Offer Interrupt and adopt after relay refuses Adopt as busy #605

User story

As the owner, I want a way forward when relay says an idle-looking session is busy, so that I can still take it over from my phone.

Acceptance criteria

• A busy refusal of Adopt shows the Interrupt and adopt button on that row.
• The toast keeps relay's reason on one line.
• A tap on Interrupt and adopt sends interrupt: true for that row id only.

What I'd notice

After "Can't adopt: the session is not idle…", the row offers Interrupt and adopt instead of a dead end.

Context

Relay's own idle check (registry, transcript, child processes) can disagree with the outside row's idle state. Today the toast tells the person to ask to interrupt, and the idle row has no button that does it. Found while working #597.

Tasks

• Planner: contract.
• Row state after a busy refusal; spec against fakerelay's adopt.busy.

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