[uss_qualifier/scenarios] Clarify and fix down-USS test for SCD0005 (#1368)

Co-authored-by: Michael Barroco <michael@orbitalize.com>

Author: BenjaminPelletier

monitoring/uss_qualifier/scenarios/astm/utm/off_nominal_planning/down_uss.md

@@ -71,24 +71,33 @@ However, since:
 - the virtual USS is declared as down at the DSS,
 - it does not respond for operational intent details, and
 - the conflicting operational intent is in the 'Accepted' state,
-The tested USS should evaluate the conflicting operational intent as having the lowest bound priority status, i.e. a priority strictly lower than the lowest priority allowed by the local regulation.
+
+the tested USS should evaluate the conflicting operational intent as having the lowest bound priority status, i.e. a priority strictly lower than the lowest priority allowed by the local regulation.
 
 As such, the tested USS may either:
 - Successfully plan Flight 1 over the conflicting operational intent, or
 - Decide to be more conservative and reject the planning of Flight 1.
 
 #### 🛑 Successful planning check
-All flight intent data provided is correct and the USS should have either successfully planned Flight 1 per **[astm.f3548.v21.SCD0005](../../../../requirements/astm/f3548/v21.md)**,
-or rejected properly the planning if it decided to be more conservative with such conflicts.
-If the USS indicates that the injection attempt failed, this check will fail.
+All flight intent data provided is correct and **[astm.f3548.v21.SCD0005](../../../../requirements/astm/f3548/v21.md)** allows the USS to plan an operational
+intent in conflict with the pre-existing operational intent managed by a down USS by applying the lowest-bound priority
+to that operational intent.  If the USS indicates that the injection attempt failed, this check will fail.
 
-Do take note that if the USS rejects the planning, this check will not fail, but the following *Rejected planning check*
-will. Refer to this check for more information.
+If the USS rejects the requested flight, this check will not fail, but the following *Rejected planning check* will.
+Refer to this check for more information.
 
 #### ℹ️ Rejected planning check
-All flight intent data provided is correct and the USS should have either successfully planned Flight 1 or rejected
-properly the planning if it decided to be more conservative with such conflicts.
-If the USS rejects the planning, this check will produce a low severity finding per **[astm.f3548.v21.SCD0005](../../../../requirements/astm/f3548/v21.md)**.
+ASTM F3548-21 does not require USSs to accept flight requests in all circumstances not prohibited by F3548-21.  USSs may
+(generally) apply any number of additional rules to determine whether or not a flight planning action is accepted by the
+USS.  For instance, a USS may say, "even though we're allowed to plan over unactivated op intents managed by down USSs,
+we choose not to in order to avoid the small risk the USS may not realize it is down and start that flight any way."
+
+For this reason, a USS may reject the planning request above while still complying with SCD0005 by applying the correct
+priority to the pre-existing operational intent.  Therefore, a rejection of the planning request does not indicate
+non-compliance with SCD0005.  However, because InterUSS uses successful planning as a means to measure whether a USS is
+in compliance with SCD0005, rejecting the planning attempt means that the primary mechanism for inferring compliance
+with **[astm.f3548.v21.SCD0005](../../../../requirements/astm/f3548/v21.md)** is not available.  In this case, this check will produce a low-severity finding
+to note InterUSS's inability to use this primary mechanism for SCD0005 compliance verification.
 
 #### 🛑 Injection fidelity check
 

monitoring/uss_qualifier/scenarios/astm/utm/off_nominal_planning/down_uss.py

@@ -41,7 +41,7 @@
     cleanup_flights,
     submit_flight,
 )
-from monitoring.uss_qualifier.scenarios.scenario import TestScenario
+from monitoring.uss_qualifier.scenarios.scenario import ScenarioLogicError, TestScenario
 from monitoring.uss_qualifier.suites.suite import ExecutionContext
 
 
@@ -250,22 +250,29 @@ def _plan_flight_conflict_planned(self):
             # TODO(#1326): Validate that flight as planned still allows this scenario to proceed
             flight1_planned = as_planned
 
-            if resp.activity_result == PlanningActivityResult.Completed:
-                validator.expect_shared(flight1_planned)
-            elif resp.activity_result == PlanningActivityResult.Rejected:
-                with self.check(
-                    "Rejected planning", [self.tested_uss.participant_id]
-                ) as check:
+            with self.check(
+                "Rejected planning", [self.tested_uss.participant_id]
+            ) as check:
+                if resp.activity_result == PlanningActivityResult.Rejected:
                     msg = f"{self.tested_uss.participant_id} indicated {resp.activity_result}"
                     if "notes" in resp and resp.notes:
                         msg += f' with notes "{resp.notes}"'
                     else:
                         msg += " with no notes"
                     check.record_failed(
-                        summary="Warning (not a failure): planning got rejected, USS may have been more conservative",
+                        summary="Warning (not a failure): flight was rejected, USS may have been more conservative",
                         details=msg,
                     )
+
+            if resp.activity_result == PlanningActivityResult.Completed:
+                validator.expect_shared(flight1_planned)
+            elif resp.activity_result == PlanningActivityResult.Rejected:
                 validator.expect_not_shared()
+            else:
+                raise ScenarioLogicError(
+                    f"OpIntentValidator should have ensured that resp.activity_result was Completed or Rejected, but instead it was {resp.activity_result}"
+                )
+
         self.end_test_step()
 
     def _clear_op_intents(self):