refactor(ci|tests): improve validation coverage and refine workflows

- Add unit test for handling headers without trailing newlines.
- Simplify `.github/workflows/pre-commit.yml` by removing unused triggers.
- Update `.github/workflows/main.yml` to enforce correct gating and improve clarity.

Author: allnes

.github/workflows/main.yml

@@ -2,7 +2,11 @@ name: Build application
 
 on:
   push:
-  pull_request:
+    branches:
+      - master
+  workflow_run:
+    workflows: ["PR Compliance"]
+    types: [completed]
   merge_group:
   schedule:
     - cron: '0 0 * * *'
@@ -17,6 +21,7 @@ concurrency:
 
 jobs:
   pre-commit:
+    if: ${{ github.event_name != 'workflow_run' || github.event.workflow_run.conclusion == 'success' }}
     uses: ./.github/workflows/pre-commit.yml
   ubuntu:
     needs:

.github/workflows/pre-commit.yml

@@ -1,16 +1,10 @@
 name: Pre-commit checks
 
 on:
-  push:
   workflow_call:
-  workflow_run:
-    workflows: ["PR Compliance"]
-    types: [completed]
 
 jobs:
   pre-commit:
-    if: >-
-      ${{ github.event_name != 'workflow_run' || github.event.workflow_run.conclusion == 'success' }}
     runs-on: ubuntu-24.04
     container:
       image: ghcr.io/learning-process/ppc-ubuntu:1.1

tests/test_validate_pr_main.py

@@ -60,6 +60,12 @@ def test_load_event_payload(self):
         finally:
             os.unlink(path_ok)
 
+    def test_split_headers_without_trailing_newline(self):
+        # Cover branch where a header has no trailing newline at EOF
+        body = "## 1. Full name and group"
+        sections = self.v._split_sections_by_headers(body)
+        self.assertIn("## 1. Full name and group", sections)
+
 
 class DummyHTTPResponse:
     def __init__(self, payload: bytes):