Revert "fix(trajectory): stop negative metrics from inverting regression signals (#2621)"

This reverts commit 5dcf3e7b2f.

src/core/trajectory.ts

@@ -34,7 +34,7 @@ export interface TrajectoryRegression {
   from_date: string;   // YYYY-MM-DD
   to_value: number;
   to_date: string;
-  delta_pct: number;   // negative for a numeric drop; may be < -1 across zero
+  delta_pct: number;   // negative for a drop; range typically [-1, 0)
 }
 
 export interface TrajectoryStats {
@@ -82,10 +82,8 @@ function cosineSim(a: Float32Array, b: Float32Array): number {
  *
  * Iterates per-metric (so trajectories that interleave mrr + arr + team_size
  * don't trip false regressions across metric boundaries). Within each metric,
- * walks consecutive value pairs; a pair fires when the newer value is lower
- * than the older value by at least the threshold. The relative delta uses
- * `abs(older)` as the denominator so negative-valued metrics (net income,
- * cash flow, etc.) do not invert improvement and regression.
+ * walks consecutive value pairs; a pair fires when
+ * `(newer - older) / older <= -threshold`.
  *
  * Pre-condition: caller passed points sorted by (valid_from ASC, fact_id ASC).
  * The engine's `findTrajectory` enforces this. No re-sort here.
@@ -113,7 +111,7 @@ export function detectRegressions(
       // Guard against division-by-zero: a metric starting at exactly 0
       // can't compute a relative delta. Skip.
       if (oldVal === 0) continue;
-      const delta = (newVal - oldVal) / Math.abs(oldVal);
+      const delta = (newVal - oldVal) / oldVal;
       if (delta <= -threshold) {
         out.push({
           metric,

test/trajectory.test.ts

@@ -1,70 +0,0 @@
-import { describe, expect, test } from 'bun:test';
-import type { TrajectoryPoint } from '../src/core/engine.ts';
-import {
-  DEFAULT_REGRESSION_THRESHOLD,
-  detectRegressions,
-} from '../src/core/trajectory.ts';
-
-function point(args: {
-  id: number;
-  metric?: string;
-  value: number;
-  date: string;
-}): TrajectoryPoint {
-  return {
-    fact_id: args.id,
-    valid_from: new Date(args.date),
-    metric: args.metric ?? 'net_income',
-    value: args.value,
-    unit: 'USD',
-    period: 'monthly',
-    event_type: null,
-    text: `${args.metric ?? 'net_income'} = ${args.value}`,
-    source_session: null,
-    source_markdown_slug: null,
-    embedding: null,
-  };
-}
-
-describe('detectRegressions', () => {
-  test('keeps existing positive-valued drop behavior', () => {
-    const regs = detectRegressions([
-      point({ id: 1, metric: 'mrr', value: 200000, date: '2026-01-01' }),
-      point({ id: 2, metric: 'mrr', value: 150000, date: '2026-02-01' }),
-    ], DEFAULT_REGRESSION_THRESHOLD);
-
-    expect(regs).toHaveLength(1);
-    expect(regs[0]).toMatchObject({
-      metric: 'mrr',
-      from_value: 200000,
-      to_value: 150000,
-    });
-    expect(regs[0].delta_pct).toBeCloseTo(-0.25, 4);
-  });
-
-  test('does not flag a negative-valued metric improving toward zero', () => {
-    const regs = detectRegressions([
-      point({ id: 1, value: -1000, date: '2026-01-01' }),
-      point({ id: 2, value: -500, date: '2026-02-01' }),
-    ], DEFAULT_REGRESSION_THRESHOLD);
-
-    expect(regs).toEqual([]);
-  });
-
-  test('flags a negative-valued metric worsening away from zero', () => {
-    const regs = detectRegressions([
-      point({ id: 1, value: -500, date: '2026-01-01' }),
-      point({ id: 2, value: -1000, date: '2026-02-01' }),
-    ], DEFAULT_REGRESSION_THRESHOLD);
-
-    expect(regs).toHaveLength(1);
-    expect(regs[0]).toMatchObject({
-      metric: 'net_income',
-      from_value: -500,
-      to_value: -1000,
-      from_date: '2026-01-01',
-      to_date: '2026-02-01',
-    });
-    expect(regs[0].delta_pct).toBeCloseTo(-1.0, 4);
-  });
-});