diff --git a/packages/server/src/server/agent/providers/claude/agent.env.test.ts b/packages/server/src/server/agent/providers/claude/agent.env.test.ts
index 0806a0dbc6..6d268e932c 100644
--- a/packages/server/src/server/agent/providers/claude/agent.env.test.ts
+++ b/packages/server/src/server/agent/providers/claude/agent.env.test.ts
@@ -30,16 +30,20 @@ function createQueryMock(events: unknown[]): Query {
 }
 
 describe("Claude SDK env", () => {
-  test.each(["node", "bun", process.execPath])(
-    "identifies the spawned %s process as Paseo after clearing parent session env",
-    async (command) => {
+  test.each(
+    ["node", "bun", process.execPath].flatMap((command) =>
+      [undefined, "Paseo", "custom-client"].map((entrypoint) => ({ command, entrypoint })),
+    ),
+  )(
+    "preserves explicit launch identity $entrypoint in $command while clearing inherited session env",
+    async ({ command, entrypoint }) => {
       let output = "";
       let exited = Promise.resolve<unknown[]>([]);
       const query = claudeQuery(
         { prompt: "", options: {} },
         {
           runtimeSettings: { env: { CLAUDE_CODE_ENTRYPOINT: "sdk-ts" } },
-          launchEnv: { CLAUDE_CODE_ENTRYPOINT: "sdk-cli" },
+          launchEnv: entrypoint === undefined ? {} : { CLAUDE_CODE_ENTRYPOINT: entrypoint },
           queryFactory: ({ options }) => {
             if (!options.spawnClaudeCodeProcess) {
               throw new Error("Missing Claude process launcher");
@@ -65,7 +69,10 @@ describe("Claude SDK env", () => {
 
       try {
         expect(await exited).toEqual([0, null]);
-        expect(JSON.parse(output)).toEqual({ entrypoint: "Paseo", parentSession: null });
+        expect(JSON.parse(output)).toEqual({
+          ...(entrypoint === undefined ? {} : { entrypoint }),
+          parentSession: null,
+        });
       } finally {
         query.close();
       }
diff --git a/packages/server/src/server/agent/providers/claude/query.ts b/packages/server/src/server/agent/providers/claude/query.ts
index c8fe4ba036..0f9525d5b1 100644
--- a/packages/server/src/server/agent/providers/claude/query.ts
+++ b/packages/server/src/server/agent/providers/claude/query.ts
@@ -73,8 +73,9 @@ function applyRuntimeSettingsToClaudeOptions(
         runtimeSettings,
         overlays: [launchEnv],
       });
-      // Set our identity after sanitization clears the parent session's entrypoint.
-      providerEnvSpec.envOverlay.CLAUDE_CODE_ENTRYPOINT = "Paseo";
+      // Session-open hooks may explicitly supply a client identity. Keep inherited
+      // SDK/parent identities cleared while honoring this launch-only contribution.
+      providerEnvSpec.envOverlay.CLAUDE_CODE_ENTRYPOINT = launchEnv?.CLAUDE_CODE_ENTRYPOINT;
       const providerEnv = createExternalProcessEnv(spawnOptions.env, providerEnvSpec.envOverlay);
       const selfNodeCommand = isDefaultRuntime
         ? buildSelfNodeCommand(resolved.args, providerEnv)
diff --git a/packages/server/src/server/plugins/agent-configuration.e2e.test.ts b/packages/server/src/server/plugins/agent-configuration.e2e.test.ts
index 9f62075125..a3e4e273a4 100644
--- a/packages/server/src/server/plugins/agent-configuration.e2e.test.ts
+++ b/packages/server/src/server/plugins/agent-configuration.e2e.test.ts
@@ -1,10 +1,10 @@
-import { mkdtemp, rm } from "node:fs/promises";
+import { mkdtemp, rm, writeFile } from "node:fs/promises";
 import { tmpdir } from "node:os";
 import path from "node:path";
 import { fileURLToPath } from "node:url";
 import { expect, test } from "vitest";
 import { DaemonClient } from "../test-utils/daemon-client.js";
-import type { AgentSessionConfig } from "../agent/agent-sdk-types.js";
+import type { AgentClient, AgentSessionConfig } from "../agent/agent-sdk-types.js";
 import { createTestAgentClient } from "../test-utils/fake-agent-client.js";
 import { createTestPaseoDaemon } from "../test-utils/paseo-daemon.js";
 
