fix(mobile-native-chat): supply a boundary only to a text-bearing send

An image echo reconciles by counting turns AFTER its tail and has no other
retirement path, so the tail supplied from a read that already carried its own
echo excluded the very row it was waiting for: the "Queued" photo bubble stuck
for the life of the session and the transcript row rendered as bare marker text
with no photo. A regression against main, and against the earlier revision of
this fix that pinned only captioned echoes.

The glue matcher is the only consumer a supplied tail helps. Everything that
reconciles relative to its own tail keeps whatever it captured.

mobile/src/session/mobile-native-chat-pending-baseline.test.ts

@@ -141,15 +141,24 @@ describe('rebaseMobileNativeChatPendingBaselines', () => {
     expect(rebased[0]?.baselineResolved).toBe(true)
   })
 
-  // A null tail counts from the top of the transcript, so an image turn already
-  // in this read would claim the send and take the user's fresh photo with it.
-  it('pins a caption-less image echo that captured no tail at all', () => {
+  // A supplied tail would sit at or after this send's own echo, and an image
+  // echo counts turns AFTER its tail — so it would exclude the very row it is
+  // waiting for, and image entries have no other retirement path.
+  it('never supplies a tail to a caption-less image echo either', () => {
     const rebased = rebaseMobileNativeChatPendingBaselines(history, [
       { ...unresolved('p1', ''), images: ['file:///a.png'] },
       { ...unresolved('p2', '', 2), images: ['file:///b.png'] }
     ])
-    expect(rebased.map((item) => item.baselineTailMessageId)).toEqual(['m2', 'm2'])
+    expect(rebased.map((item) => item.baselineTailMessageId)).toEqual([null, null])
     expect(rebased.map((item) => item.expectedOccurrence)).toEqual([1, 2])
     expect(rebased.every((item) => item.baselineResolved)).toBe(true)
   })
+
+  // Same rule for a text-empty entry with no images: it reconciles by counting
+  // image-source turns after its tail, so a supplied tail strands it too.
+  it('never supplies a tail to a text-empty entry', () => {
+    const rebased = rebaseMobileNativeChatPendingBaselines(history, [unresolved('p1', '   ')])
+    expect(rebased[0]?.baselineTailMessageId).toBe(null)
+    expect(rebased[0]?.baselineResolved).toBe(true)
+  })
 })

mobile/src/session/mobile-native-chat-pending-baseline.ts

@@ -24,10 +24,13 @@ import type { MobileNativeChatPendingMessage } from './mobile-native-chat-pendin
  * the host while the send time comes from the phone. Counting it as history puts
  * the ordinal one past anything the transcript can supply.
  *
- * Which is why a CAPTIONED image echo is left alone entirely: it binds its
- * preview by an ordinal counted over the whole transcript, so its tail and its
- * ordinal have to describe the same read. Supplying one without the other leaves
- * it matching nothing, forever. Everything else matches relative to its tail.
+ * And only a TEXT-bearing send is given one. The glue matcher is the sole
+ * consumer that a supplied tail helps; every other one is harmed by it. An image
+ * echo reconciles by counting turns AFTER its tail, so a tail taken from a read
+ * that already carries its echo excludes that echo and the bubble can never
+ * retire — image entries have no other retirement path. A captioned one is worse
+ * still: it binds by an ordinal counted over the whole transcript, so a tail
+ * without a matching recount leaves it claiming nothing at all.
  */
 export function rebaseMobileNativeChatPendingBaselines(
   messages: readonly NativeChatMessage[],
@@ -41,9 +44,9 @@ export function rebaseMobileNativeChatPendingBaselines(
     if (item.baselineResolved) {
       return item
     }
-    const bindsByAbsoluteOrdinal =
-      Boolean(item.images?.length) && normalizeReconcileText(item.text) !== ''
-    return item.baselineTailMessageId !== null || bindsByAbsoluteOrdinal
+    const reconcilesAgainstItsOwnTail =
+      Boolean(item.images?.length) || normalizeReconcileText(item.text) === ''
+    return item.baselineTailMessageId !== null || reconcilesAgainstItsOwnTail
       ? { ...item, baselineResolved: true }
       : { ...item, baselineResolved: true, baselineTailMessageId }
   })

mobile/src/session/use-mobile-native-chat-drafts-glued-pending.test.ts

@@ -292,6 +292,24 @@ describe('useMobileNativeChatDrafts glued pending sends', () => {
     // A send held here would sit as a live segment at the head of its run, so
     // the cursor could never reach a later pair — the stuck bubble would take
     // the whole feature down with it for the rest of the session.
+    // An image entry retires ONLY by binding its preview, so a supplied tail
+    // that excluded its own echo would leave the bubble — and the photo — stuck
+    // for the life of the session.
+    it('retires a photo whose image echo arrives with the read', async () => {
+      await mount([], true)
+      act(() => {
+        const origin = state?.captureSendOrigin('')
+        if (origin) {
+          state?.acceptSend(origin, '', ['file:///new.png'])
+        }
+      })
+
+      const withEcho = [assistantTurn('m1', 'ready', 1000), imageTurn('m2', '/tmp/new.png', 5000)]
+      await update(withEcho)
+      expect(state?.pending).toEqual([])
+      expect(state?.imagePreviewsByMessageId).toEqual({ m2: ['file:///new.png'] })
+    })
+
     it('leaves a later pair able to glue after the late read resolved the first send', async () => {
       await mount([], true)
       act(() => send('run the tests'))
@@ -325,23 +343,6 @@ describe('useMobileNativeChatDrafts glued pending sends', () => {
       expect(renderedPendingTexts(olderIdentical, state)).toEqual(['fix the', 'bug'])
     })
 
-    // The preview pass runs before the rebase, so an entry with no boundary
-    // would bind the user's fresh photo to whatever image turn the read carries.
-    it('does not bind a photo sent before the read to an image turn already in it', async () => {
-      await mount([], false, false)
-      act(() => {
-        const origin = state?.captureSendOrigin('')
-        if (origin) {
-          state?.acceptSend(origin, '', ['file:///new.png'])
-        }
-      })
-
-      const olderImage = [imageTurn('m1', '/old/photo.png', 1000)]
-      await update(olderImage)
-      expect(state?.imagePreviewsByMessageId).toEqual({})
-      expect(state?.pending.map((item) => item.images)).toEqual([['file:///new.png']])
-    })
-
     it('still retires them once their own glued row lands', async () => {
       await mount([], false, false)
       rapidSend('fix the', 'bug')