diff --git a/script/helpers.py b/script/helpers.py
index fc2a3607fbd..0086a00e858 100644
--- a/script/helpers.py
+++ b/script/helpers.py
@@ -238,6 +238,72 @@ class _ConflictWalk:
     rejects: set[str]
 
 
+@cache
+def _get_test_config_components(component: str, platform: str) -> frozenset[str]:
+    """Return the components referenced by a component's test config for a platform.
+
+    Loads ``tests/components/<component>/test.<platform>.yaml`` and extracts the
+    top-level component keys (and list ``platform:`` values). This lets the
+    conflict splitter see components that are only pulled in via a test config
+    (e.g. nRF52 ``network`` tests that also enable ``openthread``), which a
+    purely static AUTO_LOAD/CONFLICTS_WITH parse cannot discover -- notably for
+    components like ``api`` whose ``AUTO_LOAD`` is a callable.
+
+    Failures (missing file, parse error) are treated as empty so the splitter
+    never crashes on a malformed or absent test config.
+    """
+    from esphome import yaml_util
+
+    test_file = (
+        Path(root_path) / "tests" / "components" / component / f"test.{platform}.yaml"
+    )
+    if not test_file.exists():
+        return frozenset()
+    try:
+        config = yaml_util.load_yaml(test_file)
+    except Exception:  # noqa: BLE001 - never let a bad test config crash grouping
+        # Matches analyze_component_buses, which loads these same files and
+        # silently tolerates parse failures; surfacing it only here would be
+        # inconsistent and noisy.
+        return frozenset()
+    if not isinstance(config, dict):
+        return frozenset()
+    return frozenset(_extract_components_from_yaml(config))
+
+
+@cache
+def _conflict_walk(comp: str, platform: str) -> _ConflictWalk:
+    """Build the platform-aware conflict walk for a single component.
+
+    Seeds the walk with the component itself plus any components pulled in via
+    its ``test.<platform>.yaml`` config, then folds in each seed's static
+    AUTO_LOAD closure and CONFLICTS_WITH declarations. Cached per
+    ``(component, platform)`` since the test-config seeds are platform-specific.
+    """
+    seeds = {comp} | set(_get_test_config_components(comp, platform))
+    walk = _ConflictWalk(loaded=set(seeds), rejects=set())
+    stack = list(seeds)
+    while stack:
+        metadata = parse_component_metadata(stack.pop())
+        walk.rejects |= metadata.conflicts_with
+        new = metadata.auto_load - walk.loaded
+        walk.loaded |= new
+        stack.extend(new)
+    return walk
+
+
+def components_conflict(a: str, b: str, platform: str) -> bool:
+    """Return True if components ``a`` and ``b`` cannot share a build on ``platform``.
+
+    Uses the same platform-aware conflict walk as :func:`split_conflicting_groups`
+    so callers (e.g. the no-bus redistribution in ``test_build_components.py``)
+    agree with how groups were originally split. The conflict relation is
+    symmetric even when only one side declares CONFLICTS_WITH.
+    """
+    wa, wb = _conflict_walk(a, platform), _conflict_walk(b, platform)
+    return not wa.rejects.isdisjoint(wb.loaded) or not wb.rejects.isdisjoint(wa.loaded)
+
+
 def split_conflicting_groups(
     grouped_components: dict[tuple[str, str], list[str]],
 ) -> dict[tuple[str, str], list[str]]:
@@ -250,33 +316,24 @@ def split_conflicting_groups(
     conflict relation is treated as symmetric even when only one side
     declares it (e.g. ethernet rejects wifi but wifi does not declare the
     reverse).
+
+    The walk is platform-aware: in addition to the static AUTO_LOAD closure,
+    each ``(component, platform)`` walk is seeded with the components found in
+    that component's ``test.<platform>.yaml`` config. This catches conflicts
+    that only exist on a given platform and are expressed through the test
+    config rather than static metadata -- e.g. on nRF52 the ``network``/``api``
+    test configs also enable ``openthread``, which ``zigbee`` declares a
+    conflict with, so ``api`` and ``zigbee`` end up split there. On ESP32 those
+    test configs have no ``openthread``, so the components still group together.
     """
-    batch = {c for comps in grouped_components.values() for c in comps}
-
-    walks: dict[str, _ConflictWalk] = {}
-    for comp in batch:
-        walk = _ConflictWalk(loaded={comp}, rejects=set())
-        stack = [comp]
-        while stack:
-            metadata = parse_component_metadata(stack.pop())
-            walk.rejects |= metadata.conflicts_with
-            new = metadata.auto_load - walk.loaded
-            walk.loaded |= new
-            stack.extend(new)
-        walks[comp] = walk
-
-    def conflicts(a: str, b: str) -> bool:
-        wa, wb = walks[a], walks[b]
-        return not wa.rejects.isdisjoint(wb.loaded) or not wb.rejects.isdisjoint(
-            wa.loaded
-        )
-
     result: dict[tuple[str, str], list[str]] = {}
     for (platform, signature), components in grouped_components.items():
         buckets: list[list[str]] = []
         for comp in components:
             for bucket in buckets:
-                if not any(conflicts(comp, other) for other in bucket):
+                if not any(
+                    components_conflict(comp, other, platform) for other in bucket
+                ):
                     bucket.append(comp)
                     break
             else:
diff --git a/script/test_build_components.py b/script/test_build_components.py
index 651268609e1..ce2a35add35 100755
--- a/script/test_build_components.py
+++ b/script/test_build_components.py
@@ -40,6 +40,7 @@ from script.analyze_component_buses import (
     uses_local_file_references,
 )
 from script.helpers import (
+    components_conflict,
     get_component_test_files,
     is_validate_only_file,
     parse_test_filename,
@@ -788,14 +789,35 @@ def run_grouped_component_tests(
             if plat == platform and sig != NO_BUSES_SIGNATURE
         ]
 
