diff --git a/apps/desktop/src/main/ipc.ts b/apps/desktop/src/main/ipc.ts
index 3df36b1..52d465c 100644
--- a/apps/desktop/src/main/ipc.ts
+++ b/apps/desktop/src/main/ipc.ts
@@ -244,11 +244,9 @@ function ensurePi(projectDir: string, sessionFile?: string, fresh = false): Prom
   return startup;
 }
 
-async function bindPi(projectDir: string, sessionFile: string): Promise<PiProcess> {
+async function bindPi(projectDir: string, sessionFile: string, mayWrite = true): Promise<PiProcess> {
   const pi = await ensurePi(projectDir, sessionFile);
-  // Everything reached through bindPi may write the session file (rename, fork,
-  // clone, compact), so claim the write before it happens.
-  markBusy(sessionFile, Date.now() + SETTLE_GRACE_MS);
+  if (mayWrite) markBusy(sessionFile, Date.now() + SETTLE_GRACE_MS);
   return pi;
 }
 
@@ -682,6 +680,15 @@ const handlers: HandlerMap = {
     }
   },
 
+  getContextInspector: async ({ projectDir, sessionFile }) => {
+    try {
+      const pi = sessionFile ? await bindPi(projectDir, sessionFile, false) : await ensurePi(projectDir);
+      return { inspector: await pi.getContextInspector() };
+    } catch (err) {
+      return { error: errorMessage(err) };
+    }
+  },
+
   compact: async ({ projectDir, sessionFile }) => {
     try {
       const pi = await bindPi(projectDir, sessionFile);
diff --git a/apps/desktop/src/main/pi/client.ts b/apps/desktop/src/main/pi/client.ts
index bd22ad4..a0d6bfa 100644
--- a/apps/desktop/src/main/pi/client.ts
+++ b/apps/desktop/src/main/pi/client.ts
@@ -2,6 +2,8 @@ import { fileURLToPath } from "node:url";
 import { spawn, type ChildProcessWithoutNullStreams } from "node:child_process";
 import { isTuiFrameType, tuiHostFrameSchema, type TuiClientFrame, type TuiHostFrame } from "../../shared/tui-frames.ts";
 import type { AuthProviderInfo } from "../../shared/rpc-schema.ts";
+import type { ContextInspector } from "../../shared/pi-types.ts";
+import { contextInspectorSchema } from "../../shared/tui-frames.ts";
 import { drainLines, serializeCommand, type PiCommand, type PiMessage } from "./protocol.ts";
 
 /**
@@ -176,6 +178,12 @@ export class PiProcess {
     return this.frameRequest<AuthProviderInfo[]>((requestId) => ({ type: "nativepi_tui_get_providers", requestId }));
   }
 
+  getContextInspector(): Promise<ContextInspector> {
+    return this.frameRequest<unknown>((requestId) => ({ type: "nativepi_tui_get_context_inspector", requestId })).then(
+      (data) => contextInspectorSchema.parse(data),
+    );
+  }
+
   loginProvider(providerId: string, authType: "api_key" | "oauth"): Promise<void> {
     return this.frameRequest<true>(
       (requestId) => ({ type: "nativepi_tui_login", requestId, providerId, authType }),
diff --git a/apps/desktop/src/main/pi/host/entry.ts b/apps/desktop/src/main/pi/host/entry.ts
index f0ce7d0..d04d0f4 100644
--- a/apps/desktop/src/main/pi/host/entry.ts
+++ b/apps/desktop/src/main/pi/host/entry.ts
@@ -4,6 +4,7 @@ import type { ExtensionUIContext } from "@earendil-works/pi-coding-agent";
 import { isTuiFrameType, type TuiClientFrame, type TuiHostFrame } from "../../../shared/tui-frames.ts";
 import { toNotice, toPromptRequest } from "../../../shared/providerAuth.ts";
 import { shapeProviders } from "../../../shared/providerShape.ts";
+import type { ContextInspector } from "../../../shared/pi-types.ts";
 import { hostInternals, withTerminalUi, type HostInternals } from "./uiContext.ts";
 
 /**
@@ -91,6 +92,10 @@ function handleClientFrame(frame: TuiClientFrame): void {
     void respondProviders(frame.requestId);
     return;
   }
+  if (frame.type === "nativepi_tui_get_context_inspector") {
+    void respondContextInspector(frame.requestId);
+    return;
+  }
   if (frame.type === "nativepi_tui_login") {
     void respondLogin(frame.requestId, frame.providerId, frame.authType);
     return;
@@ -102,6 +107,21 @@ function handleClientFrame(frame: TuiClientFrame): void {
   internals?.handle(frame);
 }
 
