From a4a21b095ea7c0daa953351107640347f16dea04 Mon Sep 17 00:00:00 2001
From: Ramesh Padmanabhaiah <22363102+codeforester@users.noreply.github.com>
Date: Mon, 19 Oct 2026 23:37:57 +0530
Subject: [PATCH 1/2] refactor(git): centralize linked-worktree validity checks

---
 base_api_manifest.yaml          |  2 +-
 docs/api-reference.md           |  1 +
 docs/v2-api-contract.md         |  2 +-
 docs/v2-symbol-map.md           |  2 +-
 lib/bash/git/README.md          |  9 ++++++++
 lib/bash/git/lib_git.sh         | 12 +++++++++++
 lib/bash/git/tests/lib_git.bats | 37 +++++++++++++++++++++++++++++++++
 scripts/api-manifest            | 25 ++++++++++++++++++----
 8 files changed, 83 insertions(+), 7 deletions(-)

diff --git a/base_api_manifest.yaml b/base_api_manifest.yaml
index 423c9d9..18fb7b9 100644
--- a/base_api_manifest.yaml
+++ b/base_api_manifest.yaml
@@ -108,7 +108,7 @@ modules:
     dependencies: std,str
     optional_commands: git,awk,grep,mktemp,rm,sleep
     artifacts: lib/bash/git/lib_git.sh,lib/bash/git/README.md,lib/bash/git/tests/lib_git.bats
-    public_symbols: base_git_branch_merged_to_ref,base_git_branch_upstream,base_git_check_script_up_to_date,base_git_detect_default_branch,base_git_get_current_branch,base_git_list_remote_branches,base_git_list_worktree_branches,base_git_update_repo,base_git_worktree_path_for_branch
+    public_symbols: base_git_branch_merged_to_ref,base_git_branch_upstream,base_git_check_script_up_to_date,base_git_detect_default_branch,base_git_get_current_branch,base_git_list_remote_branches,base_git_list_worktree_branches,base_git_update_repo,base_git_worktree_path_for_branch,base_git_worktree_path_is_valid
     signature_source: lib/bash/git/README.md
     inputs: documented per symbol in the module README and API charter
     outputs: documented per symbol; named outputs are caller-owned
diff --git a/docs/api-reference.md b/docs/api-reference.md
index 717ac37..8844576 100644
--- a/docs/api-reference.md
+++ b/docs/api-reference.md
@@ -165,6 +165,7 @@ statuses, and side effects are normative in the linked module README and
 - `base_git_list_worktree_branches` — signature: see [`lib/bash/git/README.md`](../lib/bash/git/README.md).
 - `base_git_update_repo` — signature: see [`lib/bash/git/README.md`](../lib/bash/git/README.md).
 - `base_git_worktree_path_for_branch` — signature: see [`lib/bash/git/README.md`](../lib/bash/git/README.md).
+- `base_git_worktree_path_is_valid` — signature: see [`lib/bash/git/README.md`](../lib/bash/git/README.md).
 
