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diff --git a/packages/exec-backend/src/service.ts b/packages/exec-backend/src/service.ts
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+++ b/packages/exec-backend/src/service.ts
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+import { defineService } from "@dispatch/kernel";
+import type { ExecBackend } from "./backend.js";
+
+/**
+ * Resolve an `ExecBackend` for a given computer.
+ *
+ * - `computerId` **undefined** → local (today's behavior; `LocalExecBackend`).
+ * - `computerId` **set** → remote (SSH; wired by `host-bin` + the `ssh` package
+ *   in a later wave — the `SshExecBackend` implements the same `ExecBackend`
+ *   interface).
+ *
+ * The resolver is SYNCHRONOUS by design: it returns a backend whose methods are
+ * async, so any remote connection acquisition happens lazily inside the first
+ * backend method call, not at resolver-call time. This keeps the resolver
+ * side-effect-free — merely resolving a backend never opens a connection; only
+ * when a tool actually executes does the (remote) backend connect.
+ */
+export type ExecBackendResolver = (computerId?: string) => ExecBackend;
+
+/**
+ * Typed service handle for the `ExecBackend` resolver.
+ *
+ * The `exec-backend` extension provides this via `host.provideService`.
+ * Tool extensions resolve their per-call backend from it (injected at
+ * activation by `host-bin`).
+ */
+export const execBackendHandle = defineService<ExecBackendResolver>("exec-backend/resolver");