feat(FN-2327): standardize dashboard runtime logging pipeline

- Add a shared runtime logger contract and dashboard runtime logger implementation for structured diagnostics
- Route dashboard CLI/runtime logs through the TUI sink and replace ad-hoc console diagnostics in server paths
- Update CLI and dashboard tests to assert structured runtime logging behavior across sync and error flows
- Document the structured logging architecture updates and include a changeset for @runfusion/fusion

packages/dashboard/src/runtime-logger.ts

@@ -0,0 +1,82 @@
+export type RuntimeLogLevel = "info" | "warn" | "error";
+
+export interface RuntimeLogContext {
+  [key: string]: unknown;
+}
+
+export interface RuntimeLogSink {
+  (level: RuntimeLogLevel, scope: string, message: string, context?: RuntimeLogContext): void;
+}
+
+export interface RuntimeLogger {
+  readonly scope: string;
+  info(message: string, context?: RuntimeLogContext): void;
+  warn(message: string, context?: RuntimeLogContext): void;
+  error(message: string, context?: RuntimeLogContext): void;
+  child(scope: string): RuntimeLogger;
+}
+
+let sink: RuntimeLogSink = defaultRuntimeLogSink;
+
+function defaultRuntimeLogSink(
+  level: RuntimeLogLevel,
+  scope: string,
+  message: string,
+  context?: RuntimeLogContext,
+): void {
+  const line = `[${scope}] ${message}`;
+  const args = context === undefined ? [line] : [line, context];
+  try {
+    switch (level) {
+      case "info":
+        console.log(...args);
+        break;
+      case "warn":
+        console.warn(...args);
+        break;
+      case "error":
+        console.error(...args);
+        break;
+    }
+  } catch {
+    // Logging must never throw into runtime flows.
+  }
+}
+
+function emit(level: RuntimeLogLevel, scope: string, message: string, context?: RuntimeLogContext): void {
+  try {
+    sink(level, scope, message, context);
+  } catch {
+    // Logging must never throw into runtime flows.
+  }
+}
+
+export function createRuntimeLogger(scope: string): RuntimeLogger {
+  return {
+    scope,
+    info(message, context) {
+      emit("info", scope, message, context);
+    },
+    warn(message, context) {
+      emit("warn", scope, message, context);
+    },
+    error(message, context) {
+      emit("error", scope, message, context);
+    },
+    child(childScope) {
+      return createRuntimeLogger(`${scope}:${childScope}`);
+    },
+  };
+}
+
+export function setRuntimeLogSink(nextSink: RuntimeLogSink | null | undefined): void {
+  sink = nextSink ?? defaultRuntimeLogSink;
+}
+
+export function getRuntimeLogSink(): RuntimeLogSink {
+  return sink;
+}
+
+export function resetRuntimeLogSink(): void {
+  sink = defaultRuntimeLogSink;
+}