feat(cashu): C1b — persist escrow-mode overrides and surface the backend in About

docs/cashu/README.md

@@ -366,12 +366,21 @@ Every phase, without exception, carries these standing requirements:
   (`rust/src/api/settings.rs`, new `rust/src/api/` entries as needed).
 - Dart: parse the same tags in `MostroInstance.fromTags`
   (`lib/features/about/models/mostro_instance.dart`, mirroring `BondPolicy`);
-  `escrowModeProvider`; show a "Payment backend: Lightning / Cashu (mint URL,
-  locktime)" section in the About screen; dev-only override toggle in settings.
+  `escrowModeProvider`. About reports **what the node advertises**, so the two
+  backends are mutually exclusive on screen: a node advertising Cashu gets a
+  "Cashu escrow" section (mint, locktime, settlement margin) *instead of* the
+  Lightning Network section, while a Lightning or silent node renders exactly
+  what it does today. The client-side override never changes what About says —
+  it is surfaced only in the `kDebugMode` settings card, which shows the
+  effective resolution next to the toggle.
+- Persistence note: the overrides live in the settings k/v store, which is real
+  on SQLite and a stub on IndexedDB, so on web they apply for the session only
+  (tracked in #233).
 - Companion (out of this repo): upstream PR to `mostrod` adding the tags of §4.1.
 - **Done when:** against any current daemon the app shows Lightning and behaves
-  identically; flipping the override flips the provider and the About section; unit
-  tests for tag parsing + resolution order.
+  identically; flipping the override flips the resolved mode and the dev card's
+  effective state — **not** the About section, which reports only what the node
+  advertised; unit tests for tag parsing + resolution order.
 - Est. size: S (~400–600 lines).
 
 #### C2 — Cashu wallet core (Rust, cdk)

lib/features/about/models/mostro_instance.dart

@@ -14,6 +14,23 @@ enum BondPolicy { unsupported, disabled, enabled }
 /// Which side of a trade a bond applies to (`bond_apply_to` tag).
 enum BondApplyTo { take, make, both }
 
+/// Settlement backend a Mostro daemon runs, from its `escrow_mode` tag.
+///
+/// Tri-state for the same reason as [BondPolicy]:
+/// - [unknown]: the tag is absent — a daemon that predates the Cashu feature.
+///   Not the same as knowing it runs Lightning.
+/// - [lightning]: `escrow_mode="lightning"`, or any value this client does not
+///   implement. A backend we cannot trade Cashu with reads as Lightning, the
+///   setting that leaves every Cashu path shut.
+/// - [cashu]: `escrow_mode="cashu"` — the remaining `cashu_*` tags are
+///   meaningful.
+///
+/// Mirrors Rust's `EscrowMode` (`rust/src/mostro/escrow_mode.rs`). This models
+/// what the *node advertises*; whether a Cashu path may actually run is a
+/// separate, stricter question answered by Rust (`is_cashu_mode()`, surfaced as
+/// `isCashuAvailableProvider`).
+enum EscrowMode { unknown, lightning, cashu }
+
 /// Dart model parsed from a Nostr Kind 38385 (Mostro instance status) event.
 ///
 /// All fields are derived from individual tags — the event `content` is empty
@@ -50,6 +67,10 @@ class MostroInstance {
     this.bondBaseAmountSats,
     this.bondSlashNodeSharePct,
     this.bondPayoutClaimWindowDays,
+    this.escrowMode = EscrowMode.unknown,
+    this.cashuMintUrl,
+    this.cashuEscrowLocktimeDays,
+    this.cashuSettlementMarginDays,
   });
 
   /// Mostro daemon pubkey (from `d` tag).
@@ -113,6 +134,24 @@ class MostroInstance {
   /// Days to claim a payout before forfeit, `> 0`.
   final int? bondPayoutClaimWindowDays;
 
+  // ── Settlement backend ──────────────────────────────────────────────────────
+
+  /// Which backend settles trades on this node; defaults to
+  /// [EscrowMode.unknown]. See [EscrowMode].
+  final EscrowMode escrowMode;
+
+  // The three Cashu parameters are non-null only when [escrowMode] is
+  // [EscrowMode.cashu]; otherwise, or on an absent/invalid tag, they are null.
+
+  /// Mint this node pins for every escrow. There is no per-order negotiation.
+  final String? cashuMintUrl;
+
+  /// NUT-11 locktime the seller must set on the escrow token, in days.
+  final int? cashuEscrowLocktimeDays;
+
+  /// How close to escrow expiry the node stops accepting `fiat-sent`, in days.
+  final int? cashuSettlementMarginDays;
+
   // ── Factory ─────────────────────────────────────────────────────────────────
 
