feat(journal): _build_transcript caps content and message window

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_journal_closeout.py

@@ -22,3 +22,32 @@ def test_filter_excludes_daily_prep_messages():
     assert "Good morning — here is today's plan…" not in contents
     assert "I want to focus on the auth refactor today." in contents
     assert "Got it. I'll keep tool calls quiet." in contents
+
+
+def test_build_transcript_labels_roles_and_caps_content():
+    from fabledassistant.services.journal_closeout import _build_transcript
+
+    msgs = [
+        _msg("user", "hello"),
+        _msg("assistant", "hi"),
+        _msg("user", "x" * 600),
+    ]
+    out = _build_transcript(msgs)
+    lines = out.splitlines()
+    assert lines[0] == "USER: hello"
+    assert lines[1] == "ASSISTANT: hi"
+    # Third line content truncated to 500 chars
+    assert lines[2].startswith("USER: ")
+    assert len(lines[2]) == len("USER: ") + 500
+
+
+def test_build_transcript_keeps_only_last_20_messages():
+    from fabledassistant.services.journal_closeout import _build_transcript
+
+    msgs = [_msg("user", f"msg-{i}") for i in range(30)]
+    out = _build_transcript(msgs)
+    lines = out.splitlines()
+    assert len(lines) == 20
+    # Newest 20 means msg-10 through msg-29
+    assert lines[0] == "USER: msg-10"
+    assert lines[-1] == "USER: msg-29"