feat(spawn): add --model to launch spawned agents on a chosen model

scripts/drivers/types/claude-code/type.conf

@@ -3,6 +3,7 @@ name=claude-code
 template=template.md
 cli=claude
 spawnable=yes
+model_arg=--model
 detect=CLAUDE_CODE_SESSION_ID
 detect_proc=claude claude-code claude-*
 hooks_file=.claude/settings.local.json

scripts/drivers/types/codex/type.conf

@@ -3,6 +3,7 @@ name=codex
 template=template.md
 cli=codex
 spawnable=yes
+model_arg=-m
 detect=CODEX_SANDBOX CODEX_THREAD_ID
 detect_proc=codex codex-*
 hooks_file=.codex/hooks.json

scripts/drivers/types/grok-build/type.conf

@@ -3,6 +3,7 @@ name=grok-build
 template=template.md
 cli=grok
 spawnable=yes
+model_arg=--model
 detect=GROK_SESSION_ID
 detect_proc=grok grok-*
 hooks_file=.grok/rules/agmsg.md

scripts/spawn.sh

@@ -37,6 +37,10 @@ set -euo pipefail
 #                      as the agent is launched (fire-and-forget)
 #   --ready-timeout N  seconds to wait for readiness before giving up
 #                      (default 90; on timeout, prints status=timeout, exit 3)
+#   --model <id>       launch the agent on a specific model. The id is passed
+#                      through to the CLI unchecked (the CLI rejects unknown
+#                      ids); the flag spelling comes from the type's manifest
+#                      `model_arg=`. Refused for a type with no model_arg.
 #
 # Readiness: by default spawn blocks until the new agent's watcher attaches and
 # is receiving (it prints `status=ready ...`), so a leader can safely send work
@@ -104,6 +108,7 @@ SPLIT="h"            # h | v
 TERMINAL_TMPL=""     # --terminal override (resolved below if empty)
 WAIT_READY=1         # block until the spawned agent's watcher attaches
 READY_TIMEOUT=90     # seconds to wait for readiness before giving up
+MODEL_ID=""          # --model: pass-through model id for the launched CLI
 
 while [ $# -gt 0 ]; do
   case "$1" in
@@ -114,6 +119,7 @@ while [ $# -gt 0 ]; do
     --terminal) TERMINAL_TMPL="${2:?--terminal needs a template}"; shift 2 ;;
     --no-wait) WAIT_READY=0; shift ;;
     --ready-timeout) READY_TIMEOUT="${2:?--ready-timeout needs seconds}"; shift 2 ;;
+    --model) MODEL_ID="${2:?--model needs a model id}"; shift 2 ;;
     *) die "unknown option: $1" ;;
   esac
 done
@@ -158,6 +164,16 @@ if [ -n "$CLI_BIN" ]; then
 elif [ -z "$SPAWN_LAUNCHER" ]; then
   die "agent type '$AGENT_TYPE' manifest declares neither a 'cli' binary nor a 'spawn' launcher"
 fi
+
+# --model is pass-through: the model id is handed to the CLI unchecked (the CLI
+# rejects an unknown id), so agmsg never has to track each vendor's model list.
+# The flag SPELLING differs per CLI, so it comes from the manifest `model_arg=`
+# (e.g. claude-code/grok-build use --model, codex uses -m). A type with no
+# model_arg has no known flag, so --model is refused rather than guessed.
+MODEL_ARG="$(agmsg_type_get "$AGENT_TYPE" model_arg)"
+if [ -n "$MODEL_ID" ] && [ -z "$MODEL_ARG" ]; then
+  die "agent type '$AGENT_TYPE' does not support --model (no model_arg in its manifest)"
+fi
 # Resolve the node launcher path from the manifest (not hardcoded), if any.
 SPAWN_AGENT=""
 if [ -n "$SPAWN_LAUNCHER" ]; then
@@ -278,7 +294,12 @@ BOOT="$BOOT.command"
     printf '  --project %q \\\n' "$PROJECT"
     printf '  --initial-input %q\n' "$ACTAS_PROMPT"
   else
-    printf '%q %q\n' "$CLI_BIN" "$ACTAS_PROMPT"
+    # Direct-CLI launch: `<cli> [<model_arg> <model_id>] "/<cmd> actas <name>"`.
+    # model_arg is the manifest flag spelling (not %q-quoted — a bare flag like
+    # --model or -m); the model id is quoted.
+    printf '%q' "$CLI_BIN"
+    [ -n "$MODEL_ID" ] && printf ' %s %q' "$MODEL_ARG" "$MODEL_ID"
+    printf ' %q\n' "$ACTAS_PROMPT"
   fi
   echo 'rm -f "$0" 2>/dev/null'   # self-clean once the agent exits
   echo 'exec "${SHELL:-/bin/bash}" -i'

