feat(api): prompt loader (header split) + curated canon-log digest

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

api/tests/test_prompts.py

@@ -0,0 +1,35 @@
+import json
+from pathlib import Path
+
+from app.prompts import render_digest, system_prompt
+
+VALID = json.loads((Path(__file__).parent / "fixtures" / "canon_log_valid.json").read_text())
+
+
+def test_system_prompt_strips_the_header():
+    body = system_prompt("narrator")
+    assert isinstance(body, str) and body.strip() != ""
+    # The human-facing markdown title above the '---' is not part of the prompt.
+    assert "# Narrator prompt" not in body
+
+
+def test_digest_has_the_narrative_context():
+    d = render_digest(VALID)
+    assert "Location: the Greywater docks" in d
+    assert "Arrived at Greywater by barge before dawn" in d
+    assert "Established facts:" in d
+    assert "the harbourmaster is named Oda Fenn" in d
+    assert "Companions present: Brannoc Thane, Cadwyn Vell" in d
+    assert "Active quest: The Missing Ledger — Find who took Fenn's ledger" in d
+    assert "Fortune: Fortune spits on you" in d
+    assert "Player: Aldric, a sellsword" in d
+    assert d.rstrip().endswith("Describe the scene as it is now.")
+
+
+def test_digest_omits_raw_numbers_and_ids():
+    d = render_digest(VALID)
+    # §7/§2: no disposition integers, no ids, no schema_version leak into the prompt.
+    assert "disposition" not in d
+    assert "40" not in d and "15" not in d      # the deserter dispositions
+    assert "brannoc_thane" not in d             # ids stay out; names only
+    assert "schema_version" not in d