 ### `gh`
 
diff --git a/docs/v2-api-contract.md b/docs/v2-api-contract.md
index b551b9f..59846ac 100644
--- a/docs/v2-api-contract.md
+++ b/docs/v2-api-contract.md
@@ -215,7 +215,7 @@ signature/effects reference; this table makes coverage auditable.
 | std validation/reflection | `base_std_assert_variable_name`, `base_std_assert_indexed_array`, `base_std_assert_associative_array`, `base_std_command_path`, `base_std_function_exists`, `base_std_assert_function_exists`, `base_std_assert_not_null`, `base_std_assert_integer`, `base_std_assert_integer_range`, `base_std_assert_arg_count`, `base_std_assert_command_exists`, `base_std_assert_file_exists`, `base_std_assert_executable`, `base_std_assert_dir_exists` | Predicates return status; explicit `assert_*` APIs are intentional fail-fast precondition checks; named outputs are validated before writes. |
 | std miscellaneous | `base_std_safe_cd`, `base_std_safe_unalias`, `base_std_get_my_source_dir`, `base_std_ask_yes_no`, `base_std_wait_for_enter` | `safe_cd` changes `PWD`; source-dir writes one validated output; interactive functions return recoverable EOF/non-TTY statuses. |
 | file | `base_file_section_exists`, `base_file_section_needs_update`, `base_file_update_file_section` | Read-only predicates do not mutate; update is idempotent, symlink-preserving, atomic, metadata-preserving, and conflict-aware. |
-| git | `base_git_detect_default_branch`, `base_git_worktree_path_for_branch`, `base_git_list_worktree_branches`, `base_git_branch_upstream`, `base_git_branch_merged_to_ref`, `base_git_list_remote_branches`, `base_git_update_repo`, `base_git_get_current_branch`, `base_git_check_script_up_to_date` | Usage and contract errors return `2`; recoverable Git failures and false predicates return `1` unless a function documents a specific status. Read-only inspections use named outputs/stdout as documented; freshness outcomes are `3` dirty, `4` behind, and `5` diverged. |
+| git | `base_git_detect_default_branch`, `base_git_worktree_path_for_branch`, `base_git_list_worktree_branches`, `base_git_branch_upstream`, `base_git_branch_merged_to_ref`, `base_git_list_remote_branches`, `base_git_update_repo`, `base_git_get_current_branch`, `base_git_check_script_up_to_date`, `base_git_worktree_path_is_valid` | Usage and contract errors return `2`; recoverable Git failures and false predicates return `1` unless a function documents a specific status. Read-only inspections use named outputs/stdout as documented; freshness outcomes are `3` dirty, `4` behind, and `5` diverged. `base_git_worktree_path_is_valid` returns success only for an existing linked worktree whose Git metadata is valid; ordinary repositories, missing paths, and stale linked-worktree metadata return `1` without diagnostics. |
 | gh (stable since `2.0.0`; private process implementation dependency shipped in `2.1.0`) | `base_gh_require_cli`, `base_gh_auth_status_diagnostics`, `base_gh_report_command_failure`, `base_gh_run`, `base_gh_repo_from_remote_url`, `base_gh_infer_repo_from_origin`, `base_gh_repo_default_branch`, `base_gh_api_with_retry` | Usage and contract errors return `2`; recoverable GitHub failures return `1` unless the helper preserves the underlying `gh` status. Diagnostics go stderr; repository/API values use named outputs; retries are bounded and mutation-aware. The public API remains compatible through v2.x; the private process dependency is included in the v2.1.0 artifact. |
 | str | `base_str_lower`, `base_str_upper`, `base_str_ltrim`, `base_str_rtrim`, `base_str_trim`, `base_str_contains`, `base_str_starts_with`, `base_str_ends_with`, `base_str_split`, `base_str_join` | String transforms/predicates preserve caller values until validation succeeds; split/join use validated named outputs. |
 | arg | `base_arg_parse` | Parses into caller-owned validated arrays/maps and leaves them unchanged on failure. |
diff --git a/docs/v2-symbol-map.md b/docs/v2-symbol-map.md
index 4286b46..0bcb534 100644
--- a/docs/v2-symbol-map.md
+++ b/docs/v2-symbol-map.md
@@ -49,7 +49,7 @@ is part of the caller's intended policy.
 | Module | Legacy names | v2 names |
 | --- | --- | --- |
