diff --git a/bzl/bundle_rules.bzl b/bzl/bundle_rules.bzl
index 737dc62f0..ef55ed3df 100644
--- a/bzl/bundle_rules.bzl
+++ b/bzl/bundle_rules.bzl
@@ -64,10 +64,12 @@ DocsBundleInfo = provider(
         "entries": "Ordered entries, one per source directory, including its final documentation-tree location.",
         "own_source_files": "This bundle's direct source files, excluding nested bundles.",
         "sourcelinks": "Source-code-link JSON files together with their owning repository.",
-        "external_runfiles": "Documentation source files not read from the workspace at runtime.",
-        # Bundle-owned supporting/runtime files. Unlike host-owned docs data,
-        # these are resolved at this bundle's mount.
-        "data": "Bundle-owned supporting/runtime files resolved at the bundle's mount.",
+        "external_runfiles": "Documentation source files from external repositories needed in runfiles.",
+        # Bundle-owned generated/supporting files. Both bundle data and
+        # docs(data = [...]) are build inputs; unlike host-owned docs data,
+        # these are resolved at this bundle's mount (for example, a generated
+        # index.rst).
+        "data": "Bundle-owned generated/supporting files resolved at the bundle's mount.",
     },
 )
 
@@ -488,12 +490,13 @@ _bundle_source_files = rule(
     doc = "Exposes direct bundle sources without nested bundle sources.",
 )
 
-def bundle_source_files(name, bundle, visibility = None):
+def bundle_source_files(name, bundle, visibility = None, tags = None):
     """Create a target containing only the direct sources of a bundle."""
     _bundle_source_files(
         name = name,
         bundle = bundle,
         visibility = visibility,
+        tags = tags,
     )
     return ":" + name
 
diff --git a/default_conf.py.tpl b/default_conf.py.tpl
index d7455cbb2..026d84720 100644
--- a/default_conf.py.tpl
+++ b/default_conf.py.tpl
@@ -10,13 +10,17 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 # *******************************************************************************
-# Default Sphinx configuration emitted by the ``docs()`` macro.
+# Default Sphinx configuration emitted by the ``docs()`` and
+# ``docs_bundle()`` macros.
 # SCORE Docs-as-Code owns these baseline settings.  Projects needing further
 # Sphinx configuration can provide their own conf.py instead.
 
 project = {PROJECT}
 project_url = {PROJECT_URL}
 version = "0.0.0"
+# ``docs_bundle(entry_doc = ...)`` may use a non-index entry page. The regular
+# project-level docs() build uses the default value, ``index``.
+master_doc = {ENTRY_DOC}
 
 # Allow feature IDs that use the Bazel module name without its first
 # underscore-separated prefix (for example, ``score_docs_as_code`` becomes
diff --git a/docs.bzl b/docs.bzl
index 46cb7622d..8c1f0d39e 100644
--- a/docs.bzl
+++ b/docs.bzl
@@ -11,8 +11,15 @@
 # SPDX-License-Identifier: Apache-2.0
 # *******************************************************************************
 
-"""
-Easy streamlined way for S-CORE docs-as-code.
+"""Public Bazel macros for building and composing S-CORE documentation.
+
+The ``docs_bundle`` macro describes which documentation files belong to a
+reusable bundle and how nested bundles are composed. Source-bearing bundles
+also create a ``<name>.__internal__.needs_local`` export containing Needs from
+their own sources. This first version only supports self-contained bundles;
+references to Needs defined outside the bundle remain unresolved until
+cross-bundle imports are added. The top-level ``docs`` macro continues to use
+its existing project-wide ``needs_json`` export.
 """
 
 # Multiple approaches are available to build the same documentation output:
@@ -74,7 +81,16 @@ def _module_name_without_prefix():
         return ""
     return module_name.split("_", 1)[-1]
 
+def _bundle_internal_target(name, target):
+    """Return the conventional name for a target internal to a bundle."""
+    return name + ".__internal__." + target
+
 def _generated_conf_impl(ctx):
+    """Generate a Sphinx config at the source-root path expected by sphinxdocs.
+
+    ``entry_doc`` determines which document Sphinx treats as the project root
+    when a bundle's entry page is not named ``index``.
+    """
     output = ctx.actions.declare_file(ctx.attr.output_path)
     ctx.actions.expand_template(
         template = ctx.file.template,
@@ -83,6 +99,7 @@ def _generated_conf_impl(ctx):
             "{PROJECT}": repr(ctx.attr.project),
             "{PROJECT_URL}": repr(ctx.attr.project_url),
             "{REQUIRED_IN_ID}": repr([ctx.attr.required_in_id]) if ctx.attr.required_in_id else "[]",
+            "{ENTRY_DOC}": repr(ctx.attr.entry_doc),
         },
     )
     return [DefaultInfo(files = depset([output]))]
@@ -93,6 +110,7 @@ _generated_conf = rule(
         "project": attr.string(mandatory = True),
         "project_url": attr.string(mandatory = True),
         "required_in_id": attr.string(mandatory = True),
+        "entry_doc": attr.string(default = "index"),
         "output_path": attr.string(mandatory = True),
         "template": attr.label(
             allow_single_file = True,
@@ -114,7 +132,22 @@ def _is_needs_json_target(label):
     """
     return str(label).rsplit(":", 1)[-1] == "needs_json"
 
