diff --git a/docs/install-sync.md b/docs/install-sync.md
index d92dcb1..52a6df7 100644
--- a/docs/install-sync.md
+++ b/docs/install-sync.md
@@ -27,6 +27,7 @@ powershell -ExecutionPolicy Bypass -File .\scripts\install-skill.ps1 -Skill repa
 powershell -ExecutionPolicy Bypass -File .\scripts\install-skill.ps1 -Skill regression-validation-gate-runner
 powershell -ExecutionPolicy Bypass -File .\scripts\install-skill.ps1 -Skill review-bundle-audit
 powershell -ExecutionPolicy Bypass -File .\scripts\install-skill.ps1 -Skill review-context-builder
+powershell -ExecutionPolicy Bypass -File .\scripts\install-skill.ps1 -Skill routing-behavior-diff-audit
 ```
 
 Use `-Force` to back up and replace an existing installed copy:
@@ -38,6 +39,7 @@ powershell -ExecutionPolicy Bypass -File .\scripts\install-skill.ps1 -Skill repa
 powershell -ExecutionPolicy Bypass -File .\scripts\install-skill.ps1 -Skill regression-validation-gate-runner -Force
 powershell -ExecutionPolicy Bypass -File .\scripts\install-skill.ps1 -Skill review-bundle-audit -Force
 powershell -ExecutionPolicy Bypass -File .\scripts\install-skill.ps1 -Skill review-context-builder -Force
+powershell -ExecutionPolicy Bypass -File .\scripts\install-skill.ps1 -Skill routing-behavior-diff-audit -Force
 ```
 
 `-All` installs only registry rows with an installable status and `default` install policy. Optional Skills must be named explicitly.
diff --git a/registry/skills-index.md b/registry/skills-index.md
index 379292a..9bb0479 100644
--- a/registry/skills-index.md
+++ b/registry/skills-index.md
@@ -20,6 +20,7 @@ Existing CCPE content is not migrated here.
 | `regression-validation-gate-runner` | Dry-run or execute project-declared regression and validation gates from a manifest while capturing logs, exit codes, durations, skipped gates, and changed-file notes. | `C:\Users\wangq\Documents\Codex\skills-vault\skills\regression-validation-gate-runner` | `installed` | `default` | `C:\Users\wangq\.agents\skills\regression-validation-gate-runner` | none |
 | `review-bundle-audit` | Preflight review, handoff, release, CCRA, Web upload, or code-review bundle directories for required files, manifests, sidecars, reports, zip readability, warnings, and blockers. | `C:\Users\wangq\Documents\Codex\skills-vault\skills\review-bundle-audit` | `installed` | `default` | `C:\Users\wangq\.agents\skills\review-bundle-audit` | none |
 | `review-context-builder` | Build file-first review, audit, planning, release, handoff, PR, or Agent invocation context indexes and manifests from configured local source roots, patterns, and metadata. | `C:\Users\wangq\Documents\Codex\skills-vault\skills\review-context-builder` | `installed` | `default` | `C:\Users\wangq\.agents\skills\review-context-builder` | none |
+| `routing-behavior-diff-audit` | Compare before/after selector, classifier, or routing outputs for targeted changes, collateral non-target changes, no-call changes, missing cases, and expected-route mismatch changes. | `C:\Users\wangq\Documents\Codex\skills-vault\skills\routing-behavior-diff-audit` | `installed` | `default` | `C:\Users\wangq\.agents\skills\routing-behavior-diff-audit` | none |
 | `voice-generation` | Generate spoken audio from Markdown scripts using the local `voice-gen` CLI and MiniMax `mmx`, including custom voice clone registration and voice registry management. | `D:\AI\ClaudeCode\voice-ge` | `installed` | `conditional` | `C:\Users\wangq\.agents\skills\voice-generation` | none |
 
 ## Status Values
diff --git a/skills/routing-behavior-diff-audit/README.md b/skills/routing-behavior-diff-audit/README.md
new file mode 100644
index 0000000..fe75407
--- /dev/null
+++ b/skills/routing-behavior-diff-audit/README.md
@@ -0,0 +1,43 @@
+# Routing Behavior Diff Audit
+
+Source Skill for deterministic before/after routing result comparison.
+
+The canonical entry point is `SKILL.md`; the deterministic diff engine is in `scripts/routing_behavior_diff_audit.py`.
