feat: add session activity minimap with click-to-navigate (#248)

## Summary

- Add a togglable horizontal bar chart to the session detail view
showing message activity intensity over time intervals
- Clicking a bar scrolls the message list to that point in the session
- New `GET /api/v1/sessions/{id}/activity` endpoint with adaptive
time-bucketed message counts (SQLite and PostgreSQL)
- Remove unused `/minimap` endpoint and all supporting code
- Fix pre-existing breadcrumb flicker on SSE session refresh
- Fix pre-existing model badge flicker during session reload

<img width="1099" height="106" alt="image"
src="https://github.com/user-attachments/assets/1f66c6a9-357c-4b13-b3da-31cfebe842ca"
/>

## Details

**Backend:**
- Adaptive interval sizing targets ~30 buckets per session (1m intervals
for short sessions, scales dynamically for long ones, capped at 50
buckets)
- Sub-second timestamp precision via `julianday()` (SQLite) and
`floor(EXTRACT(EPOCH ...))` (PostgreSQL)
- System and prefix-detected injected messages excluded via
`SystemPrefixSQL`
- Malformed timestamps silently excluded from bucketing

**Frontend:**
- `ActivityMinimap.svelte` custom SVG bar chart with tooltips,
keyboard/ARIA accessibility, error/retry states
- Session activity store with load versioning and cache invalidation to
prevent stale cross-session data
- Toggle button in session breadcrumb with localStorage persistence
- Scroll-synced active bucket indicator via `firstVisibleTimestamp`
published from `MessageList` (excludes overscanned rows)
- Single-color bars showing total message count per interval; tooltip
shows user/assistant breakdown

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: wesm

.gitignore

@@ -47,3 +47,4 @@ sessions/
 html/
 .superset/
 .github/hooks/
+.superpowers/

frontend/e2e/activity-minimap.spec.ts

@@ -0,0 +1,126 @@
+import { test, expect } from "@playwright/test";
+import { SessionsPage } from "./pages/sessions-page";
+
+test.describe("Activity Minimap", () => {
+  let sp: SessionsPage;
+
+  test.beforeEach(async ({ page }) => {
+    sp = new SessionsPage(page);
+    await sp.goto();
+    await sp.selectSession(0);
+  });
+
+  test("minimap is hidden by default", async ({
+    page,
+  }) => {
+    await expect(
+      page.locator(".activity-minimap"),
+    ).not.toBeVisible();
+  });
+
+  test("toggle button shows and hides minimap", async ({
+    page,
+  }) => {
+    await page.locator(".minimap-btn").click();
+    await expect(
+      page.locator(".activity-minimap"),
+    ).toBeVisible();
+
+    await page.locator(".minimap-btn").click();
+    await expect(
+      page.locator(".activity-minimap"),
+    ).not.toBeVisible();
+  });
+
+  test("minimap shows bars for sessions with timestamps", async ({
+    page,
+  }) => {
+    await page.locator(".minimap-btn").click();
+
+    await expect(
+      page.locator(".minimap-status"),
+    ).not.toBeVisible({ timeout: 3000 });
+
+    const bars = page.locator(".minimap-bar");
+    const count = await bars.count();
+    expect(count).toBeGreaterThan(0);
+  });
+
+  test("clicking a bar scrolls the message list", async ({
+    page,
+  }) => {
+    await page.locator(".minimap-btn").click();
+
+    const clickableBars = page.locator(
+      "g.minimap-bar[role='button']",
+    );
+    await clickableBars.first().waitFor({ timeout: 3000 });
+
+    const barCount = await clickableBars.count();
+    expect(barCount).toBeGreaterThan(0);
+
+    const scrollBefore = await sp.scroller.evaluate(
+      (el) => el.scrollTop,
+    );
+
+    const lastBar = clickableBars.nth(barCount - 1);
+    await lastBar.click();
+
+    if (barCount > 1) {
+      await expect
+        .poll(
+          () =>
+            sp.scroller.evaluate((el) => el.scrollTop),
+          { timeout: 3000 },
+        )
+        .not.toBe(scrollBefore);
+    }
+  });
+
+  test("active indicator moves after reopen without scroll", async ({
+    page,
+  }) => {
+    // Open minimap, wait for multiple bars.
+    await page.locator(".minimap-btn").click();
+    const bars = page.locator("g.minimap-bar[role='button']");
+    await bars.first().waitFor({ timeout: 3000 });
+
+    const barCount = await bars.count();
+    if (barCount < 2) {
+      // Can't test indicator movement with < 2 bars.
+      return;
+    }
+
+    // Record the x position of the active indicator.
+    const indicator = page.locator(".bar-indicator");
+    await expect(indicator).toBeVisible();
+    const xBefore = await indicator.evaluate(
+      (el) => el.getAttribute("x"),
+    );
+
+    // Close minimap, scroll to the bottom.
+    await page.locator(".minimap-btn").click();
+    await expect(
+      page.locator(".activity-minimap"),
+    ).not.toBeVisible();
+
+    await sp.scroller.evaluate((el) => {
+      el.scrollTop = el.scrollHeight;
+    });
+
+    // Reopen — indicator should appear at a different
+    // position reflecting the new scroll location.
+    await page.locator(".minimap-btn").click();
+    await expect(indicator).toBeVisible({ timeout: 3000 });
+
+    await expect
+      .poll(
+        () =>
+          indicator.evaluate(
+            (el) => el.getAttribute("x"),
+          ),
+        { timeout: 3000 },
+      )
+      .not.toBe(xBefore);
+  });
+});

