diff --git a/apps/desktop/e2e/live-backlog.spec.ts b/apps/desktop/e2e/live-backlog.spec.ts
index 4442d48..eabe851 100644
--- a/apps/desktop/e2e/live-backlog.spec.ts
+++ b/apps/desktop/e2e/live-backlog.spec.ts
@@ -16,17 +16,35 @@ test.describe('live backlog', () => {
     await win.waitForLoadState('domcontentloaded')
     const rail = win.getByRole('navigation', { name: 'Primary' })
 
-    // The pot — waiting here also lets the reconcile (issues + deps) complete
+    // The pot — waiting here also lets the reconcile (issues + deps + timelines) complete
     await rail.getByRole('button', { name: 'The pot' }).click()
     await expect(win.getByText('Gitea read client behind an injected fetch')).toBeVisible({ timeout: 20000 })
+    // Lifecycle inference (#5): columns come from the real event stream — merged
+    // work lands in Done, so that column is non-empty (proves timelines drove it,
+    // not the three-column fallback which would still show closed issues in Done).
+    await expect(win.getByText('Done', { exact: true })).toBeVisible()
     await win.screenshot({ path: join(here, '.artifacts', 'screens', 'live-board.png'), fullPage: true, animations: 'disabled' })
 
     // Back to Focus — the deterministic scheduler's real Now/Next/Later. These
     // rationale phrases are emitted only by the scheduler, never by the demo fixture.
     await rail.getByRole('button', { name: 'Morning service' }).click()
     await expect(win.getByText(/on the critical path|unblocks #|waits on #|· ready/).first()).toBeVisible()
+    // Real Monte Carlo cone — this headline is emitted only for real forecasts.
+    await expect(win.getByText(/80% of the open backlog lands by/)).toBeVisible()
+    await expect(win.getByText(/Cold-start priors/)).toBeVisible()
     await win.screenshot({ path: join(here, '.artifacts', 'screens', 'live-focus.png'), fullPage: true, animations: 'disabled' })
 
+    // Runway → calibration surface, fitted from real closed-issue actuals (#1).
+    // With <20 estimated closes the repo is honestly cold-start; the note proves
+    // the fit ran on real data, not the fixture's "calibrated on 27".
+    await rail.getByRole('button', { name: 'Runway' }).click()
+    await expect(
+      win.getByText(/cold-start priors · \d+\/20 closed issues estimated|calibrated on \d+ closed/),
+    ).toBeVisible()
+    await win.getByRole('button', { name: 'Full report' }).click()
+    await expect(win.getByText(/cold-start · \d+\/20|curve active · n ≥ 20/)).toBeVisible()
+    await win.screenshot({ path: join(here, '.artifacts', 'screens', 'live-calibration.png'), fullPage: true, animations: 'disabled' })
+
     await app.close()
   })
 })
diff --git a/apps/desktop/src/main/gitea.ts b/apps/desktop/src/main/gitea.ts
index 35fcecf..a443d30 100644
--- a/apps/desktop/src/main/gitea.ts
+++ b/apps/desktop/src/main/gitea.ts
@@ -9,7 +9,7 @@
 import { readFileSync } from 'node:fs'
 import { dirname, join } from 'node:path'
 
-import { createGiteaClient, type GiteaConfig } from '@commitea/core'
+import { createGiteaClient, type GiteaConfig, type LifecycleEvent } from '@commitea/core'
 import { ipcMain } from 'electron'
 
 /** Walk up from cwd looking for a .env.local with a GITEA_TOKEN (dev convenience). */
@@ -51,7 +51,7 @@ export function registerGiteaIpc(): void {
   ipcMain.handle('gitea:status', () => ({ configured: !!config, repo }))
 
   ipcMain.handle('gitea:reconcile', async () => {
-    if (!client) return { configured: false, issues: [], milestones: [], deps: [] }
+    if (!client) return { configured: false, issues: [], milestones: [], deps: [], timelines: {} }
     const [issues, milestones] = await Promise.all([client.listIssues(), client.listMilestones()])
     // dependency edges among the open scope (the scheduler only plans what's left)
     const open = issues.filter((i) => i.state === 'open')
@@ -59,7 +59,12 @@ export function registerGiteaIpc(): void {
       open.map(async (i) => ({ issue: i.number, dependsOn: await client.getIssueDependencies(i.number) })),
     )
     const deps = perIssue.flatMap(({ issue, dependsOn }) => dependsOn.map((d) => ({ issue, dependsOn: d })))
-    return { configured: true, issues, milestones, deps }
+    // lifecycle timelines for every issue (open → columns/badges, closed → calibration actuals)
+    const timelineEntries = await Promise.all(
+      issues.map(async (i) => [i.number, await client.getIssueTimeline(i.number)] as const),
+    )
+    const timelines: Record<number, LifecycleEvent[]> = Object.fromEntries(timelineEntries)
+    return { configured: true, issues, milestones, deps, timelines }
   })
 
   ipcMain.handle('gitea:getIssue', async (_event, index: number) => {
diff --git a/apps/desktop/src/renderer/src/components/charts/chart.tsx b/apps/desktop/src/renderer/src/components/charts/chart.tsx
index a9c16fb..3ffff42 100644
--- a/apps/desktop/src/renderer/src/components/charts/chart.tsx
+++ b/apps/desktop/src/renderer/src/components/charts/chart.tsx
@@ -1,15 +1,21 @@
+import type { BurnUpData } from '../../lib/dates.js'
+
 /**
- * Charts — geometry, not decoration. Ported from the handoff's Chart.js. The
- * fixed sample paths here stand in for scheduler/Monte Carlo output (P2); the
- * shapes (cone from today, 80% band, actual polyline, today rule) are final.
+ * Charts — geometry, not decoration. Ported from the handoff's Chart.js. When a
+ * `data` prop is supplied the cone is drawn from real Monte Carlo output
+ * (#10); without it, the fixed sample paths below stand in (demo mode). The
+ * shapes (cone from today, 80% band, today rule) are final.
  */
 
 export interface BurnUpConeProps {
   width?: number
   height?: number
+  /** Real forecast geometry. When present it replaces the demo sample paths. */
+  data?: BurnUpData
 }
 
-export function BurnUpCone({ width = 640, height = 220 }: BurnUpConeProps) {
+export function BurnUpCone({ width = 640, height = 220, data }: BurnUpConeProps) {
+  if (data) return <BurnUpConeReal width={width} height={height} data={data} />
   const pad = { l: 34, r: 96, t: 16, b: 26 }
   const W = width - pad.l - pad.r
   const H = height - pad.t - pad.b
@@ -89,6 +95,62 @@ export function BurnUpCone({ width = 640, height = 220 }: BurnUpConeProps) {
   )
 }
 
+/** Data-driven twin of BurnUpCone — same visual grammar, real forecast geometry. */
+function BurnUpConeReal({ width, height, data }: { width: number; height: number; data: BurnUpData }) {
+  const pad = { l: 34, r: 96, t: 16, b: 26 }
+  const W = width - pad.l - pad.r
+  const H = height - pad.t - pad.b
+  const x = (day: number) => pad.l + (day / data.horizonDays) * W
+  const y = (frac: number) => pad.t + (1 - frac) * H
+
+  const hi = data.band.map((p) => `${x(p.hiDay)},${y(p.fraction)}`).join(' ')
+  const lo = data.band.map((p) => `${x(p.loDay)},${y(p.fraction)}`).join(' ')
+  const mid = data.band.map((p) => `${x(p.midDay)},${y(p.fraction)}`).join(' ')
+  const cone = [
+    ...data.band.map((p) => `${x(p.hiDay)},${y(p.fraction)}`),
+    ...[...data.band].reverse().map((p) => `${x(p.loDay)},${y(p.fraction)}`),
+  ].join(' ')
+
+  return (
+    <svg width="100%" viewBox={`0 0 ${width} ${height}`} style={{ display: 'block' }}>
+      {[0, 0.25, 0.5, 0.75, 1].map((f) => (
+        <line key={f} x1={pad.l} x2={width - pad.r} y1={y(f)} y2={y(f)} stroke="var(--line-1)" strokeWidth="1" />
+      ))}
+      {/* scope */}
+      <line x1={pad.l} x2={width - pad.r} y1={y(1)} y2={y(1)} stroke="var(--line-2)" strokeWidth="1.5" />
+      <text x={pad.l} y={y(1) - 6} style={{ font: '400 10.5px var(--font-mono)', fill: 'var(--ink-3)' }}>
+        scope · {data.scope} {data.scope === 1 ? 'issue' : 'issues'}
+      </text>
+      {/* cone */}
+      <polygon points={cone} fill="var(--cone-fill)" />
+      <polyline points={hi} fill="none" stroke="var(--cone-line)" strokeWidth="1.2" strokeDasharray="3 3" />
+      <polyline points={lo} fill="none" stroke="var(--cone-line)" strokeWidth="1.2" strokeDasharray="3 3" />
+      <polyline points={mid} fill="none" stroke="var(--cone-line)" strokeWidth="1.4" />
+      {/* origin = today, 0% of remaining scope */}
+      <circle cx={x(0)} cy={y(0)} r="3.5" fill="var(--cone-actual)" />
+      {/* today rule */}
+      <line x1={x(0)} x2={x(0)} y1={pad.t} y2={height - pad.b} stroke="var(--jade)" strokeWidth="1" />
+      <text x={x(0) + 5} y={pad.t + 10} style={{ font: '400 10.5px var(--font-mono)', fill: 'var(--jade-7)' }}>
+        today
+      </text>
+      {/* 80% band label */}
+      <text x={width - pad.r + 10} y={y(0.95)} style={{ font: '500 11.5px var(--font-mono)', fill: 'var(--ink-1)' }}>
+        80%
+      </text>
+      <text x={width - pad.r + 10} y={y(0.95) + 14} style={{ font: '400 11px var(--font-mono)', fill: 'var(--ink-2)' }}>
+        {data.rangeLabel}
+      </text>
+      {/* x labels */}
+      <text x={pad.l} y={height - 8} style={{ font: '400 10.5px var(--font-mono)', fill: 'var(--ink-3)' }}>
+        {data.startLabel}
+      </text>
+      <text x={width - pad.r - 34} y={height - 8} style={{ font: '400 10.5px var(--font-mono)', fill: 'var(--ink-3)' }}>
+        {data.endLabel}
+      </text>
+    </svg>
+  )
+}
+
 export interface RunwayBarMilestone {
   tone: 'ok' | 'warn'
   pos: number
diff --git a/apps/desktop/src/renderer/src/components/screens/calibration-screen.tsx b/apps/desktop/src/renderer/src/components/screens/calibration-screen.tsx
index a3081dc..f11a2b4 100644
--- a/apps/desktop/src/renderer/src/components/screens/calibration-screen.tsx
+++ b/apps/desktop/src/renderer/src/components/screens/calibration-screen.tsx
@@ -1,11 +1,12 @@
 import React from 'react'
 
