diff --git a/packages/pi/src/effort-history.ts b/packages/pi/src/effort-history.ts
index 5fe70775..c8cbfb1b 100644
--- a/packages/pi/src/effort-history.ts
+++ b/packages/pi/src/effort-history.ts
@@ -88,3 +88,69 @@ export function collectPiEffortHistory(
 
   return transitions
 }
+
+type SessionEntryWithParent = SessionEntryLike & {
+  id: string
+  parentId?: string | null
+  firstKeptEntryId?: unknown
+}
+
+type SessionManagerLeaf = {
+  getLeafId?: () => string | null
+  [key: string]: unknown
+}
+
+export function resolveSessionLeafId(
+  sessionManager: SessionManagerLeaf,
+): string | null | undefined {
+  return sessionManager.getLeafId?.()
+}
+
+/**
+ * Compaction-aware active entry list, mirroring the host SDK's
+ * buildContextEntries: latest compaction plus kept entries replace the
+ * summarized prefix. Implemented locally because some Pi-compatible hosts
+ * (oh-my-pi) lack the SDK method while sharing the entry model.
+ *
+ * `undefined` means the leaf is unknown and selects the latest entry; `null`
+ * means an explicit no-leaf state and returns an empty list; a string selects
+ * that leaf. Callers must preserve the distinction and not coalesce an absent
+ * leaf method into `null`.
+ */
+export function buildContextEntries(
+  entries: readonly SessionEntryWithParent[],
+  leafId?: string | null,
+): SessionEntryWithParent[] {
+  const byId = new Map(entries.map((entry) => [entry.id, entry]))
+  let leaf: SessionEntryWithParent | undefined
+  if (leafId === null) return []
+  if (leafId) leaf = byId.get(leafId)
+  leaf ??= entries.at(-1)
+  if (!leaf) return []
+  const path: SessionEntryWithParent[] = []
+  let current: SessionEntryWithParent | undefined = leaf
+  while (current) {
+    path.push(current)
+    current = current.parentId ? byId.get(current.parentId) : undefined
+  }
+  path.reverse()
+
+  let compaction: SessionEntryWithParent | undefined
+  for (const entry of path) {
+    if (entry.type === 'compaction') compaction = entry
+  }
+  if (!compaction) return path
+
+  const compactionIndex = path.findIndex((entry) => entry.id === compaction.id)
+  if (compactionIndex < 0) return path
+  const contextEntries: SessionEntryWithParent[] = [compaction]
+  let foundFirstKept = false
+  for (let index = 0; index < compactionIndex; index++) {
+    const entry = path[index]
+    if (!entry) continue
+    if (entry.id === compaction.firstKeptEntryId) foundFirstKept = true
+    if (foundFirstKept) contextEntries.push(entry)
+  }
+  contextEntries.push(...path.slice(compactionIndex + 1))
+  return contextEntries
+}
diff --git a/packages/pi/src/index.ts b/packages/pi/src/index.ts
index 669a2640..d137b85b 100644
--- a/packages/pi/src/index.ts
+++ b/packages/pi/src/index.ts
@@ -17,7 +17,11 @@ import type {
 import type { ExtensionAPI } from '@earendil-works/pi-coding-agent'
 
 import { registerCommands } from './commands.ts'
-import { collectPiEffortHistory } from './effort-history.ts'
+import {
+  buildContextEntries,
+  collectPiEffortHistory,
+  resolveSessionLeafId,
+} from './effort-history.ts'
 import { streamCortexKitAnthropic } from './stream.ts'
 
 async function loginAnthropic(
@@ -72,7 +76,10 @@ export default function cortexKitPiAnthropicAuth(pi: ExtensionAPI) {
     const sessionId = ctx.sessionManager.getSessionId()
     if (!sessionId) return
     const transitions = collectPiEffortHistory(
-      ctx.sessionManager.buildContextEntries(),
+      buildContextEntries(
+        ctx.sessionManager.getEntries(),
+        resolveSessionLeafId(ctx.sessionManager),
+      ),
       ctx.sessionManager.getBranch(),
     )
     effortHistoryBySession.delete(sessionId)
diff --git a/packages/pi/src/tests/effort-history.test.ts b/packages/pi/src/tests/effort-history.test.ts
index 236bdc21..63fc3b95 100644
--- a/packages/pi/src/tests/effort-history.test.ts
+++ b/packages/pi/src/tests/effort-history.test.ts
@@ -1,5 +1,9 @@
 import { describe, expect, test } from 'bun:test'
-import { collectPiEffortHistory } from '../effort-history.ts'
+import {
+  buildContextEntries,
+  collectPiEffortHistory,
+  resolveSessionLeafId,
+} from '../effort-history.ts'
 
