Fix presets with sighash flags in app playground

diff --git a/dev-tools/playground/presets.py b/dev-tools/playground/presets.py
index b4205b6..f109730 100644
--- a/dev-tools/playground/presets.py
+++ b/dev-tools/playground/presets.py
@@ -167,6 +167,11 @@ class PsbtSpec:
     small `fee` with a change remainder gives a net receive. If every output has
     an explicit amount there is no free variable, so `fee` must equal
     `total_in - sum(outputs)` exactly (else it's a mistake and we raise).
+
+    All of that assumes the transaction is complete, which holds only as long as
+    every input commits to all the amounts — i.e. uses SIGHASH_DEFAULT or
+    SIGHASH_ALL (or omits the field). If there are other sighash flags, every
+    output must set `amount` explicitly, and `fee` is ignored.
     """
     inputs: List[PsbtInputSpec]
     outputs: List[PsbtOutputSpec]
@@ -181,19 +186,42 @@ def build_psbt_from_spec(policy, spec: PsbtSpec) -> PSBT:
     verbatim. `spec.fee` is always honored — via the remainder if there is one,
     otherwise as a checked invariant against `total_in - sum(outputs)`. A
     per-input `sighash` is copied onto the built PSBT input.
+
+    Exception: if any input sets a `sighash` that doesn't commit to all the
+    amounts, the transaction is not required to balance (see `PsbtSpec`), so every
+    output must set `amount`, and `spec.fee` is neither used nor checked — outputs
+    may exceed the inputs.
     """
-    from test_utils.txmaker import createPsbt  # local import (heavy)
+    # local imports (heavy module)
+    from test_utils.txmaker import createPsbt, sighash_commits_to_all_amounts
 
     input_amounts = [i.amount for i in spec.inputs]
     input_is_external = [i.external for i in spec.inputs]
+    input_sighashes = [i.sighash for i in spec.inputs]
     total_in = sum(input_amounts)
 
+    # SIGHASH_DEFAULT / SIGHASH_ALL still fix every amount, so they keep the
+    # ordinary balanced treatment, exactly like an unset sighash.
+    unbalanced = not all(
+        sighash_commits_to_all_amounts(sighash) for sighash in input_sighashes
+    )
+
     remainder_indices = [n for n, o in enumerate(spec.outputs) if o.amount is None]
     if len(remainder_indices) > 1:
         raise ValueError("at most one output may omit `amount` (the remainder)")
     explicit_total = sum(o.amount for o in spec.outputs if o.amount is not None)
 
-    if remainder_indices:
+    if unbalanced:
+        # No fee to spread around: such a sighash leaves the transaction open, so
+        # there is nothing for a remainder output to absorb.
+        if remainder_indices:
+            raise ValueError(
+                "every output must set `amount` when an input sets a `sighash` "
+                "that doesn't commit to all the amounts: such a transaction need "
+                "not balance, so there is no fee for a remainder output to absorb"
+            )
+        output_amounts = [o.amount for o in spec.outputs]
+    elif remainder_indices:
         remainder = total_in - explicit_total - spec.fee
         if remainder < 0:
             raise ValueError(
@@ -220,16 +248,11 @@ def build_psbt_from_spec(policy, spec: PsbtSpec) -> PSBT:
         output_amounts = [o.amount for o in spec.outputs]
     output_is_change = [o.is_change for o in spec.outputs]
 
-    psbt = createPsbt(
-        policy, input_amounts, output_amounts, output_is_change, input_is_external
+    return createPsbt(
+        policy, input_amounts, output_amounts, output_is_change, input_is_external,
+        input_sighashes,
     )
 
-    for i, inp in enumerate(spec.inputs):
-        if inp.sighash is not None:
-            psbt.inputs[i].sighash = inp.sighash
-
-    return psbt
-
 
