diagnose(1874): instrument the synthesized commit wait and add a dispatchable stall loop

.github/workflows/1874-diagnose.yml

@@ -0,0 +1,112 @@
+name: 1874 Diagnose
+
+on:
+  workflow_dispatch:
+    inputs:
+      iterations:
+        description: 'Loop iterations per job'
+        required: false
+        default: '25'
+  push:
+    branches:
+      - diagnose/1874-commit-stall
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  stall-loop:
+    name: ${{ matrix.arch }} ${{ matrix.mode }} stall loop
+    runs-on: macos-26
+    timeout-minutes: 90
+    strategy:
+      fail-fast: false
+      matrix:
+        mode: [isolated, pair]
+        arch: [x86_64, arm64]
+    env:
+      IOS_RUNTIME_VERSION: '26.2'
+      AGENT_DEVICE_IOS_RUNNER_DERIVED_PATH: ${{ github.workspace }}/.tmp/ios-runner-derived
+      AGENT_DEVICE_XCUITEST_INCLUDE_UNIT_TESTS: '1'
+      AGENT_DEVICE_XCUITEST_ARCHS: ${{ matrix.arch }}
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Setup toolchain
+        uses: ./.github/actions/setup-node-pnpm
+
+      - name: Restore and build iOS XCTest runner
+        uses: ./.github/actions/setup-apple-runner-build
+        with:
+          derived-path: ${{ env.AGENT_DEVICE_IOS_RUNNER_DERIVED_PATH }}
+          cache-key-prefix: ios-runner-prebuilt
+          cache-key-suffix: -ios-${{ env.IOS_RUNTIME_VERSION }}-1874-${{ matrix.arch }}
+          gate: swift-runner-ios
+          xcuitest-platform: ios
+          xcuitest-destination: generic/platform=iOS Simulator
+
+      - name: Boot iOS test simulator
+        id: ios-simulator
+        uses: ./.github/actions/boot-ios-test-simulator
+        with:
+          runtime-version: ${{ env.IOS_RUNTIME_VERSION }}
+          preferred-device-name: iPhone 17 Pro
+
+      - name: Stall loop
+        run: |
+          set -euo pipefail
+          XCTESTRUN_PATH="$(find "$AGENT_DEVICE_IOS_RUNNER_DERIVED_PATH/Build/Products" -maxdepth 1 -name '*.xctestrun' -print -quit)"
+          test -n "$XCTESTRUN_PATH"
+          UDID="${{ steps.ios-simulator.outputs.simulator-udid }}"
+          ITER="${{ github.event.inputs.iterations || '25' }}"
+
+          if [ "${{ matrix.mode }}" = "pair" ]; then
+            EXTRA_ONLY_TESTING=(-only-testing:AgentDeviceRunnerUITests/RunnerTests/testBareDelayedTypeFailsWhenTappedInputDisappearsMidCommand)
+          else
+            EXTRA_ONLY_TESTING=()
+          fi
+
+          sys_prof="$(system_profiler SPHardwareDataType 2>/dev/null | grep -E 'Chip|Cores|Memory' || true)"
+          echo "HOST: $sys_prof" | tee stall-summary.txt
+
+          pass=0; fail=0
+          for i in $(seq 1 "$ITER"); do
+            LOG=".tmp/stall-run-$i.log"
+            set +e
+            xcodebuild test-without-building \
+              -xctestrun "$XCTESTRUN_PATH" \
+              -destination "platform=iOS Simulator,id=$UDID" \
+              -only-testing:AgentDeviceRunnerUITests/RunnerTests/testBareTypeUsesTappedInputWhenSoftwareKeyboardIsHidden \
+              ${EXTRA_ONLY_TESTING[@]+"${EXTRA_ONLY_TESTING[@]}"} \
+              > "$LOG" 2>&1
+            rc=$?
+            set -e
+            if grep -q "testBareTypeUsesTappedInputWhenSoftwareKeyboardIsHidden]' passed" "$LOG"; then
+              pass=$((pass+1)); verdict=pass
+            else
+              fail=$((fail+1)); verdict=STALL
+            fi
+            phase="$(grep -o 'phase=type-all durationMs=[0-9.]*' "$LOG" | tail -1)"
+            polls="$(grep -c 'DEBUG-1874] poll' "$LOG" || true)"
+            echo "iter=$i verdict=$verdict rc=$rc $phase polls=$polls" | tee -a stall-summary.txt
+            if [ "$verdict" = "STALL" ]; then
+              grep 'DEBUG-1874' "$LOG" | head -40 | tee -a stall-summary.txt
+              cp "$LOG" ".tmp/stall-failure-$i.log"
+            fi
+          done
+
+          echo "RESULT arch=${{ matrix.arch }} mode=${{ matrix.mode }}: $pass passed, $fail stalled of $ITER" | tee -a stall-summary.txt
+
+      - name: Upload stall evidence
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: stall-evidence-${{ matrix.arch }}-${{ matrix.mode }}
+          path: |
+            stall-summary.txt
+            .tmp/stall-failure-*.log
+          if-no-files-found: ignore

