The file explorer on the phone

The other half of EXPLORER.md: a folder button on the session header opens
the machine's filesystem, starting where the session works.

It draws **over** the session in the same `Box`, so the session under it
stays composed -- its event stream keeps flowing, its draft and scroll
position stay where they were, and coming back from a file costs nothing.
Back steps one level inside it (editor, viewer, directory, parent) and only
closes from where it opened; the platform gesture, the button and the swipe
all go through the one function, so they cannot mean different things.

The viewer is a `LazyColumn` of lines rather than one `Text`, because text
layout is linear in the text and a twenty-thousand-line file in a single
`Text` measures all of it to draw a screenful. Lines do not wrap and share
one horizontal scroll, so a logical line is a visual line and the gutter
cannot come to number the wrong text; the gutter's width is measured from
the digit count of the line count in the style it is drawn in. The editor
is a `BasicTextField` with a `VisualTransformation` carrying the scanner's
spans, which is the one Compose API that colours a field's own text rather
than replacing the field.

`fileLanguage` reads the same table `fenceLanguage` does, so a language
added for fences is a language added for files.

A file that changed on the machine while it was open here refuses to be
overwritten and asks, with what each of the three answers costs. That is
the ordinary case, not the exotic one: an agent editing the file somebody
is reading is what this whole feature is for.

The speedometer moves off the header into the session settings dialog,
where the session's other about-the-session controls are, and the folder
takes a place between the usage chart and the cog -- widest scope to
narrowest, cog at the end, as Iris asked. Both benchmark scripts move onto
`ui-trace`'s new tap-by-label action in the same change, so the render
report is never unavailable and never pressed at a coordinate that has
stopped meaning anything; `app/bench-lib.sh` is what they share, and
`grep -n "tap [0-9]" app/*.sh` is the check.

Exercised on the emulator against the sandbox's new fixture tree, with a
screenshot or a ui-trace for each: the listing (dotfiles, directories
first, a symlink to a directory sorted with them, a name with a tab in it),
a highlighted file, binary, too big, a permission error, editing and
saving, the 409 and its Overwrite, back with unsaved edits, creating a name
that exists, creating one that does not and landing in the editor, an empty
directory, and `..` above the directory the session opened in.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

app/transcript-bench.sh

@@ -3,8 +3,9 @@
 # standard measurement for "is the transcript smooth", so a perf session
 # starts from a number instead of re-inventing this loop in /tmp.
 #
-#   ./transcript-bench.sh            restart the app, open the first
-#                                    session, scroll, report
+#   ./transcript-bench.sh            restart the app, open the session the
+#                                    server lists first, scroll, report
+#   ./transcript-bench.sh -s TITLE   open that session instead
 #   ./transcript-bench.sh -k         keep whatever screen is open now
 #   ./transcript-bench.sh -n 4       swipe cycles (default 6; one cycle is
 #                                    two swipes back and two forward)
@@ -16,33 +17,35 @@
 # went. Compare two runs of this with the same gestures, not one run
 # against a phone.
 #
-# Coordinates are the ai-app AVD's 1080x2400 screen: the report button in
-# the session top bar, and the first row of the session list.
+# The swipes are still coordinates, because a gesture across a scrolling
+# area is a distance rather than a control. Every *control* is pressed by
+# name -- see bench-lib.sh.
 set -eu
 cd "$(dirname "$0")"
 . ./android-env.sh >/dev/null 2>&1
+. ./bench-lib.sh
 
 keep=""
 cycles=6
-while getopts kn: flag; do
+session=""
+while getopts kn:s: flag; do
     case $flag in
     k) keep=1 ;;
     n) cycles=$OPTARG ;;
+    s) session=$OPTARG ;;
     *) exit 2 ;;
     esac
 done
 
 if [ -z "$keep" ]; then
-    adb shell am force-stop com.example.aiapp
-    adb shell am start -n com.example.aiapp/.MainActivity >/dev/null
-    sleep 5
-    ui-trace record -d 3000 --do 'tap 500 545' -o /tmp/bench-open.txt >/dev/null 2>&1
-    sleep 3
+    [ -n "$session" ] || session=$(first_session_title)
+    [ -n "$session" ] || { echo "transcript-bench: no sessions to open" >&2; exit 1; }
+    open_session "$session"
 fi
 
-# First tap resets the report's "work since last copied" window, so the
-# numbers cover exactly the swipes between the two taps.
-ui-trace record -d 2000 --do 'tap 723 205' -o /tmp/bench-reset.txt >/dev/null 2>&1
+# The first copy resets the report's "work since last copied" window, so the
+# numbers cover exactly the swipes between the two.
+copy_render_report /tmp/bench-reset.txt
 adb logcat -c
 
 DO=""
@@ -56,7 +59,7 @@ while [ "$i" -lt "$cycles" ]; do
 done
 eval ui-trace record -d $((cycles * 4400 + 2000)) $DO -o /tmp/bench-scroll.txt >/dev/null 2>&1
 
-ui-trace record -d 2000 --do 'tap 723 205' -o /tmp/bench-report.txt >/dev/null 2>&1
+copy_render_report /tmp/bench-report.txt
 sleep 1
 adb logcat -d -s ai-app:I | sed -n '/ai-app render report/,$p' | sed 's/^.*ai-app  : //'
 adb logcat -d 2>/dev/null | grep -i "duplicate unit key" | head -3 || true