Show a replayed session's images instead of dropping them

An imported session showed no screenshots. `text_of` kept only `text`
blocks, so every image in the replayed tail was silently discarded -- while
the *live* translator has always saved them into the session's `files/` and
referenced them. Two readings of the same records, and the one used for
history was the lesser.

`save_image` moves out of `Translator` to a free function both paths call,
since the naming scheme for that directory should exist once. `events_from`
now takes the session directory to write into, which means the conversion
has to happen where that directory exists -- so `Seed` carries the raw
JSONL and `launch` turns it into events, rather than `routes` doing it
before the session is created.

Costs nothing in tokens, which is the point worth recording: this writes
into ai-app's own session directory and the phone fetches a reference only
when it draws one. Nothing here is ever written to the CLI's stdin -- it
reads its own session file, and the only things this app sends it are typed
messages, control requests and `/compact`.

Verified against the 133 MB session behind the 2026-08-29 incident: 45
images in the replayed tail, written as real PNGs and served over the files
route, with the transcript itself staying at 756 KB of references.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VETa8afmpWaYezLCqJhDB8

server/src/session/mod.rs

@@ -831,7 +831,7 @@ fn spawn_import_sync(
             if lines <= cursor.lines {
                 continue;
             }
-            match import::replay_after(&transport, &cursor.path, cursor.lines).await {
+            match import::replay_after(&transport, &cursor.path, cursor.lines, &dir).await {
                 Ok(events) => {
                     tracing::info!(
                         "{} grew by {} lines with nothing from here; replaying {} events",
@@ -866,10 +866,14 @@ pub struct Seed {
     /// Where that session's file is and how much of it has been shown, so
     /// the session can keep itself up to date afterwards.
     pub cursor: import::Cursor,
-    /// Replayed into the transcript so the phone shows the conversation it
-    /// is joining. The CLI reads the real file itself, so this is what the
-    /// reader sees rather than what the model is given.
-    pub events: Vec<Event>,
+    /// The tail of that session's file, as the raw JSONL.
+    ///
+    /// Turned into events in `launch`, not before, because doing so writes
+    /// out the images the records carry and that needs the session
+    /// directory to write them into -- which does not exist until the
+    /// session does. The CLI reads the real file itself, so this only ever
+    /// decides what the *reader* sees.
+    pub records: String,
 }
 
 fn launch(
@@ -890,7 +894,7 @@ fn launch(
         claude::write_resume_token(&dir, &seed.resume);
         import::write_cursor(&dir, &seed.cursor);
         let at = now();
-        for event in seed.events {
+        for event in import::events_from(&seed.records, &dir) {
             transcript.append(event, at)?;
         }
     }