@@ -17,7 +17,12 @@
 # only trimmed ~17% of the goal vs ~88% for this per-module skip (measured on this
 # reactor). A small upstream SpotBugs early-exit (skip the run when no application class
 # matches the screener) would make onlyAnalyze competitive; if that ever lands, switch
-# to onlyAnalyze and delete this script.
+# to onlyAnalyze and delete this script (tracked in #1455 / spotbugs/spotbugs#3796).
+#
+# On top of the skips, the changed reactor modules are exported as SPOTBUGS_SCOPE_ARGS
+# ("-pl <changed> -am") so the lane builds only those modules plus their upstream
+# dependencies instead of the full reactor. The -am-pulled unchanged dependencies still
+# carry the injected skip: they compile (complete aux-classpath) but are not analysed.
 #
 # Run from the repository root.  Usage: compute-spotbugs-skip.sh <base-sha>
 set -euo pipefail
@@ -27,6 +32,23 @@ base="${1:?base sha required}"
 # count as changed; D keeps deletion-only changes (e.g. a removed ruleset) visible.
 changed=$(git diff --name-only --no-renames --diff-filter=ACMD "${base}...HEAD")
 
+# Reactor module dirs from ddk-parent's <modules> (strip the leading ../), and the
+# subset that bears sources. ddk-parent is NOT in its own <modules>, so it can never be
+# skip-injected — which prevents an accidental inherited (global) skip. Both lists are
+# computed up front because the full-scan early-exit below needs the source-bearing set
+# for its report-presence gate.
+module_dirs=$(grep -oE '<module>\.\./[^<]+</module>' ddk-parent/pom.xml \
+  | sed -E 's#.*\.\./([^<]+)</module>#\1#')
+all_source_modules=""
+while IFS= read -r mod; do
+  [ -n "$mod" ] || continue
+  if [ -f "${mod}/META-INF/MANIFEST.MF" ] && [ -d "${mod}/src" ]; then
+    all_source_modules="${all_source_modules:+${all_source_modules} }${mod}"
+  fi
+done <<EOF
+${module_dirs}
+EOF
+
 # 1) A change to shared build/config can affect any module -> full scan (skip nothing).
 #    ddk-configuration holds the analyzers' rulesets and filters (e.g. the SpotBugs
 #    exclusion-filter), so a change there must re-scan everything, not skip silently.
@@ -36,6 +58,16 @@ while IFS= read -r f; do
   [ -n "$f" ] || continue
   case "$f" in
     pom.xml | ddk-parent/* | .mvn/* | *.target | ddk-target/* | .github/* | ddk-configuration/* | *[Ss]pot[Bb]ugs*[Ee]xclude*)
+      # KEPT must be set on every path: in a workflow `if:` an unset env var is
+      # null, which coerces to 0 and compares EQUAL to '0' — wrongly skipping
+      # the build. "all" marks the full-scan case (only "0" relaxes the gate).
+      # EXPECT_REPORTS lists every source-bearing module so the gate verifies a
+      # full scan analysed all of them (not just >=1) — a mojo death swallowed by
+      # --fail-never can't pass as long as one sibling reported.
+      if [ -n "${GITHUB_ENV:-}" ]; then
+        echo "SPOTBUGS_KEPT=all" >> "$GITHUB_ENV"
+        echo "SPOTBUGS_EXPECT_REPORTS=${all_source_modules}" >> "$GITHUB_ENV"
+      fi
       echo "Build/config change ($f) -> full SpotBugs scan (no skips)."
       exit 0
       ;;
@@ -49,13 +81,7 @@ EOF
 #    grep's no-match exit would otherwise kill the script under pipefail.
 changed_mods=$(printf '%s\n' "${changed}" | { grep '/' || true; } | cut -d/ -f1 | sort -u)
 