-def docs_bundle(
+def _bundle_sphinx_strip_prefix(source_dir):
+    """Return the source prefix used by a Sphinx action for this repository."""
+    source_prefix = join_path(native.package_name(), source_dir)
+    repository = native.repo_name()
+    if repository:
+        # External repository files use ``../<canonical-repo>/`` in short_path,
+        # while the main repository uses paths without that leading segment.
+        source_prefix = join_path(
+            "../" + repository,
+            source_prefix,
+        )
+    if source_prefix:
+        source_prefix += "/"
+    return source_prefix
+
+def _declare_docs_bundle(
     name,
     source_dir = None,
     srcs = [],
@@ -125,7 +158,7 @@ def docs_bundle(
     code_targets = [],
     visibility = None,
     **kwargs):
-    """A docs bundle, optionally composed of others.
+    """Declare the reusable bundle and return inputs needed by local exports.
 
     Args:
       name: target name.
@@ -182,7 +215,9 @@ def docs_bundle(
         sourcelinks.append(code_targets_sourcelinks)
 
     # Store the source directory relative to the workspace so bundle consumers
-    # can locate the original files without copying them.
+    # can locate the original files without copying them. The internal rule
+    # keeps this path in its provider; the Needs build below uses the same
+    # source root so docnames and link targets remain stable.
     pkg = native.package_name()
     strip_prefix = join_path(pkg, source_dir) if source_dir != None else ""
 
@@ -212,6 +247,139 @@ def docs_bundle(
         **kwargs
     )
 
