fix(fusion_clock): code-review hardening [19.0.5.0.1]

- _cron_generate: per-rule savepoint isolation (one bad rule can't abort the
  whole daily batch)
- fclk_attach_recurrence: clear an existing recurrence first (no orphaned rule
  generating forever)
- fclk_apply_planner_cell: collapse split rows (search was limit=1 after the
  UNIQUE drop, orphaning extras)
- fclk_release_shift: reject non-posted/open shifts (raw-POST guard)
- delete_open_shift: report success=false when nothing was deleted + JS surfaces it
- _generate: log before removing an empty recurrence
Tests added for collapse, re-attach, draft-release.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

fusion_clock/models/clock_recurrence.py

@@ -96,7 +96,9 @@ class FusionClockScheduleRecurrence(models.Model):
             seed = Schedule.search(
                 [('recurrence_id', '=', rec.id)], order='schedule_date desc', limit=1)
             if not seed:
-                # No anchor row -> nothing to repeat; drop the empty rule.
+                # No anchor row left -> nothing to repeat; drop the empty rule.
+                _logger.info(
+                    "Fusion Clock: recurrence %s has no shifts left; removing it.", rec.id)
                 rec.unlink()
                 continue
             anchor = Schedule.search(
@@ -150,5 +152,13 @@ class FusionClockScheduleRecurrence(models.Model):
 
     @api.model
     def _cron_generate(self):
-        """Roll every recurrence's horizon forward (called daily)."""
-        self.search([])._generate()
+        """Roll every recurrence's horizon forward (called daily). Each rule is
+        isolated in its own savepoint so one bad recurrence can't abort
+        generation for all the others."""
+        for rec in self.search([]):
+            try:
+                with self.env.cr.savepoint():
+                    rec._generate()
+            except Exception:
+                _logger.exception(
+                    "Fusion Clock: recurrence %s failed to generate; skipping.", rec.id)