test(diff): automate DiffView/CodeBlock horizontal-scroll coverage (closes #21) (#101)

Turns the manual QA ask ("verify DiffView + CodeBlock horizontal-scroll
on-device with a populated diff") into two automated layers:

1. Unit (deterministic, runs in `npm test` now): extracted the shared
   ScrollView props into src/lib/scroll-config.ts (WIDE_CONTENT_SCROLL_CONFIG)
   so DiffView.tsx and CodeBlock.tsx spread the SAME plain object their tests
   assert on — no react-native-renderer needed. Added a source-scan
   regression test (wide-content-scroll.regression.test.ts) that fails if
   either component loses its ScrollView wiring or reintroduces
   numberOfLines truncation.

2. E2E (Maestro): .maestro/flows/diff-scroll.yaml opens a session with a
   pre-seeded wide edit-diff tool call and a wide fenced code block, then
   swipes each horizontal ScrollView left and asserts the off-screen marker
   text becomes visible. mock-opencode-server.ts gained a --seed-diff mode
   that serves this session via GET /session/:id/message (pre-existing
   history), not SSE — issue #90 (a separate SSE-render bug) is being fixed
   independently, and this flow must not depend on it landing first. Wired
   the new flow + port 4100 into run-e2e-flows.sh and activation-e2e.yml.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

.github/workflows/activation-e2e.yml

@@ -120,12 +120,15 @@ jobs:
           # different directories, for all-sessions.yaml). 4099 is a fresh normal-mode
           # instance shared by directory-picker.yaml and variant-picker.yaml (its fake
           # file tree / provider variants / project list don't affect each other).
+          # 4100 is normal mode + --seed-diff (one session with a pre-existing wide
+          # edit-diff tool call + wide code block, for diff-scroll.yaml / issue #21).
           # All bind 0.0.0.0 so the emulator can reach them via 10.0.2.2.
           nohup node tests/fixtures/mock-opencode-server.ts --port 4096 > /tmp/mock-4096.log 2>&1 &
           nohup node tests/fixtures/mock-opencode-server.ts --port 4097 --fail-auth > /tmp/mock-4097.log 2>&1 &
           nohup node tests/fixtures/mock-opencode-server.ts --port 4098 --seed-sessions > /tmp/mock-4098.log 2>&1 &
           nohup node tests/fixtures/mock-opencode-server.ts --port 4099 > /tmp/mock-4099.log 2>&1 &
-          for port in 4096 4097 4098 4099; do
+          nohup node tests/fixtures/mock-opencode-server.ts --port 4100 --seed-diff > /tmp/mock-4100.log 2>&1 &
+          for port in 4096 4097 4098 4099 4100; do
             for i in $(seq 1 30); do
               if curl -sf --connect-timeout 1 -m 3 "http://127.0.0.1:${port}/global/health" > /dev/null 2>&1; then
                 echo "mock server on ${port} responded (may be 401, that's expected on 4097)"
@@ -167,6 +170,7 @@ jobs:
           echo "--- 4097 (fail-auth) ---"; cat /tmp/mock-4097.log || true
           echo "--- 4098 (seed-sessions) ---"; cat /tmp/mock-4098.log || true
           echo "--- 4099 (normal, directory-picker + variant-picker) ---"; cat /tmp/mock-4099.log || true
+          echo "--- 4100 (seed-diff) ---"; cat /tmp/mock-4100.log || true
 
       - name: Upload screenshots
         if: always()