+    return struct(
+        source_dir_globbed = source_dir_globbed,
+        sourcelinks = sourcelinks,
+    )
+
+def docs_bundle(
+    name,
+    source_dir = None,
+    srcs = [],
+    data = [],
+    entry_doc = "index",
+    bundles = [],
+    scan_code = [],
+    code_targets = [],
+    visibility = None,
+    **kwargs):
+    """Declare a reusable documentation bundle."""
+    bundle = _declare_docs_bundle(
+        name = name,
+        source_dir = source_dir,
+        srcs = srcs,
+        data = data,
+        entry_doc = entry_doc,
+        bundles = bundles,
+        scan_code = scan_code,
+        code_targets = code_targets,
+        visibility = visibility,
+        **kwargs
+    )
+    source_dir_globbed = bundle.source_dir_globbed
+    sourcelinks = bundle.sourcelinks
+
+    if source_dir_globbed or srcs:
+        # ``bundle_source_files`` is important here: using the complete bundle
+        # would also feed nested child sources into this Sphinx invocation and
+        # export their Needs under the parent's local target. Ownership stays
+        # one-way: every source-bearing bundle exports only its own sources.
+        own_sources = bundle_source_files(
+            name = _bundle_internal_target(name, "needs_sources"),
+            bundle = ":" + name,
+            visibility = visibility,
+            tags = ["manual"],
+        )
+
+        # Sphinx expects conf.py below the source root. Prefer a caller-provided
+        # config, and otherwise generate the same default config used by docs().
+        config_file_path = join_path(source_dir, "conf.py")
+        if native.glob([config_file_path], allow_empty = True):
+            needs_config = ":" + config_file_path
+        else:
+            needs_config = ":" + _bundle_internal_target(name, "needs_conf")
+            _generated_conf(
+                name = _bundle_internal_target(name, "needs_conf"),
+                project = name,
+                project_url = "",
+                required_in_id = "",
+                entry_doc = entry_doc,
+                output_path = config_file_path,
+                tags = ["manual"],
+            )
+
+        # A Needs export also carries source-code-link metadata. Reuse the
+        # bundle's existing link file when there is one; create an empty file
+        # for the common no-code-target case; and merge multiple files when
+        # both deprecated scan_code and code_targets contributed inputs.
+        if len(sourcelinks) == 0:
+            needs_sourcelinks = ":" + _bundle_internal_target(name, "needs_sourcelinks_json")
+            _sourcelinks_json(
+                name = _bundle_internal_target(name, "needs_sourcelinks_json"),
+                srcs = [],
+            )
+        elif len(sourcelinks) == 1:
+            needs_sourcelinks = sourcelinks[0]
+        else:
+            needs_sourcelinks_name = _bundle_internal_target(name, "needs_sourcelinks_json")
+            merge_bundle_sourcelinks(
+                name = needs_sourcelinks_name,
+                bundle = ":" + name,
+                visibility = visibility,
+            )
+            needs_sourcelinks = ":" + needs_sourcelinks_name
+
+        # This is the Sphinx executable used by the action below. The extension
+        # and PlantUML helper are explicit because a bundle-local export is a
+        # standalone Sphinx invocation, not the host docs() invocation.
+        needs_deps = all_requirements + [
+            Label("//src:plantuml_for_python"),
+            Label("//src/extensions/score_sphinx_bundle:score_sphinx_bundle"),
+        ]
+        needs_sphinx_build = _bundle_internal_target(name, "needs_sphinx_build")
+        sphinx_build_binary(
+            name = needs_sphinx_build,
+            deps = needs_deps,
+            visibility = visibility,
+            tags = ["manual"],
+        )
+
+        source_strip_prefix = _bundle_sphinx_strip_prefix(source_dir)
+
+        # The source files are declared with their workspace-relative paths,
+        # while sphinxdocs expects the prefix to remove from those paths before
+        # placing them below the temporary Sphinx source root.
+        #
+        # Build the own export from this bundle's sources only. References to
+        # Needs owned by another bundle are intentionally unsupported until
+        # cross-bundle imports are added.
+        needs_local = _bundle_internal_target(name, "needs_local")
+        sphinx_docs(
+            name = needs_local,
+            srcs = [own_sources],
+            config = needs_config,
+            # ``sphinxdocs`` removes this string literally from short_path.
+            # Keep the separator so a source_dir/conf.py is relocated as
+            # conf.py rather than /conf.py.
+            strip_prefix = source_strip_prefix,
+            extra_opts = [
+                "-W",
+                "--keep-going",
+                "-T",
+                "--define=score_bundle_needs_export=1",
+                # Prevent the non-Bazel fallback query from importing the
+                # host project's external Needs into this standalone export.
+                "--define=external_needs_source=[]",
+                "--define=score_sourcelinks_json=$(location " + str(needs_sourcelinks) + ")",
+            ],
+            formats = ["needs"],
+            sphinx = ":" + needs_sphinx_build,
+            tools = [needs_sourcelinks],
+            visibility = visibility,
+            allow_persistent_workers = False,
+            tags = ["manual"],
+        )
+
 def _missing_requirements(deps):
     """Add Python hub dependencies if they are missing."""
     found = []
@@ -381,7 +549,7 @@ def docs(
 
     # The public bundle carries both the complete source tree and the
     # transitive source-code links of every nested bundle.
-    docs_bundle(
+    _declare_docs_bundle(
         name = "docs_bundle",
         source_dir = source_dir,
         data = data,
diff --git a/docs/reference/bazel_macros.rst b/docs/reference/bazel_macros.rst
index 9459c5c6f..642a27e6e 100644
--- a/docs/reference/bazel_macros.rst
+++ b/docs/reference/bazel_macros.rst
@@ -216,6 +216,14 @@ Signature: ``docs_bundle(name, source_dir = None, srcs = [], data = [], entry_do
   error. See :ref:`howto_mount_external_sources` for a worked example and
   :ref:`docs_concept_mounts` for the composition and transitivity semantics.
 
+- ``needs_local`` (internal target)
+  A source-bearing bundle creates ``<name>.__internal__.needs_local`` with the
+  Needs declared by its own sources. The standalone build is intentionally
+  self-contained in this version: references to Needs defined outside the
+  bundle remain unresolved and fail strict builds. Cross-bundle imports and
+  merged exports are planned for a later change. Data-only bundles do not
+  create a Needs target.
+
 .. note::
 
    A bundle is **placement-free**: its ``mount_at`` and ``attach_to`` are assigned
diff --git a/src/extensions/score_metamodel/__init__.py b/src/extensions/score_metamodel/__init__.py
index 01c788293..44c038ade 100644
--- a/src/extensions/score_metamodel/__init__.py
+++ b/src/extensions/score_metamodel/__init__.py
@@ -243,6 +243,7 @@ def _clear_needs_defaults(app: Sphinx):
 
 def setup(app: Sphinx) -> dict[str, str | bool]:
     app.add_config_value("external_needs_source", "", rebuild="env")
+    app.add_config_value("score_bundle_needs_export", False, rebuild="env")
     app.add_config_value("score_metamodel_yaml", "", rebuild="env")
     app.add_config_value("required_in_id", [], rebuild="env")
     config_setdefault(app.config, "needs_id_required", True)
diff --git a/src/extensions/score_metamodel/external_needs.py b/src/extensions/score_metamodel/external_needs.py
index 51f927a21..22588ca44 100644
--- a/src/extensions/score_metamodel/external_needs.py
+++ b/src/extensions/score_metamodel/external_needs.py
@@ -130,30 +130,39 @@ def parse_external_needs_sources_from_bazel_query() -> list[ExternalNeedsSource]
     return res
 
