feat(backend): scaffold PodMan agent pipeline + token server

Express server with /health and a LiveKit token endpoint. Module skeletons
for the full loop: vision (Gemini), GitHub fusion, collision detector (pure,
testable), intervention engine, and continual-learning memory store. Approve
native build scripts (esbuild/genai/protobufjs) at the workspace root.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/src/collision/detector.ts

@@ -0,0 +1,50 @@
+import type { Collision, EngineerContext, GithubStateSnapshot } from '@podman/shared';
+
+/**
+ * Fuse live engineer contexts (from vision) with GitHub state to find overlaps:
+ * two or more engineers editing the same file — especially when unpushed.
+ *
+ * Pure function: easy to unit-test, no I/O. Callers supply the GitHub snapshot.
+ */
+export function detectCollisions(
+  contexts: EngineerContext[],
+  githubStateByFile: Record<string, GithubStateSnapshot> = {},
+  now: string = new Date().toISOString(),
+): Collision[] {
+  const byFile = new Map<string, EngineerContext[]>();
+  for (const ctx of contexts) {
+    if (!ctx.currentFile) continue;
+    const list = byFile.get(ctx.currentFile) ?? [];
+    list.push(ctx);
+    byFile.set(ctx.currentFile, list);
+  }
+
+  const collisions: Collision[] = [];
+  for (const [file, group] of byFile) {
+    if (group.length < 2) continue;
+
+    const engineers = [...new Set(group.map((g) => g.engineerId))];
+    if (engineers.length < 2) continue;
+
+    const github = githubStateByFile[file];
+    const unpushed = group.some((g) => g.hasUnpushedChanges) || github?.unpushed === true;
+    const sharedSymbol = group.every(
+      (g) => g.currentSymbol && g.currentSymbol === group[0]!.currentSymbol,
+    )
+      ? group[0]!.currentSymbol
+      : undefined;
+
+    collisions.push({
+      id: `${group[0]!.podId}:${file}:${engineers.sort().join(',')}`,
+      podId: group[0]!.podId,
+      file,
+      symbol: sharedSymbol,
+      engineers,
+      severity: unpushed ? 'critical' : sharedSymbol ? 'warn' : 'info',
+      githubState: github,
+      detectedAt: now,
+    });
+  }
+
+  return collisions;
+}