diff --git a/.github/actions/classify-pr/action.yml b/.github/actions/classify-pr/action.yml
index 6dfe906..68d1eb3 100644
--- a/.github/actions/classify-pr/action.yml
+++ b/.github/actions/classify-pr/action.yml
@@ -1,9 +1,20 @@
-name: "Classify PR substance"
-description: "Determines whether a PR touches substantive files or only CI/config (workflow-only) files. Outputs substantive=true|false."
+name: "Classify PR scope"
+description: "Reports whether a PR has changes that should trigger this caller's work, given a path scope. A file 'triggers' iff it matches the caller's scope and is not in the exclude list. Outputs triggers=true|false."
+inputs:
+  paths:
+    description: "Newline-separated list of path prefixes / files defining positive scope. A file triggers iff it equals one of these paths or is inside one (i.e., starts with `<path>/`). Empty means everything is in scope. Mutually exclusive with `exclude-paths`."
+    required: false
+    default: ""
+  exclude-paths:
+    description: "Newline-separated list of path prefixes / files defining negative scope. A file does NOT trigger if it equals one of these or is inside one. Default ignores `.gitignore` and `.pre-commit-config.yaml`. Override entirely (e.g. include the package's sibling subpackage and re-list defaults if you want them kept)."
+    required: false
+    default: |
+      .gitignore
+      .pre-commit-config.yaml
 outputs:
-  substantive:
-    description: "true if the PR touches substantive files; false if all changes are confined to .github/**, .pre-commit-config.yaml, .gitignore, or LICENSE."
-    value: ${{ steps.classify.outputs.substantive }}
+  triggers:
+    description: "true if the PR has at least one changed file that matches the configured scope; false otherwise."
+    value: ${{ steps.classify.outputs.triggers }}
 runs:
   using: "composite"
   steps:
@@ -13,27 +24,82 @@ runs:
         GH_TOKEN: ${{ github.token }}
         REPO: ${{ github.repository }}
         PR_NUMBER: ${{ github.event.pull_request.number }}
+        PATHS: ${{ inputs.paths }}
+        EXCLUDE_PATHS: ${{ inputs.exclude-paths }}
       run: |
         set -euo pipefail
+        # Normalize: treat whitespace-only inputs as empty. This matters
+        # because reusables that auto-append a value (e.g. `subdir`) into
+        # `paths` produce a list of all-empty lines when the appended
+        # value is also empty — bash's [ -n ] would otherwise misread that
+        # as "positive scope set", flipping the action into the wrong mode.
+        has_content() {
+          while IFS= read -r line; do
+            [ -n "$line" ] && return 0
+          done <<< "$1"
+          return 1
+        }
+        has_content "$PATHS" || PATHS=""
+        has_content "$EXCLUDE_PATHS" || EXCLUDE_PATHS=""
+
+        if [ -n "$PATHS" ] && [ -n "$EXCLUDE_PATHS" ]; then
+          # If paths is set, exclude-paths is ignored (caller is using positive scope).
+          # Surface a warning rather than failing so the user notices.
+          echo "::warning::classify-pr: 'paths' and 'exclude-paths' are mutually exclusive; using 'paths'."
+          EXCLUDE_PATHS=""
+        fi
         if [ -z "${PR_NUMBER:-}" ]; then
-          echo "Not a pull_request event; defaulting to substantive=true."
-          echo "substantive=true" >> "$GITHUB_OUTPUT"
+          echo "Not a pull_request event; defaulting to triggers=true."
+          echo "triggers=true" >> "$GITHUB_OUTPUT"
           exit 0
         fi
         files=$(gh api --paginate "repos/${REPO}/pulls/${PR_NUMBER}/files" --jq '.[].filename')
         if [ -z "$files" ]; then
-          echo "No files reported for PR #${PR_NUMBER}; defaulting to substantive=true."
-          echo "substantive=true" >> "$GITHUB_OUTPUT"
+          echo "No files reported for PR #${PR_NUMBER}; defaulting to triggers=true."
+          echo "triggers=true" >> "$GITHUB_OUTPUT"
           exit 0
         fi
         echo "Changed files:"
         printf '  %s\n' $files
-        substantive=false
+
+        # Helper: check if a file matches any entry in a newline-separated list.
+        # An entry matches iff the file equals the entry, or the file starts with `<entry>/`.
+        matches_list() {
+          local file=$1
+          local list=$2
+          while IFS= read -r entry; do
+            [ -z "$entry" ] && continue
+            if [ "$file" = "$entry" ] || [[ "$file" == "$entry"/* ]]; then
+              return 0
+            fi
+          done <<< "$list"
+          return 1
+        }
+
+        if [ -n "$PATHS" ]; then
+          echo "Positive scope: any file matching one of the paths."
+          printf '  %s\n' $PATHS
+        else
+          echo "Default scope: any file outside the exclude list."
+          printf '  exclude: %s\n' $EXCLUDE_PATHS
+        fi
+
+        triggers=false
         while IFS= read -r file; do
-          case "$file" in
-            .github/*|.pre-commit-config.yaml|.gitignore|LICENSE) ;;
-            *) substantive=true; break ;;
-          esac
+          if [ -n "$PATHS" ]; then
+            # Positive scope: file triggers iff it matches one of the listed paths.
+            if matches_list "$file" "$PATHS"; then
+              triggers=true
+              break
+            fi
+          else
+            # Negative scope: file triggers iff it is NOT in the exclude list.
+            if ! matches_list "$file" "$EXCLUDE_PATHS"; then
+              triggers=true
+              break
+            fi
+          fi
         done <<< "$files"
-        echo "substantive=${substantive}"
-        echo "substantive=${substantive}" >> "$GITHUB_OUTPUT"
+
+        echo "triggers=${triggers}"
+        echo "triggers=${triggers}" >> "$GITHUB_OUTPUT"
diff --git a/.github/workflows/CheckCompatBounds.yml b/.github/workflows/CheckCompatBounds.yml
index 02af007..d9de634 100644
--- a/.github/workflows/CheckCompatBounds.yml
+++ b/.github/workflows/CheckCompatBounds.yml
@@ -9,10 +9,15 @@ on:
         required: false
         type: string
       project:
-        description: "The value is passed to Julia's `--project` flag during buildpkg."
+        description: "Deprecated alias for `subdir`. Value passed to Julia's `--project` flag during buildpkg. When `subdir` is set, it takes precedence."
         default: '@.'
         required: false
         type: string
+      subdir:
+        description: "Subdirectory containing the package's Project.toml. When set, both buildpkg's `--project` and the check-compat-bounds workspace-root resolve to `<subdir>`. Empty (default) uses repo root."
+        default: ""
+        required: false
+        type: string
       cache:
         description: "Use the julia-actions/cache action for caching."
         default: true
@@ -74,10 +79,10 @@ jobs:
         if: "${{ inputs.buildpkg }}"
         with:
           localregistry: "${{ inputs.localregistry }}"
-          project: "${{ inputs.project }}"
+          project: "${{ inputs.subdir != '' && inputs.subdir || inputs.project }}"
 
