feat(context): render retry repair mandate as final user turn (#293)

buildRetryFeedbackEntry was L1/SYSTEM, so PromptRenderer folded it into the
leading system block — far from the assistant/tool transcript and weaker than
the original stage task. Flip it to USER role and give the renderer an explicit
trailing repair-mandate slot (a sourceType set, extensible for recovery later):
repair mandates are lifted out of the inline flow and emitted once as the final
message, after the tool evidence and the steering anchor. retryFeedback is
already in REQUIRED_SOURCE_TYPES so it stays unprunable. Golden renderer test
proves the final message is the repair USER mandate and leading system no longer
carries it.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

testing/kernel/src/test/kotlin/ContextFeedbackTest.kt

@@ -50,7 +50,7 @@ class ContextFeedbackTest {
     }
 
     @Test
-    fun `latest retry event for the stage becomes a labeled L1 system entry`() {
+    fun `latest retry event for the stage becomes a labeled L1 user repair mandate`() {
         val events = listOf(
             stored(payload = RetryAttemptedEvent(SessionId("s"), StageId("impl"), 1, 3, "old reason")),
             stored(payload = RetryAttemptedEvent(SessionId("s"), StageId("other"), 1, 3, "other stage")),
@@ -59,7 +59,8 @@ class ContextFeedbackTest {
         val entry = buildRetryFeedbackEntry(events, StageId("impl"))!!
         assertEquals("retryFeedback", entry.sourceType)
         assertEquals(ContextLayer.L1, entry.layer)
-        assertEquals(EntryRole.SYSTEM, entry.role)
+        // #293: USER role so it renders as the trailing repair mandate, not folded into leading system.
+        assertEquals(EntryRole.USER, entry.role)
         assertTrue(entry.content.contains("Attempt 2 of 3"), "content: ${entry.content}")
         assertTrue(entry.content.contains("tests failed: NPE in FooTest"), "content: ${entry.content}")
     }