[Bug]: Context window indicator is hidden by default without an in-app notice

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/desktop

Steps to reproduce

Launch T3 Code 0.0.39-nightly.20260903.1262.
Open a project on its main branch.
Start or resume a thread and complete at least one turn.
Inspect the composer footer for the context-window indicator.
Create or open a thread in a branch/worktree and repeat the test.
Open Settings → General → Legacy features.

Expected behavior

Context-window usage should remain visible in the composer by default. If the indicator is intentionally disabled or moved, the UI should provide an in-app notice or discoverable affordance explaining how to restore it. Visibility should be consistent across main and branch/worktree threads.

Actual behavior

The context-window indicator is completely absent in both main and branch/worktree threads. No icon, percentage, placeholder, or notice appears in the composer, preventing passive monitoring of context consumption.

PR #9190 introduced contextWindowMeterEnabled with a default value of false. ChatComposer passes null instead of the available context-window state when this setting is disabled, so the indicator is hidden across all threads regardless of branch state.

Impact

Major degradation or frequent failure

Version or commit

0.0.39-nightly.20260903.1262

Environment

Windows 11 Pro 25H2

Logs or stack traces

Screenshots, recordings, or supporting files

No response

Workaround

Proposed fix

Restore contextWindowMeterEnabled to true by default. If the indicator must remain opt-in, preserve it for existing users during migration and display an in-app notice showing where it can be re-enabled.

Start by reviewing PR #9190 and the contextWindowMeterEnabled handling in ChatComposer under apps/desktop. Reproduce the missing indicator in both main and branch/worktree threads, then verify that it is visible by default or that the UI provides a discoverable way to restore it.