       - name: "Check compat upper bounds"
         uses: ITensor/ITensorActions/.github/actions/check-compat-bounds@main
         with:
-          workspace-root: "${{ inputs.workspace-root }}"
+          workspace-root: "${{ inputs.subdir != '' && inputs.subdir || inputs.workspace-root }}"
           mode: "${{ inputs.mode }}"
diff --git a/.github/workflows/CompatHelper.yml b/.github/workflows/CompatHelper.yml
index 9ab7dfe..cfa7809 100644
--- a/.github/workflows/CompatHelper.yml
+++ b/.github/workflows/CompatHelper.yml
@@ -14,6 +14,11 @@ on:
         default: ""
         required: false
         type: string
+      subdir:
+        description: "Subdirectory containing the package's Project.toml. When set, CompatHelper bumps `<subdir>/Project.toml` plus `<subdir>/{docs,examples,test}/Project.toml` if present. Empty (default) uses repo root."
+        default: ""
+        required: false
+        type: string
 
 jobs:
   compathelper:
@@ -73,6 +78,7 @@ jobs:
           # (see https://docs.github.com/en/actions/security-for-github-actions/security-guides/automatic-token-authentication#using-the-github_token-in-a-workflow).
           GITHUB_TOKEN: ${{ secrets.COMPATHELPER_PAT || secrets.GITHUB_TOKEN }}
           LOCALREGISTRY: ${{ inputs.localregistry }}
+          SUBDIR: ${{ inputs.subdir }}
           TOKEN_OWNER: ${{ steps.token-owner.outputs.login }}
         run: |
           import CompatHelper
@@ -106,7 +112,9 @@ jobs:
               push!(registries, Pkg.RegistrySpec(; url=registry_url, name=registry_name))
             end
           end
+          subdir = get(ENV, "SUBDIR", "")
           subdirs = ["", "docs", "examples", "test"]
+          isempty(subdir) || (subdirs = joinpath.(subdir, subdirs))
           token_owner = get(ENV, "TOKEN_OWNER", "")
           # If TOKEN_OWNER contains a JSON error body (happens when only GITHUB_TOKEN
           # is available, e.g. in private repos without COMPATHELPER_PAT), treat it as
diff --git a/.github/workflows/IntegrationTest.yml b/.github/workflows/IntegrationTest.yml
index 77e7051..a513ec1 100644
--- a/.github/workflows/IntegrationTest.yml
+++ b/.github/workflows/IntegrationTest.yml
@@ -22,6 +22,23 @@ on:
         default: ""
         required: false
         type: string
+      subdir:
+        description: "Run the downstream tests against the package in this subdirectory."
+        default: ""
+        required: false
+        type: string
+      paths:
+        description: "Newline-separated list of path prefixes / files defining positive scope for the substantive-PR check. A file triggers IntegrationTest iff it equals one of these paths or starts with `<path>/`. Empty means no positive-scope filter; the check falls back to `exclude-paths`. Mutually exclusive with `exclude-paths`."
+        default: ""
+        required: false
+        type: string
+      exclude-paths:
+        description: "Newline-separated list of path prefixes / files defining negative scope for the substantive-PR check. A file does NOT trigger IntegrationTest if it matches one of these. Default ignores `.gitignore` and `.pre-commit-config.yaml`."
+        default: |
+          .gitignore
+          .pre-commit-config.yaml
+        required: false
+        type: string
       run-on-draft:
         description: "When true, run integration tests even on draft PRs"
         default: false
@@ -53,6 +70,21 @@ jobs:
         pkg: ${{ fromJSON(inputs.pkgs) }}
 