+async function respondContextInspector(requestId: string): Promise<void> {
+  try {
+    if (!currentSession) throw new Error("No active Pi session");
+    const session = currentSession;
+    const usage = session.getContextUsage();
+    const inspector: ContextInspector = {
+      usedTokens: usage?.tokens ?? null,
+      contextWindow: usage?.contextWindow ?? session.model?.contextWindow ?? 0,
+    };
+    send({ type: "nativepi_tui_reply", requestId, data: inspector });
+  } catch (err) {
+    send({ type: "nativepi_tui_reply", requestId, error: err instanceof Error ? err.message : String(err) });
+  }
+}
+
 async function respondProviders(requestId: string): Promise<void> {
   try {
     const providers = await shapeProviders(await providerRuntime());
diff --git a/apps/desktop/src/renderer/components/Composer.tsx b/apps/desktop/src/renderer/components/Composer.tsx
index 701bba5..b99e76c 100644
--- a/apps/desktop/src/renderer/components/Composer.tsx
+++ b/apps/desktop/src/renderer/components/Composer.tsx
@@ -1,8 +1,8 @@
 import { ArrowBendUpRightIcon, CaretDownIcon, CheckIcon, GitBranchIcon, PaperPlaneRightIcon, PlusIcon, TreeStructureIcon } from "../../shared/icons.ts"
 import { CircleNotchIcon } from "@phosphor-icons/react/CircleNotch";
 import { PaperclipIcon } from "@phosphor-icons/react/Paperclip";
-import { useEffect, useId, useMemo, useRef, useState } from "react";
-import type { AssistantMessage } from "../../shared/pi-types.ts";
+import { useEffect, useMemo, useRef, useState } from "react";
+import type { AssistantMessage, ContextInspector as ContextInspectorData } from "../../shared/pi-types.ts";
 import { draftKeyFor } from "../../shared/messages.ts";
 import { ACCEPTED_IMAGE_TYPES } from "../lib/attachments.ts";
 import { classifyDrop, draggingFiles, mentionPath } from "../lib/drops.ts";
@@ -18,6 +18,7 @@ import { Button } from "@/components/ui/button.tsx";
 import { Input } from "@/components/ui/input.tsx";
 import { Menu, MenuItem, MenuPopup, MenuTrigger } from "@/components/ui/menu.tsx";
 import { Kbd } from "@/components/ui/kbd.tsx";
+import { Dialog, DialogContent, DialogDescription, DialogHeader, DialogTitle } from "@/components/ui/dialog.tsx";
 import { SCROLLBAR_GUTTER_OFFSET, cn } from "@/lib/utils.ts";
 import ComposerAttachments from "./ComposerAttachments.tsx";
 import ComposerInput from "./ComposerInput.tsx";
@@ -625,8 +626,9 @@ function ContextWindow() {
   const entries = useAppStore((s) => activeConversation(s).entries);
   const streaming = useAppStore((s) => activeConversation(s).streaming);
   const model = useAppStore((s) => s.model);
-  const [pinned, setPinned] = useState(false);
-  const panelId = useId();
+  const projectDir = useAppStore((s) => s.activeProjectPath);
+  const sessionFile = useAppStore((s) => s.activeSessionFile);
+  const [open, setOpen] = useState(false);
 
   // Walking the whole transcript backwards on every keystroke in the composer is
   // what this used to do; the answer only changes when the transcript does.
@@ -646,7 +648,13 @@ function ContextWindow() {
   }, [entries, streaming]);
 
   const total = model?.contextWindow ?? 0;
-  const percent = total ? Math.min(100, Math.round((used / total) * 100)) : 0;
+  const inspection = useRequest(
+    async () => (open && projectDir ? await rpc.request.getContextInspector({ projectDir, sessionFile: sessionFile ?? undefined }) : null),
+    [open, projectDir, sessionFile, entries, streaming],
+  );
+  const inspectedUsed = inspection.data?.inspector?.usedTokens ?? used;
+  const inspectedTotal = inspection.data?.inspector?.contextWindow || total;
+  const percent = inspectedTotal ? Math.min(100, Math.round((inspectedUsed / inspectedTotal) * 100)) : 0;
 
