fix(write-path): a search hit's excerpt under snippet no longer 500s the prior-art route (#4768)

#4768 "Write-path prior-art route 500s when a nameless search hit carries
its excerpt under `snippet`": _prior_art_line read item["snippet"] as a
snippet record's field dict, but a search hit carries its matched passage
there as a string. Read the name only from a dict.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_write_path_trigger.py

@@ -956,6 +956,17 @@ def test_prior_art_line_keeps_language_and_attribution_together():
     assert "· python" in both and "shared by alex" in both
 
 
+def test_prior_art_line_takes_a_search_hit_whose_snippet_is_its_excerpt():
+    """A search hit carries its matched passage as a STRING under `snippet` —
+    the key a snippet record uses for its field dict. Reading it as the dict
+    500'd the write-path route on any nameless hit."""
+    from scribe.services.plugin_context import _prior_art_line
+    hit = {"id": 7, "title": "Paging contract", "snippet": "…the cursor is opaque…"}
+    assert _prior_art_line(hit, "similar 0.61", None) == '> - #7 [similar 0.61] "Paging contract"'
+    record = {"id": 8, "title": "long composed title", "snippet": {"name": "paginate"}}
+    assert _prior_art_line(record, "similar 0.70", None) == '> - #8 [similar 0.70] "paginate"'
+
+
 # --- the route between them --------------------------------------------------
 
 def test_route_reads_every_arg_the_hook_sends():