diff --git a/src/main/index.ts b/src/main/index.ts
index 104f31b6e84..ba293c7a190 100644
--- a/src/main/index.ts
+++ b/src/main/index.ts
@@ -16,6 +16,7 @@ import { closeAllWatchers } from './ipc/filesystem-watcher'
 import { registerCoreHandlers } from './ipc/register-core-handlers'
 import { registerMobileHandlers } from './ipc/mobile'
 import { initTelemetry, shutdownTelemetry, trackAppOpenedOnce } from './telemetry/client'
+import { initCohortClassifier } from './telemetry/cohort-classifier'
 import { resolveConsent } from './telemetry/consent'
 import { triggerStartupNotificationRegistration } from './ipc/notifications'
 import { OrcaRuntimeService } from './runtime/orca-runtime'
@@ -399,6 +400,13 @@ app.whenReady().then(async () => {
   // the Store reference, seeds common props, and resets per-session burst
   // caps. Actual transport initialization is still gated by both flags.
   initTelemetry(store)
+  // Why: cohort-classifier reads the repo count synchronously at every emit
+  // for cohort-extended events. The Store has been sync-loaded above, and
+  // this init runs before any IPC handler is registered and before any
+  // window loads — so the classifier is hydrated before any `track()` call,
+  // regardless of whether it originates from the renderer, an IPC handler,
+  // or `trackAppOpenedOnce` / `did-finish-load`.
+  initCohortClassifier(store)
   stats = new StatsCollector()
   claudeUsage = new ClaudeUsageStore(store)
   codexUsage = new CodexUsageStore(store)
diff --git a/src/main/ipc/pty.ts b/src/main/ipc/pty.ts
index 0b37df9d699..3b4a1748cab 100644
--- a/src/main/ipc/pty.ts
+++ b/src/main/ipc/pty.ts
@@ -28,6 +28,7 @@ import { applyTerminalAttributionEnv } from '../attribution/terminal-attribution
 import { registerPty, unregisterPty } from '../memory/pty-registry'
 import { track } from '../telemetry/client'
 import { classifyError } from '../telemetry/classify-error'
+import { getCohortAtEmit } from '../telemetry/cohort-classifier'
 import {
   agentKindSchema,
   launchSourceSchema,
@@ -945,7 +946,8 @@ export function registerPtyHandlers(
           const classified = classifyError(err)
           track('agent_error', {
             agent_kind: errorAgentKind,
-            error_class: classified.error_class
+            error_class: classified.error_class,
+            ...getCohortAtEmit()
           })
         }
         throw err
@@ -1101,7 +1103,8 @@ export function registerPtyHandlers(
           track('agent_started', {
             agent_kind: agentKindParse.data,
             launch_source: launchSourceParse.data,
-            request_kind: requestKindParse.data
+            request_kind: requestKindParse.data,
+            ...getCohortAtEmit()
           })
         }
       }
diff --git a/src/main/ipc/repos.ts b/src/main/ipc/repos.ts
index b6239163cdb..712ea66e3b7 100644
--- a/src/main/ipc/repos.ts
+++ b/src/main/ipc/repos.ts
@@ -30,6 +30,7 @@ import { getSshGitProvider } from '../providers/ssh-git-dispatch'
 import { getActiveMultiplexer } from './ssh'
 import { normalizeSparseDirectories } from './sparse-checkout-directories'
 import { track } from '../telemetry/client'
+import { getCohortAtEmit } from '../telemetry/cohort-classifier'
 import type { RepoMethod } from '../../shared/telemetry-events'
 
 // Why: `method` answers "which entry point did the user take?", not "what did
@@ -46,7 +47,11 @@ function emitRepoAdded(method: RepoMethod, alreadyExisted: boolean): void {
   if (alreadyExisted) {
     return
   }
-  track('repo_added', { method })
+  // Why: cohort must read AFTER `store.addRepo()` lands so the just-added
+  // repo is counted — every call site below already emits post-addRepo, so
+  // `getCohortAtEmit()` here returns the user's Nth `repo_added` as `N`.
+  // See docs/onboarding-funnel-cohort-addendum.md §Read-vs-write ordering.
+  track('repo_added', { method, ...getCohortAtEmit() })
 }
 
 // Why: module-scoped so the abort handle survives window re-creation on macOS.
@@ -391,6 +396,7 @@ export function registerRepoHandlers(mainWindow: BrowserWindow, store: Store): v
         // other invocation is using it. Leaking a freshly-made empty folder on
         // a rare race is strictly safer than deleting a directory the winning
         // call (and the user) now owns.
+        emitRepoAdded('folder_picker', true)
         return { repo: raceWinner }
       }
 
diff --git a/src/main/ipc/telemetry.test.ts b/src/main/ipc/telemetry.test.ts
index 9e1b9231cc5..2fcfbf8bfad 100644
--- a/src/main/ipc/telemetry.test.ts
+++ b/src/main/ipc/telemetry.test.ts
@@ -16,13 +16,15 @@ const {
   trackMock,
   setOptInMock,
   persistBannerAcknowledgeMock,
-  consumeConsentMutationTokenMock
+  consumeConsentMutationTokenMock,
+  getCohortAtEmitMock
 } = vi.hoisted(() => ({
   handleMock: vi.fn(),
   trackMock: vi.fn(),
   setOptInMock: vi.fn(),
   persistBannerAcknowledgeMock: vi.fn(),
-  consumeConsentMutationTokenMock: vi.fn()
+  consumeConsentMutationTokenMock: vi.fn(),
+  getCohortAtEmitMock: vi.fn()
 }))
 
 vi.mock('electron', () => ({ ipcMain: { handle: handleMock } }))
@@ -34,6 +36,9 @@ vi.mock('../telemetry/client', () => ({
 vi.mock('../telemetry/burst-cap', () => ({
   consumeConsentMutationToken: consumeConsentMutationTokenMock
 }))
+vi.mock('../telemetry/cohort-classifier', () => ({
+  getCohortAtEmit: getCohortAtEmitMock
+}))
 
 import { _resetStoreForTests, registerTelemetryHandlers } from './telemetry'
 
