diff --git a/packages/opencode/src/mcp/index.ts b/packages/opencode/src/mcp/index.ts
index 05f12fa2ee45..07dc000c8b54 100644
--- a/packages/opencode/src/mcp/index.ts
+++ b/packages/opencode/src/mcp/index.ts
@@ -398,11 +398,7 @@ const layer = Layer.effect(
             defs: listed,
             instructions: mcpClient.getInstructions()?.trim(),
           } satisfies CreateResult
-        }).pipe(
-          Effect.catchCause((cause) =>
-            Effect.tryPromise(() => mcpClient.close()).pipe(Effect.ignore, Effect.andThen(Effect.failCause(cause))),
-          ),
-        )
+        }).pipe(Effect.catchCause((cause) => terminate(mcpClient).pipe(Effect.andThen(Effect.failCause(cause)))))
       },
       Effect.map((result): CreateResult => result),
       Effect.catchCause((cause) => {
@@ -439,6 +435,21 @@ const layer = Layer.effect(
       Effect.catch(() => Effect.succeed([] as number[])),
     )
 
+    function terminate(client: MCPClient) {
+      return Effect.gen(function* () {
+        const pid = client.transport instanceof StdioClientTransport ? client.transport.pid : null
+        if (typeof pid === "number") {
+          const pids = yield* descendants(pid)
+          for (const dpid of pids) {
+            try {
+              process.kill(dpid, "SIGTERM")
+            } catch {}
+          }
+        }
+        yield* Effect.tryPromise(() => client.close()).pipe(Effect.ignore)
+      })
+    }
+
     function watch(s: State, name: string, client: MCPClient, bridge: EffectBridge.Shape, timeout?: number) {
       client.onclose = () => {
         if (s.clients[name] !== client) return
@@ -534,23 +545,7 @@ const layer = Layer.effect(
             s.clients = {}
             s.defs = {}
             s.instructions = {}
-            yield* Effect.forEach(
-              clients,
-              (client) =>
-                Effect.gen(function* () {
-                  const pid = client.transport instanceof StdioClientTransport ? client.transport.pid : null
-                  if (typeof pid === "number") {
-                    const pids = yield* descendants(pid)
-                    for (const dpid of pids) {
-                      try {
-                        process.kill(dpid, "SIGTERM")
-                      } catch {}
-                    }
-                  }
-                  yield* Effect.tryPromise(() => client.close()).pipe(Effect.ignore)
-                }),
-              { concurrency: "unbounded" },
-            )
+            yield* Effect.forEach(clients, terminate, { concurrency: "unbounded" })
             pendingOAuthTransports.clear()
           }),
         )
@@ -565,7 +560,7 @@ const layer = Layer.effect(
       delete s.defs[name]
       delete s.instructions[name]
       if (!client) return Effect.void
-      return Effect.tryPromise(() => client.close()).pipe(Effect.ignore)
+      return terminate(client)
     }
 
     const storeClient = Effect.fnUntraced(function* (
@@ -584,7 +579,7 @@ const layer = Layer.effect(
       if (instructions) s.instructions[name] = instructions
       else delete s.instructions[name]
       watch(s, name, client, bridge, timeout)
-      if (previous) yield* Effect.tryPromise(() => previous.close()).pipe(Effect.ignore)
+      if (previous) yield* terminate(previous)
       return s.status[name]
     })
 
diff --git a/packages/opencode/test/fixture/mcp-lifecycle-stdio.ts b/packages/opencode/test/fixture/mcp-lifecycle-stdio.ts
index b01ed921cfd4..7a2eb2e13106 100644
--- a/packages/opencode/test/fixture/mcp-lifecycle-stdio.ts
+++ b/packages/opencode/test/fixture/mcp-lifecycle-stdio.ts
@@ -2,10 +2,21 @@ import { Server } from "@modelcontextprotocol/sdk/server/index.js"
 import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js"
 import { ListToolsRequestSchema } from "@modelcontextprotocol/sdk/types.js"
 
