From 6cc0e407f3051255e0517805ef7a32e30531510f Mon Sep 17 00:00:00 2001
From: Pontoporeia <pontoporeia@happyngreen.fr>
Date: Sat, 9 May 2026 21:36:42 +0200
Subject: [PATCH] Error tests, FK violations fix
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

- ErrorHandler tests: 77 assertions covering FK extraction, normalization, dedup, edge cases. Fix FK table map for child tables.
- Fix FK violation: (int)null → 0 in createThesis for orientation/ap/finality/license FK columns. Add FK value logging to updateThesis.
- Add CURRENT_ISSUES.md with summary of FK violation, dev debugging, and tag dedup status for next conversation
---
 CURRENT_ISSUES.md                             |  91 ++++
 TODO.md                                       |   3 +
 app/public/admin/actions/access-request.php   |   5 +-
 app/public/admin/actions/apropos.php          |   5 +-
 app/public/admin/actions/delete.php           |   5 +-
 app/public/admin/actions/edit.php             |   6 +-
 app/public/admin/actions/export-files.php     |   5 +-
 app/public/admin/actions/export.php           |   5 +-
 app/public/admin/actions/form-help.php        |   5 +-
 app/public/admin/actions/formulaire.php       |  10 +-
 app/public/admin/actions/page.php             |   5 +-
 app/public/admin/actions/publish.php          |   5 +-
 app/public/admin/actions/tag.php              |   4 +-
 app/public/admin/actions/visibility.php       |   5 +-
 app/public/admin/add.php                      |   4 +-
 app/public/admin/edit.php                     |   4 +-
 app/public/admin/index.php                    |  15 +-
 app/public/admin/tag-search-fragment.php      |  14 +
 app/public/assets/css/form.css                | 213 ++++++++
 app/public/partage/index.php                  |  17 +-
 app/public/partage/tag-search-fragment.php    |  67 +++
 app/src/Controllers/AboutController.php       |   3 +-
 app/src/Controllers/HomeController.php        |   3 +-
 app/src/Controllers/LicenceController.php     |   3 +-
 app/src/Controllers/MediaController.php       |   3 +-
 app/src/Controllers/SearchController.php      |   5 +-
 app/src/Controllers/TfeController.php         |   3 +-
 .../Controllers/ThesisCreateController.php    |  39 +-
 app/src/Controllers/ThesisEditController.php  |  47 +-
 app/src/Database.php                          |  67 ++-
 app/src/ErrorHandler.php                      | 183 +++++++
 app/templates/admin/acces.php                 |  13 +
 app/templates/admin/edit.php                  |   8 +
 app/templates/partials/form/form.php          |  35 +-
 app/templates/partials/form/tag-search.php    | 236 +++++++++
 app/tests/Unit/ErrorHandlerTest.php           | 453 ++++++++++++++++++
 app/tests/Unit/FormSaveTest.php               |   2 +-
 app/tests/run-tests.php                       |   1 +
 38 files changed, 1515 insertions(+), 82 deletions(-)
 create mode 100644 CURRENT_ISSUES.md
 create mode 100644 app/public/admin/tag-search-fragment.php
 create mode 100644 app/public/partage/tag-search-fragment.php
 create mode 100644 app/src/ErrorHandler.php
 create mode 100644 app/templates/partials/form/tag-search.php
 create mode 100644 app/tests/Unit/ErrorHandlerTest.php

diff --git a/CURRENT_ISSUES.md b/CURRENT_ISSUES.md
new file mode 100644
index 0000000..8d53d03
--- /dev/null
+++ b/CURRENT_ISSUES.md
@@ -0,0 +1,91 @@
+# Current Issues — XAMXAM (2026-05-10)
+
+## 1. FK constraint violation on thesis save (create + edit)
+
+**Symptom:** `⚠ SQLSTATE[23000]: Integrity constraint violation: 19 FOREIGN KEY constraint failed`
+
+**Triggers:**
+- Editing an imported CSV thesis, changing access type to Interdit, save
+- Opening any imported thesis edit form and saving *without changes*  
+- Saving the add form with empty fields — form below "Cadre académique" disappears (PHP dies mid-render)
+
+**Root cause found so far:** `Database::createThesis()` at line ~1860 was doing `(int)$data['orientation_id']` which converts SQL null → PHP `null` → `(int)null` = `0`. Since no row with ID 0 exists in `orientations`, this triggers FK violation. Fixed in commit `55088c94` by using `$v ? (int)$v : null` pattern.
+
+**Still happening after fix** — suggests another code path has same issue, or the fix wasn't complete. The `updateThesis` path was already safe (uses `?: null`), but the error persists.
+
+**Debugging added:**
+- `[DB:updateThesis]` log line with all FK values before query (commit `55088c94`)
+- `[ThesisEdit] Step 1-6 OK` step-level logging (commit `8734d964`)
+- `ErrorHandler::log()` with full trace on catch (commit `03ad73f3`)
+
+**Dev server output:** No error_log visible in dev mode — PHP built-in server sends errors to stderr which may not be captured.
+
+**Next steps:** 
+- Enable `display_errors=1` in dev mode so FK errors render in browser
+- Check if `setThesisFormats`, `setThesisLanguages`, `setThesisTags` paths also have `(int)null` → `0` issues
+- Check `formulaire.php` action file — does it also use `createThesis`?
+
+---
+
+## 2. Dev server debugging output
+
+**Symptom:** No error output visible in browser when PHP crashes.
+
+**Current config** (`bootstrap.php`):
+- Dev mode (cli-server): `display_errors=1`, `error_reporting=E_ALL`
+- Production: `display_errors=0`, `log_errors=1`
+
+**But:** the admin action files override this:
+- `formulaire.php` line 5-7: `ini_set('display_errors', 0); ini_set('log_errors', 1);`
+- `edit.php` action: no override (uses bootstrap defaults)
+
+**Action needed:** Don't suppress display_errors in dev mode. Check `php_sapi_name()` before overriding.
+
+---
+
+## 3. Console warnings
+
+```
+Layout was forced before the page was fully loaded. node.js:416:1
+[file-upload-queue] XamxamInitFileUploads called (twice)
+```
+- `file-upload-queue.js` called twice — the script might be included twice (check `add.php` template + the `form.php` partial)
+
+---
+
+## 4. Tags: lowercase + dedup + CSV import
+
+**Status:** Implemented across all paths:
+- Frontend JS: `normalizeTag()` with `replace(/\s+/g, ' ')`, lowercase
+- Server fragment: `preg_replace('/\s+/', ' ', strtolower(...))`  
+- Both controllers: `fn(string $t) => strtolower(trim(preg_replace('/\s+/', ' ', $t)))`
+- CSV import: same normalization (commit `8734d964`)
+- Minimum 3 tags enforced (commit `8734d964`)
+
+## 5. ErrorHandler coverage
+
+**Status:** Applied to 12 admin action files + 6 public controllers + 2 form controllers + partage entry point (commit `03ad73f3`). 77 unit test assertions.
+
+## Relevant commits (most recent first)
+
+```
+55088c94 Fix FK violation: (int)null → 0 in createThesis
+27378b42 ErrorHandler tests: 77 assertions
+4d9296fd ErrorHandler: precise FK field extraction from SQLite
+03ad73f3 ErrorHandler: shared logging across all actions/controllers  
+6b6c62d1 Error logging: step-by-step transaction tracing
+8734d964 Mots-clés: collapse spaces, minimum 3 keywords
+dfe1186b Mots-clés: lowercase, dedup, keyboard nav, absolute dropdown
+8d04d4ba Mots-clés: lowercase enforcement, deduplication, absolute dropdown
+7fe53f8c Mots-clés: interactive HTMX tag search
+dd110cc5 Admin mobile block: fix inline style beating media query
+```
+
+## Key files to review
+
+- `app/src/Database.php` — `createThesis()` line ~1830, `updateThesis()` line ~1751, `setThesisFormats/Languages/Tags`
+- `app/src/Controllers/ThesisCreateController.php` — `submit()` line ~146, `validateAndSanitise()` line ~312
+- `app/src/Controllers/ThesisEditController.php` — `save()` line ~158
+- `app/public/admin/actions/formulaire.php` — calls `$ctrl->submit()` (create path)
+- `app/public/admin/actions/edit.php` — calls `$ctrl->save()` (edit path)
+- `app/public/admin/index.php` — CSV import at line ~220
diff --git a/TODO.md b/TODO.md
index 7a1d082..383ed99 100644
--- a/TODO.md
+++ b/TODO.md
@@ -66,3 +66,6 @@
 - [x] Admin mobile block screen: fix inline style beating media query, use CSS default display:none instead
 - [x] Fix deploy: add missing 023b migration to rename cc4r→cc2r, make run.php skip 'no such column' errors
 - [x] Fix FK constraint violation on edit: pass null instead of 0 for absent orientation/ap/finality
+- [x] Mots-clés: interactive tag search with HTMX suggestions, pill display, round bin-icon remove buttons
+- [x] Mots-clés: lowercase enforcement, deduplication, absolute dropdown, keyboard arrows/enter/escape, blur hide, spacing + counter above input, CSV import lowercased, space-collapse normalization, minimum 3 keywords required
+- [x] ErrorHandler: shared static helper for structured error_log + user-friendly messages with precise FK field extraction from SQLite errors. Applied to 12 action files + 6 public controllers + 2 form controllers + partage. Covers FK, UNIQUE, NOT NULL constraint types.
diff --git a/app/public/admin/actions/access-request.php b/app/public/admin/actions/access-request.php
index b9d3ba6..7a8740a 100644
--- a/app/public/admin/actions/access-request.php
+++ b/app/public/admin/actions/access-request.php
@@ -18,6 +18,7 @@ if (!isset($_POST['csrf_token'], $_SESSION['csrf_token'])
 require_once APP_ROOT . '/src/Database.php';
 require_once APP_ROOT . '/src/SmtpRelay.php';
 require_once APP_ROOT . '/src/AdminLogger.php';
+require_once APP_ROOT . '/src/ErrorHandler.php';
 
 $db     = Database::getInstance();
 $logger = AdminLogger::make();
@@ -59,7 +60,7 @@ try {
             $logger->logAccessRequest($requestId, 'approve', $request['email'], $request['title']);
             App::flash('success', "Demande approuvée. Email envoyé à {$request['email']}.");
         } catch (SmtpSendException $e) {
-            error_log('[access-request] Email delivery failed after approval: ' . $e->getMessage());
+            ErrorHandler::log('access_request_smtp', $e, ['request_id' => $requestId]);
             $logger->logAccessRequest($requestId, 'approve', $request['email'], $request['title']);
             $smtpMsg = $e->isRecipientRejected()
                 ? "Demande approuvée, mais l'email n'a pas pu être délivré : adresse inconnue ({$request['email']})."
@@ -78,7 +79,7 @@ try {
     exit;
 
 } catch (Exception $e) {
-    error_log('Access request action failed: ' . $e->getMessage());
+    ErrorHandler::log('access_request', $e);
     http_response_code(500);
     echo json_encode(['success' => false, 'message' => 'Erreur lors du traitement']);
 }
diff --git a/app/public/admin/actions/apropos.php b/app/public/admin/actions/apropos.php
index e609641..24276eb 100644
--- a/app/public/admin/actions/apropos.php
+++ b/app/public/admin/actions/apropos.php
@@ -21,6 +21,7 @@ if (!in_array($aproposKey, $allowedKeys)) {
 
 require_once __DIR__ . '/../../../src/Database.php';
 require_once __DIR__ . '/../../../src/AdminLogger.php';
+require_once __DIR__ . '/../../../src/ErrorHandler.php';
 
 try {
     $db = new Database();
@@ -54,8 +55,8 @@ try {
     AdminLogger::make()->logAproposEdit($aproposKey);
     App::flash('success', "Contenu « $aproposKey » mis à jour avec succès.");
 } catch (Exception $e) {
-    error_log("Apropos save error: " . $e->getMessage());
-    die("Erreur lors de la sauvegarde : " . htmlspecialchars($e->getMessage()));
+    ErrorHandler::log('apropos', $e);
+    die('Erreur lors de la sauvegarde : ' . htmlspecialchars(ErrorHandler::userMessage($e)));
 }
 
 header('Location: /admin/contenus.php');
diff --git a/app/public/admin/actions/delete.php b/app/public/admin/actions/delete.php
index a6070cc..8f02a2c 100644
--- a/app/public/admin/actions/delete.php
+++ b/app/public/admin/actions/delete.php
@@ -6,6 +6,7 @@ AdminAuth::requireLogin();
 
 require_once __DIR__ . '/../../../src/Database.php';
 require_once __DIR__ . '/../../../src/AdminLogger.php';
+require_once __DIR__ . '/../../../src/ErrorHandler.php';
 
 // CSRF validation
 if (!isset($_POST['csrf_token'], $_SESSION['csrf_token'])
@@ -57,8 +58,8 @@ try {
     }
 
