From e6165d23bb2f2df4b25aa791aaac3a81cd835b1a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Adri=C3=A0=20Arrufat?= <adria.arrufat@gmail.com>
Date: Thu, 27 Aug 2026 14:53:32 +0200
Subject: [PATCH] mcp: release a large HTTP response buffer after the reply

The transport already drops its staging buffer past 256 KB, but the
connection buffer that receives the copy lives for the whole keep-alive
connection and was only ever cleared, so one screenshot pinned its
capacity per open connection. Apply the same threshold there.

Claude-Session: https://claude.ai/code/session_01S9t1TX3vTKunaXdnatbcjB
---
 src/mcp/HttpServer.zig | 5 +++++
 src/mcp/Transport.zig  | 4 ++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/mcp/HttpServer.zig b/src/mcp/HttpServer.zig
index e1394cd4a..744d9c332 100644
--- a/src/mcp/HttpServer.zig
+++ b/src/mcp/HttpServer.zig
@@ -35,6 +35,7 @@ const App = @import("../App.zig");
 const sys_net = @import("../sys/net.zig");
 
 const Server = @import("Server.zig");
+const Transport = @import("Transport.zig");
 const router = @import("router.zig");
 
 const log = lp.log;
@@ -379,6 +380,10 @@ fn handleConn(self: *HttpServer, socket: posix.socket_t) void {
         _ = arena.reset(.retain_capacity);
         out.clearRetainingCapacity();
         self.serve(&out.writer, arena.allocator(), &request) catch return;
+        if (out.writer.buffer.len > Transport.large_response) {
+            out.deinit();
+            out = .init(self.allocator);
+        }
         if (!request.head.keep_alive or http_server.reader.state == .closing) return;
     }
 }
diff --git a/src/mcp/Transport.zig b/src/mcp/Transport.zig
index e81bae88f..eb94045f7 100644
--- a/src/mcp/Transport.zig
+++ b/src/mcp/Transport.zig
@@ -25,7 +25,8 @@ const protocol = @import("protocol.zig");
 
 const Self = @This();
 
-const large_response = 256 * 1024;
+/// A screenshot response is hundreds of KB; don't keep that parked.
+pub const large_response = 256 * 1024;
 
 writer: *std.Io.Writer,
 mutex: std.Io.Mutex = .init,
@@ -56,7 +57,6 @@ pub fn sendResponse(self: *Self, response: anytype) !void {
     try self.writer.writeAll(self.aw.writer.buffered());
     try self.writer.flush();
 
-    // A screenshot response is hundreds of KB; don't keep that parked.
     if (self.aw.writer.buffer.len > large_response) {
         const allocator = self.aw.allocator;
         self.aw.deinit();