tests/test_spawn.bats

@@ -10,7 +10,7 @@ setup() {
   # a terminal. PATH is prepended so the stubs win.
   export STUB_BIN="$TEST_SKILL_DIR/stub-bin"
   mkdir -p "$STUB_BIN"
-  for bin in claude codex grok; do
+  for bin in claude codex grok hermes; do
     printf '#!/usr/bin/env bash\nexit 0\n' > "$STUB_BIN/$bin"
     chmod +x "$STUB_BIN/$bin"
   done
@@ -167,6 +167,51 @@ teardown() {
   [[ "$output" != *"--trust"* ]]
 }
 
+# --- --model (#135): per-type model flag, pass-through id ---
+
+@test "spawn --model: claude-code launch includes its --model flag + id" {
+  bash "$SCRIPTS/join.sh" myteam existing claude-code "$PROJ"
+  run bash "$SCRIPTS/spawn.sh" claude-code alice --project "$PROJ" --model claude-opus-4-8 --no-wait
+  [ "$status" -eq 0 ]
+  boot="$(cat "$CAPTURE")"
+  run cat "$boot"
+  [[ "$output" == *"claude --model claude-opus-4-8"* ]]
+  [[ "$output" == *"actas"* ]]
+}
+
+@test "spawn --model: codex launch uses its -m model flag" {
+  bash "$SCRIPTS/join.sh" myteam existing claude-code "$PROJ"
+  run bash "$SCRIPTS/spawn.sh" codex alice --project "$PROJ" --model gpt-5 --no-wait
+  [ "$status" -eq 0 ]
+  boot="$(cat "$CAPTURE")"
+  run cat "$boot"
+  [[ "$output" == *"codex -m gpt-5"* ]]
+}
+
+@test "spawn --model: grok-build launch uses its --model flag" {
+  bash "$SCRIPTS/join.sh" myteam existing claude-code "$PROJ"
+  run bash "$SCRIPTS/spawn.sh" grok-build alice --project "$PROJ" --model grok-build --no-wait
+  [ "$status" -eq 0 ]
+  boot="$(cat "$CAPTURE")"
+  run cat "$boot"
+  [[ "$output" == *"grok --model grok-build"* ]]
+}
+
+@test "spawn --model: refused for a type with no model_arg in its manifest" {
+  run bash "$SCRIPTS/spawn.sh" hermes foo --project "$PROJ" --model whatever --no-wait
+  [ "$status" -ne 0 ]
+  [[ "$output" =~ "does not support --model" ]]
+}
+
+@test "spawn: no --model leaves the launch flag-free" {
+  bash "$SCRIPTS/join.sh" myteam existing claude-code "$PROJ"
+  run bash "$SCRIPTS/spawn.sh" claude-code alice --project "$PROJ" --no-wait
+  [ "$status" -eq 0 ]
+  boot="$(cat "$CAPTURE")"
+  run cat "$boot"
+  [[ "$output" != *"--model"* ]]
+}
+
 @test "spawn: actas prompt uses the install command name (not hardcoded agmsg)" {
   # Rename the skill dir to a custom command name and re-point SCRIPTS so the
   # script resolves SKILL_DIR basename = the custom name.