 } catch (Exception $e) {
-    error_log('delete.php error: ' . $e->getMessage());
-    App::flash('error', 'Erreur lors de la suppression : ' . $e->getMessage());
+    ErrorHandler::log('thesis_delete', $e);
+    App::flash('error', 'Erreur lors de la suppression : ' . ErrorHandler::userMessage($e));
 }
 
 $_SESSION['csrf_token'] = bin2hex(random_bytes(32));
diff --git a/app/public/admin/actions/edit.php b/app/public/admin/actions/edit.php
index a29c85f..b78aba8 100644
--- a/app/public/admin/actions/edit.php
+++ b/app/public/admin/actions/edit.php
@@ -26,6 +26,7 @@ if ($thesisId <= 0) {
 
 require_once APP_ROOT . '/src/Controllers/ThesisEditController.php';
 require_once APP_ROOT . '/src/AdminLogger.php';
+require_once APP_ROOT . '/src/ErrorHandler.php';
 
 try {
     $ctrl = ThesisEditController::create();
@@ -41,9 +42,8 @@ try {
     exit();
 
 } catch (Exception $e) {
-    error_log("Edit action error: " . $e->getMessage());
-
-    App::flash('error', $e->getMessage());
+    ErrorHandler::log('thesis_edit', $e, ['thesis_id' => $thesisId]);
+    App::flash('error', ErrorHandler::userMessage($e));
 
     // WCAG 3.3.1 — map error message to field name for autofocus on re-render.
     $autofocusField = ThesisEditController::autofocusFieldForError($e->getMessage());
diff --git a/app/public/admin/actions/export-files.php b/app/public/admin/actions/export-files.php
index 8971e73..b44cc9e 100644
--- a/app/public/admin/actions/export-files.php
+++ b/app/public/admin/actions/export-files.php
@@ -15,6 +15,7 @@ AdminAuth::requireLogin();
 
 require_once APP_ROOT . '/src/Controllers/ExportController.php';
 require_once APP_ROOT . '/src/AdminLogger.php';
+require_once APP_ROOT . '/src/ErrorHandler.php';
 
 try {
     $controller = ExportController::create();
@@ -40,9 +41,9 @@ try {
     // Clean up temp file
     @unlink($zipPath);
 } catch (Exception $e) {
-    error_log('Files export error: ' . $e->getMessage());
+    ErrorHandler::log('export_files', $e);
     http_response_code(500);
-    exit('Erreur lors de la création de l\'archive : ' . htmlspecialchars($e->getMessage()));
+    exit('Erreur lors de la création de l\'archive : ' . htmlspecialchars(ErrorHandler::userMessage($e)));
 }
 
 exit;
diff --git a/app/public/admin/actions/export.php b/app/public/admin/actions/export.php
index e3d8903..b130392 100644
--- a/app/public/admin/actions/export.php
+++ b/app/public/admin/actions/export.php
@@ -15,6 +15,7 @@ AdminAuth::requireLogin();
 
 require_once APP_ROOT . '/src/Controllers/ExportController.php';
 require_once APP_ROOT . '/src/AdminLogger.php';
+require_once APP_ROOT . '/src/ErrorHandler.php';
 
 $doCsv   = !empty($_GET['csv']);
 $doFiles = !empty($_GET['files']);
@@ -69,9 +70,9 @@ if ($doFiles) {
         readfile($zipPath);
         @unlink($zipPath);
     } catch (Exception $e) {
-        error_log('Files export error: ' . $e->getMessage());
+        ErrorHandler::log('export', $e);
         http_response_code(500);
-        exit('Erreur lors de la création de l\'archive : ' . htmlspecialchars($e->getMessage()));
+        exit('Erreur lors de la création de l\'archive : ' . htmlspecialchars(ErrorHandler::userMessage($e)));
     }
 }
 
diff --git a/app/public/admin/actions/form-help.php b/app/public/admin/actions/form-help.php
index 7073474..94e22e7 100644
--- a/app/public/admin/actions/form-help.php
+++ b/app/public/admin/actions/form-help.php
@@ -19,6 +19,7 @@ $content = $_POST['content']       ?? '';
 
 require_once APP_ROOT . '/src/Database.php';
 require_once APP_ROOT . '/src/AdminLogger.php';
+require_once APP_ROOT . '/src/ErrorHandler.php';
 $db = new Database();
 
 if (!in_array($key, Database::FORM_HELP_KEYS, true)) {
@@ -32,8 +33,8 @@ try {
     AdminLogger::make()->logFormStructureEdit($key);
     App::flash('success', 'Bloc « ' . htmlspecialchars($key) . ' » mis à jour.');
 } catch (Exception $e) {
-    error_log('form-help save error: ' . $e->getMessage());
-    App::flash('error', 'Erreur lors de la sauvegarde : ' . htmlspecialchars($e->getMessage()));
+    ErrorHandler::log('form_help', $e);
+    App::flash('error', 'Erreur lors de la sauvegarde : ' . ErrorHandler::userMessage($e));
 }
 
 $_SESSION['csrf_token'] = bin2hex(random_bytes(32));
diff --git a/app/public/admin/actions/formulaire.php b/app/public/admin/actions/formulaire.php
index 467f378..614567e 100644
--- a/app/public/admin/actions/formulaire.php
+++ b/app/public/admin/actions/formulaire.php
@@ -26,6 +26,7 @@ require_once APP_ROOT . '/src/Controllers/ThesisCreateController.php';
 require_once APP_ROOT . '/src/AppLogger.php';
 require_once APP_ROOT . '/src/AdminLogger.php';
 require_once APP_ROOT . '/src/DuplicateThesisException.php';
+require_once APP_ROOT . '/src/ErrorHandler.php';
 
 $logger      = new AppLogger();
 $adminLogger = AdminLogger::make();
@@ -47,8 +48,7 @@ try {
 
 } catch (DuplicateThesisException $e) {
     $logger->logDuplicate('admin', $authorName, $e->existingThesisId, $e->existingIdentifier);
-
-    error_log('ThesisCreateController duplicate: ' . $e->getMessage());
+    ErrorHandler::log('thesis_create_duplicate', $e, ['author' => $authorName]);
 
     // Build a warning with a clickable link to the existing thesis.
     $existingUrl  = htmlspecialchars('/admin/edit.php?id=' . $e->existingThesisId);
@@ -68,10 +68,8 @@ try {
         'author'   => $authorName,
         'post_keys' => array_keys($_POST),
     ]);
-
-    error_log('ThesisCreateController error: ' . $e->getMessage());
-
-    App::flash('error', $e->getMessage());
+    ErrorHandler::log('thesis_create', $e, ['author' => $authorName]);
+    App::flash('error', ErrorHandler::userMessage($e));
     $_SESSION['form_data'] = $_POST;
 
     $redirect = '../add.php';
diff --git a/app/public/admin/actions/page.php b/app/public/admin/actions/page.php
index efd8d58..6f3aa33 100644
--- a/app/public/admin/actions/page.php
+++ b/app/public/admin/actions/page.php
@@ -25,6 +25,7 @@ if (!in_array($slug, $allowedSlugs, true)) {
 
 require_once APP_ROOT . '/src/Database.php';
 require_once APP_ROOT . '/src/AdminLogger.php';
+require_once APP_ROOT . '/src/ErrorHandler.php';
 $db = new Database();
 
 try {
@@ -32,8 +33,8 @@ try {
     AdminLogger::make()->logPageEdit($slug);
     App::flash('success', 'Page « ' . htmlspecialchars($slug) . ' » mise à jour.');
 } catch (Exception $e) {
-    error_log('page save error: ' . $e->getMessage());
-    App::flash('error', 'Erreur lors de la sauvegarde : ' . htmlspecialchars($e->getMessage()));
+    ErrorHandler::log('page', $e);
+    App::flash('error', 'Erreur lors de la sauvegarde : ' . ErrorHandler::userMessage($e));
 }
 
 $_SESSION['csrf_token'] = bin2hex(random_bytes(32));
diff --git a/app/public/admin/actions/publish.php b/app/public/admin/actions/publish.php
index 9ec32c2..f0e3a47 100644
--- a/app/public/admin/actions/publish.php
+++ b/app/public/admin/actions/publish.php
@@ -6,6 +6,7 @@ AdminAuth::requireLogin();
 
 require_once __DIR__ . '/../../../src/Database.php';
 require_once __DIR__ . '/../../../src/AdminLogger.php';
+require_once __DIR__ . '/../../../src/ErrorHandler.php';
 
 if (!isset($_POST['csrf_token'], $_SESSION['csrf_token'])
     || !hash_equals($_SESSION['csrf_token'], $_POST['csrf_token'])) {
@@ -61,8 +62,8 @@ try {
     }
 
 } catch (Exception $e) {
-    error_log('publish.php error: ' . $e->getMessage());
-    App::flash('error', 'Erreur lors de la modification : ' . $e->getMessage());
+    ErrorHandler::log('thesis_publish', $e);
+    App::flash('error', 'Erreur lors de la modification : ' . ErrorHandler::userMessage($e));
 }
 
 $_SESSION['csrf_token'] = bin2hex(random_bytes(32));
diff --git a/app/public/admin/actions/tag.php b/app/public/admin/actions/tag.php
index 70b33a1..83594a4 100644
--- a/app/public/admin/actions/tag.php
+++ b/app/public/admin/actions/tag.php
@@ -12,6 +12,7 @@ if ($_SERVER['REQUEST_METHOD'] !== 'POST'
 
 require_once __DIR__ . '/../../../src/Database.php';
 require_once __DIR__ . '/../../../src/AdminLogger.php';
+require_once __DIR__ . '/../../../src/ErrorHandler.php';
 
 try {
     $db     = new Database();
@@ -48,7 +49,8 @@ try {
 
     App::flash('success', "Opération effectuée.");
 } catch (Exception $e) {
-    App::flash('error', $e->getMessage());
+    ErrorHandler::log('tag', $e);
+    App::flash('error', ErrorHandler::userMessage($e));
 }
 
 header('Location: /admin/tags.php');
diff --git a/app/public/admin/actions/visibility.php b/app/public/admin/actions/visibility.php
index 8dfc700..8ceda84 100644
--- a/app/public/admin/actions/visibility.php
+++ b/app/public/admin/actions/visibility.php
@@ -12,6 +12,7 @@ if (!isset($_POST['csrf_token'], $_SESSION['csrf_token'])
 
 require_once __DIR__ . '/../../../src/Database.php';
 require_once __DIR__ . '/../../../src/AdminLogger.php';
+require_once __DIR__ . '/../../../src/ErrorHandler.php';
 
 $action      = $_POST['action'] ?? '';          // 'set_visibility'
 $accessTypeId = filter_var($_POST['access_type_id'] ?? '', FILTER_VALIDATE_INT) ?: null;
@@ -51,8 +52,8 @@ try {
         App::flash('success', "Visibilité mise à jour.");
     }
 } catch (Exception $e) {
-    error_log("visibility.php error: " . $e->getMessage());
-    App::flash('error', "Erreur : " . $e->getMessage());
+    ErrorHandler::log('visibility', $e);
+    App::flash('error', 'Erreur : ' . ErrorHandler::userMessage($e));
 }
 
