diff --git a/web/modules/custom/figli_compta_ledger/js/home.js b/web/modules/custom/figli_compta_ledger/js/home.js
index 328caab..a51f678 100644
--- a/web/modules/custom/figli_compta_ledger/js/home.js
+++ b/web/modules/custom/figli_compta_ledger/js/home.js
@@ -57,6 +57,12 @@
   // more than enough rounds to walk the entire MIN_LOADABLE_DATE..
   // MAX_LOADABLE_DATE span at EXTEND_MONTHS per round.
   const MAX_ENSURE_SCROLLABLE_ROUNDS = 30;
+  // How often to poll for other users' changes (see pollForChanges()) --
+  // a plain setInterval rather than anything push-based (no Socket.io/
+  // websocket infra for a 6-person internal tool); this is far more
+  // frequent than table content actually changes, but the requests are
+  // cheap and it keeps everyone's view close to live.
+  const POLL_INTERVAL_MS = 8000;
 
   // Absolute bounds on how far the window can extend. Without these,
   // loadOlder()/loadNewer() kept pushing windowStart/windowEnd outward
@@ -148,6 +154,23 @@
     return fetchLignes(API_BASE + '?' + params.toString());
   }
 
+  // Any ligne_comptable changed after `tsSeconds` (a Unix timestamp) --
+  // backs the polling in pollForChanges() below, so one user's edit
+  // shows up in everyone else's table without a manual reload. `changed`
+  // is stored as a Unix timestamp internally; JSON:API exposes it as an
+  // ISO 8601 string in *responses* but only accepts the raw timestamp as
+  // a *filter value* -- confirmed live (an ISO string filter value
+  // silently matched everything instead of narrowing the query).
+  async function fetchChangedSince(tsSeconds) {
+    const params = new URLSearchParams();
+    params.set('include', 'field_repartition,field_repartition.field_compte,field_client,field_entree_liee');
+    params.set('filter[changedFilter][condition][path]', 'changed');
+    params.set('filter[changedFilter][condition][operator]', '>');
+    params.set('filter[changedFilter][condition][value]', String(tsSeconds));
+    params.set('sort', 'changed');
+    return fetchLignes(API_BASE + '?' + params.toString());
+  }
+
   async function fetchClientNames() {
     // page[limit]=200 is silently clamped to core's hard cap of 50 by
     // JSON:API (Query\OffsetPage::SIZE_MAX) -- with 106 client terms,
@@ -186,32 +209,45 @@
   // full edit form. Fetches a fresh CSRF token each time (core's
   // /session/token) rather than caching one -- this is an occasional
   // action, not worth the complexity of handling a stale cached token.
-  async function updateLigneType(nid, type) {
+  // `changed` (the row's last-known changed timestamp) lets the server
+  // reject a save-over-a-stale-view instead of silently overwriting
+  // someone else's concurrent edit -- see LedgerActionsController::
+  // checkConflict(). The thrown error's `.status` lets callers tell a
+  // 409 conflict apart from any other failure.
+  async function updateLigneType(nid, type, changed) {
     const tokenRes = await fetch('/session/token');
     const token = await tokenRes.text();
     const res = await fetch('/lignes/' + nid + '/type', {
       method: 'POST',
       headers: { 'Content-Type': 'application/json', 'X-CSRF-Token': token },
-      body: JSON.stringify({ type }),
+      body: JSON.stringify({ type, changed }),
     });
     const json = await res.json().catch(() => ({}));
-    if (!res.ok) throw new Error(json.error || ('/lignes/' + nid + '/type a répondu ' + res.status));
+    if (!res.ok) {
+      const err = new Error(json.error || ('/lignes/' + nid + '/type a répondu ' + res.status));
+      err.status = res.status;
+      throw err;
+    }
     return json;
   }
 
   // POST /lignes/{nid}/champ -- change client/facture/libellé without
-  // opening the full edit form. Same fresh-token-per-call reasoning as
-  // updateLigneType() above.
-  async function updateLigneField(nid, field, value) {
+  // opening the full edit form. Same fresh-token-per-call and conflict-
+  // detection reasoning as updateLigneType() above.
+  async function updateLigneField(nid, field, value, changed) {
     const tokenRes = await fetch('/session/token');
     const token = await tokenRes.text();
     const res = await fetch('/lignes/' + nid + '/champ', {
       method: 'POST',
       headers: { 'Content-Type': 'application/json', 'X-CSRF-Token': token },
-      body: JSON.stringify({ field, value }),
+      body: JSON.stringify({ field, value, changed }),
     });
     const json = await res.json().catch(() => ({}));
-    if (!res.ok) throw new Error(json.error || ('/lignes/' + nid + '/champ a répondu ' + res.status));
+    if (!res.ok) {
+      const err = new Error(json.error || ('/lignes/' + nid + '/champ a répondu ' + res.status));
+      err.status = res.status;
+      throw err;
+    }
     return json;
   }
 
