diff --git a/packages/core/src/__tests__/session-manager/spawn.test.ts b/packages/core/src/__tests__/session-manager/spawn.test.ts
index d06dbbe3a3..a6f1ea853a 100644
--- a/packages/core/src/__tests__/session-manager/spawn.test.ts
+++ b/packages/core/src/__tests__/session-manager/spawn.test.ts
@@ -21,6 +21,7 @@ import type {
   Agent,
   Workspace,
   Tracker,
+  Issue,
 } from "../../types.js";
 import {
   setupTestContext,
@@ -1089,6 +1090,78 @@ describe("spawn", () => {
     expect(mockRuntime.create).not.toHaveBeenCalled();
   });
 
+  function registryWithTracker(mockTracker: Tracker): PluginRegistry {
+    return {
+      ...mockRegistry,
+      get: vi.fn().mockImplementation((slot: string) => {
+        if (slot === "runtime") return mockRuntime;
+        if (slot === "agent") return mockAgent;
+        if (slot === "workspace") return mockWorkspace;
+        if (slot === "tracker") return mockTracker;
+        return null;
+      }),
+    };
+  }
+
+  function baseMockTracker(issue: Partial<Issue> & Pick<Issue, "id" | "state">): Tracker {
+    return {
+      name: "mock-tracker",
+      getIssue: vi.fn().mockResolvedValue({
+        title: "Test issue",
+        description: "",
+        url: "https://example.com/issues/1",
+        labels: [],
+        ...issue,
+      }),
+      isCompleted: vi.fn().mockResolvedValue(issue.state === "closed" || issue.state === "cancelled"),
+      issueUrl: vi.fn().mockReturnValue("https://example.com/issues/1"),
+      branchName: vi.fn().mockReturnValue(`feat/${issue.id}`),
+      generatePrompt: vi.fn().mockResolvedValue("Work on issue"),
+    };
+  }
+
+  it("rejects spawn when tracker issue is closed", async () => {
+    const mockTracker = baseMockTracker({ id: "42", state: "closed" });
+    const sm = createSessionManager({
+      config,
+      registry: registryWithTracker(mockTracker),
+    });
+
+    await expect(sm.spawn({ projectId: "my-app", issueId: "42" })).rejects.toThrow(
+      /Issue 42 is closed/,
+    );
+    expect(mockWorkspace.create).not.toHaveBeenCalled();
+    expect(mockRuntime.create).not.toHaveBeenCalled();
+  });
+
+  it("rejects spawn when tracker issue is cancelled", async () => {
+    const mockTracker = baseMockTracker({ id: "99", state: "cancelled" });
+    const sm = createSessionManager({
+      config,
+      registry: registryWithTracker(mockTracker),
+    });
+
+    await expect(sm.spawn({ projectId: "my-app", issueId: "99" })).rejects.toThrow(
+      /Issue 99 is cancelled/,
+    );
+    expect(mockWorkspace.create).not.toHaveBeenCalled();
+    expect(mockRuntime.create).not.toHaveBeenCalled();
+  });
+
+  it("allows spawn when tracker issue is in_progress", async () => {
+    const mockTracker = baseMockTracker({ id: "INT-50", state: "in_progress" });
+    const sm = createSessionManager({
+      config,
+      registry: registryWithTracker(mockTracker),
+    });
+
+    const session = await sm.spawn({ projectId: "my-app", issueId: "INT-50" });
+
+    expect(session.issueId).toBe("INT-50");
+    expect(mockWorkspace.create).toHaveBeenCalled();
+    expect(mockRuntime.create).toHaveBeenCalled();
+  });
+
   it("spawns without issue tracking when no issueId provided", async () => {
     const sm = createSessionManager({ config, registry: mockRegistry });
 
