fix(fleet): tell the operator when the fleet transport is missing (#1240)

`mosaic fleet --help` reads "Manage the local Mosaic tmux fleet" and every
roster the CLI scaffolds sets `transport: tmux`, but neither `tools/install.sh`
nor `tools/_scripts/mosaic-doctor` contained the string "tmux" at all. A
greenfield host therefore came out of the installer able to install a fleet,
start a fleet, and run no seat, with `mosaic fleet ps` as the operator's first
and only signal.

Measured on mosaic-sbx-dev (Debian, no tmux, framework installed): `mosaic-doctor`
reported 11 warnings and not one of them named the reason no seat could launch.

The installer gets a warning, not a `require_cmd` hard failure: tmux is required
by the fleet, not by mosaic. Hosts that install this to run `mosaic claude` and
never scaffold a roster are common, and failing their install over a binary they
do not need would be wrong. The check runs in `--check` mode too — "what is the
state of this host" is the question `--check` is asked.

Both checks read the roster's own `transport:` rather than assuming tmux, so a
host declaring something else is pointed at the binary it actually needs instead
of at the wrong package.

The two implementations are deliberately parallel and each carries a comment
pointing at the other. They are separate because the installer must answer this
before the framework's own scripts are guaranteed to be on disk. One harness
drives BOTH from the shipped text — the functions are extracted from the scripts
by awk rather than copied — so the pair cannot drift silently, and the test
cannot keep passing after the shipped copy changes.

The harness is wired into `test:framework-shell`. Without that it would have
tripped the #1017 enumeration guard as UNENUMERATED, which is the guard doing
its job: a check nothing runs is not a check.

Evidence:
- red: the harness fails against origin/next ("could not extract
  fleet_declared_transport"); `grep -ci tmux` on both files at origin/next = 0.
- green on real hosts, all four branches:
  - dev (no tmux, no roster)  -> WARN naming tmux, points at `mosaic fleet init`
  - dev (no tmux, v2 roster)  -> WARN naming the roster, points at `mosaic fleet start`
  - dev installer --check     -> WARN saying start "reports success and no seat comes up"
  - canary (tmux present)     -> `[OK] Fleet transport available: tmux` under --verbose,
                                 silent by default (pass() is verbose-gated), installer silent
- harness green on node:24-alpine/busybox, the CI base image.
- `bash -n` x3, `pnpm typecheck` 45/45, fleet specs 342 passed,
  enumeration guard OK, its self-test OK, prettier clean.

Refs #1240. Upstream of #1237/#1243 and #1241/#1244: a correct fix for either of
those still leaves this host with no live seat.

packages/mosaic/framework/tools/_scripts/mosaic-doctor

@@ -225,6 +225,54 @@ else
   warn "mosaic-ensure-sequential-thinking helper missing"
 fi
 
+# Fleet transport binary (#1240).
+#
+# `mosaic fleet --help` reads "Manage the local Mosaic tmux fleet" and every
+# roster the CLI scaffolds sets `transport: tmux`, but nothing in the install
+# path provides tmux and, until now, nothing here noticed it was absent. On a
+# greenfield host that produced a fleet which installed clean, started clean,
+# and had no live seat; `mosaic fleet ps` was the operator's first and only
+# signal that anything was wrong.
+#
+# The roster's own `transport:` is read rather than assumed, so a host that
+# declares something other than tmux is told about the binary it actually
+# needs. Absent a roster the check still runs — `mosaic fleet init` will
+# scaffold a tmux fleet on this host, and finding out beforehand is the point.
+#
+# `tools/install.sh` carries a deliberately parallel check at the end of its
+# summary. The two are separate because the installer must be able to say this
+# before the framework's own scripts are guaranteed to be on disk; keep their
+# wording in step.
+fleet_declared_transport() {
+  local roster="$MOSAIC_HOME/fleet/roster.yaml"
+  local declared=""
+
+  if [[ -f "$roster" ]]; then
+    declared="$(sed -n 's/^[[:space:]]*transport:[[:space:]]*//p' "$roster" | head -1 |
+      tr -d '"'\''' | tr -d '\r' | awk '{print $1}')"
+  fi
+
+  printf '%s\n' "${declared:-tmux}"
+}
+
+check_fleet_transport() {
+  local transport
+  transport="$(fleet_declared_transport)"
+
+  if command -v "$transport" >/dev/null 2>&1; then
+    pass "Fleet transport available: $transport"
+    return
+  fi
+
+  if [[ -f "$MOSAIC_HOME/fleet/roster.yaml" ]]; then
+    warn "Fleet transport '$transport' is not installed — this host has a roster and no seat can launch. Install it (e.g. sudo apt-get install -y $transport), then 'mosaic fleet start'."
+  else
+    warn "Fleet transport '$transport' is not installed — 'mosaic fleet' cannot run seats here. Install it (e.g. sudo apt-get install -y $transport) before 'mosaic fleet init'."
+  fi
+}
+
+check_fleet_transport
+
 # Legacy migration surfaces should no longer contain symlink trees.
 legacy_paths=(
   "$HOME/.claude/agent-guides"

