Add Path Tracer onion timeline fork/merge with ghost branches and Seer feed.

Operators fork at hop N to run persona ensembles in parallel on the target agent until mining links; winners merge back into the canonical SQLite-persisted session with WS and Seer events plus mermaid branch graphs in the UI.

server/web/src/help/pathTracerTimeline.test.ts

@@ -0,0 +1,54 @@
+/**
+ * @vitest-environment node
+ */
+import { describe, expect, it } from 'vitest';
+import {
+  branchStatusClass,
+  ghostBranchesByHop,
+  mergeMermaidStyles,
+  pickMergeCandidate,
+} from './pathTracerTimeline';
+import type { PathTraceTimelineBranch } from './pathTracerTimeline';
+
+function branch(partial: Partial<PathTraceTimelineBranch>): PathTraceTimelineBranch {
+  return {
+    id: 'b1',
+    fork_hop_index: 0,
+    status: 'running',
+    is_ghost: true,
+    ...partial,
+  };
+}
+
+describe('pathTracerTimeline', () => {
+  it('groups ghost branches by fork hop', () => {
+    const map = ghostBranchesByHop([
+      branch({ id: 'a', fork_hop_index: 1 }),
+      branch({ id: 'b', fork_hop_index: 1 }),
+      branch({ id: 'c', fork_hop_index: 0 }),
+    ]);
+    expect(map.get(1)?.map((b) => b.id)).toEqual(['a', 'b']);
+    expect(map.get(0)?.map((b) => b.id)).toEqual(['c']);
+  });
+
+  it('prefers won branch for merge candidate', () => {
+    const pick = pickMergeCandidate([
+      branch({ id: 'run', status: 'running' }),
+      branch({ id: 'win', status: 'won', mining_linked: true, hashrate: 120 }),
+    ]);
+    expect(pick?.id).toBe('win');
+  });
+
+  it('maps status to CSS class', () => {
+    expect(branchStatusClass('won')).toBe('won');
+    expect(branchStatusClass('running')).toBe('running');
+    expect(branchStatusClass('failed')).toBe('failed');
+  });
+
+  it('appends mermaid classDef styles once', () => {
+    const raw = 'graph TD\n  a --> b';
+    const styled = mergeMermaidStyles(raw);
+    expect(styled).toContain('classDef won');
+    expect(mergeMermaidStyles(styled)).toBe(styled);
+  });
+});