.maestro/flows/diff-scroll.yaml

@@ -0,0 +1,119 @@
+appId: cc.agentlabs.opencode
+name: "DiffView + CodeBlock horizontal scroll - wide diff/code line reachable by swipe (closes #21)"
+---
+# GitHub issue #21 ("QA: verify DiffView + CodeBlock horizontal-scroll
+# on-device with a populated diff"). Two rendering fixes shipped earlier were
+# code-audited but never verified with real, wide content on a real
+# (emulated) device:
+#   - src/components/chat/DiffView.tsx: diff lines render inside a horizontal
+#     ScrollView (previously truncated with numberOfLines={1}).
+#   - src/components/markdown/CodeBlock.tsx: code renders inside a horizontal
+#     ScrollView (previously long lines wrapped/mangled).
+#
+# The CI job starts `node tests/fixtures/mock-opencode-server.ts --port 4100
+# --seed-diff` on the runner host BEFORE this flow runs. --seed-diff
+# pre-populates ONE session (id "seed-diff", directory /mock/project — the
+# default connection's directory) whose single assistant message already
+# contains:
+#   - a completed `edit` tool part with a wide "add" diff line (renders via
+#     ToolCallCard -> EditDetail -> DiffView once the card is expanded)
+#   - a text part with a wide fenced code block (renders via Markdown ->
+#     CodeBlock)
+# Both wide lines are ~220 filler characters (no spaces, so they can't
+# word-wrap) followed by a distinct marker token. This is loaded via GET
+# /session/seed-diff/message when the session is opened (selectSession),
+# NOT delivered over SSE — issue #90 (a separate SSE-render bug) is being
+# fixed independently, and this flow must not depend on it landing first.
+#
+# Caveat for whoever debugs a flake here: assertVisible/assertNotVisible on
+# a substring deep inside ONE very wide, unwrapped Text node is coarser than
+# it looks — Maestro (like most accessibility-tree-based mobile test
+# frameworks) determines visibility per ELEMENT, not per glyph, and there are
+# open Maestro issues about partially-visible elements being reported as
+# fully visible (mobile-dev-inc/maestro #1275, #2411). The filler is made
+# very wide (~220 chars, comfortably wider than any emulator screen at this
+# monospace font size) specifically to keep the marker's actual rendered
+# position off past the right edge at rest. Screenshots are taken at every
+# step so a flake here can be diagnosed visually, not just from the
+# assertion's pass/fail.
+
+- launchApp:
+    clearState: true
+- assertVisible:
+    id: "telemetry-consent-card"
+- tapOn:
+    id: "telemetry-decline-button"
+
+- assertVisible:
+    text: "No Connection"
+- tapOn:
+    id: "add-connection-button"
+- tapOn:
+    id: "connect-ip-input"
+- inputText: "127.0.0.1:4100"
+- hideKeyboard
+- tapOn:
+    id: "connect-submit-button"
+
+# 40s margin: see activation-positive.yaml — the connect handshake's own
+# fetches are individually capped at 30s (src/lib/sdk.ts REQUEST_TIMEOUT_MS).
+- extendedWaitUntil:
+    visible:
+      id: "connection-status-dot"
+    timeout: 40000
+- takeScreenshot: diffscroll-S1_connected
+
+# The seeded session must appear on the home tab's own-directory list (no
+# SSE, no roots=true — this is the plain GET /session directory-scoped path).
+- extendedWaitUntil:
+    visible:
+      text: "Wide Diff Session"
+    timeout: 15000
+- tapOn:
+    id: "session-item-seed-diff"
+- extendedWaitUntil:
+    visible:
+      id: "chat-message-input"
+    timeout: 15000
+
+# History loaded via GET /session/seed-diff/message (not SSE) must already
+# render both the tool card and the markdown code block.
+- assertVisible:
+    text: "Edit wide_diff_target.ts"
+- assertVisible:
+    text: "Here is a wide code sample"
+- takeScreenshot: diffscroll-S2_history_loaded
+
+# --- CodeBlock: the wide fenced code block is already expanded (no tap
+# needed — Markdown renders it immediately, unlike the collapsible tool card).
+- assertVisible:
+    id: "code-block-scroll"
+- assertNotVisible:
+    text: "ZZZ_CODE_SCROLL_TARGET_ZZZ"
+- takeScreenshot: diffscroll-S3_codeblock_marker_offscreen
+- swipe:
+    from:
+      id: "code-block-scroll"
+    direction: LEFT
+- assertVisible:
+    text: "ZZZ_CODE_SCROLL_TARGET_ZZZ"
+- takeScreenshot: diffscroll-S4_codeblock_marker_revealed
+
+# --- DiffView: lives inside the collapsible tool card's detail section, so
+# expand it first.
+- tapOn:
+    text: "Edit wide_diff_target.ts"
+- assertVisible:
+    text: "src/wide_diff_target.ts"
+- assertVisible:
+    id: "diff-view-scroll"
+- assertNotVisible:
+    text: "ZZZ_DIFF_SCROLL_TARGET_ZZZ"
+- takeScreenshot: diffscroll-S5_diffview_marker_offscreen
+- swipe:
+    from:
+      id: "diff-view-scroll"
+    direction: LEFT
+- assertVisible:
+    text: "ZZZ_DIFF_SCROLL_TARGET_ZZZ"
+- takeScreenshot: diffscroll-S6_diffview_marker_revealed