@@ -82,6 +87,8 @@ describe('telemetry IPC handlers', () => {
     persistBannerAcknowledgeMock.mockReset()
     consumeConsentMutationTokenMock.mockReset()
     consumeConsentMutationTokenMock.mockReturnValue(true)
+    getCohortAtEmitMock.mockReset()
+    getCohortAtEmitMock.mockReturnValue({ nth_repo_added: 0 })
     _resetStoreForTests()
   })
   afterEach(() => {
@@ -102,12 +109,53 @@ describe('telemetry IPC handlers', () => {
 
   // ── telemetry:track ──────────────────────────────────────────────────
 
-  it('forwards a well-typed track call to track()', () => {
+  it('forwards a well-typed track call to track() and injects cohort for COHORT_EXTENDED events', () => {
     registerWith({ installId: 'x', existedBeforeTelemetryRelease: false, optedIn: true })
+    getCohortAtEmitMock.mockReturnValue({ nth_repo_added: 2 })
     const handler = handlers.get('telemetry:track')!
     handler({}, 'app_opened', {})
     expect(trackMock).toHaveBeenCalledTimes(1)
-    expect(trackMock).toHaveBeenCalledWith('app_opened', {})
+    expect(trackMock).toHaveBeenCalledWith('app_opened', { nth_repo_added: 2 })
+  })
+
+  // The IPC handler's selectivity is load-bearing: schemas are `.strict()`,
+  // so injecting `nth_repo_added` on a non-cohort event would silently
+  // drop the entire event at the validator. Events outside `COHORT_EXTENDED`
+  // must reach `track()` unmodified.
+  it('does NOT inject cohort on events outside COHORT_EXTENDED', () => {
+    registerWith({ installId: 'x', existedBeforeTelemetryRelease: false, optedIn: true })
+    const handler = handlers.get('telemetry:track')!
+    handler({}, 'settings_changed', { setting_key: 'editorAutoSave', value_kind: 'bool' })
+    expect(trackMock).toHaveBeenCalledTimes(1)
+    expect(trackMock).toHaveBeenCalledWith('settings_changed', {
+      setting_key: 'editorAutoSave',
+      value_kind: 'bool'
+    })
+    expect(getCohortAtEmitMock).not.toHaveBeenCalled()
+  })
+
+  // The renderer-only Setup-step events fire from React `onClick` and
+  // depend on the IPC handler injecting cohort — call sites stay
+  // synchronous and pass only their own props.
+  it('injects cohort for add_repo_setup_step_action (renderer-only event)', () => {
+    registerWith({ installId: 'x', existedBeforeTelemetryRelease: false, optedIn: true })
+    getCohortAtEmitMock.mockReturnValue({ nth_repo_added: 1 })
+    const handler = handlers.get('telemetry:track')!
+    handler({}, 'add_repo_setup_step_action', { action: 'skip' })
+    expect(trackMock).toHaveBeenCalledWith('add_repo_setup_step_action', {
+      action: 'skip',
+      nth_repo_added: 1
+    })
+  })
+
+  // Fail-soft: a degraded classifier returns `{ nth_repo_added: undefined }`.
+  // The schemas declare the field optional, so the event still validates.
+  it('forwards undefined cohort when the classifier returns undefined', () => {
+    registerWith({ installId: 'x', existedBeforeTelemetryRelease: false, optedIn: true })
+    getCohortAtEmitMock.mockReturnValue({ nth_repo_added: undefined })
+    const handler = handlers.get('telemetry:track')!
+    handler({}, 'app_opened', {})
+    expect(trackMock).toHaveBeenCalledWith('app_opened', { nth_repo_added: undefined })
   })
 
   it('drops track calls with a non-string name', () => {
@@ -129,12 +177,13 @@ describe('telemetry IPC handlers', () => {
 
   it('treats null/undefined props as an empty object', () => {
     registerWith({ installId: 'x', existedBeforeTelemetryRelease: false, optedIn: true })
+    getCohortAtEmitMock.mockReturnValue({ nth_repo_added: 0 })
     const handler = handlers.get('telemetry:track')!
     handler({}, 'app_opened', null)
     handler({}, 'app_opened', undefined)
     expect(trackMock).toHaveBeenCalledTimes(2)
-    expect(trackMock).toHaveBeenNthCalledWith(1, 'app_opened', {})
-    expect(trackMock).toHaveBeenNthCalledWith(2, 'app_opened', {})
+    expect(trackMock).toHaveBeenNthCalledWith(1, 'app_opened', { nth_repo_added: 0 })
+    expect(trackMock).toHaveBeenNthCalledWith(2, 'app_opened', { nth_repo_added: 0 })
   })
 
   // ── telemetry:setOptIn — input narrowing ─────────────────────────────
diff --git a/src/main/ipc/telemetry.ts b/src/main/ipc/telemetry.ts
index 1bfddc07d41..c8e15815092 100644
--- a/src/main/ipc/telemetry.ts
+++ b/src/main/ipc/telemetry.ts
@@ -38,8 +38,10 @@
 import { ipcMain } from 'electron'
 import { consumeConsentMutationToken } from '../telemetry/burst-cap'
 import { persistBannerAcknowledgeWithoutEmitting, setOptIn, track } from '../telemetry/client'
+import { getCohortAtEmit } from '../telemetry/cohort-classifier'
 import { resolveConsent, type ConsentState } from '../telemetry/consent'
 import type { Store } from '../persistence'
+import { isCohortExtendedEvent } from '../../shared/telemetry-events'
 import type { EventName, EventProps } from '../../shared/telemetry-events'
 import type { OptInVia } from '../../shared/telemetry-events'
 
