diff --git a/packages/opencode/test/cli/run/run-process.test.ts b/packages/opencode/test/cli/run/run-process.test.ts
index bd5847e2723c..dee8d8a614ca 100644
--- a/packages/opencode/test/cli/run/run-process.test.ts
+++ b/packages/opencode/test/cli/run/run-process.test.ts
@@ -318,13 +318,15 @@ describe("opencode run (non-interactive subprocess)", () => {
     ({ llm, opencode }) =>
       Effect.gen(function* () {
         yield* llm.hang
-        const run = yield* opencode.startRun("wait forever")
-        yield* llm.wait(1)
-        run.interrupt()
-        const result = yield* run.result
+        const result = yield* Effect.gen(function* () {
+          const run = yield* opencode.startRun("wait forever")
+          yield* llm.wait(1)
+          run.interrupt()
+          return yield* run.result
+        }).pipe(Effect.timeout("24 seconds"))
 
         expect(result.exitCode).not.toBe(0)
-        expect(result.durationMs).toBeLessThan(30_000)
+        expect(result.durationMs).toBeLessThan(24_000)
       }),
     30_000,
   )
diff --git a/packages/opencode/test/cli/serve/serve-process.test.ts b/packages/opencode/test/cli/serve/serve-process.test.ts
index 6dbea372b2cd..9be9e9e28ddf 100644
--- a/packages/opencode/test/cli/serve/serve-process.test.ts
+++ b/packages/opencode/test/cli/serve/serve-process.test.ts
@@ -3,8 +3,9 @@
 // catches bugs spanning argv → server boot → routing → instance loading.
 //
 // `serve` is long-lived: the harness returns a handle (url/port/kill/exited)
-// and kills the process when the test scope closes. The OS-assigned port is
-// parsed off the "listening on http://..." line.
+// and kills the process when the test scope closes. The bound port is parsed
+// off the "listening on http://..." line — `--port 0` asks for 4096 first and
+// falls back to an OS-assigned port only if that bind fails.
 import { describe, expect } from "bun:test"
 import { Effect } from "effect"
 import { HttpClient } from "effect/unstable/http"
@@ -24,9 +25,11 @@ describe("opencode serve (subprocess)", () => {
         const client = yield* HttpClient.HttpClient
         const res = yield* client.get(`${server.url}/global/health`)
         expect(res.status).toBe(200)
-        // GlobalHealth schema is { success: true, ... } | { success: false, error }.
+        // GlobalHealth returns { healthy: true, version } (handlers/global.ts).
         // We don't lock in further shape here — any 200 with parseable JSON is
-        // enough proof the routing + auth-bypass + instance loading is alive.
+        // enough proof that argv → server boot → routing works. It does NOT
+        // prove instance loading: `serve` runs with instance: false and the
+        // global health route loads no instance (src/cli/effect-cmd.ts).
         const body = yield* res.json
         expect(body).toBeDefined()
       }),
@@ -40,22 +43,28 @@ describe("opencode serve (subprocess)", () => {
     "kills the subprocess on scope close",
     ({ opencode }) =>
       Effect.gen(function* () {
-        // Inner scope so we can observe `.exited` resolving after it closes.
-        const exitedPromise = yield* Effect.scoped(
+        const client = yield* HttpClient.HttpClient
+        const handle = yield* Effect.scoped(
           Effect.gen(function* () {
             const server = yield* opencode.serve()
-            // Capture the Promise, not the resolved value — scope closes after
-            // this gen returns, at which point the finalizer kills the child.
-            return server.exited
+            const response = yield* client.get(`${server.url}/global/health`)
+            expect(response.status).toBe(200)
+            return { url: server.url, exited: server.exited }
           }),
         )
-        // After scope close: finalizer fired, process must have exited.
-        const code = yield* Effect.promise(() => exitedPromise)
-        // Bun reports the exit code; SIGTERM-killed processes return non-null
-        // (typically 143 on POSIX). We just require resolution within a sane
-        // window — anything else means the kill didn't take.
