feat(pi): make pi() the Pi Durable agent

[eersnington]

@rivet-dev/pi now has one agent: pi() runs Pi Durable. The actor built on pi-coding-agent's AgentSession is removed.

import { createRegistry } from "@earendil-works/pi-durable";
import { pi } from "@rivet-dev/pi";

// No sandbox: Pi's read, write, and edit tools work on files in the actor's own SQLite database.
const agent = pi({ model: "anthropic/claude-opus-5-5", registry: createRegistry() });

• One agent. pi() is the former piDurable() and imports from @rivet-dev/pi. Types drop the Durable part: PiOptions, PiActions, PiPromptResult.
• Deprecated alias. @rivet-dev/pi/durable still exports piDurable (the same function as pi) and the old PiDurable* type names, marked @deprecated.
• Old actors keep their data. An actor stored by the removed pi() starts under the new one. pi_sandbox is created only when it is missing, so the actor keeps its sandbox, and pi_session and pi_entry stay as they are.
• Pi Durable 1.0.3 sandbox env. The sandbox ExecutionEnv moves to @rivet-dev/sandbox-adapter/pi and implements 1.0.3's interface (openBinaryReader with scanLines, argv exec, the onOutput stream info). On 0.5.0, read and bash fail in a sandbox once Pi Durable 1.0.3 or later is installed.
• Sandbox on first use. Pi Durable builds the env for every model request and tool call. The sandbox now connects only when a sandbox tool runs, so a plain chat turn or a custom tool never creates one, and a sandbox outage fails only the calls that need it.
• Any Pi Durable 1.x. The @earendil-works/pi-durable and @earendil-works/chord peers are ^1.0.0. The adapter depends on Pi Durable directly, so users install only one copy.
• Files without a sandbox. With no sandbox, files live in the actor's database (databaseEnv, table pi_file). A ranged read loads only the bytes it needs. There is no shell, so bash returns shell_unavailable.
• Fresh credentials. The app's credentials source is read on every model call, so a login, logout, or new key applies to the next call instead of after the actor sleeps.

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This is part 1 of 2 in a stack:

•  2  docs(agents): document pi() as the Pi Durable agent #336
•  1  feat(pi): make pi() the Pi Durable agent #335 👈

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