Move the tools' arguments and the host rules to proto

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

crates/proto/src/tools.rs

@@ -0,0 +1,36 @@
+//! The four tools' arguments, decoded from the model's JSON then re-serialised. Shared by
+//! `brokerd` (which validates them) and `toolkit` (inside the container, which runs them), so the
+//! two must agree on one definition.
+
+use serde::{Deserialize, Serialize};
+
+/// The arguments for `read_file`.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
+pub struct ReadFileArgs {
+    pub path: String,
+}
+
+/// The arguments for `write_file`.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
+pub struct WriteFileArgs {
+    pub path: String,
+    pub content: String,
+}
+
+/// The arguments for `shell`.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
+pub struct ShellArgs {
+    pub command: String,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub cwd: Option<String>,
+}
+
+/// The arguments for `http_fetch`.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
+pub struct HttpFetchArgs {
+    pub url: String,
+}