test(gate): expect uniform tool-result frame in compressed-context assertion

The tool-output framing feature (2912799f) wraps every tool result in a
'[tool exit=N]' header before it enters context. Compression still runs
(blank lines stripped); the test predated the frame and asserted the bare
compressed body. Update to the framed contract — invariant #6 unchanged.

testing/integration/src/test/kotlin/ToolCallGateTest.kt

@@ -377,11 +377,12 @@ class ToolCallGateTest {
         orchestrator.run(SessionId("compress"), singleStageGraph(), config)
 
         // The second inference carries round-1's tool result in its context pack — compressed
-        // (blank lines stripped), not raw. Raw output stays authoritative on the executor's
-        // event path (invariant #6); the compressor only shapes the derived context entry.
+        // (blank lines stripped), not raw, under the uniform `[tool exit=N]` frame the model sees.
+        // Raw output stays authoritative on the executor's event path (invariant #6); the compressor
+        // only shapes the derived context entry.
         val secondPack = provider.requests[1].contextPack
         val toolEntry = secondPack.layers.values.flatten().first { it.sourceType == "toolResult" }
-        assertEquals("line1\nline2\nline3", toolEntry.content)
+        assertEquals("[file_write exit=0]\nline1\nline2\nline3", toolEntry.content)
     }
 
     @Test