scripts/run-e2e-flows.sh

@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 #
 # Runs the Maestro activation E2E flows against the mock opencode servers the
-# workflow started on the host (ports 4096-4099). Invoked as a single line from
+# workflow started on the host (ports 4096-4100). Invoked as a single line from
 # activation-e2e.yml's emulator-runner `script:` so cd/trap/loop actually work.
 #
 # Networking: `adb reverse` maps each mock port so the emulator's own
@@ -11,14 +11,14 @@ set -uo pipefail
 
 ROOT="$(pwd)"                       # capture BEFORE any cd, so diag paths are absolute
 APK="android/app/build/outputs/apk/release/app-release.apk"
-FLOWS=(activation-positive activation-negative-401 directory-picker all-sessions variant-picker)
+FLOWS=(activation-positive activation-negative-401 directory-picker all-sessions variant-picker diff-scroll)
 mkdir -p "$ROOT/artifacts/screenshots" "$ROOT/artifacts/diag"
 
 echo "== installing APK =="
 adb install "$APK"
 
 echo "== forwarding mock ports into the emulator (adb reverse) =="
-for p in 4096 4097 4098 4099; do adb reverse "tcp:$p" "tcp:$p"; done
+for p in 4096 4097 4098 4099 4100; do adb reverse "tcp:$p" "tcp:$p"; done
 adb reverse --list
 
 # Decisive probe: can the EMULATOR actually reach the host mock via 127.0.0.1?

src/components/chat/DiffView.tsx

@@ -1,4 +1,5 @@
 import { View, Text, StyleSheet, Platform, ScrollView } from "react-native"
+import { WIDE_CONTENT_SCROLL_CONFIG } from "../../lib/scroll-config"
 
 const mono = Platform.OS === "ios" ? "Menlo" : "monospace"
 
@@ -76,7 +77,7 @@ export function DiffView({ before, after, isDark }: Props) {
 
   return (
     <View style={[s.container, isDark && s.containerDark]}>
-      <ScrollView horizontal showsHorizontalScrollIndicator>
+      <ScrollView {...WIDE_CONTENT_SCROLL_CONFIG} testID="diff-view-scroll">
         <View>
           {lines.map((line, idx) => (
             <View

src/components/markdown/CodeBlock.tsx

@@ -1,6 +1,7 @@
 import { useState } from "react"
 import { View, Text, TouchableOpacity, StyleSheet, useColorScheme, Platform, ScrollView } from "react-native"
 import * as Clipboard from "expo-clipboard"
+import { WIDE_CONTENT_SCROLL_CONFIG } from "../../lib/scroll-config"
 
 interface Props {
   code: string
@@ -27,7 +28,7 @@ export function CodeBlock({ code, language }: Props) {
           <Text style={[styles.copyBtn, isDark && styles.copyBtnDark]}>{copied ? "Copied!" : "Copy"}</Text>
         </TouchableOpacity>
       </View>
-      <ScrollView horizontal showsHorizontalScrollIndicator contentContainerStyle={styles.codeScroll}>
+      <ScrollView {...WIDE_CONTENT_SCROLL_CONFIG} testID="code-block-scroll" contentContainerStyle={styles.codeScroll}>
         <Text style={[styles.code, isDark && styles.codeDark]} selectable>
           {code}
         </Text>

