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/deterministic/src/test/kotlin/PromptRendererOrderingTest.kt

@@ -53,6 +53,30 @@ class PromptRendererOrderingTest {
         Unit
     }
 
+    @Test
+    fun `retry repair mandate renders as the final user turn after the tool transcript`() = kotlinx.coroutines.runBlocking {
+        // #293: even though the repair mandate is stamped mid-transcript by input order, the renderer
+        // must lift it to the very end (after assistant/tool evidence) and never fold it into system.
+        val builder = DefaultContextPackBuilder(DefaultContextCompressor())
+        val entries = listOf(
+            entry("sys", ContextLayer.L0, EntryRole.SYSTEM, "systemPrompt"),
+            entry("task", ContextLayer.L1, EntryRole.USER, "agentPrompt"),
+            entry("repair", ContextLayer.L1, EntryRole.USER, "retryFeedback"),
+            entry("call1", ContextLayer.L2, EntryRole.ASSISTANT, "assistantToolCall", sourceId = "tool1"),
+            entry("result1", ContextLayer.L2, EntryRole.TOOL, "toolResult", sourceId = "tool1"),
+        )
+        val pack = builder.build(ContextPackId("p"), sessionId, stageId, entries, TokenBudget(limit = 4000))
+
+        val messages = PromptRenderer.render(pack)
+        assertEquals("user" to "repair", messages.last().role to messages.last().content)
+        assertEquals(1, messages.count { it.content == "repair" }, "mandate must appear exactly once")
+        org.junit.jupiter.api.Assertions.assertFalse(
+            messages.first().content.contains("repair"),
+            "leading system must not carry the repair mandate",
+        )
+        Unit
+    }
+
     @Test
     fun `without ordinals the live user turn still renders last (router chat fallback)`() {
         // Packs built outside DefaultContextPackBuilder (router chat) leave ordinal at 0;