feat: phase 3-5 — workflow engine, background subagents, multi-modal, cache shape, inline diff

Phase 3: Dynamic Workflow Engine
- VM sandbox (node:vm) with agent/parallel/pipeline API, Claude Code compatible
- Workflow file discovery (.boocode/workflows/*.js + ~/.boocode/workflows/*.js)
- Workflow manager with session/chat creation and inference dispatch
- Built-in catalog: deep-research, review-code, find-issues
- Resumability cache: SHA-256 hash of agent spec, in-memory Map

Phase 4: Background Subagents
- background-task.ts service: spawn/poll/cancel lifecycle
- spawn_subagent, subagent_status, subagent_result tools in ALL_TOOLS

Phase 5: Multi-modal + Cache Shape
- Multi-modal stub with type defs and hook point in payload.ts
- CacheShapeBadge component in trace viewer (colored bar + %)

apps/web/src/hooks/useSessionStream.ts

@@ -79,6 +79,7 @@ function channelDeltaToLegacyFrame(delta: ChannelDeltaWsFrame): WsFrame | null {
         output: delta.output,
         truncated: delta.truncated!,
         ...(delta.error ? { error: delta.error } : {}),
+        ...(delta.diff ? { diff: delta.diff } : {}),
       };
     case 'error':
       return {
@@ -172,6 +173,7 @@ function applyFrame(state: State, frame: WsFrame): State {
         finished_at: null,
         created_at: new Date().toISOString(),
         metadata: null,
+        ...(frame.compare_group_id ? { compare_group_id: frame.compare_group_id } : {}),
       };
       return { ...state, messages: [...state.messages, newMsg] };
     }
@@ -195,21 +197,18 @@ function applyFrame(state: State, frame: WsFrame): State {
       return { ...state, messages: next };
     }
     case 'tool_result': {
+      const toolResultsBase = {
+        tool_call_id: frame.tool_call_id,
+        output: frame.output,
+        truncated: frame.truncated,
+        ...(frame.error ? { error: frame.error } : {}),
+        ...(frame.diff ? { diff: frame.diff } : {}),
+      };
       const exists = state.messages.some((m) => m.id === frame.tool_message_id);
       if (exists) {
         const next = state.messages.map((m) =>
           m.id === frame.tool_message_id
-            ? {
-                ...m,
-                role: 'tool' as const,
-                tool_results: {
-                  tool_call_id: frame.tool_call_id,
-                  output: frame.output,
-                  truncated: frame.truncated,
-                  ...(frame.error ? { error: frame.error } : {}),
-                },
-                status: 'complete' as const,
-              }
+            ? { ...m, role: 'tool' as const, tool_results: toolResultsBase, status: 'complete' as const }
             : m,
         );
         return { ...state, messages: next };
@@ -222,12 +221,7 @@ function applyFrame(state: State, frame: WsFrame): State {
         content: '',
         kind: 'message',
         tool_calls: null,
-        tool_results: {
-          tool_call_id: frame.tool_call_id,
-          output: frame.output,
-          truncated: frame.truncated,
-          ...(frame.error ? { error: frame.error } : {}),
-        },
+        tool_results: toolResultsBase,
         status: 'complete',
         last_seq: 0,
         tokens_used: null,
@@ -258,6 +252,7 @@ function applyFrame(state: State, frame: WsFrame): State {
               ...(frame.finished_at !== undefined ? { finished_at: frame.finished_at } : {}),
               ...(frame.model !== undefined ? { model: frame.model } : {}),
               ...(frame.metadata !== undefined ? { metadata: frame.metadata } : {}),
+              ...(frame.compare_group_id !== undefined ? { compare_group_id: frame.compare_group_id } : {}),
             }
           : m,
       );
@@ -301,6 +296,7 @@ function applyFrame(state: State, frame: WsFrame): State {
                   ...m,
                   status: 'failed' as const,
                   ...(errorMeta ? { metadata: errorMeta } : {}),
+                  ...(frame.compare_group_id !== undefined ? { compare_group_id: frame.compare_group_id } : {}),
                 }
               : m,
           )