diff --git a/skillopt_sleep/harvest_sources.py b/skillopt_sleep/harvest_sources.py
index e4d89056..c1925531 100644
--- a/skillopt_sleep/harvest_sources.py
+++ b/skillopt_sleep/harvest_sources.py
@@ -12,6 +12,17 @@
 from skillopt_sleep.harvest_pi import harvest_pi
 from skillopt_sleep.types import SessionDigest
 
+SUPPORTED_SOURCES = (
+    "claude",
+    "codex",
+    "copilot",
+    "copilot_cli",
+    "cursor",
+    "pi",
+    "opencode",
+    "auto",
+)
+
 
 def harvest_for_config(
     cfg,
@@ -26,10 +37,17 @@ def harvest_for_config(
     `skillopt_sleep.harvest.harvest`); the other sources have no repeat
     filter to report yet and leave it untouched.
     """
-    source = cfg.get("transcript_source", "claude")
+    raw_source = cfg.get("transcript_source", "claude")
+    source = (raw_source or "claude").strip().lower()
     scope = cfg.get("projects", "invoked")
     invoked_project = cfg.get("invoked_project", "")
 
+    if source not in SUPPORTED_SOURCES:
+        supported = ", ".join(SUPPORTED_SOURCES)
+        raise ValueError(
+            f"Unknown transcript source '{raw_source}'. Supported sources: {supported}"
+        )
+
     if source == "codex":
         return harvest_codex(
             cfg.codex_archived_sessions_dir,
diff --git a/tests/test_sleep_engine.py b/tests/test_sleep_engine.py
index bece0e97..ef3b27be 100644
--- a/tests/test_sleep_engine.py
+++ b/tests/test_sleep_engine.py
@@ -788,6 +788,28 @@ def test_auto_source_keeps_existing_codex_then_claude_precedence(self):
 
         cursor_harvest.assert_not_called()
 
+    def test_harvest_for_config_rejects_unknown_source(self):
+        from skillopt_sleep.harvest_sources import SUPPORTED_SOURCES, harvest_for_config
+
+        cfg = load_config(transcript_source="unknown_engine", invoked_project="/repo/project")
+        with self.assertRaises(ValueError) as ctx:
+            harvest_for_config(cfg)
+
+        msg = str(ctx.exception)
+        self.assertIn("Unknown transcript source 'unknown_engine'", msg)
+        self.assertIn("Supported sources:", msg)
+        for expected in SUPPORTED_SOURCES:
+            self.assertIn(expected, msg)
+
+    def test_harvest_for_config_accepts_empty_and_case_insensitive_source(self):
+        from skillopt_sleep.harvest_sources import harvest_for_config
+
+        expected = [SessionDigest(session_id="claude-session", project="/repo/project")]
+        for s in ("", "claude", "CLAUDE", "Claude"):
+            cfg = load_config(transcript_source=s, invoked_project="/repo/project")
+            with mock.patch("skillopt_sleep.harvest_sources.harvest", return_value=expected):
+                self.assertEqual(harvest_for_config(cfg), expected)
+
     def test_harvest_codex_filters_project_and_cli_source(self):
         from skillopt_sleep.__main__ import _cfg_from_args
         from skillopt_sleep.harvest_sources import harvest_for_config