Show a session's subagents as subcards, each with a read-only transcript

A subagent is a second transcript owned by a session, in the same event
model, with no process and no controls. The claude translator routes lines
carrying parent_tool_use_id to a per-subagent translator and transcript
under <session>/subagents/<tool_use_id>; three routes expose the list, a
transcript page and the SSE stream. Echo grows /subagent [n] as the rig.

On the phone a card with subagents ends in a chevron expander, collapsed by
default, opening to outlined subcards styled like dev-updater's components;
a subcard opens SessionScreen in read-only form, addressed through
TranscriptAddress so paging, cache and stream are shared.

Design in SUBAGENTS.md; choices awaiting review in DECISIONS.md.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

server/src/session/llama.rs

@@ -77,6 +77,7 @@ impl LlamaDriver {
     /// in a different currency: two servers holding the same model is twice the
     /// memory, and the second would bind a different port while the phone kept
     /// talking to the first.
+    #[allow(clippy::too_many_arguments)]
     pub fn launch(
         meta: &SessionConfig,
         provider: &ProviderConfig,
@@ -85,6 +86,10 @@ impl LlamaDriver {
         transcript: &Path,
         session_dir: &Path,
         sink: EventSink,
+        // llama.cpp has no notion of a Task call, so this is accepted only
+        // to keep one shape across every driver's launch -- see
+        // `SUBAGENTS.md`'s "Server layout".
+        _subagents: Arc<super::subagent::Subagents>,
     ) -> Result<Self> {
         let model = meta.model.as_deref().context(
             "a llama.cpp session needs a model -- one of the downloaded ones, by its key",