Copilot inline completions unavailable for identical Verilog files opened by Vivado

Copilot inline completions unavailable only for identical Verilog files opened by Vivado## Summary

Copilot inline completions are available in a newly created Verilog file, but unavailable in a Verilog file with identical content when that file is opened by Xilinx Vivado through VS Code configured as Vivado's external editor.

The same Vivado workflow worked previously. Reinstalling VS Code did not resolve this regression.

## Environment

- OS: Windows
- VS Code: 1.135.0
- Built-in GitHub Copilot Chat: 0.63.0
- File type: Verilog (`.v`)
- External tool: Xilinx Vivado

## Exact comparison

| Item | Working file | Failing file |
| --- | --- | --- |
| Content | Identical | Identical |
| File extension | `.v` | `.v` |
| VS Code language mode | Verilog | Verilog |
| Encoding | UTF-8 | UTF-8 |
| End of line | CRLF | CRLF |
| Copilot account/subscription | Same | Same |
| Result | Inline completion appears | `No inline suggestions available` |

The only observed difference is the way the editor is opened: the failing file is opened from Vivado.

## Steps to reproduce

1. In VS Code, create a new `.v` file and paste the code below.
2. At the incomplete `always @(*) begin` block, invoke **Editor: Trigger Inline Suggestion**. An inline completion is returned.
3. Configure the same VS Code installation as Vivado's external editor and open an otherwise identical `.v` file from Vivado.
4. At the exact same location, wait for a suggestion or invoke **Editor: Trigger Inline Suggestion**.

```verilog
module pc_reg(
clk,
rst_n,
pc_out
);

input clk;
input rst_n;
output reg [31:0] pc_out;

always @(posedge clk or posedge rst_n)
if (!rst_n)
pc_out <= 0;
else
pc_out <= pc_out + 4;

always @(*) begin
endmodule
```

## Actual result

The Vivado-opened file never receives an inline completion. The Copilot status item changes to the slashed-circle icon and displays `无内联建议可用` (`No inline suggestions available`).

## Expected result

The identical Vivado-opened Verilog file should receive inline completions just like the newly created file.

## Settings verified

```json
{
"editor.inlineSuggest.enabled": true,
"editor.inlineSuggest.suppressSuggestions": false,
"github.copilot.enable": {
"*": true,
"verilog": true,
"systemverilog": true
},
"security.workspace.trust.enabled": false
}
```

Copilot is authenticated and its subscription token is active. The problem is not resolved by reinstalling VS Code.

## Relevant extension-host messages

```text
No bundle location found for extension GitHub.copilot-chat
Failed to create database. Falling back to in-memory db: Error: unable to open database file
```

I can provide comparison screenshots and additional sanitized diagnostics on request. No proprietary source files are attached.