fix(session-memory): add debug log for custom content, tighten test assertion

- Add log.debug when sessionSaveContent override is used (symmetric with blockSessionSave)
- Change override test assertion from toContain to toBe for precision

src/hooks/bundled/session-memory/handler.test.ts

@@ -618,7 +618,7 @@ describe("session-memory hook", () => {
     const files = (await fs.readdir(memoryDir)).filter((f) => f.endsWith(".md"));
     expect(files.length).toBeGreaterThan(0);
     const content = await fs.readFile(path.join(memoryDir, files[0]), "utf-8");
-    expect(content).toContain("Custom summary from upstream hook");
+    expect(content).toBe("Custom summary from upstream hook");
     expect(content).not.toContain("original");
   });
 

src/hooks/bundled/session-memory/handler.ts

@@ -353,6 +353,11 @@ const saveSessionToMemory: HookHandler = async (event) => {
     // An empty string is a valid redaction signal — hooks may intentionally
     // set it to persist a blank marker while avoiding transcript retention.
     const customContent = context.sessionSaveContent;
+    if (typeof customContent === "string") {
+      log.debug("Using custom session content from upstream hook", {
+        length: customContent.length,
+      });
+    }
     const entry = typeof customContent === "string" ? customContent : entryParts.join("\n");
 
     // Write under memory root with alias-safe file validation.