Synopsis : normalisation SÛRE des text ajouté par formulaire

- fins de ligne \r\n/\r → \n,
- blocs de lignes vides → \n\n, è
- espaces/tabulations/NBSP → espace unique,
- trim.
Les retours à la ligne simples intra-paragraphe sont LAISSÉS INTACTS :
une coupure de ligne peut être une vraie frontière de mot (→ espace)
ou une coupure du mot ("dyna\nmiques" → "dynamiques"),
indistinguables sans dictionnaire — automatiser corromprait l'entrée
("poursuivantsur").

Migration batch 045 (backfill des données existantes) RETIRÉE : le
nettoyage automatique fiable des synopsis existants est impossible.
Chaque modification est testée (277 tests PHPUnit).

tests/phpunit/ThesisCreateValidationTest.php

@@ -263,6 +263,96 @@ class ThesisCreateValidationTest extends TestCase
         $this->assertStringContainsString('Bold synopsis', $data['synopsis']);
     }
 
+    // ── Whitespace normalisation (safe, unambiguous subset only) ────────────────
+    // Single newlines inside a paragraph are deliberately LEFT untouched: they can
+    // be a word boundary (→ space) or a word split across a line ("dyna\nmiques"
+    // → "dynamiques") and are indistinguishable, so we never guess and risk
+    // corrupting valid input (e.g. "se poursuivant\nsur" → "poursuivantsur").
+
+    public function testSingleIntraParagraphNewlineIsLeftUntouched(): void
+    {
+        // A mid-word line break is ambiguous (could be a real split or a wrap),
+        // so we do not auto-alter it — the author is responsible for cleaning it.
+        $post = $this->validPost();
+        $post['synopsis'] = "…les dyn\namiques complexes…";
+
+        $data = $this->validate($post);
+        $this->assertSame("…les dyn\namiques complexes…", $data['synopsis']);
+    }
+
+    public function testWordWrapSingleNewlineNotMerged(): void
+    {
+        // We must NOT merge two real words across a line break ("poursuivantsur").
+        $post = $this->validPost();
+        $post['synopsis'] = "se poursuivant\nsur une seconde ligne";
+
+        $data = $this->validate($post);
+        $this->assertSame(
+            "se poursuivant\nsur une seconde ligne",
+            $data['synopsis']
+        );
+    }
+
+    public function testLegitimateParagraphBreakPreserved(): void
+    {
+        $post = $this->validPost();
+        $post['synopsis'] = "Premier paragraphe\n\nSecond paragraphe";
+
+        $data = $this->validate($post);
+        $this->assertSame(
+            "Premier paragraphe\n\nSecond paragraphe",
+            $data['synopsis']
+        );
+    }
+
+    public function testMultipleBlankLinesCollapseToSingleParagraphBreak(): void
+    {
+        $post = $this->validPost();
+        $post['synopsis'] = "A\n\n\n\nB";
+
+        $data = $this->validate($post);
+        $this->assertSame("A\n\nB", $data['synopsis']);
+    }
+
+    public function testMixedWindowsAndUnixLineEndingsNormalised(): void
+    {
+        $post = $this->validPost();
+        $post['synopsis'] = "une pause\r\n\r\ner une future";
+
+        $data = $this->validate($post);
+        // \r\n and \r line-endings all collapse to \n, and blank lines mark
+        // a single paragraph separator.
+        $this->assertSame("une pause\n\ner une future", $data['synopsis']);
+    }
+
+    public function testConsecutiveSpacesAndTabsCollapse(): void
+    {
+        $post = $this->validPost();
+        $post['synopsis'] = "Très    espacé\t\ttab";
+
+        $data = $this->validate($post);
+        $this->assertSame('Très espacé tab', $data['synopsis']);
+    }
+
+    public function testNonBreakingSpacesNormalised(): void
+    {
+        $post = $this->validPost();
+        // Word pasted NBSP (U+00A0) between words must become a regular space.
+        $post['synopsis'] = "Premier\u{00A0}mot second mot";
+
+        $data = $this->validate($post);
+        $this->assertSame('Premier mot second mot', $data['synopsis']);
+    }
+
+    public function testSynopsisSingleLineFieldTrimmed(): void
+    {
+        $post = $this->validPost();
+        $post['synopsis'] = "   texte qui flotte  ";
+
+        $data = $this->validate($post);
+        $this->assertSame('texte qui flotte', $data['synopsis']);
+    }
+
     // ── Author processing ────────────────────────────────────────────────────
 
     public function testMultipleAuthorsAreSorted(): void