@@ -72,3 +72,71 @@ test("the configuration example saves Codex options and injects launch-only MCP
     await rm(directory, { recursive: true, force: true });
   }
 }, 60_000);
+
+test("session-open entrypoint contributions are optional and rederived for existing agents", async () => {
+  const directory = await mkdtemp(path.join(tmpdir(), "paseo-entrypoint-hook-"));
+  const launches: { provider: string; env?: Record<string, string> }[] = [];
+  function recordingProvider(provider: "claude" | "codex"): AgentClient {
+    const inner = createTestAgentClient(provider);
+    return {
+      provider: inner.provider,
+      capabilities: inner.capabilities,
+      isAvailable: () => inner.isAvailable(),
+      fetchCatalog: (options) => inner.fetchCatalog(options),
+      createSession: async (...args: Parameters<typeof inner.createSession>) => {
+        launches.push({ provider, env: args[1]?.env });
+        return inner.createSession(...args);
+      },
+      resumeSession: async (...args: Parameters<typeof inner.resumeSession>) => {
+        launches.push({ provider, env: args[2]?.env });
+        return inner.resumeSession(...args);
+      },
+    };
+  }
+  const daemon = await createTestPaseoDaemon({
+    daemonVersion: "0.14.0-beta.2",
+    agentClients: { claude: recordingProvider("claude"), codex: recordingProvider("codex") },
+    mcpEnabled: false,
+  });
+  const client = new DaemonClient({
+    url: `ws://127.0.0.1:${daemon.port}/ws`,
+    appVersion: "0.14.0-beta.2",
+  });
+  try {
+    await writeFile(
+      path.join(directory, "paseo-plugin.json"),
+      JSON.stringify({ id: "entrypoint-test", requirements: { paseo: ">=0.14.0-beta.2" } }),
+    );
+    await writeFile(
+      path.join(directory, "index.server.ts"),
+      `
+export default function contribute(server) {
+  return server.before("agent.session_open", ({ request }) => {
+    if (request.provider !== "claude") return;
+    return { ...request, env: { ...request.env, CLAUDE_CODE_ENTRYPOINT: "custom-client" } };
+  });
+}
+`,
+    );
+    await client.connect();
+    await client.fetchAgents({ subscribe: {} });
+    const existing = await client.createAgent({ provider: "claude", cwd: directory });
+    expect(launches.at(-1)?.env?.CLAUDE_CODE_ENTRYPOINT).toBeUndefined();
+    await client.patchDaemonConfig({ pluginsEnabled: true });
+    await client.installDirectoryPlugin(directory);
+    await daemon.daemon.agentManager.reloadAgentSession(existing.id);
+    expect(launches.at(-1)?.env?.CLAUDE_CODE_ENTRYPOINT).toBe("custom-client");
+    await client.createAgent({ provider: "claude", cwd: directory });
+    expect(launches.at(-1)?.env?.CLAUDE_CODE_ENTRYPOINT).toBe("custom-client");
+    await client.createAgent({ provider: "codex", cwd: directory });
+    expect(launches.at(-1)).toMatchObject({ provider: "codex" });
+    expect(launches.at(-1)?.env?.CLAUDE_CODE_ENTRYPOINT).toBeUndefined();
+    await client.disablePlugin("entrypoint-test");
+    await daemon.daemon.agentManager.reloadAgentSession(existing.id);
+    expect(launches.at(-1)?.env?.CLAUDE_CODE_ENTRYPOINT).toBeUndefined();
+  } finally {
+    await client.close();
+    await daemon.close();
+    await rm(directory, { recursive: true, force: true });
+  }
+}, 60_000);