src/components/wide-content-scroll.regression.test.ts

@@ -0,0 +1,45 @@
+import { test } from "node:test"
+import assert from "node:assert/strict"
+import { readFileSync } from "node:fs"
+import { fileURLToPath } from "node:url"
+import path from "node:path"
+
+// GitHub issue #21 ("QA: verify DiffView + CodeBlock horizontal-scroll
+// on-device with a populated diff"). The underlying fixes were:
+//   - src/components/chat/DiffView.tsx: wrap diff lines in a horizontal
+//     ScrollView (previously truncated with numberOfLines={1}).
+//   - src/components/markdown/CodeBlock.tsx: wrap code in a horizontal
+//     ScrollView (previously long lines wrapped/mangled).
+//
+// This repo's runtime is React Native, so these components can't be rendered
+// with node:test (no react-test-renderer / RN jest preset is set up here —
+// see package.json's "test" script, which only globs plain .test.ts files).
+// Instead of skipping component-level coverage, this test reads the actual
+// .tsx source and asserts on its structure: it's a plain-text/regex check,
+// but it directly targets the two markers that would prove a regression —
+// (a) the ScrollView wiring, (b) reintroducing line-truncation — so it can't
+// pass on a source file where the fix was reverted.
+
+function readComponent(relativePath: string): string {
+  const dir = path.dirname(fileURLToPath(import.meta.url))
+  return readFileSync(path.join(dir, relativePath), "utf8")
+}
+
+test("DiffView wraps diff lines in the shared horizontal-scroll ScrollView", () => {
+  const src = readComponent("chat/DiffView.tsx")
+  assert.match(src, /<ScrollView\s+\{\.\.\.WIDE_CONTENT_SCROLL_CONFIG\}/)
+  assert.doesNotMatch(src, /numberOfLines/, "DiffView must not truncate diff line text with numberOfLines")
+})
+
+test("CodeBlock wraps code in the shared horizontal-scroll ScrollView", () => {
+  const src = readComponent("markdown/CodeBlock.tsx")
+  assert.match(src, /<ScrollView\s+\{\.\.\.WIDE_CONTENT_SCROLL_CONFIG\}/)
+  assert.doesNotMatch(src, /numberOfLines/, "CodeBlock must not truncate code text with numberOfLines")
+})
+
+test("DiffView and CodeBlock both source the config from the shared, unit-tested module", () => {
+  const diffView = readComponent("chat/DiffView.tsx")
+  const codeBlock = readComponent("markdown/CodeBlock.tsx")
+  assert.match(diffView, /from ["']\.\.\/\.\.\/lib\/scroll-config["']/)
+  assert.match(codeBlock, /from ["']\.\.\/\.\.\/lib\/scroll-config["']/)
+})

src/lib/scroll-config.test.ts

@@ -0,0 +1,26 @@
+import { test } from "node:test"
+import assert from "node:assert/strict"
+import { WIDE_CONTENT_SCROLL_CONFIG } from "./scroll-config.ts"
+
+// GitHub issue #21: DiffView + CodeBlock must render wide content in a
+// horizontally-scrollable container (not wrapped, not truncated). Both
+// components spread WIDE_CONTENT_SCROLL_CONFIG onto their ScrollView (see
+// src/components/chat/DiffView.tsx and src/components/markdown/CodeBlock.tsx)
+// so asserting on this object here is asserting on the actual runtime props,
+// not a parallel copy that can drift out of sync.
+
+test("wide-content scroll config enables horizontal scrolling", () => {
+  assert.equal(WIDE_CONTENT_SCROLL_CONFIG.horizontal, true)
+})
+
+test("wide-content scroll config shows the horizontal scroll indicator", () => {
+  // Regression guard: a container that scrolls but hides its indicator is
+  // easy to mistake for content that simply doesn't overflow. Keep the
+  // indicator visible so on-device QA (and screenshots) can tell scrollable
+  // content apart from clipped/truncated content.
+  assert.equal(WIDE_CONTENT_SCROLL_CONFIG.showsHorizontalScrollIndicator, true)
+})
+
+test("wide-content scroll config has no unexpected keys", () => {
+  assert.deepEqual(Object.keys(WIDE_CONTENT_SCROLL_CONFIG).sort(), ["horizontal", "showsHorizontalScrollIndicator"])
+})

