diff --git a/README.md b/README.md
index 8bf6a02..0084053 100644
--- a/README.md
+++ b/README.md
@@ -76,9 +76,11 @@ caller's `pylock.toml`.
 
 `nab-git-commit` is a temporary input of `refresh-release-lock`, `validate-news`, `check-tagged-source`,
 `prepare-towncrier-release.yaml`, `upgrade-release-tools.yaml`, and `validate-python-release.yaml`. It is empty by
-default. When set, it must be a full 40-character commit SHA, and Nab is installed from
-`git+https://github.com/notatallshaw/nab@<sha>` instead of the release. That commit gets no cooldown: `exclude-newer`
-applies only to its dependencies. It exists until a Nab release carries the needed fix and will be removed then.
+default. When set, it must be a full 40-character commit SHA, and the whole Nab workspace is installed from
+`git+https://github.com/notatallshaw/nab@<sha>` instead of the release: `nab` from the root, and `nab-index`,
+`nab-markersets`, `nab-project`, `nab-provider`, and `nab-resolver` from their `#subdirectory=` paths, because the root
+pins them to an unreleased version. That commit gets no cooldown: `exclude-newer` applies only to its dependencies. It
+exists until a Nab release carries the needed fix and will be removed then.
 
 ## Check pull request news
 
@@ -178,10 +180,12 @@ configurations, which no guard checks. `prepare-towncrier` and `validate-release
 anywhere, a `.pre-commit-config.yml`, and a `.pre-commit-config.yaml` below the root before they run `prek`.
 
 The shared prepare and tagged validator run `refresh-release-lock` in `check` mode before release checks or publishing.
-`check-tagged-source` bundles the tagged checks for a custom tag publisher: it requires `GITHUB_REF` to be the tag of
-the checkout on `main` and checks the locks. It runs no hooks. It takes the secondary lock inputs below and needs a
-full-history checkout. For a secondary Nab lock, pass its path, selected groups, selection type, and matrix inputs to
-both workflows. A stale primary or secondary lock stops the release before artifacts are built.
+`check-tagged-source` bundles the tagged checks for a custom tag publisher: on a tag ref it requires the tag to name
+both `GITHUB_SHA` and the checkout, on `main`, and checks the locks. Any other event, such as a `workflow_dispatch` from
+`main` with a `tag` input, must check out the commit that `inputs.tag` names, on `main`. It runs no hooks. It takes the
+secondary lock inputs below and needs a full-history checkout. For a secondary Nab lock, pass its path, selected groups,
+selection type, and matrix inputs to both workflows. A stale primary or secondary lock stops the release before
+artifacts are built.
 
 For example, a tagged source job that also publishes from a PGO lock checks both files before installing build tools:
 
