TUI drops model variant after entering subagent

[sdip15fa]

The TUI can lose the selected model variant/thinking level when a subagent is invoked and then opened. The parent session stores the selected variant, but the child subagent prompt/session can be created without it, so viewing or continuing the child appears to fall back to the default thinking level.

Expected: same-model subagents without their own configured variant inherit the parent-selected variant. Subagents with explicit variants or different models should keep their own compatibility rules.

[github-actions]

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What needs to be fixed:

• No issue template was used. Bug reports must use the Bug Report template, which requires a description, steps to reproduce, and system information (OS, OpenCode version, provider/model).

Please edit this issue to address the above within 2 hours, or it will be automatically closed.

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This issue might be a duplicate of existing issues. Please check:

• Subtasks do not inherit the active model variant from the parent session #24757: Subtasks do not inherit the active model variant from the parent session (near-identical scope)
• Subtasks and task calls don’t inherit selected thinking level #20740: Subtasks and task calls don't inherit selected thinking level (same root cause)
• Same-model agents do not preserve agent-local variant at runtime #27790: Same-model agents do not preserve agent-local variant at runtime (same behavior from agent side)
• subagent model variants are parsed but not applied at runtime in v1.4.0 #21632: Subagent model variants are parsed but not applied at runtime (related variant inheritance bug)

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[github-actions]

This issue has been automatically closed because it was not updated to meet our contributing guidelines within the 2-hour window.

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