diff --git a/packages/plugins/sdk/src/environment-tasks.ts b/packages/plugins/sdk/src/environment-tasks.ts
index b7b2c56cc3e..76ca6b1787f 100644
--- a/packages/plugins/sdk/src/environment-tasks.ts
+++ b/packages/plugins/sdk/src/environment-tasks.ts
@@ -3,6 +3,8 @@ import type { PluginEnvironmentDriverBaseParams, PluginEnvironmentLease } from "
 
 // Provider IDs are opaque; providers validate their own addressing constraints.
 const providerId = z.string().min(1);
+// PRP identity.schema.json stableId.
+const runnerIdentity = z.string().regex(/^[A-Za-z0-9][A-Za-z0-9._:-]{0,159}$/);
 const identifier = z.string().regex(/^[a-zA-Z0-9][a-zA-Z0-9_-]{0,95}$/);
 const secureUrl = z.string().url().refine(value => {
   const url = new URL(value);
@@ -19,8 +21,8 @@ export const environmentTaskOperationSchema = z.discriminatedUnion("kind", [
       protocolMin: z.number().int().min(1).max(Number.MAX_SAFE_INTEGER),
       protocolMax: z.number().int().min(1).max(Number.MAX_SAFE_INTEGER),
       harness: identifier,
-      runnerId: identifier, leaseId: identifier, runId: identifier,
-      sessionId: identifier, turnId: identifier, itemId: identifier,
+      runnerId: runnerIdentity, leaseId: runnerIdentity, runId: runnerIdentity,
+      sessionId: runnerIdentity, turnId: runnerIdentity, itemId: runnerIdentity,
     }).strict().refine(value => value.protocolMin <= value.protocolMax, "Invalid PRP version range"),
     bootstrapTicket: z.string().min(1).max(65_536),
   }).strict(),
diff --git a/server/src/__tests__/environment-task-runtime.test.ts b/server/src/__tests__/environment-task-runtime.test.ts
index 221ff1be99a..d11cf7650a7 100644
--- a/server/src/__tests__/environment-task-runtime.test.ts
+++ b/server/src/__tests__/environment-task-runtime.test.ts
@@ -132,6 +132,16 @@ describe("environment task admission", () => {
     const workers = worker(); workers.call.mockRejectedValue(new Error("private-credential"));
     await expect(executeEnvironmentTask(database().db, workers as never, { companyId: "company", leaseId, operation: submit })).rejects.toThrow(/^Environment task operation unavailable; reconcile the same task before retrying$/);
   });
+  it("accepts PRP identity characters and length limits", () => {
+    for (const field of ["runnerId", "leaseId", "runId", "sessionId", "turnId", "itemId"]) {
+      for (const value of ["session:part.1", "a".repeat(160)]) {
+        expect(environmentTaskOperationSchema.safeParse({ ...submit, runner: { ...submit.runner, [field]: value } }).success).toBe(true);
+      }
+      for (const value of ["a".repeat(161), "../escape", "a/b", ""]) {
+        expect(environmentTaskOperationSchema.safeParse({ ...submit, runner: { ...submit.runner, [field]: value } }).success).toBe(false);
+      }
+    }
+  });
   it("validates the client's inclusive PRP version range", () => {
     for (const range of [{ protocolMin: 1, protocolMax: 1 }, { protocolMin: 1, protocolMax: 2 }, { protocolMin: 3, protocolMax: 5 }]) {
       expect(environmentTaskOperationSchema.safeParse({ ...submit, runner: { ...submit.runner, ...range } }).success).toBe(true);
diff --git a/server/src/__tests__/plugin-environment-driver-seam.test.ts b/server/src/__tests__/plugin-environment-driver-seam.test.ts
index ce9d286f4b3..998cff0e411 100644
--- a/server/src/__tests__/plugin-environment-driver-seam.test.ts
+++ b/server/src/__tests__/plugin-environment-driver-seam.test.ts
@@ -8,6 +8,7 @@ import {
   parseMessage,
   serializeMessage,
 } from "../../../packages/plugins/sdk/src/protocol.js";
+import type { PluginEnvironmentTaskParams } from "../../../packages/plugins/sdk/src/environment-tasks.js";
 import { definePlugin } from "../../../packages/plugins/sdk/src/define-plugin.js";
 import { startWorkerRpcHost } from "../../../packages/plugins/sdk/src/worker-rpc-host.js";
 import { pluginManifestV1Schema, type PaperclipPluginManifestV1 } from "@paperclipai/shared";
@@ -121,11 +122,17 @@ describe("plugin environment driver seam", () => {
       expect(isJsonRpcSuccessResponse(initialized)).toBe(true);
       if (!isJsonRpcSuccessResponse(initialized)) return;
       expect(initialized.result.supportedMethods).toContain("environmentTask");
-      const params = { driverKey: "fake-plugin", companyId: "company", environmentId: "environment", config: {},
-        taskId: "attempt", runId: "run", agentId: "agent", projectId: null, lease: { providerLeaseId: "attempt" }, operation: { kind: "stop" } };
+      const projectIds = ["10000000-0000-4000-8000-000000000001", "10000000-0000-4000-8000-000000000002"];
+      const params: PluginEnvironmentTaskParams = { driverKey: "fake-plugin", companyId: "company", environmentId: "environment", config: {},
+        taskId: "attempt", runId: "run", agentId: "agent", projectIds, lease: { providerLeaseId: "attempt" },
+        operation: { kind: "submit", projectIds, bootstrapTicket: "transient-test-ticket", runner: {
+          protocolMin: 1, protocolMax: 2, harness: "codex", runnerId: "runner", leaseId: "lease", runId: "run", sessionId: "session:part.1", turnId: "turn", itemId: "item",
+        } } };
+
       stdin.write(serializeMessage(createRequest("environmentTask", params, 2)));
       await waitForResponses(responses, 2);
       expect(responses[1]).toMatchObject({ result: { kind: "accepted", taskId: "attempt" } });
+      expect(calls[0]).toMatchObject({ projectIds, operation: { kind: "submit", projectIds } });
       stdin.write(serializeMessage(createRequest("environmentTask", { ...params, operation: { kind: "status" } }, 3)));
       await waitForResponses(responses, 3);
       expect(isJsonRpcErrorResponse(responses[2])).toBe(true); // Wrong response kind.