   // A ring with nothing behind it is decoration. Until Pi reports a window for
   // this model there is no reading to give, so the control is not interactive —
@@ -668,12 +676,7 @@ function ContextWindow() {
         // The figure lives in the accessible name, so the ring is not a
         // visual-only readout for anyone who can't see it.
         aria-label={`Context window ${percent}% used, ${formatTokens(used)} of ${formatTokens(total)} tokens`}
-        aria-expanded={pinned}
-        aria-controls={panelId}
-        onClick={() => setPinned((current) => !current)}
-        onKeyDown={(event) => {
-          if (event.key === "Escape") setPinned(false);
-        }}
+        onClick={() => setOpen(true)}
         className={cn(
           "flex h-8 items-center gap-1.5 rounded-lg px-1.5 outline-none hover:bg-muted focus-visible:ring-2 focus-visible:ring-ring",
           tone,
@@ -685,37 +688,66 @@ function ContextWindow() {
         </svg>
         {tight ? <span className="text-sm tabular-nums" aria-hidden="true">{percent}%</span> : null}
       </button>
-      {/*
-        Not a live region: this panel is permanently mounted and its numbers
-        change on every token, so role="status" made screen readers narrate
-        token counts continuously. It is not aria-hidden either — the button
-        above claims to expand it, and it holds the only statement anywhere in
-        the app that Pi compacts before the model limit.
-      */}
-      <div
-        id={panelId}
-        className={cn(
-          // Anchored left on a phone, where this control has wrapped into the
-          // middle of the toolbar and a right-anchored 18rem panel would hang
-          // off the side of the screen.
-          "pointer-events-none absolute bottom-full left-0 mb-2 hidden w-72 max-w-[calc(100vw-2rem)] rounded-xl border bg-popover p-4 text-popover-foreground shadow-lg group-hover:block group-focus-within:block sm:left-auto sm:right-0",
-          pinned && "block",
-        )}
-      >
-        <div className="flex items-baseline justify-between gap-4">
-          <p className="text-sm font-semibold">Context window</p>
-          <p className={cn("text-xs tabular-nums", tone)}>
-            {percent}% · {formatTokens(used)}/{formatTokens(total)}
-          </p>
-        </div>
-        <div className="mt-3 h-1.5 overflow-hidden rounded-full bg-muted">
-          <div className={cn("h-full rounded-full bg-current transition-[width]", tone)} style={{ width: `${percent}%` }} />
-        </div>
-        <p className="mt-3 text-xs leading-relaxed text-muted-foreground">
-          Pi automatically compacts the conversation before it reaches the model limit.
-        </p>
-      </div>
+      <ContextInspector
+        open={open}
+        onOpenChange={setOpen}
+        loading={inspection.loading}
+        inspector={inspection.data?.inspector}
+        error={inspection.data?.error ?? inspection.error ?? undefined}
+        used={inspectedUsed}
+        total={inspectedTotal}
+        percent={percent}
+      />
     </div>
   );
 }
 
+function ContextInspector({
+  open,
+  onOpenChange,
+  loading,
+  inspector,
+  error,
+  used,
+  total,
+  percent,
+}: {
+  open: boolean;
+  onOpenChange: (open: boolean) => void;
+  loading: boolean;
+  inspector?: ContextInspectorData;
+  error?: string;
+  used: number;
+  total: number;
+  percent: number;
+}) {
+  return (
+    <Dialog open={open} onOpenChange={onOpenChange}>
+      <DialogContent className="max-w-xl gap-5">
+        <DialogHeader>
+          <DialogTitle className="font-heading text-base font-semibold">Context window</DialogTitle>
+          <DialogDescription className="text-sm text-muted-foreground">
+            Pi’s latest context-window measurement for this conversation.
+          </DialogDescription>
+        </DialogHeader>
+
+        <section aria-label="Context usage">
+          <div className="flex items-baseline justify-between gap-4">
+            <p className="text-sm font-medium">{percent}% used</p>
+            <p className="font-mono text-xs tabular-nums text-muted-foreground">
+              {formatTokens(used)} / {formatTokens(total)} tokens
+            </p>
+          </div>
+          <div className="mt-2 h-2 overflow-hidden rounded-full bg-muted" aria-hidden="true">
+            <div className="h-full rounded-full bg-foreground transition-[width]" style={{ width: `${percent}%` }} />
+          </div>
+        </section>
+
+        {loading ? <p className="text-sm text-muted-foreground">Reading the active Pi session…</p> : null}
+        {error ? <p className="text-sm text-destructive">Could not inspect this context: {error}</p> : null}
+        {inspector?.usedTokens === null ? <p className="text-sm text-muted-foreground">Pi has not received a context measurement from this model yet.</p> : null}
+      </DialogContent>
+    </Dialog>
+  );
+}
+
diff --git a/apps/desktop/src/shared/pi-types.ts b/apps/desktop/src/shared/pi-types.ts
index e01d3dd..8edf83c 100644
--- a/apps/desktop/src/shared/pi-types.ts
+++ b/apps/desktop/src/shared/pi-types.ts
@@ -166,6 +166,12 @@ export interface SessionStats {
   cost: number;
 }
 