 
-def extend_needs_json_exporter(config: Config, params: list[str]) -> None:
+def register_project_url_export(
+    config: Config,
+    *,
+    exported_project_url: str | None = None,
+) -> None:
+    """Add ``project_url`` to the Needs JSON export.
+
+    By default, the value comes from the Sphinx configuration and an empty
+    value is reported as a configuration error. ``exported_project_url`` is an
+    explicit replacement for the JSON value; supplying it also makes an empty
+    replacement valid without changing the active Sphinx configuration.
     """
-    This will add each param to app.config as a config value.
-    Then it will overwrite the needs.json exporter to include these values.
-    """
-
-    for p in params:
-        # Note: we are currently addinig these values to config after config-inited.
-        # This is wrong. But good enough.
-        config.add(p, default="", rebuild="env", types=(), description="")
+    # ``project_url`` is a SCORE-specific configuration value, so register it
+    # before accessing it. This currently happens during ``config-inited``;
+    # moving the declaration into extension setup is a separate cleanup.
+    config.add("project_url", default="", rebuild="env", types=(), description="")
+    configured_project_url = config.project_url
+    if exported_project_url is None and not configured_project_url:
+        logger.error(
+            "Config value 'project_url' is not set. "
+            + "Please set it in your Sphinx config."
+        )
 
-        if not getattr(config, p):
-            logger.error(
-                f"Config value '{p}' is not set. "
-                + "Please set it in your Sphinx config."
-            )
+    project_url = (
+        configured_project_url if exported_project_url is None else exported_project_url
+    )
 
-    # Patch json exporter to include our custom fields
-    # Note: yeah, NeedsList is the json exporter!
+    # Patch json exporter to include our custom field.
+    # Note: ``NeedsList`` is the sphinx-needs JSON exporter.
     orig_function = NeedsList._finalise  # pyright: ignore[reportPrivateUsage]
 
     def temp(self: NeedsList):
-        for p in params:
-            self.needs_list[p] = getattr(config, p)  # pyright: ignore[reportUnknownMemberType]
+        self.needs_list["project_url"] = project_url
 
         orig_function(self)
 
@@ -228,7 +237,12 @@ def add_external_docs_sources(e: ExternalNeedsSource, config: Config):
 
 
 def connect_external_needs(app: Sphinx, config: Config):
-    extend_needs_json_exporter(config, ["project_url"])
+    # Bundle-local exports intentionally leave project_url empty, while host
+    # builds retain the existing missing-value diagnostic.
+    register_project_url_export(
+        config,
+        exported_project_url="" if config.score_bundle_needs_export else None,
+    )
 
     # Local external needs from DATA (e.g. :needs_json or :docs_sources)
     external_needs = get_external_needs_source(app.config.external_needs_source)
diff --git a/src/extensions/score_metamodel/tests/test_external_needs.py b/src/extensions/score_metamodel/tests/test_external_needs.py
index 5c8929b41..59ec1d426 100644
--- a/src/extensions/score_metamodel/tests/test_external_needs.py
+++ b/src/extensions/score_metamodel/tests/test_external_needs.py
@@ -19,6 +19,8 @@
 
 import json
 from pathlib import Path
+from types import SimpleNamespace
+from typing import cast
 
