diff --git a/skillopt_sleep/__main__.py b/skillopt_sleep/__main__.py
index 78f22f3..3a3e047 100644
--- a/skillopt_sleep/__main__.py
+++ b/skillopt_sleep/__main__.py
@@ -111,8 +111,10 @@ def _cfg_from_args(args, task_meta: Dict[str, Any] | None = None) -> Any:
         overrides["codex_home"] = os.path.abspath(args.codex_home)
     if getattr(args, "source", ""):
         overrides["transcript_source"] = args.source
-    if getattr(args, "lookback_hours", 0):
+    if getattr(args, "lookback_hours", None) is not None and args.lookback_hours != 0:
         overrides["lookback_hours"] = args.lookback_hours
+    elif getattr(args, "lookback_hours", None) == 0:
+        overrides["lookback_hours"] = 0  # explicit opt-out: scan full history
     if getattr(args, "edit_budget", 0):
         overrides["edit_budget"] = args.edit_budget
     if getattr(args, "max_sessions", 0):
diff --git a/skillopt_sleep/cycle.py b/skillopt_sleep/cycle.py
index 9375784..57b06a9 100644
--- a/skillopt_sleep/cycle.py
+++ b/skillopt_sleep/cycle.py
@@ -148,7 +148,7 @@ def run_sleep_cycle(
         # scan the entire transcript history and trigger massive LLM mining.
         if since is None:
             lookback_hours = cfg.get("lookback_hours", 72)
-            if lookback_hours and lookback_hours > 0:
+            if lookback_hours is not None and lookback_hours > 0:
                 import time
                 ref_time = clock if clock is not None else time.time()
                 cutoff = ref_time - lookback_hours * 3600
diff --git a/skillopt_sleep/harvest.py b/skillopt_sleep/harvest.py
index 84446f8..851e5f1 100644
--- a/skillopt_sleep/harvest.py
+++ b/skillopt_sleep/harvest.py
@@ -294,9 +294,10 @@ def harvest(
         if not _project_matches(d.project or "", scope, invoked_project):
             continue
         if since_iso and d.ended_at and d.ended_at < since_iso:
-            # Files are sorted newest-first by mtime; once we see one that
-            # is older than the cutoff, all remaining files are older too.
-            break
+            # Note: files are sorted by mtime but we compare the embedded
+            # ended_at timestamp — mtime can diverge (copy/touch), so we
+            # cannot break here; we must continue to check all files.
+            continue
         digests.append(d)
         if limit and len(digests) >= limit:
             break