@@ -114,12 +116,24 @@ export function registerTelemetryHandlers(store: Store): void {
     if (props !== null && props !== undefined && typeof props !== 'object') {
       return
     }
+    // Inject cohort here, at the IPC entry, only for events whose schemas
+    // declare `nth_repo_added` (see `COHORT_EXTENDED` in telemetry-events.ts).
+    // The selectivity is load-bearing: schemas are `.strict()`, so adding
+    // `nth_repo_added` to an event that does not declare it would fail Zod
+    // validation and silently drop the entire event. The renderer call sites
+    // stay synchronous (matching the existing fire-and-forget shape) and
+    // avoid an extra IPC round-trip to fetch cohort.
+    const eventName = name as EventName
+    const baseProps = (props ?? {}) as Record<string, unknown>
+    const finalProps = isCohortExtendedEvent(eventName)
+      ? { ...baseProps, ...getCohortAtEmit() }
+      : baseProps
     // The casts to `EventName` / `EventProps<EventName>` here are
     // pass-through only — this file does NOT pretend the renderer's
     // name/props are type-safe. The validator inside `track()` is the
     // single enforcement point at runtime; these casts only feed the
     // typed channel that the validator will re-check.
-    track(name as EventName, (props ?? {}) as EventProps<EventName>)
+    track(eventName, finalProps as EventProps<EventName>)
   })
 
   ipcMain.handle('telemetry:setOptIn', (_event, optedIn: unknown): Promise<void> | void => {
diff --git a/src/main/ipc/workspace-create-error-classifier.test.ts b/src/main/ipc/workspace-create-error-classifier.test.ts
new file mode 100644
index 00000000000..b4cc075d103
--- /dev/null
+++ b/src/main/ipc/workspace-create-error-classifier.test.ts
@@ -0,0 +1,76 @@
+// Spot-check the classifier against the load-bearing throws in
+// worktree-remote.ts. Not exhaustive — substring widening still requires
+// explicit review per the schema-evolution doctrine in
+// telemetry-events.ts. Add fixtures here when adding new buckets or when
+// a renamed throw site needs regression coverage.
+
+import { describe, expect, it } from 'vitest'
+import { classifyWorkspaceCreateError } from './workspace-create-error-classifier'
+
+describe('classifyWorkspaceCreateError', () => {
+  it('buckets the missing-base-ref throw as base_ref_missing', () => {
+    const err = new Error(
+      'Could not resolve a default base ref for this repo. Pick a base branch explicitly and try again.'
+    )
+    expect(classifyWorkspaceCreateError(err)).toBe('base_ref_missing')
+  })
+
+  it('buckets a branch-already-exists throw as path_collision', () => {
+    const err = new Error('Branch "feature/foo" already exists. Pick a different worktree name.')
+    expect(classifyWorkspaceCreateError(err)).toBe('path_collision')
+  })
+
+  it('buckets the suffix-exhaustion throw as path_collision', () => {
+    const err = new Error(
+      'Could not find an available worktree name for "feature". Pick a different worktree name.'
+    )
+    expect(classifyWorkspaceCreateError(err)).toBe('path_collision')
+  })
+
+  it('buckets a branch-already-exists-locally throw as path_collision', () => {
+    const err = new Error(
+      'Branch "feature/foo" already exists locally. Pick a different worktree name.'
+    )
+    expect(classifyWorkspaceCreateError(err)).toBe('path_collision')
+  })
+
+  it('buckets an existing-PR collision throw as path_collision', () => {
+    const err = new Error(
+      'Branch "feature/foo" already has PR #42. Pick a different worktree name.'
+    )
+    expect(classifyWorkspaceCreateError(err)).toBe('path_collision')
+  })
+
+  it('buckets the post-create listing-miss throw as git_failed', () => {
+    const err = new Error('Worktree created but not found in listing')
+    expect(classifyWorkspaceCreateError(err)).toBe('git_failed')
+  })
+
+  it('buckets EACCES errors as permission_denied', () => {
+    const err = Object.assign(new Error("EACCES: permission denied, mkdir '/tmp/x'"), {
+      code: 'EACCES'
+    })
+    expect(classifyWorkspaceCreateError(err)).toBe('permission_denied')
+  })
+
+  it('buckets generic git errors as git_failed', () => {
+    const err = new Error('fatal: not a git repository')
+    expect(classifyWorkspaceCreateError(err)).toBe('git_failed')
+  })
+
+  it('falls through to unknown for unrecognised errors', () => {
+    const err = new Error('something completely unexpected')
+    expect(classifyWorkspaceCreateError(err)).toBe('unknown')
+  })
+
+  it('falls through to unknown for SSH-precondition errors', () => {
+    const err = new Error('SSH connection is not available. Please reconnect and try again.')
+    expect(classifyWorkspaceCreateError(err)).toBe('unknown')
+  })
+
+  it('handles non-Error values without throwing', () => {
+    expect(classifyWorkspaceCreateError('a bare string')).toBe('unknown')
+    expect(classifyWorkspaceCreateError(undefined)).toBe('unknown')
+    expect(classifyWorkspaceCreateError(null)).toBe('unknown')
+  })
+})
diff --git a/src/main/ipc/workspace-create-error-classifier.ts b/src/main/ipc/workspace-create-error-classifier.ts
new file mode 100644
index 00000000000..5a24493fd62
--- /dev/null
+++ b/src/main/ipc/workspace-create-error-classifier.ts
@@ -0,0 +1,53 @@
+// Bucket errors thrown by `createLocalWorktree` / `createRemoteWorktree` into
+// the `workspace_create_failed` event's `error_class` enum.
+//
+// Why: the throw sites are bare `throw new Error('...')` calls in
+// worktree-remote.ts, some of which interpolate user-controlled content
+// (branch names, paths). The classifier reads `error.message` to bucket, but
+// the matched strings never cross the wire — only the enum value does. The
+// schema discipline at telemetry-events.ts §"Properties to keep off these
+// events" is what makes that safe.
+//
+// Substring set is intentionally narrow: per the schema-evolution doctrine,
+// widening this match set later requires explicit review, not silent regex
+// expansion. Anything we cannot confidently bucket falls through to `unknown`.
+
+import type { WorkspaceCreateErrorClass } from '../../shared/telemetry-events'
+
+export function classifyWorkspaceCreateError(error: unknown): WorkspaceCreateErrorClass {
+  // Why: throw sites mix capitalization ('Worktree created...' vs lowercased
+  // git messages); normalize once so all anchors below can be lowercase literals.
+  const text = (error instanceof Error ? error.message : '').toLowerCase()
+
+  if (text.includes('could not resolve a default base ref')) {
+    return 'base_ref_missing'
+  }
+  if (
+    text.includes('already exists locally') ||
+    text.includes('already exists on a remote') ||
+    text.includes('already exists. pick') ||
+    text.includes('already has pr') ||
+    text.includes('could not find an available worktree name')
+  ) {
+    return 'path_collision'
+  }
+  if (text.includes('eacces') || text.includes('eperm') || text.includes('permission denied')) {
+    return 'permission_denied'
+  }
+  // Why: anchors are intentionally specific to true git failures from
+  // worktree-remote.ts. Bare 'git ' / 'worktree' would mis-bucket SSH-relay
+  // and sparse-checkout validation errors (which the design doc routes to
+  // 'unknown'); 'created but not found in listing' covers the formerly
+  // miscased 'Worktree created but not found in listing' throw.
+  // SSH-precondition failures (e.g. 'no git provider', 'SSH connection is
+  // not available') deliberately fall through to 'unknown' — they're not
+  // git failures and bucketing them here would mask connectivity issues.
+  if (
+    text.includes('fatal:') ||
+    text.includes('git worktree') ||
+    text.includes('created but not found in listing')
+  ) {
+    return 'git_failed'
+  }
+  return 'unknown'
+}
diff --git a/src/main/ipc/worktrees.ts b/src/main/ipc/worktrees.ts
index f85a4915255..8bbd318c7a0 100644
--- a/src/main/ipc/worktrees.ts
+++ b/src/main/ipc/worktrees.ts
@@ -45,7 +45,9 @@ import { killAllProcessesForWorktree } from '../runtime/worktree-teardown'
 import { getLocalPtyProvider } from './pty'
 import { removeWorktreeSymlinks } from './worktree-symlinks'
 import { track } from '../telemetry/client'
+import { getCohortAtEmit } from '../telemetry/cohort-classifier'
 import { workspaceSourceSchema, type WorkspaceSource } from '../../shared/telemetry-events'
+import { classifyWorkspaceCreateError } from './workspace-create-error-classifier'
 