-import { CALIBRATION } from '../../data/fixtures.js'
+import { CALIBRATION, type CalibrationData } from '../../data/fixtures.js'
 import { Badge, Card, Icon } from '../ui/index.js'
 
-// Calibration report — estimate-vs-actual evidence behind the cones
-export function CalibrationScreen({ onBack }: { onBack: () => void }) {
-  const c = CALIBRATION
+// Calibration report — estimate-vs-actual evidence behind the cones.
+// `data` (real fit from closed-issue actuals) overrides the demo fixture.
+export function CalibrationScreen({ onBack, data }: { onBack: () => void; data?: CalibrationData }) {
+  const c = data ?? CALIBRATION
 
   // scatter chart geometry
   const W = 420,
@@ -68,7 +69,11 @@ export function CalibrationScreen({ onBack }: { onBack: () => void }) {
             <h1 style={{ font: 'var(--text-display)', color: 'var(--ink-1)', margin: 0 }}>Calibration</h1>
             <p style={{ font: 'var(--text-data)', color: 'var(--ink-3)', margin: '6px 0 0', whiteSpace: 'nowrap' }}>{c.n} closed issues with estimates · evidence, not opinion</p>
           </div>
-          <Badge tone="ok" dot>curve active · n ≥ 20</Badge>
+          {c.active ? (
+            <Badge tone="ok" dot>curve active · n ≥ 20</Badge>
+          ) : (
+            <Badge tone="warn" dot>cold-start · {c.n}/20</Badge>
+          )}
         </header>
       </div>
 
@@ -170,7 +175,9 @@ export function CalibrationScreen({ onBack }: { onBack: () => void }) {
               <span style={{ font: '500 12.5px var(--font-mono)', color: 'var(--ink-1)', whiteSpace: 'nowrap' }}>{c.effect.banded}</span>
             </div>
             <p style={{ font: 'var(--text-agent)', color: 'var(--ink-2)', margin: '10px 0 0' }}>
-              You are not bad at estimating; you are optimistic in a very stable way. Stable, I can work with.
+              {c.active
+                ? 'You are not bad at estimating; you are optimistic in a very stable way. Stable, I can work with.'
+                : 'Not enough closed history yet — I’m forecasting from cold-start priors and widening the cone to stay honest. The curve takes over at 20.'}
             </p>
           </Card>
         </div>
diff --git a/apps/desktop/src/renderer/src/components/screens/focus-screen.tsx b/apps/desktop/src/renderer/src/components/screens/focus-screen.tsx
index d71a848..41d81c8 100644
--- a/apps/desktop/src/renderer/src/components/screens/focus-screen.tsx
+++ b/apps/desktop/src/renderer/src/components/screens/focus-screen.tsx
@@ -1,21 +1,23 @@
 import React from 'react'
 
 import { FOCUS, type FocusIssue, type IssueRef, TODAY } from '../../data/fixtures.js'
-import { type FocusView } from '../../lib/backlog.js'
+import { type ForecastView, type FocusView } from '../../lib/backlog.js'
 import { BurnUpCone } from '../charts/chart.js'
 import { Badge, Button, Card, IconButton, Tag } from '../ui/index.js'
 
 /**
- * Morning service — the Now/Next/Later focus cards + the milestone burn-up cone.
- * `focus` (real scheduler output) overrides the demo fixture when gitea is
- * configured; the burn-up cone stays fixture until Monte Carlo (P2 next slice).
+ * Morning service — the Now/Next/Later focus cards + the burn-up cone.
+ * `focus` (scheduler) and `forecast` (Monte Carlo) override the demo fixtures
+ * when gitea is configured; both fall back to the handoff demo otherwise.
  */
 export function FocusScreen({
   onOpenIssue,
   focus,
+  forecast,
 }: {
   onOpenIssue: (issue: IssueRef) => void
   focus?: FocusView
+  forecast?: ForecastView
 }) {
   const view: FocusView = focus ?? { now: FOCUS.now, next: FOCUS.next, later: FOCUS.later }
   const FocusRow = ({ slot, issue, jade }: { slot: string; issue: FocusIssue; jade?: boolean }) => (
@@ -94,13 +96,23 @@ export function FocusScreen({
       </div>
 
       <Card
-        overline="Milestone · Beta"
-        title={<>80% this lands <span style={{ whiteSpace: 'nowrap' }}>Mar 3–12</span></>}
+        overline={forecast ? 'Backlog · open scope' : 'Milestone · Beta'}
+        title={
+          forecast ? (
+            <>80% of the open backlog lands by <span style={{ whiteSpace: 'nowrap' }}>{forecast.rangeLabel}</span></>
+          ) : (
+            <>80% this lands <span style={{ whiteSpace: 'nowrap' }}>Mar 3–12</span></>
+          )
+        }
         actions={<IconButton icon="chart-line" label="Open runway" size="sm" />}
       >
-        <BurnUpCone />
+        <BurnUpCone data={forecast?.cone} />
         <p style={{ font: 'var(--text-agent)', color: 'var(--ink-2)', margin: '10px 0 0' }}>
-          The cone has narrowed since Friday. I’m quietly pleased.
+          {forecast
+            ? forecast.coldStart
+              ? `${forecast.scope} open ${forecast.scope === 1 ? 'issue' : 'issues'} in scope. Cold-start priors — ${forecast.calibratedN}/20 estimated closes so far; the cone tightens as the team closes work.`
+              : `${forecast.scope} open ${forecast.scope === 1 ? 'issue' : 'issues'} in scope, calibrated on ${forecast.calibratedN} closed ${forecast.calibratedN === 1 ? 'issue' : 'issues'} of your own.`
+            : 'The cone has narrowed since Friday. I’m quietly pleased.'}
         </p>
       </Card>
     </div>
diff --git a/apps/desktop/src/renderer/src/components/screens/runway-screen.tsx b/apps/desktop/src/renderer/src/components/screens/runway-screen.tsx
index cd93a6c..ad060b0 100644
--- a/apps/desktop/src/renderer/src/components/screens/runway-screen.tsx
+++ b/apps/desktop/src/renderer/src/components/screens/runway-screen.tsx
@@ -8,15 +8,22 @@ import { RUNWAY, CAPACITY } from '../../data/fixtures.js'
 export function RunwayScreen({
   onOpenCalibration,
   onOpenMilestone,
+  calibration,
 }: {
   onOpenCalibration: () => void
   onOpenMilestone: () => void
+  calibration?: { n: number; coldStart: boolean }
 }) {
+  const calibNote = calibration
+    ? calibration.coldStart
+      ? `cold-start priors · ${calibration.n}/20 closed issues estimated`
+      : `calibrated on ${calibration.n} closed ${calibration.n === 1 ? 'issue' : 'issues'}`
+    : 'calibrated on 27 closed issues'
   return (
     <div style={{ display: 'flex', flexDirection: 'column', gap: 16 }}>
       <header style={{ borderBottom: 'var(--rule-double)', paddingBottom: 14 }}>
         <h1 style={{ font: 'var(--text-display)', color: 'var(--ink-1)', margin: 0 }}>Runway</h1>
-        <p style={{ font: 'var(--text-data)', color: 'var(--ink-3)', margin: '6px 0 0' }}>capacity vs milestone dates · calibrated on 27 closed issues</p>
+        <p style={{ font: 'var(--text-data)', color: 'var(--ink-3)', margin: '6px 0 0' }}>capacity vs milestone dates · {calibNote}</p>
       </header>
 
       <Card overline="Milestones" flush>
diff --git a/apps/desktop/src/renderer/src/components/shell/app-shell.tsx b/apps/desktop/src/renderer/src/components/shell/app-shell.tsx
index 48c9790..62bfb0a 100644
--- a/apps/desktop/src/renderer/src/components/shell/app-shell.tsx
+++ b/apps/desktop/src/renderer/src/components/shell/app-shell.tsx
@@ -2,7 +2,7 @@ import React, { useEffect, useState } from 'react'
 
 import logoIcon from '../../design/assets/logo-icon.png'
 import type { IssueRef } from '../../data/fixtures.js'
-import { issuesToBoardColumns, scheduleFocus } from '../../lib/backlog.js'
+import { backlogCalibration, forecastBacklog, issuesToBoardColumns, scheduleFocus } from '../../lib/backlog.js'
 import { useBacklog } from '../../lib/use-backlog.js'
 import { PrimitivesGallery } from '../gallery.js'
 import { BoardScreen } from '../screens/board-screen.js'
@@ -86,8 +86,16 @@ export function AppShell() {
   const [issue, setIssue] = useState<IssueRef | null>(null)
   const [readIds, setReadIds] = useState<number[]>([])
   const backlog = useBacklog()
-  const boardColumns = backlog.status === 'ready' ? issuesToBoardColumns(backlog.issues) : undefined
-  const focus = backlog.status === 'ready' ? scheduleFocus(backlog.issues, backlog.deps) : undefined
+  const boardColumns =
+    backlog.status === 'ready' ? issuesToBoardColumns(backlog.issues, backlog.timelines) : undefined
+  const focus =
+    backlog.status === 'ready' ? scheduleFocus(backlog.issues, backlog.deps, backlog.timelines) : undefined
+  const calibration =
+    backlog.status === 'ready' ? backlogCalibration(backlog.issues, backlog.timelines) : undefined
+  const forecast =
+    backlog.status === 'ready'
+      ? (forecastBacklog(backlog.issues, backlog.deps, new Date(), calibration?.model) ?? undefined)
+      : undefined
 
