diff --git a/.ai-context/COMMANDS.md b/.ai-context/COMMANDS.md
index 5dec535d..287b9657 100644
--- a/.ai-context/COMMANDS.md
+++ b/.ai-context/COMMANDS.md
@@ -190,6 +190,10 @@ the v1.x compatibility window; new automation should use `--debug-wrapper`.
   - `basectl gh worktree prune` previews safe merged-worktree cleanup by
     default; pass `--closed-unmerged` to include clean worktrees tied to
     closed, unmerged pull requests.
+  - `basectl gh review fetch <number>` creates a detached review worktree in
+    the peer `../<repo>-review-worktrees` root by default. An explicit
+    `--root` must resolve outside the repository; nested and symlinked nested
+    roots are rejected before GitHub or Git mutation.
   - `basectl gh project doctor --project <title>` - inspect Project metadata
     fields against the Base Project schema.
   - `basectl gh project configure --project <title>` - create or repair the
diff --git a/cli/bash/commands/basectl/subcommands/gh.sh b/cli/bash/commands/basectl/subcommands/gh.sh
index acca303c..54dace4c 100644
--- a/cli/bash/commands/basectl/subcommands/gh.sh
+++ b/cli/bash/commands/basectl/subcommands/gh.sh
@@ -650,18 +650,20 @@ base_gh_slug() {
 
 base_gh_issue_worktree_path() {
     local issue="$1" slug="$2"
-    local repo_root repo_name repo_parent slug_short
+    local repo_root repo_name repo_parent worktree_root slug_short
 
     repo_root="$(git rev-parse --show-toplevel)" || return 1
+    repo_root="$(base_gh_resolve_physical_path "$repo_root")" || return 1
     repo_name="$(basename "$repo_root")"
     repo_parent="$(dirname "$repo_root")"
+    worktree_root="$(base_gh_validate_worktree_root "$repo_parent/$repo_name-worktrees" "issue worktree root")" || return 1
     slug_short="${slug:0:40}"
     while [[ "$slug_short" == *- ]]; do
         slug_short="${slug_short%-}"
     done
     [[ -n "$slug_short" ]] || slug_short="work"
 
-    printf '%s/%s-worktrees/%s-%s\n' "$repo_parent" "$repo_name" "$issue" "$slug_short"
+    printf '%s/%s-%s\n' "$worktree_root" "$issue" "$slug_short"
 }
 
 base_gh_issue_category() {
diff --git a/cli/bash/commands/basectl/subcommands/gh_branch_worktree.sh b/cli/bash/commands/basectl/subcommands/gh_branch_worktree.sh
index efb41dfb..40c3913f 100644
--- a/cli/bash/commands/basectl/subcommands/gh_branch_worktree.sh
+++ b/cli/bash/commands/basectl/subcommands/gh_branch_worktree.sh
@@ -820,6 +820,104 @@ base_gh_resolve_physical_path() {
     (cd "$path" && pwd -P)
 }
 
