diff --git a/docs/compatibility.md b/docs/compatibility.md
index ab4a3e2..8743175 100644
--- a/docs/compatibility.md
+++ b/docs/compatibility.md
@@ -18,6 +18,12 @@ Supported platforms are Windows x64, macOS, and Linux with Node.js 24.10+. The i
 - A detached process survives ordinary MCP/CLI exit. OS session policies, containers, suspend, logout, or parent cgroup cleanup can still stop it. A later `watch` or `list` restarts it; no watchdog or login service is installed.
 - `stop` does not interrupt accepted turns. A request already in flight can complete after cancellation.
 
+## Service runtime discovery
+
+T3 service installs can run a standalone `t3` executable (`t3.exe` on Windows) from `<baseDir>/runtime/versions/<version>/` without npm package metadata. t3poll recognizes that layout only when `.install-complete` matches the version directory, and still verifies the live process and its data home. Native npm installations continue to use their platform package identity.
+
+Verified September 21, 2026 against the local Linux service running `0.0.43-nightly.20260916.1825`: `list --threads` discovered the server and read the authenticated thread list. Regression tests cover credential issuance without package metadata and rejection of missing/mismatched markers and mismatched homes.
+
 ## Stock release proof
 
 Install stock T3 in a disposable directory, outside this repository. Build its native dependencies if required by that release. Then run:
diff --git a/src/setup.ts b/src/setup.ts
index e901415..d657f69 100644
--- a/src/setup.ts
+++ b/src/setup.ts
@@ -3,7 +3,7 @@ import { createHash, randomUUID } from "node:crypto";
 import { execFile, execFileSync } from "node:child_process";
 import { promisify } from "node:util";
 import { homedir } from "node:os";
-import { dirname, join, resolve } from "node:path";
+import { basename, dirname, join, resolve } from "node:path";
 import {
   readFileSync,
   realpathSync,
@@ -107,21 +107,33 @@ export function inspectLocal(baseDir: string): LocalT3 | undefined {
       if (!hasOpenFile(state.pid, join(baseDir, "userdata/state.sqlite")))
         return;
     } else if (args[1] === "serve") {
-      // Native npm distributions run `t3 serve`, with no JS entrypoint.
-      // Verify the live executable against its platform package before using
-      // that same executable to issue or revoke credentials.
-      const pkg = JSON.parse(
-        readFileSync(join(dirname(executable), "package.json"), "utf8"),
-      );
-      // Setup's Node may run under emulation while T3 uses the host CPU.
-      if (
-        !["x64", "arm64"].some(
-          (arch) => pkg.name === `@t3code/t3-${process.platform}-${arch}`,
-        )
-      )
-        return;
+      // Native npm packages carry package.json. Service installs instead unpack
+      // a release archive into this home's runtime/versions/<version> directory.
       const binary = process.platform === "win32" ? "t3.exe" : "t3";
       if (executable !== join(dirname(executable), binary)) return;
+      const versionDir = dirname(executable);
+      const serviceRuntime =
+        existsSync(join(baseDir, "runtime", "versions")) &&
+        realpathSync(dirname(versionDir)) ===
+          realpathSync(join(baseDir, "runtime", "versions"));
+      if (serviceRuntime) {
+        if (
+          readFileSync(join(versionDir, ".install-complete"), "utf8").trim() !==
+          basename(versionDir)
+        )
+          return;
+      } else {
+        const pkg = JSON.parse(
+          readFileSync(join(versionDir, "package.json"), "utf8"),
+        );
+        // Setup's Node may run under emulation while T3 uses the host CPU.
