[Init] Initial commit - NetMesh terminal manager

components/terminal/runtime/outputFlowController.ts

@@ -0,0 +1,74 @@
+/**
+ * Watermark-based flow control for terminal output.
+ *
+ * SSH/PTY output has no back-pressure by default: the source streams as fast as
+ * it can, the main process forwards it over IPC, and the renderer queues every
+ * chunk into xterm. When output outpaces rendering (e.g. `cat` of a big file, a
+ * noisy build, `tail -f`, `yes`), the renderer-side backlog and xterm's internal
+ * buffer grow without bound — memory climbs and the whole UI, typing included,
+ * janks.
+ *
+ * This tracks bytes that have been received but not yet acknowledged by xterm's
+ * write callback. When the backlog crosses `highWaterMark` it asks the caller to
+ * pause the source; once it drains back to `lowWaterMark` it asks to resume. The
+ * hysteresis gap avoids rapid pause/resume flapping. During interactive use the
+ * backlog hovers near zero, so this never engages.
+ */
+export interface OutputFlowController {
+  /** Account bytes handed to xterm (call when a chunk is received). */
+  received(bytes: number): void;
+  /** Account bytes whose xterm write callback has fired. */
+  written(bytes: number): void;
+  /** Clear pending state; calls `onResume` if currently paused. */
+  reset(options?: { resume?: boolean }): void;
+  pendingBytes(): number;
+  isPaused(): boolean;
+}
+
+export interface OutputFlowControllerOptions {
+  highWaterMark: number;
+  lowWaterMark: number;
+  /** Asked to pause the source when the backlog crosses the high watermark. */
+  onPause: () => void;
+  /** Asked to resume the source when the backlog drains to the low watermark. */
+  onResume: () => void;
+}
+
+export function createOutputFlowController(
+  options: OutputFlowControllerOptions,
+): OutputFlowController {
+  const { highWaterMark, lowWaterMark, onPause, onResume } = options;
+  let pending = 0;
+  let paused = false;
+
+  return {
+    received(bytes: number): void {
+      if (bytes <= 0) return;
+      pending += bytes;
+      if (!paused && pending >= highWaterMark) {
+        paused = true;
+        onPause();
+      }
+    },
+    written(bytes: number): void {
+      if (bytes <= 0) return;
+      pending -= bytes;
+      if (pending < 0) pending = 0;
+      if (paused && pending <= lowWaterMark) {
+        paused = false;
+        onResume();
+      }
+    },
+    reset(options?: { resume?: boolean }): void {
+      if (paused && options?.resume !== false) onResume();
+      pending = 0;
+      paused = false;
+    },
+    pendingBytes(): number {
+      return pending;
+    },
+    isPaused(): boolean {
+      return paused;
+    },
+  };
+}