fix(bootstrapper): always process highest version for dependency discovery

When all versions are cached, keep the highest version in the work
stack so new transitive dependencies are still discovered.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Rohan Devasthale <rdevasth@redhat.com>

Author: rd4398

src/fromager/bootstrapper.py

@@ -1328,10 +1328,15 @@ def _phase_resolve(self, item: WorkItem) -> list[WorkItem]:
                 else:
                     filtered.append((source_url, version))
             if not filtered:
+                # Always process the highest version (first in
+                # resolved_versions) so new transitive dependencies
+                # are discovered even when every wheel is cached.
                 logger.info(
-                    f"all versions of {item.req.name} already cached, nothing to do"
+                    f"all versions of {item.req.name} already cached, "
+                    f"keeping highest version {resolved_versions[0][1]} "
+                    f"for dependency discovery"
                 )
-                return []
+                filtered.append(resolved_versions[0])
             resolved_versions = filtered
 
         # Build list so highest version ends up on top of the stack

tests/test_bootstrapper_iterative.py

@@ -307,16 +307,22 @@ def mock_cache(req: Requirement, version: Version) -> tuple:
         versions = {str(it.resolved_version) for it in result}
         assert versions == {"1.0", "3.0"}
 
-    def test_all_cached_returns_empty(self, tmp_context: WorkContext) -> None:
-        """If all versions are cached, returns empty list."""
+    def test_all_cached_keeps_highest_version(
+        self, tmp_context: WorkContext
+    ) -> None:
+        """If all versions are cached, keeps the highest for dependency discovery."""
         bt = bootstrapper.Bootstrapper(tmp_context, multiple_versions=True)
         item = _make_resolve_item()
 
         with (
             patch.object(
                 bt,
                 "resolve_versions",
-                return_value=[("url-1.0", Version("1.0"))],
+                return_value=[
+                    ("url-3.0", Version("3.0")),
+                    ("url-2.0", Version("2.0")),
+                    ("url-1.0", Version("1.0")),
+                ],
             ),
             patch.object(
                 bt,
@@ -326,7 +332,8 @@ def test_all_cached_returns_empty(self, tmp_context: WorkContext) -> None:
         ):
             result = bt._phase_resolve(item)
 
-        assert result == []
+        assert len(result) == 1
+        assert result[0].resolved_version == Version("3.0")
 
     def test_no_filtering_in_single_version_mode(
         self, tmp_context: WorkContext