 | file | `file_section_exists`, `file_section_needs_update`, `update_file_section` | `base_file_section_exists`, `base_file_section_needs_update`, `base_file_update_file_section` |
-| git | `git_detect_default_branch`, `git_worktree_path_for_branch`, `git_list_worktree_branches`, `git_branch_upstream`, `git_branch_merged_to_ref`, `git_list_remote_branches`, `git_update_repo`, `git_get_current_branch`, `check_script_up_to_date` | `base_git_detect_default_branch`, `base_git_worktree_path_for_branch`, `base_git_list_worktree_branches`, `base_git_branch_upstream`, `base_git_branch_merged_to_ref`, `base_git_list_remote_branches`, `base_git_update_repo`, `base_git_get_current_branch`, `base_git_check_script_up_to_date` |
+| git | `git_detect_default_branch`, `git_worktree_path_for_branch`, `git_list_worktree_branches`, `git_branch_upstream`, `git_branch_merged_to_ref`, `git_list_remote_branches`, `git_update_repo`, `git_get_current_branch`, `check_script_up_to_date` | `base_git_detect_default_branch`, `base_git_worktree_path_for_branch`, `base_git_list_worktree_branches`, `base_git_branch_upstream`, `base_git_branch_merged_to_ref`, `base_git_list_remote_branches`, `base_git_update_repo`, `base_git_get_current_branch`, `base_git_check_script_up_to_date`, `base_git_worktree_path_is_valid` |
 | gh | `gh_require_cli`, `gh_auth_status_diagnostics`, `gh_report_command_failure`, `gh_run`, `gh_repo_from_remote_url`, `gh_infer_repo_from_origin`, `gh_repo_default_branch`, `gh_api_with_retry` | `base_gh_require_cli`, `base_gh_auth_status_diagnostics`, `base_gh_report_command_failure`, `base_gh_run`, `base_gh_repo_from_remote_url`, `base_gh_infer_repo_from_origin`, `base_gh_repo_default_branch`, `base_gh_api_with_retry` |
 | str | `str_lower`, `str_upper`, `str_ltrim`, `str_rtrim`, `str_trim`, `str_contains`, `str_starts_with`, `str_ends_with`, `str_split`, `str_join` | `base_str_lower`, `base_str_upper`, `base_str_ltrim`, `base_str_rtrim`, `base_str_trim`, `base_str_contains`, `base_str_starts_with`, `base_str_ends_with`, `base_str_split`, `base_str_join` |
 | arg | `arg_parse` | `base_arg_parse` |
diff --git a/lib/bash/git/README.md b/lib/bash/git/README.md
index 845520d..0ea22a7 100644
--- a/lib/bash/git/README.md
+++ b/lib/bash/git/README.md
@@ -18,6 +18,10 @@ Source `lib/bash/std/lib_std.sh` before this library so logging and shared error
 - `base_git_worktree_path_for_branch [--result VAR] <branch> [repo]`
   Print the worktree path attached to a local branch, or store its exact value
   in `VAR` when it can contain trailing newlines.
+- `base_git_worktree_path_is_valid <path>`
+  Return success only when `path` is a valid linked Git worktree. Detached
+  linked worktrees are valid; ordinary repositories, missing paths, and stale
+  linked-worktree metadata return `1` without printing Git diagnostics.
 - `base_git_list_worktree_branches [repo]`
   Print tab-separated worktree path and branch rows. Backslash, tab, newline,
   and carriage-return bytes in paths are escaped as `\\`, `\t`, `\n`, and
@@ -70,6 +74,11 @@ base_git_worktree_path_for_branch --result worktree_path feature/topic "$PWD"
 - Worktree helpers parse Git's NUL-delimited porcelain format. Use the lookup
   helper's `--result` form whenever a path may end in one or more newlines;
   command substitution necessarily strips those bytes from stdout.
+- `base_git_worktree_path_is_valid` is intentionally limited to linked
+  worktrees: it requires a `.git` file and a successful `git -C <path>
+  rev-parse --is-inside-work-tree` probe. A `.git` directory is an ordinary
+  repository checkout, not a linked worktree, and a `.git` file whose Git
+  administrative record is stale is invalid.
 - `base_git_update_repo` only attempts updates when the checked-out branch is the detected default branch, or an explicit expected branch passed by the caller.
 - `base_git_update_repo` requires `git_repo` to be the repository root (including
   a symlink that resolves to that root); it rejects ordinary descendants rather
diff --git a/lib/bash/git/lib_git.sh b/lib/bash/git/lib_git.sh
index 8243da4..457780f 100644
--- a/lib/bash/git/lib_git.sh
+++ b/lib/bash/git/lib_git.sh
@@ -161,6 +161,18 @@ base_git_worktree_path_for_branch() {
     fi
 }
 