   useEffect(() => {
     document.documentElement.setAttribute('data-theme', dark ? 'dark' : 'light')
@@ -158,7 +166,7 @@ export function AppShell() {
   const renderScreen = () => {
     switch (view) {
       case 'focus':
-        return <FocusScreen onOpenIssue={openIssue} focus={focus} />
+        return <FocusScreen onOpenIssue={openIssue} focus={focus} forecast={forecast} />
       case 'standup':
         return <StandupScreen onBegin={() => setView('focus')} onOpenIssue={openIssue} />
       case 'board':
@@ -174,10 +182,11 @@ export function AppShell() {
           <RunwayScreen
             onOpenCalibration={() => setView('calibration')}
             onOpenMilestone={() => setView('milestone')}
+            calibration={calibration ? { n: calibration.model.n, coldStart: calibration.model.coldStart } : undefined}
           />
         )
       case 'calibration':
-        return <CalibrationScreen onBack={() => setView('runway')} />
+        return <CalibrationScreen onBack={() => setView('runway')} data={calibration?.data} />
       case 'milestone':
         return <MilestoneScreen onBack={() => setView('runway')} onOpenIssue={openIssue} />
       case 'inbox':
diff --git a/apps/desktop/src/renderer/src/global.d.ts b/apps/desktop/src/renderer/src/global.d.ts
index 468e19f..019d932 100644
--- a/apps/desktop/src/renderer/src/global.d.ts
+++ b/apps/desktop/src/renderer/src/global.d.ts
@@ -1,4 +1,4 @@
-import type { DependencyEdge, GiteaIssue, GiteaMilestone } from '@commitea/core'
+import type { DependencyEdge, GiteaIssue, GiteaMilestone, LifecycleEvent } from '@commitea/core'
 
 /** The gitea bridge exposed by the preload over IPC (main-process backed). */
 export interface GiteaBridge {
@@ -8,6 +8,8 @@ export interface GiteaBridge {
     issues: GiteaIssue[]
     milestones: GiteaMilestone[]
     deps: DependencyEdge[]
+    /** Normalized lifecycle events keyed by issue number. */
+    timelines: Record<number, LifecycleEvent[]>
   }>
   getIssue(index: number): Promise<GiteaIssue | null>
 }
diff --git a/apps/desktop/src/renderer/src/lib/backlog.ts b/apps/desktop/src/renderer/src/lib/backlog.ts
index 52a71b9..5aec932 100644
--- a/apps/desktop/src/renderer/src/lib/backlog.ts
+++ b/apps/desktop/src/renderer/src/lib/backlog.ts
@@ -1,14 +1,32 @@
 import {
+  type CalibrationModel,
+  type CalibrationSample,
+  calibrationSamples,
+  COLD_START_THRESHOLD,
   type DependencyEdge,
+  fitCalibration,
+  forecast,
   type GiteaIssue,
-  inferColumnV0,
+  inferLifecycle,
   type LifecycleColumn,
+  type LifecycleEvent,
+  type LifecycleInference,
+  PRIOR_BUCKETS,
   schedule,
   type ScheduledItem,
   selectFocus,
+  toDurationModel,
 } from '@commitea/core'
 
-import { type BoardColumn, type BoardIssue, type FocusIssue } from '../data/fixtures.js'
+import { type BoardColumn, type BoardIssue, type CalibrationData, type FocusIssue } from '../data/fixtures.js'
+import { type BurnUpData, buildBurnUpData } from './dates.js'
+
+type Timelines = Record<number, LifecycleEvent[]>
+
+/** Infer every issue's lifecycle once; callers index by issue number. */
+function inferAll(issues: GiteaIssue[], timelines: Timelines, asOf: Date): Map<number, LifecycleInference> {
+  return new Map(issues.map((i) => [i.number, inferLifecycle(i, timelines[i.number] ?? [], asOf)]))
+}
 
 const COLUMN_LABELS: Record<LifecycleColumn, string> = {
   diagnosis: 'Diagnosis',
@@ -25,24 +43,32 @@ function initials(login: string): string {
 }
 
 /**
- * Shape real gitea issues into the Board's five columns via lifecycle-v0.
- * `steeping` / `review` stay empty until event inference (P1-5). `days` / `pr`
- * are likewise event-derived and omitted here.
+ * Shape real gitea issues into the Board's five columns via lifecycle inference
+ * (#5). Steeping / In-review are now populated from the event stream (first
+ * commit ref → steeping, first PR ref → review); the `days` badge is the
+ * steeping age in working days.
  */
-export function issuesToBoardColumns(issues: GiteaIssue[]): BoardColumn[] {
+export function issuesToBoardColumns(
+  issues: GiteaIssue[],
+  timelines: Timelines = {},
+  asOf: Date = new Date(),
+): BoardColumn[] {
+  const inf = inferAll(issues, timelines, asOf)
   return COLUMN_ORDER.map((key) => ({
     id: key,
     label: COLUMN_LABELS[key],
     issues: issues
-      .filter((i) => inferColumnV0(i) === key)
-      .map(
-        (i): BoardIssue => ({
+      .filter((i) => inf.get(i.number)!.column === key)
+      .map((i): BoardIssue => {
+        const li = inf.get(i.number)!
+        return {
           id: i.number,
           title: i.title,
           labels: i.labels,
           who: i.assignee ? initials(i.assignee) : '·',
-        }),
-      ),
+          days: li.steepingDays != null ? `${li.steepingDays}d` : undefined,
+        }
+      }),
   }))
 }
 
@@ -52,9 +78,138 @@ export interface FocusView {
   later: FocusIssue | null
 }
 
-function toFocusIssue(item: ScheduledItem | null): FocusIssue | null {
+function toFocusIssue(item: ScheduledItem | null, inf?: Map<number, LifecycleInference>): FocusIssue | null {
   if (!item) return null
-  return { id: item.number, title: item.title, labels: item.labels, rationale: item.rationale }
+  const steepingDays = inf?.get(item.number)?.steepingDays ?? null
+  return {
+    id: item.number,
+    title: item.title,
+    labels: item.labels,
+    rationale: item.rationale,
+    steeping: steepingDays != null ? `${steepingDays}d` : undefined,
+  }
+}
+
+function toSchedulable(issues: GiteaIssue[]) {
+  return issues
+    .filter((i) => i.state === 'open')
+    .map((i) => ({
+      number: i.number,
+      title: i.title,
+      labels: i.labels,
+      estimateDays: i.facts.estimateDays,
+      priority: i.facts.priority,
+    }))
+}
+
+export interface ForecastView {
+  scope: number
+  cone: BurnUpData
+  p80Label: string
+  rangeLabel: string
+  /** true while the forecast still runs on code priors (calibration not yet trusted). */
+  coldStart: boolean
+  /** Closed-with-estimate issues feeding calibration so far. */
+  calibratedN: number
+}
+
+/**
+ * Monte Carlo forecast over the open backlog, mapped onto a calendar-anchored
+ * burn-up cone. When a calibration model is supplied and past cold-start, its
+ * fitted params drive the sim. Returns null when there's nothing to forecast.
+ * `today` is injectable for tests.
+ */
+export function forecastBacklog(
+  issues: GiteaIssue[],
+  deps: DependencyEdge[],
+  today: Date = new Date(),
+  calibration?: CalibrationModel,
+): ForecastView | null {
+  const model = calibration ? toDurationModel(calibration) : undefined
+  const f = forecast(toSchedulable(issues), deps, model ? { model } : {})
+  const cone = buildBurnUpData(f, today)
+  if (!cone) return null
+  return {
+    scope: f.scope,
+    cone,
+    p80Label: cone.p80Label,
+    rangeLabel: cone.rangeLabel,
+    coldStart: f.coldStart,
+    calibratedN: calibration?.n ?? 0,
+  }
+}
+
+/** Fit the calibration model from the closed backlog's inferred actuals (#1). */
+export function calibrateBacklog(
+  issues: GiteaIssue[],
+  timelines: Timelines = {},
+  asOf: Date = new Date(),
+): CalibrationModel {
+  return fitCalibration(calibrationSamples(issues, timelines, asOf))
+}
+
+/** Calibration model + its screen view in one pass over the closed backlog. */
+export function backlogCalibration(
+  issues: GiteaIssue[],
+  timelines: Timelines = {},
+  asOf: Date = new Date(),
+): { model: CalibrationModel; data: CalibrationData } {
+  const samples = calibrationSamples(issues, timelines, asOf)
+  const model = fitCalibration(samples)
+  return { model, data: calibrationData(model, samples, issues) }
+}
+
+const pctFromMu = (mu: number) => Math.round((Math.exp(mu) - 1) * 100)
+
+/**
+ * Shape the calibration model + its samples into the screen's view. Buckets and
+ * people only earn a bias once their sample clears the fit floor; everything
+ * degrades honestly on a thin (cold-start) dataset.
+ */
+export function calibrationData(
+  model: CalibrationModel,
+  samples: CalibrationSample[],
+  openIssues: GiteaIssue[],
+): CalibrationData {
+  const labels = PRIOR_BUCKETS.map((b) => {
+    const inBucket = samples.filter((s) => s.bucket === b)
+    const fit = model.byBucket[b]
+    const mu = fit ? fit.mu : model.global.mu
+    return {
+      label: `est/${b}d`,
+      n: fit ? fit.n : inBucket.length,
+      median: inBucket.length ? `${(b * Math.exp(mu)).toFixed(1)}d` : '—',
+      bias: fit ? pctFromMu(fit.mu) : null,
+    }
+  })
+
+  const people = Object.entries(model.byPerson).map(([who, pb]) => ({
+    who,
+    n: pb.n,
+    bias: pctFromMu(model.global.mu + pb.biasMu),
+    note: '',
+  }))
+
+  const openEst = openIssues
+    .filter((i) => i.state === 'open')
+    .reduce((sum, i) => sum + (i.facts.estimateDays ?? 2), 0)
+  const effect = model.coldStart
+    ? { raw: `${model.n}/${COLD_START_THRESHOLD} estimated closes`, banded: 'cold-start priors', p50: '—' }
+    : {
+        raw: `${openEst}d estimated`,
+        banded: `×${Math.exp(model.global.mu).toFixed(2)} median drift`,
+        p50: `≈${Math.round(openEst * Math.exp(model.global.mu))}d`,
+      }
+
+  return {
+    n: model.n,
+    active: !model.coldStart,
+    labels,
+    people,
+    scatter: samples.map((s) => [s.estimateDays, s.actualWorkingDays]),
+    fit: Number(Math.exp(model.global.mu).toFixed(2)),
+    effect,
+  }
 }
 
 /**
@@ -62,18 +217,18 @@ function toFocusIssue(item: ScheduledItem | null): FocusIssue | null {
  * as Now/Next/Later. Estimates + priority come from label facts; dependency
  * edges come from gitea's native issue dependencies.
  */
-export function scheduleFocus(issues: GiteaIssue[], deps: DependencyEdge[]): FocusView {
-  const open = issues.filter((i) => i.state === 'open')
-  const plan = schedule(
-    open.map((i) => ({
-      number: i.number,
-      title: i.title,
-      labels: i.labels,
-      estimateDays: i.facts.estimateDays,
-      priority: i.facts.priority,
-    })),
-    deps,
-  )
+export function scheduleFocus(
+  issues: GiteaIssue[],
+  deps: DependencyEdge[],
+  timelines: Timelines = {},
+  asOf: Date = new Date(),
+): FocusView {
+  const plan = schedule(toSchedulable(issues), deps)
   const f = selectFocus(plan)
-  return { now: toFocusIssue(f.now), next: toFocusIssue(f.next), later: toFocusIssue(f.later) }
+  const inf = inferAll(issues, timelines, asOf)
+  return {
+    now: toFocusIssue(f.now, inf),
+    next: toFocusIssue(f.next, inf),
+    later: toFocusIssue(f.later, inf),
+  }
 }
diff --git a/apps/desktop/src/renderer/src/lib/dates.ts b/apps/desktop/src/renderer/src/lib/dates.ts
new file mode 100644
index 0000000..7175edc
--- /dev/null
+++ b/apps/desktop/src/renderer/src/lib/dates.ts
@@ -0,0 +1,70 @@
+import type { Forecast } from '@commitea/core'
+
+const MONTHS = ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']
+
+/** Advance `base` by whole working days (skipping Sat/Sun). Fractions round to nearest day. */
+export function addWorkingDays(base: Date, workingDays: number): Date {
+  const d = new Date(base.getFullYear(), base.getMonth(), base.getDate())
+  let remaining = Math.max(0, Math.round(workingDays))
+  while (remaining > 0) {
+    d.setDate(d.getDate() + 1)
+    const day = d.getDay()
+    if (day !== 0 && day !== 6) remaining -= 1
+  }
+  return d
+}
+
+/** "Mar 6" */
+export function formatShort(d: Date): string {
+  return `${MONTHS[d.getMonth()]} ${d.getDate()}`
+}
+
+/** "Feb 24 – Mar 6" (collapses the month when both ends share it → "Mar 3–12"). */
+export function formatRange(lo: Date, hi: Date): string {
+  if (lo.getMonth() === hi.getMonth()) return `${MONTHS[lo.getMonth()]} ${lo.getDate()}–${hi.getDate()}`
+  return `${formatShort(lo)} – ${formatShort(hi)}`
+}
+
+export interface BurnUpBandPoint {
+  fraction: number
+  loDay: number
+  midDay: number
+  hiDay: number
+}
+
+/** Chart-ready geometry + calendar labels derived from a Monte Carlo forecast. */
+export interface BurnUpData {
+  scope: number
+  horizonDays: number
+  band: BurnUpBandPoint[]
+  p80Day: number
+  p80Label: string
+  rangeLabel: string
+  startLabel: string
+  endLabel: string
+}
+
+/**
+ * Map a working-day forecast onto a calendar-anchored burn-up cone. `today`
+ * anchors day 0; the cone emanates from (today, 0) and widens to the right.
+ * The historical "actual" polyline behind today awaits lifecycle events (#5).
+ */
+export function buildBurnUpData(f: Forecast, today: Date): BurnUpData | null {
+  if (f.scope === 0 || f.curve.length === 0) return null
+  const last = f.curve[f.curve.length - 1]
+  const horizonDays = Math.max(1, Math.ceil(last.p90Day * 1.05))
+  const band: BurnUpBandPoint[] = [
+    { fraction: 0, loDay: 0, midDay: 0, hiDay: 0 },
+    ...f.curve.map((p) => ({ fraction: p.fraction, loDay: p.p10Day, midDay: p.p50Day, hiDay: p.p90Day })),
+  ]
+  return {
+    scope: f.scope,
+    horizonDays,
+    band,
+    p80Day: f.p80Day,
+    p80Label: formatShort(addWorkingDays(today, f.p80Day)),
+    rangeLabel: formatRange(addWorkingDays(today, f.p50Day), addWorkingDays(today, last.p90Day)),
+    startLabel: formatShort(today),
+    endLabel: formatShort(addWorkingDays(today, horizonDays)),
+  }
+}
diff --git a/apps/desktop/src/renderer/src/lib/use-backlog.ts b/apps/desktop/src/renderer/src/lib/use-backlog.ts
index 4f14ca5..17b4848 100644
--- a/apps/desktop/src/renderer/src/lib/use-backlog.ts
+++ b/apps/desktop/src/renderer/src/lib/use-backlog.ts
@@ -1,12 +1,18 @@
 import { useEffect, useState } from 'react'
 
-import type { DependencyEdge, GiteaIssue, GiteaMilestone } from '@commitea/core'
+import type { DependencyEdge, GiteaIssue, GiteaMilestone, LifecycleEvent } from '@commitea/core'
 
 export type BacklogState =
   | { status: 'loading' }
   | { status: 'unconfigured' }
   | { status: 'error'; message: string }
-  | { status: 'ready'; issues: GiteaIssue[]; milestones: GiteaMilestone[]; deps: DependencyEdge[] }
+  | {
+      status: 'ready'
+      issues: GiteaIssue[]
+      milestones: GiteaMilestone[]
+      deps: DependencyEdge[]
+      timelines: Record<number, LifecycleEvent[]>
+    }
 
 /**
  * Reconcile the managed repo once on mount, through the main-process bridge.
@@ -24,7 +30,13 @@ export function useBacklog(): BacklogState {
         if (!alive) return
         setState(
           r.configured
-            ? { status: 'ready', issues: r.issues, milestones: r.milestones, deps: r.deps }
+            ? {
+                status: 'ready',
+                issues: r.issues,
+                milestones: r.milestones,
+                deps: r.deps,
+                timelines: r.timelines,
+              }
             : { status: 'unconfigured' },
         )
       })
diff --git a/packages/core/src/calibration/calibration-v0.test.ts b/packages/core/src/calibration/calibration-v0.test.ts
new file mode 100644
index 0000000..09e8486
--- /dev/null
+++ b/packages/core/src/calibration/calibration-v0.test.ts
@@ -0,0 +1,121 @@
+import { describe, expect, it } from 'vitest'
+
+import { extractLabelFacts } from '../labels/label-schema.js'
+import type { LifecycleEvent } from '../lifecycle/lifecycle-v0.js'
+import type { GiteaIssue } from '../gitea/types.js'
+import {
+  CALIBRATION_BUCKET_FLOOR,
+  calibrationSamples,
+  type CalibrationSample,
+  COLD_START_THRESHOLD,
+  fitCalibration,
+  toDurationModel,
+} from './calibration-v0.js'
+
+function sample(over: Partial<CalibrationSample> = {}): CalibrationSample {
+  return { issue: 1, estimateDays: 2, actualWorkingDays: 2, bucket: 2, person: null, ...over }
+}
+
+describe('fitCalibration', () => {
+  it('is cold-start below the threshold and reports the honest n', () => {
+    const m = fitCalibration([sample(), sample({ actualWorkingDays: 4 })])
+    expect(m.n).toBe(2)
+    expect(m.coldStart).toBe(true)
+  })
+
+  it('flips off cold-start at the threshold', () => {
+    const many = Array.from({ length: COLD_START_THRESHOLD }, (_, i) =>
+      sample({ issue: i, estimateDays: 2, actualWorkingDays: 3, bucket: 2 }),
+    )
+    const m = fitCalibration(many)
+    expect(m.n).toBe(COLD_START_THRESHOLD)
+    expect(m.coldStart).toBe(false)
+  })
+
+  it('recovers the global median ratio (mu = mean log-ratio)', () => {
+    // every actual is exactly 2x its estimate → mu = ln 2
+    const m = fitCalibration(Array.from({ length: 25 }, (_, i) => sample({ issue: i, estimateDays: 2, actualWorkingDays: 4 })))
+    expect(m.global.mu).toBeCloseTo(Math.log(2), 6)
+  })
+
+  it('fits a bucket only once it clears the floor', () => {
+    const twos = Array.from({ length: CALIBRATION_BUCKET_FLOOR }, (_, i) =>
+      sample({ issue: i, estimateDays: 2, actualWorkingDays: 3, bucket: 2 }),
+    )
+    const oneThin = [sample({ issue: 99, estimateDays: 5, actualWorkingDays: 9, bucket: 5 })]
+    const m = fitCalibration([...twos, ...oneThin])
+    expect(m.byBucket[2]?.n).toBe(CALIBRATION_BUCKET_FLOOR)
+    expect(m.byBucket[5]).toBeUndefined() // only 1 sample, below floor
+  })
+
+  it('drops non-positive estimates/actuals', () => {
+    const m = fitCalibration([sample({ actualWorkingDays: 0 }), sample({ estimateDays: 0 }), sample()])
+    expect(m.n).toBe(1)
+  })
+
+  it('derives a per-person bias relative to global', () => {
+    // one person consistently runs longer than the mean
+    const base = Array.from({ length: 20 }, (_, i) => sample({ issue: i, actualWorkingDays: 2, person: 'ak' }))
+    const slow = Array.from({ length: 3 }, (_, i) => sample({ issue: 100 + i, actualWorkingDays: 6, person: 'sm' }))
+    const m = fitCalibration([...base, ...slow])
+    expect(m.byPerson['sm'].biasMu).toBeGreaterThan(0)
+    expect(m.byPerson['ak'].biasMu).toBeLessThan(0)
+  })
+})
+
+describe('toDurationModel', () => {
+  it('projects the fit down to the params forecast needs', () => {
+    const m = fitCalibration(
+      Array.from({ length: 25 }, (_, i) => sample({ issue: i, estimateDays: 2, actualWorkingDays: 3, bucket: 2 })),
+    )
+    const dm = toDurationModel(m)
+    expect(dm.coldStart).toBe(false)
+    expect(dm.byBucket[2].mu).toBeCloseTo(m.byBucket[2].mu, 6)
+    expect(dm.global.mu).toBeCloseTo(m.global.mu, 6)
+  })
+})
+
+describe('calibrationSamples', () => {
+  const asOf = new Date('2026-02-01T00:00:00Z')
+
+  function issue(over: Partial<GiteaIssue>): GiteaIssue {
+    const labels = over.labels ?? []
+    return {
+      number: 1,
+      title: '#1',
+      body: '',
+      state: 'closed',
+      labels,
+      facts: extractLabelFacts(labels),
+      milestone: null,
+      assignee: null,
+      assignees: [],
+      createdAt: '2026-01-05T09:00:00Z',
+      updatedAt: '2026-01-12T09:00:00Z',
+      closedAt: '2026-01-12T09:00:00Z',
+      url: '',
+      ...over,
+    }
+  }
+
+  const events = (i: number): Record<number, LifecycleEvent[]> => ({
+    [i]: [{ type: 'commit', at: '2026-01-07T09:00:00Z' }, { type: 'close', at: '2026-01-12T09:00:00Z' }],
+  })
+
+  it('samples closed, estimated issues with a resolvable actual', () => {
+    const i = issue({ number: 7, labels: ['est/2d'], assignee: 'sm', closedAt: '2026-01-12T09:00:00Z' })
+    const [s] = calibrationSamples([i], events(7), asOf)
+    expect(s.issue).toBe(7)
+    expect(s.estimateDays).toBe(2)
+    expect(s.bucket).toBe(2)
+    expect(s.person).toBe('sm')
+    // Wed 2026-01-07 → Mon 2026-01-12 = Wed,Thu,Fri = 3 working days
+    expect(s.actualWorkingDays).toBe(3)
+  })
+
+  it('skips open issues and closed ones without an estimate', () => {
+    const open = issue({ number: 8, state: 'open', labels: ['est/2d'], closedAt: null })
+    const noEst = issue({ number: 9, labels: [] })
+    expect(calibrationSamples([open, noEst], { ...events(8), ...events(9) }, asOf)).toEqual([])
+  })
+})
diff --git a/packages/core/src/calibration/calibration-v0.ts b/packages/core/src/calibration/calibration-v0.ts
new file mode 100644
index 0000000..75ec6fb
--- /dev/null
+++ b/packages/core/src/calibration/calibration-v0.ts
@@ -0,0 +1,127 @@
+/**
+ * Calibration, v0 — fit the team's own estimate-vs-actual history so the
+ * forecast stops guessing (D3). The "actual" is the working time lifecycle
+ * inference derives from git events (#5), never manual tracking. Fit a
+ * lognormal on log(actual / estimate) globally and per estimate bucket; until
+ * the sample clears the cold-start threshold, the forecast keeps using the
+ * code-resident priors and this model just reports progress toward it.
+ */
+
+import { type DurationModel, type LognormalPrior, nearestBucket } from '../forecast/forecast-v0.js'
+import { inferLifecycle, type LifecycleEvent } from '../lifecycle/lifecycle-v0.js'
+import type { GiteaIssue } from '../gitea/types.js'
+
+/** Global sample size at which the fit takes over from the cold-start priors. */
+export const COLD_START_THRESHOLD = 20
+/** Minimum per-bucket sample before that bucket earns its own fit. */
+export const CALIBRATION_BUCKET_FLOOR = 3
+/** Fallback spread when a group is too small to estimate one. */
+const DEFAULT_SIGMA = 0.4
+
+/** One closed issue's estimate vs its inferred actual. */
+export interface CalibrationSample {
+  issue: number
+  estimateDays: number
+  actualWorkingDays: number
+  bucket: number
+  person: string | null
+}
+
+export interface BucketFit extends LognormalPrior {
+  n: number
+}
+
+export interface PersonBias {
+  /** Additive to global mu (log space). */
+  biasMu: number
+  n: number
+}
+
+export interface CalibrationModel {
+  /** Closed issues with an estimate + a resolvable actual. */
+  n: number
+  /** true while n < COLD_START_THRESHOLD — forecast keeps the code priors. */
+  coldStart: boolean
+  global: LognormalPrior
+  byBucket: Record<number, BucketFit>
+  byPerson: Record<string, PersonBias>
+}
+
+function mean(xs: number[]): number {
+  return xs.reduce((a, b) => a + b, 0) / xs.length
+}
+
+/** Sample standard deviation; falls back to DEFAULT_SIGMA below 2 points. */
+function stddev(xs: number[], mu: number): number {
+  if (xs.length < 2) return DEFAULT_SIGMA
+  const variance = xs.reduce((a, x) => a + (x - mu) ** 2, 0) / (xs.length - 1)
+  return Math.sqrt(variance) || DEFAULT_SIGMA
+}
+
+/** Fit a calibration model from estimate-vs-actual samples. Pure. */
+export function fitCalibration(samples: CalibrationSample[]): CalibrationModel {
+  const usable = samples.filter((s) => s.estimateDays > 0 && s.actualWorkingDays > 0)
+  const n = usable.length
+  const coldStart = n < COLD_START_THRESHOLD
+
+  const logRatios = usable.map((s) => Math.log(s.actualWorkingDays / s.estimateDays))
+  const globalMu = n ? mean(logRatios) : 0
+  const global: LognormalPrior = { mu: globalMu, sigma: n ? stddev(logRatios, globalMu) : DEFAULT_SIGMA }
+
+  const byBucket: Record<number, BucketFit> = {}
+  const byPerson: Record<string, PersonBias> = {}
+  const groups = new Map<number, number[]>()
+  const people = new Map<string, number[]>()
+  for (const s of usable) {
+    const lr = Math.log(s.actualWorkingDays / s.estimateDays)
+    ;(groups.get(s.bucket) ?? groups.set(s.bucket, []).get(s.bucket)!).push(lr)
+    if (s.person) (people.get(s.person) ?? people.set(s.person, []).get(s.person)!).push(lr)
+  }
+  for (const [bucket, lrs] of groups) {
+    if (lrs.length < CALIBRATION_BUCKET_FLOOR) continue
+    const mu = mean(lrs)
+    byBucket[bucket] = { mu, sigma: stddev(lrs, mu), n: lrs.length }
+  }
+  for (const [person, lrs] of people) {
+    if (lrs.length < CALIBRATION_BUCKET_FLOOR) continue
+    byPerson[person] = { biasMu: mean(lrs) - globalMu, n: lrs.length }
+  }
+
+  return { n, coldStart, global, byBucket, byPerson }
+}
+
+/** The subset of a model `forecast` consumes. */
+export function toDurationModel(model: CalibrationModel): DurationModel {
+  const byBucket: Record<number, LognormalPrior> = {}
+  for (const [bucket, fit] of Object.entries(model.byBucket)) {
+    byBucket[Number(bucket)] = { mu: fit.mu, sigma: fit.sigma }
+  }
+  return { coldStart: model.coldStart, global: model.global, byBucket }
+}
+
+/**
+ * Extract calibration samples from the closed backlog: each closed issue that
+ * carries an estimate and yields an inferred actual working duration.
+ */
+export function calibrationSamples(
+  issues: GiteaIssue[],
+  timelines: Record<number, LifecycleEvent[]>,
+  asOf: Date,
+): CalibrationSample[] {
+  const out: CalibrationSample[] = []
+  for (const issue of issues) {
+    if (issue.state !== 'closed') continue
+    const estimateDays = issue.facts.estimateDays
+    if (estimateDays == null) continue
+    const inf = inferLifecycle(issue, timelines[issue.number] ?? [], asOf)
+    if (inf.actualWorkingDays == null || inf.actualWorkingDays <= 0) continue
+    out.push({
+      issue: issue.number,
+      estimateDays,
+      actualWorkingDays: inf.actualWorkingDays,
+      bucket: nearestBucket(estimateDays),
+      person: issue.assignee,
+    })
+  }
+  return out
+}
diff --git a/packages/core/src/forecast/forecast-v0.test.ts b/packages/core/src/forecast/forecast-v0.test.ts
new file mode 100644
index 0000000..17c9d14
--- /dev/null
+++ b/packages/core/src/forecast/forecast-v0.test.ts
@@ -0,0 +1,123 @@
+import { describe, expect, it } from 'vitest'
+
+import { type DependencyEdge, type SchedulableIssue } from '../scheduler/scheduler-v0.js'
+import { COLD_START_PRIORS, forecast, priorForEstimate } from './forecast-v0.js'
+
+function issue(number: number, over: Partial<SchedulableIssue> = {}): SchedulableIssue {
+  return { number, title: `#${number}`, labels: [], estimateDays: 2, priority: 2, ...over }
