Initial implementation of CURSOR.

Author: RyanLamansky

CLAUDE.md

@@ -127,6 +127,9 @@ Three entry points share one per-connection undo log: implicit (statement-level
 - `INSERT ... OUTPUT INSERTED.<col>` (single-row).
 - `MERGE INTO target USING <source> ON … WHEN [NOT] MATCHED [BY TARGET|SOURCE] [AND …] THEN UPDATE|DELETE|INSERT … [OUTPUT $action, …]` — source = VALUES / SELECT / set-op / bare-table; multiple per-family AND-conditioned clauses; trailing `;` required. Msg 5324 / 8672 / 10713 / 10714 enforced. Triggers fire one INSERT → UPDATE → DELETE pass with combined affected rows. See [`docs/claude/dml.md`](docs/claude/dml.md).
 
+### Cursors
+Session-scoped T-SQL cursors: `DECLARE <name> [INSENSITIVE][SCROLL] CURSOR [LOCAL|GLOBAL][FORWARD_ONLY|SCROLL][STATIC|KEYSET|DYNAMIC|FAST_FORWARD][READ_ONLY|…] FOR <select> [FOR {READ ONLY|UPDATE [OF cols]}]`, `OPEN`, `FETCH NEXT|PRIOR|FIRST|LAST|ABSOLUTE n|RELATIVE n [FROM] <cursor> [INTO @v,…]`, `CLOSE`, `DEALLOCATE`, plus `@@FETCH_STATUS` / `@@CURSOR_ROWS` / `CURSOR_STATUS` and positioned `WHERE CURRENT OF` UPDATE/DELETE. Effective sensitivity resolves at DECLARE: non-updatable query (not a single base table with a PK/UNIQUE) → STATIC; STATIC frozen-snapshot, KEYSET frozen-membership with live value re-reads (deleted member → `@@FETCH_STATUS=-2`), DYNAMIC fully live (skips deletes, sees inserts, `@@CURSOR_ROWS=-1`). Position tracked by the logical unique key (not a RID — UPDATE relocates rows). Errors Msg 16905/16915/16916/16917/16924/16925/16929/16931 probe-confirmed verbatim. Cursor variables (`DECLARE @c CURSOR`) raise `NotSupportedException`. See [`docs/claude/cursors.md`](docs/claude/cursors.md).
+
 ### EF Core adapter coverage
 `UseSqlServerSimulator(...)` covers seven SqlParameter-downcast pairs: `DateOnly→date`, `DateTime→date`, `DateTime→smalldatetime`, `TimeOnly→time(N)`, `TimeSpan→time(N)`, `decimal→money`, `decimal→smallmoney`. Without the adapter those mappings throw at SaveChanges. MAX-string family flows through plain `UseSqlServer`.
 
@@ -146,6 +149,7 @@ Per-feature deep-dives live under `docs/claude/`. Each entry below is a trigger:
 - **`Selection`, aggregates, window functions, set ops, CASE, OFFSET/FETCH** → [`query.md`](docs/claude/query.md).
 - **UPDATE / DELETE / INSERT…SELECT / SELECT…INTO / rowversion (incl. `@@DBTS` / `MIN_ACTIVE_ROWVERSION`) / identity helpers (`@@IDENTITY` / `SCOPE_IDENTITY` / `IDENT_CURRENT` / `IDENT_INCR` / `IDENT_SEED`) / `@@ROWCOUNT` / `ROWCOUNT_BIG` / OUTPUT / MERGE** → [`dml.md`](docs/claude/dml.md).
 - **Variables, control flow (IF/WHILE/BREAK/CONTINUE/RETURN), TRY/CATCH+THROW+ERROR_*, `@@ERROR` / `@@TRANCOUNT` / `XACT_STATE`, PRINT, WAITFOR** → [`control-flow.md`](docs/claude/control-flow.md).
+- **Cursors (`DECLARE … CURSOR` / `OPEN` / `FETCH` / `CLOSE` / `DEALLOCATE`, STATIC / KEYSET / DYNAMIC sensitivity, scroll fetches, `@@FETCH_STATUS` / `@@CURSOR_ROWS` / `CURSOR_STATUS`, `WHERE CURRENT OF`)** → [`cursors.md`](docs/claude/cursors.md).
 - **CTE shapes / recursive-CTE error handling** → [`ctes.md`](docs/claude/ctes.md).
 - **JSON_VALUE / JSON_QUERY / JSON_MODIFY / JSON_OBJECT / JSON_ARRAY / JSON_PATH_EXISTS / ISJSON / OPENJSON** → [`json.md`](docs/claude/json.md).
 - **Name resolution, schema lookup, CREATE / DROP / ALTER SCHEMA TRANSFER, `OBJECT_ID` / `OBJECT_NAME` / `OBJECT_SCHEMA_NAME` / `SCHEMA_ID` / `SCHEMA_NAME` / `DB_ID` / `DB_NAME`, cross-DB read routing** → [`schemas.md`](docs/claude/schemas.md).
@@ -225,3 +229,4 @@ Per-feature deep-dives live under `docs/claude/`. Each entry below is a trigger:
 - **`STRING_SPLIT(..., ..., cast(@v as int))` — wrapped variable accepted**: the simulator's `enable_ordinal` const-only gate rejects bare `@v` (Msg 8748, matching real) but a Cast / Parenthesized wrapper around the variable slips past the gate. Real SQL Server rejects all variable-bearing shapes regardless of wrapping. No real-world emission hits this — the const-only restriction means `@v` ergonomics are weak in any form.
 - **`OPENJSON` `WITH ... AS JSON`** on `nvarchar(max)` raises `NotSupportedException` even though real SQL Server accepts the column form there (sub-tree extraction not modeled). Non-`nvarchar(max)` columns with `AS JSON` raise **Msg 13618**, matching real.
 - **`FOR SYSTEM_TIME` qualified-name format**: real SQL Server pads temp-table names in Msg 13544 with their internal allocation suffix (`#x____...___…000000000148`); the simulator emits the bare `tempdb.dbo.#x` form. Same Msg number / framing, less verbose name.
+- **Cursor edges**: cursors over a **JOIN / derived table / view** are forced to STATIC (read-only snapshot, `@@CURSOR_ROWS`=count); real SQL Server makes them DYNAMIC (`@@CURSOR_ROWS`=-1, sees mid-loop changes, `WHERE CURRENT OF` works) — the simulator only takes the updatable KEYSET/DYNAMIC path for a *direct single base table with a PK/UNIQUE* (set-op/UNION cursors are forced STATIC on the real server too, so those match). `@@CURSOR_ROWS` is `-1` throughout for DYNAMIC (real may report a transient positive count pre-fetch); a keyset `-2` (deleted-member) fetch leaves the `INTO` variables unchanged rather than zeroing/NULLing them; `FETCH` without `INTO` omits the trailing `ROWSTAT` column. See [`docs/claude/cursors.md`](docs/claude/cursors.md).