+base_git_worktree_path_is_valid() {
+    if (($# != 1)); then
+        base_std_log_error -l base_bash_libs.git "Usage: base_git_worktree_path_is_valid <path>"
+        return 2
+    fi
+
+    local path="$1"
+
+    [[ -d "$path" && -f "$path/.git" ]] || return 1
+    git -C "$path" rev-parse --is-inside-work-tree > /dev/null 2>&1 || return 1
+}
+
 base_git_list_worktree_branches() {
     if (($# > 1)); then
         base_std_log_error -l base_bash_libs.git "Usage: base_git_list_worktree_branches [repo_dir]"
diff --git a/lib/bash/git/tests/lib_git.bats b/lib/bash/git/tests/lib_git.bats
index 15ab550..b994f60 100644
--- a/lib/bash/git/tests/lib_git.bats
+++ b/lib/bash/git/tests/lib_git.bats
@@ -44,6 +44,7 @@ setup() {
             base_git_branch_merged_to_ref \
             base_git_update_repo \
             base_git_get_current_branch \
+            base_git_worktree_path_is_valid \
             base_git_check_script_up_to_date; do
             bats_run "$BASH" -c '
                 mode="$1"
@@ -205,6 +206,42 @@ setup() {
     unset -f git
 }
 
+@test "base_git_worktree_path_is_valid accepts linked worktrees and rejects other paths" {
+    local repo="$TEST_TMPDIR/repo"
+    local linked="$TEST_TMPDIR/linked worktree"
+    local detached="$TEST_TMPDIR/detached worktree"
+    local clone="$TEST_TMPDIR/clone"
+    local stale="$TEST_TMPDIR/stale worktree"
+
+    init_git_repo "$repo"
+    printf 'base\n' > "$repo/data.txt"
+    commit_all "$repo" "Initial commit"
+    git -C "$repo" worktree add -b feature "$linked" >/dev/null 2>&1
+    git -C "$repo" worktree add --detach "$detached" HEAD >/dev/null 2>&1
+    git clone --quiet "$repo" "$clone"
+    mkdir -p "$stale"
+    printf 'gitdir: %s\n' "$TEST_TMPDIR/missing-worktree-admin" > "$stale/.git"
+
+    base_git_worktree_path_is_valid "$linked"
+    base_git_worktree_path_is_valid "$detached"
+    ! base_git_worktree_path_is_valid "$repo"
+    ! base_git_worktree_path_is_valid "$clone"
+    ! base_git_worktree_path_is_valid "$stale"
+    ! base_git_worktree_path_is_valid "$TEST_TMPDIR/missing"
+}
+
+@test "base_git_worktree_path_is_valid suppresses stale metadata diagnostics" {
+    local stale="$TEST_TMPDIR/stale-worktree"
+
+    mkdir -p "$stale"
+    printf 'gitdir: %s\n' "$TEST_TMPDIR/missing-worktree-admin" > "$stale/.git"
+
+    capture_command base_git_worktree_path_is_valid "$stale"
+
+    [ "$status" -eq 1 ]
+    [ -z "$output" ]
+}
+
 @test "git worktree helpers parse canonical porcelain output" {
     git() {
         if [[ "${1:-}" == "worktree" || "${3:-}" == "worktree" ]]; then
diff --git a/scripts/api-manifest b/scripts/api-manifest
index 8feb7e7..a800be3 100755
--- a/scripts/api-manifest
+++ b/scripts/api-manifest
@@ -556,7 +556,7 @@ release_module_check() {
 check_release_tree() {
     local manifest="$1"
     local release_ref="$2"
-    local symbol
+    local symbol release_manifest="$manifest" historical_manifest=""
     local -a fields=()
     local -A release_module_sources=()
     local -A release_module_docs=()
@@ -569,6 +569,19 @@ check_release_tree() {
         error "release reference is not a local commit: $release_ref"
         return 1
     }
+    if [[ "$manifest" == "$default_manifest" ]]; then
+        historical_manifest="$(mktemp "${TMPDIR:-/tmp}/base-api-release-manifest.XXXXXX")" || return 1
+        if ! git -C "$repo_root" show "$release_ref:base_api_manifest.yaml" > "$historical_manifest" 2> /dev/null; then
+            rm -f "$historical_manifest"
+            error "release reference '$release_ref' does not contain base_api_manifest.yaml"
+            return 1
+        fi
+        # The compatibility check above verifies that every historical stable
+        # symbol remains available. The release tree check must inspect the
+        # historical manifest so additive stable APIs are allowed in a minor
+        # v2 release without pretending they were present in v2.0.0.
+        release_manifest="$historical_manifest"
+    fi
     while IFS=$'\t' read -r -a fields; do
         [[ -n "${fields[0]-}" ]] || continue
         release_module_sources["${fields[0]}"]="${fields[2]}"
@@ -576,11 +589,15 @@ check_release_tree() {
         release_module_tests["${fields[0]}"]="${fields[4]}"
         release_module_symbols["${fields[0]}"]="${fields[8]}"
         release_module_dependencies["${fields[0]}"]="${fields[5]}"
-    done < <(manifest_rows "$manifest")
+    done < <(manifest_rows "$release_manifest")
     while IFS=$'\t' read -r -a fields; do
         [[ -n "${fields[0]-}" && "${fields[14]}" == stable ]] || continue
-        release_module_check "${fields[0]}" "${fields[0]}" || return 1
-    done < <(manifest_rows "$manifest")
+        release_module_check "${fields[0]}" "${fields[0]}" || {
+            rm -f "$historical_manifest"
+            return 1
+        }
+    done < <(manifest_rows "$release_manifest")
+    rm -f "$historical_manifest"
     printf 'Stable API release reference is valid: %s\n' "$release_ref"
 }
 

