fix: convert escaped newlines to actual newlines in Claude Code output

[roomote]

This PR fixes an issue where escaped newline characters (\n) in Claude Code output were being displayed literally instead of being converted to actual line breaks.

Problem

When using the Claude Code provider, messages containing escaped newlines were displayed as literal \n characters:

\n# Claude Chat History\n\n## 2025-08-05

Instead of the expected formatted output:

# Claude Chat History

## 2025-08-05

Solution

Added .replace(/\\n/g, '\n') to convert escaped newlines to actual newlines in two places:

1. String chunks from the Claude Code process
2. Text content from assistant messages

Testing

Added comprehensive tests to verify:

• Escaped newlines in string chunks are converted correctly
• Escaped newlines in assistant message text content are converted correctly
• Mixed escape sequences are handled properly (only \n is converted)

All existing tests continue to pass.

Fixes #6709

---

Important

Converts escaped newlines to actual newlines in Claude Code output, with tests ensuring correct behavior in claude-code.ts.

• Behavior:
  • Converts escaped newlines (\n) to actual newlines in ClaudeCodeHandler in claude-code.ts.
  • Applies conversion to string chunks and assistant message text content.
• Testing:
  • Adds tests in claude-code.spec.ts for converting escaped newlines in string chunks and assistant messages.
  • Tests handle mixed escape sequences, ensuring only \n is converted.
  • All existing tests pass, ensuring no regressions.

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[roomote]

Reviewing my own code is like debugging in a mirror - everything looks backwards but the bugs are still mine.

[roomote]

Good fix! Though I'm wondering - should we also handle other escape sequences like or that might appear in Claude Code output? Currently we only handle .

[roomote]

Same consideration here - should we handle and as well?

Also, a brief comment explaining why this transformation is necessary would help future maintainers understand the context (e.g., "Convert escaped newlines from Claude Code process output to actual newlines for proper rendering").

[roomote]

Excellent test coverage! The tests thoroughly verify the newline conversion behavior.

One minor suggestion: Consider adding a test case for edge cases like empty strings or null/undefined text content to ensure the replace operation handles these gracefully.