     steps:
+      - uses: ITensor/ITensorActions/.github/actions/classify-pr@main
+        id: classify
+        with:
+          # `subdir` (the in-tree package under test) is auto-appended
+          # to the positive scope so callers don't have to repeat it.
+          paths: |
+            ${{ inputs.subdir }}
+            ${{ inputs.paths }}
+          exclude-paths: ${{ inputs.exclude-paths }}
+
+      - name: "Skip on out-of-scope PR"
+        if: "${{ steps.classify.outputs.triggers != 'true' }}"
+        run: |
+          echo "PR has no changes in this caller's scope; integration test skipped."
+
       # Decide whether this matrix leg should run, and emit `skip=true|false`.
       # Skips when the entry is a URL that needs auth and the PR is from a
       # fork (no secrets are exposed to fork PRs under `pull_request:`).
@@ -62,6 +94,7 @@ jobs:
       # `workflow_dispatch` (where secrets are in scope).
       - name: "Decide whether to run"
         id: gate
+        if: "${{ steps.classify.outputs.triggers == 'true' }}"
         env:
           PKG: ${{ matrix.pkg }}
           HEAD_REPO: ${{ github.event.pull_request.head.repo.full_name }}
@@ -93,7 +126,7 @@ jobs:
           echo "skip=false" >> "$GITHUB_OUTPUT"
       - name: "Record skipped dependency"
         id: skip_artifact
-        if: steps.gate.outputs.skip == 'true'
+        if: "${{ steps.classify.outputs.triggers == 'true' && steps.gate.outputs.skip == 'true' }}"
         env:
           PKG: ${{ matrix.pkg }}
         run: |
@@ -103,22 +136,22 @@ jobs:
           echo "key=$key" >> "$GITHUB_OUTPUT"
           echo "path=$path" >> "$GITHUB_OUTPUT"
       - name: "Upload skipped-dependency marker"
-        if: steps.gate.outputs.skip == 'true'
+        if: "${{ steps.classify.outputs.triggers == 'true' && steps.gate.outputs.skip == 'true' }}"
         uses: actions/upload-artifact@v7
         with:
           name: "integration-test-skip-${{ steps.skip_artifact.outputs.key }}"
           path: ${{ steps.skip_artifact.outputs.path }}
       - uses: actions/checkout@v6
-        if: steps.gate.outputs.skip != 'true'
+        if: "${{ steps.classify.outputs.triggers == 'true' && steps.gate.outputs.skip != 'true' }}"
         with:
           ref: ${{ github.event.pull_request.head.sha || github.sha }}
       - uses: julia-actions/setup-julia@v3
-        if: steps.gate.outputs.skip != 'true'
+        if: "${{ steps.classify.outputs.triggers == 'true' && steps.gate.outputs.skip != 'true' }}"
         with:
           version: ${{ inputs.julia-version }}
           arch: x64
       - name: "Configure git authentication for private repository"
-        if: steps.gate.outputs.skip != 'true'
+        if: "${{ steps.classify.outputs.triggers == 'true' && steps.gate.outputs.skip != 'true' }}"
         env:
           TOKEN: ${{ secrets.INTEGRATIONTEST_PAT }}
           PKG: ${{ matrix.pkg }}
@@ -129,12 +162,13 @@ jobs:
             fi
           fi
       - name: "Run the downstream tests"
-        if: steps.gate.outputs.skip != 'true'
+        if: "${{ steps.classify.outputs.triggers == 'true' && steps.gate.outputs.skip != 'true' }}"
         shell: julia --color=yes --project=downstream {0}
         env:
           PKG: ${{ matrix.pkg }}
           LOCALREGISTRY: ${{ inputs.localregistry }}
           EXTRA_DEV_PATHS: ${{ inputs.extra-dev-paths }}
+          PKG_DIR: ${{ inputs.subdir || '.' }}
           JULIA_PKG_SERVER_REGISTRY_PREFERENCE: eager
         run: |
           using Pkg
@@ -148,7 +182,7 @@ jobs:
               Pkg.Registry.add(Pkg.RegistrySpec(; url=registry_url))
             end
           end
-          dev_paths = [".", split(get(ENV, "EXTRA_DEV_PATHS", ""), "\n")...]
+          dev_paths = [get(ENV, "PKG_DIR", "."), split(get(ENV, "EXTRA_DEV_PATHS", ""), "\n")...]
           filter!(!isempty, dev_paths)
           dev_specs = [PackageSpec(; path) for path in dev_paths]
           pkg = get(ENV, "PKG", "")
diff --git a/.github/workflows/Registrator.yml b/.github/workflows/Registrator.yml
index cee6e20..3d5c6a0 100644
--- a/.github/workflows/Registrator.yml
+++ b/.github/workflows/Registrator.yml
@@ -18,6 +18,11 @@ on:
         default: "/register"
         required: false
         type: string
+      subdir:
+        description: "Subdirectory containing the package's Project.toml, relative to the repo root. Default empty means register the root package. Set to e.g. 'NDTensors' to register an in-tree subpackage; the workflow then reads `package/<subdir>/Project.toml` and posts `@JuliaRegistrator register subdir=<subdir>` so JuliaRegistrator picks up the sub-package correctly."
+        default: ""
+        required: false
+        type: string
     secrets:
       # Only needed for the local-registry path (checkout + PR). Not needed for General.
       REGISTRATOR_PAT:
@@ -83,6 +88,7 @@ jobs:
         id: meta
         env:
           OLD_REF: ${{ github.event.before }}
+          SUBDIR: ${{ inputs.subdir }}
         shell: julia --color=yes {0}
         run: |
           using TOML
@@ -108,14 +114,17 @@ jobs:
           end
 
