Simplify activity hook script and remove unused activeWorktrees function

src/vm.ts

@@ -97,9 +97,8 @@ export async function ensure(log?: (msg: string) => void): Promise<void> {
   const activityTmp = `${home}/.sandlot/.sandlot-activity.tmp`
   await Bun.write(activityTmp, [
     '#!/bin/bash',
-    'DIR=$(dirname "$CLAUDE_PROJECT_DIR")',
-    'BRANCH=$(basename "$CLAUDE_PROJECT_DIR")',
-    'echo "$1" > "$DIR/.activity-$BRANCH"',
+    'P="${CLAUDE_PROJECT_DIR%/}"',
+    'echo "$1" > "$(dirname "$P")/.activity-$(basename "$P")"',
     '',
   ].join('\n'))
   await $`chmod +x ${activityTmp}`.quiet()
@@ -181,21 +180,6 @@ export async function exec(workdir: string, command: string): Promise<{ exitCode
   }
 }
 
-/** Get host paths of worktrees where claude is currently running in the container. */
-export async function activeWorktrees(): Promise<string[]> {
-  const s = await status()
-  if (s !== "running") return []
-
-  const result = await $`container exec ${CONTAINER_NAME} bash -c ${'for pid in $(pgrep -x claude 2>/dev/null); do readlink /proc/$pid/cwd 2>/dev/null; done'}`.nothrow().quiet().text()
-
-  const home = homedir()
-  return result.trim().split("\n").filter(Boolean).map(p => {
-    if (p.startsWith("/sandlot")) return `${home}/.sandlot${p.slice("/sandlot".length)}`
-    if (p.startsWith("/host")) return `${home}/dev${p.slice("/host".length)}`
-    return p
-  })
-}
-
 /** Check if Claude is actively working in the given worktree (based on activity hook). */
 export async function isClaudeActive(worktree: string, branch: string): Promise<boolean> {
   const file = `${dirname(worktree)}/.activity-${branch}`