Ark: partial moves to Savings via an exact-amount split

Into Savings now has an amount field with a Max button. Max (or the full
balance) keeps the existing whole-balance cooperative offboard. A
partial amount first mints a vtxo of exactly that amount with a
self-send — the mailbox delivers self-sends, verified on regtest — then
offboards just that vtxo, so the number typed is the number that leaves
Spending (fees still come off what arrives, shown on the success
screen). startOffboard accepts a vtxo subset for this; an exact-match
vtxo skips the split. The unilateral exit page remains reachable from a
link under the field.

Co-Authored-By: Claude Fable 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Wvj4aoeMZwA7VUGdJP9Swi

1 files changed, 9 insertions, 3 deletions

diff --git a/src/ark/manager.js b/src/ark/manager.js
index 3b54582..5617cf1 100644
--- a/src/ark/manager.js
+++ b/src/ark/manager.js
@@ -363,13 +363,19 @@ export class ArkManager {
     return action;
   }
 
-  // ---- offboard (collaborative exit: all spendable vtxos -> one on-chain output) ----
-  async startOffboard(spk, address) {
+  // ---- offboard (collaborative exit: spendable vtxos -> one on-chain output) ----
+  // Whole vtxos only — there is no change on this path. Default is everything
+  // spendable; vtxoIds selects a subset (the feature splits an exact-amount
+  // vtxo first via a self-send when the user asks for a partial move).
+  async startOffboard(spk, address, vtxoIds) {
     if (this.pendingActions().some((a) => a.type === 'offboard')) {
       throw new Error('an offboard is already in progress');
     }
-    const inputs = this.state.vtxos.filter((v) => v.state === 'spendable');
+    const inputs = vtxoIds
+      ? vtxoIds.map((id) => this._vtxo(id))
+      : this.state.vtxos.filter((v) => v.state === 'spendable');
     if (!inputs.length) throw new Error('no spendable ark balance');
+    if (inputs.some((v) => !v || v.state !== 'spendable')) throw new Error('vtxo not spendable');
     if (this.info.maxOffboardInputs && inputs.length > this.info.maxOffboardInputs) {
       throw new Error(`too many coins for one offboard (${inputs.length}) — refresh/consolidate first`);
     }