 # ----- wallet-policy presets -------------------------------------------------
 
@@ -412,8 +435,8 @@ SIGN_PSBT_SCENARIO_PRESETS: List[PolicyPreset] = [
                 PsbtInputSpec(50_000_000, sighash=SIGHASH_ALL | SIGHASH_ANYONECANPAY),
             ],
             outputs=[
-                PsbtOutputSpec(amount=120_000_000),  # recipient
-                PsbtOutputSpec(is_change=True),      # change
+                PsbtOutputSpec(amount=120_000_000),              # recipient
+                PsbtOutputSpec(amount=80_999_000, is_change=True),  # change
             ],
         ),
     ),
@@ -429,8 +452,8 @@ SIGN_PSBT_SCENARIO_PRESETS: List[PolicyPreset] = [
                 PsbtInputSpec(50_000_000, sighash=SIGHASH_NONE),
             ],
             outputs=[
-                PsbtOutputSpec(amount=120_000_000),  # recipient
-                PsbtOutputSpec(is_change=True),      # change
+                PsbtOutputSpec(amount=120_000_000),              # recipient
+                PsbtOutputSpec(amount=80_999_000, is_change=True),  # change
             ],
         ),
     ),
diff --git a/test_utils/txmaker.py b/test_utils/txmaker.py
index 8e08f48..8331add 100644
--- a/test_utils/txmaker.py
+++ b/test_utils/txmaker.py
@@ -397,9 +397,22 @@ def fill_inout(wallet_policy: WalletPolicy, inout: Union[PartiallySignedInput, P
                 derived_key_origin = KeyOriginInfo(fpr, placeholder_der_subpath)
                 inout.hd_keypaths[derived_pubkey.pubkey] = derived_key_origin
 
-def createPsbt(wallet_policy: WalletPolicy, input_amounts: List[int], output_amounts: List[int], output_is_change: List[bool], input_is_external: Optional[List[bool]] = None) -> PSBT:
+# Sighash types that commit to every input and output: SIGHASH_DEFAULT (0x00,
+# taproot only) and SIGHASH_ALL (0x01).
+_SIGHASH_TYPES_COMMITTING_TO_ALL = (0x00, 0x01)
+
+
+def sighash_commits_to_all_amounts(sighash: Optional[int]) -> bool:
+    """True if `sighash` fixes both the input and the output set, so that a
+    transaction signed with it must balance. `None` means PSBT_IN_SIGHASH_TYPE is
+    omitted, i.e. the default, which does. Everything else (NONE or SINGLE, which
+    leave outputs open, and any type with ANYONECANPAY OR-ed on top, which leaves
+    the inputs open) does not."""
+    return sighash is None or sighash in _SIGHASH_TYPES_COMMITTING_TO_ALL
+
+
+def createPsbt(wallet_policy: WalletPolicy, input_amounts: List[int], output_amounts: List[int], output_is_change: List[bool], input_is_external: Optional[List[bool]] = None, input_sighashes: Optional[List[Optional[int]]] = None) -> PSBT:
     assert len(output_amounts) == len(output_is_change)
-    assert sum(output_amounts) <= sum(input_amounts)
 
     # input_is_external marks inputs the wallet policy does NOT own: they get a
     # foreign prevout and no key-derivation info, so the app treats them as
@@ -408,6 +421,19 @@ def createPsbt(wallet_policy: WalletPolicy, input_amounts: List[int], output_amo
         input_is_external = [False] * len(input_amounts)
     assert len(input_is_external) == len(input_amounts)
 
+    # input_sighashes[i] is the PSBT_IN_SIGHASH_TYPE of input i; None means the
+    # field is omitted, i.e. the default sighash. Defaults to all-default.
+    if input_sighashes is None:
+        input_sighashes = [None] * len(input_amounts)
+    assert len(input_sighashes) == len(input_amounts)
+
+    # A complete transaction cannot spend more than it receives. A sighash that
+    # doesn't commit to all the amounts leaves the transaction open — under
+    # ANYONECANPAY the missing value comes from inputs another signer adds — so it
+    # need not balance, and the check doesn't apply.
+    if all(sighash_commits_to_all_amounts(sighash) for sighash in input_sighashes):
+        assert sum(output_amounts) <= sum(input_amounts)
+
     vin: List[CTxIn] = [CTxIn() for _ in input_amounts]
     vout: List[CTxOut] = [CTxOut() for _ in output_amounts]
 
@@ -491,6 +517,9 @@ def createPsbt(wallet_policy: WalletPolicy, input_amounts: List[int], output_amo
         wallet_policy.descriptor_template)
 
     for input_index, input in enumerate(psbt.inputs):
+        if input_sighashes[input_index] is not None:
+            input.sighash = input_sighashes[input_index]
+
         if input_is_external[input_index]:
             # External input: only the (foreign) witness UTXO, so its amount is
             # known, but deliberately no derivation info => seen as external.