

Author: speak-agent

.github/workflows/ci-macos-ios.yml

@@ -276,13 +276,17 @@ jobs:
           #
           # THE TOOL IS DECLARED AT THE TOP LEVEL HERE AND NOT IN
           # examples/13, and the difference is which hosts the manifest has to
-          # work on. `deps` is not conditional on a target -- measured:
-          # "[target.aarch64-ios-sim.xlings] does not accept 'deps'" -- and
-          # `xim:apple-simulator-tools` exists for macosx alone, so an
+          # work on. A tool declaration is not conditional on a target --
+          # measured: "[target.aarch64-ios-sim.xlings] does not accept 'deps'"
+          # -- and `xim:apple-simulator-tools` exists for macosx alone, so an
           # unconditional declaration breaks a Linux build. This fixture is
           # macOS-only, so it can say it.
-          [xlings]
-          deps = ["xim:apple-simulator-tools"]
+          #
+          # `[xlings.workspace]` and not `[xlings] deps`, which mcpp reports as
+          # superseded: "deps is superseded by [xlings.workspace] and will stop
+          # being read. It is honoured for now."
+          [xlings.workspace]
+          "xim:apple-simulator-tools" = ""
           TOML
           cat >> /tmp/iostest/mcpp.toml << 'TOML'
 

src/build/prepare.cppm

@@ -10426,8 +10426,29 @@ prepare_build(bool print_fingerprint,
                 auto xlEnv = mcpp::config::make_xlings_env(**cfg);
                 for (auto const& spec : xlingsSpecs) {
                     auto ref = mcpp::xlings::paths::parse_xpkg_ref(spec);
-                    if (auto dir = mcpp::xlings::paths::xpkg_payload(xlEnv, ref))
+                    if (auto dir = mcpp::xlings::paths::xpkg_payload(xlEnv, ref)) {
                         ctx.xlingsDepBinDirs.push_back(*dir / "bin");
+                        // AND THE PAYLOAD ROOT, BECAUSE A FLAT LAYOUT IS A
+                        // LAYOUT THIS INDEX ALREADY SHIPS.
+                        //
+                        // `bin/` is the convention and stays first. It is not
+                        // universal: `xim:7zip` puts `7zz` straight into its
+                        // install directory, and so did the first version of
+                        // `xim:apple-simulator-tools` -- which is how this was
+                        // measured, on a macOS runner with the package
+                        // correctly installed:
+                        //
+                        //   error: runner 'simctl-run' for 'aarch64-ios-sim'
+                        //          was not found on any search path.
+                        //   Searched: .../xim-x-apple-simulator-tools/0.1.0/bin
+                        //
+                        // The directory searched was right and the program was
+                        // one level up. Two directories per package is cheaper
+                        // than a rule every recipe has to know, and a recipe
+                        // that does use `bin/` is unaffected because that entry
+                        // is still tried first.
+                        ctx.xlingsDepBinDirs.push_back(*dir);
+                    }
                 }
             }
         }