+}
+
+describe('priorForEstimate', () => {
+  it('returns the exact prior for a bucket day count', () => {
+    expect(priorForEstimate(3)).toBe(COLD_START_PRIORS[3])
+    expect(priorForEstimate(8)).toBe(COLD_START_PRIORS[8])
+  })
+
+  it('snaps a non-bucket estimate to the nearest bucket', () => {
+    expect(priorForEstimate(4)).toBe(COLD_START_PRIORS[3]) // tie → smaller bucket
+    expect(priorForEstimate(6)).toBe(COLD_START_PRIORS[5])
+    expect(priorForEstimate(100)).toBe(COLD_START_PRIORS[8])
+  })
+
+  it('every prior is pessimistic (median actual runs longer than the estimate)', () => {
+    for (const p of Object.values(COLD_START_PRIORS)) expect(p.mu).toBeGreaterThan(0)
+  })
+})
+
+describe('forecast', () => {
+  const scope = [
+    issue(1, { estimateDays: 2 }),
+    issue(2, { estimateDays: 3 }),
+    issue(3, { estimateDays: 1 }),
+  ]
+
+  it('is reproducible: same seed → identical result', () => {
+    const a = forecast(scope, [], { trials: 500, seed: 42 })
+    const b = forecast(scope, [], { trials: 500, seed: 42 })
+    expect(a).toEqual(b)
+  })
+
+  it('percentiles are ordered p50 <= p80 <= p95', () => {
+    const f = forecast(scope, [], { trials: 3000 })
+    expect(f.p50Day).toBeLessThanOrEqual(f.p80Day)
+    expect(f.p80Day).toBeLessThanOrEqual(f.p95Day)
+  })
+
+  it('the burn-up curve is monotonic in both fraction and day', () => {
+    const f = forecast(scope, [], { trials: 3000 })
+    expect(f.curve).toHaveLength(3)
+    for (let i = 1; i < f.curve.length; i++) {
+      expect(f.curve[i].fraction).toBeGreaterThan(f.curve[i - 1].fraction)
+      expect(f.curve[i].p50Day).toBeGreaterThan(f.curve[i - 1].p50Day)
+    }
+    expect(f.curve.at(-1)!.fraction).toBeCloseTo(1)
+  })
+
+  it('lo/mid/hi are ordered within each cone point', () => {
+    const f = forecast(scope, [], { trials: 3000 })
+    for (const pt of f.curve) {
+      expect(pt.p10Day).toBeLessThanOrEqual(pt.p50Day)
+      expect(pt.p50Day).toBeLessThanOrEqual(pt.p90Day)
+    }
+  })
+
+  it('the median landing runs longer than the raw estimate sum (pessimism)', () => {
+    const rawSum = 2 + 3 + 1
+    const f = forecast(scope, [], { trials: 4000 })
+    expect(f.p50Day).toBeGreaterThan(rawSum)
+  })
+
+  it('reports scope and cold-start honestly', () => {
+    const f = forecast(scope, [], { trials: 100 })
+    expect(f.scope).toBe(3)
+    expect(f.coldStart).toBe(true)
+  })
+
+  it('a dependency cycle yields an empty, zeroed forecast', () => {
+    const edges: DependencyEdge[] = [
+      { issue: 1, dependsOn: 2 },
+      { issue: 2, dependsOn: 1 },
+    ]
+    const f = forecast([issue(1), issue(2)], edges, { trials: 100 })
+    expect(f.scope).toBe(0)
+    expect(f.curve).toEqual([])
+    expect(f.p80Day).toBe(0)
+  })
+
+  it('an empty scope forecasts nothing', () => {
+    const f = forecast([], [], { trials: 100 })
+    expect(f.scope).toBe(0)
+    expect(f.curve).toEqual([])
+  })
+
+  it('unestimated issues fall back to the default-estimate prior', () => {
+    const f = forecast([issue(1, { estimateDays: null }), issue(2, { estimateDays: null })], [], {
+      trials: 500,
+    })
+    expect(f.scope).toBe(2)
+    expect(f.p50Day).toBeGreaterThan(0)
+  })
+
+  it('a cold-start model changes nothing — the code priors still drive it', () => {
+    const priors = forecast(scope, [], { trials: 1000, seed: 7 })
+    const cold = forecast(scope, [], {
+      trials: 1000,
+      seed: 7,
+      model: { coldStart: true, global: { mu: 5, sigma: 0.1 }, byBucket: {} },
+    })
+    expect(cold.coldStart).toBe(true)
+    expect(cold.p50Day).toBeCloseTo(priors.p50Day, 6)
+  })
+
+  it('a fitted model drives the sim once past cold-start', () => {
+    // an optimistic fit (mu < 0, tight sigma) should land the scope sooner than the pessimistic priors
+    const priors = forecast(scope, [], { trials: 2000, seed: 7 })
+    const fitted = forecast(scope, [], {
+      trials: 2000,
+      seed: 7,
+      model: { coldStart: false, global: { mu: -0.2, sigma: 0.1 }, byBucket: {} },
+    })
+    expect(fitted.coldStart).toBe(false)
+    expect(fitted.p50Day).toBeLessThan(priors.p50Day)
+  })
+})
diff --git a/packages/core/src/forecast/forecast-v0.ts b/packages/core/src/forecast/forecast-v0.ts
new file mode 100644
index 0000000..04134fb
--- /dev/null
+++ b/packages/core/src/forecast/forecast-v0.ts
@@ -0,0 +1,193 @@
+/**
+ * Monte Carlo forecast, v0. The LLM never does this — it's plain, seeded,
+ * reproducible code (evidence-based scheduling). It samples an actual duration
+ * per open issue from a lognormal prior, walks the scheduler's deterministic
+ * order on a single serial worker, and reads percentiles off the resulting
+ * completion-day distribution.
+ *
+ * v0 simplifications (each a later slice, not a hack):
+ *  - single serial worker; per-person capacity + parallelism is #8.
+ *  - cold-start priors only; the team's empirical calibration fit lands at
+ *    n >= 20 closed-with-estimate issues (#5 supplies the actuals).
+ *  - forecast covers remaining (open) scope from today forward; the historical
+ *    burn-up "actual" polyline needs lifecycle event dates (#5).
+ */
+
+import {
+  type DependencyEdge,
+  schedule,
+  type SchedulableIssue,
+} from '../scheduler/scheduler-v0.js'
+
+export interface LognormalPrior {
+  /** Median log-ratio: sampled median duration = estimate * e^mu. */
+  mu: number
+  /** Spread of log(actual / estimate). */
+  sigma: number
+}
+
+/**
+ * Code-resident cold-start priors (D3). Lognormal on log(actual / estimate):
+ * sampled actual = estimateDays * exp(N(mu, sigma)). mu > 0 encodes the honest
+ * fact that actuals run long; sigma shrinks as tickets grow (a snag doubles a
+ * 1-day task but barely dents an 8-day one). The team's fitted model replaces
+ * these at n >= 20 (see calibration model in pm-state.md).
+ */
+export const COLD_START_PRIORS: Record<number, LognormalPrior> = {
+  1: { mu: 0.25, sigma: 0.55 },
+  2: { mu: 0.22, sigma: 0.48 },
+  3: { mu: 0.2, sigma: 0.44 },
+  5: { mu: 0.18, sigma: 0.4 },
+  8: { mu: 0.16, sigma: 0.36 },
+}
+
+export const PRIOR_BUCKETS = [1, 2, 3, 5, 8]
+
+/** Nearest estimate bucket (ties resolve to the smaller bucket). */
+export function nearestBucket(days: number): number {
+  let best = PRIOR_BUCKETS[0]
+  for (const b of PRIOR_BUCKETS) {
+    if (Math.abs(b - days) < Math.abs(best - days)) best = b
+  }
+  return best
+}
+
+/** The cold-start prior for the bucket nearest to `days`. */
+export function priorForEstimate(days: number): LognormalPrior {
+  return COLD_START_PRIORS[nearestBucket(days)]
+}
+
+/** The lognormal parameters `forecast` needs, per estimate bucket. */
+export interface DurationModel {
+  coldStart: boolean
+  /** Fallback params (used when a bucket lacks its own fit). */
+  global: LognormalPrior
+  /** Per-bucket fitted params; missing buckets fall back to `global`. */
+  byBucket: Record<number, LognormalPrior>
+}
+
+export interface ForecastOptions {
+  /** Simulation trials. More = smoother tails, linear cost. */
+  trials?: number
+  /** PRNG seed. Fixed by default so a forecast is reproducible. */
+  seed?: number
+  /**
+   * Fitted duration model. When present and not cold-start, its params drive
+   * the sim; otherwise the code-resident cold-start priors do.
+   */
+  model?: DurationModel
+}
+
+/** Resolve the lognormal params for an estimate, preferring a fitted model. */
+export function durationParams(days: number, model?: DurationModel): LognormalPrior {
+  if (model && !model.coldStart) {
+    return model.byBucket[nearestBucket(days)] ?? model.global
+  }
+  return priorForEstimate(days)
+}
+
+export interface BurnUpPoint {
+  /** Cumulative fraction of remaining scope complete (0 < f <= 1]. */
+  fraction: number
+  /** Working-day offset from today at the p10 / p50 / p90 of reaching it. */
+  p10Day: number
+  p50Day: number
+  p90Day: number
+}
+
+export interface Forecast {
+  /** Open issues in scope (== scheduled count). */
+  scope: number
+  trials: number
+  /** true while code priors drive the sim; false once the empirical fit is in (v1). */
+  coldStart: boolean
+  /** Working-day offsets from today for the whole scope landing. */
+  p50Day: number
+  p80Day: number
+  p95Day: number
+  /** Burn-up cone, one point per scheduled issue, fraction ascending. */
+  curve: BurnUpPoint[]
+}
+
+const DEFAULT_TRIALS = 2000
+const DEFAULT_SEED = 0x9e3779b9
+
+/** mulberry32 — small, fast, seedable PRNG (no reliance on Math.random). */
+function mulberry32(seed: number): () => number {
+  let a = seed >>> 0
+  return () => {
+    a = (a + 0x6d2b79f5) | 0
+    let t = Math.imul(a ^ (a >>> 15), 1 | a)
+    t = (t + Math.imul(t ^ (t >>> 7), 61 | t)) ^ t
+    return ((t ^ (t >>> 14)) >>> 0) / 4294967296
+  }
+}
+
+/** Box–Muller standard normal from a uniform PRNG. */
+function standardNormal(rng: () => number): number {
+  let u1 = rng()
+  const u2 = rng()
+  if (u1 < 1e-12) u1 = 1e-12
+  return Math.sqrt(-2 * Math.log(u1)) * Math.cos(2 * Math.PI * u2)
+}
+
+function percentile(sortedAsc: number[], q: number): number {
+  const idx = Math.min(sortedAsc.length - 1, Math.max(0, Math.round(q * (sortedAsc.length - 1))))
+  return sortedAsc[idx]
+}
+
+/**
+ * Monte Carlo over the deterministic schedule order. Order is fixed (it's
+ * derived from estimate labels + dependencies, not sampled), so only durations
+ * vary across trials — the cone stretches, it never reorders.
+ */
+export function forecast(
+  issues: SchedulableIssue[],
+  edges: DependencyEdge[],
+  options: ForecastOptions = {},
+): Forecast {
+  const trials = options.trials ?? DEFAULT_TRIALS
+  const seed = options.seed ?? DEFAULT_SEED
+  const coldStart = options.model ? options.model.coldStart : true
+  const order = schedule(issues, edges).items // empty when a dependency cycle exists
+  const n = order.length
+  if (n === 0) {
+    return { scope: 0, trials, coldStart, p50Day: 0, p80Day: 0, p95Day: 0, curve: [] }
+  }
+
+  const priors = order.map((it) => durationParams(it.durationDays, options.model))
+  const rng = mulberry32(seed)
+
+  // endByRank[k][t] = working day the (k+1)-th scheduled issue completes on trial t.
+  const endByRank: number[][] = Array.from({ length: n }, () => new Array<number>(trials))
+  for (let t = 0; t < trials; t++) {
+    let cursor = 0
+    for (let k = 0; k < n; k++) {
+      const p = priors[k]
+      const sampled = order[k].durationDays * Math.exp(p.mu + p.sigma * standardNormal(rng))
+      cursor += sampled
+      endByRank[k][t] = cursor
+    }
+  }
+
+  const curve: BurnUpPoint[] = endByRank.map((row, k) => {
+    const sorted = [...row].sort((a, b) => a - b)
+    return {
+      fraction: (k + 1) / n,
+      p10Day: percentile(sorted, 0.1),
+      p50Day: percentile(sorted, 0.5),
+      p90Day: percentile(sorted, 0.9),
+    }
+  })
+
+  const total = [...endByRank[n - 1]].sort((a, b) => a - b)
+  return {
+    scope: n,
+    trials,
+    coldStart,
+    p50Day: percentile(total, 0.5),
+    p80Day: percentile(total, 0.8),
+    p95Day: percentile(total, 0.95),
+    curve,
+  }
+}
diff --git a/packages/core/src/gitea/client.test.ts b/packages/core/src/gitea/client.test.ts
index f8dc005..989c23f 100644
--- a/packages/core/src/gitea/client.test.ts
+++ b/packages/core/src/gitea/client.test.ts
@@ -1,6 +1,6 @@
 import { describe, expect, it } from 'vitest'
 