   /// Parse a Kind 38385 event's tag list into a [MostroInstance].
@@ -195,11 +234,32 @@ class MostroInstance {
       return value > 0 ? value : null;
     }
 
+    // An absent tag stays `unknown`, which is what lets the About screen say
+    // "not advertised" instead of claiming the node confirmed Lightning. An
+    // unrecognised backend reads as Lightning: we cannot trade Cashu with it
+    // either, and that is the reading that keeps Cashu shut.
+    EscrowMode parseEscrowMode() {
+      // `get`, not `getOptional`: only an *absent* tag is unknown. A tag that
+      // is present but blank is a node that answered, and Rust's `parse_tags`
+      // reads it as Lightning — the two parsers must agree, or the About screen
+      // and the gate disagree about the same event.
+      final raw = get('escrow_mode');
+      if (raw == null) return EscrowMode.unknown;
+      return raw.trim().toLowerCase() == 'cashu'
+          ? EscrowMode.cashu
+          : EscrowMode.lightning;
+    }
+
     // Parameters are gated on an enabled policy so a disabled or malformed
     // event never exposes live bond values (consumers key off nullability).
     final bondPolicy = parseBondPolicy();
     final isEnabled = bondPolicy == BondPolicy.enabled;
 
+    // Same gating for the Cashu parameters: a Lightning node that happens to
+    // carry a stale `cashu_mint_url` tag must not surface it as live.
+    final escrowMode = parseEscrowMode();
+    final isCashu = escrowMode == EscrowMode.cashu;
+
     return MostroInstance(
       pubKey: get('d') ?? '',
       mostroVersion: get('mostro_version'),
@@ -239,6 +299,12 @@ class MostroInstance {
               : null,
       bondPayoutClaimWindowDays:
           isEnabled ? parsePositiveInt('bond_payout_claim_window_days') : null,
+      escrowMode: escrowMode,
+      cashuMintUrl: isCashu ? getOptional('cashu_mint_url') : null,
+      cashuEscrowLocktimeDays:
+          isCashu ? parsePositiveInt('cashu_escrow_locktime_days') : null,
+      cashuSettlementMarginDays:
+          isCashu ? parseNonNegativeInt('cashu_settlement_margin_days') : null,
     );
   }
 

lib/features/about/screens/about_screen.dart

@@ -422,51 +422,84 @@ class _MostroNodeContent extends StatelessWidget {
             explanation: l10n.aboutMaxOrdersPerResponseExplanation,
           ),
 