.github/workflows/conformance-differential.yml

@@ -45,6 +45,7 @@ jobs:
     timeout-minutes: 90
     env:
       IOS_RUNTIME_VERSION: '26.2'
+      AGENT_DEVICE_XCUITEST_ARCHS: 'arm64'
       AGENT_DEVICE_STATE_DIR: ${{ github.workspace }}/.tmp/agent-device-state
       AGENT_DEVICE_IOS_RUNNER_DERIVED_PATH: ${{ github.workspace }}/.tmp/ios-runner-derived
     steps:
@@ -59,7 +60,7 @@ jobs:
         with:
           derived-path: ${{ env.AGENT_DEVICE_IOS_RUNNER_DERIVED_PATH }}
           cache-key-prefix: ios-runner-prebuilt
-          cache-key-suffix: -ios-${{ env.IOS_RUNTIME_VERSION }}
+          cache-key-suffix: -ios-${{ env.IOS_RUNTIME_VERSION }}-arm64
           gate: swift-runner-ios
           xcuitest-platform: ios
           xcuitest-destination: generic/platform=iOS Simulator

.github/workflows/ios.yml

@@ -74,6 +74,11 @@ jobs:
       AGENT_DEVICE_IOS_RUNNER_DERIVED_PATH: ${{ github.workspace }}/.tmp/ios-runner-derived
       AGENT_DEVICE_IOS_PREPARE_TIMEOUT_MS: '420000'
       AGENT_DEVICE_XCUITEST_INCLUDE_UNIT_TESTS: '1'
+      # A generic simulator destination leaves the active arch undefined and Xcode 26.6
+      # defaults it to x86_64, which runs the whole runner under Rosetta on arm64 hosts.
+      # Pin the native slice: measured ~30% faster commits on identical CI hardware
+      # (#1874 diagnosis, PR #1941).
+      AGENT_DEVICE_XCUITEST_ARCHS: 'arm64'
       AGENT_DEVICE_IOS_APP_EVENT_URL_TEMPLATE: agent-device-test-app:///automation?event={event}&payload={payload}
     steps:
       - name: Checkout
@@ -113,7 +118,7 @@ jobs:
         with:
           derived-path: ${{ env.AGENT_DEVICE_IOS_RUNNER_DERIVED_PATH }}
           cache-key-prefix: ios-runner-prebuilt
-          cache-key-suffix: -ios-${{ env.IOS_RUNTIME_VERSION }}
+          cache-key-suffix: -ios-${{ env.IOS_RUNTIME_VERSION }}-arm64
           gate: swift-runner-ios
           xcuitest-platform: ios
           xcuitest-destination: generic/platform=iOS Simulator

