fix(devin): retain flushed history in overflow sizing

packages/ai/src/providers/devin.ts

@@ -245,12 +245,18 @@ export const streamDevin: StreamFunction<"devin-agent"> = (
 								// schemas, which history maintenance cannot shrink. Re-encode
 								// only the repeated history field before choosing recovery.
 								let activeTailCount = 0;
-								for (let i = context.messages.length - 1; i >= 0; i--) {
-									const role = context.messages[i].role;
-									if (role === "user" || role === "developer") {
-										activeTailCount++;
-									} else {
-										break;
+								const lastRole = context.messages.at(-1)?.role;
+								if (lastRole === "user" || lastRole === "developer") {
+									activeTailCount = 1;
+									// A trailing developer message can accompany the current user
+									// prompt. Earlier user-role records may instead be flushed
+									// execution history and must remain eligible for compaction.
+									if (lastRole === "developer") {
+										for (let i = context.messages.length - 2; i >= 0; i--) {
+											const role = context.messages[i].role;
+											if (role !== "user" && role !== "developer") break;
+											activeTailCount++;
+										}
 									}
 								}
 								const shrinkablePrompts =

packages/ai/test/devin-large-request-recovery.test.ts

@@ -237,6 +237,30 @@ describe("streamDevin large request recovery", () => {
 		expect(result.errorMessage).toContain("trace ID: tool-execution-overflow");
 		expect(AIError.is(result.errorId, AIError.Flag.ContextOverflow)).toBe(true);
 	});
+	it("keeps prior user-role execution history eligible before the active prompt", async () => {
+		const result = await runTrailerError(
+			{
+				messages: [
+					{
+						role: "user" as const,
+						content: "execution output: ".concat("x".repeat(520 * 1024)),
+						timestamp: 1,
+					},
+					{
+						role: "user" as const,
+						content: "small active prompt",
+						timestamp: 2,
+					},
+				],
+			},
+			"invalid_argument",
+			"an internal error occurred (trace ID: user-role-history)",
+		);
+
+		expect(result.stopReason).toBe("error");
+		expect(AIError.is(result.errorId, AIError.Flag.ContextOverflow)).toBe(true);
+	});
+
 	it("keeps the trailer transient for a large current prompt split across multiple trailing user/developer messages", async () => {
 		const result = await runTrailerError(
 			{