           let
-              new = TOML.parsefile("package/Project.toml")
+              subdir = get(ENV, "SUBDIR", "")
+              project_path = isempty(subdir) ? "Project.toml" : joinpath(subdir, "Project.toml")
+
+              new = TOML.parsefile(joinpath("package", project_path))
               name = get(new, "name", "")
               uuid = get(new, "uuid", "")
               newv_str = get(new, "version", "")
 
-              isempty(name) && error("Project.toml is missing name")
-              isempty(uuid) && error("Project.toml is missing uuid")
-              isempty(newv_str) && error("Project.toml is missing version")
+              isempty(name) && error("$project_path is missing name")
+              isempty(uuid) && error("$project_path is missing uuid")
+              isempty(newv_str) && error("$project_path is missing version")
 
               newv = parse_version(newv_str, "new")
               subject = replace(readchomp(`git -C package log -1 --pretty=%s HEAD`), ['\n','\r'] => ' ')
@@ -133,11 +142,11 @@ jobs:
               oldv_str = ""
               if !isempty(old_ref)
                   try
-                      old_toml = readchomp(`git -C package show $old_ref:Project.toml`)
+                      old_toml = readchomp(`git -C package show $old_ref:$project_path`)
                       oldv_str = get(TOML.parse(old_toml), "version", "")
                   catch err
                       # Don't hard-fail on missing old Project.toml; just skip strict validation.
-                      println(stderr, "Warning: could not read Project.toml at ref '$old_ref' (treating as no prior version): $err")
+                      println(stderr, "Warning: could not read $project_path at ref '$old_ref' (treating as no prior version): $err")
                       oldv_str = ""
                   end
               end
@@ -217,9 +226,14 @@ jobs:
           IS_BREAKING: ${{ steps.meta.outputs.is_breaking }}
           SUBJECT: ${{ steps.meta.outputs.subject }}
           NEW_VERSION: ${{ steps.meta.outputs.new_version }}
+          SUBDIR: ${{ inputs.subdir }}
         run: |
           {
-            echo "@JuliaRegistrator register"
+            if [ -n "$SUBDIR" ]; then
+              echo "@JuliaRegistrator register subdir=$SUBDIR"
+            else
+              echo "@JuliaRegistrator register"
+            fi
             if [ "$IS_BREAKING" = "true" ]; then
               echo ""
               echo "Release notes:"
@@ -336,6 +350,8 @@ jobs:
 
       - name: "Update local registry"
         if: steps.meta.outputs.route == 'local'
+        env:
+          SUBDIR: ${{ inputs.subdir }}
         shell: julia --color=yes {0}
         run: |
           import Pkg
@@ -344,7 +360,9 @@ jobs:
                                   uuid="89398ba2-070a-4b16-a995-9893c55d93cf",
                                   version="0.5.7"))
           using LocalRegistry
-          register("./package"; registry="./registry", commit=false, push=false)
+          subdir = get(ENV, "SUBDIR", "")
+          pkg_path = isempty(subdir) ? "./package" : joinpath("./package", subdir)
+          register(pkg_path; registry="./registry", commit=false, push=false)
 
