fix: match path parts with fullmatch, and describe the allowlist accurately

A folder name ending in a newline matched the path pattern, because $ also
matches before a trailing newline. The docs no longer claim that reading the
extension allowlist from the base branch stops a pull request from widening
it: the pull request runs its own copy of the check either way.

Author: miscreantmoogly

.claude/CLAUDE.md

@@ -84,7 +84,8 @@ The `metadata` block with `author` and `version` fields is required. Initial ver
 - Every skill is checked on every PR, because skills on `main` are published as one set. Errors from any skill fail; warnings print only for skills the PR touches.
 - Skills are read from Git objects (`git ls-tree -r -z` plus `git cat-file --batch`), never the working tree, so modes are exact and a local run checks only committed changes.
 - Rule data lives in `.github/scripts/skill-rules/` and the check fails closed (exit 2) when a file there is malformed: `agent-types.json`, `vocabulary.json` (dimension values; unknown values only warn), `published-files.json` (root names left out of the published set) and `conformance-cases.json`.
-- The extension allowlist is not duplicated: it is parsed from the `!*.<ext>` lines of `skills/.gitignore`, read from the merge base so a PR can't widen it for itself.
+- The extension allowlist is not duplicated: it is parsed from the `!*.<ext>` lines of `skills/.gitignore`, read from the merge base, so a new extension takes effect only once its `.gitignore` change has merged.
+- Like the repository's other checks, a PR runs its own copy of the script, rules and tests, so it could edit them to pass. Maintainer review of `.github/` changes (CODEOWNERS) and the post-merge run on `main` are the controls; don't describe any in-script measure as stopping a determined PR.
 - Secrets in test fixtures are built at runtime (`"AKIA" + ...`) or stored as base64 in the conformance cases, so no file in the repository contains a literal key or invisible character.
 - `conformance-cases.json` is a language-neutral contract: every tool that validates or publishes these skills must give each case's `expect` result. The script runs it before checking any skill and exits 2 on a mismatch. A rule change needs a matching case change in the same PR.
 - Exit codes: 0 pass (warnings allowed), 1 a rule broken, 2 could not run. Never report a 2 as the PR's fault.

.github/scripts/skill_checks.py

@@ -60,7 +60,7 @@
 ZIP_LIMIT_BYTES = 1_048_576 - 65_536
 ZIP_WARNING_RATIO = 0.9
 MAX_PATH_LENGTH = 512
-SEGMENT_PATTERN = re.compile(r"^[A-Za-z0-9._-]+$")
+SEGMENT_PATTERN = re.compile(r"[A-Za-z0-9._-]+")
 WINDOWS_RESERVED_NAMES = frozenset(
     {"CON", "PRN", "AUX", "NUL"} | {f"COM{i}" for i in range(1, 10)} | {f"LPT{i}" for i in range(1, 10)}
 )
@@ -664,7 +664,7 @@ def _path_problem(path: str) -> str | None:
             return f'"{path}" has an empty, "." or ".." part'
         if segment.startswith("."):
             return f'"{path}" is a hidden file or folder ("{segment}"), which would be published; remove it'
-        if not SEGMENT_PATTERN.match(segment):
+        if not SEGMENT_PATTERN.fullmatch(segment):
             return f'"{path}" may use only letters, digits, ".", "_" and "-" in each part of its path'
         if segment.endswith("."):
             return f'"{path}" has a part that ends with a period, which Windows can\'t extract'

CONTRIBUTING.md

@@ -67,7 +67,7 @@ The frontmatter must be plain YAML that every parser reads the same way. Anchors
 Published files. Everything in the skill folder is published and installed into customers' Agent Spaces except `evals/`, `.skilleval.yaml`, `.skilleval.yml` and `CHANGELOG.md` at the skill root ([`published-files.json`](.github/scripts/skill-rules/published-files.json)). For the published files:
 
 - At most 100 files, and their zip at most 983,040 bytes (1 MiB less a margin, because zip sizes vary by tool). The check warns past 90%.
-- Each file's extension must be one that `skills/.gitignore` allows. The check reads that list from the base branch, so a pull request can't widen it for its own files.
+- Each file's extension must be one that `skills/.gitignore` allows. The check reads that list from the base branch, so a new extension takes effect only after the `skills/.gitignore` change that adds it has merged.
 - Paths use only letters, digits, `.`, `_` and `-`, are at most 512 characters, have no hidden parts (such as `.DS_Store`), no Windows-reserved names (such as `CON`) and no part ending in a period, and don't differ from another path only in case.
 - No file starts with `#!`.
 

tests/test_skill_checks.py

@@ -370,6 +370,9 @@ def test_path_rules(self):
             with self.subTest(path=path):
                 self.assertOneError(with_files(path), fragment)
 
+    def test_folder_name_with_trailing_newline_is_rejected(self):
+        self.assertOneError(with_files("references\n/a.md"), "letters, digits")
+
     def test_case_collision(self):
         self.assertOneError(with_files("references/Guide.md", "references/guide.md"), "differ only in case")