fix: align BuiltModuleSubdirectory property default in WorkspaceDependencies task

.build/tasks/WorkspaceDependencies.build.ps1

@@ -22,7 +22,15 @@
         `$BuildRoot`.
 
     .PARAMETER BuiltModuleSubdirectory
-        The parent path of the module to be built. Defaults to `module`.
+        The parent path of the module to be built, relative to `$OutputDirectory`.
+        Defaults to an empty string, which resolves the link root to the output
+        root - the same location `build.ps1` builds to and pre-pends to
+        `PSModulePath` when `BuiltModuleSubdirectory` is not set in `build.yaml`.
+        The default must stay empty because InvokeBuild dot-sources every task
+        file into the same scope and a non-empty default here would overwrite the
+        shared value for all other tasks. `Get-SamplerWorkspaceLinkedModuleRoot`
+        keeps `module` as its own parameter default for when the argument is
+        omitted entirely.
 
     .PARAMETER WorkspaceModules
         The sibling workspace modules to link into the local output module path.
@@ -41,7 +49,7 @@ param
 
     [Parameter()]
     [System.String]
-    $BuiltModuleSubdirectory = (property BuiltModuleSubdirectory 'module'),
+    $BuiltModuleSubdirectory = (property BuiltModuleSubdirectory ''),
 
     [Parameter()]
     [System.String[]]

CHANGELOG.md

@@ -7,6 +7,22 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- The `WorkspaceDependencies` build task declared its `BuiltModuleSubdirectory`
+  parameter default as `(property BuiltModuleSubdirectory 'module')` while every
+  other task file uses `''`. InvokeBuild dot-sources all imported task files into
+  the same scope and the `property` helper treats an empty string as unset, so
+  this non-empty default (dot-sourced last) overwrote the shared
+  `$BuiltModuleSubdirectory` value for every task in the build. Projects that do
+  not set `BuiltModuleSubdirectory` in `build.yaml` build to the output root, but
+  the tasks then looked for the built module under `output\module`, failing with
+  `Could not find the built module manifest for module '<Name>'. Build the module
+  before running tasks that require the built module output.` from
+  `Set-SamplerTaskVariable`. The default is now `''`, which also makes
+  `Link_Local_Workspace_Dependencies` link sibling modules into the location that
+  is actually on `PSModulePath` for the consuming project. Fixes #593.
+
 ## [0.120.0] - 2026-07-14
 
 ### Added

GitVersion.yml

@@ -1,5 +1,5 @@
 mode: ContinuousDelivery
-next-version: 0.90
+next-version: 0.90.0
 major-version-bump-message: '\s?(breaking|major|breaking\schange)'
 minor-version-bump-message: '(adds?|features?|minor)\b'
 patch-version-bump-message: '\s?(fix|patch)'

tests/QA/module.tests.ps1

@@ -110,6 +110,52 @@ Describe 'General module control' -Tags 'FunctionalQuality' {
     }
 }
 
+Describe 'Build task shared property defaults' -Tags 'FunctionalQuality' {
+    <#
+        InvokeBuild dot-sources every imported task file into the same scope, and
+        the 'property' helper treats an empty string as unset. A task file that
+        declares a non-empty default for a shared property therefore overwrites
+        the value used by every other task in the build.
+    #>
+    It 'Should use the same BuiltModuleSubdirectory property default in every build task file' {
+        $taskFilePath = Join-Path -Path $projectPath -ChildPath (Join-Path -Path '.build' -ChildPath 'tasks')
+
+        $astSearchDelegate = { $args[0] -is [System.Management.Automation.Language.CommandAst] }
+
+        $propertyDefault = @()
+
+        foreach ($taskFile in (Get-ChildItem -Path $taskFilePath -Filter '*.build.ps1'))
+        {
+            $abstractSyntaxTree = [System.Management.Automation.Language.Parser]::ParseFile($taskFile.FullName, [ref] $null, [ref] $null)
+
+            $parameterAst = @(
+                $abstractSyntaxTree.ParamBlock.Parameters |
+                    Where-Object -FilterScript {
+                        $_.Name.VariablePath.UserPath -eq 'BuiltModuleSubdirectory'
+                    }
+            )
+
+            if ($parameterAst.Count -eq 0)
+            {
+                continue
+            }
+
+            $propertyCommandAst = $parameterAst[0].DefaultValue.Find($astSearchDelegate, $true)
+
+            $propertyDefault += [PSCustomObject] @{
+                FileName = $taskFile.Name
+                Default  = $propertyCommandAst.CommandElements[2].Value
+            }
+        }
+
+        $propertyDefault.Count | Should -BeGreaterThan 0 -Because 'the build task files must declare the shared BuiltModuleSubdirectory property'
+
+        $divergentDefault = @($propertyDefault | Where-Object -FilterScript { $_.Default -ne '' })
+
+        $divergentDefault.Count | Should -Be 0 -Because ("the shared 'BuiltModuleSubdirectory' property default must be an empty string in every build task file, but these files diverge: {0}" -f ($divergentDefault.FileName -join ', '))
+    }
+}
+
 BeforeDiscovery {
     # Must use the imported module to build test cases.
     $allModuleFunctions = & $mut { Get-Command -Module $args[0] -CommandType Function } $script:moduleName

tests/Unit/tasks/WorkspaceDependencies.build.Tests.ps1

@@ -24,6 +24,35 @@ Describe 'WorkspaceDependencies.build' {
         $taskAlias.ReferencedCommand | Should -Be 'WorkspaceDependencies.build.ps1'
         $taskAlias.Definition | Should -Match 'Sampler[\/|\\]\d+\.\d+\.\d+[\/|\\]tasks[\/|\\]WorkspaceDependencies\.build\.ps1'
     }
+
+    <#
+        InvokeBuild dot-sources every imported task file into the same scope, and
+        the 'property' helper treats an empty string as unset. A non-empty default
+        here would therefore overwrite the shared $BuiltModuleSubdirectory value
+        for every other task in the build.
+    #>
+    It 'Should default the BuiltModuleSubdirectory property to an empty string' {
+        $taskFilePath = (Get-Alias -Name 'WorkspaceDependencies.build.Sampler.ib.tasks').Definition
+
+        $abstractSyntaxTree = [System.Management.Automation.Language.Parser]::ParseFile($taskFilePath, [ref] $null, [ref] $null)
+
+        $parameterAst = @(
+            $abstractSyntaxTree.ParamBlock.Parameters |
+                Where-Object -FilterScript {
+                    $_.Name.VariablePath.UserPath -eq 'BuiltModuleSubdirectory'
+                }
+        )
+
+        $parameterAst.Count | Should -Be 1
+
+        $astSearchDelegate = { $args[0] -is [System.Management.Automation.Language.CommandAst] }
+
+        $propertyCommandAst = $parameterAst[0].DefaultValue.Find($astSearchDelegate, $true)
+
+        $propertyCommandAst.CommandElements[0].Value | Should -Be 'property'
+        $propertyCommandAst.CommandElements[1].Value | Should -Be 'BuiltModuleSubdirectory'
+        $propertyCommandAst.CommandElements[2].Value | Should -Be '' -Because 'a non-empty default leaks into the shared build scope of every other task'
+    }
 }
 
 Describe 'Link_Local_Workspace_Dependencies' {