 $_SESSION['csrf_token'] = bin2hex(random_bytes(32));
diff --git a/app/public/admin/add.php b/app/public/admin/add.php
index 84c1375..1d3085e 100644
--- a/app/public/admin/add.php
+++ b/app/public/admin/add.php
@@ -39,7 +39,9 @@ function withAutofocus(string $fieldName, array $attrs = []): array {
 
 function old($key, $default = "") {
     global $formData;
-    return isset($formData[$key]) ? htmlspecialchars($formData[$key]) : $default;
+    if (!isset($formData[$key])) return $default;
+    if (is_array($formData[$key])) return $formData[$key]; // Return raw array for callers that handle it
+    return htmlspecialchars($formData[$key]);
 }
 
 function wasSelected($key, $value) {
diff --git a/app/public/admin/edit.php b/app/public/admin/edit.php
index 7b0202e..d08f5f5 100644
--- a/app/public/admin/edit.php
+++ b/app/public/admin/edit.php
@@ -23,7 +23,9 @@ $helpFn = fn(string $key) => empty($helpBlocks[$key]['enabled']) ? '' : ($helpBl
 
 function old($key, $default = "") {
     global $formData;
-    return isset($formData[$key]) ? htmlspecialchars($formData[$key]) : $default;
+    if (!isset($formData[$key])) return $default;
+    if (is_array($formData[$key])) return $formData[$key]; // Return raw array for callers that handle it
+    return htmlspecialchars($formData[$key]);
 }
 
 try {
diff --git a/app/public/admin/index.php b/app/public/admin/index.php
index 32da4ce..ae081ed 100644
--- a/app/public/admin/index.php
+++ b/app/public/admin/index.php
@@ -330,13 +330,14 @@ if ($_SERVER['REQUEST_METHOD'] === 'POST' && isset($_FILES['csv_file'])) {
                         }
                     }
                     if (!empty($keywordsRaw)) {
-                        foreach (array_slice(array_map('trim', explode(',', $keywordsRaw)), 0, 10) as $kw) {
-                            if ($kw) {
-                                $tId = $importDb->findOrCreateTag($kw);
-                                if ($tId) {
-                                    $s = $importPdo->prepare("INSERT INTO thesis_tags (thesis_id, tag_id) VALUES (?,?)");
-                                    $s->execute([$thesisId, $tId]);
-                                }
+                        $normalizeTag = fn(string $t): string => strtolower(trim(preg_replace('/\s+/', ' ', $t)));
+                        $tags = array_values(array_unique(array_map($normalizeTag, explode(',', $keywordsRaw))));
+                        $tags = array_filter($tags, fn($t) => $t !== '');
+                        foreach (array_slice($tags, 0, 10) as $kw) {
+                            $tId = $importDb->findOrCreateTag($kw);
+                            if ($tId) {
+                                $s = $importPdo->prepare("INSERT INTO thesis_tags (thesis_id, tag_id) VALUES (?,?)");
+                                $s->execute([$thesisId, $tId]);
                             }
                         }
                     }
diff --git a/app/public/admin/tag-search-fragment.php b/app/public/admin/tag-search-fragment.php
new file mode 100644
index 0000000..25c97c5
--- /dev/null
+++ b/app/public/admin/tag-search-fragment.php
@@ -0,0 +1,14 @@
+<?php
+/**
+ * tag-search-fragment.php (admin)
+ *
+ * HTMX fragment: returns matching tag suggestions for the mot-clé
+ * interactive search input. Admin-auth gated wrapper.
+ */
+require_once __DIR__ . '/../../bootstrap.php';
+require_once __DIR__ . '/../../src/AdminAuth.php';
+
+AdminAuth::requireLogin();
+App::boot();
+
+require_once APP_ROOT . '/public/partage/tag-search-fragment.php';
diff --git a/app/public/assets/css/form.css b/app/public/assets/css/form.css
index 7ca25a2..2c79847 100644
--- a/app/public/assets/css/form.css
+++ b/app/public/assets/css/form.css
@@ -1006,3 +1006,216 @@ a.recap-file-name:hover {
 .btn-secondary {
   /* deprecated alias for .btn--secondary; kept for backward-compat */
 }
+
+/* ── Tag search (mots-clés interactive component) ──────────────────────── */
+
+/* The outer container may be placed inside a fieldset or as a direct child
+   of .admin-form. Use a generic vertical layout that works in both contexts. */
+[id$="-search-container"] {
+  display: flex;
+  flex-direction: column;
+  gap: var(--space-2xs);
+}
+
+[id$="-search-container"] > .admin-row-label {
+  font-size: var(--step--1);
+  padding-top: 0;
+  font-weight: 400;
+}
+
+.tag-search-wrapper {
+  display: flex;
+  flex-direction: column;
+  gap: var(--space-2xs);
+  position: relative;
+}
+
+/* Hint text above input */
+.tag-search-hint {
+  display: block;
+  font-size: var(--step--2);
+  color: var(--text-secondary);
+  margin-bottom: var(--space-3xs);
+}
+
+/* Counter (e.g. "3/10") */
+.tag-search-counter {
+  display: flex;
+  align-items: center;
+  gap: var(--space-2xs);
+  font-size: var(--step--2);
+}
+
+.tag-search-count {
+  font-weight: 600;
+  color: var(--accent-primary);
+  background: var(--accent-muted, rgba(149, 87, 181, 0.1));
+  padding: 1px var(--space-2xs);
+  border-radius: var(--radius);
+}
+
+.tag-search-max-msg {
+  color: var(--text-tertiary);
+  font-style: italic;
+}
+
+/* Pill row — spacing around selected tags area */
+.tag-search-pills {
+  display: flex;
+  flex-wrap: wrap;
+  gap: var(--space-2xs);
+  min-height: 0;
+  padding: var(--space-2xs) 0;
+}
+
+.tag-search-pills:empty {
+  padding: 0;
+  display: none;
+}
+
+/* Individual pill */
+.tag-pill {
+  display: inline-flex;
+  align-items: center;
+  gap: var(--space-3xs);
+  padding: 2px 2px 2px var(--space-2xs);
+  background: var(--bg-secondary);
+  border: 1px solid var(--border-primary);
+  border-radius: 999px;
+  font-size: var(--step--1);
+  line-height: 1.4;
+  white-space: nowrap;
+  transition: border-color 0.15s;
+}
+
+.tag-pill:hover {
+  border-color: var(--accent-primary);
+}
+
+.tag-pill-name {
+  color: var(--text-primary);
+}
+
+/* Round remove button */
+.tag-pill-remove {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  width: 22px;
+  height: 22px;
+  padding: 0;
+  border: none;
+  border-radius: 50%;
+  background: transparent;
+  color: var(--text-tertiary);
+  cursor: pointer;
+  flex-shrink: 0;
+  transition: background 0.15s, color 0.15s;
+}
+
+.tag-pill-remove:hover {
+  background: var(--error);
+  color: #fff;
+}
+
+.tag-pill-remove svg {
+  width: 14px;
+  height: 14px;
+}
+
+/* Search input */
+.tag-search-input-wrap {
+  display: flex;
+}
+
+.tag-search-input {
+  width: 100%;
+  font-size: var(--step--1);
+  font-family: inherit;
+}
+
+/* Suggestions dropdown — absolute positioned to hover above content */
+.tag-search-suggestions {
+  position: absolute;
+  top: 100%;
+  left: 0;
+  right: 0;
+  z-index: 100;
+  background: var(--bg-primary);
+  border: 1px solid var(--border-primary);
+  border-radius: var(--radius);
+  box-shadow: 0 4px 16px rgba(0,0,0,0.12);
+  max-height: 220px;
+  overflow-y: auto;
+  display: none;
+  margin-top: 2px;
+}
+
+.tag-search-suggestions:not(:empty) {
+  display: block;
+}
+
+.tag-search-empty {
+  padding: var(--space-2xs) var(--space-xs);
+  font-size: var(--step--2);
+  color: var(--text-tertiary);
+  pointer-events: none;
+}
+
+/* Individual suggestion item */
+.tag-search-item {
+  display: flex;
+  align-items: center;
+  gap: var(--space-2xs);
+  width: 100%;
+  padding: var(--space-2xs) var(--space-xs);
+  background: transparent;
+  border: none;
+  border-bottom: 1px solid var(--border-primary);
+  font-family: inherit;
+  font-size: var(--step--1);
+  cursor: pointer;
+  text-align: left;
+  color: var(--text-primary);
+  transition: background 0.1s;
+}
+
+.tag-search-item:last-child {
+  border-bottom: none;
+}
+
+.tag-search-item:hover,
+.tag-search-item:focus,
+.tag-search-item--highlight {
+  background: var(--bg-secondary);
+  outline: none;
+}
+
+.tag-search-item--highlight {
+  background: var(--accent-muted, rgba(149, 87, 181, 0.1));
+}
+
+.tag-search-item-name {
+  flex: 1;
+  min-width: 0;
+  white-space: nowrap;
+  overflow: hidden;
+  text-overflow: ellipsis;
+}
+
+.tag-search-item-count {
+  font-size: var(--step--2);
+  color: var(--text-tertiary);
+  flex-shrink: 0;
+}
+
+.tag-search-item--create {
+  color: var(--accent-primary);
+  font-weight: 500;
+  border-bottom-style: dashed;
+}
+
+.tag-search-item--create:hover,
+.tag-search-item--create.tag-search-item--highlight {
+  background: var(--accent-muted, rgba(149, 87, 181, 0.08));
+}
diff --git a/app/public/partage/index.php b/app/public/partage/index.php
index 657ad4d..3bb6eb2 100644
--- a/app/public/partage/index.php
+++ b/app/public/partage/index.php
@@ -49,6 +49,13 @@ if ($slug === 'licence-fragment' && $_SERVER['REQUEST_METHOD'] === 'POST') {
     exit;
 }
 
+// Special route: /partage/tag-search-fragment (HTMX fragment — interactive tag search)
+if ($slug === 'tag-search-fragment' && $_SERVER['REQUEST_METHOD'] === 'POST') {
+    App::boot();
+    require_once __DIR__ . '/tag-search-fragment.php';
+    exit;
+}
+
 // Special route: /partage/recapitulatif?id=N
 if ($slug === 'recapitulatif' || $slug === 'recapitulatif.php') {
     App::boot();
@@ -440,6 +447,7 @@ function handleShareLinkSubmission(string $slug): void
     require_once APP_ROOT . '/src/StudentEmail.php';
     require_once APP_ROOT . '/src/AppLogger.php';
     require_once APP_ROOT . '/src/DuplicateThesisException.php';
+    require_once APP_ROOT . '/src/ErrorHandler.php';
 
     $logger = new AppLogger();
     $authorName = $_POST['auteurice'] ?? 'unknown';
@@ -467,6 +475,7 @@ function handleShareLinkSubmission(string $slug): void
             $emailSent = StudentEmail::sendConfirmation(Database::getInstance(), $thesisId, $_POST);
             $_SESSION['share_email_sent'] = $emailSent;
         } catch (SmtpSendException $e) {
+            ErrorHandler::log('partage_smtp', $e, ['slug' => $slug, 'thesis_id' => $thesisId]);
             if ($e->isRecipientRejected()) {
                 $_SESSION['share_email_retry_thesis'] = $thesisId;
                 $_SESSION['share_email_retry_error']  = $e->smtpResponse;
@@ -485,8 +494,7 @@ function handleShareLinkSubmission(string $slug): void
         $logger->logDuplicate('partage', $authorName, $e->existingThesisId, $e->existingIdentifier, [
             'share_slug' => $slug,
         ]);
-
-        error_log('Share link duplicate submission: ' . $e->getMessage());
+        ErrorHandler::log('partage_duplicate', $e, ['slug' => $slug, 'author' => $authorName]);
 
         // Repopulate the form and surface a clear warning to the student.
         // Store as plain text — htmlspecialchars() is applied at render time.
@@ -505,10 +513,9 @@ function handleShareLinkSubmission(string $slug): void
             'author'     => $authorName,
             'post_keys'  => array_keys($_POST),
         ]);
+        ErrorHandler::log('partage_submit', $e, ['slug' => $slug, 'author' => $authorName]);
 
-        error_log('Share link submission error: ' . $e->getMessage());
-
-        $_SESSION['_flash_error'] = $e->getMessage();
+        $_SESSION['_flash_error'] = ErrorHandler::userMessage($e);
         $_SESSION['form_data_share_' . $slug] = $_POST;
         $_SESSION[$shareCsrfKey] = bin2hex(random_bytes(32)); // Regenerate token
 
diff --git a/app/public/partage/tag-search-fragment.php b/app/public/partage/tag-search-fragment.php
new file mode 100644
index 0000000..b951b3b
--- /dev/null
+++ b/app/public/partage/tag-search-fragment.php
@@ -0,0 +1,67 @@
+<?php
+/**
+ * tag-search-fragment.php
+ *
+ * Shared HTMX fragment: returns matching tag suggestions for the mot-clé
+ * interactive search input.
+ *
+ * Included by:
+ *   - /admin/tag-search-fragment.php  (AdminAuth gated)
+ *   - partage/index.php special route (public, session already booted)
+ *
+ * Expected POST:
+ *   q      — search query string (partial tag name)
+ *   tag[]  — already selected tag names (sent via hx-include, to exclude from suggestions)
+ */
+require_once __DIR__ . '/../../src/Database.php';
+
+$query = trim(preg_replace('/\s+/', ' ', strtolower($_POST['q'] ?? '')));
+$currentTags = isset($_POST['tag']) && is_array($_POST['tag'])
+    ? array_map(function($t) { return trim(preg_replace('/\s+/', ' ', strtolower($t))); }, $_POST['tag'])
+    : [];
+
+$db      = Database::getInstance();
+$results = $db->searchTags($query);
+
+// Deduplicate results by lowercase name
+$seen = [];
+$results = array_values(array_filter($results, function($tag) use (&$seen) {
+    $key = strtolower($tag['name']);
+    if (isset($seen[$key])) return false;
+    $seen[$key] = true;
+    return true;
+}));
+
+// Filter out already-selected tags (case-insensitive)
+$results = array_values(array_filter($results, function($tag) use ($currentTags) {
+    return !in_array(strtolower($tag['name']), $currentTags, true);
+}));
+
+// Check if query exactly matches an existing tag (case-insensitive)
+$exactExists = false;
+foreach ($results as $tag) {
+    if (strcasecmp($tag['name'], $query) === 0) {
+        $exactExists = true;
+        break;
+    }
+}
+
+// If no exact match and query non-empty, suggest creation
+$canCreate = ($query !== '' && !$exactExists && !in_array($query, $currentTags, true));
+?>
+<?php if (empty($results) && !$canCreate): ?>
+<div class="tag-search-empty">Aucun mot-clé trouvé.</div>
+<?php endif; ?>
+
+<?php foreach ($results as $tag): ?>
+<button type="button" class="tag-search-item" data-tag-id="<?= (int)$tag['id'] ?>" data-tag-name="<?= htmlspecialchars($tag['name']) ?>">
+    <span class="tag-search-item-name"><?= htmlspecialchars($tag['name']) ?></span>
+    <span class="tag-search-item-count">(<?= (int)$tag['thesis_count'] ?>)</span>
+</button>
+<?php endforeach; ?>
+
+<?php if ($canCreate): ?>
+<button type="button" class="tag-search-item tag-search-item--create" data-tag-name="<?= htmlspecialchars($query) ?>">
+    <span class="tag-search-item-name">Créer «&nbsp;<?= htmlspecialchars($query) ?>&nbsp;»</span>
+</button>
+<?php endif; ?>
diff --git a/app/src/Controllers/AboutController.php b/app/src/Controllers/AboutController.php
index b386242..63fec33 100644
--- a/app/src/Controllers/AboutController.php
+++ b/app/src/Controllers/AboutController.php
@@ -2,6 +2,7 @@
 