       - name: "Create PR to registry"
         if: steps.meta.outputs.route == 'local'
diff --git a/.github/workflows/Tests.yml b/.github/workflows/Tests.yml
index 4b8e92a..d78f1fb 100644
--- a/.github/workflows/Tests.yml
+++ b/.github/workflows/Tests.yml
@@ -13,8 +13,8 @@ on:
         required: false
         type: string
       project:
-        description: "The value is passed to Julia's `--project` flag"
-        default: '@.'
+        description: "Deprecated alias for `subdir`. Value passed to Julia's `--project` flag. Set `subdir` instead. Will be removed in a future major release."
+        default: "@."
         required: false
         type: string
       group:
@@ -67,6 +67,28 @@ on:
         default: "yes"
         required: false
         type: string
+      test-args:
+        description: "Newline-separated list of arguments passed to `Pkg.test(; test_args=...)`. Surfaces julia-actions/julia-runtest's `test_args` input. Useful when `runtests.jl` selects test groups via ARGS rather than the GROUP env-var."
+        default: ""
+        required: false
+        type: string
+      subdir:
+        description: "Subdirectory containing the package's Project.toml. When set, Julia activates `<subdir>` for buildpkg and runtest. Empty (default) activates the repo root."
+        default: ""
+        required: false
+        type: string
+      paths:
+        description: "Newline-separated list of path prefixes / files defining positive scope for the substantive-PR check. A file triggers tests iff it equals one of these paths or starts with `<path>/`. Empty means no positive-scope filter; the check falls back to `exclude-paths`. Mutually exclusive with `exclude-paths`."
+        default: ""
+        required: false
+        type: string
+      exclude-paths:
+        description: "Newline-separated list of path prefixes / files defining negative scope for the substantive-PR check. A file does NOT trigger if it matches one of these. Default ignores `.gitignore` and `.pre-commit-config.yaml`. Override entirely (e.g. add a sibling subpackage and re-list defaults if you want them kept)."
+        default: |
+          .gitignore
+          .pre-commit-config.yaml
+        required: false
+        type: string
       continue-on-error:
         description: "Prevent the workflow run from failing if/when the job fails"
         required: false
@@ -118,10 +140,26 @@ jobs:
     runs-on: "${{ inputs.self-hosted && 'self-hosted' || inputs.os }}"
     timeout-minutes: ${{ inputs.timeout-minutes }}
     steps:
+      - uses: ITensor/ITensorActions/.github/actions/classify-pr@main
+        id: classify
+        with:
+          # `subdir` (the package being tested) is auto-appended to
+          # the positive scope so callers don't have to repeat it.
+          paths: |
+            ${{ inputs.subdir }}
+            ${{ inputs.paths }}
+          exclude-paths: ${{ inputs.exclude-paths }}
+
+      - name: "Skip on out-of-scope PR"
+        if: "${{ steps.classify.outputs.triggers != 'true' }}"
+        run: |
+          echo "PR has no changes in this caller's scope; tests skipped."
+
       - uses: actions/checkout@v6
+        if: "${{ steps.classify.outputs.triggers == 'true' }}"
 
       - name: "Install apt packages"
-        if: "${{ inputs.apt-packages != '' && runner.os == 'Linux' }}"
+        if: "${{ steps.classify.outputs.triggers == 'true' && inputs.apt-packages != '' && runner.os == 'Linux' }}"
         env:
           APT_PACKAGES: ${{ inputs.apt-packages }}
         run: |
@@ -132,23 +170,25 @@ jobs:
           sudo apt-get install -y $APT_PACKAGES
 
       - name: "Setup Julia ${{ inputs.julia-version }}"
+        if: "${{ steps.classify.outputs.triggers == 'true' }}"
         uses: julia-actions/setup-julia@v3
         with:
           version: "${{ inputs.julia-version }}"
           arch: "${{ inputs.julia-arch || runner.arch }}"
 
       - uses: julia-actions/cache@v2
-        if: "${{ inputs.cache }}"
+        if: "${{ steps.classify.outputs.triggers == 'true' && inputs.cache }}"
         with:
           token: "${{ secrets.GITHUB_TOKEN }}"
 
       - uses: julia-actions/julia-buildpkg@v1
-        if: "${{ inputs.buildpkg }}"
+        if: "${{ steps.classify.outputs.triggers == 'true' && inputs.buildpkg }}"
         with:
           localregistry: "${{ inputs.localregistry }}"
+          project: "${{ inputs.subdir != '' && inputs.subdir || inputs.project }}"
 
       - name: "Export extra environment variables"
-        if: "${{ inputs.extra-env != '' }}"
+        if: "${{ steps.classify.outputs.triggers == 'true' && inputs.extra-env != '' }}"
         shell: "bash"
         env:
           EXTRA_ENV: ${{ inputs.extra-env }}
@@ -156,12 +196,14 @@ jobs:
           printf '%s\n' "$EXTRA_ENV" >> "$GITHUB_ENV"
 