packages/mosaic/framework/tools/_scripts/test-fleet-transport-check.sh

@@ -0,0 +1,215 @@
+#!/usr/bin/env bash
+# Covers the #1240 fleet-transport checks in `mosaic-doctor` and in
+# `tools/install.sh`.
+#
+# Both checks answer the same question — "can a seat actually launch on this
+# host?" — from two different places, because the installer has to be able to
+# answer it before the framework's own scripts are guaranteed to be on disk.
+# Two implementations of one rule is exactly the shape that drifts, so this
+# harness drives BOTH, in one file, from the same table of cases.
+#
+# The functions are extracted from the shipped scripts rather than copied here.
+# A test that carries its own copy of the logic is a test that keeps passing
+# after the shipped copy changes — the failure mode this whole change is about.
+# Extraction is by exact function header and a closing brace in column one; if
+# either script is reshaped so that stops matching, the extraction yields
+# nothing and this fails loudly instead of silently measuring an empty string.
+set -euo pipefail
+
+SCRIPT_DIR=$(cd -- "$(dirname -- "$0")" && pwd)
+DOCTOR="$SCRIPT_DIR/mosaic-doctor"
+# framework/tools/_scripts -> framework/tools -> framework -> mosaic -> packages -> repo
+INSTALLER=$(cd -- "$SCRIPT_DIR/../../../../.." && pwd)/tools/install.sh
+
+fail() {
+  echo "FAIL: $*" >&2
+  exit 1
+}
+
+[ -f "$DOCTOR" ] || fail "missing mosaic-doctor at $DOCTOR"
+[ -f "$INSTALLER" ] || fail "missing install.sh at $INSTALLER"
+
+ROOT=$(mktemp -d)
+trap 'rm -rf "$ROOT"' EXIT
+
+# The cases below run with PATH set to a directory that deliberately does not
+# contain a shell, and a PATH assignment on a command also governs how that
+# command is looked up — so bash has to be named absolutely or it becomes the
+# thing that is missing.
+BASH_BIN=$(command -v bash) || fail "host is missing 'bash'"
+
+# A PATH containing exactly the utilities these functions use and nothing else.
+# The absent-transport cases are only meaningful on a PATH where the transport
+# is genuinely unresolvable, and this host (like most) has tmux in /usr/bin —
+# so the system path cannot be part of the path under test.
+FAKE_BIN="$ROOT/bin"
+mkdir -p "$FAKE_BIN"
+for utility in sed head tr awk; do
+  utility_path=$(command -v "$utility") || fail "host is missing '$utility'"
+  ln -s "$utility_path" "$FAKE_BIN/$utility"
+done
+
+if PATH="$FAKE_BIN" command -v tmux >/dev/null 2>&1; then
+  fail "'tmux' is resolvable on the minimal test path; absent-transport cases are not measurable"
+fi
+
+# Extract a function by its exact header, up to a closing brace in column one.
+extract_function() {
+  local source_file="$1"
+  local function_name="$2"
+  local destination="$3"
+
+  awk -v name="$function_name" '
+    $0 == name "() {" { collecting = 1 }
+    collecting { print }
+    collecting && $0 == "}" { exit }
+  ' "$source_file" > "$destination"
+
+  grep -qF "$function_name() {" "$destination" ||
+    fail "could not extract '$function_name' from $source_file — has it been renamed or reshaped?"
