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/compute-diff.ts

@@ -0,0 +1,132 @@
+/**
+ * Compact unified-diff generator for write-tool results.
+ *
+ * Produces a minimal unified diff string (---/+++ header + +/- lines) from
+ * old/new text pairs so the frontend can render an inline diff snippet
+ * without pulling in a full diff library.
+ */
+
+// Write-tool names that can produce file diffs.
+export const WRITE_TOOL_NAMES = new Set([
+  'edit_file',
+  'create_file',
+  'delete_file',
+  'apply_pending',
+]);
+
+/**
+ * Compute a compact unified diff from old → new text.
+ *
+ * @param oldStr  The original text (empty for creates)
+ * @param newStr  The replacement text (empty for deletes)
+ * @param filePath  Display path for the file header
+ * @returns A unified-diff string, or empty string if old === new
+ */
+export function computeDiff(oldStr: string, newStr: string, filePath: string): string {
+  if (oldStr === newStr) return '';
+
+  const oldLines = oldStr.split('\n');
+  const newLines = newStr.split('\n');
+
+  // For empty old → new file (create), show all lines as additions
+  if (oldStr.length === 0 && newStr.length > 0) {
+    const header = `--- /dev/null\n+++ b/${filePath}\n`;
+    const body = newLines.map((line) => `+${line}`).join('\n');
+    return header + body;
+  }
+
+  // For old → empty (delete), show all lines as removals
+  if (newStr.length === 0 && oldStr.length > 0) {
+    const header = `--- a/${filePath}\n+++ /dev/null\n`;
+    const body = oldLines.map((line) => `-${line}`).join('\n');
+    return header + body;
+  }
+
+  // Simple line-by-line diff for edit: collect changed lines with context.
+  // Uses a straightforward algorithm: find the first differing line and the
+  // last differing line, then output the block with +/- markers.
+  const header = `--- a/${filePath}\n+++ b/${filePath}\n`;
+
+  const maxLen = Math.max(oldLines.length, newLines.length);
+  let firstDiff = -1;
+  let lastDiff = -1;
+
+  for (let i = 0; i < maxLen; i++) {
+    const a = i < oldLines.length ? oldLines[i] : undefined;
+    const b = i < newLines.length ? newLines[i] : undefined;
+    if (a !== b) {
+      if (firstDiff === -1) firstDiff = i;
+      lastDiff = i;
+    }
+  }
+
+  if (firstDiff === -1) return '';
+
+  // Add context lines around the changed block (up to 2 lines each side)
+  const contextBefore = 2;
+  const contextAfter = 2;
+  const start = Math.max(0, firstDiff - contextBefore);
+  const end = Math.min(maxLen - 1, lastDiff + contextAfter);
+
+  // Build the unified diff hunk
+  const hunkLines: string[] = [];
+  const hunkOldStart = start + 1; // 1-indexed
+  const hunkNewStart = start + 1;
+  const hunkOldLen = end - start + 1;
+  const hunkNewLen = end - start + 1;
+
+  for (let i = start; i <= end; i++) {
+    const oldLine = i < oldLines.length ? oldLines[i] : undefined;
+    const newLine = i < newLines.length ? newLines[i] : undefined;
+
+    if (oldLine === newLine) {
+      hunkLines.push(` ${oldLine ?? ''}`);
+    } else {
+      if (oldLine !== undefined) {
+        hunkLines.push(`-${oldLine}`);
+      }
+      if (newLine !== undefined) {
+        hunkLines.push(`+${newLine}`);
+      }
+    }
+  }
+
+  const hunkHeader = `@@ -${hunkOldStart},${hunkOldLen} +${hunkNewStart},${hunkNewLen} @@\n`;
+  return header + hunkHeader + hunkLines.join('\n');
+}
+
+/**
+ * Check whether a tool name corresponds to a file-modifying write tool
+ * that should produce a diff in its tool result.
+ */
+export function isWriteTool(name: string): boolean {
+  return WRITE_TOOL_NAMES.has(name);
+}
+
+/**
+ * Extract a diff string from tool call args for write tools.
+ * Returns empty string if the tool doesn't produce diffs or args are missing.
+ */
+export function diffFromToolArgs(name: string, args: Record<string, unknown>, filePath?: string): string {
+  switch (name) {
+    case 'edit_file': {
+      const oldStr = String(args.old_string ?? '');
+      const newStr = String(args.new_string ?? '');
+      const path = filePath ?? String(args.file_path ?? 'file');
+      return computeDiff(oldStr, newStr, path);
+    }
+    case 'create_file': {
+      const content = String(args.content ?? '');
+      const path = filePath ?? String(args.file_path ?? 'file');
+      return computeDiff('', content, path);
+    }
+    case 'delete_file':
+      // No content available at queue time — actual content is read at apply time.
+      return '';
+    case 'apply_pending':
+      // Meta-tool — individual changes produce their own diffs.
+      return '';
+    default:
+      return '';
+  }
+}

apps/server/src/services/inference/multi-modal.ts

@@ -0,0 +1,56 @@
+// vDeepSeek (stub): multi-modal (image) attachment support.
+//
+// When a message carries images, DeepSeek V4 models can process them
+// natively via the @ai-sdk/deepseek provider. This module provides the
+// helper types and functions to detect and convert image attachments.
+//
+// FULL INTEGRATION requires:
+//   1. Storing image data alongside messages (message_parts with kind='image'
+//      or a dedicated attachments table with base64-encoded data).
+//   2. Extending OpenAiMessage.content from `string | null` to
+//      `string | null | Array<{ type: 'text'; text: string } | { type: 'image'; image: string }>`
+//      in apps/server/src/services/inference/payload.ts.
+//   3. Updating toModelMessages() in stream-phase-adapter.ts to emit AI SDK
+//      content arrays with image parts for multimodal user messages.
+//
+// None of the above is done yet — this file is a type scaffold.
+
+import type { Message } from '../../types/api.js';
+
+/** Shape of a decoded image attachment ready for the AI SDK. */
+export interface ImageAttachment {
+  /** Base64-encoded image data (no data URI prefix — raw bytes). */
+  data: string;
+  /** MIME type (e.g. 'image/png', 'image/jpeg', 'image/webp'). */
+  mimeType: string;
+}
+
+/**
+ * Check if a user message has image content that can be forwarded to a
+ * multimodal model. Currently a stub — always returns false until the
+ * message-pipeline stores image attachments addressably.
+ */
+export function hasImageAttachments(_message: Message): boolean {
+  // TODO(vDeepSeek): scan message_parts for kind='image' or inspect
+  // message.content for inline data URIs (data:image/...).
+  return false;
+}
+
+/**
+ * Convert internal image attachments to the format expected by the AI SDK
+ * ModelMessage content array.
+ *
+ * The @ai-sdk/deepseek provider accepts images as:
+ *   { type: 'image'; image: 'data:image/png;base64,...' }
+ *
+ * @param attachments — List of decoded image attachments.
+ * @returns AI SDK inline file parts suitable for ModelMessage.content.
+ */
+export function imageAttachmentsToParts(
+  attachments: ImageAttachment[],
+): Array<{ type: 'image'; image: string }> {
+  return attachments.map((a) => ({
+    type: 'image' as const,
+    image: `data:${a.mimeType};base64,${a.data}`,
+  }));
+}

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 } : {}),
       });
     })
   );