 // Why: worktrees discovered on disk (not created via Orca's UI) have no
 // persisted WorktreeMeta, so mergeWorktree falls back to `lastActivityAt: 0`.
@@ -229,10 +231,27 @@ export function registerWorktreeHandlers(
         throw new Error('Folder mode does not support creating worktrees.')
       }
 
-      // Remote repos route all git operations through the relay
-      const result = repo.connectionId
-        ? await createRemoteWorktree(args, repo, store, mainWindow)
-        : await createLocalWorktree(args, repo, store, mainWindow, runtime)
+      const sourceParse = workspaceSourceSchema.safeParse(args.telemetrySource)
+      const source: WorkspaceSource = sourceParse.success ? sourceParse.data : 'unknown'
+
+      let result: CreateWorktreeResult
+      try {
+        // Why: only wrap the helpers themselves. The pre-validation throws
+        // above (`Repo not found`, `Folder mode does not support creating
+        // worktrees`) signal IPC-shape bugs, not the user-visible
+        // git/filesystem failures the funnel cares about — bucketing them
+        // into `unknown` would pollute the failure taxonomy.
+        result = repo.connectionId
+          ? await createRemoteWorktree(args, repo, store, mainWindow)
+          : await createLocalWorktree(args, repo, store, mainWindow, runtime)
+      } catch (error) {
+        track('workspace_create_failed', {
+          source,
+          error_class: classifyWorkspaceCreateError(error),
+          ...getCohortAtEmit()
+        })
+        throw error
+      }
 
       // Why: emit `workspace_created` only after the underlying create has
       // resolved (the helpers throw on failure, so reaching this line means
@@ -242,11 +261,10 @@ export function registerWorktreeHandlers(
       // baseBranch; an unspecified baseBranch means "branch from default
       // HEAD", which is the not-from-existing-branch case. We never send
       // the branch name itself.
-      const sourceParse = workspaceSourceSchema.safeParse(args.telemetrySource)
-      const source: WorkspaceSource = sourceParse.success ? sourceParse.data : 'unknown'
       track('workspace_created', {
         source,
-        from_existing_branch: typeof args.baseBranch === 'string' && args.baseBranch.length > 0
+        from_existing_branch: typeof args.baseBranch === 'string' && args.baseBranch.length > 0,
+        ...getCohortAtEmit()
       })
 
       return result
diff --git a/src/main/persistence.ts b/src/main/persistence.ts
index 8f88719b97b..c8166b85ef9 100644
--- a/src/main/persistence.ts
+++ b/src/main/persistence.ts
@@ -470,6 +470,16 @@ export class Store {
     return this.state.repos.map((repo) => this.hydrateRepo(repo))
   }
 
+  /**
+   * O(1) read of the persisted repo count. Use this when you only need the
+   * count (e.g. cohort-classifier) — `getRepos()` hydrates each repo and
+   * may run a synchronous git subprocess via `getGitUsername()`, which is
+   * wasteful when the caller only reads `.length`.
+   */
+  getRepoCount(): number {
+    return this.state.repos.length
+  }
+
   getRepo(id: string): Repo | undefined {
     const repo = this.state.repos.find((r) => r.id === id)
     return repo ? this.hydrateRepo(repo) : undefined
diff --git a/src/main/telemetry/client.ts b/src/main/telemetry/client.ts
index 03b8effc7f9..c346bd41b5f 100644
--- a/src/main/telemetry/client.ts
+++ b/src/main/telemetry/client.ts
@@ -33,6 +33,7 @@ import { PostHog } from 'posthog-node'
 import type { CommonProps, EventName, EventProps, OptInVia } from '../../shared/telemetry-events'
 import type { Store } from '../persistence'
 import { consumeBurstToken, resetBurstCapsForSession } from './burst-cap'
+import { getCohortAtEmit } from './cohort-classifier'
 import { resolveConsent, type ConsentState } from './consent'
 import { commonPropsSchema, validate } from './validator'
 