+
+## Original Source
+
+```text
+Original source: C:\Users\wangq\Documents\Codex\ccpe-system\requirements\skills-vault\2026-06-19-routing-behavior-diff-audit.md
+Migration date: 2026-06-19
+Migration status: first public Skill implementation
+Behavior preserved: deterministic routing-result diff only; no selector edits, expected-label updates, or patch-closure judgment
+Known gaps: Markdown support is limited to fenced JSON/YAML blocks; product-specific meaning remains outside this Skill
+```
+
+## Layout
+
+```text
+SKILL.md
+README.md
+agents/openai.yaml
+fixtures/before.example.json
+fixtures/after.example.json
+scripts/routing_behavior_diff_audit.py
+tests/test_routing_behavior_diff_audit.py
+```
+
+## Usage
+
+```powershell
+conda run -n skills-vault python .\scripts\routing_behavior_diff_audit.py `
+  --before-results C:\path\before.json `
+  --after-results C:\path\after.json `
+  --output-dir C:\path\helper-outputs `
+  --targeted-case CASE-001
+```
+
+## Tests
+
+```powershell
+conda run -n skills-vault python -B -m unittest discover -s skills/routing-behavior-diff-audit/tests -v
+```
diff --git a/skills/routing-behavior-diff-audit/SKILL.md b/skills/routing-behavior-diff-audit/SKILL.md
new file mode 100644
index 0000000..d0f5c16
--- /dev/null
+++ b/skills/routing-behavior-diff-audit/SKILL.md
@@ -0,0 +1,92 @@
+---
+name: routing-behavior-diff-audit
+description: Use when Codex needs to compare before/after selector, routing, QPI, classifier, rules-engine, triage, assignment, or model-governance outputs to identify targeted route changes, collateral non-target changes, no-call changes, missing cases, and new or resolved expected-route mismatches before review, release, handoff, CCRA/local review, or regression closeout.
+---
+
+# Routing Behavior Diff Audit
+
+## Purpose
+
+Run a deterministic before/after behavior diff for rules-based routing outputs. Use the bundled script to compare case IDs, routes, optional expected routes, missing cases, no-call transitions, and targeted versus non-target changes.
+
+This Skill reports observed differences only. It must not edit routing rules, change regression cases, update expected labels, infer product meaning, or decide whether a patch should close.
+
+## Command
+
+```powershell
+conda run -n skills-vault python .\scripts\routing_behavior_diff_audit.py `
+  --before-results C:\path\before-results `
+  --after-results C:\path\after-results `
+  --output-dir C:\path\review-run `
+  --case-id-field case_id `
+  --route-field route `
+  --expected-route-field expected_route `
+  --targeted-case CASE-001
+```
+
+When installed under `C:\Users\wangq\.agents\skills\routing-behavior-diff-audit`, run from that Skill directory or use the installed script path.
+
+## Inputs
+
+- `--before-results`: JSON, JSONL, or Markdown file, or a directory containing those files.
+- `--after-results`: JSON, JSONL, or Markdown file, or a directory containing those files.
+- `--output-dir`: directory where reports are written.
+- `--case-id-field`: field containing the stable case ID. Default: `case_id`.
+- `--route-field`: field containing the routing decision. Default: `route`.
+- `--expected-route-field`: optional field containing the expected route for failure comparison.
+- `--targeted-case`: repeatable case ID that the patch intentionally targets.
+- `--targeted-cases-file`: optional JSON/YAML list, or object with `targeted_cases`, `case_ids`, or `cases`.
+
+JSON is the stable input target. Directory inputs are scanned recursively for `.json`, `.jsonl`, `.md`, and `.markdown`; Markdown support expects a fenced JSON or YAML block.
+
+## Outputs
+
+The script writes under `output_dir`:
+
+```text
+routing-behavior-diff.md
+routing-behavior-diff.json
+```
+
+The JSON report includes:
+
+- `total_cases_compared`
+- `unchanged_cases`
+- `changed_cases`
+- `targeted_changes`
+- `non_target_changes`
+- `new_failures`
+- `resolved_failures`
+- `missing_before_cases`
+- `missing_after_cases`
+- `diff_table`
+- `machine_readable_summary`
+
+`machine_readable_summary.status` is `PASS`, `ATTENTION`, or `FAIL` for automation routing only. It is not a patch approval, owner approval, CCRA decision, or release decision.
+
+## Comparison Rules
+
+- Compare only case IDs present in both before and after for `total_cases_compared`.
+- Classify after-only IDs as `missing_before_cases`.
+- Classify before-only IDs as `missing_after_cases`.
+- Treat a common case as changed when the route, expected route, no-call status, or expected-route failure status changes.
+- Classify changed cases listed by `--targeted-case` or `--targeted-cases-file` as `targeted_changes`.
+- Classify all other changed cases as `non_target_changes`.
+- Compute `new_failures` and `resolved_failures` only when `--expected-route-field` is supplied and present in the records.
+- Treat empty, null-like, and common no-call spellings such as `no_call`, `no-call`, and `no call` as no-call values.
+
+## Safety
+
+- Read only configured before/after result paths and optional targeted-cases file.
+- Write only `routing-behavior-diff.md` and `routing-behavior-diff.json` under `output_dir`.