       - name: "Run tests ${{ inputs.self-hosted && '' || format('on {0}', inputs.os) }} with Julia v${{ inputs.julia-version }}"
+        if: "${{ steps.classify.outputs.triggers == 'true' }}"
         uses: julia-actions/julia-runtest@v1
         with:
-          project: "${{ inputs.project }}"
+          project: "${{ inputs.subdir != '' && inputs.subdir || inputs.project }}"
           depwarn: "${{ inputs.julia-runtest-depwarn }}"
           coverage: "${{ inputs.coverage }}"
           prefix: "${{ inputs.test-prefix }}"
+          test_args: "${{ inputs.test-args }}"
           # On LTS, accept that newer dep versions may not be reachable —
           # let Pkg resolve to whatever satisfies both the workspace compat
           # and transitive constraints. `auto` (the default) would otherwise
@@ -174,20 +216,20 @@ jobs:
           JULIA_NUM_THREADS: "${{ inputs.nthreads }}"
 
       - name: "Upload artifacts"
-        if: "${{ always() && inputs.upload-artifacts-path != '' }}"
+        if: "${{ always() && steps.classify.outputs.triggers == 'true' && inputs.upload-artifacts-path != '' }}"
         uses: actions/upload-artifact@v7
         with:
           name: "artifacts-${{ inputs.os }}-julia-${{ inputs.julia-version }}${{ inputs.group != '' && format('-{0}', inputs.group) || '' }}"
           path: "${{ inputs.upload-artifacts-path }}"
 
       - uses: julia-actions/julia-processcoverage@v1
-        if: "${{ inputs.coverage }}"
+        if: "${{ steps.classify.outputs.triggers == 'true' && inputs.coverage }}"
         with:
           directories: "${{ inputs.coverage-directories }}"
 
       - name: "Report coverage with Codecov"
         uses: codecov/codecov-action@v6
-        if: "${{ inputs.coverage }}"
+        if: "${{ steps.classify.outputs.triggers == 'true' && inputs.coverage }}"
         with:
           files: lcov.info
           token: "${{ secrets.CODECOV_TOKEN }}"
diff --git a/.github/workflows/VersionCheck.yml b/.github/workflows/VersionCheck.yml
index 19934f5..5819a92 100644
--- a/.github/workflows/VersionCheck.yml
+++ b/.github/workflows/VersionCheck.yml
@@ -13,6 +13,24 @@ on:
         default: ""
         required: false
         type: string
+      subdir:
+        description: "Subdirectory containing the package's Project.toml. When set, VersionCheck reads `<subdir>/Project.toml` for the version-bump check. Empty (default) reads root Project.toml."
+        default: ""
+        required: false
+        type: string
+      paths:
+        description: "Newline-separated list of path prefixes / files defining positive scope for the substantive-PR check. A file triggers VersionCheck iff it equals one of these paths or starts with `<path>/`. Empty means no positive-scope filter; the check falls back to `exclude-paths`. Mutually exclusive with `exclude-paths`."
+        default: ""
+        required: false
+        type: string
+      exclude-paths:
+        description: "Newline-separated list of path prefixes / files defining negative scope for the substantive-PR check. A file does NOT trigger VersionCheck if it matches one of these. Default ignores `.gitignore`, `.pre-commit-config.yaml`, and `.github` (workflow / config metadata changes don't require a version bump)."
+        default: |
+          .gitignore
+          .pre-commit-config.yaml
+          .github
+        required: false
+        type: string
 
 jobs:
   version-check:
@@ -27,45 +45,57 @@ jobs:
 
       - uses: ITensor/ITensorActions/.github/actions/classify-pr@main
         id: classify
+        with:
+          # `subdir` (the in-tree package whose Project.toml is checked) is
+          # auto-appended to the positive scope so callers don't have to
+          # repeat it.
+          paths: |
+            ${{ inputs.subdir }}
+            ${{ inputs.paths }}
+          exclude-paths: ${{ inputs.exclude-paths }}
 
-      - name: "Skip version check on non-substantive PR"
-        if: steps.classify.outputs.substantive != 'true'
+      - name: "Skip version check on out-of-scope PR"
+        if: steps.classify.outputs.triggers != 'true'
         run: |
-          echo "PR classified as non-substantive (only .github/**, .pre-commit-config.yaml, .gitignore, LICENSE)."
-          echo "No version bump is required. Reporting success without running the real check."
+          echo "PR has no changes in this caller's scope; no version bump required. Reporting success."
 
