Move subagents into session side panel

SUBAGENTS.md

@@ -1,8 +1,8 @@
 # Subagents
 
 A session's subagents -- helpers started by Claude Code's Task tool or Codex's
-collaboration tools -- each get a transcript of their own, listed under the
-session's card and readable in the same transcript view the session has.
+collaboration tools -- each get a transcript of their own, listed in a panel
+over the open session and readable in the same transcript view the session has.
 Designed 2026-09-05; extended to Codex's multiplexed app-server threads on
 2026-09-13. The decisions Bryan has not yet reviewed are in `DECISIONS.md`.
 
@@ -253,29 +253,31 @@ The per-subagent status is only read when the list route is asked for.
   because a subagent that is thinking reports nothing meanwhile and would sink
   below one that just finished.
 - **Holding a subcard selects it, and several at a time**, exactly as the
-  import list works, with the selection bar drawn inside the session's card
-  rather than at the bottom of the screen: this selection belongs to one card,
-  and a bar down there would read as acting on the whole list. One card at a
-  time -- picking a row in another card moves the selection rather than adding
-  to it, since one Delete is one request against one parent. Delete is
+  import list works, with the selection bar drawn inside the panel rather than
+  at the bottom of the session: this selection belongs to the subagent list,
+  and a bar under the composer would read as acting on the conversation.
+  Delete is
   *disabled*, with the reason in words, while anything selected is still
   running. Deleting confirms first, dims the rows it is acting on
-  (`BusyItem`), and on success takes them out of that card and off the
-  session's count without refetching anything else. The phone's cached copy of
+  (`BusyItem`), and on success takes them out of the panel without refetching
+  anything else. The phone's cached copy of
   a deleted subagent's transcript is purged with it.
-- `SessionSummary.subagents: Int`. A card with a non-zero count ends in an
-  expander row -- a full-width `Chevron(Pointing.Down)` row that flips to
-  `Pointing.Up` -- collapsed by default. Expanding fetches
-  `/sessions/{id}/subagents` and draws one `OutlinedCard` per subagent,
-  indented inside the session card, the way dev-updater draws a project's
-  components: title, then the status word and a relative time. The
-  expansion state is per session id and survives a refresh of the list.
-- Tapping a subcard opens `Screen.Subagent`, which is `SessionScreen` in
-  **read-only** form: the same transcript, paging, cache, selection,
+- The main session list does not expand or count subagents. Swiping left over
+  an open session pulls an 88%-wide panel in from the right and fetches
+  `/sessions/{id}/subagents`; it draws one `OutlinedCard` per subagent: title,
+  then the status word and a relative time. The transcript remains composed
+  under the panel, so its event stream, draft and scroll position stay live.
+  Horizontal scrollers inside the transcript win the gesture. Collapsing one,
+  or starting over any ordinary part of the session, gives the gesture back to
+  the panel; Android keeps its own edge Back gesture. Swiping right on the
+  panel, tapping outside it, or Back closes it.
+- Tapping a subcard opens a `SessionScreen` layer in **read-only** form: the
+  same transcript, paging, cache, selection,
   images and status row, with the composer, the process button, the model
   picker, the files button, the settings cog and the usage bar left out.
-  The header shows the subagent's title with the session's title beneath
-  it. Back returns to the list.
+  The header shows the subagent's title with the session's title beneath it.
+  It is another layer over the still-composed session and its panel; Back
+  returns to the panel.
 - Addressing: `fetchTranscript`, `EventStream`, `TranscriptSource` and the
   cache take a transcript address rather than a session id --
   `sessions/{id}` or `sessions/{id}/subagents/{sub}` -- so the cache nests a