diff --git a/bin/fm-spawn.sh b/bin/fm-spawn.sh
index fe659b54b6c..95c446bca50 100755
--- a/bin/fm-spawn.sh
+++ b/bin/fm-spawn.sh
@@ -1490,6 +1490,16 @@ LAUNCH=${LAUNCH//__PIEXT__/$sq_piext}
 LAUNCH=${LAUNCH//__PITURNEND__/$sq_piturnend}
 LAUNCH=${LAUNCH//__PIWATCH__/$sq_piwatch}
 LAUNCH=${LAUNCH//__OPINPUT__/$sq_opinput}
+# Crewmate panes are created by a long-lived tmux/herdr daemon that does not
+# inherit firstmate's current environment, so a bare `claude` in the pane falls
+# back to the default ~/.claude store even when firstmate itself runs under a
+# different CLAUDE_CONFIG_DIR (for example a work-vs-personal subscription split).
+# Forward firstmate's own resolved store onto the claude launch so the crewmate
+# uses the same credential/config firstmate is authenticated with. Only when set;
+# an unset value is the single-store default and needs no prefix.
+if [ "$HARNESS" = claude ] && [ -n "${CLAUDE_CONFIG_DIR:-}" ]; then
+  LAUNCH="CLAUDE_CONFIG_DIR=$(shell_quote "$CLAUDE_CONFIG_DIR") $LAUNCH"
+fi
 if [ "$KIND" = secondmate ]; then
   sq_home=$(shell_quote "$PROJ_ABS")
   LAUNCH="FM_ROOT_OVERRIDE= FM_STATE_OVERRIDE= FM_DATA_OVERRIDE= FM_PROJECTS_OVERRIDE= FM_CONFIG_OVERRIDE= FM_HOME=$sq_home $LAUNCH"
diff --git a/tests/fm-spawn-dispatch-profile.test.sh b/tests/fm-spawn-dispatch-profile.test.sh
index 3a8dfb3a4e7..4f0695e7e5e 100755
--- a/tests/fm-spawn-dispatch-profile.test.sh
+++ b/tests/fm-spawn-dispatch-profile.test.sh
@@ -84,10 +84,15 @@ run_spawn() {
   local home=$1 wt=$2 fakebin=$3 launchlog=$4
   shift 4
   : > "$launchlog"
+  # CLAUDE_CONFIG_DIR is forwarded onto claude launches by fm-spawn, so pin it
+  # explicitly (empty by default) instead of leaking the invoking shell's value,
+  # which would make launch assertions depend on the developer's environment.
+  # A test opts in to the set case via FM_TEST_CLAUDE_CONFIG_DIR.
   FM_ROOT_OVERRIDE='' FM_HOME="$home" \
     FM_STATE_OVERRIDE="$home/state" FM_DATA_OVERRIDE="$home/data" \
     FM_PROJECTS_OVERRIDE="$home/projects" FM_CONFIG_OVERRIDE="$home/config" \
     FM_SPAWN_NO_GUARD=1 FM_FAKE_PANE_PATH="$wt" TMUX="fake,1,0" \
+    CLAUDE_CONFIG_DIR="${FM_TEST_CLAUDE_CONFIG_DIR:-}" \
     FM_FAKE_LAUNCH_LOG="$launchlog" GROK_HOME="$home/grok-home" PATH="$fakebin:$PATH" \
     "$SPAWN" "$@" 2>&1
 }
@@ -436,6 +441,55 @@ test_batch_forwards_shared_profile_flags() {
   pass "batch dispatch forwards shared --harness, --model, and --effort to every pair"
 }
 
+test_claude_forwards_firstmate_config_dir_when_set() {
+  local rec id out status launch
+  id=profile-claude-cfgdir-z17
+  rec=$(make_spawn_case profile-claude-cfgdir claude "$id")
+  read_case_record "$rec"
+
+  out=$(FM_TEST_CLAUDE_CONFIG_DIR="/opt/test/claude-work" \
+    run_spawn "$HOME_DIR" "$WT_DIR" "$FAKEBIN_DIR" "$LAUNCH_LOG" "$id" "$PROJ_DIR")
+  status=$?
+  expect_code 0 "$status" "claude spawn with CLAUDE_CONFIG_DIR set should succeed"
+  launch=$(cat "$LAUNCH_LOG")
+  assert_contains "$launch" "CLAUDE_CONFIG_DIR='/opt/test/claude-work' CLAUDE_CODE_ENABLE_PROMPT_SUGGESTION=false claude" \
+    "claude launch did not forward firstmate's CLAUDE_CONFIG_DIR to the crewmate pane"
+  pass "claude forwards firstmate's CLAUDE_CONFIG_DIR so the crewmate uses the same credential store"
+}
+
+test_claude_omits_config_dir_prefix_when_unset() {
+  local rec id out status launch
+  id=profile-claude-nocfgdir-z18
+  rec=$(make_spawn_case profile-claude-nocfgdir claude "$id")
+  read_case_record "$rec"
+
+  # run_spawn pins CLAUDE_CONFIG_DIR empty by default, exercising the single-store
+  # default path where fm-spawn adds no prefix.
+  out=$(run_spawn "$HOME_DIR" "$WT_DIR" "$FAKEBIN_DIR" "$LAUNCH_LOG" "$id" "$PROJ_DIR")
+  status=$?
+  expect_code 0 "$status" "claude spawn without CLAUDE_CONFIG_DIR should succeed"
+  launch=$(cat "$LAUNCH_LOG")
+  assert_not_contains "$launch" "CLAUDE_CONFIG_DIR=" \
+    "claude launch must not add a config-dir prefix when firstmate has no CLAUDE_CONFIG_DIR set"
+  pass "claude omits the config-dir prefix when firstmate runs with the single-store default"
+}
+
+test_non_claude_harness_ignores_config_dir() {
+  local rec id out status launch
+  id=profile-codex-nocfgdir-z19
+  rec=$(make_spawn_case profile-codex-nocfgdir codex "$id")
+  read_case_record "$rec"
+
+  out=$(FM_TEST_CLAUDE_CONFIG_DIR="/opt/test/claude-work" \
+    run_spawn "$HOME_DIR" "$WT_DIR" "$FAKEBIN_DIR" "$LAUNCH_LOG" "$id" "$PROJ_DIR")
+  status=$?
+  expect_code 0 "$status" "codex spawn with CLAUDE_CONFIG_DIR set should succeed"
+  launch=$(cat "$LAUNCH_LOG")
+  assert_not_contains "$launch" "CLAUDE_CONFIG_DIR=" \
+    "non-claude harness launch must not receive the claude-specific config-dir prefix"
+  pass "non-claude harnesses do not receive the claude CLAUDE_CONFIG_DIR prefix"
+}
+
 test_active_dispatch_profile_does_not_block_secondmate_launch() {
   local rec id sm out status
   id=profile-secondmate-z16
@@ -472,6 +526,9 @@ test_pi_signed_threads_shared_pi_profile_and_preserves_identity
 test_pi_signed_missing_binary_refuses_before_endpoint_or_metadata
 test_pi_signed_persistent_secondmate_uses_pi_extensions_and_identity
 test_batch_forwards_shared_profile_flags
+test_claude_forwards_firstmate_config_dir_when_set
+test_claude_omits_config_dir_prefix_when_unset
+test_non_claude_harness_ignores_config_dir
 test_active_dispatch_profile_does_not_block_secondmate_launch
 
 echo "# all fm-spawn-dispatch-profile tests passed"