.github/workflows/perf-nightly.yml

@@ -32,6 +32,7 @@ jobs:
     timeout-minutes: 80
     env:
       IOS_RUNTIME_VERSION: '26.2'
+      AGENT_DEVICE_XCUITEST_ARCHS: 'arm64'
       AGENT_DEVICE_STATE_DIR: ${{ github.workspace }}/.tmp/agent-device-state
       AGENT_DEVICE_IOS_RUNNER_DERIVED_PATH: ${{ github.workspace }}/.tmp/ios-runner-derived
       AGENT_DEVICE_IOS_PREPARE_TIMEOUT_MS: '420000'
@@ -47,7 +48,7 @@ jobs:
         with:
           derived-path: ${{ env.AGENT_DEVICE_IOS_RUNNER_DERIVED_PATH }}
           cache-key-prefix: ios-runner-prebuilt
-          cache-key-suffix: -ios-${{ env.IOS_RUNTIME_VERSION }}
+          cache-key-suffix: -ios-${{ env.IOS_RUNTIME_VERSION }}-arm64
           gate: swift-runner-ios
           xcuitest-platform: ios
           xcuitest-destination: generic/platform=iOS Simulator

.github/workflows/replays-manual.yml

@@ -91,6 +91,7 @@ jobs:
     timeout-minutes: 80
     env:
       IOS_RUNTIME_VERSION: '26.2'
+      AGENT_DEVICE_XCUITEST_ARCHS: 'arm64'
       AGENT_DEVICE_STATE_DIR: ${{ github.workspace }}/.tmp/agent-device-state
       AGENT_DEVICE_IOS_RUNNER_DERIVED_PATH: ${{ github.workspace }}/.tmp/ios-runner-derived
       AGENT_DEVICE_IOS_PREPARE_TIMEOUT_MS: '420000'
@@ -111,7 +112,7 @@ jobs:
         with:
           derived-path: ${{ env.AGENT_DEVICE_IOS_RUNNER_DERIVED_PATH }}
           cache-key-prefix: ios-runner-prebuilt
-          cache-key-suffix: -ios-${{ env.IOS_RUNTIME_VERSION }}
+          cache-key-suffix: -ios-${{ env.IOS_RUNTIME_VERSION }}-arm64
           gate: swift-runner-ios
           xcuitest-platform: ios
           xcuitest-destination: generic/platform=iOS Simulator

.github/workflows/xctest-nightly.yml

@@ -78,8 +78,10 @@ jobs:
       # methods exist at all. Dropping it would build a different variant (cache miss) whose
       # bundle contains no tests, and `xcodebuild` reports running zero tests as success — the
       # "silent 0-test green" this lane would then be. The test-count assertion below is the
-      # backstop for exactly that.
+      # backstop for exactly that. AGENT_DEVICE_XCUITEST_ARCHS rides the cache key too: dropping
+      # it silently reverts the runner to Xcode's x86_64 default under Rosetta.
       IOS_RUNTIME_VERSION: '26.2'
+      AGENT_DEVICE_XCUITEST_ARCHS: 'arm64'
       AGENT_DEVICE_XCUITEST_INCLUDE_UNIT_TESTS: '1'
       AGENT_DEVICE_IOS_RUNNER_DERIVED_PATH: ${{ github.workspace }}/.tmp/ios-runner-derived
       RESULT_BUNDLE_PATH: ${{ github.workspace }}/.tmp/xctest-nightly/RunnerTests.xcresult
@@ -103,7 +105,7 @@ jobs:
         with:
           derived-path: ${{ env.AGENT_DEVICE_IOS_RUNNER_DERIVED_PATH }}
           cache-key-prefix: ios-runner-prebuilt
-          cache-key-suffix: -ios-${{ env.IOS_RUNTIME_VERSION }}
+          cache-key-suffix: -ios-${{ env.IOS_RUNTIME_VERSION }}-arm64
           gate: swift-runner-ios
           xcuitest-platform: ios
           xcuitest-destination: generic/platform=iOS Simulator

apple/runner/AgentDeviceRunner/AgentDeviceRunnerUITests/RunnerTests+SynthesizedTextEntry.swift

