[agents] Support Rift Btrfs workspaces in worktree scripts

Automatically detect Rift Btrfs workspace environments in
create_worktree.sh and cleanup_worktree.sh. When running under Rift, use
rift subagent fork and rift subagent close (with fallback to standard
fork/close) instead of creating Git worktrees. Update v8-workflow skill
documentation accordingly.

Change-Id: I55ea398d6a6ff2c38e8a3a85ea4209612a6a7de9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/7978998
Commit-Queue: Darius Mercadier <dmercadier@chromium.org>
Reviewed-by: Darius Mercadier <dmercadier@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#108156}

agents/scripts/cleanup_worktree.sh

@@ -10,12 +10,30 @@ if [ -z "$TASK_ID" ]; then
   exit 1
 fi
 
+TOPLEVEL=$(git rev-parse --show-toplevel 2>/dev/null)
 COMMON_DIR=$(git rev-parse --git-common-dir 2>/dev/null)
-if [ -z "$COMMON_DIR" ]; then
+if [ -z "$COMMON_DIR" ] || [ -z "$TOPLEVEL" ]; then
   echo "Error: Not in a git repository."
   exit 1
 fi
 V8_ROOT="$(cd "$COMMON_DIR/.." && pwd)"
+WS_ROOT="$(dirname "$TOPLEVEL")"
+
+if command -v rift >/dev/null 2>&1 && [ -f "$WS_ROOT/.rift_prime_directive.json" ]; then
+  CURRENT_WS="$(basename "$WS_ROOT")"
+  RIFT_PARENT_DIR="$(dirname "$WS_ROOT")"
+
+  if [[ "$TASK_ID" == "${CURRENT_WS}_subagent_"* ]] || [ -d "$RIFT_PARENT_DIR/$TASK_ID" ]; then
+    SUBAGENT_WS="$TASK_ID"
+  else
+    SUBAGENT_WS="${CURRENT_WS}_subagent_${TASK_ID}"
+  fi
+
+  if ! rift -y subagent close "$TASK_ID" > /dev/null 2>&1; then
+    rift close -y "$SUBAGENT_WS" > /dev/null 2>&1
+  fi
+  exit 0
+fi
 
 BRANCH_NAME="task-$TASK_ID"
 WORKTREE_PATH="$V8_ROOT/worktrees/$BRANCH_NAME"

agents/scripts/create_worktree.sh

@@ -8,12 +8,43 @@ if [ -z "$TASK_ID" ]; then
   exit 1
 fi
 
+TOPLEVEL=$(git rev-parse --show-toplevel 2>/dev/null)
 COMMON_DIR=$(git rev-parse --git-common-dir 2>/dev/null)
-if [ -z "$COMMON_DIR" ]; then
+if [ -z "$COMMON_DIR" ] || [ -z "$TOPLEVEL" ]; then
   echo "Error: Not in a git repository."
   exit 1
 fi
 V8_ROOT="$(cd "$COMMON_DIR/.." && pwd)"
+WS_ROOT="$(dirname "$TOPLEVEL")"
+
+if command -v rift >/dev/null 2>&1 && [ -f "$WS_ROOT/.rift_prime_directive.json" ]; then
+  CURRENT_WS="$(basename "$WS_ROOT")"
+  RIFT_PARENT_DIR="$(dirname "$WS_ROOT")"
+  REPO_DIR_NAME="$(basename "$TOPLEVEL")"
+
+  if [[ "$TASK_ID" == "${CURRENT_WS}_subagent_"* ]]; then
+    SUBAGENT_WS="$TASK_ID"
+  else
+    SUBAGENT_WS="${CURRENT_WS}_subagent_${TASK_ID}"
+  fi
+  WORKTREE_PATH="$RIFT_PARENT_DIR/$SUBAGENT_WS/$REPO_DIR_NAME"
+
+  if [ ! -d "$WORKTREE_PATH" ]; then
+    # Attempt Rift's subagent fork command as documented in the rift skill.
+    # Fallback to standard 'rift fork' if the subagent subcommand fails or is unsupported.
+    if ! rift -y subagent fork "$TASK_ID" > /dev/null 2>&1; then
+      rift fork -y "$SUBAGENT_WS" --no-build > /dev/null 2>&1
+    fi
+  fi
+
+  if [ ! -d "$WORKTREE_PATH" ]; then
+    echo "Error: Failed to create rift workspace $SUBAGENT_WS" >&2
+    exit 1
+  fi
+
+  echo "$WORKTREE_PATH"
+  exit 0
+fi
 
 BRANCH_NAME="task-$TASK_ID"
 WORKTREE_PATH="$V8_ROOT/worktrees/$BRANCH_NAME"

agents/skills/v8-workflow/SKILL.md

@@ -36,7 +36,11 @@ development:
 
 ## 3. Available Tools
 
-- **[create_worktree.sh](../../scripts/create_worktree.sh)**: Automates the git
-  worktree isolation and setup process. Use this at the start of every new task.
+- **[create_worktree.sh](../../scripts/create_worktree.sh)**: Automates task
+  isolation and setup. Automatically detects whether the repository is in a
+  standard Git checkout (creating a Git worktree) or a Rift Btrfs workspace
+  (forking an isolated Btrfs subvolume). Use this at the start of every new
+  task.
 - **[cleanup_worktree.sh](../../scripts/cleanup_worktree.sh)**: Safely removes
-  task worktrees and prunes remnants once a CL is landed or abandoned.
+  task workspaces (Git worktrees or Rift subvolumes) and prunes remnants once a
+  CL is landed or abandoned.