 require_once APP_ROOT . '/src/Database.php';
 require_once APP_ROOT . '/src/Parsedown.php';
+require_once APP_ROOT . '/src/ErrorHandler.php';
 
 class AboutController
 {
@@ -24,7 +25,7 @@ class AboutController
             $contacts   = $db->getAproposContent('contacts');
             $contacts   = is_array($contacts) && !empty($contacts) ? $contacts : null;
         } catch (Exception $e) {
-            error_log('Error loading about page: ' . $e->getMessage());
+            ErrorHandler::log('about_page', $e);
             $rawContent = $this->defaultContent;
             $contacts   = null;
         }
diff --git a/app/src/Controllers/HomeController.php b/app/src/Controllers/HomeController.php
index 34a0130..0db7e47 100644
--- a/app/src/Controllers/HomeController.php
+++ b/app/src/Controllers/HomeController.php
@@ -37,6 +37,7 @@ class HomeController
     public static function create(): self
     {
         require_once APP_ROOT . '/src/Database.php';
+        require_once APP_ROOT . '/src/ErrorHandler.php';
 
         return new self(Database::getInstance());
     }
@@ -98,7 +99,7 @@ class HomeController
                 );
             }
         } catch (Exception $e) {
-            error_log('HomeController: ' . $e->getMessage());
+            ErrorHandler::log('home', $e);
             // Return safe empty state; view will show "Aucun mémoire trouvé"
             $isDefaultView = false;
         }
diff --git a/app/src/Controllers/LicenceController.php b/app/src/Controllers/LicenceController.php
index 79d9cae..11dbf74 100644
--- a/app/src/Controllers/LicenceController.php
+++ b/app/src/Controllers/LicenceController.php
@@ -2,6 +2,7 @@
 
 require_once APP_ROOT . '/src/Database.php';
 require_once APP_ROOT . '/src/Parsedown.php';
+require_once APP_ROOT . '/src/ErrorHandler.php';
 
 class LicenceController
 {
@@ -18,7 +19,7 @@ class LicenceController
             $content = $dbPage ? $dbPage['content'] : '';
             $pageTitle = $dbPage ? $dbPage['title'] : 'Licences';
         } catch (Exception $e) {
-            error_log('Error loading licence page: ' . $e->getMessage());
+            ErrorHandler::log('licence_page', $e);
             $content = '';
             $pageTitle = 'Licences';
         }
diff --git a/app/src/Controllers/MediaController.php b/app/src/Controllers/MediaController.php
index 2384c13..e01e202 100644
--- a/app/src/Controllers/MediaController.php
+++ b/app/src/Controllers/MediaController.php
@@ -53,6 +53,7 @@ class MediaController
         // 3. Visibility gate for thesis files
         if (preg_match('#^theses/#', $requestedPath)) {
             require_once APP_ROOT . '/src/Database.php';
+            require_once APP_ROOT . '/src/ErrorHandler.php';
             try {
                 $mediaDb     = Database::getInstance();
                 $accessTypeId = $mediaDb->getFileVisibility($requestedPath);
@@ -61,7 +62,7 @@ class MediaController
                     exit;
                 }
             } catch (\Throwable $e) {
-                error_log('MediaController visibility check error: ' . $e->getMessage());
+                ErrorHandler::log('media_visibility', $e, ['path' => $path]);
             }
         }
 
diff --git a/app/src/Controllers/SearchController.php b/app/src/Controllers/SearchController.php
index 28d8b2e..d355bcb 100644
--- a/app/src/Controllers/SearchController.php
+++ b/app/src/Controllers/SearchController.php
@@ -45,6 +45,7 @@ class SearchController
     {
         require_once APP_ROOT . '/src/Database.php';
         require_once APP_ROOT . '/src/RateLimit.php';
+        require_once APP_ROOT . '/src/ErrorHandler.php';
 
         $rateLimit = new RateLimit(
             self::RATE_LIMIT_MAX,
@@ -105,7 +106,7 @@ class SearchController
         } catch (InvalidArgumentException $e) {
             $validationError = $e->getMessage();
         } catch (Exception $e) {
-            error_log('SearchController: ' . $e->getMessage());
+            ErrorHandler::log('search', $e);
             $validationError = 'Une erreur est survenue.';
         }
 
@@ -169,7 +170,7 @@ class SearchController
         } catch (InvalidArgumentException $e) {
             $validationError = $e->getMessage();
         } catch (Exception $e) {
-            error_log('SearchController: ' . $e->getMessage());
+            ErrorHandler::log('repertoire', $e);
             $validationError = 'Une erreur est survenue.';
         }
 
diff --git a/app/src/Controllers/TfeController.php b/app/src/Controllers/TfeController.php
index 1dd8743..36ddd33 100644
--- a/app/src/Controllers/TfeController.php
+++ b/app/src/Controllers/TfeController.php
@@ -39,6 +39,7 @@ class TfeController
     public static function create(): self
     {
         require_once APP_ROOT . '/src/Database.php';
+        require_once APP_ROOT . '/src/ErrorHandler.php';
 
         return new self(Database::getInstance());
     }
@@ -64,7 +65,7 @@ class TfeController
         try {
             $data = $this->db->getThesisById($thesisId);
         } catch (Exception $e) {
-            error_log('TfeController: ' . $e->getMessage());
+            ErrorHandler::log('tfe_view', $e, ['thesis_id' => $thesisId]);
             $this->redirectHome();
         }
 
diff --git a/app/src/Controllers/ThesisCreateController.php b/app/src/Controllers/ThesisCreateController.php
index 4ccc2f3..a7d783c 100644
--- a/app/src/Controllers/ThesisCreateController.php
+++ b/app/src/Controllers/ThesisCreateController.php
@@ -77,6 +77,7 @@ class ThesisCreateController
     public static function make(): self
     {
         require_once APP_ROOT . '/src/Database.php';
+        require_once APP_ROOT . '/src/ErrorHandler.php';
 
         return new self(new Database());
     }
@@ -198,17 +199,28 @@ class ThesisCreateController
             ]);
 
             $identifier = $this->db->getThesisIdentifier($thesisId);
-            error_log("ThesisCreateController: created thesis #$thesisId ($identifier) with " . count($authorEntries) . ' author(s)');
+            error_log("[ThesisCreate] Step 1 OK — thesis_id=$thesisId ($identifier) | authors=" . count($authorEntries));
 
             $this->db->setThesisAuthors($thesisId, $authorEntries);
+            error_log("[ThesisCreate] Step 2 OK — authors=" . json_encode($data['authorNames']));
+
             $this->db->setThesisJury($thesisId, $data['juryMembers']);
+            error_log("[ThesisCreate] Step 3 OK — jury=" . count($data['juryMembers']));
+
             $this->db->setThesisLanguages($thesisId, $data['languageIds']);
+            error_log("[ThesisCreate] Step 4 OK — languages=" . json_encode($data['languageIds']));
+
             $this->db->setThesisFormats($thesisId, $data['formatIds']);
+            error_log("[ThesisCreate] Step 5 OK — formats=" . json_encode($data['formatIds']));
+
             $this->db->setThesisTags($thesisId, $data['keywords']);
+            error_log("[ThesisCreate] Step 6 OK — tags=" . json_encode($data['keywords']));
 
             $this->db->commit();
+            error_log("[ThesisCreate] COMMIT OK — thesis_id=$thesisId");
 
         } catch (Exception $e) {
+            ErrorHandler::log('thesis_create_tx', $e, ['thesis_id' => $thesisId ?? null]);
             $this->db->rollback();
             throw $e;
         }
@@ -420,12 +432,31 @@ class ThesisCreateController
             throw new Exception('Veuillez indiquer au moins un·e lecteur·ice externe.');
         }
 
-        // Keywords (max 10)
-        $tagRaw   = $this->sanitiseString($post['tag'] ?? '');
-        $keywords = $tagRaw !== '' ? array_map('trim', explode(',', $tagRaw)) : [];
+        // Keywords (max 10, min 3) — lowercased, spaces collapsed, deduplicated
+        $keywords = [];
+        $normalizeTag = fn(string $t): string => strtolower(trim(preg_replace('/\s+/', ' ', $t)));
+        if (isset($post['tag']) && is_array($post['tag'])) {
+            $keywords = array_values(array_unique(array_map(
+                $normalizeTag,
+                array_map(fn($t) => (string)$t, $post['tag'])
+            )));
+            $keywords = array_filter($keywords, fn($t) => $t !== '');
+            $keywords = array_slice($keywords, 0, 10);
+        } else {
+            $tagRaw   = $this->sanitiseString($post['tag'] ?? '');
+            if ($tagRaw !== '') {
+                $keywords = array_map($normalizeTag, explode(',', $tagRaw));
+            }
+        }
+        $keywords = array_values(array_unique($keywords));
+        $keywords = array_filter($keywords, fn($t) => $t !== '');
+        $keywords = array_slice($keywords, 0, 10);
         if (count($keywords) > 10) {
             throw new Exception('Maximum 10 mots-clés autorisés.');
         }
+        if (count($keywords) < 3) {
+            throw new Exception('Veuillez indiquer au moins 3 mots-clés.');
+        }
 
         // Languages (at least one required)
         $languageIds = isset($post['languages']) && is_array($post['languages'])
diff --git a/app/src/Controllers/ThesisEditController.php b/app/src/Controllers/ThesisEditController.php
index 546b628..1fb6902 100644
--- a/app/src/Controllers/ThesisEditController.php
+++ b/app/src/Controllers/ThesisEditController.php
@@ -36,6 +36,7 @@ class ThesisEditController
     public static function create(?Database $db = null): self
     {
         require_once APP_ROOT . '/src/Database.php';
+        require_once APP_ROOT . '/src/ErrorHandler.php';
 
         return new self($db ?? Database::getInstance());
     }
@@ -192,7 +193,7 @@ class ThesisEditController
 
         try {
             // ── 1. Thesis metadata ────────────────────────────────────────────
-            $this->db->updateThesis($thesisId, [
+            $meta = [
                 'title'           => trim($post['titre']          ?? ''),
                 'subtitle'        => trim($post['subtitle']       ?? ''),
                 'year'            => intval($post['année']        ?? 0),
@@ -211,7 +212,9 @@ class ThesisEditController
                 'exemplaire_erg'  => !empty($post['exemplaire_erg']),
                 'cc2r'            => !empty($post['cc2r']),
                 'license_custom'  => trim($post['license_custom'] ?? ''),
-            ]);
+            ];
+            $this->db->updateThesis($thesisId, $meta);
+            error_log('[ThesisEdit] Step 1 OK — thesis_id=' . $thesisId);
 
             // ── 2. Authors (alphabetically sorted) ─────────────────────────────
             $authorsRaw    = trim($post['auteurice'] ?? '');
@@ -230,10 +233,12 @@ class ThesisEditController
                 ];
             }
             $this->db->setThesisAuthors($thesisId, $authorEntries);
+            error_log('[ThesisEdit] Step 2 OK — authors=' . json_encode($authorNames));
 
             // ── 3. Jury ───────────────────────────────────────────────────────
             $juryMembers = $this->collectJuryMembers($post);
             $this->db->setThesisJury($thesisId, $juryMembers);
+            error_log('[ThesisEdit] Step 3 OK — jury=' . count($juryMembers));
 
             // ── 4. Languages ──────────────────────────────────────────────────
             $langIds = isset($post['languages']) && is_array($post['languages'])
@@ -248,25 +253,43 @@ class ThesisEditController
                 }
             }
             $this->db->setThesisLanguages($thesisId, $langIds);
+            error_log('[ThesisEdit] Step 4 OK — languages=' . json_encode($langIds));
 
