diff --git a/CHANGELOG.md b/CHANGELOG.md
index b933140..7b8e52e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -85,10 +85,12 @@ across the whole thing, honestly*.
   paths re-prefixed so the by-file/focus join stays coherent (Phase 2). The
   scc-measured **codebase statistics** recover too: each sub-package's totals are
   re-aggregated from the *one* cached `scc --by-file` walk, sliced to its subtree
-  (reuse, never re-walk), labelled per package (`api/codebase-stats`) — Phase 2b,
-  first increment. A single package / declared workspace is unchanged
-  (byte-identical). Declared workspaces (npm/pnpm/yarn/nx/turbo/lerna) are healthy
-  and don't alarm.
+  (reuse, never re-walk), labelled per package (`api/codebase-stats`). **Code
+  duplication** recovers with its engine re-routed per sub-package — jscpd *in*
+  each node package (npm), lizard over the inventory file list sliced to the
+  subtree — labelled (`svc/duplication`). (Phase 2b.) A single package / declared
+  workspace is unchanged (byte-identical). Declared workspaces
+  (npm/pnpm/yarn/nx/turbo/lerna) are healthy and don't alarm.
 - **`lizard`** as a true multi-language complexity + duplication engine, and a
   **Focus Areas** view synthesising the forensic axes (#36–#38).
 - **Command profiles** + a **`.checkup.yml`** override layer (stack / checks /
diff --git a/bin/checkup.sh b/bin/checkup.sh
index 2d882c3..21a0496 100755
--- a/bin/checkup.sh
+++ b/bin/checkup.sh
@@ -1370,7 +1370,40 @@ DUP_INTENT=$(jq -n '{
     fail_means: "≥5% duplication. Refactor toward shared helpers when the same pattern recurs 3+ times. NOTE: Classic ASP/VBScript has no tokeniser in either engine, so .asp duplication is not measured."
 }')
 
-if [ "$DETECT_ENGINE_DUPLICATION" = "jscpd" ]; then
+# Per-package recovery (#78 increment 3): duplication is engine-routed (jscpd on
+# node packages, lizard elsewhere). On an undeclared fan-out, measure EACH
+# assessment root with its OWN engine — jscpd runs IN the package (npm, cwd =
+# the child), lizard reads the inventory file list sliced to the subtree. Single
+# package / declared workspace → one iteration at "." reusing the whole-tree
+# engine + probes, no cd, SLUG_NS empty → byte-identical to before (the gate).
+for TOPO_ROOT in "${TOPO_ASSESSMENT_ROOTS[@]}"; do
+_RECOVER_CWD="$PWD"; SLUG_NS=""; DUP_SUBTREE="."
+if [ "$TOPO_ROOT" = "." ]; then
+    DUP_ENGINE="$DETECT_ENGINE_DUPLICATION"; DUP_REASON_R="$DUP_REASON"
+else
+    cd "$TARGET/$TOPO_ROOT" 2>/dev/null || { cd "$_RECOVER_CWD"; continue; }
+    SLUG_NS="$TOPO_ROOT"; DUP_SUBTREE="$TOPO_ROOT"
+    echo -e "${BLUE}📦 Sub-package: $TOPO_ROOT${NC}"
+    # Re-route the engine for THIS child (mirrors the whole-tree routing, scoped to
+    # the subtree): a node package (own package.json + JS/TS-dominant source, or no
+    # scc read) with npm → jscpd; else lizard-parseable source under the child →
+    # lizard; else an honest skip. The child's stack is read from the ONE cached scc
+    # walk, sliced to the subtree (reuse, never re-walk).