       - name: "Fetch base branch"
-        if: steps.classify.outputs.substantive == 'true'
+        if: steps.classify.outputs.triggers == 'true'
         run: git fetch --depth=1 origin "${{ github.base_ref }}"
 
       - uses: julia-actions/setup-julia@v3
-        if: steps.classify.outputs.substantive == 'true'
+        if: steps.classify.outputs.triggers == 'true'
         with:
           version: ${{ inputs.julia-version }}
 
       - name: "Check version was bumped"
-        if: steps.classify.outputs.substantive == 'true'
+        if: steps.classify.outputs.triggers == 'true'
         shell: julia --color=yes {0}
+        env:
+          SUBDIR: ${{ inputs.subdir }}
         run: |
           using TOML
 
+          subdir = get(ENV, "SUBDIR", "")
+          project_path = isempty(subdir) ? "Project.toml" : joinpath(subdir, "Project.toml")
+
           base_ref = ENV["GITHUB_BASE_REF"]
           base_project_text = try
-              read(`git show "origin/$base_ref:Project.toml"`, String)
+              read(`git show "origin/$base_ref:$project_path"`, String)
           catch err
-              println("Could not read Project.toml on origin/$base_ref ($err); skipping check.")
+              println("Could not read $project_path on origin/$base_ref ($err); skipping check.")
               exit(0)
           end
           base_project = TOML.parse(base_project_text)
-          current_project = TOML.parse(read("Project.toml", String))
+          current_project = TOML.parse(read(project_path, String))
 
           if !haskey(base_project, "version")
-              println("Base branch Project.toml has no version field; skipping check.")
+              println("Base branch $project_path has no version field; skipping check.")
               exit(0)
           end
           if !haskey(current_project, "version")
               error(
-                  "Project.toml on this branch has no version field, but the base " *
+                  "$project_path on this branch has no version field, but the base " *
                   "branch ($base_ref) does. Restore the version field and bump it."
               )
           end
@@ -75,13 +105,13 @@ jobs:
 
           if current_version > base_version
               println(
-                  "OK: Project.toml version bumped from $base_version " *
+                  "OK: $project_path version bumped from $base_version " *
                   "(origin/$base_ref) to $current_version (PR head)."
               )
           else
               error(
-                  "Project.toml version was not bumped. Current version $current_version " *
+                  "$project_path version was not bumped. Current version $current_version " *
                   "is not greater than the version $base_version on the base branch " *
-                  "($base_ref). Bump the version in Project.toml."
+                  "($base_ref). Bump the version in $project_path."
               )
           end
diff --git a/README.md b/README.md
index c036082..f1c46fc 100644
--- a/README.md
+++ b/README.md
@@ -148,8 +148,12 @@ the full matrix even on draft PRs, set it to `true`:
 |---|---|---|---|
 | `julia-version` | string | `"1"` | Julia version passed to `julia-actions/setup-julia`. |
 | `julia-arch` | string | runner arch | Architecture of Julia to be used. |
-| `project` | string | `"@."` | Value passed to Julia's `--project` flag. |
+| `subdir` | string | `""` | Subdirectory containing the package's Project.toml (for an in-tree subpackage). When set, Julia activates `<subdir>` for buildpkg and runtest, and `<subdir>` is auto-appended to `paths` so the per-package classify-pr step considers files inside it as in-scope. |
+| `project` | string | `"@."` | Deprecated alias for `subdir`. Value passed to Julia's `--project` flag. Set `subdir` instead; will be removed in a future major release. |
 | `group` | string | `""` | Test group selector. Exposed to tests via the `GROUP` environment variable so a `runtests.jl` can selectively run a subset. |
+| `test-args` | string | `""` | Newline-separated arguments forwarded to `Pkg.test(; test_args=...)` (via `julia-actions/julia-runtest`'s `test_args` input). Useful when `runtests.jl` selects test groups via `ARGS` rather than the `GROUP` env-var. |
+| `paths` | string | `""` | Positive scope for the substantive-PR check: a file triggers tests iff it equals one of these paths or starts with `<path>/`. Newline-separated. Mutually exclusive with `exclude-paths`. The `subdir` input (if set) is auto-appended. |
+| `exclude-paths` | string | `.gitignore`<br>`.pre-commit-config.yaml` | Negative scope: a file does NOT trigger tests if it matches one of these paths. Default ignores pure metadata files only — workflow file edits (`.github/workflows/**`) do count, by design. Override entirely (defaults are not implicitly preserved). |
 | `self-hosted` | bool | `false` | Run on a self-hosted runner instead of `os`. |
 | `os` | string | `"ubuntu-latest"` | Runner image used when `self-hosted` is `false`. |
 | `nthreads` | number | `1` | Value of `JULIA_NUM_THREADS`. |
@@ -430,6 +434,7 @@ jobs:
 |---|---|---|---|
 | `julia-version` | string | `"1"` | Julia version passed to `julia-actions/setup-julia`. |
 | `localregistry` | string | `""` | Newline-separated list of extra registry URLs (besides General) to scan for dependency updates. |
+| `subdir` | string | `""` | Subdirectory containing the package's Project.toml (for an in-tree subpackage). When set, CompatHelper bumps `<subdir>/Project.toml` plus its `<subdir>/{docs,examples,test}/Project.toml` siblings if present. Empty (default) bumps the standard root + docs + examples + test set. |
 