-        if platform_groups:
-            # Distribute no_buses components round-robin across existing groups
-            for i, comp in enumerate(no_buses_comps):
-                sig, _ = platform_groups[i % len(platform_groups)]
-                grouped_components[(platform, sig)].append(comp)
-        else:
-            # No other groups for this platform - keep no_buses components together
-            grouped_components[(platform, NO_BUSES_SIGNATURE)] = no_buses_comps
+        # Distribute no_buses components round-robin across existing groups,
+        # but never place a component into a group it conflicts with. Conflict
+        # splitting (split_conflicting_groups) may have created sibling groups
+        # like "no_buses__conflict1" precisely to keep incompatible components
+        # apart (e.g. on nRF52, network pulls in openthread which zigbee
+        # conflicts with); redistribution must not silently undo that split.
+        leftover: list[str] = []
+        for i, comp in enumerate(no_buses_comps):
+            placed = False
+            # Try groups starting at the round-robin offset to keep the spread.
+            for offset in range(len(platform_groups)):
+                sig, comps = platform_groups[(i + offset) % len(platform_groups)]
+                if any(components_conflict(comp, other, platform) for other in comps):
+                    continue
+                # comps is the same list object stored in grouped_components, so
+                # this also extends the group in grouped_components.
+                comps.append(comp)
+                placed = True
+                break
+            if not placed:
+                leftover.append(comp)
+
+        if leftover:
+            # Components that conflict with every existing group stay together in
+            # their own no_buses group (they were grouped before, so they don't
+            # conflict with each other).
+            grouped_components.setdefault((platform, NO_BUSES_SIGNATURE), []).extend(
+                leftover
+            )
 
     groups_to_test = []
     individual_tests = set()  # Use set to avoid duplicates
diff --git a/tests/components/api/test.nrf52-adafruit.yaml b/tests/components/api/test.nrf52-adafruit.yaml
index 9229d68aa3a..18bf23d7106 100644
--- a/tests/components/api/test.nrf52-adafruit.yaml
+++ b/tests/components/api/test.nrf52-adafruit.yaml
@@ -1,4 +1,7 @@
 network:
   enable_ipv6: true
 
+openthread:
+  tlv: 0E080000000000010000
+
 api:
diff --git a/tests/components/mdns/test.nrf52-adafruit.yaml b/tests/components/mdns/test.nrf52-adafruit.yaml
index 6aff688ff49..c24d0a19087 100644
--- a/tests/components/mdns/test.nrf52-adafruit.yaml
+++ b/tests/components/mdns/test.nrf52-adafruit.yaml
@@ -1,4 +1,7 @@
 network:
   enable_ipv6: true
 