+  # An unterminated extraction would be a syntax error the moment it is sourced,
+  # but saying so here names the cause instead of leaving a bash parse error.
+  bash -n "$destination" ||
+    fail "extracted '$function_name' does not parse; the closing brace was probably not found"
+}
+
+extract_function "$DOCTOR" fleet_declared_transport "$ROOT/doctor-declared.sh"
+extract_function "$DOCTOR" check_fleet_transport "$ROOT/doctor-check.sh"
+extract_function "$INSTALLER" check_fleet_transport "$ROOT/installer-check.sh"
+
+# Build a MOSAIC_HOME, optionally with a roster declaring a transport.
+make_home() {
+  local home="$ROOT/$1"
+  local declared="${2-}"
+
+  rm -rf "$home"
+  mkdir -p "$home"
+  if [ -n "$declared" ]; then
+    mkdir -p "$home/fleet"
+    cat > "$home/fleet/roster.yaml" <<EOF
+version: 2
+generation: 1
+transport: $declared
+agents: []
+EOF
+  fi
+  printf '%s\n' "$home"
+}
+
+# Run the doctor's check against a given home and path, capturing which
+# reporter the check chose. The real `pass` prints only under `--verbose` and
+# the real `warn` always prints; these stubs make both unconditional on
+# purpose, because what is under test is the severity the check selects, not
+# whether the default verbosity happens to show it. A check that warned where
+# it should pass would otherwise be invisible here.
+run_doctor_check() {
+  local home="$1"
+  local path="$2"
+
+  MOSAIC_HOME="$home" PATH="$path" "$BASH_BIN" --noprofile --norc -c '
+    set -euo pipefail
+    warn() { echo "[WARN] $*"; }
+    pass() { echo "[OK] $*"; }
+    MOSAIC_HOME="$1"
+    source "$2"
+    source "$3"
+    check_fleet_transport
+  ' _ "$home" "$ROOT/doctor-declared.sh" "$ROOT/doctor-check.sh" 2>&1
+}
+
+run_installer_check() {
+  local home="$1"
+  local path="$2"
+
+  MOSAIC_HOME="$home" PATH="$path" "$BASH_BIN" --noprofile --norc -c '
+    set -euo pipefail
+    warn() { echo "[WARN] $*"; }
+    C="" RESET=""
+    MOSAIC_HOME="$1"
+    source "$2"
+    check_fleet_transport
+  ' _ "$home" "$ROOT/installer-check.sh" 2>&1
+}
+
+# A transport that exists. Named tmux because that is what the default roster
+# declares; the binary never runs, it only has to resolve.
+PRESENT_BIN="$ROOT/present-bin"
+mkdir -p "$PRESENT_BIN"
+printf '#!/usr/bin/env bash\nexit 0\n' > "$PRESENT_BIN/tmux"
+chmod +x "$PRESENT_BIN/tmux"
+PATH_WITH_TMUX="$PRESENT_BIN:$FAKE_BIN"
+
+# ── absent, no roster ────────────────────────────────────────────────────────
+# Nothing has been configured yet, so the honest thing to point at is `init`.
+home=$(make_home no-roster)
+
+output=$(run_doctor_check "$home" "$FAKE_BIN")
+echo "$output" | grep -qF '[WARN]' || fail "doctor did not warn when tmux was absent"
+echo "$output" | grep -qF 'tmux' || fail "doctor warning did not name the transport"
+echo "$output" | grep -qF 'mosaic fleet init' || fail "doctor did not point a rosterless host at init"
+
+output=$(run_installer_check "$home" "$FAKE_BIN")
+echo "$output" | grep -qF '[WARN]' || fail "installer did not warn when tmux was absent"
