Regression: new session always opens in a separate/minimized window instead of the active editor's main tab area

**Environment:**
- Extension: anthropic.claude-code (currently 2.1.274, 2.1.273 also present locally from a prior auto-update)
- VSCode: 1.138.0 (commit 7debcd0e2acdea1c52de81bf9ee1620444407dda), Linux x64
- Connected via VSCode Remote - WSL (Linux 6.18.33.2-microsoft-standard-WSL2)
- claudeCode.preferredLocation tried: panel and sidebar - no change in behavior

**Expected behavior:**
Running "Claude Code: Open new tab" opens the session as a tab in the main editor area of the currently active/focused VSCode window, alongside other open tabs. This was the consistent behavior for a long time.

**Actual behavior:**
- The new session never opens as a tab in the main editor area - it always opens in a split/panel layout.
- When more than one VSCode window is open, the new session opens in a different (even minimized) window instead of the currently active one.
- Changing claudeCode.preferredLocation between panel and sidebar has no effect on this behavior.
- This has been happening for some time; not tied to a specific recent update as far as I can tell.

**Steps to reproduce:**
1. Have two VSCode windows open (one active with existing tabs, one minimized).
2. Run "Claude Code: Open new tab" from the Command Palette in the active window.
3. Observe: the new session opens in the minimized window instead, as a new split tab - not in the main editor group of the active window.

Start by reproducing "Claude Code: Open new tab" with two VSCode windows, including a minimized window, and compare the active window with the resulting session location. Trace the command's window and editor-group selection behavior, then verify that the session opens in the active window's main editor area without changing the preferred-location setting.

Written by the indexing model from the issue text.