-# 3) Reactor module dirs from ddk-parent's <modules> (strip the leading ../).
-#    ddk-parent is NOT in its own <modules>, so it can never be skip-injected — which
-#    is what prevents an accidental inherited (global) skip.
-module_dirs=$(grep -oE '<module>\.\./[^<]+</module>' ddk-parent/pom.xml \
-  | sed -E 's#.*\.\./([^<]+)</module>#\1#')
-
-# 4) Idempotently inject the skip property; handle poms with and without <properties>.
+# 3) Idempotently inject the skip property; handle poms with and without <properties>.
 #    sed -i.bak + rm is portable across GNU (CI) and BSD (local) sed.
 inject_skip() {
   local pom="$1/pom.xml"
@@ -69,15 +95,20 @@ inject_skip() {
   rm -f "$pom.bak"
 }
 
-# 5) Skip every reactor module that was not touched by this PR. Kept bundles with
-#    sources are expected to produce a SARIF; the gate checks each one.
+# 4) Skip every reactor module that was not touched by this PR. Kept modules with a
+#    bundle MANIFEST are expected to produce an analysis report — the gate checks this
+#    so a swallowed resolution/compile failure can never pass as "nothing to scan".
 kept=0
 skipped=0
+kept_pl=""
 expect_reports=""
 while IFS= read -r mod; do
   [ -n "$mod" ] || continue
   if printf '%s\n' "${changed_mods}" | grep -qx "$mod"; then
     kept=$((kept + 1))
+    kept_pl="${kept_pl:+${kept_pl},}../${mod}"
+    # Only bundles with sources reliably emit a report (a source-less bundle,
+    # e.g. pure branding, has nothing for the analyzer to write a SARIF about).
     if [ -f "${mod}/META-INF/MANIFEST.MF" ] && [ -d "${mod}/src" ]; then
       expect_reports="${expect_reports:+${expect_reports} }${mod}"
     fi
@@ -91,15 +122,38 @@ EOF
 
 # The gate's presence check needs to distinguish "all modules skip-injected"
 # (zero reports is the expected state) from "the analysis silently died".
-# Only source-less modules changed (feature / target / repository) counts as
-# nothing to scan: SpotBugs cannot write a report for a bundle without classes.
-if [ -z "$expect_reports" ]; then
-  kept=0
+# If the only changed modules are source-less (feature / target / repository — nothing
+# any analyzer can report), fold into the docs-only no-op: export KEPT=0 so the lane
+# skips the Maven step, gate, and upload instead of failing the merged-report presence
+# check on output that could never exist.
+if [ "$kept" -eq 0 ] || [ -z "$expect_reports" ]; then
+  effective_kept=0
+else
+  effective_kept=$kept
 fi
 if [ -n "${GITHUB_ENV:-}" ]; then
-  echo "SPOTBUGS_KEPT=${kept}" >> "$GITHUB_ENV"
+  echo "SPOTBUGS_KEPT=${effective_kept}" >> "$GITHUB_ENV"
+fi
+
+# 5) Scope the reactor to the changed modules + their upstream dependencies. ddk-target
+#    is always kept in the -pl list: the target-definition artifact is referenced by
+#    target-platform-configuration, not by any MANIFEST, so -am never pulls it — without
+#    it in the reactor Tycho falls back to a local-repository copy, which fails on a
+#    cold cache and can silently resolve a stale target definition on a warm one.
+#    With no analysable changed module (docs-only, or source-less-only) no scope args
+#    are exported; the workflow skips the Maven step entirely on SPOTBUGS_KEPT=0.
+if [ "$effective_kept" -gt 0 ] && [ -n "${GITHUB_ENV:-}" ]; then
+  echo "SPOTBUGS_SCOPE_ARGS=-pl ../ddk-target,${kept_pl} -am" >> "$GITHUB_ENV"
   echo "SPOTBUGS_EXPECT_REPORTS=${expect_reports}" >> "$GITHUB_ENV"
 fi
 
-echo "SpotBugs scope: scanning ${kept} changed module(s), skipping ${skipped} unchanged."
+echo "SpotBugs scope: scanning ${effective_kept} changed module(s), skipping ${skipped} unchanged."
 echo "Changed modules: ${changed_mods:-<none>}"
+if [ "$kept" -gt 0 ] && [ "$effective_kept" -eq 0 ]; then
+  echo "Only source-less modules changed (no analysable sources) -> no-op (KEPT=0)."
+fi
+if [ "$effective_kept" -gt 0 ]; then
+  echo "Reactor scope args: -pl ../ddk-target,${kept_pl} -am"
+else
+  echo "Reactor scope args: <full reactor>"
+fi
@@ -177,10 +177,11 @@ jobs:
           restore-keys: ${{ runner.os }}-maven-publish-
 