 import pytest
 import score_metamodel.external_needs as ext_needs
@@ -30,7 +32,91 @@
     get_external_needs_source,
     parse_external_needs_sources_from_DATA,
 )
+from sphinx.application import Sphinx
 from sphinx.config import Config
+from sphinx_needs.needsfile import NeedsList
+
+
+def test_register_project_url_export_reports_missing_config(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """The host export reports a missing project URL as a configuration error."""
+    errors: list[str] = []
+    monkeypatch.setattr(NeedsList, "_finalise", lambda _needs_list: None)
+    monkeypatch.setattr(ext_needs.logger, "error", errors.append)
+
+    ext_needs.register_project_url_export(Config())
+
+    assert errors == [
+        "Config value 'project_url' is not set. Please set it in your Sphinx config."
+    ]
+
+
+def test_register_project_url_export_uses_configured_value(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """The host export writes the configured project URL to the JSON document."""
+    config = Config()
+    config.project_url = "https://example.test/host"
+
+    monkeypatch.setattr(NeedsList, "_finalise", lambda _needs_list: None)
+    ext_needs.register_project_url_export(config)
+
+    needs_list = cast(NeedsList, SimpleNamespace(needs_list={}))
+    NeedsList._finalise(needs_list)  # pyright: ignore[reportPrivateUsage] - white-box test
+
+    assert needs_list.needs_list["project_url"] == "https://example.test/host"
+
+
+def test_register_project_url_export_can_override_exported_value(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """An export override does not mutate the active Sphinx configuration."""
+    config = Config()
+    config.project_url = "https://example.test/host"
+
+    def no_op_finalise(_needs_list: NeedsList) -> None:
+        pass
+
+    monkeypatch.setattr(NeedsList, "_finalise", no_op_finalise)
+    ext_needs.register_project_url_export(config, exported_project_url="")
+
+    needs_list = cast(NeedsList, SimpleNamespace(needs_list={}))
+    NeedsList._finalise(needs_list)  # pyright: ignore[reportPrivateUsage] - white-box test
+
+    assert needs_list.needs_list["project_url"] == ""
+    assert config.project_url == "https://example.test/host"
+
+
+@pytest.mark.parametrize(
+    ("bundle_needs_export", "exported_project_url"),
+    [(False, None), (True, "")],
+)
+def test_connect_external_needs_selects_project_url_export_mode(
+    monkeypatch: pytest.MonkeyPatch,
+    bundle_needs_export: bool,
+    exported_project_url: str | None,
+) -> None:
+    """Only bundle-local exports replace the project URL in the JSON output."""
+    observed: list[str | None] = []
+
+    def record_exporter_call(
+        _config: Config,
+        *,
+        exported_project_url: str | None,
+    ) -> None:
+        observed.append(exported_project_url)
+
+    monkeypatch.setattr(ext_needs, "register_project_url_export", record_exporter_call)
+
+    config = Config()
+    config.external_needs_source = "[]"
+    config.score_bundle_needs_export = bundle_needs_export
+    ext_needs.connect_external_needs(
+        cast(Sphinx, SimpleNamespace(config=config)), config
+    )
+
+    assert observed == [exported_project_url]
 
