canary: probe what an incremental admission rebuild recompiles (do not merge)

.github/workflows/ci-macos.yml

@@ -523,13 +523,68 @@ jobs:
           echo "seconds=$seconds" >> "$GITHUB_OUTPUT"
           exit "$status"
 
+      # CANARY (do not merge): measure what an incremental rebuild recompiles.
+      - name: Canary probe incremental rebuilds
+        if: always() && steps.hosted-compile.outcome == 'success'
+        continue-on-error: true
+        timeout-minutes: 40
+        run: |
+          set +e -u
+          report() {
+            local log="$1" name="$2" seconds="$3"
+            echo "== probe $name: ${seconds}s"
+            echo "   GenerateAssetSymbols tasks: $(grep -cE '^GenerateAssetSymbols ' "$log")"
+            echo "   CompileAssetCatalog tasks: $(grep -cE '^CompileAssetCatalog' "$log")"
+            echo "   EmitSwiftModule/SwiftEmitModule cmux: $(grep -cE "^(SwiftEmitModule|EmitSwiftModule) .*\(in target 'cmux' " "$log")"
+            grep -oE "^SwiftCompile normal arm64 [^ ]+ \(in target '[^']+'" "$log" | sed -E "s/.*target '//;s/'//" | sort | uniq -c | sort -rn | head -8 | sed 's/^/   /'
+            { echo "### probe $name: ${seconds}s"; grep -oE "^SwiftCompile normal arm64 [^ ]+ \(in target '[^']+'" "$log" | sed -E "s/.*target '//;s/'//" | sort | uniq -c | sort -rn | head -5; } >> "$GITHUB_STEP_SUMMARY"
+          }
+          probe() {
+            local name="$1" log="$RUNNER_TEMP/probe-$1.txt" started=$SECONDS
+            CMUX_CI_BUILD_SCHEMES=cmux-unit scripts/ci/compile-app-host-test-product.sh canonical-build \
+              "$CMUX_COMPILE_ADMISSION_DERIVED_DATA" \
+              "$PWD/.ci-source-packages" \
+              "$CMUX_COMPILE_ADMISSION_CAS" \
+              "$log" > /dev/null 2>&1 || echo "probe $name build failed"
+            report "$log" "$name" "$((SECONDS - started))"
+          }
+          src=/private/tmp/cmux-ci/src
+          stat -f '%Sm %N' "$src/Assets.xcassets" "$src/Assets.xcassets/AppIcon.appiconset" 2>/dev/null || true
+          find "$src/Assets.xcassets" -type f | head -2 | xargs stat -f '%Sm %N' 2>/dev/null || true
+          probe null
+          touch "$src/cmuxTests/CmuxSSHURLRequestTests.swift"
+          probe test-file-mtime
+          touch "$src/Assets.xcassets"
+          probe assets-dir-mtime
+          touch "$src/Sources/Sidebar/GPUSpinner.swift"
+          probe app-file-mtime
+          # Where does the first "Resolve Package Graph" spend ~45 s?
+          manifests="$HOME/Library/Caches/org.swift.swiftpm/manifests"
+          echo "manifest cache: $(du -sh "$manifests" 2>/dev/null | cut -f1) entries=$(sqlite3 "$manifests/manifest.db" 'select count(*) from MANIFEST_CACHE' 2>/dev/null)"
+          resolve_probe() {
+            local name="$1" started=$SECONDS
+            (cd "$src" && xcodebuild -project cmux.xcodeproj -scheme cmux-unit -configuration Debug \
+              -derivedDataPath "$CMUX_COMPILE_ADMISSION_DERIVED_DATA" \
+              -clonedSourcePackagesDirPath "$src/.ci-source-packages" \
+              -packageCachePath "$src/.ci-source-packages/.package-cache" \
+              -skipPackageUpdates -resolvePackageDependencies > "$RUNNER_TEMP/resolve-$name.txt" 2>&1)
+            echo "== resolve $name: $((SECONDS - started))s rc=$?"
+            echo "### resolve $name: $((SECONDS - started))s" >> "$GITHUB_STEP_SUMMARY"
+          }
+          resolve_probe warm-manifests
+          mv "$manifests" "$manifests.aside" 2>/dev/null
+          resolve_probe no-manifest-cache
+          echo "manifest cache rebuilt: entries=$(sqlite3 "$manifests/manifest.db" 'select count(*) from MANIFEST_CACHE' 2>/dev/null)"
+          resolve_probe rebuilt-manifests
+
       # Adoption sets a per-user Xcode default. Only a build whose inputs were
       # just replayed should ignore inode changes, so a reused runner does not
       # carry it into an unrelated job.
       - name: Forget the adopted-build inode override
         if: always() && steps.seed-derived-data.outcome != 'skipped'
         continue-on-error: true
-        run: defaults delete com.apple.dt.XCBuild IgnoreFileSystemDeviceInodeChanges || true
+        run: |
+          defaults delete com.apple.dt.XCBuild IgnoreFileSystemDeviceInodeChanges || true
 
       - name: Generate Xcode build metrics receipt
         id: build-metrics

scripts/ci/compile-app-host-test-product.sh

@@ -128,6 +128,7 @@ build() {
   # job warning-budget scope; subsequent schemes reuse the same app objects.
   # shellcheck disable=SC2016 # Xcode expands $(inherited), not the shell
   for scheme in cmux cmux-unit cmux-numeric-locale cmux-cli-tests; do
+    case " ${CMUX_CI_BUILD_SCHEMES:-$scheme} " in *" $scheme "*) ;; *) continue ;; esac
     xcodebuild -project cmux.xcodeproj -scheme "$scheme" -configuration Debug \
       -derivedDataPath "$derived_data" \
       -clonedSourcePackagesDirPath "$source_packages" \