+base_gh_normalize_absolute_path() {
+    local path="$1"
+    local component
+    local -a components=() normalized=()
+
+    [[ "$path" == /* ]] || return 1
+    local IFS='/'
+    read -r -a components <<< "$path"
+    for component in "${components[@]}"; do
+        case "$component" in
+            ''|.)
+                ;;
+            ..)
+                if ((${#normalized[@]} > 0)); then
+                    normalized=("${normalized[@]:0:${#normalized[@]}-1}")
+                fi
+                ;;
+            *)
+                normalized+=("$component")
+                ;;
+        esac
+    done
+
+    if ((${#normalized[@]} == 0)); then
+        printf '/\n'
+    else
+        (IFS=/; printf '/%s\n' "${normalized[*]}")
+    fi
+}
+
+base_gh_resolve_path_for_creation() {
+    local path="$1"
+    local candidate suffix physical_candidate
+
+    [[ -n "$path" ]] || return 1
+    if [[ "$path" != /* ]]; then
+        path="$PWD/$path"
+    fi
+
+    candidate="$path"
+    suffix=""
+    while [[ ! -e "$candidate" ]]; do
+        [[ "$candidate" != "/" ]] || return 1
+        suffix="/$(basename "$candidate")$suffix"
+        candidate="$(dirname "$candidate")"
+    done
+    [[ -d "$candidate" ]] || return 1
+
+    physical_candidate="$(cd "$candidate" && pwd -P)" || return 1
+    base_gh_normalize_absolute_path "$physical_candidate$suffix"
+}
+
+base_gh_path_is_within_physical_root() {
+    local path="$1"
+    local root="$2"
+    local candidate
+
+    candidate="$path"
+    while [[ ! -e "$candidate" ]]; do
+        [[ "$candidate" != "/" ]] || return 1
+        candidate="$(dirname "$candidate")" || return 1
+    done
+    [[ -d "$candidate" ]] || return 1
+    candidate="$(cd "$candidate" && pwd -P)" || return 1
+
+    while :; do
+        [[ "$candidate" -ef "$root" ]] && return 0
+        [[ "$candidate" == "/" ]] && return 1
+        candidate="$(cd "$candidate/.." && pwd -P)" || return 1
+    done
+}
+
+base_gh_validate_worktree_root() {
+    local requested="$1"
+    local label="${2:-worktree root}"
+    local repo_root resolved_root
+
+    repo_root="$(git rev-parse --show-toplevel 2>/dev/null)" || {
+        base_gh_error "Unable to resolve the repository root before validating $label."
+        return 1
+    }
+    repo_root="$(base_gh_resolve_physical_path "$repo_root")" || {
+        base_gh_error "Unable to resolve the physical repository root before validating $label."
+        return 1
+    }
+    resolved_root="$(base_gh_resolve_path_for_creation "$requested")" || {
+        base_gh_error "Unable to resolve $label '$requested'."
+        return 1
+    }
+
+    if base_gh_path_is_within_physical_root "$resolved_root" "$repo_root"; then
+        base_gh_error "Refusing $label '$requested': it resolves inside repository root '$repo_root'. Use a peer directory outside the repository."
+        return 1
+    fi
+
+    printf '%s\n' "$resolved_root"
+}
+
 base_gh_list_worktree_branches() {
     base_git_list_worktree_branches .
 }
diff --git a/cli/bash/commands/basectl/subcommands/gh_review.sh b/cli/bash/commands/basectl/subcommands/gh_review.sh
index 1876faac..d41248dc 100644
--- a/cli/bash/commands/basectl/subcommands/gh_review.sh
+++ b/cli/bash/commands/basectl/subcommands/gh_review.sh
@@ -46,7 +46,8 @@ Options:
   --name <slug>       Required lower-case kebab-case review name.
   --repo <owner/name> Pull request repository. Defaults to origin and must
                       match the checkout's origin repository.
-  --root <path>       Review worktree root. Defaults to ../<repo>-review-worktrees.
+  --root <path>       Review worktree root outside the repository. Defaults to
+                      ../<repo>-review-worktrees; nested roots are rejected.
   --refresh           Replace an existing clean review worktree with the current PR head.
   -h, --help          Show this help text.
 EOF
@@ -129,6 +130,7 @@ base_gh_review_default_root() {
 
 base_gh_review_resolve_root() {
     local requested="${1:-}"
+    local validate_root="${2:-0}"
     local root
 
