Refactor: Remove unused preferSseStream method from TransportInterface

The preferSseStream method was defined in TransportInterface and implemented
as a no-op in HttpTransport, StdioTransport, and the MockTransport.
Codebase analysis confirmed that this method was not called anywhere,
nor was it part of the documented external API in README.md or examples.

The HttpTransport currently does not support Server-Sent Events (SSE),
and the MCP specification (2025-03-26) makes SSE an optional feature for
servers. As the method provided no functionality towards current or
planned SSE capabilities and was unused, it has been removed to simplify
the interface and reduce potential confusion.

This change involved:
- Removing the method definition from TransportInterface.
- Removing the implementations from HttpTransport, StdioTransport, and MockTransport.
- Verifying that all tests and linters pass after the removal.

Author: google-labs-jules[bot]

src/Transport/HttpTransport.php

@@ -266,20 +266,4 @@ public function getResponse(): ResponseInterface
         }
         return $this->response;
     }
-
-    /**
-     * Indicates a preference for using Server-Sent Events (SSE) for streaming responses, if applicable.
-     *
-     * Transports that support SSE (like HttpTransport) can use this hint to switch
-     * their response mode. Other transports can ignore this.
-     *
-     * @param bool $prefer True to prefer SSE, false otherwise.
-     */
-    public function preferSseStream(bool $prefer = true): void
-    {
-        // Default implementation does nothing, to be overridden by transports that support SSE.
-        // In a real HttpTransport that supports SSE, this method would set a flag
-        // to change response content-type and formatting in the send() method.
-        // For this simplified version, it remains a no-op.
-    }
 }

src/Transport/StdioTransport.php

@@ -203,15 +203,4 @@ public function isStreamOpen(): bool
     {
         return false;
     }
-
-    /**
-     * Indicates a preference for using Server-Sent Events (SSE) for streaming responses, if applicable.
-     * StdioTransport does not support SSE, so this is a no-op.
-     *
-     * @param bool $prefer True to prefer SSE, false otherwise.
-     */
-    public function preferSseStream(bool $prefer = true): void
-    {
-        // StdioTransport does not support SSE.
-    }
 }

src/Transport/TransportInterface.php

@@ -69,14 +69,4 @@ public function isClosed(): bool;
      * @return bool True if a stream is actively open, false otherwise.
      */
     public function isStreamOpen(): bool;
-
-    /**
-     * Hints to the transport that Server-Sent Events (SSE) are preferred for the response stream, if applicable.
-     *
-     * Transports that support SSE (e.g., HttpTransport) can use this to modify
-     * how they format and send responses. Transports that do not support SSE can ignore this hint.
-     *
-     * @param bool $prefer True to indicate a preference for SSE streaming, false otherwise.
-     */
-    public function preferSseStream(bool $prefer = true): void;
 }

tests/Util/MockTransport.php

@@ -80,12 +80,6 @@ public function log(string $message): void
         // error_log("MockTransport Log: " . $message); // For debugging tests
     }
 
-    public function preferSseStream(bool $prefer = true): void
-    {
-        // No-op for this mock implementation.
-        // Could store the preference if tests need to assert it was called.
-    }
-
     /**
      * Checks if the transport stream is currently open.
      * For this mock, defaults to false. Can be made configurable if needed.