Track dirty state to skip discard prompt for unchanged drafts

When a draft is loaded and the user hasn't made any changes, closing
the composer should not show the discard prompt since nothing would
be lost.

- Add isDirty field to ComposerState
- Set isDirty: true on all content-modifying actions
- Set isDirty: false on restore_from_draft, clear, and initial state
- Update onPressCancel to only show prompt if no draft or isDirty

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/view/com/composer/Composer.tsx

@@ -413,21 +413,31 @@ export const ComposePost = ({
   const onPressCancel = useCallback(() => {
     if (textInput.current?.maybeClosePopup()) {
       return
-    } else if (
-      thread.posts.some(
-        post =>
-          post.shortenedGraphemeLength > 0 ||
-          post.embed.media ||
-          post.embed.link,
-      )
-    ) {
+    }
+
+    const hasContent = thread.posts.some(
+      post =>
+        post.shortenedGraphemeLength > 0 || post.embed.media || post.embed.link,
+    )
+
+    // Show discard prompt if there's content AND either:
+    // - No draft is loaded (new composition)
+    // - Draft is loaded but has been modified
+    if (hasContent && (!composerState.draftId || composerState.isDirty)) {
       closeAllDialogs()
       Keyboard.dismiss()
       discardPromptControl.open()
     } else {
       onClose()
     }
-  }, [thread, closeAllDialogs, discardPromptControl, onClose])
+  }, [
+    thread,
+    composerState.draftId,
+    composerState.isDirty,
+    closeAllDialogs,
+    discardPromptControl,
+    onClose,
+  ])
 
   useImperativeHandle(cancelRef, () => ({onPressCancel}))
 

src/view/com/composer/state/composer.ts

@@ -104,6 +104,8 @@ export type ComposerState = {
   mutableNeedsFocusActive: boolean
   /** ID of the draft being edited, if any. Used to update existing draft on save. */
   draftId?: string
+  /** Whether the composer has been modified since loading a draft. */
+  isDirty: boolean
 }
 
 export type ComposerAction =
@@ -145,6 +147,7 @@ export function composerReducer(
     case 'update_postgate': {
       return {
         ...state,
+        isDirty: true,
         thread: {
           ...state.thread,
           postgate: action.postgate,
@@ -154,6 +157,7 @@ export function composerReducer(
     case 'update_threadgate': {
       return {
         ...state,
+        isDirty: true,
         thread: {
           ...state.thread,
           threadgate: action.threadgate,
@@ -174,6 +178,7 @@ export function composerReducer(
       }
       return {
         ...state,
+        isDirty: true,
         thread: {
           ...state.thread,
           posts: nextPosts,
@@ -196,6 +201,7 @@ export function composerReducer(
       })
       return {
         ...state,
+        isDirty: true,
         thread: {
           ...state.thread,
           posts: nextPosts,
@@ -221,6 +227,7 @@ export function composerReducer(
       }
       return {
         ...state,
+        isDirty: true,
         activePostIndex: nextActivePostIndex,
         mutableNeedsFocusActive: true,
         thread: {
@@ -305,6 +312,7 @@ export function composerReducer(
         activePostIndex: 0,
         mutableNeedsFocusActive: true,
         draftId: draft.id,
+        isDirty: false,
         thread: {
           posts,
           postgate: draft.postgate || state.thread.postgate,
@@ -317,6 +325,7 @@ export function composerReducer(
         activePostIndex: 0,
         mutableNeedsFocusActive: true,
         draftId: undefined,
+        isDirty: false,
         thread: {
           posts: [
             {
@@ -699,6 +708,7 @@ export function createComposerState({
   return {
     activePostIndex: 0,
     mutableNeedsFocusActive: false,
+    isDirty: false,
     thread: {
       posts: [
         {