diff --git a/changelog.d/+dispatch-tag-check.bugfix.md b/changelog.d/+dispatch-tag-check.bugfix.md
new file mode 100644
index 0000000..26536b4
--- /dev/null
+++ b/changelog.d/+dispatch-tag-check.bugfix.md
@@ -0,0 +1,3 @@
+Let `check-tagged-source` accept a `workflow_dispatch` or other non-tag run, such as one from `main` with a `tag` input,
+when the checkout is the commit that tag names and that commit is on `main`. Tag runs still require the tag,
+`GITHUB_SHA`, and the checkout to match.
diff --git a/changelog.d/+nab-workspace.bugfix.md b/changelog.d/+nab-workspace.bugfix.md
new file mode 100644
index 0000000..0413461
--- /dev/null
+++ b/changelog.d/+nab-workspace.bugfix.md
@@ -0,0 +1,2 @@
+Install the whole Nab workspace from the `nab-git-commit` commit: `nab` and its `nab-index`, `nab-markersets`,
+`nab-project`, `nab-provider`, and `nab-resolver` sub-packages, which the root pins to an unreleased version.
diff --git a/check-tagged-source/action.yml b/check-tagged-source/action.yml
index 234505d..b2ad79d 100644
--- a/check-tagged-source/action.yml
+++ b/check-tagged-source/action.yml
@@ -34,13 +34,18 @@ runs:
     - name: Verify the exact release tag
       shell: bash
       env:
-        TAG: ${{ github.ref_name }}
+        TAG: ${{ github.event.inputs.tag || github.ref_name }}
       run: |
         set -euo pipefail
-        test "$GITHUB_REF" = "refs/tags/$TAG"
         git check-ref-format "refs/tags/$TAG"
-        test "$(git rev-parse "refs/tags/$TAG^{commit}")" = "$GITHUB_SHA"
-        test "$GITHUB_SHA" = "$(git rev-parse HEAD)"
+        commit=$(git rev-parse "refs/tags/$TAG^{commit}")
+        if [[ "$GITHUB_REF" == refs/tags/* ]]; then
+          test "$GITHUB_REF" = "refs/tags/$TAG"
+          test "$commit" = "$GITHUB_SHA"
+          test "$GITHUB_SHA" = "$(git rev-parse HEAD)"
+        else
+          test "$commit" = "$(git rev-parse HEAD)"
+        fi
         git merge-base --is-ancestor HEAD origin/main
     - uses: $/refresh-release-lock
       with:
diff --git a/refresh-release-lock/action.yml b/refresh-release-lock/action.yml
index 58c3927..bd47065 100644
--- a/refresh-release-lock/action.yml
+++ b/refresh-release-lock/action.yml
@@ -68,9 +68,15 @@ runs:
         NAB_GIT_COMMIT: ${{ inputs.nab-git-commit }}
       run: |
         set -euo pipefail
-        requirement="nab>=0.0.22"
-        if [[ -n "$NAB_GIT_COMMIT" ]]; then requirement=git+https://github.com/notatallshaw/nab@$NAB_GIT_COMMIT; fi
-        "$GITHUB_ACTION_PATH/../tools/install_live_tools.sh" "$RUNNER_TEMP/lock-tools" "$requirement"
+        requirements=("nab>=0.0.22")
+        if [[ -n "$NAB_GIT_COMMIT" ]]; then
+          source=git+https://github.com/notatallshaw/nab@$NAB_GIT_COMMIT
+          requirements=("nab @ $source")
+          for package in nab-index nab-markersets nab-project nab-provider nab-resolver; do
+            requirements+=("$package @ $source#subdirectory=$package")
+          done
+        fi
+        "$GITHUB_ACTION_PATH/../tools/install_live_tools.sh" "$RUNNER_TEMP/lock-tools" "${requirements[@]}"
     - name: Resolve all project groups and extras
       shell: bash
       env:
diff --git a/tests/refresh_release_lock/test_refresh.py b/tests/refresh_release_lock/test_refresh.py
index 3decc32..436e14c 100644
--- a/tests/refresh_release_lock/test_refresh.py
+++ b/tests/refresh_release_lock/test_refresh.py
@@ -225,15 +225,30 @@ def test_refresh_rejects_invalid_nab_commit(tmp_path: Path, action_scripts: Path
     assert "nab-git-commit must be a full 40-character commit SHA" in result.stderr
 
 
+_NAB_COMMIT: Final = "0123456789abcdef0123456789abcdef01234567"
+_NAB_SOURCE: Final = f"git+https://github.com/notatallshaw/nab@{_NAB_COMMIT}"
+
+
 @pytest.mark.parametrize(
-    ("commit", "requirement"),
+    ("commit", "requirements"),
     [
-        pytest.param("", "nab>=0.0.22", id="release"),
-        pytest.param("0123456789abcdef0123456789abcdef01234567", None, id="git-commit"),
+        pytest.param("", ["nab>=0.0.22"], id="release"),
+        pytest.param(
+            _NAB_COMMIT,
+            [
+                f"nab @ {_NAB_SOURCE}",
+                f"nab-index @ {_NAB_SOURCE}#subdirectory=nab-index",
+                f"nab-markersets @ {_NAB_SOURCE}#subdirectory=nab-markersets",
+                f"nab-project @ {_NAB_SOURCE}#subdirectory=nab-project",
+                f"nab-provider @ {_NAB_SOURCE}#subdirectory=nab-provider",
+                f"nab-resolver @ {_NAB_SOURCE}#subdirectory=nab-resolver",
+            ],
+            id="git-commit-workspace",
+        ),
     ],
 )
 def test_refresh_installs_selected_nab(
-    tmp_path: Path, action_scripts: Path, commit: str, requirement: str | None
+    tmp_path: Path, action_scripts: Path, commit: str, requirements: list[str]
 ) -> None:
     installer = tmp_path / "tools/install_live_tools.sh"
     installer.parent.mkdir()
@@ -251,10 +266,7 @@ def test_refresh_installs_selected_nab(
     )
 
     assert result.returncode == 0, result.stderr
-    assert (tmp_path / "installed").read_text().splitlines() == [
-        f"{tmp_path}/lock-tools",
-        requirement or f"git+https://github.com/notatallshaw/nab@{commit}",
-    ]
+    assert (tmp_path / "installed").read_text().splitlines() == [f"{tmp_path}/lock-tools", *requirements]
 