       - name: Scope SpotBugs to the PR's changed modules
-        # Injects <spotbugs.skip>true> into unchanged module poms so the per-module
-        # SpotBugs fork is skipped for them (the lever that actually scopes the cost).
-        # Full compile is preserved (correct aux-classpath); a build/config change ->
-        # full scan. pull_request only; master/snapshot run a full scan.
+        # Injects <spotbugs.skip>true> into unchanged module poms so their analysis is
+        # skipped, and exports SPOTBUGS_SCOPE_ARGS (-pl <changed> -am) so only the
+        # changed modules and their upstream deps build at all (skip-injected deps
+        # compile for the aux-classpath but are not analysed). A build/config change ->
+        # full scan, full reactor. pull_request only; master/snapshot run a full scan.
         run: bash .github/scripts/compute-spotbugs-skip.sh "${{ github.event.pull_request.base.sha }}"
 
       - name: SpotBugs report (SARIF)
@@ -189,8 +190,12 @@ jobs:
         # working tree is dirty here; this job releases nothing, so we tell Tycho's jgit
         # build-qualifier to use the last commit's timestamp instead of failing (the
         # repo keeps jgit.dirtyWorkingTree=error for maven-verify / releases).
+        # Skipped entirely when the scope step kept no modules (e.g. a docs-only
+        # PR): every module would carry spotbugs.skip, so the compile output
+        # would be unused. The gate below relaxes on the same condition.
+        if: env.SPOTBUGS_KEPT != '0'
         run: |
-          mvn -T 2C -f ./ddk-parent/pom.xml --batch-mode --fail-never \
+          mvn -T 2C -f ./ddk-parent/pom.xml ${SPOTBUGS_SCOPE_ARGS:-} --batch-mode --fail-never \
             compile \
             spotbugs:spotbugs \
             -Dspotbugs.sarifOutput=true \
@@ -220,6 +225,8 @@ jobs:
         # suppresses even compile/resolution failures) — never a clean pass.
         # Exception: the scope step skip-injected every module (no reactor module
         # changed, e.g. a docs-only PR), where zero reports is the expected state.
+        # Each scanned source-bearing module must additionally have produced its
+        # own SARIF, so a partially-dead scoped build cannot hide either.
         run: |
           set -eu
           if [ "${SPOTBUGS_KEPT:-}" = "0" ]; then
 
@@ -91,9 +91,15 @@ the count-gate *stricter* than `:check` (over-fail, never under-fail), each guar
 
 ## Two operational rules
 
-- **`compile` must be full-reactor** (`-f ddk-parent/pom.xml`, no `-pl`). PMD's
-  type-resolving rules need the complete aux-classpath; a `-pl` subset produces
-  false positives (the trailing-`Throwable` case).
+- **A changed module must compile against its complete aux-classpath**, or PMD's
+  type-resolving rules false-positive (the trailing-`Throwable` case). A bare `-pl <module>`
+  subset breaks this, but `-pl <changed> -am` does not: `--also-make` restores the module's
+  dependency closure, which compiles for the classpath even though those deps carry the
+  analysis skip. Tycho adds each bundle's MANIFEST requirements (`Require-Bundle`,
+  `Import-Package`) to the Maven project model, so `-am` pulls in reactor siblings required
+  that way too. `ddk-target` is the one edge with no MANIFEST reference at all, so it is
+  pinned explicitly into every scoped reactor (a cold cache without it fails loudly rather
+  than resolving a stale target).
 - **Merge SARIFs from SARIF files only.** Code Scanning accepts one run per category,
   so per-module SARIFs are merged (jq) before upload. The `ddk-parent` aggregator emits
   plain-XML `checkstyle-result.xml`; the merge must filter to JSON-parseable files.