-        const SizedBox(height: AppSpacing.xl),
-        _SectionHeader(title: l10n.aboutLightningNetworkSection),
-        const SizedBox(height: AppSpacing.md),
-        if (node.lndVersion != null)
-          _NodeInfoRowInfo(
-            label: l10n.aboutLndVersionLabel,
-            value: node.lndVersion!,
-            explanation: l10n.aboutLndVersionExplanation,
-          ),
-        if (node.lndNodePublicKey != null)
-          _NodeInfoRowCopyable(
-            label: l10n.aboutLndNodePublicKeyLabel,
-            value: node.lndNodePublicKey!,
-            explanation: l10n.aboutLndNodePublicKeyExplanation,
-          ),
-        if (node.lndCommitHash != null)
-          _NodeInfoRowInfo(
-            label: l10n.aboutLndCommitLabel,
-            value: _truncateHash(node.lndCommitHash!),
-            explanation: l10n.aboutLndCommitExplanation,
-          ),
-        if (node.lndNodeAlias != null)
-          _NodeInfoRowInfo(
-            label: l10n.aboutLndNodeAliasLabel,
-            value: node.lndNodeAlias!,
-            explanation: l10n.aboutLndNodeAliasExplanation,
-          ),
-        if (node.lndChains != null)
+        // Settlement backend. About reports what *this node* runs, so the two
+        // backends are mutually exclusive here: a Cashu node gets the Cashu
+        // section and no Lightning one. A node that advertises nothing
+        // (EscrowMode.unknown — every daemon in the wild today) keeps the
+        // Lightning section it has always shown.
+        if (node.escrowMode == EscrowMode.cashu) ...[
+          const SizedBox(height: AppSpacing.xl),
+          _SectionHeader(title: l10n.aboutCashuEscrowSection),
+          const SizedBox(height: AppSpacing.md),
+          // Shown unconditionally: a Cashu node with no mint is misconfigured,
+          // and saying so is more useful than an empty section. Rendered in
+          // full rather than through the copyable row, whose 20-character
+          // abbreviation would hide the mint's host — the one part that
+          // matters here.
           _NodeInfoRowInfo(
-            label: l10n.aboutSupportedChainsLabel,
-            value: node.lndChains!,
-            explanation: l10n.aboutSupportedChainsExplanation,
-          ),
-        if (node.lndNetworks != null)
-          _NodeInfoRowInfo(
-            label: l10n.aboutSupportedNetworksLabel,
-            value: node.lndNetworks!,
-            explanation: l10n.aboutSupportedNetworksExplanation,
-          ),
-        if (node.lndUris != null)
-          _NodeInfoRowCopyable(
-            label: l10n.aboutLndNodeUriLabel,
-            value: node.lndUris!,
-            explanation: l10n.aboutLndNodeUriExplanation,
-          ),
+            label: l10n.aboutCashuMintUrlLabel,
+            value: node.cashuMintUrl ?? l10n.aboutCashuMintNotAdvertised,
+            explanation: l10n.aboutCashuMintUrlExplanation,
+          ),
+          if (node.cashuEscrowLocktimeDays != null)
+            _NodeInfoRowInfo(
+              label: l10n.aboutCashuLocktimeLabel,
+              value: l10n.aboutDaysValue(node.cashuEscrowLocktimeDays!),
+              explanation: l10n.aboutCashuLocktimeExplanation,
+            ),
+          if (node.cashuSettlementMarginDays != null)
+            _NodeInfoRowInfo(
+              label: l10n.aboutCashuSettlementMarginLabel,
+              value: l10n.aboutDaysValue(node.cashuSettlementMarginDays!),
+              explanation: l10n.aboutCashuSettlementMarginExplanation,
+            ),
+        ] else ...[
+          const SizedBox(height: AppSpacing.xl),
+          _SectionHeader(title: l10n.aboutLightningNetworkSection),
+          const SizedBox(height: AppSpacing.md),
+          if (node.lndVersion != null)
+            _NodeInfoRowInfo(
+              label: l10n.aboutLndVersionLabel,
+              value: node.lndVersion!,
+              explanation: l10n.aboutLndVersionExplanation,
+            ),
+          if (node.lndNodePublicKey != null)
+            _NodeInfoRowCopyable(
+              label: l10n.aboutLndNodePublicKeyLabel,
+              value: node.lndNodePublicKey!,
+              explanation: l10n.aboutLndNodePublicKeyExplanation,
+            ),
+          if (node.lndCommitHash != null)
+            _NodeInfoRowInfo(
+              label: l10n.aboutLndCommitLabel,
+              value: _truncateHash(node.lndCommitHash!),
+              explanation: l10n.aboutLndCommitExplanation,
+            ),
+          if (node.lndNodeAlias != null)
+            _NodeInfoRowInfo(
+              label: l10n.aboutLndNodeAliasLabel,
+              value: node.lndNodeAlias!,
+              explanation: l10n.aboutLndNodeAliasExplanation,
+            ),
+          if (node.lndChains != null)
+            _NodeInfoRowInfo(
+              label: l10n.aboutSupportedChainsLabel,
+              value: node.lndChains!,
+              explanation: l10n.aboutSupportedChainsExplanation,
+            ),
+          if (node.lndNetworks != null)
+            _NodeInfoRowInfo(
+              label: l10n.aboutSupportedNetworksLabel,
+              value: node.lndNetworks!,
+              explanation: l10n.aboutSupportedNetworksExplanation,
+            ),
+          if (node.lndUris != null)
+            _NodeInfoRowCopyable(
+              label: l10n.aboutLndNodeUriLabel,
+              value: node.lndUris!,
+              explanation: l10n.aboutLndNodeUriExplanation,
+            ),
+        ],
       ],
     );
   }