 
 def test_empty_list():
diff --git a/src/tests/docs_bzl/README.md b/src/tests/docs_bzl/README.md
index 78a846b18..21ae04e6b 100644
--- a/src/tests/docs_bzl/README.md
+++ b/src/tests/docs_bzl/README.md
@@ -23,7 +23,8 @@ docs_bzl/
 │   ├── subdirectory_bundle/
 │   ├── external_bundle/
 │   ├── local_version_mismatch/
-│   └── invalid_bundle_placements/
+│   ├── invalid_bundle_placements/
+│   └── upward_bundles/
 └── test_<scenario>.py
 ```
 
@@ -36,6 +37,12 @@ The cross-module compatibility test creates its consumer in a temporary
 workspace, so this repository's production ``MODULE.bazel`` stays free of test
 dependencies while the test still traverses real Bzlmod module boundaries.
 
+The ``upward_bundles`` scenario is a rough specification for cross-bundle Needs
+propagation: local exports remain limited to a bundle's own sources, while a
+separate upward export merges explicitly declared direct ancestors. It also
+covers source-less ancestors and the rule that undeclared transitive ancestors
+are not inherited.
+
 Note that these tests run `bazel` commands, so they are slow. They need to be executed
 sequentially. Use sparingly. They do not call `bazel clean`, so the persistent
 Bazel server and its action, repository, and disk caches are reused between
diff --git a/src/tests/docs_bzl/scenarios/local_bundle/BUILD b/src/tests/docs_bzl/scenarios/local_bundle/BUILD
new file mode 100644
index 000000000..eacb95077
--- /dev/null
+++ b/src/tests/docs_bzl/scenarios/local_bundle/BUILD
@@ -0,0 +1,22 @@
+# *******************************************************************************
+# Copyright (c) 2026 Contributors to the Eclipse Foundation
+#
+# See the NOTICE file(s) distributed with this work for additional
+# information regarding copyright ownership.
+#
+# This program and the accompanying materials are made available under the
+# terms of the Apache License 2.0 which is available at
+# https://www.apache.org/licenses/LICENSE-2.0
+#
+# SPDX-License-Identifier: Apache-2.0
+# *******************************************************************************
+
+load("//:docs.bzl", "docs_bundle")
+
+# A source-bearing bundle exports the Needs declared by its own documentation
+# through the internal ``needs_local`` target. This fixture deliberately has no
+# cross-bundle references; those are handled by a later hierarchy change.
+docs_bundle(
+    name = "platform",
+    source_dir = "platform",
+)
diff --git a/src/tests/docs_bzl/scenarios/local_bundle/platform/conf.py b/src/tests/docs_bzl/scenarios/local_bundle/platform/conf.py
new file mode 100644
index 000000000..eaedf413a
--- /dev/null
+++ b/src/tests/docs_bzl/scenarios/local_bundle/platform/conf.py
@@ -0,0 +1,17 @@
+# *******************************************************************************
+# Copyright (c) 2026 Contributors to the Eclipse Foundation
+#
+# See the NOTICE file(s) distributed with this work for additional
+# information regarding copyright ownership.
+#
+# This program and the accompanying materials are made available under the
+# terms of the Apache License 2.0 which is available at
+# https://www.apache.org/licenses/LICENSE-2.0
+#
+# SPDX-License-Identifier: Apache-2.0
+# *******************************************************************************
+
+project = "Platform bundle"
+version = "main"
+extensions = ["score_sphinx_bundle"]
+required_in_id = ["platform"]
diff --git a/src/tests/docs_bzl/scenarios/local_bundle/platform/index.rst b/src/tests/docs_bzl/scenarios/local_bundle/platform/index.rst
new file mode 100644
index 000000000..aeae38a58
--- /dev/null
+++ b/src/tests/docs_bzl/scenarios/local_bundle/platform/index.rst
@@ -0,0 +1,35 @@
+..
+   # *******************************************************************************
+   # Copyright (c) 2026 Contributors to the Eclipse Foundation
+   #
+   # See the NOTICE file(s) distributed with this work for additional
+   # information regarding copyright ownership.
+   #
+   # This program and the accompanying materials are made available under the
+   # terms of the Apache License 2.0 which is available at
+   # https://www.apache.org/licenses/LICENSE-2.0
+   #
+   # SPDX-License-Identifier: Apache-2.0
+   # *******************************************************************************
+
+Platform
+========
+
+.. feat:: Platform seat heating
+   :id: feat__platform_seat_heating
+   :version: 1
+   :security: NO
+   :safety: QM
+   :status: valid
+
+.. feat_req:: Platform seat heating availability
+   :id: feat_req__platform__seat_heating
+   :version: 1
+   :reqtype: Functional
+   :security: NO
+   :safety: QM
+   :status: valid
+   :valid_from: v1.0
+   :satisfied_by: feat__platform_seat_heating
+
+   The platform makes the seat heating capability available.
diff --git a/src/tests/docs_bzl/scenarios/upward_bundles/BUILD b/src/tests/docs_bzl/scenarios/upward_bundles/BUILD
new file mode 100644
index 000000000..9ad3139e3
--- /dev/null
+++ b/src/tests/docs_bzl/scenarios/upward_bundles/BUILD
@@ -0,0 +1,42 @@
+# *******************************************************************************
+# Copyright (c) 2026 Contributors to the Eclipse Foundation
+#
+# See the NOTICE file(s) distributed with this work for additional
+# information regarding copyright ownership.
+#
+# This program and the accompanying materials are made available under the
