diff --git a/.github/workflows/measure-unread-surface.yml b/.github/workflows/measure-unread-surface.yml
new file mode 100644
index 0000000..6cd44f6
--- /dev/null
+++ b/.github/workflows/measure-unread-surface.yml
@@ -0,0 +1,65 @@
+# Measure the file surface no scan has ever read.
+#
+# The sweep fetches one file per skill (SKILL.md), so every verdict describes
+# the documentation. This samples SKILL.md from the registry, extracts the
+# paths each one names, and reports how much executable code ships alongside
+# that no scan has looked at.
+
+name: Measure Unread Surface
+
+on:
+  workflow_dispatch:
+    inputs:
+      sample:
+        description: "How many random skills to fetch (0.55s each, so 300 ~= 3 min)"
+        type: string
+        default: "300"
+      seed:
+        description: "Sampling seed, fixed so the number is reproducible"
+        type: string
+        default: "20260816"
+
+permissions:
+  contents: read
+
+jobs:
+  measure:
+    name: Sample SKILL.md and extract referenced paths
+    runs-on: ubuntu-latest
+    timeout-minutes: 45
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: "3.13"
+
+      - name: Install httpx
+        run: pip install httpx
+
+      - name: Fetch the current snapshot
+        run: |
+          mkdir -p data/registry-snapshots
+          git fetch origin registry-snapshots
+          git show origin/registry-snapshots:data/registry-snapshots/latest.json \
+            > data/registry-snapshots/latest.json
+          echo "Snapshot: $(jq -r .created_at data/registry-snapshots/latest.json)"
+
+      - name: Measure
+        env:
+          SAMPLE: ${{ github.event.inputs.sample }}
+          SEED: ${{ github.event.inputs.seed }}
+        run: |
+          python scripts/extract-referenced-files.py \
+            data/registry-snapshots/latest.json \
+            --sample "$SAMPLE" --seed "$SEED" \
+            --json referenced-files.json
+
+      - name: Upload the path map
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: referenced-files
+          path: referenced-files.json
+          retention-days: 14
diff --git a/scripts/extract-referenced-files.py b/scripts/extract-referenced-files.py
new file mode 100644
index 0000000..35b63b7
--- /dev/null
+++ b/scripts/extract-referenced-files.py
@@ -0,0 +1,214 @@
+#!/usr/bin/env python3
+"""Find the files a skill ships that no scan has ever read.
+
+Every sweep this project has run fetches exactly one file per skill::
+
+    content = await client.get_skill_file(meta.slug)   # path defaults to SKILL.md
+
+So all 74,158 verdicts are verdicts on the documentation. The registry serves
+the rest of the tree happily -- ``scripts/buddy-algorithm.js`` and
+``scripts/generate-image.ts`` both return real content -- which means a skill
+whose SKILL.md is clean and whose script beacons to a C2 is invisible to us, to
+a reviewer skimming the listing, and to the user. That is the definition of
+hidden behaviour, and it is the only place worth hunting for real malware.
+
+This is step one: extract the paths each SKILL.md references, so the size of
+the unread surface can be measured before anything is fetched.
+
+Deliberately conservative. A path is only reported when the skill *names* it in
+a way that implies execution or inclusion. Guessing at conventional layouts
+would inflate the count with files that do not exist, and an inflated
+denominator is how you end up reporting a blind spot larger than the one you
+have.
+
+Usage:
+    extract-referenced-files.py <snapshot.json> [--json out.json] [--limit N]
+"""
+
+from __future__ import annotations
+
+import argparse
+import asyncio
+import json
+import random
+import re
+import sys
+from collections import Counter
+from pathlib import Path
+from typing import Any
+
+BASE_URL = "https://clawhub.ai/api/v1"
+
+# Interpreters and runners whose argument is a file the skill expects to run.
+_RUNNERS = r"(?:node|python3?|bun|deno|ts-node|tsx|bash|sh|zsh|ruby|perl|php|Rscript)"
+
+# Ways a SKILL.md names a file it ships. Each must capture the path in group 1.
+_PATTERNS: list[tuple[re.Pattern[str], str]] = [
+    # Executed by an interpreter: `node scripts/foo.js`, `python3 ./bin/x.py`.
+    # ${SKILL_DIR}/ and ./ prefixes are stripped by _clean.
+    (
+        re.compile(
+            rf"\b{_RUNNERS}\s+(?:\$\{{SKILL_DIR\}}/|\./)?"
+            r"([\w./-]+\.(?:js|mjs|cjs|ts|tsx|py|sh|bash|rb|pl|php|R))\b"
+        ),
+        "executed",
+    ),
+    # Explicit "Read `path`" instructions, which the agent will follow.
+    (
+        re.compile(r"\b(?:Read|read|Load|load|See|see)\s+`([\w./-]+\.[\w]+)`"),
+        "read-instruction",
+    ),
+    # Markdown link or bare mention of a repo-relative source/doc file.
+    (
+        re.compile(
+            r"[\(\[`\s](?:\./)?"
+            r"((?:scripts|bin|lib|src|tools|references|assets|specs)/[\w./-]+"
+            r"\.(?:js|mjs|cjs|ts|tsx|py|sh|bash|rb|pl|php|R|md|json|ya?ml|toml))"
+        ),
+        "referenced",
+    ),
+]
+
+# Paths that are not part of the skill: the file we already scan, and things
+# that belong to the user's project rather than the package.
