diff --git a/gstack-upgrade/migrations/v0.16.2.0.sh b/gstack-upgrade/migrations/v0.16.2.0.sh
index 534db737b..1f3f73cbd 100755
--- a/gstack-upgrade/migrations/v0.16.2.0.sh
+++ b/gstack-upgrade/migrations/v0.16.2.0.sh
@@ -11,7 +11,8 @@
 # Affected: users who ran /office-hours before this version
 set -euo pipefail
 
-. "${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
+_gstack_migration_dir="${BASH_SOURCE[0]//\\//}"; _gstack_migration_dir="${_gstack_migration_dir%/*}"
+. "${_gstack_migration_dir}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${_gstack_migration_dir}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
 gstack_state_root_select; GSTACK_HOME="$_gstack_sr_root"
 PROFILE_FILE="$GSTACK_HOME/builder-profile.jsonl"
 
diff --git a/gstack-upgrade/migrations/v1.0.0.0.sh b/gstack-upgrade/migrations/v1.0.0.0.sh
index f43ea3f6b..91cc93173 100755
--- a/gstack-upgrade/migrations/v1.0.0.0.sh
+++ b/gstack-upgrade/migrations/v1.0.0.0.sh
@@ -13,7 +13,8 @@
 # Affected: every user on v0.19.x and below who upgrades to v1.x
 set -euo pipefail
 
-. "${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
+_gstack_migration_dir="${BASH_SOURCE[0]//\\//}"; _gstack_migration_dir="${_gstack_migration_dir%/*}"
+. "${_gstack_migration_dir}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${_gstack_migration_dir}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
 gstack_state_root_select; GSTACK_HOME="$_gstack_sr_root"
 PROMPTED_FLAG="$GSTACK_HOME/.writing-style-prompted"
 PENDING_FLAG="$GSTACK_HOME/.writing-style-prompt-pending"
diff --git a/gstack-upgrade/migrations/v1.17.0.0.sh b/gstack-upgrade/migrations/v1.17.0.0.sh
index 7048c7363..16c8ef69b 100755
--- a/gstack-upgrade/migrations/v1.17.0.0.sh
+++ b/gstack-upgrade/migrations/v1.17.0.0.sh
@@ -38,7 +38,8 @@ if [ "$SYNC_MODE" = "off" ] || [ -z "$SYNC_MODE" ]; then
 fi
 
 # Skip if no brain-sync git repo exists.
-. "${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
+_gstack_migration_dir="${BASH_SOURCE[0]//\\//}"; _gstack_migration_dir="${_gstack_migration_dir%/*}"
+. "${_gstack_migration_dir}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${_gstack_migration_dir}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
 gstack_state_root_select
 if [ ! -d "$_gstack_sr_root/.git" ]; then
   exit 0
diff --git a/gstack-upgrade/migrations/v1.27.0.0.sh b/gstack-upgrade/migrations/v1.27.0.0.sh
index e43466e38..182f6b654 100755
--- a/gstack-upgrade/migrations/v1.27.0.0.sh
+++ b/gstack-upgrade/migrations/v1.27.0.0.sh
@@ -44,7 +44,8 @@ fi
 # ---------------------------------------------------------------------------
 # Configuration
 # ---------------------------------------------------------------------------
-. "${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
+_gstack_migration_dir="${BASH_SOURCE[0]//\\//}"; _gstack_migration_dir="${_gstack_migration_dir%/*}"
+. "${_gstack_migration_dir}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${_gstack_migration_dir}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
 gstack_state_root_select; GSTACK_HOME="$_gstack_sr_root"
 SKILLS_DIR="${HOME}/.claude/skills"
 BIN_DIR="${SKILLS_DIR}/gstack/bin"
diff --git a/gstack-upgrade/migrations/v1.37.0.0.sh b/gstack-upgrade/migrations/v1.37.0.0.sh
index c975e6bd5..3499c16fa 100755
--- a/gstack-upgrade/migrations/v1.37.0.0.sh
+++ b/gstack-upgrade/migrations/v1.37.0.0.sh
@@ -38,7 +38,8 @@ if [ -z "${HOME:-}" ]; then
   exit 0
 fi
 