+echo "$output" | grep -qF 'reports success and no seat comes up' ||
+  fail "installer warning did not say what the missing transport actually breaks"
+
+# ── absent, roster present ───────────────────────────────────────────────────
+# A configured fleet that cannot launch is a stronger statement than a
+# hypothetical one, and the message says so.
+home=$(make_home with-roster tmux)
+
+output=$(run_doctor_check "$home" "$FAKE_BIN")
+echo "$output" | grep -qF '[WARN]' || fail "doctor did not warn with a roster present and tmux absent"
+echo "$output" | grep -qF 'roster' || fail "doctor did not mention the roster it found"
+echo "$output" | grep -qF 'mosaic fleet start' || fail "doctor did not point a configured host at start"
+
+# ── present ──────────────────────────────────────────────────────────────────
+# Silence from the installer, and a pass (not a warning) from the audit.
+for home_name in no-roster with-roster; do
+  home="$ROOT/$home_name"
+
+  output=$(run_doctor_check "$home" "$PATH_WITH_TMUX")
+  if echo "$output" | grep -qF '[WARN]'; then
+    fail "doctor warned about the transport while tmux was present ($home_name)"
+  fi
+  echo "$output" | grep -qF '[OK]' || fail "doctor did not record a pass with tmux present ($home_name)"
+
+  output=$(run_installer_check "$home" "$PATH_WITH_TMUX")
+  if [ -n "$output" ]; then
+    fail "installer was not silent with tmux present ($home_name): $output"
+  fi
+done
+
+# ── the roster declares something other than tmux ────────────────────────────
+# The roster is read, not assumed. A host that declares a different transport
+# is told about the binary it actually needs, and never about tmux — being sent
+# to install the wrong package is worse than no advice at all.
+home=$(make_home other-transport zellij)
+
+output=$(run_doctor_check "$home" "$PATH_WITH_TMUX")
+echo "$output" | grep -qF 'zellij' || fail "doctor ignored the roster's declared transport"
+if echo "$output" | grep -qF 'tmux'; then
+  fail "doctor named tmux for a host whose roster declares zellij"
+fi
+
+output=$(run_installer_check "$home" "$PATH_WITH_TMUX")
+echo "$output" | grep -qF 'zellij' || fail "installer ignored the roster's declared transport"
+if echo "$output" | grep -qF 'tmux'; then
+  fail "installer named tmux for a host whose roster declares zellij"
+fi
+
+# ── a quoted or trailing-comment transport value ─────────────────────────────
+# YAML permits both and neither is exotic; a check that installs `tmux"` or
+# reads `tmux # default` as a binary name would send the operator nowhere.
+home=$(make_home quoted-transport '"tmux"   # the only transport today')
+
+output=$(run_doctor_check "$home" "$PATH_WITH_TMUX")
+echo "$output" | grep -qF '[OK] Fleet transport available: tmux' ||
+  fail "doctor did not parse a quoted/commented transport value: $output"
+
+output=$(run_installer_check "$home" "$PATH_WITH_TMUX")
+if [ -n "$output" ]; then
+  fail "installer did not parse a quoted/commented transport value: $output"
+fi
+
+echo "ok - fleet transport checks (mosaic-doctor + install.sh)"

