contextTier setting in settings.json is persisted but not applied on session start (defaults to 200k)

[willc121]

Describe the bug

The contextTier setting in ~/.copilot/settings.json is persisted by the CLI but is not applied at session start. As a result, fresh sessions default to the 200k context window even when the user has explicitly opted in to the long-context tier via /model.

The model setting (model) and reasoning effort (effortLevel) from settings.json ARE applied on session start. Only contextTier silently gets dropped.

Affected version

GitHub Copilot CLI 1.0.55-1

Steps to reproduce the behavior

1. Open copilot and run /model. Select a model that supports a long-context tier (in my case Claude Opus 4.7 (1M context)(Internal only)) and choose the long-context option.
2. Confirm ~/.copilot/settings.json now contains:

   {
     "model": "claude-opus-4.7-1m-internal",
     "contextTier": "long_context"
   }

3. Exit the CLI (or run /restart).
4. Start a new session and run /context.

Expected behavior

The new session honors the persisted contextTier: "long_context" setting and starts with the 1M token context window.

Actual behavior

The new session starts with the default 200k context window. The session.model_change event written at session start in ~/.copilot/session-state/<id>/events.jsonl looks like:

{"type":"session.model_change","data":{"newModel":"claude-opus-4.7-1m-internal"}}

Note the absence of contextTier. The model is applied from settings.json but the persisted context tier is not.

To get the long-context window back, I have to re-run /model and reselect the long-context tier every single session, which then emits a session.model_change event WITH contextTier: "long_context" and works correctly for that session only.

Additional context

• The CLI binary contains code paths that:
  • Write contextTier correctly to settings.json from /model: Rt.contextTier = lt === "long_context" ? "long_context" : void 0
  • Apply contextTier when a model change event includes it: "contextTier" in e.data && (this.contextTier = e.data.contextTier ?? void 0)
• But the session-start path that applies the persisted model field to the new session does not appear to include the persisted contextTier. Looks like the load-and-apply step at session start needs to read contextTier from settings.json and forward it into the initial session.model_change event (or equivalent).
• OS: macOS (Darwin, ARM)
• Shell: zsh
• Terminal: Terminal.app
• I confirmed this against three fresh sessions created today (after a CLI restart). All three emitted session.model_change events with the model but no contextTier.