Function handleSave

projects/electron/src/modules/code/yjsStorage.ts:128–208

* Save a YJS document to disk. * Uses atomic write (temp file + rename) to prevent corruption. * Merges incoming data with existing disk state to never lose data. * Serializes saves per document to prevent race conditions.

(id: string, data: Uint8Array)

 * Serializes saves per document to prevent race conditions.
 */
async function handleSave(id: string, data: Uint8Array): Promise<void> {
    // Chain this save after any pending save for the same document
    const prevSave = saveQueues.get(id) ?? Promise.resolve()

    const currentSave = prevSave.then(async () => {
        await ensureStorageDir()

        const filePath = getDocPath(id)
        const tempPath = `${filePath}.tmp.${Date.now()}.${Math.random().toString(36).slice(2)}`

        let doc: Y.Doc | null = null
        try {
            // Load existing state if present
            let existingData: Buffer | null = null
            try {
                existingData = await fs.readFile(filePath)
            } catch (error) {
                if ((error as NodeJS.ErrnoException).code !== "ENOENT") {
                    throw error
                }
                // File doesn't exist yet, that's fine
            }

            // Fast path: if incoming data exactly matches existing, skip the save
            if (existingData && existingData.length === data.length) {
                let identical = true
                for (let i = 0; i < data.length; i++) {
                    if (existingData[i] !== data[i]) {
                        identical = false
                        break
                    }
                }
                if (identical) {
                    logger.debug(`[YjsStorage] Skipped save (unchanged): ${id} (${data.length} bytes)`)
                    return
                }
            }

            // Merge with existing data to never lose updates
            doc = new Y.Doc()

            if (existingData) {
                Y.applyUpdate(doc, new Uint8Array(existingData))
            }

            // Apply incoming update (merges with existing via CRDT)
            Y.applyUpdate(doc, data)

            // Encode merged state
            const mergedState = Y.encodeStateAsUpdate(doc)

            // Atomic write: write to temp file, then rename
            await fs.writeFile(tempPath, mergedState)
            await fs.rename(tempPath, filePath)

            logger.debug(`[YjsStorage] Saved document: ${id} (${mergedState.length} bytes)`)
        } catch (error) {
            // Clean up temp file if it exists