+- Do not edit selectors, routing rules, regression cases, expected labels, review bundles, model cards, or governance artifacts.
+- Do not decide acceptance, lifecycle status, patch closure, release readiness, or owner approval.
+
+## Validation
+
+After changing diff behavior, run:
+
+```powershell
+conda run -n skills-vault python -B -m unittest discover -s skills/routing-behavior-diff-audit/tests -v
+conda run -n skills-vault python -B C:\Users\wangq\.codex\skills\.system\skill-creator\scripts\quick_validate.py skills/routing-behavior-diff-audit
+```
diff --git a/skills/routing-behavior-diff-audit/agents/openai.yaml b/skills/routing-behavior-diff-audit/agents/openai.yaml
new file mode 100644
index 0000000..6df2798
--- /dev/null
+++ b/skills/routing-behavior-diff-audit/agents/openai.yaml
@@ -0,0 +1,4 @@
+interface:
+  display_name: "Routing Behavior Diff Audit"
+  short_description: "Compare before/after routing outputs"
+  default_prompt: "Use $routing-behavior-diff-audit to compare before and after routing results and write routing-behavior-diff reports."
diff --git a/skills/routing-behavior-diff-audit/fixtures/after.example.json b/skills/routing-behavior-diff-audit/fixtures/after.example.json
new file mode 100644
index 0000000..d3f85cd
--- /dev/null
+++ b/skills/routing-behavior-diff-audit/fixtures/after.example.json
@@ -0,0 +1,12 @@
+[
+  {
+    "case_id": "CASE-001",
+    "route": "qpi-revised",
+    "expected_route": "qpi-revised"
+  },
+  {
+    "case_id": "CASE-002",
+    "route": "review",
+    "expected_route": "review"
+  }
+]
diff --git a/skills/routing-behavior-diff-audit/fixtures/before.example.json b/skills/routing-behavior-diff-audit/fixtures/before.example.json
new file mode 100644
index 0000000..0e704de
--- /dev/null
+++ b/skills/routing-behavior-diff-audit/fixtures/before.example.json
@@ -0,0 +1,12 @@
+[
+  {
+    "case_id": "CASE-001",
+    "route": "qpi",
+    "expected_route": "qpi"
+  },
+  {
+    "case_id": "CASE-002",
+    "route": "no_call",
+    "expected_route": "review"
+  }
+]
diff --git a/skills/routing-behavior-diff-audit/scripts/routing_behavior_diff_audit.py b/skills/routing-behavior-diff-audit/scripts/routing_behavior_diff_audit.py
new file mode 100644
index 0000000..dbf03ea
--- /dev/null
+++ b/skills/routing-behavior-diff-audit/scripts/routing_behavior_diff_audit.py
@@ -0,0 +1,491 @@
+from __future__ import annotations
+
+import argparse
+import json
+import pathlib
+import re
+import sys
+from typing import Any
+
+
+RESULT_KEYS = ("results", "cases", "records", "items", "diff_table")
+SUPPORTED_SUFFIXES = {".json", ".jsonl", ".md", ".markdown"}
+NO_CALL_VALUES = {"", "none", "null", "no_call", "no-call", "no call", "nocall", "no decision"}
+
+
+def main(argv: list[str] | None = None) -> int:
+    args = parse_args(argv)
+    targeted_cases, targeted_errors = load_targeted_cases(args.targeted_case, args.targeted_cases_file)
+    before_cases, before_errors = load_case_map(
+        args.before_results,
+        args.case_id_field,
+        args.route_field,
+        args.expected_route_field,
+        "before",
+    )
+    after_cases, after_errors = load_case_map(
+        args.after_results,
+        args.case_id_field,
+        args.route_field,
+        args.expected_route_field,
+        "after",
+    )
+    blocking_errors = [*targeted_errors, *before_errors, *after_errors]
+
+    if blocking_errors:
+        summary = empty_summary(blocking_errors)
+        write_reports(args.output_dir, summary)
+        print(f"routing-behavior-diff-audit: {len(blocking_errors)} blocking error(s)", file=sys.stderr)
+        return 1
+
+    summary = compare_cases(before_cases, after_cases, targeted_cases)
+    write_reports(args.output_dir, summary)
+    print(str(args.output_dir / "routing-behavior-diff.json"))
+    return 0
+
+
+def parse_args(argv: list[str] | None) -> argparse.Namespace:
+    parser = argparse.ArgumentParser(
+        description="Compare before/after rules-based routing outputs and write deterministic diff reports.",
+    )
+    parser.add_argument("--before-results", required=True, type=pathlib.Path)
+    parser.add_argument("--after-results", required=True, type=pathlib.Path)
+    parser.add_argument("--output-dir", required=True, type=pathlib.Path)
+    parser.add_argument("--case-id-field", default="case_id")
+    parser.add_argument("--route-field", default="route")
+    parser.add_argument("--expected-route-field", default=None)
+    parser.add_argument("--targeted-case", action="append", default=[])
+    parser.add_argument("--targeted-cases-file", type=pathlib.Path)
+    return parser.parse_args(argv)
+
+
+def load_targeted_cases(raw_cases: list[str], cases_file: pathlib.Path | None) -> tuple[set[str], list[str]]:
+    targeted = {str(case_id) for case_id in raw_cases}
+    errors: list[str] = []
+    if not cases_file:
+        return targeted, errors
+    if not cases_file.exists():
+        return targeted, [f"Targeted cases file not found: {cases_file}"]
+
+    try:
+        loaded = parse_file(cases_file)
+    except ValueError as exc:
+        return targeted, [f"Unable to parse targeted cases file {cases_file}: {exc}"]
+
+    candidate: Any = loaded
+    if isinstance(candidate, dict):
+        for key in ("targeted_cases", "case_ids", "cases"):
+            if key in candidate:
+                candidate = candidate[key]
+                break
+    if not isinstance(candidate, list):
+        return targeted, [f"Targeted cases file must contain a list or object with targeted_cases/case_ids/cases: {cases_file}"]
+
+    for item in candidate:
+        if isinstance(item, dict):
+            for key in ("case_id", "id"):
+                if key in item:
+                    targeted.add(str(item[key]))
+                    break
+        else:
+            targeted.add(str(item))
+    return targeted, errors
+
+
+def load_case_map(
+    root: pathlib.Path,
+    case_id_field: str,
+    route_field: str,
+    expected_route_field: str | None,
+    side: str,
+) -> tuple[dict[str, dict[str, Any]], list[str]]:
+    errors: list[str] = []
+    if not root.exists():
+        return {}, [f"{side} results path not found: {root}"]
+
+    files = collect_input_files(root)
+    if not files:
+        return {}, [f"{side} results path contains no supported files: {root}"]
+
+    cases: dict[str, dict[str, Any]] = {}
+    for path in files:
+        try:
+            parsed = parse_file(path)
+        except ValueError as exc:
+            errors.append(f"Unable to parse {side} file {path}: {exc}")
+            continue
+
+        records = extract_records(parsed)
+        if not records:
+            errors.append(f"No records found in {side} file: {path}")
+            continue
+
+        for record in records:
+            if not isinstance(record, dict):
+                errors.append(f"Record in {side} file is not an object: {path}")
+                continue
+            if case_id_field not in record:
+                errors.append(f"Record missing case id field '{case_id_field}' in {side} file: {path}")
+                continue
+            case_id = stable_string(record[case_id_field])
+            if case_id in cases:
+                errors.append(f"Duplicate case id '{case_id}' in {side} inputs")
+                continue
+            cases[case_id] = {
+                "case_id": case_id,
+                "route": normalize_value(record.get(route_field)),
+                "expected_route": normalize_value(record.get(expected_route_field)) if expected_route_field else None,
+                "source_file": str(path),
+            }
+    return cases, errors
+
+
+def collect_input_files(root: pathlib.Path) -> list[pathlib.Path]:
+    if root.is_file():
+        return [root] if root.suffix.lower() in SUPPORTED_SUFFIXES else []
+    return sorted(path for path in root.rglob("*") if path.is_file() and path.suffix.lower() in SUPPORTED_SUFFIXES)
+
+
+def parse_file(path: pathlib.Path) -> Any:
+    suffix = path.suffix.lower()
+    text = path.read_text(encoding="utf-8")
+    if suffix == ".json":
+        return json.loads(text)
+    if suffix == ".jsonl":
+        records = []
+        for line_number, line in enumerate(text.splitlines(), start=1):
+            stripped = line.strip()
+            if not stripped:
+                continue
+            try:
+                records.append(json.loads(stripped))
+            except json.JSONDecodeError as exc:
+                raise ValueError(f"invalid JSONL on line {line_number}: {exc}") from exc
+        return records
+    if suffix in {".md", ".markdown"}:
+        return parse_markdown_summary(text, path)
+    raise ValueError(f"unsupported suffix: {suffix}")
+
+
+def parse_markdown_summary(text: str, path: pathlib.Path) -> Any:
+    fences = re.findall(r"```(?:json|yaml|yml)?\s*\n(.*?)\n```", text, flags=re.DOTALL | re.IGNORECASE)
+    errors: list[str] = []
+    for fence in fences:
+        try:
+            return json.loads(fence)
+        except json.JSONDecodeError as exc:
+            errors.append(f"json: {exc}")
+        yaml_loaded = try_load_yaml(fence)
+        if yaml_loaded is not None:
+            return yaml_loaded
+    raise ValueError(f"no parseable JSON/YAML fenced block found in Markdown summary {path}; {'; '.join(errors)}")
+
+
+def try_load_yaml(text: str) -> Any:
+    try:
+        import yaml  # type: ignore[import-not-found]
+    except ImportError:
+        return None
+    try:
+        return yaml.safe_load(text)
+    except Exception:
+        return None
+
+
+def extract_records(parsed: Any) -> list[Any]:
+    if isinstance(parsed, list):
+        return parsed
+    if isinstance(parsed, dict):