 const entry = (
   id: string,
@@ -52,3 +56,103 @@ describe('Pi Fable 5.1 effort history', () => {
     ])
   })
 })
+
+describe('buildContextEntries', () => {
+  const contextEntry = (
+    id: string,
+    parentId: string | null,
+    type = 'message',
+    extra: Record<string, unknown> = {},
+  ) => ({ id, parentId, type, ...extra })
+
+  test('uses the latest entry when the host has no leaf method', () => {
+    const entries = [contextEntry('a', null), contextEntry('b', 'a')]
+    expect(
+      buildContextEntries(entries, undefined).map((entry) => entry.id),
+    ).toEqual(['a', 'b'])
+  })
+
+  test('preserves an absent host leaf method as undefined', () => {
+    const host = { getEntries: () => [] }
+    expect(resolveSessionLeafId(host)).toBeUndefined()
+    expect(
+      buildContextEntries(
+        [contextEntry('a', null), contextEntry('b', 'a')],
+        resolveSessionLeafId(host),
+      ).map((entry) => entry.id),
+    ).toEqual(['a', 'b'])
+  })
+
+  test('preserves an explicit null host leaf', () => {
+    const host = { getLeafId: () => null }
+    expect(resolveSessionLeafId(host)).toBeNull()
+  })
+
+  test('returns no entries for an explicit null leaf', () => {
+    const entries = [contextEntry('a', null)]
+    expect(buildContextEntries(entries, null)).toEqual([])
+  })
+
+  test('follows a leaf path from the root', () => {
+    const entries = [
+      contextEntry('a', null),
+      contextEntry('b', 'a'),
+      contextEntry('c', 'b'),
+      contextEntry('other', 'a'),
+    ]
+    expect(buildContextEntries(entries, 'c').map((entry) => entry.id)).toEqual([
+      'a',
+      'b',
+      'c',
+    ])
+  })
+
+  test('keeps a compaction and entries starting at firstKeptEntryId', () => {
+    const entries = [
+      contextEntry('a', null),
+      contextEntry('kept', 'a'),
+      contextEntry('drop', 'kept'),
+      contextEntry('compact', 'drop', 'compaction', {
+        firstKeptEntryId: 'kept',
+      }),
+      contextEntry('after', 'compact'),
+    ]
+    expect(
+      buildContextEntries(entries, 'after').map((entry) => entry.id),
+    ).toEqual(['compact', 'kept', 'drop', 'after'])
+  })
+
+  test('returns the full path when there is no compaction', () => {
+    const entries = [contextEntry('a', null), contextEntry('b', 'a')]
+    expect(buildContextEntries(entries, 'b').map((entry) => entry.id)).toEqual([
+      'a',
+      'b',
+    ])
+  })
+
+  test('uses only the latest compaction on the path', () => {
+    const entries = [
+      contextEntry('a', null),
+      contextEntry('kept1', 'a'),
+      contextEntry('compact1', 'kept1', 'compaction', {
+        firstKeptEntryId: 'kept1',
+      }),
+      contextEntry('kept2', 'compact1'),
+      contextEntry('compact2', 'kept2', 'compaction', {
+        firstKeptEntryId: 'kept2',
+      }),
+      contextEntry('after', 'compact2'),
+    ]
+    expect(
+      buildContextEntries(entries, 'after').map((entry) => entry.id),
+    ).toEqual(['compact2', 'kept2', 'after'])
+  })
+
+  test('passes branch summaries through unchanged', () => {
+    const summary = contextEntry('summary', 'a', 'branch_summary', {
+      summary: 'branch',
+    })
+    const entries = [contextEntry('a', null), summary]
+    expect(buildContextEntries(entries, 'summary')).toEqual(entries)
+  })
+})