diff --git a/src/resources/extensions/gsd/doctor.ts b/src/resources/extensions/gsd/doctor.ts
index 7ffb29830..a11490545 100644
--- a/src/resources/extensions/gsd/doctor.ts
+++ b/src/resources/extensions/gsd/doctor.ts
@@ -1144,8 +1144,31 @@ export async function runGSDDoctor(basePath: string, options?: { fix?: boolean;
             unitId: taskUnitId,
             message: `Task ${task.id} is marked done but summary is missing`,
             file: relTaskFile(basePath, milestoneId, slice.id, task.id, "SUMMARY"),
-            fixable: false,
+            fixable: true,
           });
+          // Write a stub summary so validate-milestone can proceed.
+          // This prevents infinite skip loops when tasks are marked done
+          // without summaries (#820).
+          if (shouldFix("task_done_missing_summary")) {
+            const stubPath = join(
+              basePath, ".gsd", "milestones", milestoneId, "slices", slice.id, "tasks",
+              `${task.id}-SUMMARY.md`,
+            );
+            const stubContent = [
+              `---`,
+              `status: done`,
+              `result: unknown`,
+              `doctor_generated: true`,
+              `---`,
+              ``,
+              `# ${task.id}: ${task.title || "Unknown"}`,
+              ``,
+              `Summary stub generated by \`/gsd doctor\` — task was marked done but no summary existed.`,
+              ``,
+            ].join("\n");
+            await saveFile(stubPath, stubContent);
+            fixesApplied.push(`created stub summary for ${taskUnitId}`);
+          }
         }
 
         if (!task.done && hasSummary) {