feat(compression): add type definitions and barrel exports

Define CompressionMode (off/lite/standard/aggressive/ultra), CompressionConfig, CompressionStats, CompressionResult interfaces. Add barrel index.ts re-exporting all public functions.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

open-sse/services/compression/index.ts

@@ -0,0 +1,31 @@
+/**
+ * Compression Pipeline — Phase 1 (Lite mode)
+ *
+ * Modular prompt compression that runs BEFORE the existing reactive context manager.
+ * Lite mode: 5 techniques, ~10-15% token savings, <1ms latency.
+ */
+
+// Types
+export type {
+  CompressionMode,
+  CompressionConfig,
+  CompressionStats,
+  CompressionResult,
+} from "./types";
+export { DEFAULT_COMPRESSION_CONFIG } from "./types";
+
+// Lite compression techniques
+export {
+  applyLiteCompression,
+  collapseWhitespace,
+  dedupSystemPrompt,
+  compressToolResults,
+  removeRedundantContent,
+  replaceImageUrls,
+} from "./lite";
+
+// Strategy selector
+export { selectCompressionStrategy, getEffectiveMode, applyCompression } from "./strategySelector";
+
+// Stats tracking
+export { estimateCompressionTokens, createCompressionStats, trackCompressionStats } from "./stats";

open-sse/services/compression/types.ts

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+/**
+ * Compression Pipeline Types — Phase 1 (Lite mode)
+ *
+ * Modular prompt compression that runs BEFORE the existing reactive context manager.
+ */
+
+/** Compression mode levels (only 'off' and 'lite' are active in Phase 1) */
+export type CompressionMode = "off" | "lite" | "standard" | "aggressive" | "ultra";
+
+/** Compression configuration stored in DB */
+export interface CompressionConfig {
+  enabled: boolean;
+  defaultMode: CompressionMode;
+  autoTriggerTokens: number;
+  cacheMinutes: number;
+  preserveSystemPrompt: boolean;
+  comboOverrides: Record<string, CompressionMode>;
+}
+
+/** Per-request compression statistics */
+export interface CompressionStats {
+  originalTokens: number;
+  compressedTokens: number;
+  savingsPercent: number;
+  techniquesUsed: string[];
+  mode: CompressionMode;
+  timestamp: number;
+}
+
+/** Result of a compression operation */
+export interface CompressionResult {
+  body: Record<string, unknown>;
+  compressed: boolean;
+  stats: CompressionStats | null;
+}
+
+/** Default compression config values */
+export const DEFAULT_COMPRESSION_CONFIG: CompressionConfig = {
+  enabled: false,
+  defaultMode: "off",
+  autoTriggerTokens: 0,
+  cacheMinutes: 5,
+  preserveSystemPrompt: true,
+  comboOverrides: {},
+};