+const pidFile = process.env.MCP_LIFECYCLE_PID_FILE
+if (pidFile) await Bun.write(pidFile, String(process.pid))
+
+const childPidFile = process.env.MCP_LIFECYCLE_CHILD_PID_FILE
+if (childPidFile) {
+  const child = Bun.spawn([process.execPath, "-e", "await new Promise(() => {})"], {
+    stdin: "ignore",
+    stdout: "ignore",
+    stderr: "ignore",
+  })
+  await Bun.write(childPidFile, String(child.pid))
+}
+
 if (process.argv.includes("--hang")) {
-  const pidFile = process.env.MCP_LIFECYCLE_PID_FILE
   if (!pidFile) throw new Error("MCP_LIFECYCLE_PID_FILE is required")
-  await Bun.write(pidFile, String(process.pid))
   await new Promise(() => {})
 }
 
diff --git a/packages/opencode/test/mcp/lifecycle.test.ts b/packages/opencode/test/mcp/lifecycle.test.ts
index 80c8fd22f886..18a23761d9a3 100644
--- a/packages/opencode/test/mcp/lifecycle.test.ts
+++ b/packages/opencode/test/mcp/lifecycle.test.ts
@@ -528,6 +528,100 @@ it.instance("local stdio timeout terminates the real server process", () =>
   }),
 )
 
+it.instance("disconnect and replacement terminate real local MCP process trees", () =>
+  Effect.gen(function* () {
+    const test = yield* TestInstance
+    const files = {
+      previous: {
+        parent: path.join(test.directory, "previous-parent.pid"),
+        child: path.join(test.directory, "previous-child.pid"),
+      },
+      current: {
+        parent: path.join(test.directory, "current-parent.pid"),
+        child: path.join(test.directory, "current-child.pid"),
+      },
+    }
+    yield* Effect.addFinalizer(() =>
+      Effect.promise(async () => {
+        for (const file of Object.values(files).flatMap((item) => Object.values(item))) {
+          if (!(await Bun.file(file).exists())) continue
+          try {
+            process.kill(Number(await Bun.file(file).text()), "SIGKILL")
+          } catch {}
+        }
+      }),
+    )
+    const stopped = (label: string, pids: readonly [number, number]) =>
+      Effect.forEach(
+        [
+          ["parent", pids[0]],
+          ["child", pids[1]],
+        ] as const,
+        ([name, pid]) =>
+          pollWithTimeout(
+            Effect.sync(() => {
+              try {
+                process.kill(pid, 0)
+                return undefined
+              } catch {
+                return true
+              }
+            }),
+            `${label} ${name} stdio fixture process was not terminated`,
+            "1 second",
+          ),
+        { discard: true },
+      )
+
+    const mcp = yield* MCP.Service
+    yield* mcp.add("process-tree", {
+      type: "local",
+      command: [process.execPath, stdioFixture],
+      environment: {
+        MCP_LIFECYCLE_PID_FILE: files.previous.parent,
+        MCP_LIFECYCLE_CHILD_PID_FILE: files.previous.child,
+      },
+    })
+    const previous = yield* pollWithTimeout(
+      Effect.promise(async () => {
+        if (!(await Bun.file(files.previous.parent).exists()) || !(await Bun.file(files.previous.child).exists())) {
+          return undefined
+        }
+        return [
+          Number(await Bun.file(files.previous.parent).text()),
+          Number(await Bun.file(files.previous.child).text()),
+        ] as const
+      }),
+      "previous stdio fixture did not publish its process tree",
+    )
+
+    yield* mcp.add("process-tree", {
+      type: "local",
+      command: [process.execPath, stdioFixture],
+      environment: {
+        MCP_LIFECYCLE_PID_FILE: files.current.parent,
+        MCP_LIFECYCLE_CHILD_PID_FILE: files.current.child,
+      },
+    })
+    const current = yield* pollWithTimeout(
+      Effect.promise(async () => {
+        if (!(await Bun.file(files.current.parent).exists()) || !(await Bun.file(files.current.child).exists())) {
+          return undefined
+        }
+        return [
+          Number(await Bun.file(files.current.parent).text()),
+          Number(await Bun.file(files.current.child).text()),
+        ] as const
+      }),
+      "current stdio fixture did not publish its process tree",
+    )
+    yield* stopped("previous", previous)
+
+    yield* mcp.disconnect("process-tree")
+    yield* stopped("current", current)
+  }),
+)
+
 it.instance("remote timeout aborts both real HTTP transport attempts", () =>
   Effect.gen(function* () {
     const server = yield* hangingLifecycleServer()