feat(#373): prediction integration for cost estimation

- Create PredictionService for pre-task cost/token estimates
- Refresh common predictions on startup
- Integrate predictions into LLM telemetry tracker
- Add GET /api/telemetry/estimate endpoint
- Graceful degradation when no prediction data available
- Add unit tests for prediction service

Refs #373

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/api/src/mosaic-telemetry/prediction.service.ts

@@ -0,0 +1,161 @@
+import { Injectable, Logger, OnModuleInit } from "@nestjs/common";
+import {
+  TaskType,
+  Complexity,
+  Provider,
+  type PredictionQuery,
+  type PredictionResponse,
+} from "@mosaicstack/telemetry-client";
+import { MosaicTelemetryService } from "./mosaic-telemetry.service";
+
+/**
+ * Common model-provider combinations used for pre-fetching predictions.
+ * These represent the most frequently used LLM configurations.
+ */
+const COMMON_MODELS: { model: string; provider: Provider }[] = [
+  { model: "claude-sonnet-4-5", provider: Provider.ANTHROPIC },
+  { model: "claude-opus-4", provider: Provider.ANTHROPIC },
+  { model: "claude-haiku-4-5", provider: Provider.ANTHROPIC },
+  { model: "gpt-4o", provider: Provider.OPENAI },
+  { model: "gpt-4o-mini", provider: Provider.OPENAI },
+];
+
+/**
+ * Common task types to pre-fetch predictions for.
+ */
+const COMMON_TASK_TYPES: TaskType[] = [
+  TaskType.IMPLEMENTATION,
+  TaskType.PLANNING,
+  TaskType.CODE_REVIEW,
+];
+
+/**
+ * Common complexity levels to pre-fetch predictions for.
+ */
+const COMMON_COMPLEXITIES: Complexity[] = [Complexity.LOW, Complexity.MEDIUM];
+
+/**
+ * PredictionService
+ *
+ * Provides pre-task cost and token estimates using crowd-sourced prediction data
+ * from the Mosaic Telemetry server. Predictions are cached by the underlying SDK
+ * with a 6-hour TTL.
+ *
+ * This service is intentionally non-blocking: if predictions are unavailable
+ * (telemetry disabled, server unreachable, no data), all methods return null
+ * without throwing errors. Task execution should never be blocked by prediction
+ * failures.
+ *
+ * @example
+ * ```typescript
+ * const estimate = this.predictionService.getEstimate(
+ *   TaskType.IMPLEMENTATION,
+ *   "claude-sonnet-4-5",
+ *   Provider.ANTHROPIC,
+ *   Complexity.LOW,
+ * );
+ * if (estimate?.prediction) {
+ *   console.log(`Estimated cost: ${estimate.prediction.cost_usd_micros}`);
+ * }
+ * ```
+ */
+@Injectable()
+export class PredictionService implements OnModuleInit {
+  private readonly logger = new Logger(PredictionService.name);
+
+  constructor(private readonly telemetry: MosaicTelemetryService) {}
+
+  /**
+   * Refresh common predictions on startup.
+   * Runs asynchronously and never blocks module initialization.
+   */
+  onModuleInit(): void {
+    if (!this.telemetry.isEnabled) {
+      this.logger.log("Telemetry disabled - skipping prediction refresh");
+      return;
+    }
+
+    // Fire-and-forget: refresh in the background
+    this.refreshCommonPredictions().catch((error: unknown) => {
+      const msg = error instanceof Error ? error.message : String(error);
+      this.logger.warn(`Failed to refresh common predictions on startup: ${msg}`);
+    });
+  }
+
+  /**
+   * Get a cost/token estimate for a given task configuration.
+   *
+   * Returns the cached prediction from the SDK, or null if:
+   * - Telemetry is disabled
+   * - No prediction data exists for this combination
+   * - The prediction has expired
+   *
+   * @param taskType - The type of task to estimate
+   * @param model - The model name (e.g. "claude-sonnet-4-5")
+   * @param provider - The provider enum value
+   * @param complexity - The complexity level
+   * @returns Prediction response with estimates and confidence, or null
+   */
+  getEstimate(
+    taskType: TaskType,
+    model: string,
+    provider: Provider,
+    complexity: Complexity
+  ): PredictionResponse | null {
+    try {
+      const query: PredictionQuery = {
+        task_type: taskType,
+        model,
+        provider,
+        complexity,
+      };
+
+      return this.telemetry.getPrediction(query);
+    } catch (error: unknown) {
+      const msg = error instanceof Error ? error.message : String(error);
+      this.logger.warn(`Failed to get prediction estimate: ${msg}`);
+      return null;
+    }
+  }
+
+  /**
+   * Refresh predictions for commonly used (taskType, model, provider, complexity) combinations.
+   *
+   * Generates the cross-product of common models, task types, and complexities,
+   * then batch-refreshes them from the telemetry server. The SDK caches the
+   * results with a 6-hour TTL.
+   *
+   * This method is safe to call at any time. If telemetry is disabled or the
+   * server is unreachable, it completes without error.
+   */
+  async refreshCommonPredictions(): Promise<void> {
+    if (!this.telemetry.isEnabled) {
+      return;
+    }
+
+    const queries: PredictionQuery[] = [];
+
+    for (const { model, provider } of COMMON_MODELS) {
+      for (const taskType of COMMON_TASK_TYPES) {
+        for (const complexity of COMMON_COMPLEXITIES) {
+          queries.push({
+            task_type: taskType,
+            model,
+            provider,
+            complexity,
+          });
+        }
+      }
+    }
+
+    this.logger.log(`Refreshing ${String(queries.length)} common prediction queries...`);
+
+    try {
+      await this.telemetry.refreshPredictions(queries);
+      this.logger.log(`Successfully refreshed ${String(queries.length)} predictions`);
+    } catch (error: unknown) {
+      const msg = error instanceof Error ? error.message : String(error);
+      this.logger.warn(`Failed to refresh predictions: ${msg}`);
+    }
+  }
+}