Initial release: full Arma 3 mod management toolchain

Pipeline: parse HTML presets, compare modlists, download from Caddy
file server, create junctions/symlinks to Arma 3 Server directory.
Includes update/sync flows, missing-mod reporting, OS compat layer,
shared config, dep checker, comprehensive test suite (71 tests).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

arma_modlist_tools/reporter.py

@@ -0,0 +1,95 @@
+"""
+arma_modlist_tools.reporter
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Build and persist a report of mods that are required by the modlists but
+absent from the file server.
+
+The report includes a ``group`` field per missing mod so downstream tools
+(``sync_missing.py``) know exactly where to place it when it becomes
+available on the server, without needing to re-read ``comparison.json``.
+
+Typical usage::
+
+    from arma_modlist_tools.reporter import build_missing_report, save_missing_report
+
+    report = build_missing_report(comparison, server_index)
+    save_missing_report(report, cfg.missing_report)
+"""
+
+from __future__ import annotations
+
+import json
+from datetime import datetime, timezone
+from pathlib import Path
+
+
+def build_missing_report(comparison: dict, server_index: dict) -> dict:
+    """
+    Cross-reference every mod in *comparison* against *server_index* and
+    return a report of mods that are not on the server.
+
+    :param comparison:    Dict as returned by :func:`~arma_modlist_tools.compare.compare_presets`.
+    :param server_index:  Dict as returned by :func:`~arma_modlist_tools.fetcher.build_server_index`.
+    :returns: Report dict::
+
+        {
+          "generated_at": "2026-04-07T12:00:00+00:00",
+          "total_mods":   80,
+          "on_server":    2,
+          "missing":      78,
+          "missing_mods": [
+            {
+              "name":     "CBA_A3",
+              "steam_id": "450814997",
+              "url":      "https://steamcommunity.com/...",
+              "group":    "shared"
+            },
+            ...
+          ]
+        }
+    """
+    by_steam_id: dict = server_index.get("by_steam_id", {})
+    by_name:     dict = server_index.get("by_name", {})
+
+    from .fetcher import _normalize_name  # reuse existing helper
+
+    def _on_server(mod: dict) -> bool:
+        if mod.get("steam_id") and mod["steam_id"] in by_steam_id:
+            return True
+        return _normalize_name(mod.get("name", "")) in by_name
+
+    # Flatten all mods with their group label
+    all_mods: list[tuple[dict, str]] = []
+    for mod in comparison["shared"]["mods"]:
+        all_mods.append((mod, "shared"))
+    for preset_name, data in comparison["unique"].items():
+        for mod in data["mods"]:
+            all_mods.append((mod, preset_name))
+
+    missing_mods = []
+    on_server_count = 0
+
+    for mod, group in all_mods:
+        if _on_server(mod):
+            on_server_count += 1
+        else:
+            missing_mods.append({
+                "name":     mod["name"],
+                "steam_id": mod.get("steam_id"),
+                "url":      mod.get("url"),
+                "group":    group,
+            })
+
+    return {
+        "generated_at": datetime.now(timezone.utc).isoformat(),
+        "total_mods":   len(all_mods),
+        "on_server":    on_server_count,
+        "missing":      len(missing_mods),
+        "missing_mods": missing_mods,
+    }
+
+
+def save_missing_report(report: dict, path: Path) -> None:
+    """Write *report* as indented JSON to *path*, creating parent dirs as needed."""
+    path.parent.mkdir(parents=True, exist_ok=True)
+    path.write_text(json.dumps(report, indent=2, ensure_ascii=False), encoding="utf-8")