feat(sequence): combined fragments (alt/opt/loop) + OAuth example (#13)

Expand type-sequence.md with fragment frames, async open arrowheads,
complexity budget, and anti-patterns. Add bearer+refresh special examples
(light/dark/full) without changing the cold-cache trio. Wire README/SKILL
budget and a verify script that drives lint-skin.py.

Co-authored-by: wolf10drc <alaa@golead.io>

scripts/verify-sequence-oauth.py

@@ -0,0 +1,129 @@
+#!/usr/bin/env python3
+"""Structural + skin-lint verification for sequence combined-fragment work.
+
+Drives the real shipped artifacts (type-sequence.md, oauth examples, lint-skin.py).
+Exit 0 only when all gates pass. Intended for local/PR checks alongside:
+  python scripts/lint-skin.py --all --baseline
+"""
+
+from __future__ import annotations
+
+import re
+import subprocess
+import sys
+from pathlib import Path
+
+ROOT = Path(__file__).resolve().parent.parent
+TYPE_SEQ = ROOT / "skills/diagram-design/references/type-sequence.md"
+ASSETS = ROOT / "skills/diagram-design/assets"
+COLD = [
+    ASSETS / "example-sequence.html",
+    ASSETS / "example-sequence-dark.html",
+    ASSETS / "example-sequence-full.html",
+]
+OAUTH = [
+    ASSETS / "example-sequence-oauth.html",
+    ASSETS / "example-sequence-oauth-dark.html",
+    ASSETS / "example-sequence-oauth-full.html",
+]
+LINT = ROOT / "scripts/lint-skin.py"
+
+
+def fail(msg: str) -> None:
+    print(f"FAIL: {msg}", file=sys.stderr)
+    raise SystemExit(1)
+
+
+def ok(msg: str) -> None:
+    print(f"OK: {msg}")
+
+
+def main() -> int:
+    if not TYPE_SEQ.is_file():
+        fail(f"missing {TYPE_SEQ}")
+
+    text = TYPE_SEQ.read_text(encoding="utf-8")
+    required_sections = [
+        "## Combined fragments",
+        "### Open arrowhead (async)",
+        "## Complexity budget",
+        "## Anti-patterns",
+        "arrow-open",
+    ]
+    for needle in required_sections:
+        if needle not in text:
+            fail(f"type-sequence.md missing {needle!r}")
+    for op in ("ALT", "OPT", "LOOP"):
+        if op not in text:
+            fail(f"type-sequence.md missing operator {op}")
+    if "[token valid]" not in text and "guard" not in text.lower():
+        fail("type-sequence.md missing guard documentation")
+    ok("type-sequence.md fragments + async + budget present")
+
+    for path in COLD:
+        if not path.is_file():
+            fail(f"cold-cache example missing: {path.name}")
+        body = path.read_text(encoding="utf-8")
+        if "cold cache" not in body.lower() and "Article request" not in body:
+            fail(f"{path.name} no longer looks like the cold-cache example")
+        if "ALT" in body and "example-sequence-oauth" not in path.name:
+            # cold-cache must not grow an ALT frame (special example only)
+            # allow the word only in unrelated comments; require no ALT operator tab content
+            if re.search(r">ALT<", body):
+                fail(f"{path.name} unexpectedly contains ALT fragment tab")
+    ok("cold-cache sequence trio intact (no ALT tab)")
+
+    for path in OAUTH:
+        if not path.is_file():
+            fail(f"oauth example missing: {path.name}")
+        body = path.read_text(encoding="utf-8")
+        if ">ALT<" not in body and ">ALT</text>" not in body:
+            # tab text is ALT
+            if not re.search(r">\s*ALT\s*<", body):
+                fail(f"{path.name} missing ALT operator label")
+        if "[token valid]" not in body:
+            fail(f"{path.name} missing [token valid] guard")
+        if "[else" not in body and "[else · 401]" not in body:
+            fail(f"{path.name} missing else-region guard")
+        if "arrow-open" not in body:
+            fail(f"{path.name} missing arrow-open async marker")
+        if "Bearer" not in body and "BEARER" not in body:
+            fail(f"{path.name} missing bearer call")
+    ok("oauth trio has ALT two-region structure + async open")
+
+    # Drive real skin linter entry point on new files
+    cmd = [
+        sys.executable,
+        str(LINT),
+        *[str(p) for p in OAUTH],
+    ]
+    proc = subprocess.run(cmd, cwd=ROOT, capture_output=True, text=True)
+    print(proc.stdout, end="")
+    if proc.stderr:
+        print(proc.stderr, end="", file=sys.stderr)
+    if proc.returncode != 0:
+        fail(f"lint-skin.py failed on oauth examples (exit {proc.returncode})")
+    if "0 finding(s)" not in proc.stdout:
+        fail("lint-skin.py did not report 0 findings on oauth examples")
+    ok("lint-skin.py clean on oauth examples")
+
+    # Full repo gate
+    proc2 = subprocess.run(
+        [sys.executable, str(LINT), "--all", "--baseline"],
+        cwd=ROOT,
+        capture_output=True,
+        text=True,
+    )
+    print(proc2.stdout, end="")
+    if proc2.returncode != 0:
+        fail(f"lint-skin.py --all --baseline failed (exit {proc2.returncode})")
+    if "0 finding(s)" not in proc2.stdout:
+        fail("lint-skin.py --all --baseline did not report 0 findings")
+    ok("lint-skin.py --all --baseline green")
+
+    print("ALL GATES PASSED")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())