[Container App] Fix az containerapp exec crash on non-ASCII (emoji) terminal output

[after2842]

Related command
az containerapp exec

Description
az containerapp exec crashes with UnicodeEncodeError whenever a container's
stdout/stderr contains characters the local terminal's codec cannot encode
(emoji, non-Latin scripts). On a cp1252 Windows console, e.g. the lobster emoji
U+1F99E:
UnicodeEncodeError: 'charmap' codec can't encode character '\U0001f99e' ...
File "_ssh_utils.py", line 108, in _decode_and_output_to_terminal

Root cause: in _decode_and_output_to_terminal, the container bytes decode to a
str correctly (UTF-8), but print() then re-encodes that str to the
console's encoding (cp1252), which raises UnicodeEncodeError. The surrounding
try/except only caught UnicodeDecodeError, so the encode-side failure was
uncaught and tore down the exec session.

Fix: route terminal output through a new _write_to_terminal() helper that
prints natively on capable (UTF-8) terminals, and on UnicodeEncodeError falls
back to encoding with errors="backslashreplace" written to sys.stdout.buffer
— so unencodable characters degrade gracefully instead of crashing. Also
separates the decode and print steps and corrects a misleading
"Failed to encode" → "Failed to decode" log message.

Testing Guide

• New unit tests: azdev test test_ssh_utils (covers the fallback, the print
  fast path, and end-to-end decode+output of emoji without disconnecting).
• Manual repro: on a cp1252 console (set PYTHONLEGACYWINDOWSSTDIO=1), run a
  container command that prints an emoji
  (az containerapp exec ... --command "printf '\xf0\x9f\xa6\x9e\n'"):
  crashes before this change, prints the character (or its \U0001f99e escape)
  and keeps the session alive after.

History Notes
[Container App] Fix az containerapp exec crash on non-ASCII (emoji) terminal output

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[yonzhan]

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[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds resilient terminal output handling for the Container Apps SSH exec session so that characters not representable in the host console's encoding (e.g., emoji on a cp1252 Windows terminal) don't crash the session.

Changes:

• Introduced _write_to_terminal helper that prints normally when possible and falls back to encoding with backslashreplace via sys.stdout.buffer when the console codec cannot encode the text.
• Refactored _decode_and_output_to_terminal to decode first, then route output through the new helper; also fixed a misleading log message ("encode" -> "decode").
• Added unit tests covering the fast path, the unencodable-character fallback, and end-to-end decode+output behavior.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/azure-cli/azure/cli/command_modules/containerapp/_ssh_utils.py	New _write_to_terminal fallback writer; _decode_and_output_to_terminal reworked to use it and corrected log wording.
src/azure-cli/azure/cli/command_modules/containerapp/tests/latest/test_ssh_utils.py	New tests verifying fast path, encoding fallback, and that emoji output does not disconnect.

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[after2842]

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