packages/mosaic/package.json

@@ -25,7 +25,7 @@
     "lint": "eslint src",
     "typecheck": "tsc --noEmit",
     "test": "vitest run --passWithNoTests && pnpm run test:framework-shell",
-    "test:framework-shell": "bash framework/tools/quality/scripts/check-test-enumeration.sh && bash framework/tools/quality/scripts/test-check-test-enumeration.sh && python3 src/lease-broker/daemon_deadline_unittest.py && python3 src/lease-broker/normative_fragments_unittest.py && python3 src/lease-broker/promotion_binding_unittest.py && python3 src/lease-broker/promotion_trigger_unittest.py && python3 src/lease-broker/receipt_challenge_unittest.py && python3 src/lease-broker/context_recovery_unittest.py && python3 src/lease-broker/recovery_runtime_unittest.py && python3 src/lease-broker/recovery_b1_adversarial_unittest.py && python3 src/lease-broker/receipt_observer_client_unittest.py && python3 src/lease-broker/invariant_r_unittest.py && python3 src/lease-broker/framework_skill_portability_unittest.py && python3 src/mutator-gate/runtime_tools_unittest.py && python3 src/mutator-gate/runtime_launch_guard_unittest.py && python3 src/mutator-gate/version_coupling_unittest.py && python3 framework/tools/lease-broker/check-runtime-launches.py --root ../.. && bash framework/tools/codex/test-pr-diff-context.sh && bash framework/tools/qa/test-deps-preflight.sh && bash framework/tools/git/test-pr-review-gitea-comment.sh && bash framework/tools/git/test-pr-review-repo-host-override.sh && bash framework/tools/git/test-ci-queue-wait-branch-absent.sh && bash framework/tools/git/test-ci-queue-wait-tristate.sh && bash framework/tools/git/test-ci-queue-wait-github-checks.sh && bash framework/tools/git/test-pr-merge-queue-branch.sh && bash framework/tools/git/test-pr-merge-head-pin.sh && bash framework/tools/git/test-pr-merge-message-field.sh && bash framework/tools/git/test-git-credential-mosaic.sh && bash framework/tools/git/test-gitea-token-identity.sh && bash framework/tools/woodpecker/test-terminal-green-contract.sh && bash framework/tools/_scripts/test-install-ordering-guard.sh && bash framework/tools/_scripts/test-mosaic-init-rce.sh && bash framework/tools/tmux/agent-send.test.sh && bash framework/tools/wake/test-wake-store-ack.sh && bash framework/tools/wake/test-wake-store-enqueue-race.sh && bash framework/tools/wake/test-wake-digest-hmac.sh && bash framework/tools/wake/test-wake-digest-quarantine.sh && bash framework/tools/wake/test-wake-detector.sh && bash framework/tools/wake/test-wake-fn-oracle.sh && bash framework/tools/wake/test-wake-reconcile.sh && bash framework/tools/wake/test-wake-beacon.sh && bash framework/tools/wake/test-wake-preimage.sh && bash framework/tools/wake/test-wake-install.sh"
+    "test:framework-shell": "bash framework/tools/quality/scripts/check-test-enumeration.sh && bash framework/tools/quality/scripts/test-check-test-enumeration.sh && python3 src/lease-broker/daemon_deadline_unittest.py && python3 src/lease-broker/normative_fragments_unittest.py && python3 src/lease-broker/promotion_binding_unittest.py && python3 src/lease-broker/promotion_trigger_unittest.py && python3 src/lease-broker/receipt_challenge_unittest.py && python3 src/lease-broker/context_recovery_unittest.py && python3 src/lease-broker/recovery_runtime_unittest.py && python3 src/lease-broker/recovery_b1_adversarial_unittest.py && python3 src/lease-broker/receipt_observer_client_unittest.py && python3 src/lease-broker/invariant_r_unittest.py && python3 src/lease-broker/framework_skill_portability_unittest.py && python3 src/mutator-gate/runtime_tools_unittest.py && python3 src/mutator-gate/runtime_launch_guard_unittest.py && python3 src/mutator-gate/version_coupling_unittest.py && python3 framework/tools/lease-broker/check-runtime-launches.py --root ../.. && bash framework/tools/codex/test-pr-diff-context.sh && bash framework/tools/qa/test-deps-preflight.sh && bash framework/tools/git/test-pr-review-gitea-comment.sh && bash framework/tools/git/test-pr-review-repo-host-override.sh && bash framework/tools/git/test-ci-queue-wait-branch-absent.sh && bash framework/tools/git/test-ci-queue-wait-tristate.sh && bash framework/tools/git/test-ci-queue-wait-github-checks.sh && bash framework/tools/git/test-pr-merge-queue-branch.sh && bash framework/tools/git/test-pr-merge-head-pin.sh && bash framework/tools/git/test-pr-merge-message-field.sh && bash framework/tools/git/test-git-credential-mosaic.sh && bash framework/tools/git/test-gitea-token-identity.sh && bash framework/tools/woodpecker/test-terminal-green-contract.sh && bash framework/tools/_scripts/test-install-ordering-guard.sh && bash framework/tools/_scripts/test-mosaic-init-rce.sh && bash framework/tools/_scripts/test-fleet-transport-check.sh && bash framework/tools/tmux/agent-send.test.sh && bash framework/tools/wake/test-wake-store-ack.sh && bash framework/tools/wake/test-wake-store-enqueue-race.sh && bash framework/tools/wake/test-wake-digest-hmac.sh && bash framework/tools/wake/test-wake-digest-quarantine.sh && bash framework/tools/wake/test-wake-detector.sh && bash framework/tools/wake/test-wake-fn-oracle.sh && bash framework/tools/wake/test-wake-reconcile.sh && bash framework/tools/wake/test-wake-beacon.sh && bash framework/tools/wake/test-wake-preimage.sh && bash framework/tools/wake/test-wake-install.sh"
   },
   "dependencies": {
     "@mosaicstack/brain": "workspace:*",

