doc: use offset file in predefined workflow script

Replace manual wc -c pattern with server-maintained offset file.
Document offset in help.md session file listing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

doc/IDEAS.md

@@ -84,10 +84,10 @@ echo "name=tester    agent=tester    cwd=$cwd" > s/new
 # Send a prompt to a session and return only the new output.
 send() {
     sid=$1; shift
-    offset=$(wc -c < s/$sid/chat)
     printf '%s' "$*" > s/$sid/prompt
     while [ "$(cat s/$sid/state)" = "idle" ]; do sleep 0.2; done
     while [ "$(cat s/$sid/state)" != "idle" ]; do sleep 1; done
+    offset=$(cat s/$sid/offset)
     tail -c +$((offset + 1)) s/$sid/chat
 }
 

doc/help.md

@@ -40,6 +40,7 @@ ollie/
       agent       active agent (r/w)
       backend     active backend (r/w)
       chat        conversation log (ro)
+      offset      byte offset of chat EOF before last prompt submit (ro)
       ctl         control (w)                stop, kill, clear, compact, rn <name>
       ctxsz       context size (ro)
       cwd         working directory (r/w)