fix: confine compare-evidence output to the successor private artifact root

CHANGELOG.md

@@ -8,6 +8,8 @@ This project uses a Keep a Changelog-style structure. Until a tagged release is
 
 ### Changed
 
+- `compare-evidence` now accepts `--output` only inside the successor run's private artifact root, as `compare-runs` and `compare-targets` already did, and checks it after both runs validate so a rejected path no longer creates parent directories. Scripts that wrote the comparison elsewhere must point `--output` at the `--after` run's artifact root; the saved-evidence example and the command usage line show the new form.
+
 - Node.js 22 or later is now required (package `engines`, `doctor`, the Web capability contract and the documentation). Node.js 20 reached end of life on 2026-04-30 and is no longer supported or tested. CI runs Node.js 22 and 24 on Ubuntu, Windows and macOS; workflow actions move to versions that run on Node.js 24 and are pinned by commit, and the browser E2E workflows pin Ubuntu 24.04. Contributors install test dependencies with `npm install` through a root `package.json`, which also stops an unrelated parent-directory `package.json` from capturing the install.
 
 - HTTP target observation always runs through the logged, size-bounded network session under the saved run policy. The second retrieval path, reachable only by direct library callers, did not reject content encodings, cap total bytes or keep a request log; it was removed. No CLI command used it.

docs/cli-reference.md

@@ -512,7 +512,7 @@ Notes:
 Compare validated saved evidence before and after a change, for private review.
 
 Usage:
-  accessibility-audit compare-evidence --before <run.json> --after <run.json> --output <new-private-comparison.json>
+  accessibility-audit compare-evidence --before <run.json> --after <run.json> --output <after-artifacts/new-private-comparison.json>
 
 Notes:
   - Both runs and their saved files are revalidated. Results describe byte changes, not accessibility outcomes.
@@ -524,7 +524,7 @@ Notes:
 変更前後の検証済み保存証拠を、非公開レビュー用に比較します。
 
 使用方法:
-  accessibility-audit compare-evidence --before <run.json> --after <run.json> --output <new-private-comparison.json>
+  accessibility-audit compare-evidence --before <run.json> --after <run.json> --output <after-artifacts/new-private-comparison.json>
 
 注意:
   - Both runs and their saved files are revalidated. Results describe byte changes, not accessibility outcomes.

shared/skill/references/saved-evidence.md

@@ -84,10 +84,12 @@ in addition to registered artifact snapshots.
 ## Private before/after comparison
 
 ```text
-node <skill_root>/scripts/accessibility-audit.mjs compare-evidence --before before/run.json --after after/run.json --output comparison.private.json
+node <skill_root>/scripts/accessibility-audit.mjs compare-evidence --before before/run.json --after after/run.json --output after/artifacts/comparison.private.json
 ```
 
-Both runs and their referenced files must validate. Results group captures by
+The output must be a new file inside the after-run's private artifact root
+(`after/artifacts` in this example). Both runs and their referenced files must
+validate. Results group captures by
 screening requirement, exact target reference and evidence type. Status is
 `added`, `removed`, `bytes_changed` or `bytes_unchanged`. `context_changed` separately
 identifies changes to the declared version, target context or environment, even

shared/skill/scripts/compare-audit-evidence.mjs

@@ -3,6 +3,14 @@ import { pathToFileURL } from "node:url";
 import { assertNewOutputPath, assertStableFile, assertValidatedRunStable, readStableFile, validateAuditRun, writeNewJson } from "./lib/audit-run.mjs";
 import { compareEvidenceReferences } from "./lib/run-evidence.mjs";
 