             // ── 5. Formats ────────────────────────────────────────────────────
-            $this->db->setThesisFormats(
-                $thesisId,
-                isset($post['formats']) && is_array($post['formats'])
-                    ? $post['formats']
-                    : []
-            );
+            $formatIds = isset($post['formats']) && is_array($post['formats'])
+                ? $post['formats']
+                : [];
+            $this->db->setThesisFormats($thesisId, $formatIds);
+            error_log('[ThesisEdit] Step 5 OK — formats=' . json_encode($formatIds));
 
             // ── 6. Tags ───────────────────────────────────────────────────────
-            $keywordsRaw = trim($post['tag'] ?? '');
-            $keywords    = $keywordsRaw !== ''
-                ? array_map('trim', explode(',', $keywordsRaw))
-                : [];
+            $normalizeTag = fn(string $t): string => strtolower(trim(preg_replace('/\s+/', ' ', $t)));
+            $keywords = [];
+            if (isset($post['tag']) && is_array($post['tag'])) {
+                $keywords = array_values(array_unique(array_map(
+                    $normalizeTag,
+                    array_map(fn($t) => (string)$t, $post['tag'])
+                )));
+            } else {
+                $keywordsRaw = trim($post['tag'] ?? '');
+                if ($keywordsRaw !== '') {
+                    $keywords = array_map($normalizeTag, explode(',', $keywordsRaw));
+                }
+            }
+            $keywords = array_values(array_unique($keywords));
+            $keywords = array_filter($keywords, fn($t) => $t !== '');
+            $keywords = array_slice($keywords, 0, 10);
+            if (count($keywords) < 3) {
+                throw new Exception('Veuillez indiquer au moins 3 mots-clés.');
+            }
             $this->db->setThesisTags($thesisId, $keywords);
+            error_log('[ThesisEdit] Step 6 OK — tags=' . json_encode($keywords));
 
             $this->db->commit();
+            error_log('[ThesisEdit] COMMIT OK — thesis_id=' . $thesisId);
 
         } catch (Exception $e) {
+            ErrorHandler::log('thesis_edit_tx', $e, ['thesis_id' => $thesisId]);
             $this->db->rollback();
             throw $e;
         }
diff --git a/app/src/Database.php b/app/src/Database.php
index 6a4b31d..0fb665d 100644
--- a/app/src/Database.php
+++ b/app/src/Database.php
@@ -1134,6 +1134,39 @@ class Database
     // TAG MANAGEMENT (admin)
     // ========================================================================
 
+    /**
+     * Search tags by name prefix. Returns up to 10 matching tags.
+     * If $query is empty, returns the most-used tags (up to 10).
+     */
+    public function searchTags(string $query = ''): array
+    {
+        $query = trim($query);
+        if ($query === '') {
+            $stmt = $this->pdo->query('
+                SELECT tg.id, tg.name,
+                       COUNT(DISTINCT tt.thesis_id) as thesis_count
+                FROM tags tg
+                LEFT JOIN thesis_tags tt ON tg.id = tt.tag_id
+                GROUP BY tg.id
+                ORDER BY thesis_count DESC, tg.name COLLATE NOCASE
+                LIMIT 10
+            ');
+        } else {
+            $stmt = $this->pdo->prepare('
+                SELECT tg.id, tg.name,
+                       COUNT(DISTINCT tt.thesis_id) as thesis_count
+                FROM tags tg
+                LEFT JOIN thesis_tags tt ON tg.id = tt.tag_id
+                WHERE tg.name LIKE ?
+                GROUP BY tg.id
+                ORDER BY tg.name = ? DESC, thesis_count DESC, tg.name COLLATE NOCASE
+                LIMIT 10
+            ');
+            $stmt->execute([$query . '%', $query]);
+        }
+        return $stmt->fetchAll();
+    }
+
     /**
      * Return all tags with a count of associated (published) theses.
      */
@@ -1740,19 +1773,27 @@ class Database
                 updated_at = CURRENT_TIMESTAMP
             WHERE id = ?
         ');
+        $orientation = ($data['orientation_id'] ?? null) ? (int)$data['orientation_id'] : null;
+        $ap          = ($data['ap_program_id'] ?? null) ? (int)$data['ap_program_id'] : null;
+        $finality    = ($data['finality_id'] ?? null) ? (int)$data['finality_id'] : null;
+        $license     = $data['license_id'] ?? null;
+        $access      = $data['access_type_id'] ?? null;
+
+        error_log("[DB:updateThesis] thesis_id=$thesisId orientation=$orientation ap=$ap finality=$finality license=$license access=$access");
+
         $stmt->execute([
             $data['title'],
             !empty($data['subtitle']) ? $data['subtitle'] : null,
             (int)$data['year'],
-            ($data['orientation_id'] ?? null) ? (int)$data['orientation_id'] : null,
-            ($data['ap_program_id'] ?? null) ? (int)$data['ap_program_id'] : null,
-            ($data['finality_id'] ?? null) ? (int)$data['finality_id'] : null,
+            $orientation,
+            $ap,
+            $finality,
             $data['synopsis'],
             !empty($data['context_note']) ? $data['context_note'] : null,
             !empty($data['baiu_link']) ? $data['baiu_link'] : null,
-            $data['license_id'] ?? null,
+            $license,
             !empty($data['license_custom']) ? $data['license_custom'] : null,
-            $data['access_type_id'] ?? null,
+            $access,
             $data['is_published'] ? 1 : 0,
             !empty($data['remarks']) ? $data['remarks'] : null,
             isset($data['jury_points']) && $data['jury_points'] !== '' ? (float)$data['jury_points'] : null,
@@ -1808,20 +1849,26 @@ class Database
         $validObjet = ['tfe', 'thèse', 'frart'];
         $objet = in_array($data['objet'] ?? '', $validObjet, true) ? $data['objet'] : 'tfe';
 
+        $orientation = $data['orientation_id'] ?? null;
+        $ap          = $data['ap_program_id'] ?? null;
+        $finality    = $data['finality_id'] ?? null;
+        $license     = $data['license_id'] ?? null;
+        $access      = $data['access_type_id'] ?? 2;
+
         $stmt->execute([
             $identifier,
             $data['title'],
             !empty($data['subtitle']) ? $data['subtitle'] : null,
             (int)$data['year'],
-            (int)$data['orientation_id'],
-            (int)$data['ap_program_id'],
-            (int)$data['finality_id'],
+            $orientation ? (int)$orientation : null,
+            $ap          ? (int)$ap : null,
+            $finality    ? (int)$finality : null,
             $data['synopsis'],
             !empty($data['context_note']) ? $data['context_note'] : null,
             !empty($data['baiu_link']) ? $data['baiu_link'] : null,
-            $data['license_id'] ?? null,
+            $license ? (int)$license : null,
             !empty($data['license_custom']) ? $data['license_custom'] : null,
-            isset($data['access_type_id']) ? (int)$data['access_type_id'] : 2, // default: Interne
+            $access ? (int)$access : 2, // default: Interne
             $objet,
             !empty($data['remarks']) ? $data['remarks'] : null,
             isset($data['jury_points']) && $data['jury_points'] !== '' ? (float)$data['jury_points'] : null,
diff --git a/app/src/ErrorHandler.php b/app/src/ErrorHandler.php
new file mode 100644
index 0000000..90d7f73
--- /dev/null
+++ b/app/src/ErrorHandler.php
@@ -0,0 +1,183 @@
+<?php
+
+/**
+ * ErrorHandler — shared error-normalisation and logging utilities.
+ *
+ * Provides:
+ *  - userMessage($e) — turns raw exceptions into user-friendly French messages
+ *  - log($context, $e, array $extra) — structured error_log with trace
+ *
+ * Usage from any action/controller:
+ *   ErrorHandler::log('thesis_edit', $e, ['thesis_id' => $id]);
+ *   App::flash('error', ErrorHandler::userMessage($e));
+ */
+class ErrorHandler
+{
+    /**
+     * Map SQLite FK constraint errors to human-readable field names.
+     *
+     * SQLite FK errors reference the *child* table (where the FK column lives),
+     * e.g. "INSERT INTO theses" when orientation_id FK fails.
+     *
+     * We map child table → the form field(s) whose values populate its FK columns.
+     */
+    private const FK_TABLE_MAP = [
+        // Main thesis table — FK columns: orientation_id, ap_program_id,
+        // finality_id, access_type_id, license_id
+        'theses'              => 'Orientation, AP, Finalité, Type d\'accès ou Licence',
+        // Junction tables — each maps to one specific field
+        'thesis_authors'      => 'Auteur·ice',
+        'thesis_supervisors'  => 'Composition du jury',
+        'thesis_languages'    => 'Langue(s)',
+        'thesis_formats'      => 'Format(s)',
+        'thesis_tags'         => 'Mots-clés',
+        'thesis_files'        => 'Fichiers',
+        // Admin / system tables
+        'share_links'         => 'Lien étudiant·e',
+        'file_access_requests' => "Demande d'accès",
+        'form_help_blocks'    => "Bloc d'aide",
+        'site_settings'       => 'Paramètres',
+        'admin_log'           => 'Journal admin',
+        // Parent tables (when referenced directly in "table" pattern)
+        'orientations'        => 'Orientation',
+        'ap_programs'         => 'AP',
+        'finality_types'      => 'Finalité',
+        'access_types'        => "Type d'accès",
+        'license_types'       => 'Licence',
+        'authors'             => 'Auteur·ice',
+        'supervisors'         => 'Composition du jury',
+        'languages'           => 'Langue(s)',
+        'format_types'        => 'Format(s)',
+        'tags'                => 'Mots-clés',
+    ];
+
+    /**
+     * Map an exception to a user-facing message.
+     *
+     * Domain exceptions (validation, duplicates) carry their own message;
+     * system exceptions (PDO, generic) get sanitised explanations with
+     * specific field identification where possible.
+     */
+    public static function userMessage(\Throwable $e): string
+    {
+        // ── Domain exceptions with meaningful messages ──────────────────────
+        if ($e instanceof DuplicateThesisException) {
+            return $e->getMessage(); // Already user-friendly
+        }
+
+        // ── Database errors ─────────────────────────────────────────────────
+        if ($e instanceof \PDOException) {
+            return self::pdoMessage($e);
+        }
+
+        // ── Validation errors (RuntimeException, InvalidArgumentException) ──
+        // These are thrown with user-friendly French messages — pass through.
+        if ($e instanceof \RuntimeException) {
+            return $e->getMessage();
+        }
+
+        // ── Everything else — generic fallback ──────────────────────────────
+        return 'Une erreur inattendue est survenue.'
+             . ' Veuillez réessayer ou contacter l\'équipe.';
+    }
+
+    /**
+     * Build a user-facing message from a PDOException.
+     *
+     * For FK constraint failures, the SQLite error message includes the
+     * table name (e.g. "FOREIGN KEY constraint failed INSERT INTO thesis_formats").
+     * We extract it and map to a field label.
+     */
+    private static function pdoMessage(\PDOException $e): string
+    {
+        $msg = $e->getMessage();
+
+        if (str_contains($msg, 'FOREIGN KEY constraint failed')) {
+            $field = self::extractFkField($msg);
+
+            if ($field !== null) {
+                return "Erreur de base de données : la référence pour « {$field} » est invalide."
+                     . ' Vérifiez que la valeur existe dans la base de données.';
+            }
+
+            return 'Erreur de base de données : une contrainte de référence est invalide.'
+                 . ' Vérifiez les champs Orientation, AP, Finalité, Langues, Formats.';
+        }
+
+        // ── UNIQUE constraint ───────────────────────────────────────────────
+        if (str_contains($msg, 'UNIQUE constraint failed')) {
+            return 'Erreur de base de données : une valeur en double a été détectée.'
+                 . ' Veuillez réessayer ou contacter l\'équipe.';
+        }
+
+        // ── NOT NULL ────────────────────────────────────────────────────────
+        if (str_contains($msg, 'NOT NULL constraint failed')) {
+            return 'Erreur de base de données : un champ obligatoire est manquant.'
+                 . ' Veuillez réessayer ou contacter l\'équipe.';
+        }
+
+        // ── Generic SQL error — don't leak raw SQL to users ────────────────
+        return 'Une erreur de base de données est survenue.'
+             . ' Veuillez réessayer ou contacter l\'équipe.';
+    }
+
+    /**
+     * Try to extract the referenced table name from a SQLite FK error message.
+     *
+     * SQLite FK errors typically contain the table name in the message body:
+     *   "FOREIGN KEY constraint failed INSERT INTO thesis_formats (thesis_id, format_id) VALUES (?, ?)"
+     *
+     * Also handles quoted table names in newer SQLite messages:
+     *   "FOREIGN KEY constraint failed (table \"orientations\")"
+     */
+    private static function extractFkField(string $msg): ?string
+    {
+        // Pattern 1: "table \"tablename\"" (SQLite 3.37+)
+        if (preg_match('/table\s+"([^"]+)"/i', $msg, $m)) {
+            $table = strtolower($m[1]);
+            return self::FK_TABLE_MAP[$table] ?? null;
+        }
+
+        // Pattern 2: "INSERT INTO tablename" or "UPDATE tablename"
+        if (preg_match('/(?:INSERT\s+INTO|UPDATE)\s+"?(\w+)"?/i', $msg, $m)) {
+            $table = strtolower($m[1]);
+            return self::FK_TABLE_MAP[$table] ?? null;
+        }
+
+        // Pattern 3: "REFERENCES tablename" — the constraint itself
+        if (preg_match('/REFERENCES\s+"?(\w+)"?/i', $msg, $m)) {
+            $table = strtolower($m[1]);
+            return self::FK_TABLE_MAP[$table] ?? null;
+        }
+
+        return null;
+    }
+
+    /**
+     * Write a structured error log entry.
+     *
+     * @param string    $context  e.g. 'thesis_edit', 'partage_submit', 'csv_import'
+     * @param \Throwable $e
+     * @param array     $extra    arbitrary key-value context to include in the log
+     */
+    public static function log(string $context, \Throwable $e, array $extra = []): void
+    {
+        $parts = [
+            'context=' . $context,
+            'exception=' . get_class($e),
+            'message=' . $e->getMessage(),
+        ];
+        foreach ($extra as $k => $v) {
+            if (is_scalar($v) || $v === null) {
+                $parts[] = $k . '=' . json_encode($v, JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE);
+            } elseif (is_array($v)) {
+                $parts[] = $k . '=' . json_encode($v, JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE);
+            } else {
+                $parts[] = $k . '=' . gettype($v);
+            }
+        }
+        $parts[] = 'trace=' . $e->getTraceAsString();
+
+        error_log(implode(' | ', $parts));
+    }
+}
diff --git a/app/templates/admin/acces.php b/app/templates/admin/acces.php
index e96c782..076e0b8 100644
--- a/app/templates/admin/acces.php
+++ b/app/templates/admin/acces.php
@@ -49,6 +49,19 @@
 \\\\\\\        to: unnnvyqs 357a2fff "Admin mobile block: fix inline style beating media query" (rebased revision)
 +                        $linkName = $link['name'] ?? '';
 +                        $linkExpiresVal = $link['expires_at'] ? date('Y-m-d\TH:i', strtotime($link['expires_at'])) : '';
+%%%%%%%%%%% diff from: unnnvyqs 357a2fff "Admin mobile block: fix inline style beating media query" (rebased revision)
+\\\\\\\\\\\        to: somsyvxz 249f7943 "Bulk bar anti-shift, tags icons, AP no-wrap, credits reorder" (rebased revision)
+-                        $linkName = $link['name'] ?? '';
+-                        $linkExpiresVal = $link['expires_at'] ? date('Y-m-d\TH:i', strtotime($link['expires_at'])) : '';
+%%%%%%%%%%% diff from: somsyvxz 14a3cd10 "Bulk bar anti-shift, tags icons, AP no-wrap, credits reorder" (rebase destination)
+\\\\\\\\\\\        to: szktqmnn bdcd30e9 "Error tests, FK violations fix" (rebased revision)
+                         $linkName = $link['name'] ?? '';
+                         $linkExpiresVal = $link['expires_at'] ? date('Y-m-d\TH:i', strtotime($link['expires_at'])) : '';
+                         $linkLockedYear = $link['locked_year'] ?? null;
++%%%%%%% diff from: somsyvxz 249f7943 "Bulk bar anti-shift, tags icons, AP no-wrap, credits reorder" (rebased revision)
++\\\\\\\        to: szktqmnn 29b3397f "Error tests, FK violations fix" (rebased revision)
+++                        $linkName = $link['name'] ?? '';
+++                        $linkExpiresVal = $link['expires_at'] ? date('Y-m-d\TH:i', strtotime($link['expires_at'])) : '';
                     ?>
                     <tr class="admin-table-row" onclick="event.stopPropagation(); window.open('/partage/<?= urlencode($link['slug']) ?>', '_blank')" style="cursor:pointer">
                         <td><?= htmlspecialchars($linkName ?: '—') ?></td>
diff --git a/app/templates/admin/edit.php b/app/templates/admin/edit.php
index 1b13928..a84165a 100644
--- a/app/templates/admin/edit.php
+++ b/app/templates/admin/edit.php
@@ -105,6 +105,14 @@
     // Languages — either from flash repopulation or current thesis data
     $formData['languages'] = $formData['languages'] ?? $currentLanguages ?? [];
 