@@ -291,6 +327,13 @@
       rows.push({
         id: node.id,
         nid: attrs.drupal_internal__nid,
+        // ISO 8601 string (ok as an opaque token here, only ever
+        // compared for equality/passed straight back to the server) --
+        // sent back on the next inline edit so the server can detect
+        // "someone else saved this line in between" and reject instead
+        // of silently overwriting. See LedgerActionsController::
+        // checkConflict() and pollForChanges()/mergeChangedRows() below.
+        changed: attrs.changed,
         date: attrs.field_date_ligne,
         type: attrs.field_type_ligne,
         client: clientTerm ? clientTerm.attributes.name : null,
@@ -352,6 +395,9 @@
         // group again for every other sortie that happens to link to
         // the same entrée.
         resolvedLinkGroups: new Set(),
+        // Unix timestamp (seconds) -- everything with `changed` after
+        // this has appeared since the last poll. See pollForChanges().
+        lastPollTs: null,
         // Which row's type badge is currently showing its inline <select>
         // instead of the badge -- only one at a time.
         editingTypeId: null,
@@ -817,6 +863,57 @@
         }
         await Promise.all(toFetch.map((nid) => this.fetchGroupFromNid(nid).catch(() => {})));
       },
+      // Live multi-user updates without websocket/Socket.io infra --
+      // plain polling (see POLL_INTERVAL_MS) is simple, fits the
+      // existing fetch-based architecture, and is plenty for a
+      // 6-person internal tool. A failed poll is silent and just tried
+      // again next tick (matches other background-refresh code here);
+      // lastPollTs is deliberately *not* advanced on failure, so a
+      // transient network blip doesn't miss whatever changed during it.
+      startPolling() {
+        setInterval(() => this.pollForChanges(), POLL_INTERVAL_MS);
+      },
+      async pollForChanges() {
+        try {
+          const { data, includedMap } = await fetchChangedSince(this.lastPollTs);
+          if (data.length) {
+            this.mergeChangedRows(buildRows(data, includedMap));
+          }
+          this.lastPollTs = Math.floor(Date.now() / 1000);
+        } catch (err) {
+          // silent -- see comment above.
+        }
+      },
+      // Patches already-loaded rows in place (mutates each row's own
+      // properties via Object.assign, not the `rows`/`groupExtraRows`
+      // arrays themselves) so Vue's reactivity updates just the
+      // affected cells, without re-triggering the `rows` watcher (and
+      // so ensureLinkedReconciliationResolved()) for routine polls that
+      // only touch content already known locally. A row currently being
+      // edited is left alone entirely -- overwriting its value out from
+      // under an in-progress keystroke would be worse than a few
+      // seconds of staleness; it'll pick up on the next poll once
+      // editing finishes. Genuinely new lines (not loaded at all yet)
+      // that fall inside the current window get appended -- that's the
+      // one case that *does* need the array reassigned, since there's
+      // no existing row object to mutate.
+      mergeChangedRows(changedRows) {
+        const isBeingEdited = (id) => this.editingTypeId === id || (this.editingCell && this.editingCell.id === id);
+        const known = new Map([...this.rows, ...this.groupExtraRows].map((r) => [r.id, r]));
+        const newOnes = [];
+        for (const fresh of changedRows) {
+          if (isBeingEdited(fresh.id)) continue;
+          const existing = known.get(fresh.id);
+          if (existing) {
+            Object.assign(existing, fresh);
+          } else if (fresh.date >= this.windowStart && fresh.date < this.windowEnd) {
+            newOnes.push(fresh);
+          }
+        }
+        if (newOnes.length) {
+          this.rows = [...this.rows, ...newOnes].sort((a, b) => (a.date || '').localeCompare(b.date || ''));
+        }
+      },
       startEditType(item) {
         this.typeUpdateError = null;
         this.editingTypeId = item.id;
@@ -832,11 +929,12 @@
         this.editingTypeId = null;
         if (newType === item.type) return;
         try {
-          const result = await updateLigneType(item.nid, newType);
+          const result = await updateLigneType(item.nid, newType, item.changed);
           const row = this.rows.find((r) => r.id === item.id);
           if (row) {
             row.type = newType;
             row.linkable = LINKABLE_TYPES.includes(newType);
+            row.changed = result.changed;
             if (result.entree_liee_cleared) {
               row.entreeLieeIds = [];
               row.entreeLieeLabels = [];
@@ -845,6 +943,7 @@
           this.reloadWindow();
         } catch (err) {
           this.typeUpdateError = err.message;
+          if (err.status === 409) this.refreshSingleRow(item.id, item.nid);
         }
       },
       startEditCell(item, field) {
@@ -863,9 +962,12 @@
         this.editingCell = null;
         if (newValue === (item[field] || '')) return;
         try {
-          const result = await updateLigneField(item.nid, field, newValue);
+          const result = await updateLigneField(item.nid, field, newValue, item.changed);
           const row = this.rows.find((r) => r.id === item.id);
-          if (row) row[field] = result.value;
+          if (row) {
+            row[field] = result.value;
+            row.changed = result.changed;
+          }
           // A client name with no existing match gets created on the fly
           // (server-side) rather than rejected -- reflect it in the
           // filter dropdown/datalist immediately instead of only after a
@@ -875,6 +977,25 @@
           }
         } catch (err) {
           this.typeUpdateError = err.message;
+          if (err.status === 409) this.refreshSingleRow(item.id, item.nid);
+        }
+      },
+      // 409 conflict from saveType()/saveCell() above -- someone else
+      // saved this exact line in between. Re-fetch just this one node
+      // and patch it in place, so the row reflects their change right
+      // away instead of staying stuck on the stale view that caused the
+      // rejection (the user would otherwise hit the same conflict again
+      // on retry without understanding why).
+      async refreshSingleRow(id, nid) {
+        try {
+          const { data, includedMap } = await fetchLignesByNids([nid]);
+          if (!data.length) return;
+          const [freshRow] = buildRows(data, includedMap);
+          const existing = this.rows.find((r) => r.id === id) || this.groupExtraRows.find((r) => r.id === id);
+          if (existing) Object.assign(existing, freshRow);
+        } catch (err) {
+          // Best effort -- the error banner from the conflict itself
+          // already told the user to reload if this doesn't work out.
         }
       },
       onCellHover(evt) {
@@ -1343,6 +1464,9 @@
       fetchYearsList().then((years) => { this.allYearsList = years; }).catch(() => {});
       fetchOuvertureEcarts().then((ecarts) => { this.ouvertureEcarts = ecarts; }).catch(() => {});
       jQuery(document).on('dialog:afterclose', () => this.reloadWindow());
+
+      this.lastPollTs = Math.floor(Date.now() / 1000);
+      this.startPolling();
     },
   };
 