+        for key in RESULT_KEYS:
+            value = parsed.get(key)
+            if isinstance(value, list):
+                return value
+        if "case_id" in parsed or "id" in parsed:
+            return [parsed]
+    return []
+
+
+def compare_cases(before_cases: dict[str, dict[str, Any]], after_cases: dict[str, dict[str, Any]], targeted_cases: set[str]) -> dict[str, Any]:
+    before_ids = set(before_cases)
+    after_ids = set(after_cases)
+    common_ids = sorted(before_ids & after_ids)
+    missing_before = sorted(after_ids - before_ids)
+    missing_after = sorted(before_ids - after_ids)
+
+    unchanged: list[str] = []
+    changed: list[str] = []
+    targeted_changes: list[str] = []
+    non_target_changes: list[str] = []
+    new_failures: list[str] = []
+    resolved_failures: list[str] = []
+    diff_table: list[dict[str, Any]] = []
+
+    for case_id in common_ids:
+        before = before_cases[case_id]
+        after = after_cases[case_id]
+        before_failure = is_failure(before)
+        after_failure = is_failure(after)
+        route_changed = before["route"] != after["route"]
+        expected_changed = before["expected_route"] != after["expected_route"]
+        failure_status_changed = before_failure != after_failure
+        no_call_changed = is_no_call(before["route"]) != is_no_call(after["route"])
+        row_changed = route_changed or expected_changed or failure_status_changed or no_call_changed
+        change_type = build_change_type(route_changed, expected_changed, failure_status_changed, no_call_changed)
+
+        if row_changed:
+            changed.append(case_id)
+            if case_id in targeted_cases:
+                targeted_changes.append(case_id)
+            else:
+                non_target_changes.append(case_id)
+        else:
+            unchanged.append(case_id)
+
+        if not before_failure and after_failure:
+            new_failures.append(case_id)
+        if before_failure and not after_failure:
+            resolved_failures.append(case_id)
+
+        diff_table.append(
+            {
+                "case_id": case_id,
+                "change_type": change_type,
+                "targeted": case_id in targeted_cases,
+                "before_route": before["route"],
+                "after_route": after["route"],
+                "before_expected_route": before["expected_route"],
+                "after_expected_route": after["expected_route"],
+                "route_changed": route_changed,
+                "expected_route_changed": expected_changed,
+                "before_failure": before_failure,
+                "after_failure": after_failure,
+                "failure_status_changed": failure_status_changed,
+                "no_call_changed": no_call_changed,
+                "before_source_file": before["source_file"],
+                "after_source_file": after["source_file"],
+            }
+        )
+
+    for case_id in missing_before:
+        after = after_cases[case_id]
+        diff_table.append(
+            {
+                "case_id": case_id,
+                "change_type": "missing_before",
+                "targeted": case_id in targeted_cases,
+                "before_route": None,
+                "after_route": after["route"],
+                "before_expected_route": None,
+                "after_expected_route": after["expected_route"],
+                "route_changed": True,
+                "expected_route_changed": after["expected_route"] is not None,
+                "before_failure": None,
+                "after_failure": is_failure(after),
+                "failure_status_changed": None,
+                "no_call_changed": None,
+                "before_source_file": None,
+                "after_source_file": after["source_file"],
+            }
+        )
+
+    for case_id in missing_after:
+        before = before_cases[case_id]
+        diff_table.append(
+            {
+                "case_id": case_id,
+                "change_type": "missing_after",
+                "targeted": case_id in targeted_cases,
+                "before_route": before["route"],
+                "after_route": None,
+                "before_expected_route": before["expected_route"],
+                "after_expected_route": None,
+                "route_changed": True,
+                "expected_route_changed": before["expected_route"] is not None,
+                "before_failure": is_failure(before),
+                "after_failure": None,
+                "failure_status_changed": None,
+                "no_call_changed": None,
+                "before_source_file": before["source_file"],
+                "after_source_file": None,
+            }
+        )
+
+    status = "ATTENTION" if non_target_changes or missing_before or missing_after or new_failures else "PASS"
+    return {