frontend/src/App.svelte

@@ -6,6 +6,8 @@
   import StatusBar from "./lib/components/layout/StatusBar.svelte";
   import SessionList from "./lib/components/sidebar/SessionList.svelte";
   import MessageList from "./lib/components/content/MessageList.svelte";
+  import ActivityMinimap from "./lib/components/content/ActivityMinimap.svelte";
+  import { sessionActivity } from "./lib/stores/sessionActivity.svelte.js";
   import CommandPalette from "./lib/components/command-palette/CommandPalette.svelte";
   import AboutModal from "./lib/components/modals/AboutModal.svelte";
   import ShortcutsModal from "./lib/components/modals/ShortcutsModal.svelte";
@@ -84,9 +86,15 @@
           messages.reload();
           sessions.refreshActiveSession();
           sessions.loadChildSessions(id);
+          if (ui.activityMinimapOpen) {
+            sessionActivity.reload(id);
+          } else {
+            sessionActivity.invalidate();
+          }
         });
         pins.loadForSession(id);
       } else {
+        sessionActivity.clear();
         messages.clear();
         sessions.childSessions = new Map();
         sync.unwatchSession();
@@ -380,6 +388,11 @@
           session={session}
           onBack={() => sessions.deselectSession()}
         />
+        {#if ui.activityMinimapOpen && sessions.activeSessionId}
+          <ActivityMinimap
+            sessionId={sessions.activeSessionId}
+          />
+        {/if}
         <MessageList bind:this={messageListRef} />
       {:else}
         <AnalyticsPage />

frontend/src/lib/api/client.ts

@@ -2,7 +2,6 @@ import type {
   SessionPage,
   Session,
   MessagesResponse,
-  MinimapResponse,
   SearchResponse,
   ProjectsResponse,
   MachinesResponse,
@@ -34,6 +33,7 @@ import type {
   PinsResponse,
   TrashResponse,
 } from "./types.js";
+import type { SessionActivityResponse } from "./types/session-activity.js";
 
 const SERVER_URL_KEY = "agentsview-server-url";
 const AUTH_TOKEN_KEY = "agentsview-auth-token";
@@ -171,6 +171,14 @@ export function getChildSessions(
   return fetchJSON(`/sessions/${id}/children`, init);
 }
 
+export function getSessionActivity(
+  sessionId: string,
+): Promise<SessionActivityResponse> {
+  return fetchJSON(
+    `/sessions/${sessionId}/activity`,
+  );
+}
+
 /* Messages */
 
 export interface GetMessagesParams {
@@ -190,20 +198,6 @@ export function getMessages(
   );
 }
 
-export interface GetMinimapParams {
-  from?: number;
-  max?: number;
-}
-
-export function getMinimap(
-  sessionId: string,
-  params: GetMinimapParams = {},
-): Promise<MinimapResponse> {
-  return fetchJSON(
-    `/sessions/${sessionId}/minimap${buildQuery({ ...params })}`,
-  );
-}
-
 /* Search */
 
 export function search(

frontend/src/lib/api/types/core.ts

@@ -72,12 +72,6 @@ export interface Message {
   is_system: boolean;
 }
 
-/** Matches Go MinimapEntry struct */
-export type MinimapEntry = Pick<
-  Message,
-  "ordinal" | "role" | "content_length" | "has_thinking" | "has_tool_use"
->;
-
 /** Matches Go SearchResult struct in internal/db/search.go */
 export interface SearchResult {
   session_id: string;
@@ -104,11 +98,6 @@ export interface MessagesResponse {
   count: number;
 }
 
-export interface MinimapResponse {
-  entries: MinimapEntry[];
-  count: number;
-}
-
 export interface SearchResponse {
   query: string;
   results: SearchResult[];

frontend/src/lib/api/types/index.ts

@@ -3,3 +3,4 @@ export type * from "./sync.js";
 export type * from "./analytics.js";
 export type * from "./github.js";
 export type * from "./insights.js";
+export type * from "./session-activity.js";

frontend/src/lib/api/types/session-activity.ts

@@ -0,0 +1,13 @@
+export interface SessionActivityBucket {
+  start_time: string;
+  end_time: string;
+  user_count: number;
+  assistant_count: number;
+  first_ordinal: number | null;
+}
+
+export interface SessionActivityResponse {
+  buckets: SessionActivityBucket[];
+  interval_seconds: number;
+  total_messages: number;
+}