Add browser security headers, implement upload temp directory management, and enhance SSE handling.

public/js/sse.js

@@ -0,0 +1,50 @@
+/** Reusable Server-Sent Events parser for browser and test environments. */
+export class SseParseError extends Error {
+    constructor(message, details = {}) {
+        super(message);
+        this.name = "SseParseError";
+        Object.assign(this, details);
+    }
+}
+
+function parseEvent(block, {onComment, onRetry} = {}) {
+    if (!block) return null;
+    let event = "message";
+    const data = [];
+    let id;
+    let retry;
+    for (const line of block.split(/\r?\n/)) {
+        if (line.startsWith(":")) { onComment?.(line.slice(1).trimStart()); continue; }
+        const separator = line.indexOf(":");
+        const field = separator < 0 ? line : line.slice(0, separator);
+        const value = separator < 0 ? "" : line.slice(separator + 1).replace(/^ /, "");
+        if (field === "event") event = value;
+        else if (field === "data") data.push(value);
+        else if (field === "id" && !value.includes("\u0000")) id = value;
+        else if (field === "retry" && /^\d+$/.test(value)) { retry = Number(value); onRetry?.(retry); }
+    }
+    if (!data.length) return null;
+    return {event, data: data.join("\n"), ...(id !== undefined ? {id} : {}), ...(retry !== undefined ? {retry} : {})};
+}
+
+export function createSseParser(options = {}) {
+    let buffer = "";
+    return {
+        push(text) {
+            buffer += text;
+            const blocks = buffer.split(/\r?\n\r?\n/);
+            buffer = blocks.pop() || "";
+            return blocks.map(block => parseEvent(block, options)).filter(Boolean);
+        },
+        finish() {
+            const event = parseEvent(buffer, options);
+            buffer = "";
+            return event ? [event] : [];
+        }
+    };
+}
+
+export function parseSseData(event) {
+    try { return JSON.parse(event.data); }
+    catch (error) { throw new SseParseError("Malformed SSE JSON payload.", {cause: error, event}); }
+}