ci: fold the PowerShell installer job into the tests-os Windows lanes

installer-tests.yml predates nothing it still owned. Its pytest step
(test_source_launcher_stages.py) is platforms("windows") and already runs in
both tests-os Windows lanes, so every installer PR ran it twice. The
`installer` lane never gated anything on its own either: every path that set
it also sets `python`, which gates tests-os.

The two standalone scripts/tests/*.ps1 suites become one platforms("windows")
pytest file parametrized over Windows PowerShell 5.1 and pwsh 7, so
list_os_marked_tests picks them up with everything else. The `installer` lane
goes away from the classifier, detect-changes, ci.yaml and the
all-checks-pass gate; the classifier contract now pins that install.ps1 and
its suites turn `python` on.

.github/actions/detect-changes/action.yml

@@ -45,9 +45,6 @@ outputs:
   npm_lock:
     description: Post/update the semantic package-lock.json diff PR comment.
     value: ${{ steps.classify.outputs.npm_lock }}
-  installer:
-    description: Run the PowerShell installer tests on a Windows runner.
-    value: ${{ steps.classify.outputs.installer }}
   bootstrap:
     description: Run the bootstrap installer lane (install.sh sandbox + stamp verification).
     value: ${{ steps.classify.outputs.bootstrap }}

.github/workflows/bootstrap-installer.yml

@@ -2,8 +2,8 @@ name: Bootstrap installer
 
 # Exercises the bootstrap-installer path on PRs that can affect it: the
 # POSIX shell installer (scripts/install.sh), its generated pin fragments,
-# and the version stamp the `complete` stage ships. The PowerShell installer
-# keeps its own Windows-only lane (installer-tests.yml); this lane runs the
+# and the version stamp the `complete` stage ships. The PowerShell installer's
+# native tests run in the tests-os Windows lanes; this lane runs the
 # protocol/stamp cross-checks plus a whole current installer against a tiny
 # application graph. The latter runs real PM/uv and generated launchers, not
 # every production extra. Tool download/hash tests remain separate.

.github/workflows/ci.yaml

@@ -72,7 +72,6 @@ jobs:
       deps: ${{ steps.gate-lanes.outputs.deps }}
       uv_lock: ${{ steps.gate-lanes.outputs.uv_lock }}
       npm_lock: ${{ steps.gate-lanes.outputs.npm_lock }}
-      installer: ${{ steps.gate-lanes.outputs.installer }}
       bootstrap: ${{ steps.gate-lanes.outputs.bootstrap }}
       desktop_updater: ${{ steps.gate-lanes.outputs.desktop_updater }}
       rust: ${{ steps.gate-lanes.outputs.rust }}
@@ -147,13 +146,6 @@ jobs:
     if: needs.detect.outputs.frontend == 'true'
     uses: ./.github/workflows/js-tests.yml
 
-  installer-tests:
-    name: Installer tests
-    needs: detect
-    # Windows-only, and only for PRs that touch install.ps1 or its tests.
-    if: needs.detect.outputs.installer == 'true'
-    uses: ./.github/workflows/installer-tests.yml
-
   rust-tests:
     name: Rust tests
     needs: detect
@@ -166,8 +158,8 @@ jobs:
     name: Bootstrap installer
     needs: detect
     # The bootstrap-installer path: install.sh, the pin fragments it embeds,
-    # and the version stamp it ships. The PowerShell installer has its own
-    # Windows-only lane above (installer-tests).
+    # and the version stamp it ships. The PowerShell installer's native tests
+    # are platforms("windows") pytest files and run in tests-os.
     if: needs.detect.outputs.bootstrap == 'true'
     uses: ./.github/workflows/bootstrap-installer.yml
 
@@ -300,7 +292,6 @@ jobs:
       - tests-os
       - lint
       - js-tests
-      - installer-tests
       - rust-tests
       - bootstrap-installer
       - e2e-desktop

.github/workflows/installer-tests.yml

@@ -1,59 +0,0 @@
-name: Installer tests
-
-# scripts/install.ps1's PowerShell tests. They exercise the installer as a real
-# subprocess, and every path contract they assert (8.3 short-name aliases,
-# Git Bash layouts, provider-cmdlet behavior) is Windows-specific — so they need
-# a Windows runner. Before this workflow existed the files were in the tree but
-# nothing ever ran them.
-
-on:
-  workflow_call:
-
-permissions:
-  contents: read
-
-concurrency:
-  group: installer-tests-${{ github.ref_type == 'tag' && github.run_id || github.ref }}
-  cancel-in-progress: ${{ github.ref_type != 'tag' }}
-
-jobs:
-  powershell:
-    name: PowerShell installer tests
-    runs-on: windows-latest
-    timeout-minutes: 15
-    steps:
-      - name: Checkout code
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
-
-      # Windows PowerShell 5.1 as well as pwsh 7: install.ps1 is delivered via
-      # `irm | iex` into whatever shell the user already has, and 5.1 is what
-      # ships with Windows. A construct that only parses under 7 is a broken
-      # installer for most of the people hitting it.
-      - name: 8.3 short-path normalization (pwsh 7)
-        shell: pwsh
-        run: pwsh -NoProfile -ExecutionPolicy Bypass -File scripts/tests/test-install-ps1-longpath.ps1
-
-      - name: 8.3 short-path normalization (Windows PowerShell 5.1)
-        shell: powershell
-        run: powershell -NoProfile -ExecutionPolicy Bypass -File scripts/tests/test-install-ps1-longpath.ps1
-
-      - name: System Node and npm compatibility (pwsh 7)
-        shell: pwsh
-        run: pwsh -NoProfile -ExecutionPolicy Bypass -File scripts/tests/test-install-ps1-node-compatibility.ps1
-
-      - name: System Node and npm compatibility (Windows PowerShell 5.1)
-        shell: powershell
-        run: powershell -NoProfile -ExecutionPolicy Bypass -File scripts/tests/test-install-ps1-node-compatibility.ps1
-
-      - name: Prepare native publication-test tools
-        uses: ./.github/actions/setup-pm
-
-      - name: Prepare isolated acceptance-test dependencies
-        shell: bash
-        run: python -m scripts.ci.python_packages pytest==9.1.1 pytest-asyncio==1.3.0 ruamel.yaml==0.18.17 packaging==26.0 distlib==0.4.3
-
-      - name: Whole-script launcher publication (PowerShell 5.1 and 7)
-        shell: bash
-        env:
-          HERMES_TEST_FILE_RETRIES: '0'
-        run: bash scripts/run_tests.sh tests/pm/test_source_launcher_stages.py -k powershell_stage -q -j 1