+# terms of the Apache License 2.0 which is available at
+# https://www.apache.org/licenses/LICENSE-2.0
+#
+# SPDX-License-Identifier: Apache-2.0
+# *******************************************************************************
+
+load("//:docs.bzl", "docs_bundle")
+
+# This scenario specifies the intended split between a bundle's own Needs and
+# the Needs inherited from explicitly declared direct ancestors. It is a rough
+# draft for the later propagation implementation.
+docs_bundle(
+    name = "platform",
+    source_dir = "platform",
+)
+
+docs_bundle(
+    name = "component",
+    source_dir = "component",
+    # Expected future API: make the platform export available as direct
+    # resolution context and merge it into component's upward export.
+    upward_bundles = ["platform"],
+)
+
+docs_bundle(
+    name = "application",
+    # Declaring only component must not implicitly include platform.
+    upward_bundles = ["component"],
+)
+
+# A source-less hierarchy group must not be accepted as a direct Needs ancestor.
+docs_bundle(
+    name = "invalid_child",
+    upward_bundles = ["application"],
+)
diff --git a/src/tests/docs_bzl/scenarios/upward_bundles/component/conf.py b/src/tests/docs_bzl/scenarios/upward_bundles/component/conf.py
new file mode 100644
index 000000000..918b8540e
--- /dev/null
+++ b/src/tests/docs_bzl/scenarios/upward_bundles/component/conf.py
@@ -0,0 +1,17 @@
+# *******************************************************************************
+# Copyright (c) 2026 Contributors to the Eclipse Foundation
+#
+# See the NOTICE file(s) distributed with this work for additional
+# information regarding copyright ownership.
+#
+# This program and the accompanying materials are made available under the
+# terms of the Apache License 2.0 which is available at
+# https://www.apache.org/licenses/LICENSE-2.0
+#
+# SPDX-License-Identifier: Apache-2.0
+# *******************************************************************************
+
+project = "Component bundle"
+version = "main"
+extensions = ["score_sphinx_bundle"]
+required_in_id = ["component"]
diff --git a/src/tests/docs_bzl/scenarios/upward_bundles/component/index.rst b/src/tests/docs_bzl/scenarios/upward_bundles/component/index.rst
new file mode 100644
index 000000000..3c1666f7e
--- /dev/null
+++ b/src/tests/docs_bzl/scenarios/upward_bundles/component/index.rst
@@ -0,0 +1,36 @@
+..
+   # *******************************************************************************
+   # Copyright (c) 2026 Contributors to the Eclipse Foundation
+   #
+   # See the NOTICE file(s) distributed with this work for additional
+   # information regarding copyright ownership.
+   #
+   # This program and the accompanying materials are made available under the
+   # terms of the Apache License 2.0 which is available at
+   # https://www.apache.org/licenses/LICENSE-2.0
+   #
+   # SPDX-License-Identifier: Apache-2.0
+   # *******************************************************************************
+
+Component
+=========
+
+.. comp:: Seat heating controller
+   :id: comp__component_seat_heating_controller
+   :version: 1
+   :security: NO
+   :safety: QM
+   :status: valid
+   :belongs_to: feat__platform_seat_heating
+
+.. comp_req:: Controller temperature control
+   :id: comp_req__component__temperature_control
+   :version: 1
+   :reqtype: Functional
+   :security: NO
+   :safety: QM
+   :status: valid
+   :derived_from: feat_req__platform__seat_heating
+   :satisfied_by: comp__component_seat_heating_controller
+
+   The controller regulates the requested heating level.
diff --git a/src/tests/docs_bzl/scenarios/upward_bundles/platform/conf.py b/src/tests/docs_bzl/scenarios/upward_bundles/platform/conf.py
new file mode 100644
index 000000000..eaedf413a
--- /dev/null
+++ b/src/tests/docs_bzl/scenarios/upward_bundles/platform/conf.py
@@ -0,0 +1,17 @@
+# *******************************************************************************
+# Copyright (c) 2026 Contributors to the Eclipse Foundation
+#
+# See the NOTICE file(s) distributed with this work for additional
+# information regarding copyright ownership.
+#
+# This program and the accompanying materials are made available under the
+# terms of the Apache License 2.0 which is available at
+# https://www.apache.org/licenses/LICENSE-2.0
+#
+# SPDX-License-Identifier: Apache-2.0
+# *******************************************************************************
+
+project = "Platform bundle"
+version = "main"
+extensions = ["score_sphinx_bundle"]
+required_in_id = ["platform"]
diff --git a/src/tests/docs_bzl/scenarios/upward_bundles/platform/index.rst b/src/tests/docs_bzl/scenarios/upward_bundles/platform/index.rst
new file mode 100644
index 000000000..aeae38a58
--- /dev/null
+++ b/src/tests/docs_bzl/scenarios/upward_bundles/platform/index.rst
@@ -0,0 +1,35 @@
+..
+   # *******************************************************************************
+   # Copyright (c) 2026 Contributors to the Eclipse Foundation
+   #
+   # See the NOTICE file(s) distributed with this work for additional
+   # information regarding copyright ownership.
+   #
+   # This program and the accompanying materials are made available under the
+   # terms of the Apache License 2.0 which is available at
+   # https://www.apache.org/licenses/LICENSE-2.0
+   #
+   # SPDX-License-Identifier: Apache-2.0
+   # *******************************************************************************
