Phase 15: extend debug diag with compaction source and delivery branch

Log sourceInferred, isIdle, deliveryBranch on session_compact and
mid_turn_deliver after steer for B-003 troubleshooting.

Co-authored-by: Cursor <cursoragent@cursor.com>

test/diag.test.ts

@@ -22,6 +22,12 @@ describe("buildReinjectDiagSnapshot", () => {
 				[{ name: "beta" }],
 				new Set(["gamma"]),
 				["alpha"],
+				{
+					compactionSource: "auto",
+					sourceInferred: true,
+					deliveryBranch: "steer",
+					isIdle: false,
+				},
 			),
 		).toEqual({
 			tracked: ["alpha"],
@@ -29,6 +35,10 @@ describe("buildReinjectDiagSnapshot", () => {
 			registered: ["beta"],
 			planned: ["alpha"],
 			pending: ["alpha"],
+			compactionSource: "auto",
+			sourceInferred: true,
+			deliveryBranch: "steer",
+			isIdle: false,
 		});
 	});
 });