From 857df0d374bb6b567b0e19e09171d33757d19c60 Mon Sep 17 00:00:00 2001
From: Ramesh Padmanabhaiah <22363102+codeforester@users.noreply.github.com>
Date: Wed, 4 Nov 2026 00:13:36 +0530
Subject: [PATCH 2/2] fix(git): reject submodules as linked worktrees

---
 CHANGELOG.md                    |  4 ++++
 docs/v2-api-contract.md         |  2 +-
 lib/bash/git/README.md          |  8 +++++---
 lib/bash/git/lib_git.sh         | 13 +++++++++++++
 lib/bash/git/tests/lib_git.bats | 16 ++++++++++++++++
 5 files changed, 39 insertions(+), 4 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index f888308..68cd037 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -12,6 +12,10 @@ and versions are tracked in the repo-root `VERSION` file.
 - Moved hosted macOS validation to the pinned macOS 15 runner while preserving
   the logical macOS 14 compatibility and release-platform contract.
 
+### Fixed
+
+- Reject Git submodule checkouts when validating linked worktree paths.
+
 ## [2.2.2] - 2026-10-08
 
 ### Documentation
diff --git a/docs/v2-api-contract.md b/docs/v2-api-contract.md
index 59846ac..d8a5e00 100644
--- a/docs/v2-api-contract.md
+++ b/docs/v2-api-contract.md
@@ -215,7 +215,7 @@ signature/effects reference; this table makes coverage auditable.
 | std validation/reflection | `base_std_assert_variable_name`, `base_std_assert_indexed_array`, `base_std_assert_associative_array`, `base_std_command_path`, `base_std_function_exists`, `base_std_assert_function_exists`, `base_std_assert_not_null`, `base_std_assert_integer`, `base_std_assert_integer_range`, `base_std_assert_arg_count`, `base_std_assert_command_exists`, `base_std_assert_file_exists`, `base_std_assert_executable`, `base_std_assert_dir_exists` | Predicates return status; explicit `assert_*` APIs are intentional fail-fast precondition checks; named outputs are validated before writes. |
 | std miscellaneous | `base_std_safe_cd`, `base_std_safe_unalias`, `base_std_get_my_source_dir`, `base_std_ask_yes_no`, `base_std_wait_for_enter` | `safe_cd` changes `PWD`; source-dir writes one validated output; interactive functions return recoverable EOF/non-TTY statuses. |
 | file | `base_file_section_exists`, `base_file_section_needs_update`, `base_file_update_file_section` | Read-only predicates do not mutate; update is idempotent, symlink-preserving, atomic, metadata-preserving, and conflict-aware. |
-| git | `base_git_detect_default_branch`, `base_git_worktree_path_for_branch`, `base_git_list_worktree_branches`, `base_git_branch_upstream`, `base_git_branch_merged_to_ref`, `base_git_list_remote_branches`, `base_git_update_repo`, `base_git_get_current_branch`, `base_git_check_script_up_to_date`, `base_git_worktree_path_is_valid` | Usage and contract errors return `2`; recoverable Git failures and false predicates return `1` unless a function documents a specific status. Read-only inspections use named outputs/stdout as documented; freshness outcomes are `3` dirty, `4` behind, and `5` diverged. `base_git_worktree_path_is_valid` returns success only for an existing linked worktree whose Git metadata is valid; ordinary repositories, missing paths, and stale linked-worktree metadata return `1` without diagnostics. |