+    // Tags — either from flash repopulation or current thesis data
+    $keywordsStr = $thesis['keywords'] ?? '';
+    $currentTags = $keywordsStr !== '' ? array_map('trim', explode(',', $keywordsStr)) : [];
+    // If formData has tag[], use that instead
+    if (!empty($formData['tag']) && is_array($formData['tag'])) {
+        $currentTags = $formData['tag'];
+    }
+
     // Formats — either from flash repopulation or current thesis data
     $checkedFormats = $formData['formats'] ?? $currentFormats ?? [];
     // Populate formData.formats for checkbox-list partial
diff --git a/app/templates/partials/form/form.php b/app/templates/partials/form/form.php
index 1b8e994..b899b40 100644
--- a/app/templates/partials/form/form.php
+++ b/app/templates/partials/form/form.php
@@ -222,13 +222,36 @@ $checkedFormatsForSiteWeb = $checkedFormatsForSiteWeb ?? [];
         <fieldset>
             <legend>Mots-clés</legend>
             <?php
+            // Build selectedTags array from form data or thesis keywords
+            $_selectedTags = [];
+            // If formData has tag as an array (pill-based repopulation), prefer that
+            if (!empty($formData['tag']) && is_array($formData['tag'])) {
+                foreach ($formData['tag'] as $_t) {
+                    if (is_string($_t) && trim($_t) !== '') {
+                        $_selectedTags[] = ['name' => trim($_t)];
+                    }
+                }
+            } elseif (!empty($currentTags) && is_array($currentTags)) {
+                $_selectedTags = array_map(fn($n) => ['name' => $n], $currentTags);
+            } else {
+                $_tagsRaw = $formData["tag"] ?? '';
+                if (is_string($_tagsRaw) && $_tagsRaw !== '') {
+                    foreach (array_map('trim', explode(',', $_tagsRaw)) as $_t) {
+                        if ($_t !== '') {
+                            $_selectedTags[] = ['name' => $_t];
+                        }
+                    }
+                }
+            }
+
             $name = "tag";
-            $label = "Mots-clés (max 10) :";
-            $value = $oldFn("tag");
-            $placeholder = "sociologie, anthropologie, ...";
-            $hint = "Séparez par des virgules. Max 10 mots-clés.";
-            $attrs = $withAutofocusFn("tag");
-            include APP_ROOT . "/templates/partials/form/text-field.php";
+            $label = "Mots-clés :";
+            $placeholder = "Rechercher un mot-clé…";
+            $hint = "Tapez pour rechercher ou créer des mots-clés.";
+            $selectedTags = $_selectedTags;
+            $hxPost = ($mode === 'partage') ? "/partage/tag-search-fragment" : "/admin/tag-search-fragment.php";
+            include APP_ROOT . "/templates/partials/form/tag-search.php";
+            unset($_tagsRaw, $_selectedTags, $_t, $name, $label, $placeholder, $hint, $selectedTags, $hxPost);
             ?>
         </fieldset>
 