@@ -436,7 +437,10 @@ export function trackAppOpenedOnce(): void {
     return
   }
   appOpenedTrackedThisSession = true
-  track('app_opened', {})
+  // Why: `nth_repo_added: 0` on `app_opened` is the canonical session-zero
+  // / pre-repo cohort signal — a user who has launched but never added a
+  // repo. See docs/onboarding-funnel-cohort-addendum.md.
+  track('app_opened', { ...getCohortAtEmit() })
 }
 
 export async function shutdownTelemetry(): Promise<void> {
diff --git a/src/main/telemetry/cohort-classifier.test.ts b/src/main/telemetry/cohort-classifier.test.ts
new file mode 100644
index 00000000000..2d1593cde8e
--- /dev/null
+++ b/src/main/telemetry/cohort-classifier.test.ts
@@ -0,0 +1,101 @@
+// Pins the cohort-classifier contract: synchronous read of
+// `store.getRepoCount()`, fail-soft to `undefined` on any failure mode,
+// at most one warn per session. See docs/onboarding-funnel-cohort-addendum.md.
+
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+import type { Repo } from '../../shared/types'
+import type { Store } from '../persistence'
+import {
+  _resetSessionWarnFlagForTests,
+  _setStoreForTests,
+  getCohortAtEmit,
+  initCohortClassifier
+} from './cohort-classifier'
+
+function makeFakeStore(getRepos: () => Repo[]): Store {
+  // Both reads delegate to the same `getRepos` thunk so existing tests stay
+  // meaningful: a throw or a list change is observed identically through
+  // either accessor.
+  return {
+    getRepos: vi.fn(getRepos),
+    getRepoCount: vi.fn(() => getRepos().length)
+  } as unknown as Store
+}
+
+function makeRepos(n: number): Repo[] {
+  return Array.from({ length: n }, (_, i) => ({ id: `repo-${i}` }) as unknown as Repo)
+}
+
+describe('cohort-classifier', () => {
+  beforeEach(() => {
+    vi.spyOn(console, 'warn').mockImplementation(() => {})
+    _setStoreForTests(null)
+    _resetSessionWarnFlagForTests()
+  })
+  afterEach(() => {
+    vi.restoreAllMocks()
+    _setStoreForTests(null)
+  })
+
+  it('returns the current repo count', () => {
+    initCohortClassifier(makeFakeStore(() => makeRepos(3)))
+    expect(getCohortAtEmit()).toEqual({ nth_repo_added: 3 })
+  })
+
+  // The session-zero / pre-repo cohort signal: a launch with no repos must
+  // emit `0`, not `undefined`. Filtering `nth_repo_added = 0` on
+  // `app_opened` is the canonical way to isolate the pre-repo cohort.
+  it('returns 0 (not undefined) for an empty repo list', () => {
+    initCohortClassifier(makeFakeStore(() => []))
+    expect(getCohortAtEmit()).toEqual({ nth_repo_added: 0 })
+  })
+
+  it('returns undefined when the store is not initialized', () => {
+    expect(getCohortAtEmit()).toEqual({ nth_repo_added: undefined })
+  })
+
+  it('returns undefined and never throws when getRepos throws', () => {
+    initCohortClassifier(
+      makeFakeStore(() => {
+        throw new Error('disk fault')
+      })
+    )
+    expect(() => getCohortAtEmit()).not.toThrow()
+    expect(getCohortAtEmit()).toEqual({ nth_repo_added: undefined })
+  })
+
+  // Why: a degraded boot should not flood stderr; the warn-once flag is the
+  // breadcrumb mechanism for "why is some chunk of last week's data
+  // missing nth_repo_added?" without burning logs on every emit.
+  it('warns at most once per session even across many degraded calls', () => {
+    initCohortClassifier(
+      makeFakeStore(() => {
+        throw new Error('disk fault')
+      })
+    )
+    const warnSpy = console.warn as unknown as ReturnType<typeof vi.spyOn>
+    for (let i = 0; i < 50; i++) {
+      getCohortAtEmit()
+    }
+    expect(warnSpy).toHaveBeenCalledTimes(1)
+  })
+
+  // The session-warn flag resets on initCohortClassifier so a fresh
+  // process gets a fresh breadcrumb budget.
+  it('resets the warn flag when reinitialized', () => {
+    initCohortClassifier(
+      makeFakeStore(() => {
+        throw new Error('first')
+      })
+    )
+    getCohortAtEmit()
+    initCohortClassifier(
+      makeFakeStore(() => {
+        throw new Error('second')
+      })
+    )
+    getCohortAtEmit()
+    const warnSpy = console.warn as unknown as ReturnType<typeof vi.spyOn>
+    expect(warnSpy).toHaveBeenCalledTimes(2)
+  })
+})
diff --git a/src/main/telemetry/cohort-classifier.ts b/src/main/telemetry/cohort-classifier.ts
new file mode 100644
index 00000000000..80c01bff7c6
--- /dev/null
+++ b/src/main/telemetry/cohort-classifier.ts
@@ -0,0 +1,64 @@
+// Single source of truth for cohort state attached to telemetry events.
+// See docs/onboarding-funnel-cohort-addendum.md.
+//
+// `nth_repo_added` is the count of repos the user has at the moment the
+// event fires — read from `store.getRepoCount()`. The rule is single
+// and consistent: the value reflects current store state at emit time.
+// On `repo_added` the read happens *after* `store.addRepo` lands, so the
+// user's Nth repo addition emits `N` (the just-landed write is included).
+// On every other event, the same read returns whatever the count is —
+// including `0` for a brand-new user on `app_opened` who has never added
+// a repo. That `0` is the canonical session-zero / pre-repo cohort signal,
+// not a sentinel and not "undefined."
+//
+// Failure mode: this module never throws. On any read error or
+// store-not-yet-initialized condition, `getCohortAtEmit` returns
+// `{ nth_repo_added: undefined }`. The schemas declare the field
+// `.optional()`, so an event with an undefined cohort still validates and
+// emits — it just lands without the cohort property. This preserves the
+// telemetry rule "must never crash the app."
+
+import type { Store } from '../persistence'
+
+let storeRef: Store | null = null
+
+// Session-scoped flag analogous to `appOpenedTrackedThisSession` in
+// `client.ts`: emit one debug breadcrumb per session if the classifier
+// has to fail soft, so missing cohort data has a corresponding log line
+// without flooding stderr.
+let warnedThisSession = false
+
+export function initCohortClassifier(store: Store): void {
+  storeRef = store
+  warnedThisSession = false
+}
+
+export function getCohortAtEmit(): { nth_repo_added: number | undefined } {
+  if (!storeRef) {
+    warnOnce('store not initialized')
+    return { nth_repo_added: undefined }
+  }
+  try {
+    const length = storeRef.getRepoCount()
+    return { nth_repo_added: length }
+  } catch (err) {
+    warnOnce(err instanceof Error ? err.message : String(err))
+    return { nth_repo_added: undefined }
+  }
+}
+
+function warnOnce(reason: string): void {
+  if (warnedThisSession) {
+    return
+  }
+  warnedThisSession = true
+  console.warn('[telemetry-cohort] classifier returned undefined', { reason })
+}
+
+export function _setStoreForTests(store: Store | null): void {
+  storeRef = store
+}
+
+export function _resetSessionWarnFlagForTests(): void {
+  warnedThisSession = false
+}
diff --git a/src/main/telemetry/validator.test.ts b/src/main/telemetry/validator.test.ts
index d6619448f34..bd0bcf349bd 100644
--- a/src/main/telemetry/validator.test.ts
+++ b/src/main/telemetry/validator.test.ts
@@ -102,6 +102,54 @@ describe('validate', () => {
     expect(result.ok).toBe(false)
   })
 
