Migrate os-orchestration plugin from cc-plugins into cc-os

Renamed orchestration -> os-orchestration per naming convention, kept the
plugin's permissive delegation rule as the canonical global default, and
dropped cc-os's stricter local override so this repo behaves like every
other project (ADR-019).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

plugins/os-orchestration/.claude-plugin/plugin.json

@@ -0,0 +1,5 @@
+{
+  "name": "os-orchestration",
+  "version": "0.1.0",
+  "description": "Session orchestration rules (delegation threshold, explicit model routing on Agent spawns) injected at session start and after compaction."
+}

plugins/os-orchestration/ORCHESTRATION.md

@@ -0,0 +1,10 @@
+## Session orchestration
+
+- Do single-file, ≤2-tool-call ops directly. Don't delegate them. Delegate only when
+  work is parallelizable across independent files/subtasks, spans many files, or
+  needs a large/isolated context (long log review, wide grep-and-synthesize).
+- Every `Agent` spawn passes `model` explicitly. Default `haiku` for mechanical
+  file-edit/shell work; `sonnet` for anything requiring judgment; `opus` only for
+  genuinely hard reasoning.
+- A short orienting Read before delegating is fine when the target file/path is
+  uncertain. Don't delegate the orienting step itself.

plugins/os-orchestration/hooks/hooks.json

@@ -0,0 +1,16 @@
+{
+  "hooks": {
+    "SessionStart": [
+      {
+        "matcher": "startup|resume|clear|compact",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "python3 ${CLAUDE_PLUGIN_ROOT}/hooks/inject.py",
+            "timeout": 5
+          }
+        ]
+      }
+    ]
+  }
+}

plugins/os-orchestration/hooks/inject.py

@@ -0,0 +1,31 @@
+#!/usr/bin/env python3
+"""SessionStart hook: inject ORCHESTRATION.md as additionalContext.
+
+Fires on startup/resume/clear, and on 'compact' (matcher includes it) so the
+rules survive a context-compaction pass, not just the first turn.
+"""
+import json
+import os
+import sys
+
+PLUGIN_ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+ORCHESTRATION_FILE = os.path.join(PLUGIN_ROOT, "ORCHESTRATION.md")
+
+
+def main():
+    try:
+        with open(ORCHESTRATION_FILE) as f:
+            context = f.read()
+    except OSError:
+        return
+
+    print(json.dumps({
+        "hookSpecificOutput": {
+            "hookEventName": "SessionStart",
+            "additionalContext": context,
+        }
+    }))
+
+
+if __name__ == "__main__":
+    sys.exit(main())