+        "total_cases_compared": len(common_ids),
+        "unchanged_cases": unchanged,
+        "changed_cases": changed,
+        "targeted_changes": targeted_changes,
+        "non_target_changes": non_target_changes,
+        "new_failures": new_failures,
+        "resolved_failures": resolved_failures,
+        "missing_before_cases": missing_before,
+        "missing_after_cases": missing_after,
+        "diff_table": sorted(diff_table, key=lambda row: row["case_id"]),
+        "blocking_errors": [],
+        "machine_readable_summary": {
+            "status": status,
+            "total_cases_compared": len(common_ids),
+            "changed_count": len(changed),
+            "targeted_change_count": len(targeted_changes),
+            "non_target_change_count": len(non_target_changes),
+            "new_failure_count": len(new_failures),
+            "resolved_failure_count": len(resolved_failures),
+            "missing_before_count": len(missing_before),
+            "missing_after_count": len(missing_after),
+        },
+    }
+
+
+def build_change_type(route_changed: bool, expected_changed: bool, failure_status_changed: bool, no_call_changed: bool) -> str:
+    labels: list[str] = []
+    if route_changed:
+        labels.append("route_changed")
+    if expected_changed:
+        labels.append("expected_route_changed")
+    if failure_status_changed:
+        labels.append("failure_status_changed")
+    if no_call_changed:
+        labels.append("no_call_changed")
+    return "+".join(labels) if labels else "unchanged"
+
+
+def is_failure(case: dict[str, Any]) -> bool:
+    expected = case.get("expected_route")
+    if expected is None:
+        return False
+    return case.get("route") != expected
+
+
+def is_no_call(value: Any) -> bool:
+    if value is None:
+        return True
+    return str(value).strip().casefold() in NO_CALL_VALUES
+
+
+def normalize_value(value: Any) -> str | None:
+    if value is None:
+        return None
+    return stable_string(value)
+
+
+def stable_string(value: Any) -> str:
+    if isinstance(value, str):
+        return value
+    return json.dumps(value, ensure_ascii=False, sort_keys=True)
+
+
+def empty_summary(blocking_errors: list[str]) -> dict[str, Any]:
+    return {
+        "total_cases_compared": 0,
+        "unchanged_cases": [],
+        "changed_cases": [],
+        "targeted_changes": [],
+        "non_target_changes": [],
+        "new_failures": [],
+        "resolved_failures": [],
+        "missing_before_cases": [],
+        "missing_after_cases": [],
+        "diff_table": [],
+        "blocking_errors": blocking_errors,
+        "machine_readable_summary": {
+            "status": "FAIL",
+            "blocking_error_count": len(blocking_errors),
+            "total_cases_compared": 0,
+            "changed_count": 0,
+            "targeted_change_count": 0,
+            "non_target_change_count": 0,
+            "new_failure_count": 0,
+            "resolved_failure_count": 0,
+            "missing_before_count": 0,
+            "missing_after_count": 0,
+        },
+    }
+
+
+def write_reports(output_dir: pathlib.Path, summary: dict[str, Any]) -> None:
+    output_dir.mkdir(parents=True, exist_ok=True)
+    (output_dir / "routing-behavior-diff.json").write_text(
+        json.dumps(summary, ensure_ascii=False, indent=2) + "\n",
+        encoding="utf-8",
+    )
+    (output_dir / "routing-behavior-diff.md").write_text(render_markdown(summary), encoding="utf-8")
+
+
+def render_markdown(summary: dict[str, Any]) -> str:
+    machine = summary["machine_readable_summary"]
+    lines = [
+        "# Routing Behavior Diff",
+        "",
+        f"Status: `{machine['status']}`",
+        "",
+        "## Summary",
+        "",
+        f"- Total cases compared: {summary['total_cases_compared']}",
+        f"- Unchanged cases: {len(summary['unchanged_cases'])}",
+        f"- Changed cases: {len(summary['changed_cases'])}",
+        f"- Targeted changes: {len(summary['targeted_changes'])}",
+        f"- Non-target changes: {len(summary['non_target_changes'])}",
+        f"- New failures: {len(summary['new_failures'])}",
+        f"- Resolved failures: {len(summary['resolved_failures'])}",
+        f"- Missing before cases: {len(summary['missing_before_cases'])}",
+        f"- Missing after cases: {len(summary['missing_after_cases'])}",
+        "",
+    ]
+    if summary["blocking_errors"]:
+        lines.extend(["## Blocking Errors", ""])
+        lines.extend(f"- {error}" for error in summary["blocking_errors"])
+        lines.append("")
+
+    lines.extend(
+        [
+            "## Diff Table",
+            "",
+            "| Case ID | Change Type | Targeted | Before Route | After Route | Before Failure | After Failure | No-Call Changed |",
+            "| --- | --- | --- | --- | --- | --- | --- | --- |",