+  // ── Cohort property (nth_repo_added) ────────────────────────────────
+  // Pin the schema contract from
+  // docs/onboarding-funnel-cohort-addendum.md. The field is optional so a
+  // classifier degraded-mode `undefined` still validates; rejected shapes
+  // (negative, non-integer, string) must drop.
+
+  it('accepts app_opened with nth_repo_added=0 (the session-zero cohort signal)', () => {
+    const result = validate('app_opened', { nth_repo_added: 0 })
+    expect(result.ok).toBe(true)
+  })
+
+  it('accepts repo_added with nth_repo_added=1', () => {
+    const result = validate('repo_added', { method: 'folder_picker', nth_repo_added: 1 })
+    expect(result.ok).toBe(true)
+  })
+
+  it('accepts events without nth_repo_added (classifier degraded mode)', () => {
+    const result = validate('agent_started', {
+      agent_kind: 'claude-code',
+      launch_source: 'command_palette',
+      request_kind: 'new'
+    })
+    expect(result.ok).toBe(true)
+  })
+
+  it('rejects negative nth_repo_added', () => {
+    const result = validate('app_opened', { nth_repo_added: -1 } as never)
+    expect(result.ok).toBe(false)
+  })
+
+  it('rejects non-integer nth_repo_added', () => {
+    const result = validate('app_opened', { nth_repo_added: 1.5 } as never)
+    expect(result.ok).toBe(false)
+  })
+
+  it('rejects nth_repo_added on a non-cohort event (settings_changed)', () => {
+    // The IPC handler relies on this rejection: schemas are `.strict()`,
+    // so injecting `nth_repo_added` on an event whose schema does not
+    // declare it must drop the entire event. The selectivity guard in
+    // `telemetry:track` is what prevents that from happening in practice.
+    const result = validate('settings_changed', {
+      setting_key: 'editorAutoSave',
+      value_kind: 'bool',
+      nth_repo_added: 1
+    } as never)
+    expect(result.ok).toBe(false)
+  })
+
   // Rate-limit: at most one warn per event name per 60s. We cannot easily
   // control Date.now() without mocking time, so the coarse assertion is
   // that repeat-dropping the same event name does not emit a warn on every
diff --git a/src/renderer/src/components/sidebar/AddRepoDialog.tsx b/src/renderer/src/components/sidebar/AddRepoDialog.tsx
index b7ff3fbe95e..6bdd1e63b14 100644
--- a/src/renderer/src/components/sidebar/AddRepoDialog.tsx
+++ b/src/renderer/src/components/sidebar/AddRepoDialog.tsx
@@ -11,6 +11,7 @@ import {
 } from '@/components/ui/dialog'
 import { Button } from '@/components/ui/button'
 import { activateAndRevealWorktree } from '@/lib/worktree-activation'
+import { track } from '@/lib/telemetry'
 import { RemoteStep, CloneStep, useRemoteRepo } from './AddRepoSteps'
 import { CreateStep, useCreateRepo } from './AddRepoCreateStep'
 import { SetupStep } from './AddRepoSetupStep'
@@ -193,6 +194,7 @@ const AddRepoDialog = React.memo(function AddRepoDialog() {
 
   const handleOpenWorktree = useCallback(
     (worktree: Worktree) => {
+      track('add_repo_setup_step_action', { action: 'open_existing' })
       activateAndRevealWorktree(worktree.id)
       closeModal()
     },
@@ -200,6 +202,8 @@ const AddRepoDialog = React.memo(function AddRepoDialog() {
   )
 
   const handleCreateWorktree = useCallback(() => {
+    // Why: Setup-step "Create" affordance — fires on click intent, not on IPC arrival, mirroring the other 4 actions in this dialog.
+    track('add_repo_setup_step_action', { action: 'create_worktree' })
     // Why: small delay so the Add Project dialog close animation finishes before
     // the composer modal takes focus; otherwise the dialog teardown can steal
     // the first focus frame from the composer's prompt textarea.
@@ -210,6 +214,7 @@ const AddRepoDialog = React.memo(function AddRepoDialog() {
   }, [closeModal, openModal, repoId])
 
   const handleConfigureRepo = useCallback(() => {
+    track('add_repo_setup_step_action', { action: 'configure' })
     closeModal()
     openSettingsTarget({ pane: 'repo', repoId })
     openSettingsPage()
@@ -218,11 +223,33 @@ const AddRepoDialog = React.memo(function AddRepoDialog() {
   // Why: handleBack reuses resetState which already aborts clones and resets all fields.
   const handleBack = resetState
 
