fix(optimize): exclude a young project's founding session from cost-outlier detection (#666)

A project's first/bootstrap session is a different kind of work (one-off
scaffolding), not an expensive instance of routine work. While a project is
still young its peer sample is thin, so the leave-one-out average is dominated
by a few routine sessions and the founding session's legitimately high one-off
cost trips the >2x outlier multiplier. Exclude each young project's earliest
costed session from the outlier finding only; mature projects are unaffected so
genuine outliers still surface. Young = fewer than 2x MIN_SESSIONS_FOR_OUTLIER
costed sessions.

Fixes #664

src/optimize.ts

@@ -82,6 +82,10 @@ const MCP_NEW_CONFIG_GRACE_MS = 24 * 60 * 60 * 1000
 const BASH_DEFAULT_LIMIT = 30000
 const BASH_RECOMMENDED_LIMIT = 15000
 const MIN_SESSIONS_FOR_OUTLIER = 3
+// A project is still bootstrapping until it has twice the minimum sessions
+// needed to evaluate outliers; below that, its peer average is too thin to
+// distinguish founding work from waste.
+const YOUNG_PROJECT_SESSION_LIMIT = 2 * MIN_SESSIONS_FOR_OUTLIER
 const SESSION_OUTLIER_MULTIPLIER = 2
 const MIN_SESSION_OUTLIER_COST_USD = 1
 const SESSION_OUTLIER_PREVIEW = 5
@@ -2267,6 +2271,29 @@ export function detectSessionOutliers(projects: ProjectSummary[], excludedSessio
   }
 }
 
+function findYoungProjectFirstSessionIds(projects: ProjectSummary[]): Set<string> {
+  const firstSessionIds = new Set<string>()
+
+  for (const project of projects) {
+    const costed = project.sessions.filter(s => s.totalCostUSD > 0)
+    if (costed.length >= YOUNG_PROJECT_SESSION_LIMIT) continue
+
+    let firstSession: ProjectSummary['sessions'][number] | null = null
+    for (const session of costed) {
+      if (
+        firstSession === null
+        || new Date(session.firstTimestamp).getTime() < new Date(firstSession.firstTimestamp).getTime()
+      ) {
+        firstSession = session
+      }
+    }
+
+    if (firstSession) firstSessionIds.add(firstSession.sessionId)
+  }
+
+  return firstSessionIds
+}
+
 // ============================================================================
 // Scoring
 // ============================================================================
@@ -2391,7 +2418,8 @@ export async function scanAndDetect(
       .filter(c => !lowWorthSessionIds.has(c.sessionId))
       .map(c => c.sessionId),
   )
-  const outlierExclusions = new Set([...lowWorthSessionIds, ...contextBloatVisibleIds])
+  const firstSessionIds = findYoungProjectFirstSessionIds(projects)
+  const outlierExclusions = new Set([...lowWorthSessionIds, ...contextBloatVisibleIds, ...firstSessionIds])
   const syncDetectors: Array<() => WasteFinding | null> = [
     () => detectCacheBloat(apiCalls, projects, dateRange),
     () => detectLowReadEditRatio(toolCalls),

tests/optimize.test.ts

@@ -1,4 +1,15 @@
-import { describe, it, expect } from 'vitest'
+import { describe, it, expect, vi } from 'vitest'
+
+vi.mock('../src/providers/index.js', async (importOriginal) => {
+  type ProvidersModule = typeof import('../src/providers/index.js')
+  const actual = await importOriginal<ProvidersModule>()
+  return {
+    ...actual,
+    async discoverAllSessions() {
+      return []
+    },
+  }
+})
 
 import {
   detectJunkReads,
@@ -10,6 +21,7 @@ import {
   detectCapabilityReliability,
   detectLowWorthSessions,
   detectSessionOutliers,
+  scanAndDetect,
   computeHealth,
   computeTrend,
   buildOptimizeJsonReport,
@@ -61,6 +73,22 @@ function projectWithSessions(costs: number[], project = 'app'): ProjectSummary {
   }
 }
 
+function projectWithDeliveredSessions(costs: number[], project = 'app'): ProjectSummary {
+  const summary = projectWithSessions(costs, project)
+  for (const session of summary.sessions) {
+    session.bashBreakdown = { 'git commit -m test': { calls: 1 } }
+  }
+  return summary
+}
+
+function optimizeDateRange(day: number) {
+  const padded = String(day).padStart(2, '0')
+  return {
+    start: new Date(`2026-06-${padded}T00:00:00Z`),
+    end: new Date(`2026-06-${padded}T23:59:59Z`),
+  }
+}
+
 type TestSession = ProjectSummary['sessions'][number]
 
 function contextSession(
@@ -978,6 +1006,38 @@ describe('detectSessionOutliers', () => {
     expect(finding).not.toBeNull()
     expect(finding!.explanation).toContain('app/s4')
   })
+
+  it('scanAndDetect excludes the earliest high-cost session while the project is young', async () => {
+    const result = await scanAndDetect(
+      [projectWithDeliveredSessions([20, 1, 1, 1])],
+      optimizeDateRange(1),
+    )
+
+    const finding = result.findings.find(f => f.id === 'cost-outliers')
+    expect(finding).toBeUndefined()
+  })
+
+  it('scanAndDetect still flags a later high-cost session while the project is young', async () => {
+    const result = await scanAndDetect(
+      [projectWithDeliveredSessions([1, 20, 1, 1])],
+      optimizeDateRange(2),
+    )
+
+    const finding = result.findings.find(f => f.id === 'cost-outliers')
+    expect(finding).toBeDefined()
+    expect(finding!.explanation).toContain('app/s2')
+  })
+
+  it('scanAndDetect still flags the earliest high-cost session once the project is mature', async () => {
+    const result = await scanAndDetect(
+      [projectWithDeliveredSessions([20, 1, 1, 1, 1, 1])],
+      optimizeDateRange(3),
+    )
+
+    const finding = result.findings.find(f => f.id === 'cost-outliers')
+    expect(finding).toBeDefined()
+    expect(finding!.explanation).toContain('app/s1')
+  })
 })
 
 describe('computeHealth', () => {