diff --git a/packages/core/src/__tests__/session-manager/restore.test.ts b/packages/core/src/__tests__/session-manager/restore.test.ts
index bf9691b4a..b70a50a32 100644
--- a/packages/core/src/__tests__/session-manager/restore.test.ts
+++ b/packages/core/src/__tests__/session-manager/restore.test.ts
@@ -226,6 +226,36 @@ describe("restore", () => {
     await expect(sm.restore("app-1")).rejects.toThrow(/is merged/);
   });
 
+  it("refuses to restore sessions whose PR is closed (unmerged terminal state)", async () => {
+    const ws = "/tmp/mock-ws/app-1-closed";
+    writeMetadata(sessionsDir, "app-1", {
+      worktree: ws,
+      branch: "feat/abandoned",
+      status: "killed",
+      pr: "https://github.com/acme/repo/pull/99",
+      project: "my-app",
+      runtimeHandle: makeHandle("rt-old"),
+    });
+    // No legacy `status` maps to lifecycle.pr.state="closed", so write the
+    // canonical lifecycle directly to exercise the closed branch of step 3a.
+    updateMetadata(sessionsDir, "app-1", {
+      lifecycle: JSON.stringify({
+        version: 2,
+        session: { state: "terminated", terminatedAt: new Date().toISOString() },
+        pr: {
+          state: "closed",
+          reason: "closed_unmerged",
+          number: 99,
+          url: "https://github.com/acme/repo/pull/99",
+          lastObservedAt: new Date().toISOString(),
+        },
+      }),
+    });
+
+    const sm = createSessionManager({ config, registry: mockRegistry });
+    await expect(sm.restore("app-1")).rejects.toThrow(/is closed/);
+  });
+
   it("throws SessionNotRestorableError for working sessions", async () => {
     writeMetadata(sessionsDir, "app-1", {
       worktree: "/tmp",
diff --git a/packages/plugins/scm-github/src/index.ts b/packages/plugins/scm-github/src/index.ts
index 4683d7221..7322b1646 100644
--- a/packages/plugins/scm-github/src/index.ts
+++ b/packages/plugins/scm-github/src/index.ts
@@ -650,10 +650,13 @@ function createGitHubSCM(): SCM {
         }> = JSON.parse(raw);
 
         // Only same-repo PRs auto-associate. Fork PRs (different head owner)
-        // are someone else's work — never the session's.
+        // are someone else's work — never the session's. Strict-by-default:
+        // a missing/null/empty headOwner is rejected so a future gh API
+        // change or deleted-account edge case can't quietly let a fork PR
+        // through.
         const sameRepoPrs = prs.filter((pr) => {
           const headOwner = pr.headRepositoryOwner?.login;
-          return !headOwner || headOwner === owner;
+          return typeof headOwner === "string" && headOwner === owner;
         });
 
         if (sameRepoPrs.length === 0) return null;
diff --git a/packages/plugins/scm-github/test/index.test.ts b/packages/plugins/scm-github/test/index.test.ts
index d0d7e4d5a..e59926438 100644
--- a/packages/plugins/scm-github/test/index.test.ts
+++ b/packages/plugins/scm-github/test/index.test.ts
@@ -400,6 +400,7 @@ describe("scm-github plugin", () => {
           headRefName: "feat/my-feature",
           baseRefName: "main",
           isDraft: false,
+          headRepositoryOwner: { login: "acme" },
         },
       ]);
 
@@ -459,12 +460,37 @@ describe("scm-github plugin", () => {
           headRefName: "feat/my-feature",
           baseRefName: "main",
           isDraft: true,
+          headRepositoryOwner: { login: "acme" },
         },
       ]);
       const result = await scm.detectPR(makeSession(), project);
       expect(result?.isDraft).toBe(true);
     });
 
+    it("rejects PRs with missing/null headRepositoryOwner (strict-by-default)", async () => {
+      mockGh([
+        {
+          number: 50,
+          url: "https://github.com/acme/repo/pull/50",
+          title: "owner missing",
+          headRefName: "feat/my-feature",
+          baseRefName: "main",
+          isDraft: false,
+          headRepositoryOwner: null,
+        },
+        {
+          number: 51,
+          url: "https://github.com/acme/repo/pull/51",
+          title: "owner field absent",
+          headRefName: "feat/my-feature",
+          baseRefName: "main",
+          isDraft: false,
+        },
+      ]);
+      const result = await scm.detectPR(makeSession(), project);
+      expect(result).toBeNull();
+    });
+
     it("returns null when session.branch === project.defaultBranch", async () => {
       const result = await scm.detectPR(
         makeSession({ branch: "main" }),
@@ -1334,6 +1360,7 @@ describe("scm-github plugin", () => {
           headRefName: "feat/my-feature",
           baseRefName: "main",
           isDraft: false,
+          headRepositoryOwner: { login: "acme" },
         },
       ]);
       const a = await scm.detectPR(makeSession(), project);
@@ -1366,6 +1393,7 @@ describe("scm-github plugin", () => {
           headRefName: "feat/my-feature",
           baseRefName: "main",
           isDraft: false,
+          headRepositoryOwner: { login: "acme" },
         },
       ]);
       const after = await scm.detectPR(makeSession(), project);
@@ -1382,6 +1410,7 @@ describe("scm-github plugin", () => {
           headRefName: "feat/a",
           baseRefName: "main",
           isDraft: false,
+          headRepositoryOwner: { login: "acme" },
         },
       ]);
       mockGh([
@@ -1392,6 +1421,7 @@ describe("scm-github plugin", () => {
           headRefName: "feat/b",
           baseRefName: "main",
           isDraft: false,
+          headRepositoryOwner: { login: "acme" },
         },
       ]);
       const a = await scm.detectPR(makeSession({ branch: "feat/a" }), project);
@@ -1410,6 +1440,7 @@ describe("scm-github plugin", () => {
           headRefName: pr.branch,
           baseRefName: "main",
           isDraft: false,
+          headRepositoryOwner: { login: "acme" },
         },
       ]);
       await scm.detectPR(makeSession({ branch: pr.branch }), project);