fix: candidates carry runnable T-SQL; placeholder sql is dropped, not rendered

Measured on a 2.7 MB production plan (plan-cxpaket.sqlplan, kept out of git):
- rewrite_sql becomes option_type + sql_to_run. The old name told the model 'query rewrite only', so an index option carried no CREATE INDEX anywhere in the pipeline and the report had zero SqlBlocks. It now requires paste-ready T-SQL per option, and the report prompt makes a SqlBlock per non-null sql_to_run a hard requirement.
- verify_semantics keys on option_type === 'rewrite' rather than 'has sql', so index and statistics options are not flagged just for carrying DDL.
- dropPlaceholderSql: 'SELECT ... FROM ... OPTION (MAXDOP 1)' is not runnable and was rendered as if it were. Ellipsis SQL is now nulled, and digestForModel reports sql_truncated so the model is told not to offer a rewrite for a statement it never received.
- max_tokens 2048 -> 4096 for both calls: the larger JSON outgrew the old ceiling and the user waited 38s for 'malformed JSON'. A truncated response now says how many characters it got, and extra params still override the ceiling.
- Real plan, live: 52s, 17 cards, 3 SqlBlocks with real table names and no placeholders, 3 ScoreBars, headline 'Query Plan Timeout on Parallel Join'. 43 unit, 23 e2e.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/jev.test.ts

@@ -10,10 +10,10 @@ const digest = { sql: "SELECT", bytes: 1, subtreeCost: 1, parallel: false, nonPa
 const candidates = [
   { key: "a", title: "Covering index", diagnosis: "Scan of a million rows; no key exists on CustomerId.",
     actions: [{ title: "Create index", detail: "CREATE INDEX", effort: "medium", requires_change_control: true }],
-    rewrite_sql: null, expected: "seek instead of scan" },
+    option_type: "index", sql_to_run: "CREATE NONCLUSTERED INDEX [IX_Orders_CustomerId] ON [dbo].[Orders] ([CustomerId]) INCLUDE ([TotalDue]);", expected: "seek instead of scan" },
   { key: "b", title: "Add TOP 100", diagnosis: "Too many rows leave the scan, so cut them off.",
     actions: [{ title: "Add TOP 100", detail: "TOP 100", effort: "low", requires_change_control: false }],
-    rewrite_sql: "SELECT TOP 100", expected: "less I/O" },
+    option_type: "rewrite", sql_to_run: "SELECT TOP 100 * FROM dbo.Orders ORDER BY TotalDue DESC;", expected: "less I/O" },
 ] as any;
 
 const scored = (fit: number, safe: number, ease: number, cause: number) => ({
@@ -81,7 +81,7 @@ test("a silent jev does not accuse every option of being unsafe", () => {
 test("verify_semantics fires where semantics can actually move", async () => {
   // Real Jev scores an index create ~0.57 ("probably fine, no stated proof"), which a blanket <0.6 floor
   // flagged as unsafe on every run. Index-only options must not shout; rewrites and bad scores must.
-  const idxOnly = [{ ...candidates[0], rewrite_sql: null }, candidates[1]];
+  const idxOnly = [{ ...candidates[0], option_type: "statistics", sql_to_run: "UPDATE STATISTICS dbo.Orders WITH FULLSCAN;" }, candidates[1]];
   const mid = { byKey: { a: scored(4, 2, 2, 1), b: scored(4, 2, 2, 1) }, cross: GOOD.cross };
   const v = await judgeCandidates(digest, idxOnly, fakeJev(mid));
   assert.ok(!v.order.find((r) => r.key === "a")!.flags.includes("verify_semantics"), "index create flagged");