     if [[ -n "$requested" ]]; then
@@ -136,6 +138,9 @@ base_gh_review_resolve_root() {
     else
         root="$(base_gh_review_default_root)" || return 1
     fi
+    if ((validate_root)); then
+        root="$(base_gh_validate_worktree_root "$root" "review worktree root")" || return 1
+    fi
     mkdir -p "$root" || return 1
     (cd "$root" && pwd -P)
 }
@@ -321,7 +326,7 @@ base_gh_review_fetch() {
         }
     fi
     root="${parsed_options[root]:-}"
-    review_root="$(base_gh_review_resolve_root "$root")" || {
+    review_root="$(base_gh_review_resolve_root "$root" 1)" || {
         base_gh_error "Unable to prepare the review worktree root."
         return 1
     }
diff --git a/cli/bash/commands/basectl/tests/gh-review.bats b/cli/bash/commands/basectl/tests/gh-review.bats
index f4e77aa9..db1fdbd8 100644
--- a/cli/bash/commands/basectl/tests/gh-review.bats
+++ b/cli/bash/commands/basectl/tests/gh-review.bats
@@ -113,6 +113,72 @@ review_metadata_path() {
     jq -e '.pull_request == 2621 and .slug == "stale-worktree" and .head_sha == env.BASE_REVIEW_TEST_HEAD_SHA' "$metadata" >/dev/null
 }
 
+@test "review fetch rejects a nested worktree root before GitHub or Git mutation" {
+    local repo nested_root
+
+    create_review_repo
+    repo="$BASE_REVIEW_TEST_REPO"
+    nested_root="$repo/review-worktrees"
+
+    run_review "$repo" fetch 2621 --name nested-root --root "$nested_root"
+
+    [ "$status" -eq 1 ]
+    [[ "$output" == *"Refusing review worktree root"* ]]
+    [[ "$output" == *"inside repository root"* ]]
+    [ ! -e "$nested_root" ]
+    ! git -C "$repo" show-ref --verify --quiet refs/base-review/pr/2621/nested-root
+}
+
+@test "review fetch rejects a symlinked nested worktree root" {
+    local repo nested_link
+
+    create_review_repo
+    repo="$BASE_REVIEW_TEST_REPO"
+    nested_link="$TEST_TMPDIR/review-worktrees-link"
+    ln -s "$repo" "$nested_link"
+
+    run_review "$repo" fetch 2621 --name symlinked-root --root "$nested_link/children"
+
+    [ "$status" -eq 1 ]
+    [[ "$output" == *"Refusing review worktree root"* ]]
+    [[ "$output" == *"inside repository root"* ]]
+    ! git -C "$repo" show-ref --verify --quiet refs/base-review/pr/2621/symlinked-root
+}
+
+@test "review fetch rejects a missing-sibling traversal into the repository" {
+    local repo nested_root
+
+    create_review_repo
+    repo="$BASE_REVIEW_TEST_REPO"
+    nested_root="$TEST_TMPDIR/review-repo-shadow/../review-repo/review-worktrees"
+
+    run_review "$repo" fetch 2621 --name traversal-root --root "$nested_root"
+
+    [ "$status" -eq 1 ]
+    [[ "$output" == *"Refusing review worktree root"* ]]
+    [[ "$output" == *"inside repository root"* ]]
+    [ ! -e "$TEST_TMPDIR/review-repo/review-worktrees" ]
+    ! git -C "$repo" show-ref --verify --quiet refs/base-review/pr/2621/traversal-root
+}
+
+@test "review fetch treats glob characters in a peer root literally" {
+    local repo review_root worktree
+
+    create_review_repo
+    repo="$BASE_REVIEW_TEST_REPO"
+    review_root="$TEST_TMPDIR/review[*?]-worktrees"
+    mkdir -p "$review_root"
+    review_root="$(cd "$review_root" && pwd -P)"
+    worktree="$review_root/pr-2621-literal-glob"
+    write_review_gh_mock
+
+    run_review "$repo" fetch 2621 --name literal-glob --repo basefoundry/base --root "$review_root"
+
+    [ "$status" -eq 0 ]
+    [[ "$output" == *"CREATED $worktree"* ]]
+    [ -d "$worktree" ]
+}
+
 @test "review prune removes only a verified merged review checkout" {
     local repo review_root worktree metadata
 