+| git | `base_git_detect_default_branch`, `base_git_worktree_path_for_branch`, `base_git_list_worktree_branches`, `base_git_branch_upstream`, `base_git_branch_merged_to_ref`, `base_git_list_remote_branches`, `base_git_update_repo`, `base_git_get_current_branch`, `base_git_check_script_up_to_date`, `base_git_worktree_path_is_valid` | Usage and contract errors return `2`; recoverable Git failures and false predicates return `1` unless a function documents a specific status. Read-only inspections use named outputs/stdout as documented; freshness outcomes are `3` dirty, `4` behind, and `5` diverged. `base_git_worktree_path_is_valid` returns success only for an existing linked worktree whose resolved Git directory is below the repository's `worktrees/` administrative directory; ordinary repositories, submodules, missing paths, and stale linked-worktree metadata return `1` without diagnostics. |
 | gh (stable since `2.0.0`; private process implementation dependency shipped in `2.1.0`) | `base_gh_require_cli`, `base_gh_auth_status_diagnostics`, `base_gh_report_command_failure`, `base_gh_run`, `base_gh_repo_from_remote_url`, `base_gh_infer_repo_from_origin`, `base_gh_repo_default_branch`, `base_gh_api_with_retry` | Usage and contract errors return `2`; recoverable GitHub failures return `1` unless the helper preserves the underlying `gh` status. Diagnostics go stderr; repository/API values use named outputs; retries are bounded and mutation-aware. The public API remains compatible through v2.x; the private process dependency is included in the v2.1.0 artifact. |
 | str | `base_str_lower`, `base_str_upper`, `base_str_ltrim`, `base_str_rtrim`, `base_str_trim`, `base_str_contains`, `base_str_starts_with`, `base_str_ends_with`, `base_str_split`, `base_str_join` | String transforms/predicates preserve caller values until validation succeeds; split/join use validated named outputs. |
 | arg | `base_arg_parse` | Parses into caller-owned validated arrays/maps and leaves them unchanged on failure. |
diff --git a/lib/bash/git/README.md b/lib/bash/git/README.md
index 0ea22a7..f8d461e 100644
--- a/lib/bash/git/README.md
+++ b/lib/bash/git/README.md
@@ -76,9 +76,11 @@ base_git_worktree_path_for_branch --result worktree_path feature/topic "$PWD"
   command substitution necessarily strips those bytes from stdout.
 - `base_git_worktree_path_is_valid` is intentionally limited to linked
   worktrees: it requires a `.git` file and a successful `git -C <path>
-  rev-parse --is-inside-work-tree` probe. A `.git` directory is an ordinary
-  repository checkout, not a linked worktree, and a `.git` file whose Git
-  administrative record is stale is invalid.
+  rev-parse --is-inside-work-tree` probe whose resolved Git directory is below
+  the repository's `worktrees/` administrative directory. A `.git` directory
+  is an ordinary repository checkout, a submodule `.git` file points below
+  `modules/`, and a `.git` file whose Git administrative record is stale; all
+  three cases are invalid linked worktrees.
 - `base_git_update_repo` only attempts updates when the checked-out branch is the detected default branch, or an explicit expected branch passed by the caller.
 - `base_git_update_repo` requires `git_repo` to be the repository root (including
   a symlink that resolves to that root); it rejects ordinary descendants rather
diff --git a/lib/bash/git/lib_git.sh b/lib/bash/git/lib_git.sh
index 457780f..b5639ea 100644
--- a/lib/bash/git/lib_git.sh
+++ b/lib/bash/git/lib_git.sh
@@ -168,9 +168,22 @@ base_git_worktree_path_is_valid() {
     fi
 
