fix: sanitise newlines in integration PR titles to prevent GitHub 422 (PTFE-3249)

[matthiasL-scality]

Summary

• A parent PR title containing newline characters (e.g. from a multi-line commit message like "My feature\n* fix something") caused bert-e to forward those newlines in the integration PR title string, triggering a 422 Unprocessable Entity from GitHub's API.
• Fixed by stripping \r/\n via re.sub before composing the INTEGRATION [...] title in IntegrationBranch.get_or_create_pull_request.
• Added helpers.FakeRepo as a shared test stub, and 7 unit tests covering the sanitisation behaviour.

Root cause

# before — newlines in parent_pr.title propagated directly to GitHub API
title = 'INTEGRATION [PR#%s > %s] %s' % (
    parent_pr.id, self.dst_branch.name, parent_pr.title
)

Fix

safe_title = re.sub(r'[\r\n]+', ' ', parent_pr.title).strip()
# outer strip handles edge case where safe_title is empty (all-newlines title)
title = ('INTEGRATION [PR#%s > %s] %s' % (
    parent_pr.id, self.dst_branch.name, safe_title
)).strip()

The inner .strip() prevents a leading \n (e.g. "\nfoo" → " foo") from introducing a double space inside the formatted string. The outer .strip() handles the pathological case where the parent title consists entirely of newlines, which would otherwise leave a trailing space after the closing bracket.

Test plan

• test_newline_in_parent_title_is_stripped — core regression case
• test_carriage_return_in_parent_title_is_stripped — CRLF variant
• test_asterisk_without_newline_is_preserved — * alone is not stripped
• test_clean_title_is_unchanged — happy path, no regression
• test_integration_prefix_is_present — prefix always present
• test_trailing_newline_does_not_produce_trailing_space — trailing \n
• test_newlines_only_title_does_not_produce_trailing_space — pathological all-newlines title
• flake8 passes on all changed files

🤖 Generated with Claude Code

[codecov]

Codecov Report

❌ Patch coverage is 98.52941% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.60%. Comparing base (f88a30e) to head (58424e9).

Files with missing lines	Patch %	Lines
bert_e/tests/unit/helpers.py	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #270      +/-   ##
==========================================
+ Coverage   89.54%   89.60%   +0.05%     
==========================================
  Files          79       81       +2     
  Lines       10522    10589      +67     
==========================================
+ Hits         9422     9488      +66     
- Misses       1100     1101       +1     

Flag	Coverage Δ
integration	87.19% <100.00%> (+<0.01%)	⬆️
tests	87.15% <100.00%> (+<0.01%)	⬆️
tests-BuildFailedTest	26.68% <0.00%> (-0.01%)	⬇️
tests-QuickTest	34.22% <0.00%> (-0.01%)	⬇️
tests-RepositoryTests	26.34% <0.00%> (-0.01%)	⬇️
tests-TaskQueueTests	51.47% <100.00%> (+<0.01%)	⬆️
tests-TestBertE	65.38% <100.00%> (+<0.01%)	⬆️
tests-TestQueueing	53.70% <100.00%> (+<0.01%)	⬆️
tests-api-mock	15.37% <0.00%> (-0.10%)	⬇️
tests-noqueue	77.36% <100.00%> (+<0.01%)	⬆️
tests-noqueue-BuildFailedTest	26.68% <0.00%> (-0.01%)	⬇️
tests-noqueue-QuickTest	34.22% <0.00%> (-0.01%)	⬇️
tests-noqueue-RepositoryTests	26.34% <0.00%> (-0.01%)	⬇️
tests-noqueue-TaskQueueTests	51.47% <100.00%> (+<0.01%)	⬆️
tests-noqueue-TestBertE	61.76% <100.00%> (+<0.01%)	⬆️
tests-noqueue-TestQueueing	26.36% <0.00%> (-0.01%)	⬇️
tests-server	28.31% <0.00%> (-0.19%)	⬇️
unittests	43.44% <98.52%> (+0.44%)	⬆️
utests	28.17% <98.52%> (+0.54%)	⬆️

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