 
 @pytest.mark.parametrize(
diff --git a/tests/validate_python_release/test_tagged.py b/tests/validate_python_release/test_tagged.py
index a325176..c04dddf 100644
--- a/tests/validate_python_release/test_tagged.py
+++ b/tests/validate_python_release/test_tagged.py
@@ -120,7 +120,6 @@ def test_validator_rejects_backend_hash_mismatch(
     [
         pytest.param("lightweight", "refs/tags/0.2.0", True, id="lightweight-tag"),
         pytest.param("annotated", "refs/tags/0.2.0", True, id="annotated-tag"),
-        pytest.param("lightweight", "refs/heads/0.2.0", False, id="branch-event-on-tagged-commit"),
         pytest.param("branch", "refs/tags/0.2.0", False, id="same-name-branch"),
         pytest.param("off-main", "refs/tags/0.2.0", False, id="tagged-off-main-commit"),
     ],
@@ -163,6 +162,55 @@ def test_validator_requires_exact_tag(
     assert (result.returncode == 0) is accepted, result.stderr
 
 
+@pytest.mark.parametrize(
+    ("location", "accepted"),
+    [
+        pytest.param("check-tagged-source/action.yml", True, id="source-check"),
+        pytest.param("validate-python-release:build", False, id="build"),
+        pytest.param("release:source", False, id="self-release"),
+    ],
+)
+def test_validator_branch_event_on_tagged_commit(repository: Path, location: str, *, accepted: bool) -> None:
+    run(repository, "git", "tag", "0.2.0")
+
+    result = _run_tag_check(repository, location, "refs/heads/main", run(repository, "git", "rev-parse", "HEAD").stdout)
+
+    assert (result.returncode == 0) is accepted, result.stderr
+
+
+def test_source_check_rejects_dispatch_off_the_tag(repository: Path) -> None:
+    run(repository, "git", "tag", "0.2.0")
+    run(repository, "git", "commit", "--allow-empty", "-m", "Later change")
+    run(repository, "git", "push", "origin", "main")
+
+    result = _run_tag_check(
+        repository,
+        "check-tagged-source/action.yml",
+        "refs/heads/main",
+        run(repository, "git", "rev-parse", "HEAD").stdout,
+    )
+
+    assert result.returncode != 0
+
+
+def test_source_check_reads_the_dispatched_tag() -> None:
+    assert (
+        _tag_check("check-tagged-source/action.yml")["env"]["TAG"]
+        == "${{ github.event.inputs.tag || github.ref_name }}"
+    )
+
+
+def _run_tag_check(repository: Path, location: str, event_ref: str, event_sha: str) -> subprocess.CompletedProcess[str]:
+    return subprocess.run(
+        ["bash", "-c", _tag_check(location)["run"]],
+        cwd=repository,
+        env=os.environ | {"GITHUB_REF": event_ref, "TAG": "0.2.0", "GITHUB_SHA": event_sha.strip()},
+        text=True,
+        capture_output=True,
+        check=False,
+    )
+
+
 @pytest.mark.parametrize(
     ("tag", "filenames", "accepted"),
     [
@@ -225,11 +273,11 @@ def test_validator_requires_tag_at_the_event_commit(repository: Path, location:
     assert result.returncode != 0
 
 
-def _tag_check(location: str) -> dict[str, str]:
+def _tag_check(location: str) -> dict[str, Any]:
     root = Path(__file__).resolve().parents[2]
     if location.endswith(".yml"):
         steps = yaml.safe_load((root / location).read_text())["runs"]["steps"]
     else:
         workflow, job = location.split(":")
         steps = yaml.safe_load((root / ".github/workflows" / f"{workflow}.yaml").read_text())["jobs"][job]["steps"]
-    return cast("dict[str, str]", next(step for step in steps if step.get("name") == "Verify the exact release tag"))
+    return cast("dict[str, Any]", next(step for step in steps if step.get("name") == "Verify the exact release tag"))