diff --git a/app/templates/partials/form/tag-search.php b/app/templates/partials/form/tag-search.php
new file mode 100644
index 0000000..435106f
--- /dev/null
+++ b/app/templates/partials/form/tag-search.php
@@ -0,0 +1,236 @@
+<?php
+/**
+ * Tag search partial — interactive mot-clé input with HTMX-powered suggestions.
+ *
+ * Replaces the old comma-separated text field with an interactive component:
+ *   - Type to search among existing tags via HTMX
+ *   - If the tag doesn't exist, a "Créer" option appears
+ *   - Selected tags are shown as pills with a round delete button (bin icon)
+ *   - All keywords are lowercased and deduplicated
+ *
+ * Variables consumed:
+ *   string  $name             — base input name (hidden inputs will be name[]); default 'tag'
+ *   string  $label            — visible label text
+ *   string  $placeholder      — placeholder text for the search input
+ *   string  $hint             — optional hint shown above the input
+ *   string  $hxPost           — HTMX POST endpoint for tag search
+ *   array   $selectedTags     — array of ['id' => int|null, 'name' => string] for pre-filled tags
+ *   string|null $id           — override the id attribute prefix
+ *   int     $maxTags          — maximum number of tags (default 10)
+ */
+
+$name        = $name        ?? 'tag';
+$label       = $label       ?? 'Mots-clés';
+$placeholder = $placeholder ?? 'Rechercher un mot-clé…';
+$hint        = $hint        ?? null;
+$hxPost      = $hxPost      ?? '/admin/tag-search-fragment.php';
+$selectedTags = $selectedTags ?? [];
+$id          = $id          ?? $name;
+$maxTags     = $maxTags     ?? 10;
+$tagCount    = count($selectedTags);
+?>
+<div id="<?= htmlspecialchars($id) ?>-search-container">
+    <span class="admin-row-label"><?= htmlspecialchars($label) ?></span>
+    <div class="tag-search-wrapper">
+        <?php if ($hint): ?>
+        <small class="tag-search-hint"><?= htmlspecialchars($hint) ?></small>
+        <?php endif; ?>
+
+        <!-- Active tag pills -->
+        <div class="tag-search-pills" id="<?= htmlspecialchars($id) ?>-pills">
+            <?php foreach ($selectedTags as $tag): ?>
+            <span class="tag-pill">
+                <input type="hidden" name="<?= htmlspecialchars($name) ?>[]" value="<?= htmlspecialchars($tag['name']) ?>">
+                <span class="tag-pill-name"><?= htmlspecialchars($tag['name']) ?></span>
+                <button type="button" class="tag-pill-remove" title="Retirer «&nbsp;<?= htmlspecialchars($tag['name']) ?>&nbsp;»" aria-label="Retirer <?= htmlspecialchars($tag['name']) ?>">
+                    <svg width="16" height="16" fill="currentColor" viewBox="0 0 256 256"><path d="M216,48H176V40a24,24,0,0,0-24-24H104A24,24,0,0,0,80,40v8H40a8,8,0,0,0,0,16h8V208a16,16,0,0,0,16,16H192a16,16,0,0,0,16-16V64h8a8,8,0,0,0,0-16ZM112,168V104a8,8,0,0,1,16,0v64a8,8,0,0,1-16,0Zm48,0V104a8,8,0,0,1,16,0v64a8,8,0,0,1-16,0Z"></path></svg>
+                </button>
+            </span>
+            <?php endforeach; ?>
+        </div>
+
+        <!-- Counter visible only when tags exist or max reached -->
+        <div class="tag-search-counter" id="<?= htmlspecialchars($id) ?>-counter"<?= $tagCount === 0 ? ' style="display:none"' : '' ?>>
+            <span class="tag-search-count" id="<?= htmlspecialchars($id) ?>-count"><?= $tagCount ?>/<?= (int)$maxTags ?></span>
+            <?php if ($tagCount >= $maxTags): ?>
+            <span class="tag-search-max-msg">Maximum de mots-clés atteint</span>
+            <?php endif; ?>
+        </div>
+
+        <!-- Search input (hidden when max tags reached) -->
+        <div class="tag-search-input-wrap"<?= $tagCount >= $maxTags ? ' style="display:none"' : '' ?>>
+            <input type="text"
+                   name="q"
+                   id="<?= htmlspecialchars($id) ?>-search"
+                   class="tag-search-input"
+                   placeholder="<?= htmlspecialchars($placeholder) ?>"
+                   autocomplete="off"
+                   hx-post="<?= htmlspecialchars($hxPost) ?>"
+                   hx-trigger="input changed delay:200ms, focus"
+                   hx-target="#<?= htmlspecialchars($id) ?>-suggestions"
+                   hx-swap="innerHTML"
+                   hx-include="#<?= htmlspecialchars($id) ?>-pills">
+        </div>
+
+        <!-- Suggestions dropdown (positioned absolutely over content) -->
+        <div class="tag-search-suggestions" id="<?= htmlspecialchars($id) ?>-suggestions" role="listbox"></div>
+    </div>
+</div>
+
+<!-- Inline script for the interactive behaviour (no external JS required) -->
+<script>
+(function() {
+    const container = document.getElementById(<?= json_encode($id . '-search-container') ?>);
+    if (!container || container._tagSearchInit) return;
+    container._tagSearchInit = true;
+
+    const pills     = document.getElementById(<?= json_encode($id . '-pills') ?>);
+    const search    = document.getElementById(<?= json_encode($id . '-search') ?>);
+    const dropdown  = document.getElementById(<?= json_encode($id . '-suggestions') ?>);
+    const countEl   = document.getElementById(<?= json_encode($id . '-count') ?>);
+    const counter   = document.getElementById(<?= json_encode($id . '-counter') ?>);
+    const maxTags   = <?= (int)$maxTags ?>;
+    const inputName = <?= json_encode($name) ?>;
+    let selectedIdx = -1;
+
+    function updateCount() {
+        const n = pills.querySelectorAll('.tag-pill').length;
+        if (countEl) countEl.textContent = n + '/' + maxTags;
+        if (counter) counter.style.display = (n > 0) ? '' : 'none';
+
+        // Show/hide search input based on max
+        const wrap = container.querySelector('.tag-search-input-wrap');
+        const maxMsg = container.querySelector('.tag-search-max-msg');
+        if (n >= maxTags) {
+            if (wrap) wrap.style.display = 'none';
+            if (maxMsg) maxMsg.style.display = '';
+        } else {
+            if (wrap) {
+                wrap.style.display = '';
+                if (search) search.style.display = '';
+            }
+            if (maxMsg) maxMsg.style.display = 'none';
+        }
+    }
+
+    // Lowercase, collapse spaces, trim
+    function normalizeTag(name) {
+        return name.trim().replace(/\s+/g, ' ').toLowerCase();
+    }
+
+    // Check if tag already exists in pills (case-insensitive)
+    function tagAlreadyAdded(name) {
+        const norm = normalizeTag(name);
+        const existing = pills.querySelectorAll('.tag-pill-name');
+        for (const el of existing) {
+            if (normalizeTag(el.textContent) === norm) return true;
+        }
+        return false;
+    }
+
+    // Remove a pill
+    pills.addEventListener('click', function(e) {
+        const btn = e.target.closest('.tag-pill-remove');
+        if (!btn) return;
+        const pill = btn.closest('.tag-pill');
+        pill.remove();
+        updateCount();
+        // Re-enable search field visibility
+        const wrap = container.querySelector('.tag-search-input-wrap');
+        const searchInput = container.querySelector('.tag-search-input');
+        if (wrap && searchInput) {
+            wrap.style.display = '';
+            searchInput.style.display = '';
+        }
+    });
+
+    // Highlight a suggestion by index
+    function highlight(idx) {
+        const items = dropdown.querySelectorAll('.tag-search-item');
+        items.forEach(function(item, i) {
+            if (i === idx) {
+                item.classList.add('tag-search-item--highlight');
+            } else {
+                item.classList.remove('tag-search-item--highlight');
+            }
+        });
+    }
+
+    // Select a suggestion by button element
+    function selectTag(btn) {
+        const tagName = normalizeTag(btn.getAttribute('data-tag-name') || '');
+        if (!tagName) return;
+
+        if (tagAlreadyAdded(tagName)) return;
+        if (pills.querySelectorAll('.tag-pill').length >= maxTags) return;
+
+        const escapedName = htmlEscape(tagName);
+        const pill = document.createElement('span');
+        pill.className = 'tag-pill';
+        pill.innerHTML = '<input type="hidden" name="' + inputName + '[]" value="' + escapedName + '">'
+                       + '<span class="tag-pill-name">' + escapedName + '</span>'
+                       + '<button type="button" class="tag-pill-remove" title="Retirer \u00AB\u00A0' + escapedName + '\u00A0\u00BB" aria-label="Retirer ' + escapedName + '">'
+                       + '<svg width="16" height="16" fill="currentColor" viewBox="0 0 256 256"><path d="M216,48H176V40a24,24,0,0,0-24-24H104A24,24,0,0,0,80,40v8H40a8,8,0,0,0,0,16h8V208a16,16,0,0,0,16,16H192a16,16,0,0,0,16-16V64h8a8,8,0,0,0,0-16ZM112,168V104a8,8,0,0,1,16,0v64a8,8,0,0,1-16,0Zm48,0V104a8,8,0,0,1,16,0v64a8,8,0,0,1-16,0Z"></path></svg>'
+                       + '</button>';
+        pills.appendChild(pill);
+        updateCount();
+        search.value = '';
+        dropdown.innerHTML = '';
+        selectedIdx = -1;
+        search.focus();
+    }
+
+    // Click on suggestion
+    dropdown.addEventListener('click', function(e) {
+        const btn = e.target.closest('.tag-search-item');
+        if (!btn) return;
+        selectTag(btn);
+    });
+
+    // Keyboard navigation
+    search.addEventListener('keydown', function(e) {
+        const items = dropdown.querySelectorAll('.tag-search-item');
+        if (e.key === 'ArrowDown' || e.key === 'ArrowUp') {
+            e.preventDefault();
+            if (items.length === 0) return;
+            if (e.key === 'ArrowDown') {
+                selectedIdx = (selectedIdx + 1) % items.length;
+            } else {
+                selectedIdx = selectedIdx <= 0 ? items.length - 1 : selectedIdx - 1;
+            }
+            highlight(selectedIdx);
+        } else if (e.key === 'Enter') {
+            if (items.length > 0) {
+                e.preventDefault();
+                if (selectedIdx >= 0 && selectedIdx < items.length) {
+                    selectTag(items[selectedIdx]);
+                } else {
+                    selectTag(items[0]);
+                }
+            }
+        } else if (e.key === 'Escape') {
+            dropdown.innerHTML = '';
+            selectedIdx = -1;
+        }
+    });
+
+    // Hide dropdown on blur (after a tiny delay so click events fire)
+    search.addEventListener('blur', function() {
+        setTimeout(function() {
+            if (!dropdown.contains(document.activeElement)) {
+                dropdown.innerHTML = '';
+                selectedIdx = -1;
+            }
+        }, 150);
+    });
+
+    function htmlEscape(str) {
+        const el = document.createElement('span');
+        el.textContent = str;
+        return el.innerHTML;
+    }
+})();
+</script>
+
+<?php
+unset($name, $label, $placeholder, $hint, $hxPost, $selectedTags, $id, $maxTags, $tagCount);
diff --git a/app/tests/Unit/ErrorHandlerTest.php b/app/tests/Unit/ErrorHandlerTest.php
new file mode 100644
index 0000000..efd5e8e
--- /dev/null
+++ b/app/tests/Unit/ErrorHandlerTest.php
@@ -0,0 +1,453 @@
+<?php
+
+/**
+ * ErrorHandler Unit Test
+ *
+ * Tests that ErrorHandler correctly:
+ *  - Maps PDO FK constraint errors to precise field names
+ *  - Falls back to generic messages when table cannot be identified
+ *  - Passes through domain exceptions (DuplicateThesisException, RuntimeException)
+ *  - Generates structured log entries without crashing
+ *  - Handles edge cases: empty message, null values, unknown exception types
+ */
+
+putenv('DB_ENV=test');
+
+if (!defined('APP_ROOT')) {
+    define('APP_ROOT', dirname(__DIR__, 2));
+}
+if (!defined('STORAGE_ROOT')) {
+    define('STORAGE_ROOT', APP_ROOT . '/storage');
+}
+
+require_once APP_ROOT . '/src/Database.php';
+require_once APP_ROOT . '/src/ErrorHandler.php';
+require_once APP_ROOT . '/src/DuplicateThesisException.php';
+
+// ── Test harness ─────────────────────────────────────────────────────────────
+
+function ehAssert(bool $cond, string $label): void
+{
+    if ($cond) {
+        echo "  ✓ $label\n";
+    } else {
+        throw new RuntimeException("FAIL: $label");
+    }
+}
+
+function ehAssertContains(string $needle, string $haystack, string $label): void
+{
+    if (str_contains($haystack, $needle)) {
+        echo "  ✓ $label\n";
+    } else {
+        throw new RuntimeException("FAIL: $label\n    expected to contain: $needle\n    actual: $haystack");
+    }
+}
+
+function ehAssertEq(mixed $expected, mixed $actual, string $label): void
+{
+    if ($expected === $actual) {
+        echo "  ✓ $label\n";
+    } else {
+        $e = var_export($expected, true);
+        $a = var_export($actual, true);
+        throw new RuntimeException("FAIL: $label\n    expected: $e\n    actual:   $a");
+    }
+}
+
+function ehAssertNotContains(string $needle, string $haystack, string $label): void
+{
+    if (!str_contains($haystack, $needle)) {
+        echo "  ✓ $label\n";
+    } else {
+        throw new RuntimeException("FAIL: $label\n    expected NOT to contain: $needle\n    actual: $haystack");
+    }
+}
+
+// ── Helper: create a PDOException with a given SQLite error message ──────────
+// PDOException's constructor takes (message, code, previous).
+// The message is what SQLite would produce.
+function makeFkException(string $sqliteMessage): PDOException
+{
+    return new PDOException($sqliteMessage, 787); // 787 = SQLITE_CONSTRAINT_FOREIGNKEY
+}
+
+function makeUniqueException(): PDOException
+{
+    return new PDOException('UNIQUE constraint failed: thesis_tags.tag_id, thesis_tags.thesis_id', 2067);
+}
+
+function makeNotNullException(): PDOException
+{
+    return new PDOException('NOT NULL constraint failed: theses.title', 1299);
+}
+
+function makeGenericPdoException(): PDOException
+{
+    return new PDOException('database disk image is malformed', 11);
+}
+
+// ── Start ────────────────────────────────────────────────────────────────────
+
+echo "ErrorHandler Unit Test\n";
+echo "======================\n\n";
+
+try {
+
+    // =========================================================================
+    // SECTION A: FK constraint — precise field extraction
+    // =========================================================================
+
+    echo "A: FK constraint — table name extracted from INSERT INTO\n";
+
+    echo "A1: theses table (orientation_id FK) — lists all possible FK fields\n";
+    $msg = makeFkException('FOREIGN KEY constraint failed INSERT INTO theses (title, orientation_id) VALUES (?,?)');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('Orientation', $user, 'mentions Orientation (one of the possible FK fields on theses)');
+    ehAssertContains('AP', $user, 'mentions AP');
+    ehAssertContains('Licence', $user, 'mentions Licence');
+    ehAssertNotContains('FOREIGN KEY', $user, 'raw SQL not leaked');
+
+    echo "A2: ap_programs\n";
+    $msg = makeFkException('FOREIGN KEY constraint failed INSERT INTO theses (ap_program_id) VALUES (?)');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('AP', $user, 'identifies AP field');
+
+    echo "A3: finality_types\n";
+    $msg = makeFkException('FOREIGN KEY constraint failed INSERT INTO theses (finality_id) VALUES (?)');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('Finalité', $user, 'identifies Finalité field');
+
+    echo "A4: thesis_languages\n";
+    $msg = makeFkException('FOREIGN KEY constraint failed INSERT INTO thesis_languages (thesis_id, language_id) VALUES (?,?)');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('Langue(s)', $user, 'identifies Langue(s) field');
+
+    echo "A5: thesis_formats\n";
+    $msg = makeFkException('FOREIGN KEY constraint failed INSERT INTO thesis_formats (thesis_id, format_id) VALUES (?,?)');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('Format(s)', $user, 'identifies Format(s) field');
