complete codex docs

docs/decisions/0003-companion-programs.md

@@ -0,0 +1,29 @@
+# Decision 0003: First-Class Companion Programs
+
+## Status
+
+Accepted
+
+## Decision
+
+Companion applications such as BEC, B3, Discord bridges, log watchers, and stats collectors should be modeled as managed companion programs rather than ad hoc customer-editable startup scripts.
+
+## Reasoning
+
+- Customers should not control privileged helper commands through editable startup files.
+- Companion processes need to be started, stopped, and restarted alongside the game server.
+- PID and log handling should be centralized.
+- The same design should work across Linux and Windows/Cygwin.
+
+## Alternatives Considered
+
+- keep `_alsoRun.bat` style helper files
+- use only `pre_start` scripts
+- rely on manual customer scripts
+
+## Why Those Were Not Chosen
+
+- They are not centrally managed.
+- They are hard to secure.
+- They are difficult to cleanly stop on server shutdown.
+