+
+Platform
+========
+
+.. feat:: Platform seat heating
+   :id: feat__platform_seat_heating
+   :version: 1
+   :security: NO
+   :safety: QM
+   :status: valid
+
+.. feat_req:: Platform seat heating availability
+   :id: feat_req__platform__seat_heating
+   :version: 1
+   :reqtype: Functional
+   :security: NO
+   :safety: QM
+   :status: valid
+   :valid_from: v1.0
+   :satisfied_by: feat__platform_seat_heating
+
+   The platform makes the seat heating capability available.
diff --git a/src/tests/docs_bzl/test_local_bundle.py b/src/tests/docs_bzl/test_local_bundle.py
new file mode 100644
index 000000000..a78dc9557
--- /dev/null
+++ b/src/tests/docs_bzl/test_local_bundle.py
@@ -0,0 +1,32 @@
+# *******************************************************************************
+# Copyright (c) 2026 Contributors to the Eclipse Foundation
+#
+# See the NOTICE file(s) distributed with this work for additional
+# information regarding copyright ownership.
+#
+# This program and the accompanying materials are made available under the
+# terms of the Apache License 2.0 which is available at
+# https://www.apache.org/licenses/LICENSE-2.0
+#
+# SPDX-License-Identifier: Apache-2.0
+# *******************************************************************************
+"""Focused tests for source-bearing docs_bundle Needs exports."""
+
+from src.tests.docs_bzl.helpers import built_output, load_needs, run_scenario
+
+
+def test_source_bundle_exports_its_own_needs():
+    """A local export contains the Needs declared by the bundle's own sources."""
+    run_scenario("build", "local_bundle", ":platform.__internal__.needs_local")
+
+    needs = load_needs(
+        built_output(
+            "scenarios/local_bundle",
+            "platform.__internal__.needs_local/_build/needs/needs.json",
+        )
+    )
+
+    assert {
+        "feat__platform_seat_heating",
+        "feat_req__platform__seat_heating",
+    } <= needs.keys()
diff --git a/src/tests/docs_bzl/test_upward_bundles.py b/src/tests/docs_bzl/test_upward_bundles.py
new file mode 100644
index 000000000..92403d23f
--- /dev/null
+++ b/src/tests/docs_bzl/test_upward_bundles.py
@@ -0,0 +1,86 @@
+# *******************************************************************************
+# Copyright (c) 2026 Contributors to the Eclipse Foundation
+#
+# See the NOTICE file(s) distributed with this work for additional
+# information regarding copyright ownership.
+#
+# This program and the accompanying materials are made available under the
+# terms of the Apache License 2.0 which is available at
+# https://www.apache.org/licenses/LICENSE-2.0
+#
+# SPDX-License-Identifier: Apache-2.0
+# *******************************************************************************
+"""Rough specification tests for cross-bundle Needs propagation."""
+
+from src.tests.docs_bzl.helpers import built_output, load_needs, run_bazel, run_scenario
+
+
+def test_source_bundle_exports_own_needs_and_declared_parent_needs():
+    """A local export stays local while an upward export merges direct parents."""
+    run_scenario("build", "upward_bundles", ":component.__internal__.needs_local")
+    run_scenario("build", "upward_bundles", ":component.__internal__.needs_upward")
+
+    local_needs = load_needs(
+        built_output(
+            "scenarios/upward_bundles",
+            "component.__internal__.needs_local/_build/needs/needs.json",
+        )
+    )
+    needs = load_needs(
+        built_output(
+            "scenarios/upward_bundles",
+            "component.__internal__.needs_upward/needs.json",
+        )
+    )
+
+    assert {
+        "comp__component_seat_heating_controller",
+        "comp_req__component__temperature_control",
+    } <= local_needs.keys()
+    assert "feat_req__platform__seat_heating" not in local_needs
+
+    assert {
+        "feat__platform_seat_heating",
+        "feat_req__platform__seat_heating",
+        "comp__component_seat_heating_controller",
+        "comp_req__component__temperature_control",
+    } <= needs.keys()
+
+
+def test_source_less_bundle_does_not_inherit_undeclared_ancestor_needs():
+    """A chain only includes the explicitly declared direct ancestor."""
+    run_scenario("build", "upward_bundles", ":application.__internal__.needs_upward")
+
+    needs = load_needs(
+        built_output(
+            "scenarios/upward_bundles",
+            "application.__internal__.needs_upward/needs.json",
+        )
+    )
+
+    assert "comp__component_seat_heating_controller" in needs
+    assert "feat__platform_seat_heating" not in needs
+
+
+def test_source_less_bundle_is_rejected_as_upward_ancestor():
+    """A source-less hierarchy group cannot provide a direct local export."""
+    result = run_scenario(
+        "build",
+        "upward_bundles",
+        ":invalid_child.__internal__.needs_upward",
+        expect_error=True,
+    )
+
+    assert "has no own documentation sources" in result.stderr
+    assert "would introduce transitive dependencies" in result.stderr
+
+
+def test_data_only_bundle_does_not_get_needs_targets():
+    """Supporting-data bundles remain outside the Needs export hierarchy."""
+    run_bazel(
+        [
+            "query",
+            "//src/tests/docs_bzl/scenarios/data_files_runfiles:legacy_data_bundle.__internal__.needs_local",
+        ],
+        expect_error=True,
+    )