+  const handleSkip = useCallback(() => {
+    track('add_repo_setup_step_action', { action: 'skip' })
+    closeModal()
+    resetState()
+  }, [closeModal, resetState])
+
+  // Why: only the Setup step's "Add another project" back arrow counts as a
+  // funnel event — the in-flight Back arrows on clone/remote/create are not
+  // a Setup-step affordance. Keeping the emit scoped to this handler avoids
+  // also tagging mid-clone backs.
+  const handleSetupStepBack = useCallback(() => {
+    track('add_repo_setup_step_action', { action: 'back' })
+    handleBack()
+  }, [handleBack])
+
   return (
     <Dialog
       open={isOpen}
       onOpenChange={(open) => {
         if (!open) {
+          // Why: Radix only fires onOpenChange for internal triggers (X icon, ESC,
+          // outside-click), so this branch only runs for implicit closes — explicit
+          // Skip is handled on its own renderer-side click handler. Implicit closes
+          // on the Setup step are funnel-equivalent to Skip.
+          if (step === 'setup') {
+            track('add_repo_setup_step_action', { action: 'skip' })
+          }
           closeModal()
           resetState()
         }
@@ -243,7 +270,7 @@ const AddRepoDialog = React.memo(function AddRepoDialog() {
           {step === 'setup' && (
             <button
               className="absolute left-6 inline-flex items-center gap-1 text-xs text-muted-foreground hover:text-foreground transition-colors cursor-pointer"
-              onClick={handleBack}
+              onClick={handleSetupStepBack}
             >
               <ArrowLeft className="size-3" />
               Add another project
@@ -396,10 +423,7 @@ const AddRepoDialog = React.memo(function AddRepoDialog() {
             onOpenWorktree={handleOpenWorktree}
             onCreateWorktree={handleCreateWorktree}
             onConfigureRepo={handleConfigureRepo}
-            onSkip={() => {
-              closeModal()
-              resetState()
-            }}
+            onSkip={handleSkip}
           />
         )}
       </DialogContent>
diff --git a/src/shared/telemetry-events.test.ts b/src/shared/telemetry-events.test.ts
index 1a6f76a864a..c2285f788c7 100644
--- a/src/shared/telemetry-events.test.ts
+++ b/src/shared/telemetry-events.test.ts
@@ -5,6 +5,7 @@
 
 import { describe, expect, it } from 'vitest'
 import {
+  addRepoSetupStepActionSchema,
   AGENT_KIND_VALUES,
   agentKindSchema,
   commonPropsSchema,
@@ -110,6 +111,69 @@ describe('agent_started schema', () => {
   })
 })
 
+describe('add_repo_setup_step_action schema', () => {
+  it('accepts every Setup-step action declared in the schema', () => {
+    for (const action of addRepoSetupStepActionSchema.options) {
+      const parsed = eventSchemas.add_repo_setup_step_action.safeParse({ action })
+      expect(parsed.success).toBe(true)
+    }
+  })
+
+  it('rejects unknown action enum values', () => {
+    const parsed = eventSchemas.add_repo_setup_step_action.safeParse({
+      action: 'export_to_pdf'
+    })
+    expect(parsed.success).toBe(false)
+  })
+
+  it('rejects extra keys via .strict()', () => {
+    const parsed = eventSchemas.add_repo_setup_step_action.safeParse({
+      action: 'skip',
+      repo_name: 'orca' // raw repo names are UGC — must not cross the wire
+    })
+    expect(parsed.success).toBe(false)
+  })
+})
+
+describe('workspace_create_failed schema', () => {
+  it('accepts a valid payload', () => {
+    const parsed = eventSchemas.workspace_create_failed.safeParse({
+      source: 'sidebar',
+      error_class: 'git_failed'
+    })
+    expect(parsed.success).toBe(true)
+  })
+
+  it('rejects unknown error_class values', () => {
+    const parsed = eventSchemas.workspace_create_failed.safeParse({
+      source: 'sidebar',
+      error_class: 'cosmic_ray'
+    })
+    expect(parsed.success).toBe(false)
+  })
+
+  // Core invariant mirroring agent_error: raw error strings never cross the
+  // wire. If this test ever flips, the failure-rate lane is leaking UGC —
+  // revert the offending schema change.
+  it('rejects error_message via .strict()', () => {
+    const parsed = eventSchemas.workspace_create_failed.safeParse({
+      source: 'sidebar',
+      error_class: 'git_failed',
+      error_message: 'fatal: cannot create work tree at /Users/alice/secret'
+    })
+    expect(parsed.success).toBe(false)
+  })
+
+  it('rejects error_stack via .strict()', () => {
+    const parsed = eventSchemas.workspace_create_failed.safeParse({
+      source: 'sidebar',
+      error_class: 'git_failed',
+      error_stack: 'Error: cannot create work tree\n    at /Users/alice/...'
+    })
+    expect(parsed.success).toBe(false)
+  })
+})
+
 describe('settings_changed schema', () => {
   it('accepts whitelisted setting keys', () => {
     for (const key of SETTINGS_CHANGED_WHITELIST) {
diff --git a/src/shared/telemetry-events.ts b/src/shared/telemetry-events.ts
index 23adcc28b5a..fcfadd7c50a 100644
--- a/src/shared/telemetry-events.ts
+++ b/src/shared/telemetry-events.ts
@@ -73,6 +73,33 @@ export type ErrorClass = z.infer<typeof errorClassSchema>
 export const repoMethodSchema = z.enum(['folder_picker', 'clone_url', 'drag_drop'])
 export type RepoMethod = z.infer<typeof repoMethodSchema>
 