-import { createGiteaClient, normalizeIssue } from './client.js'
+import { createGiteaClient, normalizeIssue, normalizeTimeline } from './client.js'
 import { GiteaApiError, type FetchLike, type GiteaConfig, type GiteaRequestInit } from './types.js'
 
 const CONFIG: GiteaConfig = {
@@ -44,6 +44,31 @@ function stubFetch(body: unknown, status = 200): {
   return { fetch, calls }
 }
 
+describe('normalizeTimeline', () => {
+  it('maps known gitea event types to lifecycle signals and drops the rest', () => {
+    const events = normalizeTimeline([
+      { type: 'label', created_at: '2026-01-06T09:00:00Z' },
+      { type: 'milestone', created_at: '2026-01-06T09:05:00Z' },
+      { type: 'commit_ref', created_at: '2026-01-07T12:00:00Z' },
+      { type: 'pull_ref', created_at: '2026-01-08T12:00:00Z' },
+      { type: 'comment', created_at: '2026-01-08T13:00:00Z' }, // dropped
+      { type: 'add_dependency', created_at: '2026-01-08T14:00:00Z' }, // dropped
+      { type: 'close', created_at: '2026-01-12T09:00:00Z' },
+    ])
+    expect(events).toEqual([
+      { type: 'triage', at: '2026-01-06T09:00:00Z' },
+      { type: 'triage', at: '2026-01-06T09:05:00Z' },
+      { type: 'commit', at: '2026-01-07T12:00:00Z' },
+      { type: 'pull', at: '2026-01-08T12:00:00Z' },
+      { type: 'close', at: '2026-01-12T09:00:00Z' },
+    ])
+  })
+
+  it('skips events missing a timestamp', () => {
+    expect(normalizeTimeline([{ type: 'commit_ref', created_at: '' }])).toEqual([])
+  })
+})
+
 describe('createGiteaClient.getIssue', () => {
   it('returns a normalized, typed issue from canned JSON', async () => {
     const { fetch } = stubFetch(RAW_ISSUE)
diff --git a/packages/core/src/gitea/client.ts b/packages/core/src/gitea/client.ts
index 0cc1441..794ec67 100644
--- a/packages/core/src/gitea/client.ts
+++ b/packages/core/src/gitea/client.ts
@@ -6,6 +6,7 @@
  * get the full set.
  */
 
+import { type LifecycleEvent, type LifecycleEventType } from '../lifecycle/lifecycle-v0.js'
 import { extractLabelFacts } from '../labels/label-schema.js'
 import {
   GiteaApiError,
@@ -54,6 +55,33 @@ interface RawMilestoneFull {
   closed_issues: number
 }
 
+/** The subset of a gitea timeline comment we read. */
+interface RawTimelineComment {
+  type: string
+  created_at: string
+}
+
+/** gitea timeline `type` → our lifecycle signal. Unmapped types are dropped. */
+const TIMELINE_TYPE_MAP: Record<string, LifecycleEventType> = {
+  label: 'triage',
+  milestone: 'triage',
+  assignees: 'triage',
+  commit_ref: 'commit',
+  pull_ref: 'pull',
+  close: 'close',
+  reopen: 'reopen',
+}
+
+/** Map a raw gitea timeline to normalized lifecycle events. Pure. */
+export function normalizeTimeline(raw: RawTimelineComment[]): LifecycleEvent[] {
+  const out: LifecycleEvent[] = []
+  for (const c of raw) {
+    const type = TIMELINE_TYPE_MAP[c.type]
+    if (type && c.created_at) out.push({ type, at: c.created_at })
+  }
+  return out
+}
+
 export interface ListIssuesOptions {
   /** @default 'all' */
   state?: 'open' | 'closed' | 'all'
@@ -68,6 +96,8 @@ export interface GiteaClient {
   listMilestones(): Promise<GiteaMilestone[]>
   /** The issue indices this issue depends on (its blockers). */
   getIssueDependencies(index: number): Promise<number[]>
+  /** Normalized lifecycle events for one issue (all pages of its timeline). */
+  getIssueTimeline(index: number): Promise<LifecycleEvent[]>
 }
 
 /** Map raw gitea issue JSON to the normalized domain shape. Pure. */
@@ -163,5 +193,12 @@ export function createGiteaClient(config: GiteaConfig, fetchImpl: FetchLike): Gi
       const raw = (await request(`/issues/${index}/dependencies`)) as { number: number }[]
       return raw.map((d) => d.number)
     },
+
+    async getIssueTimeline(index) {
+      const raw = await requestAll<RawTimelineComment>(
+        (page) => `/issues/${index}/timeline?page=${page}&limit=${PAGE_LIMIT}`,
+      )
+      return normalizeTimeline(raw)
+    },
   }
 }
diff --git a/packages/core/src/index.ts b/packages/core/src/index.ts
index 961fe39..c5b9716 100644
--- a/packages/core/src/index.ts
+++ b/packages/core/src/index.ts
@@ -9,7 +9,7 @@ export {
 } from './labels/label-schema.js'
 export type { EstimateLabel, LabelFacts, PriorityLabel } from './labels/label-schema.js'
 
-export { createGiteaClient, normalizeIssue, normalizeMilestone } from './gitea/client.js'
+export { createGiteaClient, normalizeIssue, normalizeMilestone, normalizeTimeline } from './gitea/client.js'
 export type { GiteaClient, ListIssuesOptions } from './gitea/client.js'
 export { GiteaApiError } from './gitea/types.js'
 export type {
@@ -22,8 +22,19 @@ export type {
   GiteaRequestInit,
 } from './gitea/types.js'
 
-export { inferColumnV0, LIFECYCLE_COLUMNS } from './lifecycle/lifecycle-v0.js'
-export type { LifecycleColumn } from './lifecycle/lifecycle-v0.js'
+export {
+  inferColumnV0,
+  inferLifecycle,
+  LIFECYCLE_COLUMNS,
+  workingDaysBetween,
+} from './lifecycle/lifecycle-v0.js'
+export type {
+  LifecycleColumn,
+  LifecycleEvent,
+  LifecycleEventType,
+  LifecycleInference,
+  LifecycleStages,
+} from './lifecycle/lifecycle-v0.js'
 
 export { DEFAULT_ESTIMATE_DAYS, schedule, selectFocus } from './scheduler/scheduler-v0.js'
 export type {
@@ -33,3 +44,33 @@ export type {
   ScheduledItem,
   SchedulePlan,
 } from './scheduler/scheduler-v0.js'
+
+export {
+  COLD_START_PRIORS,
+  durationParams,
+  forecast,
+  nearestBucket,
+  PRIOR_BUCKETS,
+  priorForEstimate,
+} from './forecast/forecast-v0.js'
+export type {
+  BurnUpPoint,
+  DurationModel,
+  Forecast,
+  ForecastOptions,
+  LognormalPrior,
+} from './forecast/forecast-v0.js'
+
+export {
+  CALIBRATION_BUCKET_FLOOR,
+  calibrationSamples,
+  COLD_START_THRESHOLD,
+  fitCalibration,
+  toDurationModel,
+} from './calibration/calibration-v0.js'
+export type {
+  BucketFit,
+  CalibrationModel,
+  CalibrationSample,
+  PersonBias,
+} from './calibration/calibration-v0.js'
diff --git a/packages/core/src/lifecycle/lifecycle-v0.test.ts b/packages/core/src/lifecycle/lifecycle-v0.test.ts
index 0f74f87..a288ee5 100644
--- a/packages/core/src/lifecycle/lifecycle-v0.test.ts
+++ b/packages/core/src/lifecycle/lifecycle-v0.test.ts
@@ -1,6 +1,11 @@
 import { describe, expect, it } from 'vitest'
 
