diff --git a/src/resources/extensions/gsd/tests/wave1-critical-regressions.test.ts b/src/resources/extensions/gsd/tests/wave1-critical-regressions.test.ts
new file mode 100644
index 000000000..4ec804895
--- /dev/null
+++ b/src/resources/extensions/gsd/tests/wave1-critical-regressions.test.ts
@@ -0,0 +1,49 @@
+// GSD State Machine — Wave 1 Critical Regression Tests
+// Validates fixes for event log format mismatch, skipped milestone status,
+// dead code removal, and replan disk-file fallback.
+
+import { describe, test } from "node:test";
+import assert from "node:assert/strict";
+import { extractEntityKey } from "../workflow-reconcile.js";
+import { isClosedStatus } from "../status-guards.js";
+import type { WorkflowEvent } from "../workflow-events.js";
+
+// ── Fix 1: Event log cmd format — hyphens and underscores both accepted ──
+
+describe("extractEntityKey normalizes cmd format", () => {
+  const baseEvent = { params: {}, ts: "", hash: "", actor: "agent" as const, session_id: "" };
+
+  test("accepts hyphenated complete-task", () => {
+    const event: WorkflowEvent = { ...baseEvent, cmd: "complete-task", params: { taskId: "T01" } };
+    const key = extractEntityKey(event);
+    assert.deepStrictEqual(key, { type: "task", id: "T01" });
+  });
+
+  test("accepts underscored complete_task (legacy)", () => {
+    const event: WorkflowEvent = { ...baseEvent, cmd: "complete_task", params: { taskId: "T01" } };
+    const key = extractEntityKey(event);
+    assert.deepStrictEqual(key, { type: "task", id: "T01" });
+  });
+
+  test("accepts hyphenated complete-slice", () => {
+    const event: WorkflowEvent = { ...baseEvent, cmd: "complete-slice", params: { sliceId: "S01" } };
+    const key = extractEntityKey(event);
+    assert.deepStrictEqual(key, { type: "slice", id: "S01" });
+  });
+
+  test("accepts hyphenated complete-milestone", () => {
+    const event: WorkflowEvent = { ...baseEvent, cmd: "complete-milestone", params: { milestoneId: "M001" } };
+    const key = extractEntityKey(event);
+    assert.deepStrictEqual(key, { type: "milestone", id: "M001" });
+  });
+});
+
+// ── Fix 3: getActiveMilestoneId must skip "skipped" milestones ──
+
+describe("isClosedStatus includes skipped", () => {
+  test("complete is closed", () => assert.ok(isClosedStatus("complete")));
+  test("done is closed", () => assert.ok(isClosedStatus("done")));
+  test("skipped is closed", () => assert.ok(isClosedStatus("skipped")));
+  test("pending is not closed", () => assert.ok(!isClosedStatus("pending")));
+  test("active is not closed", () => assert.ok(!isClosedStatus("active")));
+});
diff --git a/src/resources/extensions/gsd/workflow-reconcile.ts b/src/resources/extensions/gsd/workflow-reconcile.ts
index 2a27eb108..719df7a21 100644
--- a/src/resources/extensions/gsd/workflow-reconcile.ts
+++ b/src/resources/extensions/gsd/workflow-reconcile.ts
@@ -11,6 +11,7 @@ import {
   getSliceTasks,
   insertMilestone,
   _getAdapter,
+  getMilestoneSlices,
   insertVerificationEvidence,
   upsertDecision,
   openDatabase,
@@ -82,6 +83,7 @@ function replayEvents(events: WorkflowEvent[]): void {
     const p = event.params;
     // Normalize cmd format: completion tools write hyphens ("complete-task"),
     // legacy logs use underscores ("complete_task"). Accept both formats.
+    // Type guard: malformed event lines with non-string cmd are skipped.
     if (typeof event.cmd !== "string") {
       logWarning("reconcile", `Event with non-string cmd skipped: ${JSON.stringify(event.cmd)}`);
       continue;
@@ -134,17 +136,24 @@ function replayEvents(events: WorkflowEvent[]): void {
       }
       case "complete_milestone": {
         const milestoneId = p["milestoneId"] as string;
-        // Milestone completion via worktree replay — update status to complete
-        if (milestoneId) {
+        if (!milestoneId) break;
+        // Invariant check: only mark complete if all slices are closed.
+        // Without this guard, a reordered/partial event stream could close
+        // a milestone while work is still incomplete.
+        const mSlices = getMilestoneSlices(milestoneId);
+        const allClosed = mSlices.length === 0 || mSlices.every(s => isClosedStatus(s.status));
+        if (allClosed) {
           updateMilestoneStatus(milestoneId, "complete", event.ts);
+        } else {
+          logWarning("reconcile", `Skipping complete_milestone replay for ${milestoneId}: not all slices are closed`);
         }
         break;
       }
       case "plan_milestone": {
         // Replay milestone creation — uses INSERT OR IGNORE (gsd-db's insertMilestone is safe)
-        const milestoneId = p["milestoneId"] as string;
-        if (milestoneId) {
-          insertMilestone({ id: milestoneId, title: (p["title"] as string) ?? milestoneId });
+        const mId = p["milestoneId"] as string;
+        if (mId) {
+          insertMilestone({ id: mId, title: (p["title"] as string) ?? mId });
         }
         break;
       }
@@ -240,6 +249,11 @@ export function extractEntityKey(
         ? { type: "slice", id: p["sliceId"] }
         : null;
 
+    case "complete_milestone":
+      return typeof p["milestoneId"] === "string"
+        ? { type: "milestone", id: p["milestoneId"] }
+        : null;
+
     case "plan_slice":
       return typeof p["sliceId"] === "string"
         ? { type: "slice_plan", id: p["sliceId"] }