+function insidePrivateRoot(root, file) {
+  const absolute = path.resolve(file), relative = path.relative(root, absolute);
+  if (!relative || path.isAbsolute(relative) || relative === ".." || relative.startsWith(`..${path.sep}`)) {
+    throw new Error("Comparison outputs must stay inside the successor private artifact root.");
+  }
+  return assertNewOutputPath(absolute);
+}
+
 export function main(argv = process.argv.slice(2)) {
   const options = {};
   for (let i = 0; i < argv.length; i += 2) {
@@ -12,7 +20,6 @@ export function main(argv = process.argv.slice(2)) {
     options[argv[i]] = argv[i + 1];
   }
   for (const flag of ["--before", "--after", "--output"]) if (!options[flag]) throw new Error(`${flag} is required`);
-  assertNewOutputPath(options["--output"]);
   const inputs = [options["--before"], options["--after"]].map((file) => {
     const snapshot = readStableFile(file);
     const run = JSON.parse(snapshot.bytes.toString("utf8").replace(/^\uFEFF/u, ""));
@@ -23,6 +30,7 @@ export function main(argv = process.argv.slice(2)) {
     return { run, snapshot, validation, rows: screenings.flatMap((artifact) => artifact.payload.observations) };
   });
   const [before, after] = inputs;
+  insidePrivateRoot(after.validation.artifactRoot, options["--output"]);
   const result = { schema_version: "1.0.0", publication: "private_by_default", before_run_id: before.run.run_id, after_run_id: after.run.run_id,
     limitation: "Byte differences are not accessibility judgements or proof that a live target still matches its capture.",
     comparisons: compareEvidenceReferences(before.rows, after.rows) };

shared/skill/scripts/lib/cli-command-registry.mjs

@@ -119,7 +119,7 @@ const definitions = [
     name: "compare-evidence",
     script: "compare-audit-evidence.mjs",
     summary: "Compare validated saved evidence before and after a change, for private review.",
-    usage: ["accessibility-audit compare-evidence --before <run.json> --after <run.json> --output <new-private-comparison.json>"],
+    usage: ["accessibility-audit compare-evidence --before <run.json> --after <run.json> --output <after-artifacts/new-private-comparison.json>"],
     notes: ["Both runs and their saved files are revalidated. Results describe byte changes, not accessibility outcomes."]
   },
   {

tests/run-evidence.test.mjs

@@ -172,15 +172,19 @@ test("bind-evidence creates a new artifact from captured bytes without changing
   assert.doesNotThrow(() => registerArtifact(f.run, bound, { runFile: f.runFile, artifactFile: output }));
 });
 
-test("comparison records before/after bytes, dates and versions without interpreting outcomes", (t) => {
+test("comparison writes inside the after-run private artifact root without interpreting outcomes", (t) => {
   const before = fixture(t);
   const after = fixture(t, { suffix: "0002", version: "release-2", bytes: Buffer.from("<main>Changed content</main>") });
   const beforeFile = path.join(before.temp, "registered.json");
   const afterFile = path.join(after.temp, "registered.json");
   writeNewJson(beforeFile, before.register());
   writeNewJson(afterFile, after.register());
-  const output = path.join(after.temp, "comparison.json");
-  pass(cli(["compare-evidence", "--before", beforeFile, "--after", afterFile, "--output", output]));
+  const output = path.join(after.artifactRoot, "comparison.json");
+  const args = ["compare-evidence", "--before", beforeFile, "--after", afterFile, "--output", output];
+  pass(cli(args));
+  const saved = fs.readFileSync(output);
+  assert.equal(cli(args).status, 1, "existing output is never overwritten");
+  assert.deepEqual(fs.readFileSync(output), saved);
   const result = json(output);
   assert.equal(result.publication, "private_by_default");
   assert.equal(result.comparisons[0].status, "bytes_changed");
@@ -200,3 +204,19 @@ test("comparison records before/after bytes, dates and versions without interpre
   const evidence = collectScreeningEvidence(before.run, [before.artifact], () => ({ bytes: before.bytes, sha256: hash(before.bytes) }));
   assert.deepEqual(evidence.errors, []);
 });
+
+test("comparison rejects outputs outside the successor private artifact root without writing", (t) => {
+  const before = fixture(t);
+  const after = fixture(t, { suffix: "0002" });
+  const beforeFile = path.join(before.temp, "registered.json");
+  const afterFile = path.join(after.temp, "registered.json");
+  writeNewJson(beforeFile, before.register());
+  writeNewJson(afterFile, after.register());
+  for (const output of [path.join(after.temp, "comparison.json"), path.join(before.artifactRoot, "comparison.json"), path.join(`${after.artifactRoot}-outside`, "comparison.json")]) {
+    const result = cli(["compare-evidence", "--before", beforeFile, "--after", afterFile, "--output", output]);
+    assert.equal(result.status, 1);
+    assert.match(result.stderr, /Comparison outputs must stay inside the successor private artifact root\./);
+    assert.equal(fs.existsSync(output), false);
+  }
+  assert.equal(fs.existsSync(`${after.artifactRoot}-outside`), false);
+});