lib/features/settings/providers/escrow_mode_provider.dart

@@ -0,0 +1,66 @@
+import 'package:flutter/foundation.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import 'package:mostro/src/rust/api/escrow.dart' as escrow_api;
+import 'package:mostro/src/rust/api/types.dart';
+
+/// The settlement backend the active Mostro node runs, as resolved by Rust.
+///
+/// Emits the current value immediately, then every time it changes: a node
+/// capability fetch, a node switch, or a developer override flip.
+///
+/// This is the **client-side resolution**, developer overrides included — it is
+/// what gates behaviour. It is deliberately *not* what the About screen shows:
+/// About reports what the node itself advertises (see `MostroInstance`), so a
+/// forced override can never make About claim a node said something it did not.
+final escrowModeProvider = StreamProvider<EscrowModeInfo>((ref) async* {
+  // Subscribe before reading the snapshot so no change is missed in between.
+  final stream = await escrow_api.onEscrowModeChanged();
+  yield await escrow_api.getEscrowMode();
+
+  while (true) {
+    yield await stream.next();
+  }
+});
+
+/// Whether a Cashu path may run against the active node.
+///
+/// The single question the rest of the app asks. Mirrors Rust's
+/// `is_cashu_mode()`: the mode must be Cashu **and** there must be a usable
+/// mint. False while loading and on error, so every Cashu path stays shut
+/// unless the node was positively identified.
+final isCashuAvailableProvider = Provider<bool>((ref) {
+  return ref.watch(escrowModeProvider).valueOrNull?.isCashuAvailable ?? false;
+});
+
+// ── Developer override ────────────────────────────────────────────────────────
+
+/// Writes the developer escrow overrides (§4.3 of `docs/cashu/README.md`).
+///
+/// Exists so a tester can work against a daemon branch that implements Cashu
+/// before it publishes the Kind 38385 tags. Every caller must be behind
+/// [kDebugMode] — release builds must not be able to force a backend the node
+/// does not run. The assertions below make a misuse fail loudly in a debug
+/// build rather than silently ship a switch to users.
+class EscrowOverrideController {
+  const EscrowOverrideController();
+
+  /// Force (or stop forcing) Cashu mode regardless of the node's tags.
+  Future<void> setForceCashu(bool forceCashu) {
+    assert(kDebugMode, 'the escrow override is a debug-only affordance');
+    return escrow_api.setEscrowModeOverride(forceCashu: forceCashu);
+  }
+
+  /// Point Cashu at a specific mint. `null` or blank clears the override.
+  ///
+  /// Throws when the URL is not an `http(s)` URL with a host — the Rust side
+  /// validates and returns an `InvalidMintUrl` marker.
+  Future<void> setMintUrl(String? mintUrl) {
+    assert(kDebugMode, 'the escrow override is a debug-only affordance');
+    return escrow_api.setCashuMintUrlOverride(mintUrl: mintUrl);
+  }
+}
+
+final escrowOverrideControllerProvider = Provider<EscrowOverrideController>(
+  (ref) => const EscrowOverrideController(),
+);

lib/features/settings/screens/settings_screen.dart

@@ -1,3 +1,4 @@
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
@@ -8,6 +9,7 @@ import 'package:mostro/l10n/app_localizations.dart';
 import 'package:mostro/features/settings/providers/nwc_provider.dart';
 import 'package:mostro/features/settings/providers/settings_provider.dart';
 import 'package:mostro/features/settings/widgets/currency_selector_dialog.dart';
+import 'package:mostro/features/settings/widgets/escrow_mode_dev_card.dart';
 import 'package:mostro/features/settings/widgets/language_selector.dart';
 import 'package:mostro/features/settings/widgets/mostro_node_selector.dart';
 import 'package:mostro/features/settings/widgets/relay_management_card.dart';
@@ -192,6 +194,11 @@ class _SettingsScreenState extends ConsumerState<SettingsScreen> {
             subtitle: truncatePubkey(mostroPubkey),
             onTap: () => showMostroNodeSelector(context),
           ),
+
+          // 9 — Escrow backend override. Debug builds only: forcing a backend
+          // the node does not run is a testing affordance, never a user
+          // setting. See docs/cashu/README.md §4.3.
+          if (kDebugMode) const EscrowModeDevCard(),
         ],
       ),
     );