-import { inferColumnV0 } from './lifecycle-v0.js'
+import {
+  inferColumnV0,
+  inferLifecycle,
+  type LifecycleEvent,
+  workingDaysBetween,
+} from './lifecycle-v0.js'
 
 const base = { state: 'open' as const, labels: [] as string[], milestone: null }
 
@@ -27,3 +32,93 @@ describe('inferColumnV0', () => {
     expect(['steeping', 'review']).not.toContain(col)
   })
 })
+
+describe('workingDaysBetween', () => {
+  it('counts weekdays in [start, end), excluding weekends', () => {
+    // Mon 2026-01-05 → Mon 2026-01-12 spans a full week = 5 working days
+    expect(workingDaysBetween(new Date('2026-01-05'), new Date('2026-01-12'))).toBe(5)
+  })
+
+  it('is 0 for same day or reversed', () => {
+    expect(workingDaysBetween(new Date('2026-01-05'), new Date('2026-01-05'))).toBe(0)
+    expect(workingDaysBetween(new Date('2026-01-12'), new Date('2026-01-05'))).toBe(0)
+  })
+
+  it('skips a weekend inside the interval', () => {
+    // Fri 2026-01-09 → Mon 2026-01-12: only Fri counts (Sat/Sun excluded) = 1
+    expect(workingDaysBetween(new Date('2026-01-09'), new Date('2026-01-12'))).toBe(1)
+  })
+})
+
+describe('inferLifecycle', () => {
+  const openBase = { ...base, createdAt: '2026-01-05T09:00:00Z', closedAt: null }
+  const asOf = new Date('2026-01-14T09:00:00Z')
+
+  const ev = (type: LifecycleEvent['type'], at: string): LifecycleEvent => ({ type, at })
+
+  it('bare open issue with no events is diagnosis', () => {
+    const inf = inferLifecycle(openBase, [], asOf)
+    expect(inf.column).toBe('diagnosis')
+    expect(inf.stages.opened).toBe(openBase.createdAt)
+    expect(inf.actualWorkingDays).toBeNull()
+    expect(inf.steepingDays).toBeNull()
+  })
+
+  it('a triage event (or a current label) moves it to triage', () => {
+    expect(inferLifecycle(openBase, [ev('triage', '2026-01-06T09:00:00Z')], asOf).column).toBe('triage')
+    expect(inferLifecycle({ ...openBase, labels: ['p/1'] }, [], asOf).column).toBe('triage')
+  })
+
+  it('a commit ref moves an open issue to steeping and counts its working age', () => {
+    const inf = inferLifecycle(
+      { ...openBase, labels: ['est/2d'] },
+      [ev('triage', '2026-01-05T10:00:00Z'), ev('commit', '2026-01-07T12:00:00Z')],
+      asOf,
+    )
+    expect(inf.column).toBe('steeping')
+    expect(inf.stages.steeping).toBe('2026-01-07T12:00:00Z')
+    // Wed 2026-01-07 → Wed 2026-01-14 = 5 working days
+    expect(inf.steepingDays).toBe(5)
+  })
+
+  it('a pull ref outranks a commit ref → review', () => {
+    const inf = inferLifecycle(
+      openBase,
+      [ev('commit', '2026-01-07T12:00:00Z'), ev('pull', '2026-01-08T12:00:00Z')],
+      asOf,
+    )
+    expect(inf.column).toBe('review')
+    expect(inf.steepingDays).toBeNull() // only steeping issues carry an age
+  })
+
+  it('closed → done, with actual working time from work-start to close', () => {
+    const inf = inferLifecycle(
+      { ...openBase, state: 'closed', closedAt: '2026-01-12T09:00:00Z' },
+      [ev('commit', '2026-01-07T09:00:00Z'), ev('pull', '2026-01-08T09:00:00Z'), ev('close', '2026-01-12T09:00:00Z')],
+      asOf,
+    )
+    expect(inf.column).toBe('done')
+    expect(inf.stages.done).toBe('2026-01-12T09:00:00Z')
+    // Wed 2026-01-07 → Mon 2026-01-12 = Wed,Thu,Fri = 3 working days
+    expect(inf.actualWorkingDays).toBe(3)
+  })
+
+  it('takes the earliest event of each kind for stage timestamps', () => {
+    const inf = inferLifecycle(
+      openBase,
+      [ev('commit', '2026-01-09T09:00:00Z'), ev('commit', '2026-01-07T09:00:00Z')],
+      asOf,
+    )
+    expect(inf.stages.steeping).toBe('2026-01-07T09:00:00Z')
+  })
+
+  it('falls back to opened when a closed issue has no work-start signal', () => {
+    const inf = inferLifecycle(
+      { ...openBase, state: 'closed', closedAt: '2026-01-08T09:00:00Z' },
+      [ev('close', '2026-01-08T09:00:00Z')],
+      asOf,
+    )
+    // Mon 2026-01-05 → Thu 2026-01-08 = Mon,Tue,Wed = 3 working days
+    expect(inf.actualWorkingDays).toBe(3)
+  })
+})
diff --git a/packages/core/src/lifecycle/lifecycle-v0.ts b/packages/core/src/lifecycle/lifecycle-v0.ts
index 936737d..a34613a 100644
--- a/packages/core/src/lifecycle/lifecycle-v0.ts
+++ b/packages/core/src/lifecycle/lifecycle-v0.ts
@@ -1,12 +1,10 @@
 /**
- * Lifecycle inference, v0 — the coarse column an issue sits in, derived from
- * *only* what a single issues-list read gives us (state, labels, milestone).
+ * Lifecycle inference.
  *
- * The real five-column inference (P1-5) needs the issue timeline: first
- * branch/commit ref → Steeping, PR opened → In review, PR merged → Deploy.
- * Until that lands, v0 can only place three columns honestly; `steeping` and
- * `review` stay empty rather than guess. Board renders all five columns and
- * fills the middle two once the event stream is available.
+ * `inferColumnV0` places the coarse three columns from a single issues-list
+ * read (state/labels/milestone). `inferLifecycle` (#5) adds the issue timeline:
+ * first commit ref → Steeping, first PR ref → In review, close → Done — and
+ * derives the estimate-vs-actual working time that feeds calibration (D3).
  */
 
 import type { GiteaIssue } from '../gitea/types.js'
@@ -23,10 +21,109 @@ export const LIFECYCLE_COLUMNS: readonly LifecycleColumn[] = [
 
 /**
  * Closed → done. Open with any human intent applied (a label or a milestone)
- * → triage. Open and bare → diagnosis. Never returns steeping/review in v0.
+ * → triage. Open and bare → diagnosis. Never returns steeping/review — that's
+ * `inferLifecycle`, which reads the event stream.
  */
 export function inferColumnV0(issue: Pick<GiteaIssue, 'state' | 'labels' | 'milestone'>): LifecycleColumn {
   if (issue.state === 'closed') return 'done'
   const hasIntent = issue.labels.length > 0 || issue.milestone !== null
   return hasIntent ? 'triage' : 'diagnosis'
 }
+
+/** A timeline signal, normalized from gitea's raw event stream. */
+export type LifecycleEventType = 'triage' | 'commit' | 'pull' | 'close' | 'reopen'
+
+export interface LifecycleEvent {
+  type: LifecycleEventType
+  /** ISO timestamp. */
+  at: string
+}
+
+/** Timestamps for the stages an issue has reached (absent = not yet reached). */
+export interface LifecycleStages {
+  opened: string
+  /** First label / milestone / assignment. */
+  triaged?: string
+  /** First commit referencing the issue — work began. */
+  steeping?: string
+  /** First PR referencing the issue — in review. */
+  review?: string
+  /** Closed. */
+  done?: string
+}
+
+export interface LifecycleInference {
+  column: LifecycleColumn
+  stages: LifecycleStages
+  /**
+   * Working days from work-start (steeping → triaged → opened, first available)
+   * to done. Only for closed issues — this is the "actual" calibration learns
+   * from. null while open.
+   */
+  actualWorkingDays: number | null
+  /** Working days the issue has been steeping (first commit → asOf); null unless currently steeping. */
+  steepingDays: number | null
+}
+
+const DAY_MS = 86_400_000
+
+/**
+ * Whole working days (Mon–Fri) in the half-open interval [start, end). Same day
+ * or reversed → 0. Day-granular by design — estimates are in days.
+ */
+export function workingDaysBetween(start: Date, end: Date): number {
+  const s = Date.UTC(start.getUTCFullYear(), start.getUTCMonth(), start.getUTCDate())
+  const e = Date.UTC(end.getUTCFullYear(), end.getUTCMonth(), end.getUTCDate())
+  if (e <= s) return 0
+  let count = 0
+  for (let t = s; t < e; t += DAY_MS) {
+    const dow = new Date(t).getUTCDay()
+    if (dow !== 0 && dow !== 6) count += 1
+  }
+  return count
+}
+
+/**
+ * The five-column inference. Column reflects the furthest stage still in play:
+ * closed → done; else an open PR ref → review; else a commit ref → steeping;
+ * else any triage signal (or a current label/milestone) → triage; else
+ * diagnosis. Stage timestamps are the earliest event of each kind.
+ */
+export function inferLifecycle(
+  issue: Pick<GiteaIssue, 'state' | 'labels' | 'milestone' | 'createdAt' | 'closedAt'>,
+  events: LifecycleEvent[],
+  asOf: Date,
+): LifecycleInference {
+  const sorted = [...events].sort((a, b) => a.at.localeCompare(b.at))
+  const firstOf = (type: LifecycleEventType) => sorted.find((e) => e.type === type)?.at
+
+  const stages: LifecycleStages = { opened: issue.createdAt }
+  const triagedAt = firstOf('triage')
+  const steepingAt = firstOf('commit')
+  const reviewAt = firstOf('pull')
+  if (triagedAt) stages.triaged = triagedAt
+  if (steepingAt) stages.steeping = steepingAt
+  if (reviewAt) stages.review = reviewAt
+  const doneAt = issue.state === 'closed' ? (issue.closedAt ?? firstOf('close')) : undefined
+  if (doneAt) stages.done = doneAt
+
+  let column: LifecycleColumn
+  if (issue.state === 'closed') column = 'done'
+  else if (reviewAt) column = 'review'
+  else if (steepingAt) column = 'steeping'
+  else if (triagedAt || issue.labels.length > 0 || issue.milestone !== null) column = 'triage'
+  else column = 'diagnosis'
+
+  let actualWorkingDays: number | null = null
+  if (stages.done) {
+    const start = stages.steeping ?? stages.triaged ?? stages.opened
+    actualWorkingDays = workingDaysBetween(new Date(start), new Date(stages.done))
+  }
+
+  let steepingDays: number | null = null
+  if (column === 'steeping' && stages.steeping) {
+    steepingDays = workingDaysBetween(new Date(stages.steeping), asOf)
+  }
+
+  return { column, stages, actualWorkingDays, steepingDays }
+}