+openthread:
+  tlv: 0E080000000000010000
+
 mdns:
diff --git a/tests/components/network/test.nrf52-adafruit.yaml b/tests/components/network/test.nrf52-adafruit.yaml
index 61889b0361b..ac2fe63739c 100644
--- a/tests/components/network/test.nrf52-adafruit.yaml
+++ b/tests/components/network/test.nrf52-adafruit.yaml
@@ -1 +1,5 @@
 network:
+  enable_ipv6: true
+
+openthread:
+  tlv: 0E080000000000010000
diff --git a/tests/components/network/test.nrf52-mcumgr.yaml b/tests/components/network/test.nrf52-mcumgr.yaml
index 61889b0361b..ac2fe63739c 100644
--- a/tests/components/network/test.nrf52-mcumgr.yaml
+++ b/tests/components/network/test.nrf52-mcumgr.yaml
@@ -1 +1,5 @@
 network:
+  enable_ipv6: true
+
+openthread:
+  tlv: 0E080000000000010000
diff --git a/tests/components/network/test.nrf52-xiao-ble.yaml b/tests/components/network/test.nrf52-xiao-ble.yaml
index 61889b0361b..ac2fe63739c 100644
--- a/tests/components/network/test.nrf52-xiao-ble.yaml
+++ b/tests/components/network/test.nrf52-xiao-ble.yaml
@@ -1 +1,5 @@
 network:
+  enable_ipv6: true
+
+openthread:
+  tlv: 0E080000000000010000
diff --git a/tests/script/test_helpers.py b/tests/script/test_helpers.py
index 82ff5e14112..886d413ccff 100644
--- a/tests/script/test_helpers.py
+++ b/tests/script/test_helpers.py
@@ -35,6 +35,8 @@ def clear_helpers_cache() -> None:
     helpers._get_github_event_data.cache_clear()
     helpers._get_changed_files_github_actions.cache_clear()
     helpers.get_components_per_integration_fixture.cache_clear()
+    helpers._get_test_config_components.cache_clear()
+    helpers._conflict_walk.cache_clear()
 
 
 @pytest.mark.parametrize(
@@ -1504,6 +1506,8 @@ def fake_components(tmp_path: Path) -> Path:
     write("callable_auto", "def AUTO_LOAD():\n    return ['beta']\n")
     write("broken", "this is not valid python !!!")
     helpers.parse_component_metadata.cache_clear()
+    helpers._get_test_config_components.cache_clear()
+    helpers._conflict_walk.cache_clear()
     return tmp_path
 
 
@@ -1624,6 +1628,47 @@ def test_split_conflicting_groups_preserves_original_signature_for_first_bucket(
     assert signature.startswith("i2c__conflict")
 
 
+def test_split_conflicting_groups_seeds_from_test_config(
+    fake_components: Path, monkeypatch: MonkeyPatch
+) -> None:
+    """A conflict reachable only via a component's test config splits the group.
+
+    ``host_user`` declares no static conflict with ``beta``, but its
+    ``test.<platform>.yaml`` pulls in ``beta_variant`` (which AUTO_LOADs
+    ``beta``). On that platform the group must split; on another platform
+    (no such test config) it must stay together.
+    """
+    monkeypatch.setattr(helpers, "root_path", str(fake_components))
+
+    # host_user has no static metadata, but its esp32 test config references
+    # beta_variant -> AUTO_LOAD beta, which conflicts with alpha.
+    tests_dir = fake_components / "tests" / "components" / "host_user"
+    tests_dir.mkdir(parents=True)
+    (tests_dir / "test.esp32.yaml").write_text("beta_variant:\n")
+    (fake_components / "esphome" / "components" / "host_user").mkdir()
+    (
+        fake_components / "esphome" / "components" / "host_user" / "__init__.py"
+    ).write_text("")
+
+    helpers.parse_component_metadata.cache_clear()
+    helpers._get_test_config_components.cache_clear()
+    helpers._conflict_walk.cache_clear()
+
+    # On esp32, host_user pulls in beta (via its test config) -> conflicts with alpha.
+    result = helpers.split_conflicting_groups(
+        {("esp32", "no_buses"): ["alpha", "host_user"]}
+    )
+    buckets = list(result.values())
+    for bucket in buckets:
+        assert not ({"alpha", "host_user"} <= set(bucket))
+
+    # On a platform without that test config, they stay grouped together.
+    result_other = helpers.split_conflicting_groups(
+        {("rp2040", "no_buses"): ["alpha", "host_user"]}
+    )
+    assert result_other == {("rp2040", "no_buses"): ["alpha", "host_user"]}
+
+
 # ---------------------------------------------------------------------------
 # get_component_test_files / is_validate_only_file
 # ---------------------------------------------------------------------------