Consolidate Odysseus agent harness and tool contracts

tests/test_youtube_prefetch_provenance.py

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+from routes.chat_helpers import youtube_prefetch_sources
+
+
+def test_successful_youtube_preprocessing_has_visible_provenance():
+    sources = youtube_prefetch_sources(
+        "Summarize https://youtu.be/jNQXAC9IVRw",
+        [
+            "instructions",
+            "[YOUTUBE VIDEO TRANSCRIPT]\nTitle: Me at the zoo\n[END TRANSCRIPT]",
+            "[YOUTUBE VIDEO COMMENTS — Top 2 by popularity]\n[END COMMENTS]",
+        ],
+    )
+
+    assert sources == [{
+        "url": "https://youtu.be/jNQXAC9IVRw",
+        "title": "Me at the zoo",
+        "acquisition": "automatic_youtube_context",
+        "evidence": "transcript+comments",
+    }]
+
+
+def test_failed_youtube_preprocessing_does_not_claim_evidence():
+    assert youtube_prefetch_sources(
+        "Summarize https://youtu.be/jNQXAC9IVRw",
+        ["Transcript unavailable; use comments if available."],
+    ) == []