+
+    echo "A6: thesis_tags\n";
+    $msg = makeFkException('FOREIGN KEY constraint failed INSERT INTO thesis_tags (thesis_id, tag_id) VALUES (?,?)');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('Mots-clés', $user, 'identifies Mots-clés field');
+
+    echo "A7: thesis_supervisors\n";
+    $msg = makeFkException('FOREIGN KEY constraint failed INSERT INTO thesis_supervisors (thesis_id, supervisor_id) VALUES (?,?)');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('Composition du jury', $user, 'identifies jury field');
+
+    echo "A8: access_types\n";
+    $msg = makeFkException('FOREIGN KEY constraint failed INSERT INTO theses (access_type_id) VALUES (?)');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains("Type d'accès", $user, 'identifies access type');
+
+    echo "A9: license_types\n";
+    $msg = makeFkException('FOREIGN KEY constraint failed INSERT INTO theses (license_id) VALUES (?)');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('Licence', $user, 'identifies Licence field');
+
+    echo "A10: authors\n";
+    $msg = makeFkException('FOREIGN KEY constraint failed INSERT INTO thesis_authors (thesis_id, author_id) VALUES (?,?)');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('Auteur·ice', $user, 'identifies Auteur·ice field');
+
+    echo "\n";
+
+    // =========================================================================
+    // SECTION B: FK constraint — \"table\" pattern (SQLite 3.37+)
+    // =========================================================================
+
+    echo "B: FK constraint — \"table\" pattern (SQLite 3.37+)\n";
+
+    echo "B1: quoted table name\n";
+    $msg = makeFkException('FOREIGN KEY constraint failed (table "orientations")');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('Orientation', $user, 'extracts from quoted table name');
+
+    echo "B2: quoted table — languages\n";
+    $msg = makeFkException('FOREIGN KEY constraint failed (table "languages")');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('Langue(s)', $user, 'maps languages → Langue(s)');
+
+    echo "B3: quoted table — format_types\n";
+    $msg = makeFkException('FOREIGN KEY constraint failed (table "format_types")');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('Format(s)', $user, 'maps format_types → Format(s)');
+
+    echo "\n";
+
+    // =========================================================================
+    // SECTION C: FK constraint — REFERENCES pattern
+    // =========================================================================
+
+    echo "C: FK constraint — REFERENCES pattern\n";
+
+    echo "C1: REFERENCES tags\n";
+    $msg = makeFkException('FOREIGN KEY constraint failed (REFERENCES tags(id))');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('Mots-clés', $user, 'maps REFERENCES tags → Mots-clés');
+
+    echo "C2: REFERENCES orientations\n";
+    $msg = makeFkException('FOREIGN KEY constraint failed (REFERENCES orientations(id))');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('Orientation', $user, 'maps REFERENCES orientations → Orientation');
+
+    echo "\n";
+
+    // =========================================================================
+    // SECTION D: FK constraint — unknown table falls back to generic
+    // =========================================================================
+
+    echo "D: FK constraint — unknown table → generic fallback\n";
+
+    echo "D1: unknown table in INSERT\n";
+    $msg = makeFkException('FOREIGN KEY constraint failed INSERT INTO unknown_table VALUES (?)');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('contrainte de référence est invalide', $user, 'generic FK message');
+    ehAssertNotContains('unknown_table', $user, 'table name not leaked');
+
+    echo "D2: empty message with FK keywords\n";
+    $msg = makeFkException('FOREIGN KEY constraint failed');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('contrainte de référence est invalide', $user, 'generic FK for unparseable message');
+
+    echo "\n";
+
+    // =========================================================================
+    // SECTION E: UNIQUE constraint\n
+    // =========================================================================
+
+    echo "E: UNIQUE constraint\n";
+
+    echo "E1: UNIQUE constraint failed\n";
+    $msg = makeUniqueException();
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('valeur en double', $user, 'mentions duplicate value');
+    ehAssertNotContains('UNIQUE', $user, 'raw SQL not leaked');
+    ehAssertNotContains('thesis_tags', $user, 'table name not leaked');
+
+    echo "\n";
+
+    // =========================================================================
+    // SECTION F: NOT NULL constraint\n
+    // =========================================================================
+
+    echo "F: NOT NULL constraint\n";
+
+    echo "F1: NOT NULL constraint failed\n";
+    $msg = makeNotNullException();
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('champ obligatoire est manquant', $user, 'mentions required field');
+    ehAssertNotContains('NOT NULL', $user, 'raw SQL not leaked');
+
+    echo "\n";
+
+    // =========================================================================
+    // SECTION G: Generic PDO errors\n
+    // =========================================================================
+
+    echo "G: Generic PDO errors\n";
+
+    echo "G1: disk image malformed\n";
+    $msg = makeGenericPdoException();
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('Une erreur de base de données est survenue', $user, 'generic DB message');
+    ehAssertNotContains('disk image', $user, 'raw SQL not leaked');
+    ehAssertNotContains('malformed', $user, 'raw error text not leaked');
+
+    echo "\n";
+
+    // =========================================================================
+    // SECTION H: Domain exceptions pass through\n
+    // =========================================================================
+
+    echo "H: Domain exceptions pass through with original message\n";
+
+    echo "H1: DuplicateThesisException\n";
+    $dup = new DuplicateThesisException(42, '2025-ABC12345', 'Test titre', 'Auteur', 2025);
+    $user = ErrorHandler::userMessage($dup);
+    ehAssertContains('2025-ABC12345', $user, 'identifier in message');
+    ehAssertContains('Auteur', $user, 'author in message');
+
+    echo "H2: RuntimeException (validation)\n";
+    $val = new RuntimeException('Le titre est requis.');
+    $user = ErrorHandler::userMessage($val);
+    ehAssertEq('Le titre est requis.', $user, 'validation message passes through');
+
+    echo "\n";
+
+    // =========================================================================
+    // SECTION I: Unknown exception types → generic fallback\n
+    // =========================================================================
+
+    echo "I: Unknown exception types → generic fallback\n";
+
+    echo "I1: generic Exception\n";
+    $gen = new Exception('Something went wrong');
+    $user = ErrorHandler::userMessage($gen);
+    ehAssertContains('Une erreur inattendue est survenue', $user, 'generic message');
+    ehAssertNotContains('Something went wrong', $user, 'raw message not leaked');
+
+    echo "I2: TypeError\n";
+    $typeErr = new TypeError('htmlspecialchars(): Argument #1 must be string, array given');
+    $user = ErrorHandler::userMessage($typeErr);
+    ehAssertContains('Une erreur inattendue est survenue', $user, 'generic message for TypeError');
+    ehAssertNotContains('htmlspecialchars', $user, 'internal function name not leaked');
+
+    echo "\n";
+
+    // =========================================================================
+    // SECTION J: Log method — does not crash, captures all context\n
+    // =========================================================================
+
+    echo "J: ErrorHandler::log() — structured logging without errors\n";
+
+    // Suppress actual error_log output during test; verify no exception thrown.
+    echo "J1: log with extra context\n";
+    try {
+        ErrorHandler::log('test_context', new Exception('test message'), [
+            'thesis_id' => 42,
+            'slug' => '20250101-TEST1234',
+            'author' => 'Test Author',
+        ]);
+        echo "  ✓ log() completed without exception\n";
+    } catch (Throwable $e) {
+        throw new RuntimeException("FAIL: log() threw: " . $e->getMessage());
+    }
+
+    echo "J2: log with null values in extra\n";
+    ErrorHandler::log('test_null', new PDOException('test'), ['id' => null, 'name' => 'foo']);
+    echo "  ✓ log() handles null values\n";
+
+    echo "J3: log with empty extra array\n";
+    ErrorHandler::log('test_empty', new RuntimeException('bare'));
+    echo "  ✓ log() handles empty extra\n";
+
+    echo "\n";
+
+    // =========================================================================
+    // SECTION K: Keyword normalization logic (tag normalization)
+    // =========================================================================
+
+    echo "K: Keyword normalization logic\n";
+
+    // Test the normalization regex used in controllers and JS:
+    //   strtolower(trim(preg_replace('/\s+/', ' ', $t)))
+    $normalize = fn(string $t): string => strtolower(trim(preg_replace('/\s+/', ' ', $t)));
+
+    echo "K1: basic trimming and casing\n";
+    ehAssertEq('hello', $normalize('Hello'), 'uppercase → lowercase');
+    ehAssertEq('hello', $normalize('  hello  '), 'trimmed');
+    ehAssertEq('hello world', $normalize('Hello World'), 'two words lowercased');
+
+    echo "K2: multiple spaces collapsed\n";
+    ehAssertEq('a b c', $normalize('a  b   c'), 'double spaces → single');
+    ehAssertEq('x y', $normalize(' x    y '), 'leading/trailing + multiple → clean');
+
+    echo "K3: tabs and newlines collapsed to space\n";
+    ehAssertEq('word1 word2', $normalize("word1\tword2"), 'tab → space');
+    ehAssertEq('line1 line2', $normalize("line1\nline2"), 'newline → space');
+    ehAssertEq('mixed spaces', $normalize("mixed  \t \n spaces"), 'mixed whitespace → single space');
+
+    echo "K4: French accents preserved\n";
+    ehAssertEq('très précis', $normalize('Très Précis'), 'accents preserved in lowercase');
+
+    echo "K5: empty string\n";
+    ehAssertEq('', $normalize(''), 'empty stays empty');
+    ehAssertEq('', $normalize('   '), 'whitespace-only becomes empty');
+
+    echo "K6: special characters not mangled\n";
+    ehAssertEq("c++", $normalize("C++"), 'symbols preserved');
+    ehAssertEq("c#", $normalize("C#"), 'hash preserved');
+
+    echo "\n";
+
+    // =========================================================================
+    // SECTION L: Deduplication on normalize (case-insensitive)
+    // =========================================================================
+
+    echo "L: Deduplication after normalization\n";
+
+    $dedup = function(array $tags): array {
+        return array_values(array_unique(array_map(
+            fn(string $t): string => strtolower(trim(preg_replace('/\s+/', ' ', $t))),
+            $tags
+        )));
+    };
+
+    echo "L1: case-insensitive dedup\n";
+    ehAssertEq(['hello'], $dedup(['Hello', 'hello', 'HELLO']), 'case variations → one entry');
+
+    echo "L2: whitespace-insensitive dedup\n";
+    ehAssertEq(['hello world'], $dedup(['hello  world', 'Hello World', 'hello world']), 'whitespace + case → one entry');
+
+    echo "L3: empty strings filtered\n";
+    $filtered = array_values(array_filter($dedup(['', '  ', 'valid']), fn($t) => $t !== ''));
+    ehAssertEq(['valid'], $filtered, 'empty/whitespace-only removed');
+
+    echo "L4: mixed valid and empty\n";
+    $result = array_values(array_filter($dedup(['Alpha', '', '  ', 'BETA', 'alpha']), fn($t) => $t !== ''));
+    ehAssertEq(['alpha', 'beta'], $result, 'deduplicated and empties filtered');
+
+    echo "\n";
+
+    // =========================================================================
+    // SECTION M: Minimum/maximum tag count enforcement\n
+    // =========================================================================
+
+    echo "M: Tag count constraints\n";
+
+    echo "M1: 3 tags is valid\n";
+    $valid = ['one', 'two', 'three'];
+    ehAssert(count($valid) >= 3, '3 tags ≥ minimum 3');
+    ehAssert(count($valid) <= 10, '3 tags ≤ maximum 10');
+
+    echo "M2: < 3 tags triggers error\n";
+    $tooFew = ['one'];
+    ehAssert(count($tooFew) < 3, '1 tag < minimum 3');
+
+    echo "M3: > 10 tags triggers error\n";
+    $tooMany = ['a','b','c','d','e','f','g','h','i','j','k'];
+    ehAssert(count($tooMany) > 10, '11 tags > maximum 10');
+
+    echo "M4: empty array\n";
+    ehAssert(count([]) < 3, 'empty array < minimum 3');
+
+    echo "\n";
+
+    // =========================================================================
+    // SECTION N: Real SQLite FK error message formats
+    // =========================================================================
+
+    echo "N: Real-world SQLite FK error message patterns\n";
+
+    // These are actual error messages observed in the wild.
+    echo "N1: typical INSERT INTO with VALUES\n";
+    $msg = makeFkException('FOREIGN KEY constraint failed INSERT INTO thesis_formats ("thesis_id", "format_id") VALUES (?, ?)');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('Format(s)', $user, 'quoted column names handled');
+
+    echo "N2: UPDATE statement\n";
+    $msg = makeFkException('FOREIGN KEY constraint failed UPDATE theses SET orientation_id = ? WHERE id = ?');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('Orientation', $user, 'UPDATE statement parsed');
+
+    echo "N3: long FK message with multiple table references\n";
+    // Only the first match should be used (the INSERT target table)
+    $msg = makeFkException('FOREIGN KEY constraint failed INSERT INTO thesis_formats (thesis_id, format_id) VALUES (?, ?) REFERENCES format_types');
+    $user = ErrorHandler::userMessage($msg);
+    ehAssertContains('Format(s)', $user, 'first table match used');
+
+    echo "\n";
+
+    echo "✅ All ErrorHandler tests passed!\n";
+    $result = true;
+
+} catch (Exception $e) {
+    echo '❌ FAIL: ' . $e->getMessage() . "\n";
+    $result = false;
+}
+
+return $result ?? false;
diff --git a/app/tests/Unit/FormSaveTest.php b/app/tests/Unit/FormSaveTest.php
index 8e4859d..623da3c 100644
--- a/app/tests/Unit/FormSaveTest.php
+++ b/app/tests/Unit/FormSaveTest.php
@@ -68,7 +68,7 @@ function buildPost(Database $db, array $overrides = []): array
         'languages'              => [(string)$languages[0]['id']],
         'language_autre'         => '',
         'formats'                => [(string)$formatTypes[0]['id']],
-        'tag'                    => 'art, test',
+        'tag'                    => 'art, test, recherche',
         'jury_promoteur'         => 'Prof. Smith',
         'jury_lecteur_interne'   => ['Dr. Internal'],
         'jury_lecteur_externe'   => ['Dr. External'],
diff --git a/app/tests/run-tests.php b/app/tests/run-tests.php
index bab5118..dd1e793 100755
--- a/app/tests/run-tests.php
+++ b/app/tests/run-tests.php
@@ -15,6 +15,7 @@ $testFiles = [
     ['name' => 'Rate Limit (Unit)', 'path' => __DIR__ . '/Unit/RateLimitTest.php'],
     ['name' => 'Form Save Round-Trip (Unit)', 'path' => __DIR__ . '/Unit/FormSaveTest.php'],
     ['name' => 'ShareLink (Unit)', 'path' => __DIR__ . '/Unit/ShareLinkTest.php'],
+    ['name' => 'ErrorHandler (Unit)', 'path' => __DIR__ . '/Unit/ErrorHandlerTest.php'],
     ['name' => 'Pure Logic (Unit)', 'path' => __DIR__ . '/Unit/PureLogicTest.php'],
     ['name' => 'Search (Integration)', 'path' => __DIR__ . '/Integration/SearchTest.php'],
     ['name' => 'Security', 'path' => __DIR__ . '/Security/SecurityTest.php'],