Classic inline ghost-text completions never fire (only NES/XtabProvider works) - unified Copilot Chat extension, VS Code 1.135.0

**Summary:** Classic inline ghost-text completions never fire, in any file/language/folder, while Next Edit Suggestions (NES) work fine.

**Environment:** VS Code 1.135.0 (commit `08d4889f9e`), GitHub Copilot Chat 0.63.0 (builtin/unified extension), Windows 10.

**Symptom:** Ghost-text inline completions do not appear when typing, tested across Python (.py, .ipynb), JavaScript, and Markdown files, across multiple unrelated workspace folders on different drives. Behavior is inconsistent/unpredictable across folders with no discernible pattern. Meanwhile Next Edit Suggestions (`XtabProvider`) fire and succeed continuously in the Copilot Chat log for the same session.

**Log evidence:** Across every session log checked (multiple folders, multiple relaunches), zero completion requests for classic ghost text ever appear — only NES/XtabProvider entries, always tagged `markdown`.

**Ruled out:**
- Signed in, active subscription confirmed (`monthly_subscriber_quota`), 0% quota used
- No GitHub Copilot content exclusion rules on account (personal account, checked)
- No Workspace Trust / Restricted Mode indicator
- `github.copilot.enable` settings correct at user/workspace/folder scope, all languages enabled
- No conflicting extensions (tested with all other extensions disabled — issue persisted)
- Cleared extension cache (`globalStorage/github.copilot-chat`) and re-signed in — no change
- Separate legacy `github.copilot` extension cannot be installed alongside the builtin on VS Code Stable (`"github.copilot-chat" is a built-in extension and not allowed to be updated in the current product quality 'stable'`), so no fallback available

**Ask:** Is this a known issue with the progressive single-extension inline-completions rollout (announced Nov 2025)? Is there a way to force-enable classic ghost text, or install the legacy extension as fallback on Stable?