+        if (
+          !["x64", "arm64"].some(
+            (arch) => pkg.name === `@t3code/t3-${process.platform}-${arch}`,
+          )
+        )
+          return;
+      }
       cli = executable;
     } else {
       cli = realpathSync(resolve(cwd, args[1]));
diff --git a/tests/setup.test.ts b/tests/setup.test.ts
index a250c53..da176e4 100644
--- a/tests/setup.test.ts
+++ b/tests/setup.test.ts
@@ -29,12 +29,22 @@ import { Service } from "../src/service.js";
 const exec = promisify(execFile);
 async function fixture(
   t: { after: (fn: () => Promise<void>) => void },
-  launch: "direct" | "absolute-link" | "relative-link" | "native" = "direct",
+  launch:
+    | "direct"
+    | "absolute-link"
+    | "relative-link"
+    | "native"
+    | "service" = "direct",
 ) {
   const root = mkdtempSync(join(tmpdir(), "t3poll setup café space-"));
   const base = join(root, "t3");
   const home = join(root, "poll");
-  const pkg = join(root, "package");
+  const native = launch === "native" || launch === "service";
+  const version = "0.0.43-nightly.20260916.1825";
+  const pkg =
+    launch === "service"
+      ? join(base, "runtime", "versions", version)
+      : join(root, "package");
   mkdirSync(base);
   mkdirSync(join(pkg, "dist"), { recursive: true });
   writeFileSync(
@@ -44,7 +54,7 @@ async function fixture(
   const cli = join(pkg, "dist/bin.mjs");
   copyFileSync(resolve("tests/fixtures/local-t3.mjs"), cli);
   const link = join(root, "t3-bin");
-  if (launch !== "direct" && launch !== "native") {
+  if (launch !== "direct" && !native) {
     if (process.platform === "win32") symlinkSync(pkg, link, "junction");
     else symlinkSync(cli, link);
   }
@@ -55,7 +65,7 @@ async function fixture(
       ? join(command, "dist", "bin.mjs")
       : command;
   let executable = process.execPath;
-  if (launch === "native") {
+  if (native) {
     // A copied Node binary gives us a real process with the native `t3 serve`
     // argv layout, without requiring a T3 download or compiler in CI.
     executable = join(pkg, process.platform === "win32" ? "t3.exe" : "t3");
@@ -73,15 +83,15 @@ async function fixture(
       'process.argv.splice(1, 0, "auth");\n' + readFileSync(cli, "utf8"),
     );
   }
-  const child = spawn(
-    executable,
-    launch === "native" ? ["serve"] : [entry, "serve"],
-    {
-      cwd: root,
-      env: { ...process.env, T3CODE_HOME: base },
-      stdio: ["ignore", "pipe", "pipe"],
-    },
-  );
+  if (launch === "service") {
+    rmSync(join(pkg, "package.json"));
+    writeFileSync(join(pkg, ".install-complete"), `${version}\n`);
+  }
+  const child = spawn(executable, native ? ["serve"] : [entry, "serve"], {
+    cwd: root,
+    env: { ...process.env, T3CODE_HOME: base },
+    stdio: ["ignore", "pipe", "pipe"],
+  });
   t.after(async () => {
     if (child.exitCode === null) {
       const stopped = once(child, "exit");
@@ -524,3 +534,40 @@ test("native discovery accepts a supported package architecture independently of
   }
   assert.equal(f.issued(), 0);
 });
+
+test("service runtime discovery and credential issuance without npm metadata", async (t) => {
+  const f = await fixture(t, "service");
+  const server = discover(f.config);
+  assert.equal(server.origin, f.origin);
+  assert.equal(server.native, true);
+  const cwd = process.cwd();
+  process.chdir(f.root);
+  try {
+    const c = await connection(f.config);
+    assert.deepEqual(await new T3(c.origin, c.tokenFile).threads(), []);
+    assert.equal(f.issued(), 1);
+  } finally {
+    process.chdir(cwd);
+  }
+});
+
+test("service discovery requires a matching install marker and home", async (t) => {
+  const f = await fixture(t, "service");
+  const marker = join(
+    f.base,
+    "runtime/versions/0.0.43-nightly.20260916.1825/.install-complete",
+  );
+  assert.ok(inspectLocal(f.base));
+  const other = join(f.root, "other");
+  mkdirSync(join(other, "userdata"), { recursive: true });
+  copyFileSync(
+    join(f.base, "userdata/server-runtime.json"),
+    join(other, "userdata/server-runtime.json"),
+  );
+  assert.equal(inspectLocal(other), undefined);
+  writeFileSync(marker, "wrong-version\n");
+  assert.equal(inspectLocal(f.base), undefined);
+  rmSync(marker);
+  assert.equal(inspectLocal(f.base), undefined);
+  assert.equal(f.issued(), 0);
+});