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/coder/src/services/pending_changes.ts

@@ -4,6 +4,8 @@ import { randomBytes } from 'node:crypto';
 import type { Sql } from '../db.js';
 import { resolveWritePath } from './write_guard.js';
 import { locateMatch } from './fuzzy-match.js';
+import { conflictIndex } from './conflict-index.js';
+import { findConflicts } from './collision-detector.js';
 
 /**
  * Write a file atomically: stage to a sibling temp file, then rename over the
@@ -170,6 +172,10 @@ export async function queueEdit(
     VALUES (${sessionId}, ${taskId}, ${resolved}, 'edit', ${diff}, ${agent})
     RETURNING *
   `;
+
+  // Register in the conflict index so concurrent worktrees see this edit.
+  conflictIndex.registerChange(resolved, sessionId, agent ?? 'unknown');
+
   return row!;
 }
 
@@ -216,6 +222,9 @@ export async function queueCreate(
     VALUES (${sessionId}, ${taskId}, ${resolved}, 'create', ${content}, ${agent})
     RETURNING *
   `;
+
+  conflictIndex.registerChange(resolved, sessionId, agent ?? 'unknown');
+
   return row!;
 }
 
@@ -238,6 +247,9 @@ export async function queueDelete(
     VALUES (${sessionId}, ${taskId}, ${resolved}, 'delete', '', ${agent})
     RETURNING *
   `;
+
+  conflictIndex.registerChange(resolved, sessionId, agent ?? 'unknown');
+
   return row!;
 }
 
@@ -260,6 +272,23 @@ export async function applyOne(
       // Re-validate path in case projectRoot has shifted
       resolveWritePath(projectRoot, change.file_path);
 
+      // Advisory collision check: log a warning if another worktree has pending
+      // edits to this file. Does NOT block the write — same non-blocking pattern
+      // as the edit guards (validateEditResult, checkDroppedImports).
+      {
+        const conflicts = conflictIndex.query(
+          [change.file_path],
+          change.session_id, // sessionId doubles as worktree identifier
+          new Map(),
+        );
+        for (const v of conflicts) {
+          console.log(
+            `[collision] ${v.filePath} — conflict with worktrees [${v.worktrees.join(', ')}] ` +
+            `agents [${v.agents.join(', ')}] severity=${v.severity}`,
+          );
+        }
+      }
+
       switch (change.operation) {
         case 'create': {
           await mkdir(dirname(change.file_path), { recursive: true });