feat(v2): add agent pane with SDK message adapter and dispatcher

Implement full agent session frontend: SDK message adapter parsing
stream-json into 9 typed message types, agent bridge for Tauri IPC,
dispatcher routing sidecar events to store, agent session store with
cost tracking, and AgentPane component with prompt input, message
rendering (text, thinking, tool calls, results, cost), and stop
button. Add Ctrl+Shift+N shortcut and sidebar agent button.

v2/src/lib/adapters/sdk-messages.ts

@@ -1,25 +1,234 @@
 // SDK Message Adapter — insulates UI from Claude Agent SDK wire format changes
 // This is the ONLY place that knows SDK internals.
-// Phase 3: full implementation
+
+export type AgentMessageType =
+  | 'init'
+  | 'text'
+  | 'thinking'
+  | 'tool_call'
+  | 'tool_result'
+  | 'status'
+  | 'cost'
+  | 'error'
+  | 'unknown';
 
 export interface AgentMessage {
   id: string;
-  type: 'text' | 'tool_call' | 'tool_result' | 'subagent_spawn' | 'subagent_stop' | 'status' | 'cost' | 'unknown';
+  type: AgentMessageType;
   parentId?: string;
   content: unknown;
   timestamp: number;
 }
 
+export interface InitContent {
+  sessionId: string;
+  model: string;
+  cwd: string;
+  tools: string[];
+}
+
+export interface TextContent {
+  text: string;
+}
+
+export interface ThinkingContent {
+  text: string;
+}
+
+export interface ToolCallContent {
+  toolUseId: string;
+  name: string;
+  input: unknown;
+}
+
+export interface ToolResultContent {
+  toolUseId: string;
+  output: unknown;
+}
+
+export interface StatusContent {
+  subtype: string;
+  message?: string;
+}
+
+export interface CostContent {
+  totalCostUsd: number;
+  durationMs: number;
+  inputTokens: number;
+  outputTokens: number;
+  numTurns: number;
+  isError: boolean;
+  result?: string;
+  errors?: string[];
+}
+
+export interface ErrorContent {
+  message: string;
+}
+
 /**
- * Adapt a raw SDK message to our internal format.
+ * Adapt a raw SDK stream-json message to our internal format.
  * When SDK changes wire format, only this function needs updating.
  */
-export function adaptSDKMessage(raw: Record<string, unknown>): AgentMessage {
-  // Phase 3: implement based on actual SDK message types
-  return {
-    id: (raw.id as string) ?? crypto.randomUUID(),
-    type: 'unknown',
-    content: raw,
-    timestamp: Date.now(),
-  };
+export function adaptSDKMessage(raw: Record<string, unknown>): AgentMessage[] {
+  const uuid = (raw.uuid as string) ?? crypto.randomUUID();
+  const timestamp = Date.now();
+  const parentId = raw.parent_tool_use_id as string | undefined;
+
+  switch (raw.type) {
+    case 'system':
+      return adaptSystemMessage(raw, uuid, timestamp);
+    case 'assistant':
+      return adaptAssistantMessage(raw, uuid, timestamp, parentId);
+    case 'user':
+      return adaptUserMessage(raw, uuid, timestamp, parentId);
+    case 'result':
+      return adaptResultMessage(raw, uuid, timestamp);
+    default:
+      return [{
+        id: uuid,
+        type: 'unknown',
+        content: raw,
+        timestamp,
+      }];
+  }
+}
+
+function adaptSystemMessage(
+  raw: Record<string, unknown>,
+  uuid: string,
+  timestamp: number,
+): AgentMessage[] {
+  const subtype = raw.subtype as string;
+
+  if (subtype === 'init') {
+    return [{
+      id: uuid,
+      type: 'init',
+      content: {
+        sessionId: raw.session_id as string,
+        model: raw.model as string,
+        cwd: raw.cwd as string,
+        tools: (raw.tools as string[]) ?? [],
+      } satisfies InitContent,
+      timestamp,
+    }];
+  }
+
+  return [{
+    id: uuid,
+    type: 'status',
+    content: {
+      subtype,
+      message: raw.status as string | undefined,
+    } satisfies StatusContent,
+    timestamp,
+  }];
+}
+
+function adaptAssistantMessage(
+  raw: Record<string, unknown>,
+  uuid: string,
+  timestamp: number,
+  parentId?: string,
+): AgentMessage[] {
+  const messages: AgentMessage[] = [];
+  const msg = raw.message as Record<string, unknown> | undefined;
+  if (!msg) return messages;
+
+  const content = msg.content as Array<Record<string, unknown>> | undefined;
+  if (!Array.isArray(content)) return messages;
+
+  for (const block of content) {
+    switch (block.type) {
+      case 'text':
+        messages.push({
+          id: `${uuid}-text-${messages.length}`,
+          type: 'text',
+          parentId,
+          content: { text: block.text as string } satisfies TextContent,
+          timestamp,
+        });
+        break;
+      case 'thinking':
+        messages.push({
+          id: `${uuid}-think-${messages.length}`,
+          type: 'thinking',
+          parentId,
+          content: { text: (block.thinking ?? block.text) as string } satisfies ThinkingContent,
+          timestamp,
+        });
+        break;
+      case 'tool_use':
+        messages.push({
+          id: `${uuid}-tool-${messages.length}`,
+          type: 'tool_call',
+          parentId,
+          content: {
+            toolUseId: block.id as string,
+            name: block.name as string,
+            input: block.input,
+          } satisfies ToolCallContent,
+          timestamp,
+        });
+        break;
+    }
+  }
+
+  return messages;
+}
+
+function adaptUserMessage(
+  raw: Record<string, unknown>,
+  uuid: string,
+  timestamp: number,
+  parentId?: string,
+): AgentMessage[] {
+  const messages: AgentMessage[] = [];
+  const msg = raw.message as Record<string, unknown> | undefined;
+  if (!msg) return messages;
+
+  const content = msg.content as Array<Record<string, unknown>> | undefined;
+  if (!Array.isArray(content)) return messages;
+
+  for (const block of content) {
+    if (block.type === 'tool_result') {
+      messages.push({
+        id: `${uuid}-result-${messages.length}`,
+        type: 'tool_result',
+        parentId,
+        content: {
+          toolUseId: block.tool_use_id as string,
+          output: block.content ?? raw.tool_use_result,
+        } satisfies ToolResultContent,
+        timestamp,
+      });
+    }
+  }
+
+  return messages;
+}
+
+function adaptResultMessage(
+  raw: Record<string, unknown>,
+  uuid: string,
+  timestamp: number,
+): AgentMessage[] {
+  const usage = raw.usage as Record<string, number> | undefined;
+
+  return [{
+    id: uuid,
+    type: 'cost',
+    content: {
+      totalCostUsd: (raw.total_cost_usd as number) ?? 0,
+      durationMs: (raw.duration_ms as number) ?? 0,
+      inputTokens: usage?.input_tokens ?? 0,
+      outputTokens: usage?.output_tokens ?? 0,
+      numTurns: (raw.num_turns as number) ?? 0,
+      isError: (raw.is_error as boolean) ?? false,
+      result: raw.result as string | undefined,
+      errors: raw.errors as string[] | undefined,
+    } satisfies CostContent,
+    timestamp,
+  }];
 }