State the Subprocess Encoding Rule Where Carriers Read Python Style

.agents/skills/python-codestyle/references/code-style.md

@@ -87,6 +87,16 @@
 - **Don't use exceptions for expected control flow.** Exceptions are for unexpected states.
 - **Don't suppress errors silently** (`except Exception: pass`). Either handle the specific
   exception and document why it's safe, or let it propagate.
+- **Don't leave a text-mode `subprocess` call to the locale's encoding.** Every call that reads
+  or writes a pipe as text (`text=True`, `universal_newlines=True`, or an `errors` argument) names
+  the encoding its child uses on that pipe. Below Python 3.15, a call that names none encodes and
+  decodes with the locale encoding unless UTF-8 Mode is on. That encoding follows the host's
+  locale, usually UTF-8 on Linux and the ANSI code page on Windows. The omission therefore looks
+  correct on a UTF-8 host. On any other, a Windows host being the common case, it misreads or
+  rejects non-ASCII output from a child writing UTF-8. No static check in the ruff, pyright, or
+  mypy toolchain looks for the omission in a subprocess call. Naming the encoding settles how the
+  bytes are translated, not what a byte or character outside that encoding is worth. Each call
+  decides that with its own `errors` argument, and the strict default decides it by raising.
 
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.claude-plugin/fleet-skills/.source-digests/python-codestyle

@@ -1 +1 @@
-78b687fa4e03cda7
+a54a634cf8810359

.claude-plugin/fleet-skills/skills/python-codestyle/references/code-style.md

@@ -87,6 +87,16 @@
 - **Don't use exceptions for expected control flow.** Exceptions are for unexpected states.
 - **Don't suppress errors silently** (`except Exception: pass`). Either handle the specific
   exception and document why it's safe, or let it propagate.
+- **Don't leave a text-mode `subprocess` call to the locale's encoding.** Every call that reads
+  or writes a pipe as text (`text=True`, `universal_newlines=True`, or an `errors` argument) names
+  the encoding its child uses on that pipe. Below Python 3.15, a call that names none encodes and
+  decodes with the locale encoding unless UTF-8 Mode is on. That encoding follows the host's
+  locale, usually UTF-8 on Linux and the ANSI code page on Windows. The omission therefore looks
+  correct on a UTF-8 host. On any other, a Windows host being the common case, it misreads or
+  rejects non-ASCII output from a child writing UTF-8. No static check in the ruff, pyright, or
+  mypy toolchain looks for the omission in a subprocess call. Naming the encoding settles how the
+  bytes are translated, not what a byte or character outside that encoding is worth. Each call
+  decides that with its own `errors` argument, and the strict default decides it by raising.
 
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.github/skills/python-codestyle/references/code-style.md

@@ -87,6 +87,16 @@
 - **Don't use exceptions for expected control flow.** Exceptions are for unexpected states.
 - **Don't suppress errors silently** (`except Exception: pass`). Either handle the specific
   exception and document why it's safe, or let it propagate.
+- **Don't leave a text-mode `subprocess` call to the locale's encoding.** Every call that reads
+  or writes a pipe as text (`text=True`, `universal_newlines=True`, or an `errors` argument) names
+  the encoding its child uses on that pipe. Below Python 3.15, a call that names none encodes and
+  decodes with the locale encoding unless UTF-8 Mode is on. That encoding follows the host's
+  locale, usually UTF-8 on Linux and the ANSI code page on Windows. The omission therefore looks
+  correct on a UTF-8 host. On any other, a Windows host being the common case, it misreads or
+  rejects non-ASCII output from a child writing UTF-8. No static check in the ruff, pyright, or
+  mypy toolchain looks for the omission in a subprocess call. Naming the encoding settles how the
+  bytes are translated, not what a byte or character outside that encoding is worth. Each call
+  decides that with its own `errors` argument, and the strict default decides it by raising.
 
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