 ### Secrets
 
@@ -600,7 +605,10 @@ jobs:
 | `julia-version` | string | `"1"` | Julia version passed to `julia-actions/setup-julia`. |
 | `pkgs` | string | **required** | JSON-array string of registered package names and/or git URLs. Use `'[]'` to configure no downstream tests. |
 | `localregistry` | string | `""` | Newline-separated list of extra registry URLs to add before resolving. |
+| `subdir` | string | `""` | Run the downstream tests against the package located in this subdirectory (rather than the repo root). When set, `<subdir>` is also auto-appended to `paths` so the per-package classify-pr considers files inside it as in-scope. |
 | `extra-dev-paths` | string | `""` | Newline-separated list of additional local package paths to develop alongside the repository root before testing downstream packages. |
+| `paths` | string | `""` | Positive scope for the substantive-PR check: a file triggers IntegrationTest iff it equals one of these paths or starts with `<path>/`. Newline-separated. Mutually exclusive with `exclude-paths`. The `subdir` input (if set) is auto-appended. |
+| `exclude-paths` | string | `.gitignore`<br>`.pre-commit-config.yaml` | Negative scope: a file does NOT trigger IntegrationTest if it matches one of these. Default ignores pure metadata files only. Override entirely. |
 | `run-on-draft` | bool | `false` | Run integration tests on draft PRs. When `false`, draft PRs skip integration tests entirely. |
 
 The companion `IntegrationTestRequest.yml` workflow (used for the `/integrationtest ...` comment trigger shown above) has its own inputs:
@@ -641,9 +649,12 @@ jobs:
 | Input | Type | Default | Description |
 |---|---|---|---|
 | `julia-version` | string | `"1"` | Julia version passed to `julia-actions/setup-julia`. |
-| `localregistry` | string | `""` | Newline-separated list of extra registry URLs to consult when determining the previously registered version. |
+| `localregistry` | string | `""` | Unused, kept for backward compat with existing callers. |
+| `subdir` | string | `""` | Subdirectory containing the package's Project.toml (for an in-tree subpackage). When set, the version-bump check reads `<subdir>/Project.toml` instead of root, and `<subdir>` is auto-appended to `paths` so the substantive-PR check is scoped to that subpackage. |
+| `paths` | string | `""` | Positive scope for the substantive-PR check: a file triggers VersionCheck iff it matches one of these paths. Newline-separated. Mutually exclusive with `exclude-paths`. |
+| `exclude-paths` | string | `.gitignore`<br>`.pre-commit-config.yaml`<br>`.github` | Negative scope: a file does NOT trigger VersionCheck if it matches one of these. Default ignores pure metadata plus `.github` (workflow-only PRs don't require a version bump). Override entirely. |
 
-The check is automatically skipped on PRs classified as non-substantive (changes limited to `.github/**`, `.pre-commit-config.yaml`, `.gitignore`, or `LICENSE`); those PRs pass without requiring a version bump.
+The version-bump check is skipped (reported as success) when classify-pr says no in-scope files changed — for example a workflow-only PR on a single-package consumer (default `exclude-paths` includes `.github`), or an NDTensors-only PR on a multi-package caller scoped to root via `exclude-paths: NDTensors`.
 
 ## Check Compat Bounds
 
@@ -685,7 +696,8 @@ jobs:
 | Input | Type | Default | Description |
 |---|---|---|---|
 | `julia-version` | string | `"1"` | Julia version passed to `julia-actions/setup-julia`. |
-| `project` | string | `"@."` | Value passed to Julia's `--project` flag during `julia-actions/julia-buildpkg`. |
+| `subdir` | string | `""` | Subdirectory containing the package's Project.toml (for an in-tree subpackage). When set, both `project` (buildpkg's `--project`) and `workspace-root` (the check-compat-bounds script's workspace root) resolve to `<subdir>`. |
+| `project` | string | `"@."` | Deprecated alias for `subdir`. Value passed to Julia's `--project` flag during `julia-actions/julia-buildpkg`. When `subdir` is set, it takes precedence. |
 | `cache` | bool | `true` | Use `julia-actions/cache`. |
 | `buildpkg` | bool | `true` | Run `julia-actions/julia-buildpkg` before the check. Disable only if the workspace is instantiated some other way. |
 | `localregistry` | string | `""` | Newline-separated list of extra registry URLs to add before resolving (forwarded to `julia-actions/julia-buildpkg`). |
@@ -851,6 +863,7 @@ jobs:
 | `localregistry` | Local registry repo (`owner/name`) for packages not in General | `""` |
 | `trigger` | Comment trigger phrase for on-demand registration | `/register` |
 | `julia-version` | Julia version used by the workflow | `1` |
+| `subdir` | Subdirectory containing the package's Project.toml (for an in-tree subpackage). When set, the workflow reads `package/<subdir>/Project.toml` instead of root and posts `@JuliaRegistrator register subdir=<subdir>`, so multi-package repos can auto-register each in-tree package via a matrix invocation. | `""` |
 
 ### Secrets