fix(bundler): treat a blank active integration as indeterminate in FR-019 (#3886)

`resolve_install_plan`'s two FR-019 guards are a truthiness test and an
`is None` test:

    if active_integration and required != active_integration:   # clash
    if active_integration is None and not integration_explicit: # indeterminate

An empty string satisfies neither, so it falls through to
`effective_integration = required` and the bundle's pinned integration is
silently adopted — the exact outcome the docstring says the guard prevents
("resolution fails instead of silently adopting the bundle's required
integration").

  active=None        -> BundlerError: ... could not be determined
  active='' (blank)  -> effective_integration='copilot'   <-- silent adopt
  active='claude'    -> BundlerError: ... targets integration 'copilot'

Normalise a blank value to None before the guards, and strip first to
match the writer (`integration_state.clean_integration_key`, which returns
`None` for empty/whitespace and strips otherwise) so a padded value is not
reported as clashing with its own unpadded form.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/specify_cli/bundler/services/resolver.py

@@ -77,6 +77,16 @@ def resolve_install_plan(
 
     # FR-019: integration-compatibility — a bundle that pins a different
     # integration than the project's active one halts (no silent change).
+    #
+    # A blank integration arrives as ``""``, not ``None`` — which is not a usable
+    # integration id but satisfied NEITHER guard below (the first is a truthiness
+    # test, the second an ``is None`` test), so a pinned bundle was silently
+    # adopted: precisely the outcome this guard exists to prevent. Treat blank as
+    # indeterminate, and strip first like the writer
+    # (``integration_state.clean_integration_key``) so a padded value is not
+    # reported as clashing with itself.
+    if active_integration is not None:
+        active_integration = active_integration.strip() or None
     effective_integration = active_integration
     if manifest.integration is not None:
         required = manifest.integration.id

tests/unit/test_bundler_resolver.py

@@ -62,6 +62,32 @@ def test_pinned_integration_with_indeterminate_active_fails():
         )
 
 
+@pytest.mark.parametrize("blank", ["", "   ", "\t"])
+def test_pinned_integration_with_blank_active_fails(blank):
+    """A blank active integration is indeterminate, not a match.
+
+    The clash guard is a truthiness test and the indeterminate guard is an
+    `is None` test, so `""` satisfied neither and fell through to
+    `effective_integration = required` — silently adopting the bundle's pinned
+    integration, the exact outcome the docstring says the guard prevents.
+    """
+    manifest = _manifest(integration={"id": "claude"})
+    with pytest.raises(BundlerError, match="could not be determined"):
+        resolve_install_plan(
+            manifest, speckit_version="0.11.2", active_integration=blank
+        )
+
+
+def test_padded_active_integration_is_not_a_clash_with_itself():
+    """A padded value must strip, like the writer's clean_integration_key,
+    rather than be reported as clashing with its own unpadded form."""
+    manifest = _manifest(integration={"id": "claude"})
+    plan = resolve_install_plan(
+        manifest, speckit_version="0.11.2", active_integration="  claude  "
+    )
+    assert plan.effective_integration == "claude"
+
+
 def test_pinned_integration_with_indeterminate_active_allows_explicit_override():
     manifest = _manifest(integration={"id": "claude"})
     plan = resolve_install_plan(