fix(ansible): write DB inventory as static YAML, not dynamic --list JSON

generate_inventory() emits Ansible's dynamic --list shape (all.hosts is a
LIST, vars under _meta) — valid only as an executable inventory script's
stdout. We were writing it to a static file and passing -i, so Ansible's yaml
plugin rejected it ("Invalid 'hosts' entry for 'all' group, requires a
dictionary, found ...list...") and fell back to implicit localhost → "no hosts
matched". Affected every steward:* scope run; surfaced on the first real
provision.

- New inventory_to_yaml(inv): convert the --list dict → a valid static YAML
  inventory (all.hosts dict keyed by host, groups under all.children, group
  vars preserved, injected per-host vars like steward_token retained).
- Wire it into runner.trigger_run, host_agent deploy + provision.
- executor writes the file as inventory.yml so the yaml plugin's extension
  check reliably claims it.
- generate_inventory unchanged (still the --list dict); conversion happens at
  write time. Unit tests added.

Scribe issue #885.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

steward/ansible/executor.py

@@ -375,7 +375,9 @@ async def start_run(
         os.chmod(tmpdir, 0o700)
         try:
             if inventory_content:
-                inv_target = os.path.join(tmpdir, "inventory")
+                # .yml so Ansible's yaml inventory plugin reliably claims it
+                # (the plugin's verify_file checks the extension).
+                inv_target = os.path.join(tmpdir, "inventory.yml")
                 with open(inv_target, "w", encoding="utf-8") as invf:
                     invf.write(inventory_content)
             else:

steward/ansible/inventory_gen.py

@@ -37,6 +37,33 @@ def generate_inventory(targets: list) -> dict:
     return inv
 
 
+def inventory_to_yaml(inv: dict) -> str:
+    """Convert the ``--list`` dict from generate_inventory into a STATIC YAML
+    inventory string.
+
+    The ``--list`` shape (``all.hosts`` is a *list*, vars under ``_meta``) is only
+    valid as the stdout of an executable dynamic-inventory script. When written to
+    a plain file and passed via ``-i``, Ansible's yaml plugin requires
+    ``all.hosts`` to be a *dict* keyed by hostname — otherwise it fails to parse
+    and silently falls back to implicit localhost. This emits that valid form.
+    """
+    import yaml
+    hostvars = (inv.get("_meta") or {}).get("hostvars") or {}
+    all_hosts = (inv.get("all") or {}).get("hosts") or []
+    root: dict = {"hosts": {h: (hostvars.get(h) or {}) for h in all_hosts}}
+    children: dict = {}
+    for key, val in inv.items():
+        if key in ("all", "_meta") or not isinstance(val, dict):
+            continue
+        grp: dict = {"hosts": {h: {} for h in (val.get("hosts") or [])}}
+        if val.get("vars"):
+            grp["vars"] = val["vars"]
+        children[key] = grp
+    if children:
+        root["children"] = children
+    return yaml.safe_dump({"all": root}, default_flow_style=False, sort_keys=True)
+
+
 async def fetch_scope_targets(db, scope: str) -> list:
     """Query AnsibleTarget objects for a given inventory scope string.
 

steward/ansible/runner.py

@@ -7,12 +7,13 @@ manual, alert-triggered, and scheduled runs all take the exact same path.
 from __future__ import annotations
 
 import asyncio
-import json
 import uuid
 from datetime import datetime, timezone
 
 from steward.ansible import executor, sources as src_module
-from steward.ansible.inventory_gen import fetch_scope_targets, generate_inventory
+from steward.ansible.inventory_gen import (
+    fetch_scope_targets, generate_inventory, inventory_to_yaml,
+)
 from steward.models.ansible import AnsibleRun, AnsibleRunStatus
 
 
@@ -53,7 +54,7 @@ async def trigger_run(
     elif inventory_scope.startswith("steward:"):
         async with app.db_sessionmaker() as db:
             targets = await fetch_scope_targets(db, inventory_scope)
-        inventory_content = json.dumps(generate_inventory(targets))
+        inventory_content = inventory_to_yaml(generate_inventory(targets))
     elif inventory_scope.startswith("repo:"):
         parts = inventory_scope.split(":", 2)
         inventory_path = parts[2] if len(parts) == 3 else ""