+/** Pi's latest read-only context-window measurement. */
+export interface ContextInspector {
+  usedTokens: number | null;
+  contextWindow: number;
+}
+
 export interface SessionSummary {
   path: string;
   id: string;
diff --git a/apps/desktop/src/shared/rpc-schema.ts b/apps/desktop/src/shared/rpc-schema.ts
index 7c46001..57f3464 100644
--- a/apps/desktop/src/shared/rpc-schema.ts
+++ b/apps/desktop/src/shared/rpc-schema.ts
@@ -16,6 +16,7 @@ import type {
   ResolvedExtension,
   RpcSessionState,
   SessionStats,
+  ContextInspector,
   SessionSearchResult,
   SessionSummary,
   SessionTreeNode,
@@ -365,6 +366,10 @@ export type HostRequests = {
     params: { projectDir: string; sessionFile: string };
     response: { stats?: SessionStats; error?: string };
   };
+  getContextInspector: {
+    params: { projectDir: string; sessionFile?: string };
+    response: { inspector?: ContextInspector; error?: string };
+  };
   compact: {
     params: { projectDir: string; sessionFile: string };
     response: { ok: boolean; error?: string };
diff --git a/apps/desktop/src/shared/tui-frames.test.ts b/apps/desktop/src/shared/tui-frames.test.ts
index f9f88ff..6e6b247 100644
--- a/apps/desktop/src/shared/tui-frames.test.ts
+++ b/apps/desktop/src/shared/tui-frames.test.ts
@@ -1,5 +1,5 @@
 import { expect, test } from "bun:test";
-import { isTuiFrameType, tuiClientFrameSchema, tuiHostFrameSchema } from "./tui-frames.ts";
+import { contextInspectorSchema, isTuiFrameType, tuiClientFrameSchema, tuiHostFrameSchema } from "./tui-frames.ts";
 
 /**
  * What keeps the side channel and Pi's protocol apart, and what keeps extension
@@ -51,3 +51,13 @@ test("a resize from the window is bounded", () => {
     tuiClientFrameSchema.safeParse({ type: "nativepi_tui_resize", surfaceId: "s1", cols: 0, rows: 24 }).success,
   ).toBe(false);
 });
+
+test("the context inspector accepts only a non-negative Pi measurement", () => {
+  const inspector = {
+    usedTokens: 42,
+    contextWindow: 200_000,
+  };
+
+  expect(contextInspectorSchema.safeParse(inspector).success).toBe(true);
+  expect(contextInspectorSchema.safeParse({ ...inspector, usedTokens: -1 }).success).toBe(false);
+});
diff --git a/apps/desktop/src/shared/tui-frames.ts b/apps/desktop/src/shared/tui-frames.ts
index 55ef623..3b32e23 100644
--- a/apps/desktop/src/shared/tui-frames.ts
+++ b/apps/desktop/src/shared/tui-frames.ts
@@ -1,4 +1,5 @@
 import { z } from "zod";
+import type { ContextInspector } from "./pi-types.ts";
 
 const authPromptSchema = z.discriminatedUnion("kind", [
   z.object({ kind: z.literal("text"), message: z.string(), placeholder: z.string().optional() }),
@@ -104,6 +105,11 @@ const completionItemSchema = z.object({
   description: z.string().max(500).optional(),
 });
 
+export const contextInspectorSchema = z.object({
+  usedTokens: z.number().int().nonnegative().nullable(),
+  contextWindow: z.number().int().nonnegative(),
+}) satisfies z.ZodType<ContextInspector>;
+
 export type TuiCompletionItem = z.infer<typeof completionItemSchema>;
 
 /** An extension autocomplete provider's answer, as `AutocompleteSuggestions`. */
@@ -206,6 +212,7 @@ export const tuiClientFrameSchema = z.discriminatedUnion("type", [
    * extensions need this round trip to reach the picker and Settings.
    */
   z.object({ type: z.literal("nativepi_tui_get_providers"), requestId: z.string().min(1).max(64) }),
+  z.object({ type: z.literal("nativepi_tui_get_context_inspector"), requestId: z.string().min(1).max(64) }),
   z.object({
     type: z.literal("nativepi_tui_login"),
     requestId: z.string().min(1).max(64),