-. "${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
+_gstack_migration_dir="${BASH_SOURCE[0]//\\//}"; _gstack_migration_dir="${_gstack_migration_dir%/*}"
+. "${_gstack_migration_dir}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${_gstack_migration_dir}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
 gstack_state_root_select; GSTACK_HOME="$_gstack_sr_root"
 MIGRATIONS_DIR="$GSTACK_HOME/.migrations"
 DONE_TOUCH="$MIGRATIONS_DIR/v1.37.0.0.done"
diff --git a/gstack-upgrade/migrations/v1.38.1.0.sh b/gstack-upgrade/migrations/v1.38.1.0.sh
index 1b23e9edd..148b68070 100755
--- a/gstack-upgrade/migrations/v1.38.1.0.sh
+++ b/gstack-upgrade/migrations/v1.38.1.0.sh
@@ -15,7 +15,8 @@
 # still run. `set -u` is fine.
 set -u
 
-. "${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
+_gstack_migration_dir="${BASH_SOURCE[0]//\\//}"; _gstack_migration_dir="${_gstack_migration_dir%/*}"
+. "${_gstack_migration_dir}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${_gstack_migration_dir}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
 gstack_state_root_select; GSTACK_HOME="$_gstack_sr_root"
 ALLOWLIST="${GSTACK_HOME}/.brain-allowlist"
 PRIVACY="${GSTACK_HOME}/.brain-privacy-map.json"
diff --git a/gstack-upgrade/migrations/v1.40.0.0.sh b/gstack-upgrade/migrations/v1.40.0.0.sh
index 177705d7f..83de735ce 100755
--- a/gstack-upgrade/migrations/v1.40.0.0.sh
+++ b/gstack-upgrade/migrations/v1.40.0.0.sh
@@ -22,7 +22,8 @@
 
 set -u
 
-. "${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
+_gstack_migration_dir="${BASH_SOURCE[0]//\\//}"; _gstack_migration_dir="${_gstack_migration_dir%/*}"
+. "${_gstack_migration_dir}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${_gstack_migration_dir}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
 gstack_state_root_select; GSTACK_HOME="$_gstack_sr_root"
 ALLOWLIST="${GSTACK_HOME}/.brain-allowlist"
 PRIVACY="${GSTACK_HOME}/.brain-privacy-map.json"
diff --git a/gstack-upgrade/migrations/v1.58.0.0.sh b/gstack-upgrade/migrations/v1.58.0.0.sh
index bd5adc24f..de119f0f6 100755
--- a/gstack-upgrade/migrations/v1.58.0.0.sh
+++ b/gstack-upgrade/migrations/v1.58.0.0.sh
@@ -20,7 +20,8 @@
 
 set -u
 
-. "${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
+_gstack_migration_dir="${BASH_SOURCE[0]//\\//}"; _gstack_migration_dir="${_gstack_migration_dir%/*}"
+. "${_gstack_migration_dir}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${_gstack_migration_dir}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
 gstack_state_root_select; GSTACK_HOME="$_gstack_sr_root"
 MIGRATION_DIR="${GSTACK_HOME}/.migrations"
 DONE="${MIGRATION_DIR}/v1.58.0.0.done"
diff --git a/gstack-upgrade/migrations/v1.65.0.0.sh b/gstack-upgrade/migrations/v1.65.0.0.sh
index 44e698a58..8c84a543c 100755
--- a/gstack-upgrade/migrations/v1.65.0.0.sh
+++ b/gstack-upgrade/migrations/v1.65.0.0.sh
@@ -34,7 +34,8 @@
 
 set -u
 
-. "${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
+_gstack_migration_dir="${BASH_SOURCE[0]//\\//}"; _gstack_migration_dir="${_gstack_migration_dir%/*}"
+. "${_gstack_migration_dir}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${_gstack_migration_dir}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
 gstack_state_root_select; GSTACK_HOME="$_gstack_sr_root"
 MIGRATION_DIR="${GSTACK_HOME}/.migrations"
 DONE="${MIGRATION_DIR}/v1.65.0.0.done"
diff --git a/gstack-upgrade/migrations/v1.78.0.0.sh b/gstack-upgrade/migrations/v1.78.0.0.sh
index 28c230aaa..29d293020 100755
--- a/gstack-upgrade/migrations/v1.78.0.0.sh
+++ b/gstack-upgrade/migrations/v1.78.0.0.sh
@@ -15,7 +15,8 @@
 set -u
 