+// Five Setup-step affordances the user can pick after `repo_added` fires (see
+// AddRepoSetupStep). One enum because every value lives on the same screen and
+// the funnel question is "which one did they pick" — adding a sixth value
+// later is additive-safe per the schema-evolution doctrine below.
+export const addRepoSetupStepActionSchema = z.enum([
+  'create_worktree',
+  'configure',
+  'skip',
+  'open_existing',
+  'back'
+])
+export type AddRepoSetupStepAction = z.infer<typeof addRepoSetupStepActionSchema>
+
+// Deliberately a separate enum from `errorClassSchema` (PTY-spawn taxonomy):
+// different domain — this one buckets git/filesystem failures thrown by
+// `createLocalWorktree` / `createRemoteWorktree`. Merging the two would lock
+// both domains to the union forever, which the schema-evolution comment
+// below warns against.
+export const workspaceCreateErrorClassSchema = z.enum([
+  'git_failed',
+  'path_collision',
+  'permission_denied',
+  'base_ref_missing',
+  'unknown'
+])
+export type WorkspaceCreateErrorClass = z.infer<typeof workspaceCreateErrorClassSchema>
+
 export const workspaceSourceSchema = z.enum([
   'command_palette',
   'sidebar',
@@ -145,14 +172,25 @@ export type SettingsChangedKey = z.infer<typeof settingsChangedKeySchema>
 // unknown keys at parse time. This is the runtime counterpart to the
 // compile-time "unions of string literals, no raw `string`" rule.
 
-const emptySchema = z.object({}).strict()
+// Cohort signal — see docs/onboarding-funnel-cohort-addendum.md. One integer
+// shared across the events listed in `COHORT_EXTENDED` below: the count of
+// repos the user has at emit time, read from `store.getRepos().length`.
+// `.int().nonnegative()` constrains malformed values to the floor;
+// `.optional()` lets the classifier's fail-soft fallback (returning
+// `undefined`) validate cleanly so a read error never crashes a track call.
+const nthRepoAddedSchema = z.number().int().nonnegative().optional()
 
-const repoAddedSchema = z.object({ method: repoMethodSchema }).strict()
+const appOpenedSchema = z.object({ nth_repo_added: nthRepoAddedSchema }).strict()
+
+const repoAddedSchema = z
+  .object({ method: repoMethodSchema, nth_repo_added: nthRepoAddedSchema })
+  .strict()
 
 const workspaceCreatedSchema = z
   .object({
     source: workspaceSourceSchema,
-    from_existing_branch: z.boolean()
+    from_existing_branch: z.boolean(),
+    nth_repo_added: nthRepoAddedSchema
   })
   .strict()
 
@@ -160,7 +198,8 @@ const agentStartedSchema = z
   .object({
     agent_kind: agentKindSchema,
     launch_source: launchSourceSchema,
-    request_kind: requestKindSchema
+    request_kind: requestKindSchema,
+    nth_repo_added: nthRepoAddedSchema
   })
   .strict()
 
@@ -172,7 +211,8 @@ const agentStartedSchema = z
 const agentErrorSchema = z
   .object({
     error_class: errorClassSchema,
-    agent_kind: agentKindSchema
+    agent_kind: agentKindSchema,
+    nth_repo_added: nthRepoAddedSchema
   })
   .strict()
 
@@ -186,6 +226,22 @@ const settingsChangedSchema = z
 const telemetryOptedInSchema = z.object({ via: optInViaSchema }).strict()
 const telemetryOptedOutSchema = z.object({ via: optInViaSchema }).strict()
 
+const addRepoSetupStepActionEventSchema = z
+  .object({ action: addRepoSetupStepActionSchema, nth_repo_added: nthRepoAddedSchema })
+  .strict()
+
+// Why: same enum-only discipline as `agent_error` — `.strict()` rejects raw
+// error strings if a future call site tries to attach `error_message` /
+// `error_stack`. The classifier in worktrees.ts reads `error.message` to
+// bucket into the enum, but those strings never cross the wire.
+const workspaceCreateFailedSchema = z
+  .object({
+    source: workspaceSourceSchema,
+    error_class: workspaceCreateErrorClassSchema,
+    nth_repo_added: nthRepoAddedSchema
+  })
+  .strict()
+
 // ── Event registry: the one record the validator consumes ───────────────
 //
 // The validator does `eventSchemas[name].safeParse(props)`. `EventMap` is
@@ -200,10 +256,12 @@ const telemetryOptedOutSchema = z.object({ via: optInViaSchema }).strict()
 // change silently blends pre- and post-change rows under one event name,
 // which cannot be unmixed after the fact.
 export const eventSchemas = {
-  app_opened: emptySchema,
+  app_opened: appOpenedSchema,
 
   repo_added: repoAddedSchema,
+  add_repo_setup_step_action: addRepoSetupStepActionEventSchema,
   workspace_created: workspaceCreatedSchema,
+  workspace_create_failed: workspaceCreateFailedSchema,
 
   agent_started: agentStartedSchema,
   agent_error: agentErrorSchema,
@@ -218,6 +276,29 @@ export type EventMap = { [N in keyof typeof eventSchemas]: z.infer<(typeof event
 export type EventName = keyof EventMap
 export type EventProps<N extends EventName> = EventMap[N]
 
+// Events whose schemas declare `nth_repo_added`. Derived from `eventSchemas`
+// at module load by probing each schema's `.shape` — there is no parallel
+// hand-maintained list to drift out of sync. The IPC `telemetry:track`
+// handler injects the cohort property only when the incoming event name is
+// in this set: the schemas are `.strict()`, so injecting `nth_repo_added`
+// on an event whose schema does not declare it would fail validation and
+// silently drop the entire event.
+//
+// Schema-additions checklist for adding a new cohort-extended event:
+//   add `nth_repo_added: nthRepoAddedSchema` to the event's schema above.
+//   That is the *only* step — this set updates automatically.
+const COHORT_EXTENDED_SET: ReadonlySet<EventName> = new Set(
+  (Object.entries(eventSchemas) as [EventName, z.ZodObject<z.ZodRawShape>][])
+    .filter(([, schema]) => 'nth_repo_added' in schema.shape)
+    .map(([name]) => name)
+)
+export const COHORT_EXTENDED: readonly EventName[] = Array.from(COHORT_EXTENDED_SET)
+export type CohortExtendedEvent = EventName
+
+export function isCohortExtendedEvent(name: EventName): name is CohortExtendedEvent {
+  return COHORT_EXTENDED_SET.has(name)
+}
+
 // Common props attached by the client — declared here so the validator knows
 // which keys to allow on every outgoing event.
 //