diff --git a/web/modules/custom/figli_compta_ledger/src/Controller/LedgerActionsController.php b/web/modules/custom/figli_compta_ledger/src/Controller/LedgerActionsController.php
index 3047ed3..63d3f1c 100644
--- a/web/modules/custom/figli_compta_ledger/src/Controller/LedgerActionsController.php
+++ b/web/modules/custom/figli_compta_ledger/src/Controller/LedgerActionsController.php
@@ -74,6 +74,10 @@ class LedgerActionsController extends ControllerBase {
       return new JsonResponse(['error' => 'Type de ligne invalide.'], 400);
     }
 
+    if ($conflict = $this->checkConflict($request, $node)) {
+      return $conflict;
+    }
+
     $node->set('field_type_ligne', $type);
 
     // A type that's no longer linkable shouldn't keep a stale
@@ -110,6 +114,7 @@ class LedgerActionsController extends ControllerBase {
       'success' => TRUE,
       'type' => $type,
       'entree_liee_cleared' => !in_array($type, self::LINKABLE_TYPES, TRUE),
+      'changed' => date(DATE_ATOM, $node->getChangedTime()),
     ]);
   }
 
@@ -137,6 +142,10 @@ class LedgerActionsController extends ControllerBase {
     }
     $fieldName = self::INLINE_EDITABLE_FIELDS[$field];
 
+    if ($conflict = $this->checkConflict($request, $node)) {
+      return $conflict;
+    }
+
     if ($field === 'client') {
       if ($value === '') {
         $node->set('field_client', NULL);
@@ -186,7 +195,37 @@ class LedgerActionsController extends ControllerBase {
       'success' => TRUE,
       'field' => $field,
       'value' => $newValue,
+      'changed' => date(DATE_ATOM, $node->getChangedTime()),
     ]);
   }
 
+  /**
+   * Optimistic-locking guard shared by both endpoints above: the
+   * frontend sends the `changed` timestamp of the row it last saw (see
+   * buildRows() in home.js), captured at load/last-successful-save
+   * time. If the node's *actual* changed time has since moved on --
+   * someone else saved this same line in between -- the two won't
+   * match, and we reject rather than silently overwrite whatever that
+   * other save touched. Absent entirely (older cached frontend, or a
+   * request that genuinely doesn't know it, e.g. a fresh row from
+   * autocreate) skips the check rather than blocking on a false
+   * mismatch -- the check is a safety net for the common case, not a
+   * hard requirement of the API contract.
+   */
+  private function checkConflict(Request $request, NodeInterface $node) {
+    $data = json_decode($request->getContent(), TRUE);
+    $clientChanged = is_array($data) ? ($data['changed'] ?? NULL) : NULL;
+    if ($clientChanged === NULL) {
+      return NULL;
+    }
+    $clientChangedTs = strtotime($clientChanged);
+    if ($clientChangedTs !== FALSE && $clientChangedTs !== (int) $node->getChangedTime()) {
+      return new JsonResponse([
+        'error' => 'Cette ligne a été modifiée par quelqu\'un d\'autre entre-temps. Rechargez la page pour voir les dernières modifications.',
+        'conflict' => TRUE,
+      ], 409);
+    }
+    return NULL;
+  }
+
 }