diff --git a/docs/command-reference.md b/docs/command-reference.md
index e10b9729..41ef1810 100644
--- a/docs/command-reference.md
+++ b/docs/command-reference.md
@@ -241,7 +241,7 @@ daily project loop commands from the local checkout.
 | `basectl gh branch stale` | Report stale local branches. Stable inspection JSON uses the shared v1 envelope. | `--days <days>`, `--format <text\|json>` |
 | `basectl gh branch prune` | Prune safe merged branches. Pass `--closed-unmerged` to include branches whose pull requests were closed without merging. | `--dry-run`, `--yes`, `--remote`, `--closed-unmerged` |
 | `basectl gh worktree prune` | Prune stale merged branch-attached worktrees. Pass `--closed-unmerged` to include clean worktrees tied to closed, unmerged pull requests; unmanaged detached worktree metadata remains an explicit `git worktree prune` operation. Use `gh review prune` for Base-owned review worktrees. | `--dry-run`, `--yes`, `--closed-unmerged` |
-| `basectl gh review fetch <number>` | Fetch a pull-request head into a Base-owned namespaced ref and create a detached review worktree. It never creates an ordinary local `pr-*` branch. | `--name <slug>`, `--repo <owner/name>`, `--root <path>`, `--refresh` |
+| `basectl gh review fetch <number>` | Fetch a pull-request head into a Base-owned namespaced ref and create a detached review worktree outside the repository. It never creates an ordinary local `pr-*` branch; an explicit `--root` inside the repository or one of its descendants is rejected before Git or GitHub mutation. | `--name <slug>`, `--repo <owner/name>`, `--root <path>`, `--refresh` |
 | `basectl gh review prune` | Preview or remove safe Base-owned detached review worktrees and their namespaced refs. The default is dry-run; open, dirty, changed, invalid, missing, and unowned checkouts are retained. | `--dry-run`, `--yes`, `--closed-unmerged`, `--pr <number>`, `--root <path>` |
 | `basectl gh project doctor` | Inspect GitHub Project metadata against the Base Project schema. | `--project <title>`, `--owner <login>`, `--schema base-project` |
 | `basectl gh project configure` | Create or repair Base-managed Project metadata. | `--project <title>`, `--owner <login>`, `--repo <owner/name>`, `--schema base-project`, `--config <path>`, `--copy-fields-from <title>`, `--replace-project`, `--initiative-option <name>`, `--dry-run` |
diff --git a/docs/github-workflow.md b/docs/github-workflow.md
index b172ee13..3cdf668f 100644
--- a/docs/github-workflow.md
+++ b/docs/github-workflow.md
@@ -408,6 +408,13 @@ Issue work should use:
 ~/work/base-worktrees/<slug>
 ```
 
+Base-supported worktree creation keeps implementation and review roots next to
+the repository, never inside it. `basectl gh issue start` prints the canonical
+peer path, and `basectl gh review fetch` rejects an explicit root that resolves
+to the repository or any descendant of it, including through a symlink. This
+keeps worktrees out of the primary checkout so workspace synchronization can
+reason about the checkout independently of unmerged work.
+
 Before creating a worktree, check whether the current checkout is already a
 linked worktree for the intended issue:
 
@@ -526,8 +533,11 @@ refs/base-review/pr/<number>/<slug>
 The worktree is detached, the review ref is not an ordinary
 `refs/heads/pr-*` branch, and the default root is next to the repository root
 represented by the common Git directory. Use `--root <path>` when a different
-review workspace is needed. Use `--refresh` only to replace an existing clean
-review checkout with the current pull-request head.
+review workspace is needed; the path must resolve outside the repository and
+its descendants. Use `--refresh` only to replace an existing clean review
+checkout with the current pull-request head. Existing nested worktrees are not
+moved or deleted automatically; inspect and migrate them explicitly after
+preserving any local work.
 The optional `--repo <owner/name>` selector must match the checkout's `origin`
 repository; use a checkout of that repository when reviewing an upstream PR.