 INSTALL_DIR="${GSTACK_INSTALL_DIR:-$HOME/.claude/skills/gstack}"
-. "${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${BASH_SOURCE[0]%/*}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
+_gstack_migration_dir="${BASH_SOURCE[0]//\\//}"; _gstack_migration_dir="${_gstack_migration_dir%/*}"
+. "${_gstack_migration_dir}/../../bin/gstack-state-root.sh" 2>/dev/null || { echo "$0: cannot resolve the gstack state root: ${_gstack_migration_dir}/../../bin/gstack-state-root.sh is missing. fix: reinstall with ./setup or /gstack-upgrade (docs/state-root.md)" >&2; exit 1; }
 gstack_state_root_select; GH="$_gstack_sr_root"
 
 mkdir -p "$GH" 2>/dev/null || exit 0
diff --git a/test/state-root-parity.test.ts b/test/state-root-parity.test.ts
index 295411129..c53902c1e 100644
--- a/test/state-root-parity.test.ts
+++ b/test/state-root-parity.test.ts
@@ -17,19 +17,28 @@ const BASH = Bun.which('bash') ?? '/bin/bash';
 
 type Row = { name: string; env: Record<string, string>; win?: boolean };
 
-function bashEval(row: Row, body: string): string {
+// On a Windows host the MSYS runtime fills HOME before Git Bash starts, so a
+// row that leaves HOME unset or empty reaches the bash twin with the runtime's
+// HOME. Those rows compare both twins under the HOME the child actually saw;
+// the unset-HOME branches themselves are covered on POSIX hosts.
+const HOST_FILLS_HOME = process.platform === 'win32';
+
+function bashEval(row: Row, body: string): { out: string; home: string } {
   const ostype = row.win ? 'msys' : 'linux-gnu';
-  const r = spawnSync(BASH, ['-c', `OSTYPE=${ostype}; . "${TWIN}" && ${body}`], {
+  const r = spawnSync(BASH, ['-c', `OSTYPE=${ostype}; printf '%s\\0' "\${HOME-}"; . "${TWIN}" && ${body}`], {
     env: { USERPROFILE: '', ...row.env, PATH: '' },
     encoding: 'utf-8',
     timeout: 10_000,
   });
   if (r.status !== 0) throw new Error(`bash twin failed for ${row.name}: ${r.stderr}`);
-  return r.stdout;
+  const split = r.stdout.indexOf('\0');
+  return { home: r.stdout.slice(0, split), out: r.stdout.slice(split + 1) };
 }
 
-function tsEnv(row: Row): Record<string, string> {
-  return { USERPROFILE: '', ...row.env };
+function tsEnv(row: Row, childHome: string): Record<string, string> {
+  const env: Record<string, string> = { USERPROFILE: '', ...row.env };
+  if (HOST_FILLS_HOME && !row.env.HOME) env.HOME = childHome;
+  return env;
 }
 
 const A = '/state/a', B = '/state/b', C = '/state/c';
@@ -63,8 +72,8 @@ const rootRows: Row[] = [
 describe('state root parity (bash twin vs lib/state-root.ts)', () => {
   for (const row of rootRows) {
     test(row.name, () => {
-      const bash = bashEval(row, 'gstack_state_root; printf x').replace(/x$/, '');
-      expect(bash).toBe(resolveStateRoot(tsEnv(row), row.win ? 'win32' : 'linux'));
+      const bash = bashEval(row, 'gstack_state_root; printf x');
+      expect(bash.out.replace(/x$/, '')).toBe(resolveStateRoot(tsEnv(row, bash.home), row.win ? 'win32' : 'linux'));
     });
   }
 
@@ -126,9 +135,9 @@ describe('config key parity (gstack_read_config_key vs readConfigKey)', () => {
     ];
     for (const row of envs) {
       for (const key of keys) {
-        const bash = bashEval(row, `gstack_read_config_key ${key}; printf x`).replace(/x$/, '');
-        const ts = readConfigKey(key, tsEnv(row), row.win ? 'win32' : 'linux') ?? '';
-        expect(`${row.name}/${key}=${bash}`).toBe(`${row.name}/${key}=${ts}`);
+        const bash = bashEval(row, `gstack_read_config_key ${key}; printf x`);
+        const ts = readConfigKey(key, tsEnv(row, bash.home), row.win ? 'win32' : 'linux') ?? '';
+        expect(`${row.name}/${key}=${bash.out.replace(/x$/, '')}`).toBe(`${row.name}/${key}=${ts}`);
       }
     }
   });