     local path="$1"
+    local git_dir common_dir git_dir_abs common_dir_abs worktrees_dir
 
     [[ -d "$path" && -f "$path/.git" ]] || return 1
     git -C "$path" rev-parse --is-inside-work-tree > /dev/null 2>&1 || return 1
+
+    git_dir="$(git -C "$path" rev-parse --git-dir 2> /dev/null)" || return 1
+    common_dir="$(git -C "$path" rev-parse --git-common-dir 2> /dev/null)" || return 1
+    git_dir_abs="$(cd -- "$git_dir" 2> /dev/null && pwd -P)" || return 1
+    common_dir_abs="$(cd -- "$common_dir" 2> /dev/null && pwd -P)" || return 1
+    worktrees_dir="$common_dir_abs/worktrees"
+
+    [[ -d "$worktrees_dir" ]] || return 1
+    case "$git_dir_abs" in
+    "$worktrees_dir"/*) return 0 ;;
+    *) return 1 ;;
+    esac
 }
 
 base_git_list_worktree_branches() {
diff --git a/lib/bash/git/tests/lib_git.bats b/lib/bash/git/tests/lib_git.bats
index b994f60..2c23f40 100644
--- a/lib/bash/git/tests/lib_git.bats
+++ b/lib/bash/git/tests/lib_git.bats
@@ -230,6 +230,22 @@ setup() {
     ! base_git_worktree_path_is_valid "$TEST_TMPDIR/missing"
 }
 
+@test "base_git_worktree_path_is_valid rejects submodule checkouts" {
+    local source_repo="$TEST_TMPDIR/submodule-source"
+    local repo="$TEST_TMPDIR/repo"
+
+    init_git_repo "$source_repo"
+    printf 'submodule\n' > "$source_repo/data.txt"
+    commit_all "$source_repo" "Initial submodule commit"
+
+    init_git_repo "$repo"
+    printf 'superproject\n' > "$repo/data.txt"
+    commit_all "$repo" "Initial superproject commit"
+    git -C "$repo" -c protocol.file.allow=always submodule add "$source_repo" submodule >/dev/null 2>&1
+
+    ! base_git_worktree_path_is_valid "$repo/submodule"
+}
+
 @test "base_git_worktree_path_is_valid suppresses stale metadata diagnostics" {
     local stale="$TEST_TMPDIR/stale-worktree"