+_SKIP = re.compile(
+    r"^(?:SKILL\.md|README\.md|package(?:-lock)?\.json|tsconfig\.json"
+    r"|\.env(?:\.example)?|node_modules/.*|\.\./.*)$",
+    re.IGNORECASE,
+)
+
+
+def _clean(path: str) -> str | None:
+    """Normalise a captured path, or return None if it is not skill-local."""
+    path = path.strip().strip("`'\"")
+    path = re.sub(r"^\$\{SKILL_DIR\}/", "", path)
+    path = re.sub(r"^\./", "", path)
+    if not path or path.startswith(("/", "~", "http")) or ".." in path:
+        return None
+    if _SKIP.match(path):
+        return None
+    # A bare filename with no directory and no extension we recognise is more
+    # likely prose than a shipped file.
+    if "." not in path:
+        return None
+    return path
+
+
+def extract(text: str) -> dict[str, str]:
+    """Return {path: how it was referenced} for one SKILL.md."""
+    found: dict[str, str] = {}
+    for pattern, kind in _PATTERNS:
+        for match in pattern.finditer(text):
+            cleaned = _clean(match.group(1))
+            if cleaned and cleaned not in found:
+                found[cleaned] = kind
+    return found
+
+
+async def sample_registry(slugs: list[str]) -> dict[str, str]:
+    """Fetch SKILL.md for each slug. Requires network reach to the registry."""
+    import httpx
+
+    out: dict[str, str] = {}
+    async with httpx.AsyncClient(timeout=20.0, follow_redirects=True) as client:
+        for i, slug in enumerate(slugs, 1):
+            try:
+                resp = await client.get(
+                    f"{BASE_URL}/skills/{slug}/file", params={"path": "SKILL.md"}
+                )
+                if resp.status_code == 200:
+                    out[slug] = resp.text
+            except Exception as exc:
+                print(f"  {slug}: {type(exc).__name__}: {exc}", flush=True)
+            if i % 50 == 0:
+                print(f"  ...fetched {i}/{len(slugs)}", flush=True)
+            await asyncio.sleep(0.55)
+    return out
+
+
+def main() -> int:
+    ap = argparse.ArgumentParser(description=__doc__)
+    ap.add_argument("snapshot", type=Path)
+    ap.add_argument("--json", type=Path, help="write {slug: {path: kind}} here")
+    ap.add_argument("--limit", type=int, default=0, help="cap skills examined")
+    ap.add_argument(
+        "--sample",
+        type=int,
+        default=0,
+        help="fetch this many random SKILL.md from the registry (needs network)",
+    )
+    ap.add_argument("--seed", type=int, default=20260816, help="sampling seed")
+    args = ap.parse_args()
+
+    snapshot = json.loads(args.snapshot.read_text(encoding="utf-8"))
+    skills: dict[str, Any] = snapshot.get("skills", {})
+
+    # The snapshot records verdicts and hashes, not content, so the text has to
+    # come from the registry. Sampling is honest about that: it reports the
+    # fraction over skills actually fetched rather than extrapolating silently.
+    if args.sample:
+        # Reproducible sampling, not cryptography: the seed is published so
+        # anyone can draw the same sample and check the number.
+        rng = random.Random(args.seed)  # noqa: S311
+        chosen = rng.sample(sorted(skills), min(args.sample, len(skills)))
+        texts = asyncio.run(sample_registry(chosen))
+        items = [(s, {"__text__": t}) for s, t in texts.items()]
+        print(f"\nfetched {len(texts)}/{len(chosen)} sampled SKILL.md\n")
+    else:
+        items = list(skills.items())
+    if args.limit:
+        items = items[: args.limit]
+
+    with_text = 0
+    no_text = 0
+    refs: dict[str, dict[str, str]] = {}
+    kinds: Counter[str] = Counter()
+    exts: Counter[str] = Counter()
+
+    for slug, rec in items:
+        text = rec.get("__text__") or rec.get("description") or ""
+        if not text:
+            no_text += 1
+            continue
+        with_text += 1
+        found = extract(text)
+        if found:
+            refs[slug] = found
+            for path, kind in found.items():
+                kinds[kind] += 1
+                exts[Path(path).suffix.lower()] += 1
+
+    total_paths = sum(len(v) for v in refs.values())
+    print(f"snapshot:                     {args.snapshot}")
+    print(f"skills in snapshot:           {len(skills):,}")
+    print(f"  with SKILL.md text held:    {with_text:,}")
+    print(f"  text not held (cannot say): {no_text:,}")
+    print()
+    print(f"skills referencing files we never scan: {len(refs):,}"
+          + (f"  ({len(refs)/with_text:.1%} of those readable)" if with_text else ""))
+    print(f"distinct referenced paths:              {total_paths:,}")
+    print()
+    print("how they are referenced:")
+    for kind, n in kinds.most_common():
+        print(f"  {kind:<18} {n:,}")
+    print()
+    print("by extension:")
+    for ext, n in exts.most_common(12):
+        print(f"  {ext or '(none)':<10} {n:,}")
+
+    executable = sum(
+        1 for v in refs.values()
+        for p in v if Path(p).suffix.lower() in
+        {".js", ".mjs", ".cjs", ".ts", ".tsx", ".py", ".sh", ".bash", ".rb", ".pl", ".php"}
+    )
+    print()
+    print(f"of those, executable code:              {executable:,}")
+
+    if args.json:
+        args.json.write_text(json.dumps(refs, indent=2), encoding="utf-8")
+        print(f"\nwrote {args.json}")
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())