@@ -40,9 +40,14 @@ extension RunnerTests {
       replacingExistingText: Bool
     ) -> SynthesizedTextEntryAction {
 #if os(iOS)
+      let postStartedAt = Date()
       let result = replacingExistingText
         ? RunnerSynthesizedTextEntry.replaceText(withApplication: app, text: text)
         : RunnerSynthesizedTextEntry.synthesizeText(withApplication: app, text: text)
+      NSLog(
+        "[DEBUG-1874] synthesize posted %d chars status=%d tookMs=%.0f",
+        text.count, result.status.rawValue, postStartedAt.timeIntervalSinceNow * -1000
+      )
       return Self.action(status: result.status, message: result.message)
 #else
       return .fallback
@@ -184,6 +189,47 @@ extension RunnerTests {
     return expectedText.hasPrefix(observedText) ? .pending : .diverged
   }
 
+  /// Length of the shared prefix of two strings. Feeds value-free commit-wait logging: the
+  /// expected-prefix walk over time distinguishes throttled delivery (grows slowly) from a
+  /// wedged pipeline (freezes) without ever logging the field's contents.
+  static func commonPrefixLength(_ lhs: String, _ rhs: String) -> Int {
+    var length = 0
+    for (l, r) in zip(lhs, rhs) {
+      if l != r { break }
+      length += 1
+    }
+    return length
+  }
+
+  /// The emitted cadence line, as a pure function so its output is assertable. Only lengths and
+  /// a timestamp are representable here; there is no String parameter, so observed field
+  /// contents cannot reach runner.log through this boundary whatever they contain.
+  static func commitCadenceLogLine(
+    elapsedMs: Int,
+    observedLen: Int,
+    expectedPrefixLen: Int
+  ) -> String {
+    "[DEBUG-1874] poll t=\(elapsedMs)ms observedLen=\(observedLen) expectedPrefixLen=\(expectedPrefixLen)"
+  }
+
+  /// The typed boundary for commit-wait cadence evidence. The poll path must log through this
+  /// function and never through a raw NSLog: every parameter is an Int, so the polled value's
+  /// contents are unrepresentable at the call site.
+  static func logCommitCadence(
+    elapsedMs: Int,
+    observedLen: Int,
+    expectedPrefixLen: Int
+  ) {
+    NSLog(
+      "%@",
+      commitCadenceLogLine(
+        elapsedMs: elapsedMs,
+        observedLen: observedLen,
+        expectedPrefixLen: expectedPrefixLen
+      )
+    )
+  }
+
   /// How the commit wait ended. Distinct from `SynthesizedTextCommitProgress`, which classifies a
   /// single observation: this is the whole wait's verdict, and it exists so the deadline can be
   /// told apart from success. The wait used to return `Void`, which made an expired deadline
@@ -265,20 +311,37 @@ extension RunnerTests {
     let expectedText = textBefore + typedText
     let placeholder = resolveTextEntryElement(app: app, target: target)?.placeholderValue
     let deadline = Date().addingTimeInterval(TextEntryTiming.synthesizedCommitTimeout)
-    return Self.awaitSynthesizedCommitOutcome(
+    let waitStartedAt = Date()
+    NSLog("[DEBUG-1874] wait start expectedLen=%ld", expectedText.count)
+    let outcome = Self.awaitSynthesizedCommitOutcome(
       expectedText: expectedText,
       placeholder: placeholder,
       isExpired: { Date() >= deadline },
       observe: {
-        editableTextValue(
+        let observedText = editableTextValue(
           for: resolveTextEntryElement(app: app, target: target),
           treatingPlaceholderAsEmpty: true
         )
+        // Cadence evidence stays value-free: the polled value is user content typed through
+        // `type` and must never reach runner.log. Lengths and the expected-prefix walk are
+        // enough to distinguish throttling (prefix grows slowly) from a wedge (it freezes).
+        Self.logCommitCadence(
+          elapsedMs: Int(waitStartedAt.timeIntervalSinceNow * -1000),
+          observedLen: observedText?.count ?? -1,
+          expectedPrefixLen: observedText.map { Self.commonPrefixLength($0, expectedText) } ?? -1
+        )
+        return observedText
       },
       // XCUI resolution shares the automation channel with the in-flight synthesized event.
       // Sparse reads let the target consume that event instead of continuously interrupting it.
       waitForNextObservation: { sleepFor(TextEntryTiming.synthesizedCommitPollInterval) }
     )
+    NSLog(
+      "[DEBUG-1874] wait outcome=%@ elapsedMs=%.0f",
+      String(describing: outcome),
+      waitStartedAt.timeIntervalSinceNow * -1000
+    )
+    return outcome
   }
 
   static func shouldUseResolvedCoordinateTextEntryRoute(

apple/runner/AgentDeviceRunner/AgentDeviceRunnerUITests/UnitTests/RunnerTests+TextEntryPolicyTests.swift