-        expect(typeof code === "number" || code === null).toBe(true)
-      }),
+
+        yield* Effect.promise(() => handle.exited)
+
+        const request = () =>
+          client.get(`${handle.url}/global/health`).pipe(Effect.exit, Effect.timeout("1 second"))
+        const first = yield* request()
+        yield* Effect.sleep("75 millis")
+        const second = yield* request()
+        yield* Effect.sleep("75 millis")
+        const third = yield* request()
+
+        expect([first, second, third].map((result) => result._tag)).toEqual(["Failure", "Failure", "Failure"])
+      }).pipe(Effect.timeout("20 seconds")),
     60_000,
   )
 })
diff --git a/packages/opencode/test/lib/cli-process.ts b/packages/opencode/test/lib/cli-process.ts
index 12e8d9c866a5..f54d35646f85 100644
--- a/packages/opencode/test/lib/cli-process.ts
+++ b/packages/opencode/test/lib/cli-process.ts
@@ -106,7 +106,9 @@ export type RunOpts = SpawnOpts & {
 // `opencode serve` is a long-lived process — it never exits on its own.
 // `serve(opts)` therefore returns a handle inside the caller's Scope: the
 // subprocess is killed when the scope closes (test end), and the URL the
-// server actually bound to (port 0 means OS-assigned) is parsed off stdout.
+// server actually bound to is parsed off stdout. Note `--port 0` does not mean
+// "OS-assigned": the server asks for 4096 first and only falls back to an
+// OS-assigned port if that bind fails (src/server/server.ts).
 export type ServeOpts = SpawnOpts & {
   readonly port?: number
   readonly hostname?: string
@@ -211,7 +213,7 @@ export function withCliFixture<A, E>(
       // on `Bun.stdin.text()` (see src/cli/cmd/run.ts — non-TTY stdin is
       // consumed as the prompt). The old Process.run wrapper defaulted to
       // ignore; ChildProcess.make defaults to pipe, so we set it explicitly.
-      const command = ChildProcess.make("bun", ["run", "--conditions=browser", cliEntry, ...args], {
+      const command = ChildProcess.make(process.execPath, ["run", "--conditions=browser", cliEntry, ...args], {
         cwd: home,
         env: { ...env, ...opts?.env },
         extendEnv: true,
@@ -283,7 +285,7 @@ export function withCliFixture<A, E>(
       const options = runOpts(opts)
       const proc = yield* Effect.acquireRelease(
         Effect.sync(() =>
-          Bun.spawn(["bun", "run", "--conditions=browser", cliEntry, ...runArgs(message, opts)], {
+          Bun.spawn([process.execPath, "run", "--conditions=browser", cliEntry, ...runArgs(message, opts)], {
             cwd: home,
             env: { ...process.env, ...env, ...options?.env },
             stdin: "ignore",
@@ -313,8 +315,10 @@ export function withCliFixture<A, E>(
 
     const serve = Effect.fn("opencode.serve")(function* (opts?: ServeOpts) {
       const argv = ["serve"]
-      // Default port 0 — let the OS pick a free port, parse the actual one
-      // off stdout. Hard-coded ports flake under parallel tests.
+      // Default port 0 — the server tries 4096 first and falls back to an
+      // OS-assigned port only if that bind fails (src/server/server.ts); the
+      // actual port is parsed off stdout. Hard-coded ports flake under
+      // parallel tests.
       argv.push("--port", String(opts?.port ?? 0))
       if (opts?.hostname) argv.push("--hostname", opts.hostname)
       if (opts?.extraArgs) argv.push(...opts.extraArgs)
@@ -324,7 +328,7 @@ export function withCliFixture<A, E>(
       // as a finalizer error during test teardown.
       const proc = yield* Effect.acquireRelease(
         Effect.sync(() =>
-          Bun.spawn(["bun", "run", "--conditions=browser", cliEntry, ...argv], {
+          Bun.spawn([process.execPath, "run", "--conditions=browser", cliEntry, ...argv], {
             cwd: home,
             env: { ...process.env, ...env, ...opts?.env },
             stdout: "pipe",
@@ -395,7 +399,7 @@ export function withCliFixture<A, E>(
       // Either way we await proc.exited so the test scope doesn't leak.
       const proc = yield* Effect.acquireRelease(
         Effect.sync(() =>
-          Bun.spawn(["bun", "run", "--conditions=browser", cliEntry, ...argv], {
+          Bun.spawn([process.execPath, "run", "--conditions=browser", cliEntry, ...argv], {
             cwd: opts?.cwd ?? home,
             env: { ...process.env, ...env, ...opts?.env },
             stdin: "pipe",