+    DUP_ENGINE="none"; DUP_REASON_R="no Node target for jscpd and no lizard-parseable source in $TOPO_ROOT"
+    _CHILD_PRIMARY=""
+    if [ "${SCC_BYFILE_OK:-false}" = true ]; then
+        _CHILD_PRIMARY=$(scc_breakdown "$(scc_keep_for_root "$TOPO_ROOT")" < "$SCC_BYFILE" \
+            | jq -c -f "$CHECKUP_HOME/lib/detect-stacks.jq" 2>/dev/null | jq -r '.[0].stack // ""' 2>/dev/null)
+    fi
+    if [ -f package.json ] && command -v npm > /dev/null 2>&1 \
+       && { [ "$_CHILD_PRIMARY" = "node" ] || [ -z "$_CHILD_PRIMARY" ]; }; then
+        DUP_ENGINE="jscpd"; DUP_REASON_R="node package → jscpd (exact-token)"
+    elif [ -n "$LIZARD_BIN" ] && [ -n "$(inventory_paths_under "$TOPO_ROOT" "$INV_LIZARD_RE" | head -c1)" ]; then
+        DUP_ENGINE="lizard"; DUP_REASON_R="lizard-parseable source → lizard -Eduplicate (identifier-unified)"
+    fi
+fi
+
+if [ "$DUP_ENGINE" = "jscpd" ]; then
     # ---- Tier 1: jscpd (Node best-fit; engine chosen by the detector, #7) ----
     echo "Command: npm run quality:duplicates"
     echo ""
@@ -1427,7 +1460,7 @@ if [ "$DETECT_ENGINE_DUPLICATION" = "jscpd" ]; then
         write_parsed "duplication" "$JSCPD_STATUS" "$DUPLICATION_LINES" "${DUPLICATION_PCT}% duplication across $DUPLICATION_LINES lines (jscpd)" "$JSCPD_TOP" "$DUP_INTENT"
     fi
     fi
-elif [ "$DETECT_ENGINE_DUPLICATION" = "lizard" ]; then
+elif [ "$DUP_ENGINE" = "lizard" ]; then
     # ---- Tier 2: lizard -Eduplicate (language-agnostic clone detection) ----
     echo "Command: lizard -Eduplicate (excluding generated/vendored/repetitive paths)"
     echo ""
@@ -1438,7 +1471,7 @@ elif [ "$DETECT_ENGINE_DUPLICATION" = "lizard" ]; then
     # list is non-empty.
     # Feed the file list via a temp file + xargs (run_tool_filelist), not a bash
     # array on argv — a large tree overflows ARG_MAX otherwise (exit 126).
-    DUP_LIST=$(mktemp); inventory_paths "$INV_LIZARD_RE" > "$DUP_LIST"
+    DUP_LIST=$(mktemp); inventory_paths_under "$DUP_SUBTREE" "$INV_LIZARD_RE" > "$DUP_LIST"
     DUP_N=$(filelist_count "$DUP_LIST")
     if [ "$DUP_N" -gt "$CHECKUP_LIZARD_MAX_FILES" ]; then
         # Single-pass clone detection holds every file's tokens in memory; on a
@@ -1460,7 +1493,7 @@ elif [ "$DETECT_ENGINE_DUPLICATION" = "lizard" ]; then
     else
         # Parse lizard's text report: each "Duplicate block:" lists the cloned
         # locations as `file:start ~ end`; the footer gives the overall rate.
-        DUP_PARSED=$(python3 - "$LAST_RAW" "$TARGET" <<'PY' || echo '{"rate":0,"count":0,"top":[]}'
+        DUP_PARSED=$(python3 - "$LAST_RAW" "$PWD" <<'PY' || echo '{"rate":0,"count":0,"top":[]}'
 import sys, json, re
 path, target = sys.argv[1], sys.argv[2]
 text = open(path, errors="replace").read()
@@ -1518,9 +1551,12 @@ PY
     fi
     fi   # end CHECKUP_LIZARD_MAX_FILES cap guard
 else
-    echo -e "${BLUE}ℹ️  Skipped — $DUP_REASON${NC}"
-    write_skipped "duplication" "$DUP_REASON" "$DUP_INTENT"
+    echo -e "${BLUE}ℹ️  Skipped — $DUP_REASON_R${NC}"
+    write_skipped "duplication" "$DUP_REASON_R" "$DUP_INTENT"
 fi
+
+cd "$_RECOVER_CWD"; SLUG_NS=""
+done
 echo ""
 
 # ─── Topology recover pass (#78) — project-built cluster C (per-package code health) ─
diff --git a/docs/architecture.md b/docs/architecture.md
index 3a5e52c..5f65948 100644
--- a/docs/architecture.md
+++ b/docs/architecture.md
@@ -212,9 +212,10 @@ dependency-health (`npm-audit`, `deps-freshness`, `circular-deps`), correctness/
 `unused-code` + `coverage` clusters (Phase 2/2b increment 1), plus the
 scc-measured **`codebase-stats`** — re-aggregated per sub-package by slicing the
 *one* cached `scc --by-file` walk to each root's subtree (`scc_keep_for_root`;
-reuse, never re-walk), so no extra scc cost (Phase 2b increment 2). Still
-root-scoped: the engine-routed `complexity` and `duplication`, which need their
-engine (eslint / lizard / jscpd) re-routed per sub-package — the remaining slice.
