Add the channel messages and the usage record to proto

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

crates/proto/src/wire.rs

@@ -1,6 +1,6 @@
 use serde::{Deserialize, Serialize};
 
-use crate::{CallId, DataClass, SessionId, Timestamp};
+use crate::{CallId, DataClass, SessionId, Timestamp, Usage};
 
 pub const PROTOCOL_VERSION: u32 = 1;
 
@@ -24,6 +24,9 @@ pub enum Message {
     ToolRequest(ToolRequest),
     ToolResponse(ToolResponse),
     Error(WireError),
+    Turn(Turn),
+    TurnEvent(TurnEvent),
+    TurnDone(TurnDone),
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
@@ -40,6 +43,12 @@ pub enum ErrorCode {
     BadVersion,
     BadMessage,
     Internal,
+    SessionFull,
+    TurnLimit,
+    SessionBusy,
+    NoSuchSession,
+    SessionExists,
+    Inference,
 }
 
 #[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
@@ -82,3 +91,63 @@ pub enum DenyReason {
     ApprovalRefused,
     ApprovalExpired,
 }
+
+// JSON: {"kind":"turn","body":{"session":"…","content":"…","resume":false}}
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
+pub struct Turn {
+    pub session: SessionId,
+    pub content: String,
+    pub resume: bool,
+}
+
+// JSON: {"event":"content","text":"…"} — the tag sits beside the fields, snake_case
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(tag = "event", deny_unknown_fields, rename_all = "snake_case")]
+pub enum TurnEvent {
+    Queued {
+        ahead: u64,
+    },
+    Waiting {
+        slot_busy: bool,
+    },
+    Progress {
+        total: u64,
+        cache: u64,
+        processed: u64,
+    },
+    Reasoning {
+        text: String,
+    },
+    Content {
+        text: String,
+    },
+    ToolCallStarted {
+        name: String,
+    },
+    ToolResult {
+        name: String,
+        class: DataClass,
+        truncated: bool,
+    },
+    ThinkingCapped {
+        tokens: u64,
+    },
+    Retrying {
+        attempt: u32,
+        after_ms: u64,
+        error: String,
+    },
+    CacheLoss {
+        expected: u64,
+        got: u64,
+    },
+}
+
+// JSON: {"kind":"turn_done","body":{"content":"…","usage":{…}}}
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
+pub struct TurnDone {
+    pub content: String,
+    pub usage: Usage,
+}