src/lib/scroll-config.ts

@@ -0,0 +1,18 @@
+// Pure (no React Native imports) horizontal-scroll configuration shared by
+// src/components/chat/DiffView.tsx and src/components/markdown/CodeBlock.tsx.
+//
+// GitHub issue #21: wide diff lines and wide code-block lines must render in
+// a horizontally-scrollable container instead of being wrap-broken or
+// truncated with `numberOfLines`. Centralizing the actual runtime props in
+// one plain object lets that decision be unit-tested with node:test (no React
+// Native renderer needed) while both components spread the SAME object onto
+// their ScrollView, so the test and the real components can't drift apart.
+export interface HorizontalScrollConfig {
+  horizontal: true
+  showsHorizontalScrollIndicator: boolean
+}
+
+export const WIDE_CONTENT_SCROLL_CONFIG: HorizontalScrollConfig = {
+  horizontal: true,
+  showsHorizontalScrollIndicator: true,
+}

tests/fixtures/mock-opencode-server.ts

@@ -68,6 +68,7 @@
 //   node tests/fixtures/mock-opencode-server.ts --port 4096
 //   node tests/fixtures/mock-opencode-server.ts --port 4097 --fail-auth
 //   node tests/fixtures/mock-opencode-server.ts --port 4098 --seed-sessions
+//   node tests/fixtures/mock-opencode-server.ts --port 4100 --seed-diff
 
 import http from "node:http"
 import { randomUUID } from "node:crypto"
@@ -88,6 +89,20 @@ export interface MockServerOptions {
    * open regression for GitHub issues #46/#48).
    */
   seedSessions?: boolean
+  /**
+   * Pre-populate a session (id "seed-diff", in DEFAULT_DIRECTORY so it shows
+   * up on the normal home-tab session list) with ONE assistant message that
+   * already contains a wide `edit` tool part (renders via DiffView) and a
+   * wide fenced code block in its text (renders via CodeBlock) — used by
+   * .maestro/flows/diff-scroll.yaml (GitHub issue #21) to prove both
+   * components' horizontal ScrollView actually scrolls on-device.
+   *
+   * Deliberately seeded as pre-existing history, fetched via GET
+   * /session/:id/message, NOT delivered over SSE — the positive-flow SSE
+   * render bug (issue #90) is being fixed separately, and this flow must not
+   * depend on it landing first.
+   */
+  seedDiff?: boolean
 }
 
 interface StoredSession {
@@ -106,6 +121,16 @@ interface StoredPart {
   messageID: string
   type: string
   text?: string
+  // Tool part fields (type: "tool") — mirrors src/lib/sdk.ts's Part interface,
+  // needed to seed a populated `edit` tool call for --seed-diff.
+  tool?: string
+  callID?: string
+  state?: {
+    status: "pending" | "running" | "completed" | "error"
+    input?: unknown
+    output?: unknown
+    title?: string
+  }
 }
 
 interface StoredMessageInfo {
@@ -166,13 +191,97 @@ export const FAKE_SERVER_PROJECTS = [
   },
 ]
 
+// Exported so .maestro/flows/diff-scroll.yaml's assertions and this file's
+// own seeding logic share one source of truth for what's "off-screen until
+// you scroll" in the seeded diff/code content.
+export const SEED_DIFF_SESSION_ID = "seed-diff"
+export const SEED_DIFF_TITLE = "Wide Diff Session"
+export const SEED_DIFF_TOOL_TITLE = "Edit wide_diff_target.ts"
+export const SEED_DIFF_LINE_MARKER = "ZZZ_DIFF_SCROLL_TARGET_ZZZ"
+export const SEED_CODE_LINE_MARKER = "ZZZ_CODE_SCROLL_TARGET_ZZZ"
+
+// Long, space-free filler so the RN <Text> can't word-wrap it — it just
+// overflows its parent, which is exactly what the horizontal ScrollView (the
+// fix under test) exists to make scrollable instead of clipped/truncated.
+const WIDE_FILLER = "x".repeat(220)
+
 export function createMockOpencodeServer(opts: MockServerOptions) {
-  const { port, failAuth = false, replyText = DEFAULT_REPLY_TEXT, replyDelayMs = 300, seedSessions = false } = opts
+  const {
+    port,
+    failAuth = false,
+    replyText = DEFAULT_REPLY_TEXT,
+    replyDelayMs = 300,
+    seedSessions = false,
+    seedDiff = false,
+  } = opts
 
   const sessions = new Map<string, StoredSession>()
   const messagesBySession = new Map<string, StoredMessage[]>()
   const sseClients = new Set<http.ServerResponse>()
 
