diff --git a/.claude/skills/preflight/SKILL.md b/.claude/skills/preflight/SKILL.md
index 6bd417a..71d580b 100644
--- a/.claude/skills/preflight/SKILL.md
+++ b/.claude/skills/preflight/SKILL.md
@@ -1,6 +1,6 @@
 ---
 name: preflight
-description: Run LibreMail's fast CI gate locally (assembleDebug + testDebugUnitTest + lintDebug + ktlintCheck + detekt) before pushing or opening a PR. Mirrors the merge gate; does NOT run emulator E2E. Use before treating a change as done.
+description: Run LibreMail's fast CI gate locally (assembleDebug + testDebugUnitTest + compileDebugAndroidTestKotlin + lintDebug + ktlintCheck + detekt) before pushing or opening a PR. Mirrors the merge gate; does NOT run emulator E2E. Use before treating a change as done.
 ---
 
 # /preflight
@@ -21,10 +21,16 @@ Run these, stopping at the first failure:
 ```bash
 ./gradlew :app:assembleDebug
 ./gradlew :app:testDebugUnitTest
+./gradlew :app:compileDebugAndroidTestKotlin
 ./gradlew :app:lintDebug
 ./gradlew :app:ktlintCheck :app:detekt
 ```
 
+`compileDebugAndroidTestKotlin` compiles the `androidTest` source set — the E2E/instrumented
+tests — without needing an emulator. `assembleDebug`, `testDebugUnitTest`, and `lintDebug` never
+compile that source set, so a change that breaks it (e.g. an instrumented test calling a UI API
+that just changed signature) passes the rest of this gate locally yet fails CI.
+
 `ktlintCheck` + `detekt` are exactly what CI's **Static analysis** job runs — they cover the
 `test`/`androidTest` source sets that `lintDebug` does not, so a style violation there fails the
 merge gate even when the build and lint are green. Add `--continue` to any command (e.g.
diff --git a/CLAUDE.md b/CLAUDE.md
index 8c0bcf7..18a3db8 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -26,10 +26,12 @@ or via Gradle Managed Devices `./gradlew e2eGroupDebugAndroidTest` (whole matrix
 `app/build.gradle.kts` must stay in lockstep with the E2E matrix in `.github/workflows/ci.yml`.
 
 **Before treating a change as done**, run the fast CI gate: `assembleDebug` +
-`testDebugUnitTest` + `lintDebug` + `ktlintCheck` + `detekt` (the `/preflight` skill does
-this). `ktlintCheck`/`detekt` cover the `test`/`androidTest` source sets that `lintDebug`
-skips, so they catch style violations that would otherwise fail CI's Static analysis gate.
-Emulator E2E is left to CI unless asked.
+`testDebugUnitTest` + `compileDebugAndroidTestKotlin` + `lintDebug` + `ktlintCheck` +
+`detekt` (the `/preflight` skill does this). `compileDebugAndroidTestKotlin` compiles the
+`androidTest` source set that the rest of the gate skips, catching E2E/instrumented-test
+compile errors before they surface only in CI. `ktlintCheck`/`detekt` cover the
+`test`/`androidTest` source sets that `lintDebug` skips, so they catch style violations that
+would otherwise fail CI's Static analysis gate. Emulator E2E is left to CI unless asked.
 
 ## Build-config gotchas