tools/install.sh

@@ -309,6 +309,43 @@ require_cmd() {
   fi
 }
 
+# Fleet transport binary (#1240).
+#
+# `mosaic fleet --help` reads "Manage the local Mosaic tmux fleet" and every
+# roster the CLI scaffolds sets `transport: tmux`, but nothing in this script
+# provides tmux and, until now, nothing in it mentioned tmux at all. A
+# greenfield host came out of this installer able to install a fleet, start a
+# fleet, and run no seat — the operator's first signal was `mosaic fleet ps`.
+#
+# Not a `require_cmd`: tmux is required by the fleet, not by mosaic. Plenty of
+# hosts install this to run `mosaic claude` and will never scaffold a roster,
+# and failing their install over a binary they do not need would be wrong. It
+# is a warning that names precisely what it blocks.
+#
+# `tools/_scripts/mosaic-doctor` carries a deliberately parallel check, so the
+# same host state gets the same answer from an audit as from an install. They
+# are separate implementations because this one has to work before the
+# framework's scripts are guaranteed to be on disk; keep their wording in step.
+check_fleet_transport() {
+  local transport=tmux
+  local roster="$MOSAIC_HOME/fleet/roster.yaml"
+  local declared=""
+
+  if [[ -f "$roster" ]]; then
+    declared="$(sed -n 's/^[[:space:]]*transport:[[:space:]]*//p' "$roster" | head -1 |
+      tr -d '"'\''' | tr -d '\r' | awk '{print $1}')"
+    [[ -n "$declared" ]] && transport="$declared"
+  fi
+
+  command -v "$transport" &>/dev/null && return 0
+
+  warn "Fleet transport '$transport' is not installed."
+  echo "  The Mosaic fleet runs its agent seats inside $transport. Without it,"
+  echo "  ${C}mosaic fleet start${RESET} reports success and no seat comes up."
+  echo "  Install it before using the fleet, e.g. ${C}sudo apt-get install -y $transport${RESET}"
+  echo "  (this does not affect ${C}mosaic claude${RESET} or the other single-runtime commands)."
+}
+
 installed_cli_version() {
   local json
   json="$(npm ls -g --depth=0 --json --prefix="$PREFIX" 2>/dev/null)" || true
@@ -870,6 +907,11 @@ if [[ "$FLAG_CHECK" == "false" ]]; then
   ok "Done."
 fi
 
+# Fleet readiness (#1240). Runs in both normal and --check mode: "what is the
+# state of this host" is exactly the question --check is asked, and a host that
+# cannot run a seat should not have to discover it from `fleet ps`.
+check_fleet_transport
+
 } # end main
 
 main "$@"