+        ]
+    )
+    if summary["diff_table"]:
+        for row in summary["diff_table"]:
+            lines.append(
+                "| "
+                + " | ".join(
+                    markdown_cell(row[key])
+                    for key in (
+                        "case_id",
+                        "change_type",
+                        "targeted",
+                        "before_route",
+                        "after_route",
+                        "before_failure",
+                        "after_failure",
+                        "no_call_changed",
+                    )
+                )
+                + " |"
+            )
+    else:
+        lines.append("| _none_ | _none_ | _none_ | _none_ | _none_ | _none_ | _none_ | _none_ |")
+
+    lines.extend(
+        [
+            "",
+            "## Machine Readable Summary",
+            "",
+            "```json",
+            json.dumps(machine, ensure_ascii=False, indent=2),
+            "```",
+            "",
+        ]
+    )
+    return "\n".join(lines)
+
+
+def markdown_cell(value: Any) -> str:
+    if value is None:
+        return ""
+    return str(value).replace("|", "\\|").replace("\n", " ")
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())
diff --git a/skills/routing-behavior-diff-audit/tests/test_routing_behavior_diff_audit.py b/skills/routing-behavior-diff-audit/tests/test_routing_behavior_diff_audit.py
new file mode 100644
index 0000000..7dc3eea
--- /dev/null
+++ b/skills/routing-behavior-diff-audit/tests/test_routing_behavior_diff_audit.py
@@ -0,0 +1,210 @@
+from __future__ import annotations
+
+import json
+import pathlib
+import shutil
+import subprocess
+import sys
+import tempfile
+import unittest
+
+
+SKILL_ROOT = pathlib.Path(__file__).resolve().parents[1]
+REPO_ROOT = pathlib.Path(__file__).resolve().parents[3]
+SCRIPT = SKILL_ROOT / "scripts" / "routing_behavior_diff_audit.py"
+TMP_ROOT = REPO_ROOT / "tmp" / "routing-behavior-diff-audit-tests"
+
+
+def run_cli(*args: str) -> subprocess.CompletedProcess[str]:
+    return subprocess.run(
+        [sys.executable, str(SCRIPT), *args],
+        text=True,
+        capture_output=True,
+        check=False,
+    )
+
+
+def write_json(path: pathlib.Path, data: object) -> pathlib.Path:
+    path.parent.mkdir(parents=True, exist_ok=True)
+    path.write_text(json.dumps(data, ensure_ascii=False, indent=2), encoding="utf-8")
+    return path
+
+
+def load_summary(output_dir: pathlib.Path) -> dict[str, object]:
+    return json.loads((output_dir / "routing-behavior-diff.json").read_text(encoding="utf-8"))
+
+
+class RoutingBehaviorDiffAuditTest(unittest.TestCase):
+    def setUp(self) -> None:
+        TMP_ROOT.mkdir(parents=True, exist_ok=True)
+        self.tmp_dir = tempfile.TemporaryDirectory(dir=TMP_ROOT)
+        self.root = pathlib.Path(self.tmp_dir.name)
+        self.before = self.root / "before.json"
+        self.after = self.root / "after.json"
+        self.output_dir = self.root / "outputs"
+
+    def tearDown(self) -> None:
+        self.tmp_dir.cleanup()
+
+    @classmethod
+    def tearDownClass(cls) -> None:
+        if TMP_ROOT.exists():
+            shutil.rmtree(TMP_ROOT)
+
+    def run_audit(self, *extra_args: str) -> tuple[subprocess.CompletedProcess[str], dict[str, object], str]:
+        result = run_cli(
+            "--before-results",
+            str(self.before),
+            "--after-results",
+            str(self.after),
+            "--output-dir",
+            str(self.output_dir),
+            "--case-id-field",
+            "case_id",
+            "--route-field",
+            "route",
+            "--expected-route-field",
+            "expected_route",
+            *extra_args,
+        )
+        summary = load_summary(self.output_dir)
+        markdown = (self.output_dir / "routing-behavior-diff.md").read_text(encoding="utf-8")
+        return result, summary, markdown
+
+    def test_unchanged_full_set_reports_all_cases_unchanged(self) -> None:
+        rows = [
+            {"case_id": "case-1", "route": "alpha", "expected_route": "alpha"},
+            {"case_id": "case-2", "route": "beta", "expected_route": "beta"},
+        ]
+        write_json(self.before, rows)
+        write_json(self.after, rows)
+
+        result, summary, markdown = self.run_audit()
+
+        self.assertEqual(result.returncode, 0, result.stderr)
+        self.assertEqual(summary["total_cases_compared"], 2)
+        self.assertEqual(summary["unchanged_cases"], ["case-1", "case-2"])
+        self.assertEqual(summary["changed_cases"], [])
+        self.assertEqual(summary["non_target_changes"], [])
+        self.assertEqual(summary["machine_readable_summary"]["status"], "PASS")
+        self.assertIn("case-1", markdown)
+
+    def test_targeted_route_changes_are_classified_separately(self) -> None:
+        write_json(self.before, [{"case_id": "case-1", "route": "alpha", "expected_route": "beta"}])
+        write_json(self.after, [{"case_id": "case-1", "route": "beta", "expected_route": "beta"}])
+
+        result, summary, _ = self.run_audit("--targeted-case", "case-1")
+
+        self.assertEqual(result.returncode, 0, result.stderr)
+        self.assertEqual(summary["changed_cases"], ["case-1"])
+        self.assertEqual(summary["targeted_changes"], ["case-1"])
+        self.assertEqual(summary["non_target_changes"], [])
+        self.assertEqual(summary["resolved_failures"], ["case-1"])
+
+    def test_non_target_collateral_changes_are_blocker_candidates(self) -> None:
+        write_json(
+            self.before,
+            [
+                {"case_id": "case-1", "route": "alpha"},
+                {"case_id": "case-2", "route": "beta"},
+            ],
+        )
+        write_json(
+            self.after,
+            [
+                {"case_id": "case-1", "route": "alpha"},
+                {"case_id": "case-2", "route": "gamma"},
+            ],
+        )
+
+        result, summary, _ = self.run_audit("--targeted-case", "case-1")
+
+        self.assertEqual(result.returncode, 0, result.stderr)
+        self.assertEqual(summary["changed_cases"], ["case-2"])
+        self.assertEqual(summary["targeted_changes"], [])
+        self.assertEqual(summary["non_target_changes"], ["case-2"])
+        self.assertEqual(summary["machine_readable_summary"]["status"], "ATTENTION")
+
+    def test_case_missing_in_before_is_reported(self) -> None:
+        write_json(self.before, [{"case_id": "case-1", "route": "alpha"}])
+        write_json(
+            self.after,
+            [
+                {"case_id": "case-1", "route": "alpha"},
+                {"case_id": "case-new", "route": "delta"},
+            ],
+        )
+
+        result, summary, _ = self.run_audit()
+
+        self.assertEqual(result.returncode, 0, result.stderr)
+        self.assertEqual(summary["missing_before_cases"], ["case-new"])
+        self.assertEqual(summary["missing_after_cases"], [])
+
+    def test_case_missing_in_after_is_reported(self) -> None:
+        write_json(
+            self.before,
+            [
+                {"case_id": "case-1", "route": "alpha"},
+                {"case_id": "case-removed", "route": "delta"},
+            ],
+        )
+        write_json(self.after, [{"case_id": "case-1", "route": "alpha"}])
+
+        result, summary, _ = self.run_audit()
+
+        self.assertEqual(result.returncode, 0, result.stderr)
+        self.assertEqual(summary["missing_before_cases"], [])
+        self.assertEqual(summary["missing_after_cases"], ["case-removed"])
+
+    def test_changed_no_call_status_is_visible_in_diff_table(self) -> None:
+        write_json(self.before, [{"case_id": "case-1", "route": "no_call"}])
+        write_json(self.after, [{"case_id": "case-1", "route": "alpha"}])
+
+        result, summary, _ = self.run_audit()
+
+        self.assertEqual(result.returncode, 0, result.stderr)
+        self.assertEqual(summary["changed_cases"], ["case-1"])
+        self.assertTrue(summary["diff_table"][0]["no_call_changed"])
+
+    def test_new_failures_and_resolved_failures_are_classified(self) -> None:
+        write_json(
+            self.before,
+            [
+                {"case_id": "case-new-fail", "route": "alpha", "expected_route": "alpha"},
+                {"case_id": "case-resolved", "route": "wrong", "expected_route": "beta"},
+            ],
+        )
+        write_json(
+            self.after,
+            [
+                {"case_id": "case-new-fail", "route": "wrong", "expected_route": "alpha"},
+                {"case_id": "case-resolved", "route": "beta", "expected_route": "beta"},
+            ],
+        )
+
+        result, summary, _ = self.run_audit()
+
+        self.assertEqual(result.returncode, 0, result.stderr)
+        self.assertEqual(summary["new_failures"], ["case-new-fail"])
+        self.assertEqual(summary["resolved_failures"], ["case-resolved"])
+
+    def test_utf8_paths_and_chinese_filenames_are_preserved(self) -> None:
+        before_dir = self.root / "之前"
+        after_dir = self.root / "之后"
+        self.before = before_dir / "路由结果.json"
+        self.after = after_dir / "路由结果.json"
+        write_json(self.before, [{"case_id": "案例一", "route": "旧路由"}])
+        write_json(self.after, [{"case_id": "案例一", "route": "新路由"}])
+
+        result, summary, markdown = self.run_audit()
+
+        self.assertEqual(result.returncode, 0, result.stderr)
+        self.assertEqual(summary["changed_cases"], ["案例一"])
+        self.assertEqual(summary["diff_table"][0]["before_route"], "旧路由")
+        self.assertEqual(summary["diff_table"][0]["after_route"], "新路由")
+        self.assertIn("案例一", markdown)
+
+
+if __name__ == "__main__":
+    unittest.main()