core+gui+cli: anticipation/rebuild dates, preserve relative settings

Fixes around the delivery/build/check date handling (karen7 regtest):

- build_will (GUI + CLI) re-anchors date_to_check to the CURRENT heirs'
  earliest future delivery before building, so an anticipated rebuild is no
  longer blocked by the stale old-will anchor (NO_FUTURE_DATE). The checks of
  the existing will keep their anchored date_to_check.
- _sync_locktime_to_built_txs now PRESERVES RELATIVE locktime/threshold
  recipes ("2y"/"150d") in WILL_SETTINGS instead of freezing them to absolute
  timestamps: the anchored comparisons (resolve_locktime_against_tx and
  resolve_date_to_check with built_locktime) already prevent the daily
  invalidate prompt. Absolute values still sync on a genuine automatic
  anticipation.
- Will.remove_stale_wallet_history drops stale wallet-LOCAL will placeholders
  before every (re)build in GUI and CLI so their coins are available again.
- check_willexecutors_and_heirs raises HeirNotFoundException outside the
  count_heirs gate: a shortened relative recipe on a signed will now triggers
  a plain rebuild ("no heirs" only when there really are none).
- is_locktime_below_threshold compares the settings on one reference frame
  (resolve_guard_threshold), no longer against the built-will anchor.

Tests: purge unit + call-site, no-heirs, guard, anticipated-rebuild
end-to-end (GUI) + CLI mirror + fixed_percent_lists_amount unit,
relative-preserve sync; conftest restores electrum.constants.net after each
test (cross-file pollution guard).

bal/cli/controller.py

@@ -43,6 +43,7 @@ from ..core.checkalive import (
     CheckAliveError,
     check_alive_expired,
     resolve_date_to_check,
+    resolve_guard_threshold,
 )
 from ..core.heirs import Heirs, is_op_return_address
 from ..core.plugin_base import BalConfig, BalPlugin
@@ -314,6 +315,28 @@ class BalController:
         executor.
         """
         will = {}
+        # Drop stale wallet-LOCAL will placeholders (mirror of the GUI
+        # build_will) so their coins are available to this build.
+        Will.remove_stale_wallet_history(
+            self.wallet, self.plugin.HISTORY_LABEL.get()
+        )
+        # A (re)build may have anticipated the delivery (shorter heir recipes)
+        # while ``date_to_check`` is still anchored to the OLD built will.
+        # Recompute it for the will being built (earliest future delivery among
+        # the CURRENT heirs), mirroring ``BalWindow.build_will``, so the
+        # anticipated dates pass the build filter.
+        _new_locktime = min(
+            (
+                Util.parse_locktime_string(h[2])
+                for h in self.heirs.values()
+            ),
+            default=None,
+        )
+        if _new_locktime:
+            self.date_to_check = resolve_date_to_check(
+                self.plugin.is_basic_mode(), self.will_settings,
+                built_locktime=_new_locktime,
+            )
         self.willexecutors = Willexecutors.get_willexecutors(
             self.plugin, update=False, task=False
         )
@@ -434,7 +457,13 @@ class BalController:
             raise _user_facing(e) from e
 
         locktime = Util.parse_locktime_string(self.will_settings["locktime"])
-        if locktime < date_to_check:
+        threshold_ts = resolve_guard_threshold(
+            self.plugin.is_basic_mode(), self.will_settings
+        )
+        if threshold_ts is not None:
+            if locktime < threshold_ts:
+                raise UserFacingException(_("locktime is lower than threshold"))
+        elif locktime < date_to_check:
             raise UserFacingException(_("locktime is lower than threshold"))
 
         if not self.no_willexecutor: