[Bug]: OpenCode threads via OpenRouter never show context-window usage in the composer

Before submitting

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

Area

apps/server

Steps to reproduce

1. Connect an OpenCode provider instance in T3 Code with an OpenRouter API key.
2. Start a new thread and select any OpenRouter-routed model (tested: z-ai/glm-5.3-flash, poolside/laguna-s-2.1:free).
3. Send several real messages back and forth so real usage accumulates.
4. Inspect the context-window meter next to the composer send button.

Expected behavior

The context-window meter should appear and update with used/max tokens, same as it does for Codex and Claude threads. Issue #7622 states OpenCode already sends turn usage to the context meter in general.

Actual behavior

The meter area next to the send button stays completely empty, with no ring and no percentage, even after multiple completed turns with real token usage.

Impact

Minor bug or occasional failure

Version or commit

0.0.34

Environment

Windows 11, T3 Code desktop app, OpenCode provider connected via OpenRouter (API key)

Logs or stack traces

None. No error is shown, the meter is simply absent.

Technical notes

• Per #7622, OpenCode's turn usage is generally forwarded to the context meter, so this may be specific to OpenRouter-routed models rather than OpenCode as a whole.
• #8382 documents the same class of bug for the Grok provider, root-caused to the adapter not emitting thread.token-usage.updated. The OpenCode-via-OpenRouter path may have the same gap, possibly because some OpenRouter models (especially free ones) omit or delay the usage field in their API response.

Workaround

None found in-app. Running opencode directly in a terminal shows a working "Context X% used" indicator outside of T3 Code.

Start in apps/server and trace the OpenCode-via-OpenRouter usage path, comparing it with the behavior described in #7622 and the adapter issue in #8382. Confirm how turn usage reaches the context meter and whether OpenRouter responses provide the expected usage data or update event. Done means the composer meter appears and updates with used/max tokens for OpenRouter-routed OpenCode threads.