fix(retrieval): make decisions findable by name + unhide committee uploads

Root cause of "agent can't find the Agasi decision in the corpus" (CMPA-55):
the decision was fully ingested, but the retrieval layer failed on the
realistic agent query — searching by case name.

- RC-A (#52): lexical tsvector covered only chunk content + halacha text,
  so a bare-name query ("אגסי") matched decisions that *cite* the case, not
  the case itself. Add meta_tsv on case_law(case_name, case_number) (SCHEMA
  V20) and OR it into the lexical halacha/chunk SQL with a match boost, so a
  name/number hit surfaces the case's own rows. Agasi: rank 4 → rank 1.
- RC-B (#53): precedent_library_list hard-defaulted source_kind=external_upload
  and never exposed the param, hiding uploaded ערר/בל"מ (internal_committee)
  decisions. Thread source_kind through service → tool → MCP tool (supports
  'internal_committee' / 'all_committees').
- #54: agent instructions (researcher/analyst/writer) — search-by-name
  protocol: add content/case-number, search both corpora, use all_committees
  before declaring "not in corpus".
- #55: chunker produced tiny fragment chunks ("דיון", "החלטה") from header
  keywords matched mid-sentence. Anchor SECTION_PATTERNS to line start +
  merge sub-min sections; exclude <50-char fragments at query time (484
  existing fragments hidden; full re-chunk tracked as #57).

Tests: scripts/test_retrieval_by_name.py (name ranks case above citer +
substantive regressions); chunker unit checks (0 tiny chunks). New findings
filed as tasks #56 (halacha source_kind leak) and #57 (re-chunk migration).

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

mcp-server/src/legal_mcp/services/db.py

@@ -1070,6 +1070,29 @@ ALTER TABLE case_law ADD COLUMN IF NOT EXISTS citation_formatted TEXT DEFAULT ''
 """
 
 
+# ── V20: case-name / case-number lexical match ────────────────────
+# RC-A fix: the V12 tsvectors cover only chunk *content* + halacha
+# text, so a bare case-name query ("אגסי") matched decisions that
+# *cite* the case rather than the case itself. case_name and
+# case_number live on the parent case_law row, so we add a dedicated
+# meta tsvector there and OR it into the lexical search — a name/number
+# hit then surfaces all of that case's chunks + halachot. 'simple'
+# config (no stemmer) preserves Hebrew names + alphanumeric case
+# numbers like "81002-01-21" exactly as V12 does for content.
+SCHEMA_V20_SQL = """
+ALTER TABLE case_law
+    ADD COLUMN IF NOT EXISTS meta_tsv tsvector
+    GENERATED ALWAYS AS (
+        to_tsvector('simple',
+            coalesce(case_name,'') || ' ' || coalesce(case_number,'')
+        )
+    ) STORED;
+
+CREATE INDEX IF NOT EXISTS idx_case_law_meta_tsv
+    ON case_law USING GIN(meta_tsv);
+"""
+
+
 async def _run_schema_migrations(pool: asyncpg.Pool) -> None:
     async with pool.acquire() as conn:
         await conn.execute(SCHEMA_SQL)
@@ -1092,7 +1115,8 @@ async def _run_schema_migrations(pool: asyncpg.Pool) -> None:
         await conn.execute(SCHEMA_V17_SQL)
         await conn.execute(SCHEMA_V18_SQL)
         await conn.execute(SCHEMA_V19_SQL)
-    logger.info("Database schema initialized (v1-v19)")
+        await conn.execute(SCHEMA_V20_SQL)
+    logger.info("Database schema initialized (v1-v20)")
 
 
 async def init_schema() -> None:
@@ -3217,6 +3241,9 @@ async def search_precedent_library_semantic(
             ON parent.id = pc.parent_chunk_id
         WHERE {' AND '.join(chunk_filters)}
           AND pc.embedding IS NOT NULL
+          -- #55: exclude tiny fragment chunks (artifacts of pre-fix
+          -- mid-sentence header splits) that carry no retrievable signal.
+          AND length(trim(pc.content)) >= 50
         ORDER BY pc.embedding <=> $1
         LIMIT $2
     """
@@ -3411,11 +3438,17 @@ async def search_precedent_library_lexical(
                h.practice_areas, h.subject_tags, h.confidence, h.rule_type,
                cl.case_number, cl.case_name, cl.court, cl.date AS decision_date,
                cl.precedent_level, cl.chair_name, cl.district,
-               ts_rank_cd(h.rule_tsv, plainto_tsquery('simple', $1)) AS score
+               GREATEST(
+                   ts_rank_cd(h.rule_tsv, plainto_tsquery('simple', $1)),
+                   ts_rank_cd(cl.meta_tsv, plainto_tsquery('simple', $1))
+               )
+               + CASE WHEN cl.meta_tsv @@ plainto_tsquery('simple', $1)
+                      THEN 1.0 ELSE 0.0 END AS score
         FROM halachot h
         JOIN case_law cl ON cl.id = h.case_law_id
         WHERE {' AND '.join(halacha_filters)}
-          AND h.rule_tsv @@ plainto_tsquery('simple', $1)
+          AND (h.rule_tsv @@ plainto_tsquery('simple', $1)
+               OR cl.meta_tsv @@ plainto_tsquery('simple', $1))
         ORDER BY score DESC
         LIMIT $2
     """
@@ -3439,14 +3472,22 @@ async def search_precedent_library_lexical(
                parent.page_number AS parent_page_number,
                cl.case_number, cl.case_name, cl.court, cl.date AS decision_date,
                cl.precedent_level, cl.practice_area, cl.chair_name, cl.district,
-               ts_rank_cd(pc.content_tsv, plainto_tsquery('simple', $1)) AS score
+               GREATEST(
+                   ts_rank_cd(pc.content_tsv, plainto_tsquery('simple', $1)),
+                   ts_rank_cd(cl.meta_tsv, plainto_tsquery('simple', $1))
+               )
+               + CASE WHEN cl.meta_tsv @@ plainto_tsquery('simple', $1)
+                      THEN 1.0 ELSE 0.0 END AS score
         FROM precedent_chunks pc
         JOIN case_law cl ON cl.id = pc.case_law_id
         LEFT JOIN precedent_chunks parent
             ON parent.id = pc.parent_chunk_id
         WHERE {' AND '.join(chunk_filters)}
           AND pc.embedding IS NOT NULL
-          AND pc.content_tsv @@ plainto_tsquery('simple', $1)
+          -- #55: exclude tiny fragment chunks (see semantic query above).
+          AND length(trim(pc.content)) >= 50
+          AND (pc.content_tsv @@ plainto_tsquery('simple', $1)
+               OR cl.meta_tsv @@ plainto_tsquery('simple', $1))
         ORDER BY score DESC
         LIMIT $2
     """