@@ -308,6 +308,31 @@ extension RunnerTests {
     XCTAssertFalse(result.repaired)
     XCTAssertEqual(result.textEntryRoute, "synthesized-first-responder-replacement")
   }
+
+  func testCommonPrefixLengthWalksTheExpectedPrefixOnly() {
+    XCTAssertEqual(Self.commonPrefixLength("hardware-keyboard", "hardware-keyboard"), 17)
+    XCTAssertEqual(Self.commonPrefixLength("h", "hardware-keyboard"), 1)
+    XCTAssertEqual(Self.commonPrefixLength("ha", "hardware-keyboard"), 2)
+    XCTAssertEqual(Self.commonPrefixLength("", "hardware-keyboard"), 0)
+    // Divergence stops the count: the app transformed the input, and the walk must not
+    // resume matching after the first differing character.
+    XCTAssertEqual(Self.commonPrefixLength("hx", "hardware-keyboard"), 1)
+    XCTAssertEqual(Self.commonPrefixLength("hardware-keyboarx", "hardware-keyboard"), 15)
+  }
+
+  func testCommitCadenceLogLineEmitsLengthsOnlyNeverContents() {
+    // Sentinel secret: even when the polled field holds credential-shaped content, the only
+    // channel into runner.log is this line, and its inputs are lengths. The exact-equality
+    // assert fails if any content-bearing parameter or interpolation is ever added.
+    let secret = "hunter2-typed-credential"
+    let line = Self.commitCadenceLogLine(
+      elapsedMs: 42,
+      observedLen: secret.count,
+      expectedPrefixLen: 8
+    )
+    XCTAssertEqual(line, "[DEBUG-1874] poll t=42ms observedLen=24 expectedPrefixLen=8")
+    XCTAssertFalse(line.contains(secret))
+  }
 #endif
 #endif
 }

scripts/build-xcuitest-apple.sh

@@ -138,6 +138,14 @@ if is_truthy "${AGENT_DEVICE_XCUITEST_INCLUDE_UNIT_TESTS:-}"; then
   SWIFT_FLAGS="$SWIFT_FLAGS -D AGENT_DEVICE_RUNNER_UNIT_TESTS"
 fi
 
+# Optional arch override. A generic simulator destination leaves the active arch
+# undefined; Xcode versions differ on the default (26.6 picks x86_64, which runs
+# under Rosetta on arm64 hosts). Set AGENT_DEVICE_XCUITEST_ARCHS=arm64 to pin it.
+ARCH_BUILD_SETTINGS=""
+if [ -n "${AGENT_DEVICE_XCUITEST_ARCHS:-}" ]; then
+  ARCH_BUILD_SETTINGS="ARCHS=$AGENT_DEVICE_XCUITEST_ARCHS"
+fi
+
 node --experimental-strip-types scripts/swift-toolchain-tmpdir.ts xcodebuild build-for-testing \
   -project "$PROJECT_PATH" \
   -scheme "$SCHEME" \
@@ -154,6 +162,7 @@ node --experimental-strip-types scripts/swift-toolchain-tmpdir.ts xcodebuild bui
   -IDEPackageSupportDisablePluginExecutionSandbox=1 \
   ENABLE_USER_SCRIPT_SANDBOXING=NO \
   OTHER_SWIFT_FLAGS="$SWIFT_FLAGS" \
+  $ARCH_BUILD_SETTINGS \
   $SIGNING_BUILD_SETTINGS
 
 node --experimental-strip-types scripts/patch-xcuitest-runner-icon.ts "$DERIVED_PATH"