feat(style-acq T1-T3): קורפוס-דוגמאות של דפנה לכותב (style_exemplars)

ממלא את ערוץ-הדוגמאות (B) של מערכת רכישת-הסגנון: הכותב מאחזר פסקאות-בלוק
אמיתיות של דפנה בזמן כתיבה, ממוקדות section+outcome+practice_area.

T1 — תשתית + backfill:
- SCHEMA_V27: טבלת style_exemplars (purpose-built — בלי תיקים מזויפים בשרשרת
  decision_paragraphs). decision_number/source/section/outcome/practice_area+embedding.
- db: insert/delete/search_style_exemplars + count_style_exemplars.
- scripts/backfill_style_exemplars.py: מפצל קורפוס דפנה (style_corpus +
  internal_committee) לסעיפים→פסקאות, embed, שמירה. אידמפוטנטי, dry-run/apply.

T2 — אחזור ממוקד:
- search_style_exemplars(section, outcome, practice_area) — section=hard filter,
  outcome/practice_area=soft. block_writer._build_precedents_context ממפה
  block→section ומאחזר (ראשי), לצד הנתיב הישן (משלים).

T3 — contrastive/adapt:
- הדוגמאות מתויגות "מבנה/קול בלבד — התאם, אל תעתיק תוכן"; פסקה מלאה (1100 תווים).

INV-LRN5 (טוהר — סגנון בלבד). G11. הרצת backfill --apply בנפרד.

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

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

@@ -1204,6 +1204,28 @@ CREATE INDEX IF NOT EXISTS idx_draft_final_pairs_case ON draft_final_pairs(case_
 CREATE INDEX IF NOT EXISTS idx_draft_final_pairs_status ON draft_final_pairs(status);
 """
 
+SCHEMA_V27_SQL = """
+-- style_exemplars (T1-T3): block-level paragraphs from Dafna's OWN decisions
+-- (style_corpus + internal_committee finals), embedded for retrieval as
+-- style exemplars at write-time. Purpose-built so we DON'T fabricate synthetic
+-- cases just to reuse decision_paragraphs. INV-LRN5: style material only — the
+-- writer is told to adapt structure/voice, copy only boilerplate, never substance.
+CREATE TABLE IF NOT EXISTS style_exemplars (
+    id UUID PRIMARY KEY DEFAULT uuid_generate_v4(),
+    decision_number TEXT DEFAULT '',
+    source TEXT DEFAULT '',                 -- style_corpus | internal_committee
+    practice_area TEXT DEFAULT '',
+    outcome TEXT DEFAULT '',                -- rejection | partial_acceptance | full_acceptance | ''
+    section TEXT DEFAULT 'other',           -- background | claims | discussion | summary | other
+    paragraph_text TEXT NOT NULL,
+    word_count INTEGER DEFAULT 0,
+    embedding vector(1024),
+    created_at TIMESTAMPTZ DEFAULT now()
+);
+CREATE INDEX IF NOT EXISTS idx_style_exemplars_section ON style_exemplars(section);
+CREATE INDEX IF NOT EXISTS idx_style_exemplars_decision ON style_exemplars(decision_number, source);
+"""
+
 
 async def _run_schema_migrations(pool: asyncpg.Pool) -> None:
     async with pool.acquire() as conn:
@@ -1234,7 +1256,8 @@ async def _run_schema_migrations(pool: asyncpg.Pool) -> None:
         await conn.execute(SCHEMA_V24_SQL)
         await conn.execute(SCHEMA_V25_SQL)
         await conn.execute(SCHEMA_V26_SQL)
-    logger.info("Database schema initialized (v1-v26)")
+        await conn.execute(SCHEMA_V27_SQL)
+    logger.info("Database schema initialized (v1-v27)")
 
 
 async def init_schema() -> None:
@@ -2329,6 +2352,85 @@ async def list_draft_final_pairs(status: str | None = None, limit: int = 200) ->
     return [dict(r) for r in rows]
 
 
+async def insert_style_exemplar(
+    decision_number: str, source: str, practice_area: str, outcome: str,
+    section: str, paragraph_text: str, word_count: int, embedding: list[float],
+) -> None:
+    """Insert one block-level style exemplar (T1 backfill)."""
+    pool = await get_pool()
+    async with pool.acquire() as conn:
+        await conn.execute(
+            """INSERT INTO style_exemplars
+                   (decision_number, source, practice_area, outcome, section,
+                    paragraph_text, word_count, embedding)
+               VALUES ($1, $2, $3, $4, $5, $6, $7, $8)""",
+            decision_number, source, practice_area, outcome, section,
+            paragraph_text, word_count, str(embedding),
+        )
+
+
+async def delete_style_exemplars(decision_number: str, source: str) -> int:
+    """Idempotent backfill: clear a decision's exemplars before re-inserting."""
+    pool = await get_pool()
+    async with pool.acquire() as conn:
+        res = await conn.execute(
+            "DELETE FROM style_exemplars WHERE decision_number = $1 AND source = $2",
+            decision_number, source,
+        )
+    try:
+        return int(res.split()[-1])
+    except (ValueError, IndexError):
+        return 0
+
+
+async def search_style_exemplars(
+    query_embedding: list[float],
+    section: str | None = None,
+    outcome: str | None = None,
+    practice_area: str | None = None,
+    limit: int = 6,
+) -> list[dict]:
+    """Retrieve Dafna's own block-level paragraphs as STYLE exemplars (T2).
+    Filters by section (block) + optionally outcome/practice_area for the closest
+    match to the block being written. Soft filters: outcome/practice_area narrow but
+    never zero-out — section is the hard filter."""
+    pool = await get_pool()
+    conditions, params, idx = [], [query_embedding, limit], 3
+    if section:
+        conditions.append(f"section = ${idx}"); params.append(section); idx += 1
+    if outcome:
+        conditions.append(f"(outcome = ${idx} OR outcome = '')"); params.append(outcome); idx += 1
+    if practice_area:
+        conditions.append(f"(practice_area = ${idx} OR practice_area = '')"); params.append(practice_area); idx += 1
+    where = f"WHERE {' AND '.join(conditions)}" if conditions else ""
+    sql = f"""
+        SELECT decision_number, source, section, outcome, practice_area,
+               paragraph_text, word_count,
+               1 - (embedding <=> $1) AS score
+        FROM style_exemplars
+        {where}
+        ORDER BY embedding <=> $1
+        LIMIT $2
+    """
+    async with pool.acquire() as conn:
+        rows = await conn.fetch(sql, *params)
+    return [dict(r) for r in rows]
+
+
+async def count_style_exemplars() -> dict:
+    """Coverage check for the backfill."""
+    pool = await get_pool()
+    async with pool.acquire() as conn:
+        total = await conn.fetchval("SELECT count(*) FROM style_exemplars")
+        by_section = await conn.fetch(
+            "SELECT section, count(*) AS n FROM style_exemplars GROUP BY section ORDER BY n DESC"
+        )
+        decisions = await conn.fetchval(
+            "SELECT count(DISTINCT decision_number) FROM style_exemplars"
+        )
+    return {"total": total, "decisions": decisions, "by_section": [dict(r) for r in by_section]}
+
+
 async def upsert_style_pattern(
     pattern_type: str,
     pattern_text: str,