Symbol a_t

The passage around this formula

…$\mathcal{T}_t$ is the tool set most recently returned by tools/list , each member carrying its own schema; $\pi_\theta$ is the model, which is expected — but not forced by anything outside its own training — to emit a call $a_t$ whose name and arguments validate against some tool in $\mathcal{T}_t$ ; $\mathrm{Call}$ is dispatch through the client to the server and back, exactly as described above; and $h_{t+1}$ is the context the model reasons over on the next step, built by appending the call and its result to what came…

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