fix: fall back to feature dir basename for empty CURRENT_BRANCH (#3026) (#3229)

* fix: fall back to feature dir basename for empty CURRENT_BRANCH (#3026)

When a feature is resolved via SPECIFY_FEATURE_DIRECTORY or .specify/feature.json
without SPECIFY_FEATURE set, get_current_branch() returns empty, so
get_feature_paths / Get-FeaturePathsEnv emitted CURRENT_BRANCH= (empty) even
though the feature directory was resolvable. Downstream scripts and agents that
expect a non-empty identifier got misleading output.

Fall back to the basename of the resolved feature directory when the branch is
empty, in both the bash (`${feature_dir##*/}`) and PowerShell
(`Split-Path -Leaf`) resolvers. An explicit SPECIFY_FEATURE still takes
precedence, so this only fills the previously-empty case.

Add bash + PowerShell regression tests: the basename fallback fires when
SPECIFY_FEATURE is unset, and an explicit SPECIFY_FEATURE still overrides it.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* Potential fix for pull request finding

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

* fix: address Copilot feedback — PS 5.1 compat + parametrize bash test

- common.ps1: replace [System.IO.Path]::TrimEndingDirectorySeparator
  (a .NET Core-only method that throws MethodNotFound on Windows
  PowerShell 5.1 / .NET Framework) with a portable String.TrimEnd,
  so the trailing-slash trim actually works on 5.1.
- tests: parametrize the bash fallback test to cover feature.json,
  SPECIFY_FEATURE_DIRECTORY, and the explicit SPECIFY_FEATURE override
  (mirrors the PowerShell test), folding in the old explicit-override
  test; add the missing blank line before the next test (PEP 8).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

scripts/powershell/common.ps1

@@ -192,6 +192,17 @@ function Get-FeaturePathsEnv {
         exit 1
     }
     
+    # When no branch context exists (no SPECIFY_FEATURE, feature resolved via
+    # SPECIFY_FEATURE_DIRECTORY or feature.json), fall back to the feature
+    # directory basename so CURRENT_BRANCH is a usable identifier rather than
+    # an empty, misleading value (issue #3026).
+    if (-not $currentBranch) {
+        # TrimEnd (not [Path]::TrimEndingDirectorySeparator, which is .NET Core
+        # only) keeps this working on Windows PowerShell 5.1 / .NET Framework.
+        $featureDirTrimmed = $featureDir.TrimEnd('/', '\')
+        $currentBranch = Split-Path -Leaf $featureDirTrimmed
+    }
+
     [PSCustomObject]@{
         REPO_ROOT     = $repoRoot
         CURRENT_BRANCH = $currentBranch