+reuse, never re-walk), so no extra scc cost — and **`duplication`**, whose engine
+is re-routed per child (jscpd *in* each node package; lizard over the inventory
+sliced to the subtree via `inventory_paths_under`) (Phase 2b). Still root-scoped:
+the engine-routed `complexity` (eslint / lizard / scc merge), the remaining slice.
 Honesty survives recovery: a
 sub-package whose toolchain can't run still `skip`s with a reason (never
 green-by-default), the floor laid in #85.
diff --git a/lib/source-inventory.sh b/lib/source-inventory.sh
index f2b9713..d88b7c0 100644
--- a/lib/source-inventory.sh
+++ b/lib/source-inventory.sh
@@ -262,6 +262,29 @@ inventory_paths() {
     done < "$SOURCE_LST"
 }
 
+# Emit (NUL-delimited) the inventory paths under <root>, RELATIVE to <root> (the
+# "<root>/" prefix stripped), filtered by [re] like inventory_paths. The
+# per-package measurement recover pass (#78): a section cd'd into a sub-package
+# needs its slice of the whole-tree inventory with CWD-relative paths (so lizard,
+# run in the package, finds them). <root> "." is the identity — the whole
+# inventory, TARGET-relative — so a single package / declared workspace is
+# byte-identical to inventory_paths. Consume like inventory_paths.
+inventory_paths_under() {
+    local root="$1" re="${2:-}" p pre
+    [ -f "${SOURCE_LST:-}" ] || return 0
+    if [ "$root" = "." ]; then
+        inventory_paths "$re"
+        return 0
+    fi
+    pre="${root#./}/"
+    while IFS= read -r -d '' p; do
+        case "$p" in "$pre"*) ;; *) continue ;; esac
+        p="${p#"$pre"}"
+        [ -z "$re" ] || [[ "$p" =~ $re ]] || continue
+        printf '%s\0' "$p"
+    done < "$SOURCE_LST"
+}
+
 # The inventory as a JSON array of paths — for filtering a scanner's findings
 # back to the tracked set (e.g. ESLint, which traverses on its own).
 inventory_json() {
diff --git a/test/source-inventory.test.sh b/test/source-inventory.test.sh
index 82768eb..3b2e5c7 100755
--- a/test/source-inventory.test.sh
+++ b/test/source-inventory.test.sh
@@ -227,6 +227,21 @@ assert_eq "git scope → .gitignore"        ".gitignore"               "$(SOURCE
 assert_eq "override:git scope → .gitignore" ".gitignore"             "$(SOURCE_SCOPE=override:git inventory_exclusion_source)"
 assert_eq "find scope → builtin excludes"  "builtin excludes (no VCS)" "$(SOURCE_SCOPE=find inventory_exclusion_source)"
 
+echo ""
+echo "inventory_paths_under: per-subtree slice, CWD-relative (#78 increment 3)"
+SOURCE_LST="$TMP/under.lst"
+printf 'api/src/a.ts\0api/src/b.js\0api/README.md\0web/app.ts\0top.ts\0' > "$SOURCE_LST"
+under() { inventory_paths_under "$@" | tr '\0' '\n' | sort | paste -sd',' -; }
+assert_eq "root '.' is the identity (whole inventory, TARGET-relative)" \
+    "api/README.md,api/src/a.ts,api/src/b.js,top.ts,web/app.ts" "$(under .)"
+assert_eq "child slice strips the '<root>/' prefix (CWD-relative)" \
+    "README.md,src/a.ts,src/b.js" "$(under api)"
+assert_eq "child slice + extension filter" \
+    "src/a.ts" "$(under api '\.ts$')"
+assert_eq "'.' identity + extension filter matches inventory_paths" \
+    "$(inventory_paths '\.ts$' | tr '\0' '\n' | sort | paste -sd',' -)" "$(under . '\.ts$')"
+assert_eq "no-match subtree → empty" "" "$(under nope)"
+
 echo ""
 echo "eslint_flat_config_root: gates the ESLint complexity slice (#79)"
 CFG="$TMP/cfgprobe"; mkdir -p "$CFG/pkg"