diff --git a/.agents/skills/comment-and-doc-style/references/line-endings.md b/.agents/skills/comment-and-doc-style/references/line-endings.md
index 7726adede..ec32e16a0 100644
--- a/.agents/skills/comment-and-doc-style/references/line-endings.md
+++ b/.agents/skills/comment-and-doc-style/references/line-endings.md
@@ -113,8 +113,10 @@ JSONC (it has `//` comments), so strip them before JSON-parsing it.
 
 Editing CRLF files programmatically with a regex has a sharper trap: `.` matches `\r`, so a
 captured line keeps its carriage return and rejoining with `\r\n` yields `CRCRLF`. A text-mode
-rewrite has the mirror failure, silently flattening CRLF to LF. Prefer line-based edits
-(`splitlines(keepends=True)`) or literal replacement over regex reassembly. In Python the
-text-mode failure is the default: `Path.read_text()` decodes through universal newlines and
-`write_text()` writes `\n` back, so a read-edit-write round trip flattens the whole file while the
-edit itself looks correct. Pass `newline=''` to both, or work in bytes.
+rewrite has the mirror failure, silently rewriting every line ending to the host's own. Prefer
+line-based edits (`splitlines(keepends=True)`) or literal replacement over regex reassembly. In
+Python the text-mode failure is the default. `Path.read_text()` decodes through universal
+newlines, and `write_text()` translates each `\n` to `os.linesep`. A read-edit-write round trip
+therefore rewrites every ending in the file while the edit itself looks correct. Work in bytes, or
+use `open()` with `newline=''` on both the read and the write. `Path.read_text()` is no substitute,
+since it accepts `newline` only on Python 3.13 and newer and raises `TypeError` below it.
diff --git a/.claude-plugin/fleet-skills/.source-digests/comment-and-doc-style b/.claude-plugin/fleet-skills/.source-digests/comment-and-doc-style
index 6e093d6ee..316a04ef8 100644
--- a/.claude-plugin/fleet-skills/.source-digests/comment-and-doc-style
+++ b/.claude-plugin/fleet-skills/.source-digests/comment-and-doc-style
@@ -1 +1 @@
-db8fb1a840099988
+d0cc83be0784f597
diff --git a/.claude-plugin/fleet-skills/skills/comment-and-doc-style/references/line-endings.md b/.claude-plugin/fleet-skills/skills/comment-and-doc-style/references/line-endings.md
index 7726adede..ec32e16a0 100644
--- a/.claude-plugin/fleet-skills/skills/comment-and-doc-style/references/line-endings.md
+++ b/.claude-plugin/fleet-skills/skills/comment-and-doc-style/references/line-endings.md
@@ -113,8 +113,10 @@ JSONC (it has `//` comments), so strip them before JSON-parsing it.
 
 Editing CRLF files programmatically with a regex has a sharper trap: `.` matches `\r`, so a
 captured line keeps its carriage return and rejoining with `\r\n` yields `CRCRLF`. A text-mode
-rewrite has the mirror failure, silently flattening CRLF to LF. Prefer line-based edits
-(`splitlines(keepends=True)`) or literal replacement over regex reassembly. In Python the
-text-mode failure is the default: `Path.read_text()` decodes through universal newlines and
-`write_text()` writes `\n` back, so a read-edit-write round trip flattens the whole file while the
-edit itself looks correct. Pass `newline=''` to both, or work in bytes.
+rewrite has the mirror failure, silently rewriting every line ending to the host's own. Prefer
+line-based edits (`splitlines(keepends=True)`) or literal replacement over regex reassembly. In
+Python the text-mode failure is the default. `Path.read_text()` decodes through universal
+newlines, and `write_text()` translates each `\n` to `os.linesep`. A read-edit-write round trip
+therefore rewrites every ending in the file while the edit itself looks correct. Work in bytes, or
+use `open()` with `newline=''` on both the read and the write. `Path.read_text()` is no substitute,
+since it accepts `newline` only on Python 3.13 and newer and raises `TypeError` below it.
diff --git a/.github/skills/comment-and-doc-style/references/line-endings.md b/.github/skills/comment-and-doc-style/references/line-endings.md
index 7726adede..ec32e16a0 100644
--- a/.github/skills/comment-and-doc-style/references/line-endings.md
+++ b/.github/skills/comment-and-doc-style/references/line-endings.md
@@ -113,8 +113,10 @@ JSONC (it has `//` comments), so strip them before JSON-parsing it.
 
 Editing CRLF files programmatically with a regex has a sharper trap: `.` matches `\r`, so a
 captured line keeps its carriage return and rejoining with `\r\n` yields `CRCRLF`. A text-mode
-rewrite has the mirror failure, silently flattening CRLF to LF. Prefer line-based edits
-(`splitlines(keepends=True)`) or literal replacement over regex reassembly. In Python the
-text-mode failure is the default: `Path.read_text()` decodes through universal newlines and
-`write_text()` writes `\n` back, so a read-edit-write round trip flattens the whole file while the
-edit itself looks correct. Pass `newline=''` to both, or work in bytes.
+rewrite has the mirror failure, silently rewriting every line ending to the host's own. Prefer
+line-based edits (`splitlines(keepends=True)`) or literal replacement over regex reassembly. In
+Python the text-mode failure is the default. `Path.read_text()` decodes through universal
+newlines, and `write_text()` translates each `\n` to `os.linesep`. A read-edit-write round trip
+therefore rewrites every ending in the file while the edit itself looks correct. Work in bytes, or
+use `open()` with `newline=''` on both the read and the write. `Path.read_text()` is no substitute,
+since it accepts `newline` only on Python 3.13 and newer and raises `TypeError` below it.
diff --git a/tests/test_repo_gate.py b/tests/test_repo_gate.py
index 3421e9bf8..c3547f869 100755
--- a/tests/test_repo_gate.py
+++ b/tests/test_repo_gate.py
@@ -66,10 +66,12 @@ def test_the_table_holds_every_check_the_cli_offers(self) -> None:
         self.assertGreaterEqual(len(repo_gate.CHECKS), 3)
 
     def test_the_patterns_compile_and_carry_no_invisible_characters(self) -> None:
-        """A shell heredoc turns a backslash escape into a control character no diff shows."""
+        """printf, echo -e, and $'...' turn an escape into a control character no diff shows."""
         for name in ("USES", "PIN", "WORKFLOW", "HTTP_STATUS"):
             with self.subTest(pattern=name):
-                self.assertTrue(re.compile(getattr(repo_gate, name).pattern))
+                pattern = getattr(repo_gate, name).pattern
+                self.assertTrue(re.compile(pattern))
+                self.assertTrue(pattern.isascii() and pattern.isprintable())
         for action in repo_gate.SHA_EXCEPTIONS:
             with self.subTest(exception=action):
                 self.assertTrue(action.isascii() and action.isprintable())