test(preemptive-compaction): add unit tests for smart compaction hook

- Add tests for compaction-logger utility (path verification)
- Add comprehensive tests for preemptive-compaction hook:
  - Disabled state behavior
  - Model filtering (Claude only)
  - Threshold checking
  - Cooldown mechanism
  - Multi-phase flow (DCP + truncation + summarize)
  - Custom threshold and model limit callbacks
  - onBeforeSummarize callback

Author: harshav167

src/hooks/preemptive-compaction/compaction-logger.test.ts

@@ -0,0 +1,29 @@
+import { describe, it, expect, mock, beforeEach } from "bun:test"
+import { getCompactionLogPath } from "./compaction-logger"
+
+// Since we can't easily mock node:fs for appendFileSync in bun:test,
+// we'll test the pure functions and verify the log path structure
+
+describe("compaction-logger", () => {
+  describe("getCompactionLogPath", () => {
+    it("#then should return a path ending with compaction.log", () => {
+      const logPath = getCompactionLogPath()
+      expect(logPath).toContain("compaction.log")
+    })
+
+    it("#then should be in opencode storage directory", () => {
+      const logPath = getCompactionLogPath()
+      expect(logPath).toContain("opencode")
+    })
+  })
+
+  // Note: logCompaction and clearCompactionLog are thin wrappers around fs operations
+  // with silent error handling. Testing them requires file system access or complex
+  // module mocking. The key behaviors are:
+  // 1. Formats log entries correctly (covered by integration)
+  // 2. Never throws errors (error handling is silent)
+  // 3. Uses correct log file path (verified above)
+  
+  // The formatting logic is verified through integration testing and manual inspection
+  // of the log output format documented in the implementation.
+})