feat: add persistent stale-while-revalidate API cache

Introduce an actor-backed persistent cache layer at the SRHTClient boundary
for read-only SourceHut data. Cache entries now store stable metadata
including key, resource type, fetched/expires/access timestamps, payload
hash, schema version, and payload size, with bounded memory and disk usage.

Add centralized cache key builders and TTL defaults for repository, file,
ticket, build, log, profile, status, and list-style resources. Support
networkOnly, cacheOnly, cacheFirstThenRefresh, and refreshIgnoringCache
policies, plus request coalescing for duplicate in-flight cache keys.

Integrate first-pass caching into high-value low-risk read paths:
- build detail and completed/active build logs
- ticket detail
- README lookup
- repository tree, blob, and linked file reads

Keep mutation paths network-only and add simple prefix invalidation after
ticket and build mutations. Add compact cached/stale UI status rows and a
Settings action to clear the persistent cache.

Add focused cache tests covering round trips, expiration, stale fallback,
policy behavior, request coalescing, prefix invalidation, size limits, LRU
pruning, expired pruning, and mutation bypass behavior. Document storage,
key, TTL, invalidation, limitations, and next recommended targets.

2 files changed, 90 insertions, 36 deletions

diff --git a/Hutch/Views/Tickets/TicketDetailView.swift b/Hutch/Views/Tickets/TicketDetailView.swift
index 0028083..92263f6 100644
--- a/Hutch/Views/Tickets/TicketDetailView.swift
+++ b/Hutch/Views/Tickets/TicketDetailView.swift
@@ -169,6 +169,12 @@ struct TicketDetailView: View {
         } else if let ticket = viewModel.ticket {
             ScrollView {
                 VStack(alignment: .leading, spacing: 0) {
+                    if let cacheMetadata = viewModel.cacheMetadata {
+                        StaleCacheStatusRow(metadata: cacheMetadata, isRefreshing: viewModel.isRefreshingCachedData)
+                            .padding(.horizontal)
+                            .padding(.vertical, 8)
+                    }
+
                     // Header
                     ticketHeader(ticket, viewModel: viewModel)
 
diff --git a/Hutch/Views/Tickets/TicketDetailViewModel.swift b/Hutch/Views/Tickets/TicketDetailViewModel.swift
index 483f749..df2fd46 100644
--- a/Hutch/Views/Tickets/TicketDetailViewModel.swift
+++ b/Hutch/Views/Tickets/TicketDetailViewModel.swift
@@ -98,7 +98,7 @@ private struct LabelsPage: Decodable, Sendable {
 @MainActor
 final class TicketDetailViewModel {
     private static func cacheKey(ownerUsername: String, trackerRid: String, ticketId: Int) -> String {
-        "ticket.detail.\(ownerUsername).\(trackerRid).\(ticketId)"
+        APICacheKeys.ticketDetail(owner: ownerUsername, trackerRid: trackerRid, ticketId: ticketId)
     }
 
     let ownerUsername: String
@@ -114,6 +114,8 @@ final class TicketDetailViewModel {
     private(set) var isPerformingAction = false
     private(set) var trackerLabels: [TicketLabel] = []
     private(set) var rawTicketResponse: String?
+    private(set) var cacheMetadata: CacheEntryMetadata?
+    private(set) var isRefreshingCachedData = false
     var commentText = ""
     var error: String?
 
@@ -291,30 +293,25 @@ final class TicketDetailViewModel {
         rawTicketResponse = nil
 
         do {
-            let result = try await client.execute(
+            let result = try await client.executeCached(
                 service: .todo,
                 query: Self.detailQuery,
                 variables: [
                     "rid": trackerRid,
                     "ticketId": ticketId
                 ],
-                responseType: TicketDetailResponse.self
-            )
-            let payload = result.tracker.ticket
-            ticket = TicketDetail(
-                id: payload.id,
-                created: payload.created,
-                updated: payload.updated,
-                title: payload.title,
-                description: payload.description,
-                status: payload.status,
-                resolution: payload.resolution,
-                authenticity: payload.authenticity,
-                submitter: payload.submitter,
-                assignees: payload.assignees,
-                labels: payload.labels
+                responseType: TicketDetailResponse.self,
+                cacheKey: Self.cacheKey(ownerUsername: ownerUsername, trackerRid: trackerRid, ticketId: ticketId),
+                resourceType: .ticketDetail,
+                ttl: APICacheTTLs.ticketDetail,
+                policy: .cacheFirstThenRefresh
             )
-            events = payload.events.results.sorted(by: Self.timelineOrder)
+            apply(result.value, metadata: result.metadata)
+            if result.isFromCache {
+                isLoading = false
+                await refreshTicketInBackground()
+                return
+            }
         } catch {
             self.error = error.userFacingMessage
         }
@@ -329,7 +326,7 @@ final class TicketDetailViewModel {
 
