Redesign acme sessions: one session per project, not per agent

Model: acme-{hash} (session with project cwd) / assistant (agent)
- Git worktree aware (uses --show-toplevel)
- CWD set on session, not agent
- Agent always named 'assistant'

data/scripts/acme/acme-ollie-ensure

@@ -1,19 +1,16 @@
 #!/bin/bash
 # acme-ollie-ensure - Ensure acme session and agent exist
 #
-# Creates session "acme" if needed, creates/selects one agent per git root.
-# Outputs the session and agent names for use by other scripts.
+# One session per project root (git worktree aware), one agent "assistant".
+# Session name: acme-{hash of project root}
 #
 # Usage: eval $(acme-ollie-ensure)
 #        Then use $OLLIE_SESSION and $OLLIE_AGENT
 
 set -euo pipefail
 
-SESSION="acme"
-
 # Get cwd from the acme window's directory context
 if [[ -n "${winid:-}" ]]; then
-    # Get window name and extract directory
     wname=$(9p read acme/$winid/tag | awk '{print $1}')
     if [[ -d "$wname" ]]; then
         cwd="$wname"
@@ -26,27 +23,25 @@ else
     cwd="$PWD"
 fi
 
-# Walk up to the repository root so all files in one checkout share an agent.
-git_root=$(git -C "$cwd" rev-parse --show-toplevel 2>/dev/null || true)
-if [[ -n "$git_root" ]]; then
-    cwd="$git_root"
+# Discover project root: git worktree root > git root > cwd
+project_root="$cwd"
+if wt_root=$(git -C "$cwd" rev-parse --show-toplevel 2>/dev/null); then
+    project_root="$wt_root"
 fi
 
-# Create a short hash from the project root for the agent name
-agent_hash=$(printf '%s' "$cwd" | md5sum | cut -c1-8)
-AGENT="$agent_hash"
+# Session name from project root hash
+session_hash=$(printf '%s' "$project_root" | md5sum | cut -c1-8)
+SESSION="acme-$session_hash"
+AGENT="assistant"
 
-# Ensure session exists
+# Ensure session exists (with project root as cwd)
 if ! ollie-9p read "session/$SESSION/env" >/dev/null 2>&1; then
-    printf 'name=%s\ncwd=%s\n' "$SESSION" "$cwd" | ollie-9p write "session/new" 2>/dev/null || true
+    printf 'name=%s\ncwd=%s\n' "$SESSION" "$project_root" | ollie-9p write "session/new" 2>/dev/null || true
 fi
 
 # Ensure agent exists
 if ! ollie-9p read "session/$SESSION/agent/$AGENT/cfg" >/dev/null 2>&1; then
-    printf 'name=%s\ncwd=%s\n' "$AGENT" "$cwd" | ollie-9p write "session/$SESSION/agent/new" 2>/dev/null || true
-else
-    # Update cwd if agent already exists
-    echo "cwd $cwd" | ollie-9p write "session/$SESSION/agent/$AGENT/ctl" 2>/dev/null || true
+    printf 'name=%s\n' "$AGENT" | ollie-9p write "session/$SESSION/agent/new" 2>/dev/null || true
 fi
 
 # Output for eval