fix: free StreamBuffer memory on write completion and error

Previously, StreamBuffer's outgoing buffer in PosixStreamingWriter and
WindowsStreamingWriter was not properly freed when writes completed with
end_of_file status or when errors occurred. The code called reset() or
clearRetainingCapacity() which retained the allocated memory instead of
freeing it.

This change calls deinit() instead of reset() in these scenarios:
- PosixStreamingWriter._onWrite(): When status is end_of_file
- PosixStreamingWriter._onError(): When an error occurs
- WindowsStreamingWriter.onWriteComplete(): When was_done and done, or on error
- WindowsStreamingWriter.onFsWriteComplete(): When canceled or on error

This ensures memory is properly released when a writer is finished, rather
than being retained indefinitely until the parent object is destroyed.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/io/PipeWriter.zig

@@ -442,7 +442,8 @@ pub fn PosixStreamingWriter(comptime Parent: type, comptime function_table: anyt
 
             this.closeWithoutReporting();
             this.is_done = true;
-            this.outgoing.reset();
+            // Free the buffer completely since we're done with this writer due to error
+            this.outgoing.deinit();
 
             onError(@ptrCast(@alignCast(this.parent)), err);
             this.close();
@@ -461,10 +462,13 @@ pub fn PosixStreamingWriter(comptime Parent: type, comptime function_table: anyt
 
             if (this.outgoing.isEmpty()) {
                 this.outgoing.cursor = 0;
-                if (status != .end_of_file) {
+                if (status == .end_of_file) {
+                    // Free the buffer completely since we're done with this writer
+                    this.outgoing.deinit();
+                } else {
                     this.outgoing.maybeShrink();
+                    this.outgoing.list.clearRetainingCapacity();
                 }
-                this.outgoing.list.clearRetainingCapacity();
             }
 
             onWrite(this.parent, written, status);
@@ -1302,6 +1306,10 @@ pub fn WindowsStreamingWriter(comptime Parent: type, function_table: anytype) ty
                 this.last_write_result = .{ .err = err };
                 log("onWrite() = {s}", .{err.name()});
 
+                // Free buffers completely on error since we're done with this writer
+                this.outgoing.deinit();
+                this.current_payload.deinit();
+
                 onError(this.parent, err);
                 this.closeWithoutReporting();
                 return;
@@ -1318,7 +1326,9 @@ pub fn WindowsStreamingWriter(comptime Parent: type, function_table: anytype) ty
             log("onWrite({d}) ({d} left)", .{ written, this.outgoing.size() });
 
             if (was_done and done) {
-                // we already call .end lets close the connection
+                // we already call .end lets close the connection - free buffers completely
+                this.outgoing.deinit();
+                this.current_payload.deinit();
                 this.last_write_result = .{ .done = written };
                 onWrite(this.parent, written, .end_of_file);
                 return;
@@ -1355,12 +1365,16 @@ pub fn WindowsStreamingWriter(comptime Parent: type, function_table: anytype) ty
             const this = bun.cast(*WindowsWriter, parent_ptr);
 
             if (was_canceled) {
-                // Canceled write - reset buffers
-                this.current_payload.reset();
+                // Canceled write - free buffers completely
+                this.current_payload.deinit();
+                this.outgoing.deinit();
                 return;
             }
 
             if (result.toError(.write)) |err| {
+                // Free buffers completely on error since we're done with this writer
+                this.outgoing.deinit();
+                this.current_payload.deinit();
                 this.close();
                 onError(this.parent, err);
                 return;