         do {
             let cacheKey = Self.cacheKey(ownerUsername: ownerUsername, trackerRid: trackerRid, ticketId: ticketId)
-            let result = try await client.executeAndCache(
+            let result = try await client.executeCached(
                 service: .todo,
                 query: Self.detailQuery,
                 variables: [
@@ -337,25 +334,14 @@ final class TicketDetailViewModel {
                     "ticketId": ticketId
                 ],
                 responseType: TicketDetailResponse.self,
-                cacheKey: cacheKey
+                cacheKey: cacheKey,
+                resourceType: .ticketDetail,
+                ttl: APICacheTTLs.ticketDetail,
+                policy: .refreshIgnoringCache
             )
-            rawTicketResponse = client.responseCache.get(forKey: cacheKey)
+            rawTicketResponse = await client.cachedPayload(forKey: cacheKey)
                 .flatMap { String(data: $0, encoding: .utf8) }
-            let payload = result.tracker.ticket
-            ticket = TicketDetail(
-                id: payload.id,
-                created: payload.created,
-                updated: payload.updated,
-                title: payload.title,
-                description: payload.description,
-                status: payload.status,
-                resolution: payload.resolution,
-                authenticity: payload.authenticity,
-                submitter: payload.submitter,
-                assignees: payload.assignees,
-                labels: payload.labels
-            )
-            events = payload.events.results.sorted(by: Self.timelineOrder)
+            apply(result.value, metadata: result.metadata)
         } catch {
             self.error = error.userFacingMessage
         }
@@ -391,6 +377,7 @@ final class TicketDetailViewModel {
             events.append(event)
             events.sort(by: Self.timelineOrder)
             commentText = ""
+            await invalidateAfterMutation()
         } catch {
             self.error = error.userFacingMessage
         }
@@ -423,6 +410,7 @@ final class TicketDetailViewModel {
                 ],
                 responseType: UpdateStatusResponse.self
             )
+            await invalidateAfterMutation()
             // Re-fetch the ticket to get updated status/resolution
             await reloadTicketPreservingDebugState()
         } catch {
@@ -457,6 +445,7 @@ final class TicketDetailViewModel {
                 ],
                 responseType: AssignUserResponse.self
             )
+            await invalidateAfterMutation()
             // Reload to reflect the change
             await reloadTicketPreservingDebugState()
         } catch {
@@ -503,6 +492,7 @@ final class TicketDetailViewModel {
                 ],
                 responseType: AssignUserResponse.self
             )
+            await invalidateAfterMutation()
             await reloadTicketPreservingDebugState()
         } catch {
             ticket = TicketDetail(
@@ -550,6 +540,7 @@ final class TicketDetailViewModel {
                 ],
                 responseType: UnassignUserResponse.self
             )
+            await invalidateAfterMutation()
             // Reload to reflect the change
             await reloadTicketPreservingDebugState()
         } catch {
@@ -575,6 +566,7 @@ final class TicketDetailViewModel {
                 ],
                 responseType: LabelTicketResponse.self
             )
+            await invalidateAfterMutation()
             await reloadTicketPreservingDebugState()
         } catch {
             self.error = error.userFacingMessage
@@ -599,6 +591,7 @@ final class TicketDetailViewModel {
                 ],
                 responseType: UnlabelTicketResponse.self
             )
+            await invalidateAfterMutation()
             await reloadTicketPreservingDebugState()
         } catch {
             self.error = error.userFacingMessage
@@ -654,6 +647,61 @@ final class TicketDetailViewModel {
         }
     }
 
+    private func refreshTicketInBackground() async {
+        guard !isRefreshingCachedData else { return }
+        isRefreshingCachedData = true
+        defer { isRefreshingCachedData = false }
+
+        do {
+            let result = try await client.executeCached(
+                service: .todo,
+                query: Self.detailQuery,
+                variables: [
+                    "rid": trackerRid,
+                    "ticketId": ticketId
+                ],
+                responseType: TicketDetailResponse.self,
+                cacheKey: Self.cacheKey(ownerUsername: ownerUsername, trackerRid: trackerRid, ticketId: ticketId),
+                resourceType: .ticketDetail,
+                ttl: APICacheTTLs.ticketDetail,
+                policy: .refreshIgnoringCache
+            )
+            apply(result.value, metadata: result.metadata)
+        } catch {
+            if ticket == nil {
+                self.error = error.userFacingMessage
+            }
+        }
+    }
+
+    private func apply(_ response: TicketDetailResponse, metadata: CacheEntryMetadata?) {
+        cacheMetadata = metadata
+        let payload = response.tracker.ticket
+        let updatedTicket = TicketDetail(
+            id: payload.id,
+            created: payload.created,
+            updated: payload.updated,
+            title: payload.title,
+            description: payload.description,
+            status: payload.status,
+            resolution: payload.resolution,
+            authenticity: payload.authenticity,
+            submitter: payload.submitter,
+            assignees: payload.assignees,
+            labels: payload.labels
+        )
+        ticket = updatedTicket
+        let updatedEvents = payload.events.results.sorted(by: Self.timelineOrder)
+        events = updatedEvents
+    }
+
+    private func invalidateAfterMutation() async {
+        await client.invalidateCache(prefix: APICacheKeys.prefix(SRHTService.todo.rawValue, "ticket"))
+        await client.invalidateCache(prefix: APICacheKeys.prefix(SRHTService.todo.rawValue, "tickets"))
+        await client.invalidateCache(prefix: APICacheKeys.prefix(SRHTService.todo.rawValue, "tracker"))
+        await client.invalidateCache(prefix: APICacheKeys.prefix("home"))
+    }
+
     static func matchesAssignee(_ entity: Entity, user: User) -> Bool {
         let assigneeCanonical = normalizedCanonicalName(entity.canonicalName)
         let userCanonical = normalizedCanonicalName(user.canonicalName)