feat: add session resume capability with automatic continuation

Add ability to resume inactive sessions and automatically continue with new
session ID. Includes message merging for preserving conversation history,
UI improvements to allow sending during inactive state, and database schema
migration. close #87

web/src/hooks/mutations/useSendMessage.ts

@@ -1,4 +1,5 @@
 import { useMutation } from '@tanstack/react-query'
+import { useRef, useState } from 'react'
 import type { ApiClient } from '@/api/client'
 import type { AttachmentMetadata, DecryptedMessage } from '@/types/api'
 import { makeClientSideId } from '@/lib/messages'
@@ -17,6 +18,11 @@ type SendMessageInput = {
     attachments?: AttachmentMetadata[]
 }
 
+type UseSendMessageOptions = {
+    resolveSessionId?: (sessionId: string) => Promise<string>
+    onSessionResolved?: (sessionId: string) => void
+}
+
 function findMessageByLocalId(
     sessionId: string,
     localId: string,
@@ -31,12 +37,18 @@ function findMessageByLocalId(
     return null
 }
 
-export function useSendMessage(api: ApiClient | null, sessionId: string | null): {
+export function useSendMessage(
+    api: ApiClient | null,
+    sessionId: string | null,
+    options?: UseSendMessageOptions
+): {
     sendMessage: (text: string, attachments?: AttachmentMetadata[]) => void
     retryMessage: (localId: string) => void
     isSending: boolean
 } {
     const { haptic } = usePlatform()
+    const [isResolving, setIsResolving] = useState(false)
+    const resolveGuardRef = useRef(false)
 
     const mutation = useMutation({
         mutationFn: async (input: SendMessageInput) => {
@@ -77,20 +89,42 @@ export function useSendMessage(api: ApiClient | null, sessionId: string | null):
 
     const sendMessage = (text: string, attachments?: AttachmentMetadata[]) => {
         if (!api || !sessionId) return
-        if (mutation.isPending) return
+        if (mutation.isPending || resolveGuardRef.current) return
         const localId = makeClientSideId('local')
-        mutation.mutate({
-            sessionId,
-            text,
-            localId,
-            createdAt: Date.now(),
-            attachments,
-        })
+        const createdAt = Date.now()
+        void (async () => {
+            let targetSessionId = sessionId
+            if (options?.resolveSessionId) {
+                resolveGuardRef.current = true
+                setIsResolving(true)
+                try {
+                    const resolved = await options.resolveSessionId(sessionId)
+                    if (resolved && resolved !== sessionId) {
+                        options.onSessionResolved?.(resolved)
+                        targetSessionId = resolved
+                    }
+                } catch (error) {
+                    haptic.notification('error')
+                    console.error('Failed to resolve session before send:', error)
+                    return
+                } finally {
+                    resolveGuardRef.current = false
+                    setIsResolving(false)
+                }
+            }
+            mutation.mutate({
+                sessionId: targetSessionId,
+                text,
+                localId,
+                createdAt,
+                attachments,
+            })
+        })()
     }
 
     const retryMessage = (localId: string) => {
         if (!api || !sessionId) return
-        if (mutation.isPending) return
+        if (mutation.isPending || resolveGuardRef.current) return
 
         const message = findMessageByLocalId(sessionId, localId)
         if (!message?.originalText) return
@@ -108,6 +142,6 @@ export function useSendMessage(api: ApiClient | null, sessionId: string | null):
     return {
         sendMessage,
         retryMessage,
-        isSending: mutation.isPending,
+        isSending: mutation.isPending || isResolving,
     }
 }