diff --git a/packages/core/src/session-manager.ts b/packages/core/src/session-manager.ts
index 86807c47b6..9edc7d2729 100644
--- a/packages/core/src/session-manager.ts
+++ b/packages/core/src/session-manager.ts
@@ -20,8 +20,10 @@ import { promisify } from "node:util";
 import {
   isIssueNotFoundError,
   isRestorable,
+  isSpawnableIssueState,
   isTerminalSession,
   NON_RESTORABLE_STATUSES,
+  IssueNotSpawnableError,
   SessionNotFoundError,
   SessionNotRestorableError,
   WorkspaceMissingError,
@@ -1258,6 +1260,26 @@ export function createSessionManager(deps: SessionManagerDeps): OpenCodeSessionM
           throw new Error(`Failed to fetch issue ${spawnConfig.issueId}: ${err}`, { cause: err });
         }
       }
+
+      if (resolvedIssue) {
+        const { state } = resolvedIssue;
+        if (state && !isSpawnableIssueState(state)) {
+          recordActivityEvent({
+            projectId: spawnConfig.projectId,
+            source: "session-manager",
+            kind: "session.spawn_rejected",
+            level: "warn",
+            summary: `spawn rejected: issue ${spawnConfig.issueId} is ${state}`,
+            data: {
+              issueId: spawnConfig.issueId,
+              issueState: state,
+              tracker: plugins.tracker.name,
+              reason: "issue_not_spawnable",
+            },
+          });
+          throw new IssueNotSpawnableError(spawnConfig.issueId, state);
+        }
+      }
     }
 
     // Get the sessions directory for this project
diff --git a/packages/core/src/types.ts b/packages/core/src/types.ts
index 87cbd6b0c5..324ddf298f 100644
--- a/packages/core/src/types.ts
+++ b/packages/core/src/types.ts
@@ -760,6 +760,13 @@ export interface Issue {
   branchName?: string;
 }
 
+/** Issue states that allow spawning a new worker session. */
+export function isSpawnableIssueState(
+  state: Issue["state"],
+): state is "open" | "in_progress" {
+  return state === "open" || state === "in_progress";
+}
+
 export interface IssueFilters {
   state?: "open" | "closed" | "all";
   labels?: string[];
@@ -1992,6 +1999,19 @@ export function isIssueNotFoundError(err: unknown): boolean {
   );
 }
 
+/** Thrown when spawn is requested for a tracker issue that is closed or cancelled. */
+export class IssueNotSpawnableError extends Error {
+  constructor(
+    public readonly issueId: string,
+    public readonly state: Exclude<Issue["state"], "open" | "in_progress">,
+  ) {
+    super(
+      `Issue ${issueId} is ${state}. Cannot spawn a session for a closed/cancelled issue.`,
+    );
+    this.name = "IssueNotSpawnableError";
+  }
+}
+
 /** Thrown when a session cannot be restored (e.g. merged, still working). */
 export class SessionNotRestorableError extends Error {
   constructor(
diff --git a/packages/web/src/app/api/spawn/route.ts b/packages/web/src/app/api/spawn/route.ts
index 8fcc37fe56..8fd194d121 100644
--- a/packages/web/src/app/api/spawn/route.ts
+++ b/packages/web/src/app/api/spawn/route.ts
@@ -1,5 +1,5 @@
 import { type NextRequest } from "next/server";
-import { recordActivityEvent } from "@aoagents/ao-core";
+import { IssueNotSpawnableError, recordActivityEvent } from "@aoagents/ao-core";
 import { validateIdentifier, validateString, validateConfiguredProject } from "@/lib/validation";
 import { getServices } from "@/lib/services";
 import { sessionToDashboard } from "@/lib/serialize";
@@ -103,6 +103,7 @@ export async function POST(request: NextRequest) {
     );
   } catch (err) {
     const { config } = await getServices().catch(() => ({ config: undefined }));
+    const statusCode = err instanceof IssueNotSpawnableError ? 409 : 500;
     if (config) {
       recordApiObservation({
         config,
@@ -111,15 +112,20 @@ export async function POST(request: NextRequest) {
         correlationId,
         startedAt,
         outcome: "failure",
-        statusCode: 500,
+        statusCode,
         projectId: typeof body.projectId === "string" ? body.projectId : undefined,
         reason: err instanceof Error ? err.message : "Failed to spawn session",
-        data: { issueId: body.issueId },
+        data: {
+          issueId: body.issueId,
+          ...(err instanceof IssueNotSpawnableError
+            ? { reason: "issue_not_spawnable", issueState: err.state }
+            : {}),
+        },
       });
     }
     return jsonWithCorrelation(
       { error: err instanceof Error ? err.message : "Failed to spawn session" },
-      { status: 500 },
+      { status: statusCode },
       correlationId,
     );
   }