+  if (seedDiff) {
+    const now = Date.now()
+    const session: StoredSession = {
+      id: SEED_DIFF_SESSION_ID,
+      slug: "seed-diff",
+      projectID: "mock-project",
+      directory: DEFAULT_DIRECTORY,
+      title: SEED_DIFF_TITLE,
+      version: "0.0.0-mock",
+      time: { created: now - 30_000, updated: now - 20_000 },
+    }
+    sessions.set(session.id, session)
+
+    const messageID = "seed-diff-msg"
+    const info: StoredMessageInfo = {
+      id: messageID,
+      sessionID: session.id,
+      role: "assistant",
+      time: { created: now - 25_000, completed: now - 20_000 },
+      modelID: "mock-model",
+      providerID: "mock",
+    }
+
+    // Populated `edit` tool call: renders via ToolCallCard -> EditDetail ->
+    // DiffView (src/components/chat/DiffView.tsx) once the card is expanded.
+    // One short unchanged line + one wide added line, so DiffView's diff has
+    // both a context row and an "add" row whose text overflows the ScrollView.
+    const toolPart: StoredPart = {
+      id: "seed-diff-tool",
+      sessionID: session.id,
+      messageID,
+      type: "tool",
+      tool: "edit",
+      callID: "seed-diff-call-1",
+      state: {
+        status: "completed",
+        title: SEED_DIFF_TOOL_TITLE,
+        input: {
+          filePath: "src/wide_diff_target.ts",
+          oldString: "const shortLine = 1",
+          newString: `const shortLine = 1\nconst wideLine = "${WIDE_FILLER}${SEED_DIFF_LINE_MARKER}"`,
+        },
+        output: "applied",
+      },
+    }
+
+    // Wide fenced code block in the reply text: renders via
+    // Markdown -> CustomRenderer.code -> CodeBlock
+    // (src/components/markdown/CodeBlock.tsx).
+    const textPart: StoredPart = {
+      id: "seed-diff-text",
+      sessionID: session.id,
+      messageID,
+      type: "text",
+      text:
+        "Here is a wide code sample:\n\n```typescript\n" +
+        `const wideCodeLine = "${WIDE_FILLER}${SEED_CODE_LINE_MARKER}"\n` +
+        "```\n",
+    }
+
+    messagesBySession.set(session.id, [{ info, parts: [toolPart, textPart] }])
+  }
+
   if (seedSessions) {
     const now = Date.now()
     const seedDefault: StoredSession = {
@@ -539,12 +648,13 @@ export function createMockOpencodeServer(opts: MockServerOptions) {
   }
 }
 
-function parseArgs(argv: string[]): { port: number; failAuth: boolean; seedSessions: boolean } {
-  const opts = { port: 4096, failAuth: false, seedSessions: false }
+function parseArgs(argv: string[]): { port: number; failAuth: boolean; seedSessions: boolean; seedDiff: boolean } {
+  const opts = { port: 4096, failAuth: false, seedSessions: false, seedDiff: false }
   for (let i = 0; i < argv.length; i++) {
     if (argv[i] === "--port") opts.port = Number(argv[++i])
     else if (argv[i] === "--fail-auth") opts.failAuth = true
     else if (argv[i] === "--seed-sessions") opts.seedSessions = true
+    else if (argv[i] === "--seed-diff") opts.seedDiff = true
   }
   return opts
 }
@@ -557,7 +667,7 @@ if (invokedDirectly) {
   const mock = createMockOpencodeServer(opts)
   mock.listen().then(() => {
     console.log(
-      `[mock-opencode-server] listening on ${mock.url} (failAuth=${opts.failAuth}, seedSessions=${opts.seedSessions})`,
+      `[mock-opencode-server] listening on ${mock.url} (failAuth=${opts.failAuth}, seedSessions=${opts.seedSessions}, seedDiff=${opts.seedDiff})`,
     )
   })
   const shutdown = () => {