tmux teammateMode passes explicit --model, loses 1M context window

Bug Description

When teammateMode: "tmux" is configured in settings.json, spawned teammate processes receive --model claude-opus-4-6 as an explicit CLI argument. This bypasses the "Default (recommended)" model resolution, which on Max/Team plans maps to Opus 4.6 with 1M context. The result is that teammates run on standard Opus 4.6 (200K context) instead of the 1M context window the parent session uses.

Steps to Reproduce

1. Configure "teammateMode": "tmux" in ~/.claude/settings.json
2. Confirm the main session uses "Default (recommended)" → Opus 4.6 with 1M context (run /model to verify)
3. Use TeamCreate to spawn a teammate
4. In the teammate's tmux pane, run /model

Expected Behavior

Teammate should inherit the parent's model resolution, including the 1M context window. Either:

• Omit --model so the child process resolves to "Default" (1M), or
• Pass the 1M-aware model identifier

Actual Behavior

Teammate process is launched with --model claude-opus-4-6 (explicit), which resolves to standard Opus 4.6 (200K context). The /model picker in the teammate pane shows:

1. Default (recommended)    Opus 4.6 with 1M context
2. Sonnet                   Sonnet 4.6
3. Sonnet (1M context)      Sonnet 4.6 with 1M context
4. Haiku                    Haiku 4.5
> 5. Opus 4.6 ✓             claude-opus-4-6       <-- selected

Option 5 is selected instead of option 1.

Evidence

Process listing shows the explicit --model flag on teammate processes:

/Users/.../.local/share/claude/versions/2.1.88 \
  --agent-id synthesis@clean-room-audit \
  --team-name clean-room-audit \
  --model claude-opus-4-6          <-- loses 1M

Main session (no --model flag) correctly resolves to Default (1M).

Environment

• Claude Code version: 2.1.88
• OS: macOS (Darwin 25.3.0, arm64)
• Plan: Max (Opus 4.6 1M context as default)
• teammateMode: "tmux" in settings.json
• Was not an issue in 0.2.77 (pre-2.x rewrite)

Impact

All tmux teammates silently run with 200K context instead of 1M, reducing capacity for large-context tasks (e.g., reading multiple source files, processing long documents). No user-visible indication unless you manually check /model in each teammate pane.