Vs Code db2i SQLRunnerTool issue on alias creation

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**Title:** `vscode-db2i-chat-sqlRunnerTool` crashes with `Cannot read properties of undefined (reading 'length')` when executing DDL statements

**Labels:** `bug`

---

**Describe the bug**

When executing DDL statements (e.g., `CREATE ALIAS`, `CREATE TABLE`, `DROP TABLE`) through the `vscode-db2i-chat-sqlRunnerTool` Copilot tool, the extension crashes with:

```
Cannot read properties of undefined (reading 'length')
(at tsx element FF > NU > sGe > hxt > dl > > > WSt > Axt > n0)
```

The statement **does execute successfully** on the server, but the tool throws before returning a result, which causes the Copilot agent to treat the call as failed and abort its workflow.

**Root cause**

In `src/aiProviders/copilot/sqlTool.ts`, the result is serialized unconditionally:

```typescript
const result = await JobManager.runSQL(trimmed);
return new LanguageModelToolResult([new LanguageModelTextPart(JSON.stringify(result))]);
```

DDL statements do not return a result set, so `runSQL()` returns `undefined`. In JavaScript, `JSON.stringify(undefined)` evaluates to `undefined` (not the string `"undefined"`), and passing `undefined` to `LanguageModelTextPart` causes the crash when the VS Code language model infrastructure reads `.length` on the value.

**Steps to reproduce**

1. Open a Copilot Chat with a DB2 for i connection active.
2. Ask the agent to run a DDL statement, e.g.:
```sql
CREATE OR REPLACE ALIAS MYLIB.TEST_ALIAS FOR SYSIBM.SYSDUMMY1
```
3. Observe the empty `Output` field in the tool call UI, followed by the error above.

**Expected behavior**

The tool should return a success message (e.g., `"Statement executed successfully."`) when `runSQL()` returns `undefined`, instead of crashing.

**Suggested fix**

```typescript
const result = await JobManager.runSQL(trimmed);
const output = result !== undefined
? JSON.stringify(result)
: 'Statement executed successfully (no result set returned).';
return new LanguageModelToolResult([new LanguageModelTextPart(output)]);
```

**Environment**

- Extension: `vscode-db2i` (codefori)
- VS Code: with GitHub Copilot Chat
- Affected file: `src/aiProviders/copilot/sqlTool.ts`
- Affected tool ID: `vscode-db2i-chat-sqlRunnerTool`

---

Read src/aiProviders/copilot/sqlTool.ts and follow the SQL runner path described in the issue, then reproduce the behavior with a DDL statement such as CREATE OR REPLACE ALIAS. Done means DDL calls return a text success message when no result set is returned, while statements with results continue to return their serialized output without crashing.

Written by the indexing model from the issue text.