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/server/src/services/inference/tool-phase.ts

@@ -19,6 +19,7 @@ import { formatUnknownToolError } from './tool-suggestions.js';
 import { resolveGrantRoot } from '../grant_resolver.js';
 import { stripToolMarkup } from './tool-call-parser.js';
 import { repairToolInput } from './tool-input-repair.js';
+import { diffFromToolArgs, isWriteTool } from './compute-diff.js';
 import type { FailureKind } from './mistake-tracker.js';
 import { insertToolTrace, updateToolTrace } from '../tool-traces.js';
 import type {
@@ -445,6 +446,16 @@ export async function executeToolPhase(
       if (SYNTHESIS_TOOLS.has(tc.name)) {
         synthEntries.push({ tc, output: tres.output, ...(tres.error ? { error: tres.error } : {}) });
       }
+      // v2.8: compute a compact unified diff for successful write-tool results.
+      // The diff is derived from tool call args (old_string/new_string for
+      // edit_file, content for create_file) and included in the WS frame so
+      // the frontend can render a DiffSnippet inline. Not persisted to message_parts
+      // (the args alone are enough to reproduce it on reload if needed).
+      const toolDiff =
+        !tres.error && tres.outcome === 'success' && isWriteTool(tc.name)
+          ? diffFromToolArgs(tc.name, tc.args as Record<string, unknown>)
+          : undefined;
+
       const stored = {
         tool_call_id: tc.id,
         output: tres.output,
@@ -467,6 +478,7 @@ export async function executeToolPhase(
         output: tres.output,
         truncated: tres.truncated,
         ...(tres.error ? { error: tres.error } : {}),
+        ...(toolDiff ? { diff: toolDiff } : {}),
       });
     })
   );